US3246568A

US3246568A - Apparatus for finishing gear-shaped workpieces

Info

Publication number: US3246568A
Application number: US351892A
Authority: US
Inventors: Hurth Fritz
Original assignee: Carl Hurth Maschinen und Zahnradfabrik GmbH and Co
Current assignee: Gleason Hurth Tooling GmbH
Priority date: 1961-08-01
Filing date: 1964-03-11
Publication date: 1966-04-19
Anticipated expiration: 1983-04-19
Also published as: GB991194A; GB991195A

Description

April 19, 1966 F. HURTH 3,246,568

SHAPED WORKPIECES APPARATUS FOR FINISHING GEAR- Filed March 11, 1964 7 Sheets-Sheet 1 F. HURTH 3,246,568 APPARATUS FOR FINISHING GEAR-SHAPED WORKPIECES April 19, 1966 7 Sheets-Sheet 3 Filed March 11, 1964 L "it uurldlrlrlllafillllII III'IIIA /7/Is' ATTORNEY F. HURTH 3,2465% D WORKPIECES Apn-ill 1,, 1966 APPARATUS FOR FINISHING GEAR-SHAPE '7 Sheets-Sheet 4,

Filed March 11, 1964 F. HURTH April 19, 1966 APPARATUS FOR FINISHING GEAR-SHAPED WORKPIECES Filed March 11, 1964 7 Sheets-Sheet 5 v i V ma A kmwt INVENTOR.

FR ITZ H U RTH ATTORNEY April 19, 1966 F. HURTH 3,46,568

APPARATUS FOR FINISHING GEAR-SHAPED WORKPIECES Filed March 11, 1964 7 Sheets-Sheet 6 Q m L Q Ln T i L Li &

INVENTOR: FRITZ HURTH April 19,, 1966 F. HURTH 3,246,568

APPARATUS FOR FINISHING GEAR-SHAPED WORKPIECES Filed March 11, 1964 7 Sheets-Sheet 7 *5 Q T il INVENTORI FRITZ HURTH Lari e,

hi5 ATTORNEY United States Patent 3,246,568 APPARATUS FOR FINESHING GEAR-SHAPED WORKPIECES Fritz Hurth, Munich-Solin, Germany, assignor to Carl Martin Maschinenand Zahnradfahrik, Munich, Germany Filed Mar. 11, 1964, Ser. No. 351,82 Ciairns priority, application Germany, Aug. 1, 1961, H 43,302; Sept. 22, 1961, H 43,704; Mar. 13, 1963, H 48,521

24 Qiaims. (Ci, 901.6)

This is a continuation-in-part of my application Serial No. 212,763, filed on July 24, 1962, and now abandoned.

The present invention relates to gear finishing machines in general, and more particularly to improvements in mounting and positioning of the work holder with respect to the tool holder, or vice versa, in gear shaving, grinding, burnishing, lapping or other types of gear finishing machines. Still more particularly, the invention relates to improvements in machines for shaving or otherwise treating gear-shaped workpieces in accordance with the crossedaxes method.

It is known to provide a gear shaving machine with a spindle which serves as a means for rapidly advancing one of the holders toward or away from the other holder and to utilize a cam which advances the movable holder toward the fixed holder when the shaving tool is or should be moved in actual mesh with the workpiece. For example, if the work holder is located below and is movable toward and away from the tool holder, the cam is rocked step-by-step and is caused to lift the work holder toward the tool holder in order to move the workpiece in requisite position with respect to the tool. A serious drawback of such shaving machines is that the cam cannot block movements of the work holder in a direction toward the tool holder since the cam merely lifts the work holder without being in a position to limit the extent to which the work holder may move toward the tool holder. In other words, such cam merely controls the maximum distance between the two holders without being capable of determining the minimum distance between the tool and the workpiece. Therefore, and if the gear shaving machine or certain of its parts are caused to vibrate or are subjected to unexpected shocks, the distance between the workpiece and the tool is likely to 'be reduced below a permissible minimum distance. Such resistance in the distance between the workpiece and the tool cannot be counteracted by a cam which is utilized for moving the work holder toward the tool holder or vice -versa. While the vibrations or shocks are normally rather small, they can affect the shaving operation since shaving of gears is a work which must be carried out with a high degree of precision. For example, vibrations may cause chatter marks in the flanks of teeth on a shaved gear or a similar workpiece.

Accordingly, it is an important object of the present invention to provide a gear finishing machine which is constructed and assembled in such a way that vibrations, shocks and other undesirable movements of the machine frame and/or of certain of its tool-or work-supporting parts cannot influence the finishing operation.

Another object of the invention is to provide a gear finishing machine wherein the minimum distance between a tool and a workpiece may be controlled with utmost precision and wherein such minimum distance is maintained under all operating conditions in an extremely simple and reliable manner.

A further object of the invention is to provide an arrangement which is capable of determining, maintaining and/or charging the minimum distance between a work holder and a tool holder in all types of gear finishing ma- 3,246,568 Patented Apr. 19, 1966 ice chines including those which are utilized for crown shaving and/or for sc-called immersion shaving.

A concomitant object of the invention is to provide a car finishing machine of the above outlined characteristics which may be rapidly converted for shaving or other treatment of different types of workpieces.

With the above objects in view, one feature of the invention resides in the provision of a gear finishing machine, particularly a gear shaving machine of the rotary crossed axes type, which comprises a frame, first holder means mounted in the frame, second holder means, guide means provided on or in the frame and operatively connected with the second holder means so as to guide the second holder means for reciprocatory movements in directions toward and away from the first holder means, and blocking means mounted in the frame proper or in one of the holder means for limiting the extent of movement of the second holder means in a direction toward the first holder means and for thereby determining the minimum distance between the two holder means. One of the holder means is arranged to support a tool, such as a gear-shaped shaving tool, and the other holder means is arranged to support a gear-shaped workpiece which is engaged by and which may be treated by the tool when the second holder means is being moved to a position at a predetermined minimum distance from the first holder means, such minimum distance being determined by the blocking means which may comprise one or more adjustable plate-like or wedge-shaped cams arranged to vary the minimum distance between the two holder means prior to, during and/ or after the finishing operation.

The machine further comprises advancing means for moving the second holder means toward or away from the first holder means and for maintaining the blocking means in firm engagement with the first and/or second holder means so that the latter holder mean may be held without any play against movements toward or away from the first holder means excepting, of course, if the operator desires to increase the distance between the two holder means.

In actual use of my machine, the teeth of a first gearshaped member are shaved or otherwise treated by the teeth of a second gear-shaped member in accordance with a predetermined schedule and in such a way that one member is caused to move rapidly into mesh with the other member, that the distance between the axes of the two members is thereupon reduced gradually whereby the teeth of the second member remove shavings from the teeth of the first member, that the movable member is gradually moved away from the other member when the removal of shavings is completed, and that the movable member is thereupon rapidly returned to its original position in which the teeth of the first member are out of mesh with the teeth of the second member. In many instances, gradual return movement of the movable member is preceded by a comparatively short period during which the speed at which the distance between the two members is being changed equals zero speed or is close to zero speed so that the teeth of the second member may treat the teeth of the first member without actually removing pronounced shavings therefrom. This insures that eventual markings or stripes are fully removed from the teeth of the first member before the two members are disengaged from each other.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved machine itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodia) ments with reference to the accompanying drawings, in which:

FIG. 1 is a side elevational view of a machine for rotary crossed-axes shaving of gears and similar workpieces which embodies one form of my invention and wherein the blocking means which determines the minimum distance between the work holder and the tool holder comprises a specially configurated rotary plate cam, a portion of the machine being broken away to reveal certain parts of the advancing means serving to drive the blocking cam without any interruptions and to thereby change the distance between the tool holder and the work holder;

FIG. 2 is a horizontal section as seen in the direction of arrows from the line IIII of FIG. 1;

FIG. 3 is a top plan view of the machine;

FIG. 3a is a developed view of the blocking cam;

FIG. 3b is a similar developed view of another blocking cam;

FIG. 30 is a developed view of a further blocking cam;

FIG. 4 is a side elevational view of a modified machine which is utilized for crown shaving of gears and similar workpieces, a portion of the machine frame and of the work holder being broken away to reveal the construction of the advancing means for the blocking means which latter is identical with the blocking means shown in FIGS. 1 to 3;

FIG. 5 is a part front elevational and part vertical sectional view of the crown shaving machine, the section of FIG. 5 being taken in the direction of arrows as seen from the line V-V of FIG. 4;

FIG. 5a is an end view of a blocking cam which may be utilized in the machine of FIGS. 4 and 5;

FIG. 5b is a diagrammatic developed view of the face of the cam shown in FIG. 5a;

FIG. 6 is a side elevational view of a further gear shaving machine wherein the blocking means comprises two spaced blocking elements which are fixed to the work holder and which may be moved in abutment with the tool holder to determine the minimum distance between the axes of the workpiece and the tool, a portion of the work holder being shown in vertical section;

FIG. 7 is a front elevational view of the machine as seen from the left-hand side of FIG. 6;

FIG. 8 is a fragmentary section through a tailstock and a cam-shaped blocking element which is adjustably mounted in the tailstock;

FIG. 9 is a larger-scale fragmentary section through the slip clutch of the drive for the machine of FIG. 7;

FIG. 10 is a section along the line XX in FIG. 9;

FIG. 11 is an axial section through a worm which is used in the machine of FIG. 7 and which is biased by axially operating spring means;

FIG. 12 is a diagrammatic view of an advancing system which may be utilized in the machine of FIGS. 6 and 7; and

FIG. 13 is an enlarged end view of a switching drum which is utilized in the system of FIG. 12.

FIG. 13a is a part front elevational and part vertical sectional view of a shaving machine with a gearing shown in FIG. 12.

FIG. 14 is a diagrammatic view of an electrical advancing system for a machine of the type shown in FIGS. 4 and 5; and

FIG. 15 is a diagrammatic view of an electrical advancing system for a machine of the type shown in FIGS. 6 and 7.

Referring now in greater detail to the illustrated embodiments, and first to FIGS. 1 to 3, there is shown a gear shaving machine of the knee-and-column type comprising a frame 10 carrying at the top of its column 1011 a horizontal plate 11 which supports a swingable tool holder 12, the latter being provided with T-clamps 14 which are slidable in an arcuate T-groove 13 and which enable the tool holder to be fixed to the plate 11 in differ- 4 erent positions of adjustment. a gear-shaped tool 15 which is rotatable about a horizontal axis and which is driven by an electric motor 16 through a gear reducer 17 or through a suitable transmission (not shown).

The front face of the column 10a is provided with a vertical guide means or ways 18 which make right angles with the plane of the plate 11 and which support and guide a work holder including a first slide in the form of a knee 19. This slide is mounted in such a way that the work holder is reciprocable along the ways 18 in directions upwardly toward and downwardly away from the tool holder 12. The front face of the slide 19 is formed with a vertical dovetailed groove which receivesthe rail 20 of a second slide 21, and it will be noted that the rail 20 is parallel with the ways 18 to permit the second slide 21 to move with respect to the first slide 19 in directions toward and away from the tool 15. The machine is provided with means (not shown) for fixing the slide 21 to the slide 19 in any of a number of positions of adjustment. The slide 21 carries a horizontal pivot pin 22 which makes right angles with the longitudinal extension of the ways 18 and which supports a rotary work table 23 for two work engaging members here shown as

tailstocks

24, 25. These tailstocks support a gear-shaped workpiece 26. By adjusting the angular position of the table 23, an operator may move the axis of the workpiece 26 into parallelism with the axis of the tool 15, or the axis of the workpiece may cross the axis of the tool, depending upon whether the machine of FIGS. 1 to 3 is utilized for shaving of cylindrical workpieces (such as spur gears) or conical workpieces (such as bevel gears). The means for fixing the table 23 in any of several positions of inclination with respect to the slide 21 is not shown in the drawings. It will be noted that the parts 19 to 25 together constitute a composite holder for the workpiece 26 and that this work holder is located at a level below the tool holder 12 and is operatively connected with the ways 18 in such a manner that it may reciprocate in a straight path upwardly toward and downwardly away from the tool holder.

The frame 10 supports a horizontal cam shaft 28 which is parallel with the pivot pin 22 and whose forward end carries a bloncking means here shown as a detachable plate cam 27. The shaft 28 is driven by an electric motor 29 through a multi-stage or infinitely variable speed transmission 30 of the type disclosed, for example, in German Patents Nos. 810,565 and 953,930, and through a worm drive including a worm 31 driven by the transmission 30 and a worm wheel 32 which is mounted on the cam shaft 28. The rear end of the cam shaft 28 carries two control earns 33, 34 which respectively cooperate with trips of

electric switches

36, 35 to regulate the operation of the shaving machine. For example, the

switches

35, 36 may be respectively connected in the circuits of electric motors 16, 29 to arrest the gear shaving machine after the cam shaft 28 has completed a full revolution.

The blocking cam 27 cooperates with a roller follower 37 which is rotatably mounted on a horizontal bolt 37a carried by the slide 19 and which tracks the face of the blocking cam so that the extent to which the slide 19 (and hence the workpiece 26) may move upwardly toward the work holder 12 depends on the configuration of the cam 27 which is located above the follower 37. The latter is biased into permanent contact with the face of the cam 27 by an advancing means here shown as a resilient package of dished springs 38 which are inserted into an upwardly extending blind bore 190 of the slide 19 and which rest on the tip of a regulating screw 39. The screw 39 is axially movable in but is held against rotation with respect to the frame 10. The axial position of the screw 39 may be adjusted by a nut 40 which is rotatably mounted in the frame 10 and which The holder 12 supports meshes with the screw so that rotation of nut 40 will cause axial displacements of the screw 39 toward or away from the blocking cam 27, depending upon whether the nut 40 is rotated in a clockwise or in an anticlockwise direction. t will be readily understood that the resilient package 38 may be replaced by a helical spring, by a package of leaf springs, by a hydraulic system, by a pneumatic system or by other advancing means as long as such advancing means can produce requisite force for moving and for maintaining the follower 37 in engagement with the face of the blocking cam 27. The nut 40 may be turned by hand or through a suitable motion transmitting mechanism. For example, the nut 40 may be combined with a worm wheel which meshes with a worm and forms therewith a drive such as the worm drive 31, 322.

The machine of FIGS. 1 to 3 operates as follows:

In the first step, the operator or operators adjust the position of the tool holder 12 with respect to the plate 11 and the angular position of the table 23 with respect to the pivot pin 22. The axis of the tool 15 may be parallel with or it may cross the axis of the workpiece 26. The blocking cam 27 is in a starting position, i.e, it maintains the slide 19 and the tailstocks 24, at such a distance from the tool 15 that the workpiece 26 may be mounted on the table 23 Once the workpiece is properly mounted between the tailstocks 24, 25, the operator starts the motors 16 and 29 whereby the motor 16 drives the tool 15 and the latter may mate with and may rotate the workpiece 26 In other words, the teeth of the tool 15 are immersed or dip into the spaces between the teeth of the workpiece 26 (hence the name immersion method of gear shaving) At the same time, the motor 29 drives the cam shaft 28 and the latter begins to rotate the blocking cam 27 so that the cam permits slight upward movement of the slide 19 which is sufficient to move the workpiece in requisite position in which it is engaged by the tool 15, and the tool removes shavings from the teeth of the workpiece Since the speed ratio of the transmission is adjustable, the operator may cause the cam shaft 28 to rotate at different speeds so that the workpiece 26 may be rapidly lifted into operative engagement with the tool 15, whereupon the angular speed of the blocking cam 27 preferably decreases for a predetermined interval of time during which the tool 15 remains in engagement with and treats the workpiece The configuration of the blocking cam 27 is shown in developed view in FIG. 3a. This cam comprises a lobe 27a whose periphery 27b constitutes the first section of the cam face 27F and which is engaged by the roller follower 37 (under the bias of the advancing means 38) when the machine of FIGS. 1 to 3 is at a standstill. The shaft 28 drives the cam 27 in a direction as indicated by the arrow 28a and, when the motor 29 is started, the follower 37 begins to track a second section 270 of the cam face 27F which extends inwardly toward the axis of the shaft 28 (the latter is assumed to be located at a level above the cam 27, as viewed in FIG. 3a) whereby the advancing means 38 compels the work holder 19-25 and hence the workpiece 26 to move upwardly and into mesh with the tool 15. The inclination of the section 270 is rather pronounced so that the workpiece is moved rapidly into mesh with the tool. The arrangement is preferably such that, when the follower 37 has already passed along the first portion 270 and tracks the right-hand portion 27c" of the section 27c (as viewed in FIG. 3a), the workpiece is located in such close proximity of the tool 15 that the teeth of the tool begin to remove shavings from the workpiece. The section 270 is followed by a section 27d of very slight inclination, i.e., the section 27d may constitute a portion of a substantially cylindrical surface which is concentric with the axis of the cam shaft 28 so that the distance between the workpiece and the tool remains unchanged or 5 is reduced very slightly when the follower 37 tracks the section 27a. During engagement between the section 27d and the follower 37, the teeth of the workpiece complete the shaving operation, and the section 27d is followed by a further section 27a of slight negative inclination with respect to the axis of the cam shaft 38. In other words, while tracking the section 27a, the follower 37 cuases the workpiece 26 to move downwardly and away from the tool 15, thus enabling the tool to run itself out while the workpiece moves out of engagement therewith. The last section 27 of the cam face 27F has a more pronounced negative inclination (i.e., it is inclined in a direction aawy from the axis of the cam shaft 28) and leads the follower 37 back onto the first section 27b to thereby completely disengage the workpiece from the tool 15 and to enable an operator to replace the workpiece by a new one.

In accordance with my invention, the transmission 30 may drive the cam shaft 28 in such a way that, when the motor 29 is started, the blocking cam 27 begins to rotate rapidly so that the follower 37 tracks the first portion 270' of the section 270 at a comparatively high speed, thus enabling the advancing means 38 to rapidly lift the workpiece 26 toward the tool 15. The transmission 30 shifts into a lower speed ratio when the follower 37 reaches the right-hand end of the portion 27c (as viewed in FIG. 3a) so that the movement of the workpiece toward the tool 15 is slowed down to a degree necessary for maintaining an efiicient shaving operation, namely, the workpiece is lifted at a speed which is low enough to insure that the serrated teeth of the tool 15 are not compelled to remove shavings of excessive thickness. When the follower 37 tracks the section 27d, the speed of the cam shaft 28 may be the same as in the preceding operation during which the follower engages the second por tion 270 of the section 270. During that stage of the operation when the follower 37 tracks the section 272, the teeth of the tool 15 may remain in mesh with the teeth of the workpiece 26 so that the latter rotates with the tool while the work holder 19-25 moves slowly downwardly and away from the tool holder 12. Such engagement between the teeth of the workpiece and the tool while the follower tracks the section 27c is advisable because the teeth of the tool are then in a position to remove markings or scratches from the flanks on the teeth of the workpiece. Such markings can develop during that stage of operation when the tool removes shavings, i.e., when the work holder moves toward the tool holder to reduce the distance between the axes of the tool and the workpiece.

In the last stage of the operation, the transmission 30 again shifts into high speed ratio and the follower 37 is caused to travel rapidly along the section 27 f in order to return into engagement with the lobe 27a of the blocking cam (section 27b) whereby the blocking cam causes the workpiece to descend rapidly in a direction away from and out of mesh with the tool 15, and the cam arrests the work holder at such a distance from the tool holder which is sufficient to permit convenient removal of the workpiece from the

tailstocks

24, 25.

It will be noted that, when the blocking cam 27 completes a full revolution, the tool 15 has completed the shaving of a workpiece and the

control cams

33, 34 may arrest the motors 16, 29 while the operator replaces the finished workpiece by a new one.

In accordance with a slight modification which is so obvious that it can be readily comprehended without a separate illustration, the configuration of the blocking cam 27 may be simplified in the following manner:

The face of this cam may consist of three sections, namely, a first section 27b which surrounds the cam lobe 27a, a second section 27c of positive inclination with respect to the axis of the cam shaft 28, and a third section 27 of negative, inclination. Thus, the section 27d of FIG. 3a may form part of the section 27c, and the section 27c may form part of the section 27]. The last portion of the section 270 may perform the function of the section 27d in cooperation with the transmission 30 which drives the cam shaft 28 at a speed which is sulficiently low to insure that the teeth of the tool may properly remove shavings from the teeth of the workpiece. In the zone of transition between the last portion of the section 270 and the first portion (corresponding to the section 27e of FIG. 3a) of the section 27f, the work holder 125 reverses the direction of its movement while the transmission 30 continues to drive the cam shaft 28 at a reduced speed so that initial disengagement between the workpiece and the tool is gradual which enables the teeth of the tool to remove eventual markings from the teeth of the workpiece. The last portion of the section 27] on such a modified blocking cam is tracked while the cam shaft 28 is driven at higher speed so that the workpiece is moved rapidly out of actual mesh with the tool and returns to a position in which it can be removed from the

tailstocks

24, 25. In other words, such modified blocking cam is utilized in combination with a transmission which regulates the speed of the cam shaft 28 in a sense to insure that the shaving operation is carried out in the same way as described in connection with FIG. 3a. Thus, while the configuration of the face on the blocking cam is simplified, the various speeds at which the transmission 30 drives the cam shaft 28 must be regulated by a somewhat more complicated mechanism.

The rotary blocking cam 27 may be replaced by a socalled wedge cam which moves back and forth and which determines the minimum distance between the workpiece and the tool while performing a linear, rather than a rotary movement. If the blocking means is a wedgelike cam, the operative connection between the motor 29 and the blocking means is changed in such a way that the blocking means moves continuously in a linear path and that its cam face may control the position of the slide 19 with respect to the ways 18 in a manner analogous to that described above.

It will be noted that the blocking cam 27 cooperates with the follower 37 of the work holder 19-25 to determine the minimum distance between the work holder and the tool holder 12 against the action of the advancing means 38 so that eventual vibration of the frame or of one or both holders can have no bearing on the minimum distance between the tool and the workpiece, particularly during such intervals when the workpiece is actually shaved by the teeth of the tool 15. The principle is the same if the position of the workpiece and of the tool 15 is reversed, i.e., if the workpiece is mounted in the holder 12 and if the tool is mounted in the holder 19-25. The heretofore described feature of my invention resides in the provision of blocking means which prevents excessive movements of a reciprocable holder in a direction toward a fixed holder regardless of whether the tool is mounted in the reciprocable holder or in the fixed holder.

FIG. 3b illustrates a different blocking cam 127 whose cam face 127F is very similar to the cam face 27F of the cam 27, excepting that the section 27c is replaced by two mutually inclined sections 127c', 127c. The remaining

sections

2711, 27d, 27c and 27] of the cam face 127F are identical with the corresponding sections of the cam face 27F. The section 1270 is tracked by the follower 37 when the transmission 30 drives the cam shaft 28 at a given speed in order to permit rapid advance of the work holder 1925 toward the tool holder 12. When the follower 37 tracks the section 127c", the teeth of the tool 15 remove shavings from the teeth of the workpiece, and such removal of shavings continues while the follower tracks the section 27d. When the follower tracks the section 27e, the teeth of the tool 15 remove markings from the teeth of the workpiece, and the follower 37 rolls along the last section 27 1 when the workpiece is caused to rapidly return to its original position in which it may be removed from the tailstocks. An important advantage of the cam 127 is that the transmission 39 may drive the shaft 29 at a constant speed, i.e., the machine may utilize a greatly simplified transmission because the configuration of the cam face 12TH by itself insures that the speed at which the workpiece moves toward and away from the tool is regulated in a manner as described in connection with FIG. 3a and that the duration of engagement between the teeth of the workpiece and of the shaving tool is sufficient to insure satisfactory removal of shavings and eradication of any markings which might have remained after the tool has ceased to remove shavings (section 271:).

FIG. 30 illustrates a blocking earn 227 whose face 227F changes its inclination gradually, i.e., without such pronounced transitions as shown between certain sections of the cam face 27F or 127R The sections 2271;, 2270, 227a", 227d, 227a and 227 of the cam face 227F respectively correspond to the sections 27b 1270, 1270", 27d, 27e and 27 of the cam face 1271 It should be mentioned here that the

cam

27, 127 or 227 is equally useful in conventional gear finishing machines of the type described in the introductory part of this disclosure, namely, in which the cam serves as a means for determining the maximum distance between the work holder and the tool holder and wherein the cam cooperates with a follower which is biased by a spring or by another advancing means in a sense to move the work holder away from the tool holder. This will be readily understood since, and insofar as the regulation of the gear finishing operation is concerned (to wit: by disregarding the novel feature that the cam may serve as a blocking means which determines the minimum distance between the workpiece and the tool), the

cam

27, 127 or 227 will regulate movements of the workpiece into engagement with or away from the tool (or vice versa) if the cam serves as an advancing means rather than a blocking means. For example, all that is necessary is to mount the cam 27 of FIG. 1 at a level below the slide 19 and to mount the resilient package 38 in the slide 19 in such a way that it biases the follower downwardly and into engagement with the face of the cam. In fact, if the cam is mounted in such a way that it controls the maximum distance between the work holder and the tool holder, the package 38 may be omitted altogether and the follower 37 of the work holder 1925 may rest by gravity on the cam face 27F.

Before proceeding with the description of certain other embodiments of my invention, I will point out the advantages of the machine which utilizes blocking cams of the type shown in FIGS. 3a to 30. Heretofore, it was customary to control movements of the tool into shaving engagement with a workpiece (or vice versa) by means of a variable speed motor, i.e., it was necessary to shift in different speeds if the operator desired to alter the speed at which the axes of the workpiece and of the tool were moved toward each other. Such operation is timeconsuming and the teeth of the tool invariably leave some markings on the teeth of the workpiece, particularly if the shaving operation is carried out by the immersion method. Attempts were made to improve the operation of such shaving machines by special distribution of shaving edges on the teeth of the tool in a manner as disclosed in a copending application Serial No. 158,407 of Fritz Hurth and assigned to the same assignee. While such distribution of shaving edges brings about substantial improvements in the shaving operation, the machine is somewhat more complicated because the rate at which the workpiece is moved in stepwise fashion toward the tool or vice versa depends on the distribution of cutting edges on the teeth of the shaving tool.

By providing a movable cam whose rotary or reciprocatory movement is not interrputed white it causes the workpiece to move toward the shaving tool or vice versa, I provide a very simple and highly satisfactory machine which prevents the formation of markings on the teeth of the workpiece. Thus, and as described in connection with FIGS. 1 to 30, movements of the

cam

27, 127 or 227 need not be interrupted at all at the time the cam causes one of the holders to reduce the distance between the axes of the tool and the workpiece. In other words, the cam may move uninterruptedly all the time while the workpiece is being moved toward and while the teeth of the workpiece remain in engagement with and are being treated by the teeth of the tool. in fact, and as explained hereinabove, movements of the cam need not be interrupted at all from the very start and all the way to the end of a working cycle including movements of the workpiece into and out of mesh with the shaving tool. Therefore, the likelihood that the shaving tool would leave undesirable scratches or other markings on the teeth of the workpiece is very remote, and it was found that the machine of my invention actually insures that the tool can treat the teeth of the workpiece to an exceptionally high degree of precision finish.

A very important feature of my machine resides in that the distance between the axes of the workpiece and the tool may be reduced continuously up to the very moment when the shaving operation is completed so that it is not necessary to interrupt the advance of the tool toward the workpiece or vice versa. The speed at which the two gear-shaped members move toward each other may be varied by interposing a transmission in the power line between a constantly driven motor and the cam and/or by imparting to the cam face a configuration which insures that the speed at which the distance between the two-gear-shaped members is being reduced is changed whenever necessary to insure that the teeth of the workpiece are shaved to an exceptionally high degree of precision finish.

The reason for reducing the speed at which the two gear-shaped members are being moved toward each other at the time when the shaving operation is about to be or is actually completed is that, otherwise, it would be necessary to immediately reverse the direction of movement when the removal of shavings is completed. Such rapid reversal in the direction of movement of the workpiece with respect to the tool or vice versa would invariably produce some markings on the teeth of the workpiece and, therefore, by utilizing a cam whose face or whose drive means insures that the transition between forward speed and return speed of the movable holder is gradual, I provide a gear shaving machine wherein the periods of idleness between consecutive stages of a shaving operation are reduced to zero and wherein the workpieces may be treated to a higher degree of precision finish than in all such gear shaving machines of which I am aware at this time.

In the embodiment of FIG. 3a, gradual transition between forward and return movements of the movable work holder 19-25 takes place when the follower 37 tracks the sections 27d, 27s of the cam face 27F, whereby the speed at which the distance between the axes of the tool and workpiece 26 changes while the follower tracks the sections 27d, 2.7e is close to zero. This obviously insures that the transition between forward and return movements of the work holder 19-25 is gradual and the tool cannot cause undesirable scratches on the teeth of the workpiece.

I have found that, when a shaving or a similar finishing operation is being carried out, it is undesirable to maintain the distance between the workpiece and the tool unchanged for an extensive period of time because the tool then produces so-called zebra stripes in the teeth of the workpiece. In order to avoid the formation of such stripes, my machine preferably operates in such a way that the interval of time during which the forward or return speed of the movable holder equals zero is rather short, that such short interval of zero speed is preceded by an interval (cam section 27d in FIG. 3a) during which the forward speed of the movable holder is low, and that such short interval of zero speed is followed by an interval (cam section 27e in FIG. 3a) during which the return movement of the holder takes place at low speed. Regardless of whether the gear shaving machine of my invention utilizes a rotary plate cam of the type shown in FIGS. 3a to Be or a movable wedge cam, its cam face is configurated in such a way that the transition between high forward speed (cam face section 270) and high return speed (cam face section 27 f) is always smooth so that zero speed is reached and passed gradually (

cam face sections

27d, 27a).

Of course, and as explained hereinabove, the same effect can be obtained even if the transition between the positive and negative inclinations of the cam face is abrupt, as long as the speed at which the cam is moved is regulated in such a way that the forward speed of the movable holder is reduced gradually before it drops to zero speed and that return movement of the movable holder immediately following zero speed is also gradual. This can be achieved by utilizing a transmission which can change the speed of cam movement to compensate for omission of certain cam face sections such as the

sections

27d, 27e of the cam face 27F shown in FIG. 3a. However, if the cam face is configurated in a manner as shown in FIGS. 3a to 3c, the cam is capable of regulating the forward and return speeds of the movable holder without necessarily changing the speed of its angular or linear movement.

FIGS. 4- and 5 illustrate a modified gear shaving machine of the knee-and-column type whose frame comprises a column 110a and a head 110b, the latter mounting an adjustable holder 55 for a tool 115. In contrast to the construction of the machine shown in FIGS. 1 to 3, the modified machine is assembled in such a way that the workpiece 126 is reciprocable in its holder in directions parallel with the axis of the tool and, in addition, the work holder is reciprocable in a straight path in directions toward and away from the tool holder 55. The manner in which the slide 19 is reciprocable along vertical guide means or ways provided on the front face of the column 11011 is the same as described in connection with FIGS. 1 to 3, and the front face of the slide 19 is again provided with a vertical dovetailed groove for the rail 29 of a second slide 21 which carries a fixed housing 46 for the vertical shaft of a rotary carriage 41. The carriage 41 supports a recipocable slide 42 which caries a pivotable base plate 43 for a tiltable table 44. Rocking movements of the table 44 are controlled by a rocking device including an adjustable guide bar 45 which is received between three rollers 46 supported on the table 44 in a manner as described in a copending application Serial No. 130,624 of Otto Rogg which is assigned to the same assignee. The bar 45 may be fixed to the housing 40 in a number of different angular positions and rocks the table 44 in synchronism with longitudinal displacements of the slide 42.

The table 44 is reciprocated by an electric motor 47 mounted on the housing 40 and by a gear train including two mating spur gears 48 which act as a gear reducer and one of which is directly driven by the output shaft of the motor 47, a pair of mating spur gears 49 which act as a reversing gear, two pairs of mating bevel gears 50, 51, a third pair of mating spur gears 52 one of which drives a horizontal spindle 53, the latter mounted in the carriage 41 and meshing with a spindle nut 54 which is fixed to and which extends downwardly from the slide 42. The adjustable holder 55 enables the tool 115 to move into a position in which its axis crosses the axis of the workpiece 126, the latter being mounted in

tailstocks

24, 25 which are carried by the tiltable table 44. If desired, the connection between the table 44 and the

tailstocks

24, 25 may comprise a turntable (not shown) which allows for rotation of the workpiece in a horizontal plane.

The machine of FIGS. 4 and 5 is utilized for crown shaving. The basic operation of such crown shaving machines is known and need not be described in greater detail. The tool 115 is driven by a suitable motor, for example, in a manner as illustrated in FIGS. 1 to 3, and rotates the workpiece 126 when the latter is lifted by the slide 19 into the range of teeth on the tool. At the same time, the motor 47 drives the gear train 4854 and brings about reciprocatory movements of the workpiece 126 with respect to the tool.

The blocking cam 27 and the advancing means 38 in the gear shaving machine of FIGS. 4 and are identical with the corresponding blocking and advancing means of FIGS. 1 to 3a. The cam 27 is readily detachable from the shaft 28 and the switch 36 controls the motor 47. The cam 27 again cooperates with a roller follower 37 against the action of the advancing means 38 to limit movements of the workpiece 126 in a direction toward the tool 115. Any movements of the workpiece in a direction away from the tool are possible only by overcoming the bias of the advancing means 38. The composite tool holder of the machine shown in FIGS. 4 and 5 includes the parts 19-21, 24, and 40-44. The means for driving the blocking cam 27 includes an electric motor, a multi-stage or infinitely variable speed transmission 30 which is driven by the motor, a worm 31 and a worm wheel 32, the ratio of the transmission 30 may be adjusted by the switch 35. The face of the cam 37 may be configuratcd as shown in FIG. 3a, 3b or 3c.

In the gear shaving machine of FIGS. 4 and 5, in which the workpiece is reciprocated with respect to a revolving gear-shaped tool, the formation of zebra stripes is avoided if the face of the blocking cam 27 is configurated as shown in FIGS. 3a to 30. Such cam insures that the teeth of the workpiece are slightly separated from the teeth of the tool before the workpiece is rapidly returned to its original position of disengagement from the tool 115. Heretofore, such crown shaving machines were operated in such a way that the workpiece was caused to reciprocate with respect to the revolving tool after the tool has completed the actual shaving operation in order to make sure that the tool would remove all stripes from the teeth of the workpiece. Such additional reciprocation of the workpiece consumes much time and reduces the output of the crown shaving machine. In accordance with my invention, removal of eventual stripes from the teeth of a shaved workpiece takes place at the time when the workpiece is moved gradually away from the tool or vice versa.

The blocking cam 27 of FIGS. 4 and 5 may be replaced by a blocking cam 327 of the type shown in FIG. 5a. This cam 327 comprises a cam face 327F having a first section 360 which causes the workpiece 126 to advance rapidly toward the tool 115 and to advance at a reduced speed when the teeth of the tool mesh with and remove shavings from the teeth of the workpiece. The first section 369 is located ahead of a second section 361 which is concentric or substantially concentric with the cam shaft 23 so that the distance between the tool 115 and workpiece 126 remains substantially unchanged or is reduced only slightly when the section 361 engages the follower 37. A third section 363 between the

sections

360, 361 serves to return the workpiece 126 to its initial position.

When the blocking cam 327 of FIG. 5a is utilized in the machine of FIGS. 4 and 5, it is mounted in such a way that, prior to starting a shaving operation, the cam face 327? maintains the axis 380 of the roller follower 38 at a maximum distance from the axis of the cam shaft 28, Le, the workpiece 126 is held at a maximum distance from the tool 115. The transmission 30 is preferably of the infinitely variable type and its ratio is adjusted by the switch in such a way that, as soon as the motor which drives this transmission is started, the cam 327 is rotated rapidly through an angle 381 whereby the workpiece 126 is advanced rapidly to mate with the tool 115. When the point 382 on the periphery of the 12 cam 327 abuts against the follower 37, the switch 35 adjusts the ratio of the transmission 30 in a sense that the shaft 28 is driven at a reduced speed while the cam 327 rotates through an angle 383. During such rotation of the cam 327, the workpiece 126 continues to move toward the tool so that the tool removes shavings until the follower 37 moves in contact with the point 384 which is located between the

sections

360, 361 of the cam face 3271 At this moment, the switch 35 again adjusts the ratio of the transmission 30 in a sense to change the speed of the shaft 28 so that the shaft 28 drives the cam 327 through an angle 385 whereby the distance between the gear 115 and workpiece 126 changes very little or remains unchanged. At this stage of the shaving operation, the speed of the transmission 30 is selected in such a way that the cam 327 requires a predetermined interval of time in order to allow the workpiece to run itself out while the tool 115 completes the shaving operation. When the follower 37 engages the point 386 on the periphery of the cam 327 (the point 386 is located between the cam face sections 361, 363), the workpiece 126 begins to move away from the tool 115 because the inclination of the section 363 is negative. At the same time, the switch 35 again adjusts the ratio of the transmission 30 in a sense to reduce the speed of the shaft 28 so that the cam 327 rotates rather slowly through an angle 387 which corresponds to the first portion of the cam face section 363. The negative inclination of this first portion (angle 387) is rather small so that initial movement of the workpiece 126 away from the tool 115 is gradual until the follower 37 reaches the point 388. In the last stage, the cam 327 rotates through an angle 389 to return the workpiece 126 to its initial position at a maximum distance from the tool 115. The follower 37 then rolls along the remaining portion of the cam face section 383.

The exact points at which the switch 35 changes the ratio of thetransmission 30 may be determined by the operator, namely, by proper selection of the control cam 34. If desired, the switch 35 may cause the transmission 30 to drive the shaft 28 at very high speed as soon as the follower 37 reaches the point 388 between the

angles

387, 389 so that the workpiece 126 may return to its initial position very rapidly as soon as it has been moved out of mesh with the tool 115.

The exact manner in which an electric switch may change the ratio of a multi-stage transmission or an infinitely variable speed transmission will be described later.

FIG. 5b illustrates the blocking cam 327 in a developed view whereby the distances between the points 390-384, 334-386 and 386-390 respectively correspond to the circumferential length of the

cam face sections

360, 361, 363.

A very important advantage of the construction shown in FIGS. 5a and 5b is that the operator may control the length of intervals during which the work holder advances at a given speed. The finish of tooth flanks on a workpiece depends on a number of factors including the speed at which the workpiece is fed toward the tool, the length of the interval during which the distance between the workpiece and the tool remains unchanged, the speed at which the workpiece moves away from the tool, and the length of intervals during which the workpiece moves toward or away from the tool. The machine of FIGS. 4 and 5, with the blocking cam 327 of FIGS. 5a and 5b, is ideally suited for such operation because the length of intervals during which the movable holder advances at a given speed (toward or away from the fixed holder) may be selected with great precision and because the various speeds may be determined in advance and with such precision as is necessary for a satisfactory shaving, grinding, lapping or burnishing operation.

In other words, the machine of FIGS. 4 and 5 comprises means (the cam 327, the transmission 30 and the springs 38) for moving the work holder at different speeds 13 (toward and away from the tool holder), and means (including the cam 34 and switch 35) for determining the length of intervals during which the work holder moves at a given speed so that shifting from one speed ratio to another speed ratio takes place in accordance with a predetermined schedule.

If desired, the electromagnetic transmission of FIGS. 4 and 5 may be replaced by a fluid-operated transmission or by a mechanical transmission. The switch is then replaced by a system of valves or by a system of links, levers or other mechanical motion transmit-ting means.

FIGS. 6 and 7 illustrate a different gear shaving machine Which comprises a frame 61 having a head 61b for an adjustable tool holder 62. The machine of FIGS. 6 and 7 is of the vertical knee-and-column type, and the holder 62 enables the tool 215 to assume a number of different positions with respect to the workpiece 226. The means for driving the tool 215 is known in this art and, therefore, is not illustrated in the drawings.

The column 61a of the frame 61 supports a vertically reciprocable slide 63 which is movable along vertical guide means or ways 64. The slide 63 supports a work table 65 which is til-table about a horizontal pivot pin 66, the latter making right angles with the longitudinal extensions of the ways 64. The table 65 carries two tailstocks 67, 68 for the workpiece 226, and the arrangement is preferably such that the axis of the workpiece 226 crosses the axis of and is driven by the tool 215 when the machine is in operation. The extent to which the table 65 may be rocked about the pivot pin 66 is regulatable by two screws 69 which are mounted on the slide 63 and whose tips are located beneath the table 65 at the opposite sides of the pivot pin 66. As a rule, the play of the table 65 with respect to the screws 69 is rather small.

The tailstocks 67, 68 respectively support substantially prismatic blocking elements 71, 71a, and portions of these blocking elements extend into cutouts or recesses provided in the upper sides of the respective tailstocks to be retained in requisite position by clamping screws 72. The blocking elements 71, 71a are preferably located at the opposite sides of and in close or immediate proximity of the tool 215 to insure that the relative position of the axis of the workpiece 226 with respect to the tool axis remains unchanged irrespective of elastic deformation of the work and tool holders. The pivotability of the table 65 about the pin 66 insures that each of the blocking elements 71, 71a may move in full face-to-face abutment with the tool holder 62. The slide 63 is reciprocable along its ways 64 by advancing means including a vertical spindle 73 which is mounted on the base 610 of the frame 61 and which may be driven by an electric motor 74 or by a handwheel 75 through a suitable transmission accommodated in the interior of the slide 63. Since the motor 74 or the handwheel 75 must advance the blocking elements 71, 71a into abutment with a fixed part, i.e., with the tool holder 62 or with another component which is rigid with the frame 61, the transmission which is mounted in the slide 63 preferably comprises a suitable slip clutch 74a (e.g., a friction clutch or the like) which permits the motor 74 or the handwheel 75 to rotate with respect to the spindle 73 when the blocking elements 71, 71a prevent further ascent of the work holder. Combined with that part of the slip clutch which slides with respect to the motor 74 is a gear member 85 which drives a worm gear 88 through a gear 86 which is preferably shiftable, and through a worm 87. The worm gear 88 is a spindle nut in mesh with the spindle 73. FIG. 9 shows on a larger scale a section through the slip clutch and illustrates that the slidable gear member 85 is provided with one or more cam means 89. A switch 91 provided on a member 96 of the clutch is connected with the motor. sends an impulse as soon as one of the cam means 89 The switch operates a control member 92 mounted in the member 96. Thus, the switch 9'1 will at once switch oil? the drive (motor 74) for the slide 63 or will switch on a timelag relay which will switch of? the motor 74 after a predetermined period of time and will eventually initiate return movement as soon as the relative movement between the motor 74 and the gear member 89 is terminated. In order to avoid the provision of a slip clutch for damping the impact, the worm 87 may be axially shifta ble and may be elastically supported (FIG. 11) in a manner as disclosed in German Patent 1,108,543 or in US. Patent 2,945,925. If desired, both methods may be combined. The worm 87 can operate a switch 87a.

The machine of FIGS. 6 and 7 need not comprise means for reciprocating the workpiece 226 axially with respect to the tool 215 because it is assumed that the axial length of the tool is sufficient to engage the workpiece along the full length thereof (see FIG. 7). The tool 215 is a hyperboloidal gear so that the shaving operation may be carried out in accordance with the so-called dipping or immersion method.

The distance between the axis of the finished workpiece 226 and the axis of the tool 215 is determined by the dimensions of the blocking elements 71, 71a which are readily removable from the machine. If the distance between the surfaces 76, 77 on the tailstocks 67, 68 (which abut against the undersides of the blocking elements 71, 71a) and the corresponding surfaces '78, 7% (which abut against the upper sides of the blocking elements 71, 71a) is the same, both blocking elements are of identical height provided, of course, that the workpiece 226 is a cylindrical spur gear. If the workpiece is a bevel gear, the height of one blocking element exceeds the height of the other blocking element so that the axis of the workpiece may be properly inclined with respect to the axis of the tool 215. Each blocking element may consist of several sections which may "be separated from each other when it becomes necessary to reduce the minimal distance between the tool and the workpiece.

The machine of FIGS. 6 and 7 operates as follows:

It is assumed that the workpiece 226 is a cylindrical spur gear. 1n the first step, the slide 63 is moved downwardly (either by starting the motor 74 or by rotating the handwheel 75) in order to provide room for insertion of the workpiece 226 between the ta'ilstocks 67, 68. The screws 69, 70 are adjusted in such a way that there remains some play between their tips and the table 65 which is sufficient to permit proper adjustments in the position of the table depending on the type of blocking elements 71, 71a momentarily used in the machine. In the next step, the blocking elements 71, 71a are clamped in the recesses of the respective tailstocks so that they may determine the shortest distance between the axes of the workpiece 226 and tool 215 as soon as their upper sides engage the surfaces 78, 79. Once the workpiece 226 and the blocking elements 71, 71a are properly mounted in the tailstocks 67, 68, the drive for the tool 215 is started to rotate the tool, and the motor 74 is also started to move the slide 63 upwardly and to thereby bring the workpiece in mesh with the tool. Upward movement of the Workpiece is terminated when the blocking elements 71, 71a abut against the surfaces 78, 79, and the height of these blocking elements is selected in such a way that the teeth of the tool 215 remove shavings from the teeth of the workpiece when the blocking elements engage the holder 62. The maximum distance between the holder 62 and the slide 63 need not exceed the minimum distance at which the workpiece may be conveniently removed from the tailstocks 67, 68.

Of course, at the time the blocking elements 71, 71a move in actual abutment with the tool holder 62, there develop some compressive stresses between the tool and the workpiece, but such stresses diminish at the same rate at which the tool removes shavings from the workpiece so that all or nearly all stresses are eliminated upon completion of the shaving operation. The slip clutch in the aforementioned transmission between the motor 74 and spindle 73 enables the motor or the handwheel to bias the blocking elements 71, 71a in constant abutment with the tool holder 62. Such bias of the

parts

73, 74, 74a eliminates any play between the tool holder 62 and the work holder 63-68. It will be noted that the

parts

73, 74, 74a constitute a portion of an advancing means for the work holder 63-68 and that the function of such advancing means is equivalent to the function of the advancing means 38.

The machine of FIGS. 6 and 7 may be readily modified in a number of ways without departing from the scope of my invention. For example, the workpiece 226 may reciprocate with respect to the tool 215 in a manner analogous to that described in connection with FIGS. 4 and 5. In such instances, prismatic blocking elements 71, 71a are preferably replaced by rollers to reduce friction with the tool holder when the workpiece and its holder are caused to reciprocate with respect to the tool holder. Furthermore, the blocking elements 71, 71a may be replaced by eccentric cams which are adjustably mounted in the tailstocks or in another part of the work holder so that, merely by angularly displacing the cams, an operator may convert the machine for shaving of differently configurated or dimensioned workpieces. If necessary, such cams may be adjusted in the course of a shaving operation in order to change the minimum distance between the workpiece and the tool in accordance with a predetermined schedule which may be analogous with the work schedule controlled, for example, by the blocking cam 27 of FIG. 3a. FIG. 8 shows a tailstock 167 which is provided with a recess 167a for an eccentrically mounted blocking element in the form of a plate cam 171. This cam is supported on a rotary eccentric shaft 171A. The position of the eccentric shaft 171A can be regulated by means of a Worm gear 172 and a worm 172a. The latter can be driven either manually or by a motor (not shown). The motor can be automatically controlled according to a program which corresponds to that described in connection with FIGS. 3a, 3b, 30. To arrest the eccentric shaft, a clamping screw 172b may be provided. In addition to this, a graduated scale as well as a pointer 1720 may be provided to enable the operator to read the turning angle. The pointer may be mounted on the worm gear or on the worm. The cam 171 is rotatable about the shaft 171A and may be arrested in any of an infinite number of positions by the clamping screw 172 mounted in the tailstock 167. The other tailstock (not shown in FIG. 8) is combined with a second blocking cam which is identical with the cam 171.

The blocking cam or cams may be combined with the spindle 73, or the upper end of this spindle may form a cam to insure gradual transition between forward and return movements of the workpiece.

FIG. 12 illustrates a modified driving arrangement for the machine of the type shown in FIGS. 6 and 7. A constant-speed electric motor 74 drives an infinitely variable speed transmission unit 406, which comprises an endless belt trained around sheaves one of which includes a fixed flange and an axially movable flange. This unit may be replaced by a multi-stage transmission. The transmission unit 406 drives a train of change-speed gears 407 and a countershaft 408 which carries one of each of three pairs of meshing gears 409. The other gear of each pair of gears 409 is mounted on a shaft 412. This shaft 412 also carries

gears

413, 414 which mesh with the

gears

413a, 414a of a reversing gearing 415 including a twin clutch 416 mounted on a worm shaft 417. The clutch 416 is of the electromagnetic type and serves to connect the

shafts

412, 417 in such a way that the shaft 417 rotates in one direction when it is driven by the gear 413 and in the opposite direction when it is driven by the gear 414. The clutch 416 may be replaced by a mechanical or hydraulic clutch.

The shaft 417 carries a worm 418 which meshes with a spindle nut 488. This nut 488 meshes with a spindle 473 and is free to rotate in but cannot move axially with reference to a slide 463. A handwheel 475 is arranged to drive the worm shaft 417 through a clutch 420 and a pair of gears 419. If desired, the gears 419 may be omitted, and the handwheel 485 then drives the shaft 417 directly through the clutch 420.

The spindle 473 corresponds to the spindle 73 of FIGS. 6 and 7, and its lower end portion is mounted in the base 461a in such a way that it may move axially but is held against rotation with reference to the frame of the machine. The base 461c carries a resilient element, here shown as a dished spring 421, which rests on a shoulder 461c' of the base 4610 and which bears against a collar 423 on the spindle 473 so that the latter is biased upwardly. The spring 421 may be replaced by a hydraulically or pneumatically operated biasing device or by a package of disked springs.

The motor 74 drives a further transmission unit 421 which in turn drives a control drum 422 in such a way that the control drum 422 rotates at low speed. The control drum carries on its periphery a series of adjustable actuating members or trips 423, 440, 441 which cooperate with a row of electric switches 424. One of the switches 424 controls a regulating motor 425 which rotates a worm drive 426 for the adjusting mechanism 427 of the transmission unit 406.

FIG. 13 illustrates the control drum 422 and one of the switches 424.

When the machine of FIG. 12 is in use, the working cycle of the slide 463 begins with the control drum 422 in the position of FIG. 13,. The motor 74 drives the transmission unit 406 and the latter is adjusted by the mechanism 427 in such a way that the slide 463 moves rapidly in upward direction so as to advance the workpiece toward the tool. When the control drum 422 rotates through an angle 431 (between the points 430, 432 in FIG. 13), the trip 423 engages one of the switches 424 and this switch completes the circuit of the motor 425 to adjust the mechanism 427 through the worm drive 426 and to change the ratio of the transmission unit 406 so that the slide 463 is lifted at a reduced speed such as is necessary for the actual feeding operation when the tool removes shavings from the teeth of the workpiece. The motor 425 is arrested when the trip 423 advances beyond the switch 424, i.e., when the control drum 422 rotates through an additional angle between the

points

432, 433 in FIG. 13. If desired, the trip 423 may be replaced by two trips one of which starts the motor 425 and the other of which opens the circuit of this motor when the drum 422 travels through an angle corresponding to the distance between the

points

432, 433.

When the control drum 422 thereupon rotates through an angle corresponding to the distance between the

points

433, 434, the blocking elements 71, 71a reach the tool holder 62 and prevent further upward movement of the spindle nut 488 and slide 463. Because the motor 74 continues to drive the transmission unit 406 and because the transmission unit continues to rotate the nut 488, the spindle 473 begins to move downwardly against the bias of the spring 421 whereby the collar 428 moves away from an electric switch 429 which disconnects the clutch 416 and which completes the circuit of a time-lag relay serving to keep the clutch 416 in idle condition for a period of time which is necessary to keep the workpiece at a given distance from the tool. The feed movement of the slide 463 is completed and the tool ceases to remove shavings.

When the control drum 422 thereupon advances the trip 440 in engagement with one of the switches 424, the ratio of the transmission unit 406 is adjusted in a sense to rotate the nut 488 at low speed and to move the slide 463 with the workpiece downwardly and away from the tool. T 6 slide 46 descends gradually while the drum 422 travels through an angle corresponding to the distance between the

points

435, 436 whereupon the trip 441 engages one of the switches 424 and causes the transmission unit 406 to change its speed ratio so that the slide 4&3 descends rapidly to actuate a switch 42% which disengages the clutch 416 whereby the shaft 417 is disconnected from the shaft 412. The switch 429a is actuated when the control drum 422 rotates through an additional angle between the

points

436, 437 in FIG. 13. The working cycle of the slide 461 is now completed and the motor 74 is turned off when the control drum 422 completes a full revolution, i.e., after the control drum rotates through an additional angle (between the points 437, 430 in FIG. 13).

The reference numeral 411 indicates a slip clutch which corresponds to the slip clutch 74a of FIG. 7 and which may be substituted of the spring 421. This slip clutch will become effective when the blocking elements 71, 71a reach the holder 62 and preferably completes the circuit of a time-lag relay which insures that the distance between the tool and the workpiece remains unchanged for a predetermined period of time before the workpiece begins to move away from the tool.

The control drum 422 determines the length of intervals during which the work holder moves at a given speed. The exact times at which the transmission unit 40b changes its speed ratio may be varied by changing the position of trips on the control drum so that the work schedule may be selected at the will of the operator. In this respect, the machine shown in FIGS. 12 and 13 is quite similar to the machine of FIGS. 4 and as described in connection with FIGS. 5a and 5b.

In summation, the machine of FIGS. 12 and 13 comprises advancing means including the motor 74 and the transmission unit 406 which is arranged to move the work holder at a plurality of speeds including lower and lighter speeds in directions toward and away from the tool holder, and the advancing means further includes control means 422, 423, 424, 440, 441 for regulating the exact length of intervals during which the work holder (including the slide 463) moves at any one of such speeds. The blocking means for the machine of FIGS. 12 and 13 may be the same as described in connection with FIGS. 6 and 7.

In the machines of FIGS. 1 to 5b, the blocking cam constitutes a component part of the advancing means for the work holder. In the machines of FIGS. 6 to 13, the blocking means is independent of the advancing means.

FIG. 14 illustrates schematically an electrical advancing system for a machine of the type shown in FIGS. 4 and 5. The reference numeral 500 indicates the main source of electrical energy and the numeral 501 indicates the source of control current. A transmission 530 is driven by a main motor 547 and drives the worm 31 which meshes with the worm wheel 32 on the shaft 23 of the blocking cam 27. The speed ratio of the transmission 530 may be adjusted by a motor 525 which corresponds to the motor 425 of FIG. 12. The circuit of the main motor 547 includes a relay 502 with contacts 503 and a holding contact 504 which is connected in the circuit of a pushbutton 505.

The circuit of the motor 525 includes a first relay 506 with contacts 507. When the relay 506 is energized, the motor 525 adjusts the speed ratio of the transmission 530 to drive the cam shaft 23 at higher speed. A second relay 508 with contacts 509 serves to adjust the motor 525 and transmission 530 in a sense to drive the cam shaft 28 at reduced speed. The

switches

535, 536 correspond to the

switches

35, 36 of FIG. 4, and these switches are respectively controlled by

cams

33, 34 which are also shown in the lower part of FIG. 14. The reference numeral 536/) indicates a switch which is controlled by the cam 34. It is obvious that the cam 34 may be replaced by two cams one of which activates the switch 535 and the other of which activates the switch 536]). This latter switch is connected in the circuit of the relay 502.

The working cycle begins at 580. The speed ratio of the transmission 530 is adjusted by the motor 525 through a lobe 510 on the cam 33, through the switch 536 and through the relay contacts 507 in such a way that the blocking cam 27 rotates at high speed. At 582, the lobe 511 closes the switch 535 so that the motor 525 receives an impulse from the

relay

508, 509 to adjust the ratio of the transmission 530 and to drive the cam shaft 78 at reduced speed. This reduced speed is the normal speed at which the workpiece 126 "(FIG 4) moves toward the tool during a gear finishing operation, i.e., when the teeth of the tool remove shavings from the teeth of the workpiece.

At 584, the lobe 512 again closes the switch 536 and causes the motor 525 to adjust the speed ratio of the transmission 530 in a sense to drive the blocking cam 27 at higher speed while the distance between the tool and the workpiece remains substantially unchanged. At 586, the lobe 513 of the cam 34 closes the switch 535 to drive the shaft 28 at reduced speed while the workpiece 126 begins to move gradually in a direction away from the tool 115. At 583, the lobe 514 of the cam 33 closes the switch 536 and causes the shaft 2% to rotate at high speed so that the workpiece 126 returns rapidly to its initial position.

At 590, the lobe 515 of the cam 34 opens the switch 5356b to deenergize the relay 502 and to arrest the main motor 547 which in turn stops the cam shaft 28. At the same time, the relay 5632 closes a switch 516 to complete the current of an electric brake 517 which locks the transmission 530 and blocking cam 27.

' FIG. 15 shows an electrically operated machine of the type illustrated in FIGS. 6 and 7. Parts 600-609 respectively correspond to the parts 500-509 and 525 shown in FIG. 14. The main motor 74 drive a transmission 630 which drives a control drum 422'. The forward and reverse clutches are identified by numerals 616a, 6161]. A time lag relay 62d performs the function mentioned in connection with FIG. 12; this relay comprises a holding contact 621 and a working contact 622. The numerals 625a, 625b indicate two locking switches.

The drum 422' cooperates with three switches 424a, 424b, 424C and carries four

adjustable trips

423a, 423b, 4230, 423d. The

numerals

407, 409, 418, 473, 429, 429a and 488 identify the same parts as in FIG. 12.

The working cycle begins at 630a by depressing the pushbutton 605. The relay 602 remains energized because the contact 604 is closed. The forward clutch 616a is operative and the locking switch 625a is open so that the reverse clutch 616b remains idle. The drum 422' rotates in the direction indicated by arrow 422d. The workpiece 226 (FIGS. 6 and 7) is caused to travel upwardly at high speed. The switch 429a was open in the lower end position of the nut 43%, but this switch closes when the workpiece 226 moves upwardly; however, such closing of the switch 429a is of no consequence because the holding contact 621 of the time-lag relay 620 is open.

At 632, the lobe 423a initiates a change in the speed ratio of the transmission 630 (via 424a, 603, 609 and 625) so that the workpiece 226 is lifted at reduced speed such as is necessary for theshaving operation. When the blocking elements 78, 79 strike against the tool holder 62 (see the position 634 in FIG. 15), the spindle 473 begins to move downwardly and the switch 429 opens to idle the forward clutch 61611. The locking switch 625a closes and a switch 62% energizes the relay 620. The work holder remains in such position for a period of time determined by the time-lag relay 620, i.e., the distance between the workpiece 226 and tool 215 remains substantially unchanged. During this interval, the trip 423!) causes the transmission 630 to change its speed ratio (via 424a, 6 98, 609, and 625) so that the transmission is ready to move the workpiece 226 at reduced speed and in a direction away from the tool 215. The lower speed is selected by the relay 608.

The drum 422 may be assembled of several annuli each of which may carry one of the trips 423a-423d or each of which may carry two or more trips. Thus, the parts 422a, 422b, 4220 are three annuli of the control drum 19 4-22 and it will be noted that the trips 423a, 4231) are mounted on the annulus 422a. Were the trip 42311 mounted on the annulus 422b, it would cooperate with the switch 4241) and would cause the transmission 630 to shift into a higher speed ratio.

When the time set by the relay 620 elapses, the contacts 621, 622 close and the contact 622 energizes the reverse clutch 616b. The locking switch 62512 opens. The contact 221 is a holding contact for the relay 620 so that the latter remains energized when the switch 62% opens while the spindle 473 returns to its original position. At 636, the trip 4230 then completes the circuit of the switch 424]) so that the transmission 630 shifts into a higher speed ratio whereby the workpiece 226 returns rapidly to its original position. Such original position is reached when the nut 488 opens the switch 62911. The relay 620 is now deenergized and the reverse clutch 616i) is idle. The switch 625b closes to make sure that the forward clutch 616a is in ready position. The main motor 74 is arrested when the trip 423d opens the switch 4240.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a gear finishing machine, in combination, first holder means; second holder means, one of said holder means being arranged to support a tool and the other of said holder means being arranged to support a workpiece; guide means operatively connected with and arranged to guide said second holder means for movement in directions toward and away from said first holder means; advancing means for moving said second holder means with reference to said first holder means; and blocking means arranged to limit the extent of movement of said second holder means toward said first holder means so as to determine the minimum distance between said holder means.

2. In a gear finishing machine, in combination, frame means; first holder means mounted in said frame means; second holder means, one of said holder means being arranged to support a tool and the other of said holder means being arranged to support a workpiece; guide means provided on said frame means and operatively connected with said second holder means for reciprocably guiding said second holder means for movements in directions toward and away from said first holder means; and blocking means for limiting the extent of movement of the second holder means toward the first holder means to determine the minimum distance between said holder means.

3. In a machine for shaving of gears with crossed axes, in combination, frame means; first holder means mounted in said frame means; second holder means, one of said holder means being arranged to support a gear-shaped tool and the other of said holder means being arranged to support a gear-shaped workpiece; guide means provided on said frame means and operatively connected with said second holder means for reciprocably guiding said second holder means for movements in a straight path and in directions toward and away from said first holder means; advancing means for moving said second holder means toward said first holder means; and blocking means for limiting the extent of movement of said second holder means toward said first holder means against the action of said advancing means.

4. In a gear finishing machine, in combination, frame eans; first holder means mounted in said frame means; second holder means, one of said holder means being arranged to support a tool and the other of said holder means being arranged to support a workpiece; guide means provided on said frame means and operatively connected with said second holder means for reciprocably guiding said second holder means for movements in directions toward and away from said first holder means; advancing means mounted in said frame for moving said second holder means in a direction toward said first holder means; and blocking means mounted in said frame means for limiting the extent of movement of said second holder means toward said first holder means against the action of said advancing means.

5. A combination as set forth in claim 4, wherein said blocking means is a cam and wherein said advancing means comprises resilient means which biases said second holder means against said cam.

6. A combination as set forth in claim 5, further comprising drive means mounted in said frame means for adjusting the position of said cam with respect to said second holder means and for thereby adjusting the minimum distance between said first and second holder means.

7. A combination as set forth in claim 6, wherein said cam is a rotary plate cam and wherein said second holder means comprises follower means arranged to track the periphery of said plate cam, said drive means comprising motor means operatively connected with and driving said earn.

8. In a gear finishing machine, in combination, frame means; first holder means mounted in said frame means; second holder means, one of said holder means being ar ranged to support a tool and the other of said holder means being arranged to support a workpiece; guide means provided on said frame means and operatively connected with said second holder means for reciprocably guiding said second holder means for movements in directions toward and away from said first holder means; advancing means mounted in said frame for moving said second holder means in a direction toward said first holder means; and blocking means for limiting the extent of movement of said second holder means toward said first holder means against the action of said advancing means, said blocking means comprising at least one blocking element mounted on one of said holder means and abutting against the other holder means when said advancing means has moved said second holder means through a selected distance in a direction toward said first holder means.

9. In a gear finishing machine, in combination, frame means; first holder means mounted in said frame means; second holder means, one of said holder means being arranged to support a tool and the other of said holder means being arranged to support a workpiece; guide means provided on said frame means and operatively connected with said second holder means for reciprocably guiding said second holder means for movements in directions toward and away from said first holder means; advancing means mounted in said frame for moving said second holder means in a direction toward said first holder means; and blocking means for limiting the extent of movement of said second holder means toward said first holder means against the action of said advancing means, said blocking means comprising at least one cam and drive means operatively connected with said cam for adjusting its position with respect to said second holder means and for thereby regulating the minimum distance between said holder means.

10. In a gear finishing machine, in combination, a frame; a tool holder adjustably fixed to said frame; a work holder; ways provided on said frame and operatively connected with said Work holder so as to guide the work holder for movements toward and away from said tool holder; advancing means mounted in said frame for moving said work holder in a direction toward said tool holder; and blocking means mounted on one of said holders and engaging the other work holder when said advancing means moves said work holder through a predetermined distance in a direction toward said tool holder so that said blocking means determines the minimum distance between said holders.

-1-ll. A combination as set forth in claim 10, further comprising a gear-shaped tool mounted in said tool holder, said blocking means comprising two spaced blocking elements fixed to said work holder and engaging said tool holder at the opposite sides of and in close proximity of said tool when said work holder has been moved through said predetermined distance toward said tool holder.

12. A combination as set forth in claim 11, wherein said blocking elements are cams and further comprising means for adjustably fixing said cams to said work holder.

13. In a gear finishing machine, in combination, frame means; first holder means mounted in said frame means; second holder means, one of said holder means being arranged to support a tool and the other of said holder means being arranged to support a workpiece; guide means provided on said frame means and operatively connected with said second holder means so as to guide said second holder means for reciprocatory movements in directions toward and away from said first holder means; spindle means mounted in said frame means and arranged to move said second holder means in a direction toward said first holder means; motor means; variable speed transmission means connecting said motor means with said spindle means; and blocking means for limiting the extent of movement of said second holder means toward said first holder means against the action of said advancing means, said blocking means comprising at least one blocking element mounted on one of said holder means and abutting against the other holder means when said second holder means is advanced through a predetermined distance in a direction toward said first holder means.

14. A combination as set forth in claim 13, wherein said transmission means comprises slip clutch means arranged to disconnect said motor means from said spindle means when said blocking element abuts against said other holder means.

15. A combination as set forth in claim 13, comprising a worm drive including a worm and a worm wheel and arranged to connect said transmisson means with said spindle means and further comprising spring means for axially holding the worm of said worm drive against the reacting force with its associated driving force.

16. In a gear finishing machine, in combination, first holder means; second holder means, one of said holder means being arranged to support a gear-shaped tool and the other of said holder means being arranged to support a gear-shaped workpiece; guide means operatively connected with said second holder means so that the second holder means is movable in directions toward and away from said first holder means; advancing means comprising a variable-speed transmission arranged to move said second holder means at a plurality of speeds, said advancing means further comprising control means for changing the speed ratio of said transmission to regulate the length of intervals during which the second holder means moves at one of said speeds; and blocking means arranged to limit the extent of movement of said second holder means toward said first holder means so as to determine the minimum distance between said holder means.

17. In a gear finishing machine, in combination, a frame member; a first holder member mounted in said frame member; a second holder member reciprocably supported by said frame member and movable toward and away from said first holder member, one of said holder members being arranged to support a rotary gearshaped tool and the other holder member being arranged to support a gear-shaped workpiece which meshes with and is treated by the tool when the second holder memher is sufiiciently close to said first holder member; advancing means including a variable-speed transmission operatively connected with said second holder member and arranged to reciprocate the same toward and away from said first holder member at a plurality of speeds, said advancing means further comprising control means for changing the speed ratio of said transmission in accordance with a predetermined schedule so that said second holder member is moved for a predetermined interval of time at each of said speeds; and blocking means arranged to arrest said second holder member at a predetermined minimum distance from said first holder member, said blocking means comprising at least one blocking element which is supported by one of said members.

18. A combination as set forth in claim 17, wherein said control means comprises a drum arranged to complete a full revolution during each working cycle of said machine, switches adjacent to the periphery of said drum and arranged to initiate changes in the speed ratio of said transmission, and actuating members adjustably mounted on said drum and arranged to actuate said switches in a predetermined sequence.

19. In a gear finishing machine, in combination, first holder means; second holder means, one of said holder means being arranged to support a tool and the other of said holder means being arranged to support a gearshaped workpiece; guide means operatively connected With and arranged to guide said second holder means for movement in directions toward and away from said first holder means; advancing means for moving said second holder means at a plurality of speeds in directions toward and away from said first holder means; and blocking means arranged to limit the extent out movement of said second holder means toward said first holder means so that the minimum distance between said holder means is determined by said blocking means, said advancing means comprising control means arranged to maintain said holder means at said minimum distance from each other for a predetermined period of true.

20. In a gear finishing machine, in combination, first holder means; second holder means, one of said holder means being arranged to support a tool and the other of said holder means being arranged to support a gearshaped workpiece; guide means operatively connected with and arranged to guide said second holder means for movement in directions toward and away from said first holder means; advancing means for moving said second holder means at a plurality of speeds in directions toward and away from said first holder means; and blocking means arranged to limit the extent of movement of said second holder means toward said first holder means so that the minimum distance between said holder means is determined by said blocking means, said advancing means comprising a variable speed transmission arranged to move said second blocking means at a low speed when the distance between said holder means approaches said minimum distance, and control means for regulating the length of intervals during which said second holder means moves at such low speed.

21. In a gear finishing machine, in combination, firame means; first holder means mounted in said frame means; second hold-er means, one of said holder means being arranged to support a gear-shaped tool and the other of said holder means being arranged to support a gearshaped workpiece; guide means provided on said frame means and operatively connected with said second holder means for reciprocably guiding said second holder means for movements in directions toward and away from said first holder means; follower means provided on said second holder means and arranged so as to transmit movement to the same when being moved; movable cam means operatively connected with said second holder means and having a cam face adapted to be tracked by said follower means and serving for regulating the distance between said first and second holder means in response to changes in position of said cam means which moves during said changes in position the tracking follower means, said cam face comprising a first section which is tracked by said follower means so as to cause the second holder means to advance in direction toward said first holder means, a second section which is subsequently tracked by said follower means so as to cause the second holder means to remain at the same distance from said first holder means, a third section which is subsequently tracked by said follower means so as to cause the second holder means to move at a predetermined speed in a direction away from said first holder means, and a fourth section which is subsequently tracked by said follower means so as to cause the second holder means to move away from said first section at another speed which is higher than said predetermined speed; and moving means for moving said cam means.

22. In a gear finishing machine, in combination, frame means; first holder means mounted in said frame means; second holder means, one of said holder means being arranged to support a gear-shaped tool and the other of said holder means being arranged to support a gear shaped workpiece; guide means provided on said frame means and operatively connected with said second holder means for reciprocably guiding said second holder means for movements in direction toward and away from said first holder means; follower means provided on said second holder means and arranged so as to transmit movement to the same when being moved; movable cam means operatively connected with said second holder means and having a cam face adapted to be tracked by said follower means and serving for regulating the distance between said first and second holder means in response to changes in position of said cam means which moves during said changes in position the tracking follower means, said cam face comprising a first section which is tracked by said follower means so as to cause the second holder means to advance at a first speed in a direction toward said first holder means, a second section which is subsequently tracked by said follower means so as to cause the second holder means to advance toward said first holder means at a reduced second speed, a third section which is subsequently tracked by said follower means so as to cause the second holder means to advance toward said first holder means at a reduced third speed not substantially exceeding zero speed, a fourth section which is subsequently tracked by said follower means so as to cause the second holder means to move at a fourth speed in a direction away from said first holder means, and a fifth section which is subsequently tracked by said follower means so as to cause the second holder means to move away from said first holder means at a fifth speed which is higher than said fourth speed, and means for moving said cam means.

23. In a gear finishing machine, in combination, frame means; first holder means mounted in said frame means; second holder means, one of said holder means being arranged to support a gear-shaped tool and the other of said holder means being arranged to support a gear-shaped workpiece; guide means provided on said frame means and operatively connected with said second holder means for reciprocably guiding said second holder means for movements in direction toward and away from said first holder means; follower means provided on said second holder means and arranged so as to transmit movement -to the same when being moved; movable cam means operatively connected with said second holder means and having a cam face adapted to be tracked by said follower means and serving for regulating the distance between said first and second holder means in response to changes in position of said cam means which moves during said changes in position the tracking follower means, said cam face comprising a first section which is tracked by said follower means so as to cause the second holder means to move toward said first holder means, and a second section which is subsequently tracked by said follower means so as to cause the second holder means to move away from said first holder means; and moving means including a variable speed transmission for moving said cam means.

24. In a gear finishing machine, in combination, frame means; first holder means mounted in said frame means; second holder means, one of said holder means being arranged to support a gear-shaped tool and the other of said holder means being arranged to support a gear-shaped workpiece; guide means provided on said frame means and operatively connected with said second holder means for reciprocably guiding said second holder means for movements in direction toward and away from said first holder means; follower means provided on said second holder means and arranged so as to transmit movement to the same when being moved; movable cam means operatively connected with said second holder means and having a cam face adapted to be tracked by said follower means and serving for regulating the distance between said first and second holder means in response to changes in position of said cam means which moves during said changes in position the tracking follower means, said cam face comprising a first section which is tracked by said follower means so as to cause said second holder means to move toward said first holder means, a second section which is subsequently tracked by said follower means so as to cause the second holder means to move toward said first holder means at a speed approximating zero speed, and a third section which is tracked by said follower means so as to cause said second holder means to move away from said first holder means; and moving means including a variable speed transmission for moving said cam means.

References Cited by the Examiner UNITED STATES PATENTS 2,387,679 10/1945 Praeg l.6

WILLIAM W. DYER, 111., Primary Examiner.

G. A. DOST, Assistant Examiner.

Claims

1. IN A GEAR FINISHING MACHINE, IN COMBINATION, FIRST HOLDER MEANS; SECOND HOLDER MEANS, ONE OF SAID HOLDER MEANS BEING ARRANGED TO SUPPORT A TOOL AND THE OTHER OF SAID HOLDER MEANS BEING ARRANGED TO SUPPORT A WORKPIECE; GUIDE MEANS OPERATIVELY CONNECTED WITH AND ARRANGED TO GUIDE SAID SECOND HOLDER MEANS FOR MOVEMENT IN DIRECTIONS TOWARD AND AWAY FROM SAID FIRST HOLDER MEANS; ADVANCING MEANS FOR MOVING SAID SECOND HOLDER MEANS WITH REFERENCE TO SAID FIRST HOLDER MEANS; AND BLOCKING