US1877174A

US1877174A - Method and apparatus for relieving hobs

Info

Publication number: US1877174A
Application number: US447011A
Authority: US
Inventors: Ernest C Head
Original assignee: Gleason Works
Current assignee: Gleason Works
Priority date: 1928-05-16
Filing date: 1930-04-24
Publication date: 1932-09-13
Anticipated expiration: 1949-09-13

Description

Sept. 13, 1932. E. c. HEAD mmnon AND APPARATUS FOR RELIEVING u OBS Original Filed May '16 1928 3 Sheets-Sheet l INVENTOR. Zr7zasi 65 6402 A TTW Sept. 13, 1932. E. c. HEAD 1,877,174-

METHOD AND APPARATUS FOR RELIEVING 30135 Original Filed May 16, 1928 3 Sheets-Sheet 2 44/ 67 154 70 T Ft 3 42 1 2 T 1517 I la 4 4 143 A 131 4 44' o o 3 j 152 w m 81 1 130 w 1 143 O '78 v 7 87 w 130 9/ 131 8A 159 I32 138 136 150 Y 90 135- v 137 85152 58 126 82 83 12 1:4 81 :1 6 l 5 INVENTOR. 4

[W2 5i C [faal Sept. 13, 1932. E. 0. HEAD 1,877,174

METHOD AND APPARATUS FOR RELIEVING HOBS Original Filed May 16. 1928 5 Sheets-Sheet 3 IN VEN TOR.

limesi C fiai B l5 ATM Patented Sept. 13, 1932 UNITED STATES PATENT OFFICE ERNEST 0. HEAD, OF ROCHESTER, NEW YORK, ASSIGNOR TO GLEASON WORKS, QF ROCHESTER, NEW YORK, A CORPORATION OF NEW YORK MET OD AND APPARATUS r03. RELIEViNG irons Original application filed May 16, 1928, Serial No. 278,208, and in Great Britain April 29, 1929. Divided i and this application filed April 24, 1930. Serial No. 447,011.

The present invention relates to a method and toapparatus for relievlng gear-cuttmg hobs and particularly hobs for cutting spiral bevel gears.

This application is a division of my pending application, Serial No. 27 8,208, filed May 16, 1928, covering a hob.

One object of this invention is to provide a relieving method, and apparatus for practicing the same, through which it will be possible to produce a gear cutting hob which will have the same cutting action after sharpening as when new.

A further object of this invention is to provide a method forrelieving taper hobs and apparatus for practicing the method, by which the teeth at the small end of the hob can be made stronger than taper hobs of previous constructions.

A still further object of this invention is to provide apparatus for accomplishing the above mentioned purposes of the invention which may be employed as a simple and inexpensive attachment to a conventional form of lathe.

Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims.

In the drawings:

Figure 1 is a side elevation and Figure 2 an end elevation of a lathe equipped with a relieving attachment constructed according to one embodiment of this invention and showing the same employed in relieving a taper hob.

Figure 3 is a fragmentary plan view, on an enlarged scale, of the lathe, showing particularly the relieving attachment;

Figure 4; is a section on. the line &-4 of Figure 3;

Figure 5 is a diagrammatic view illustrative of the relieving method, showing the rel-- ative movement that takes place between the relieving tool and the hob blank during the movement of the tool from one end of the hob to the other;

Figure 6 is a diagrammatic view further illustrative of the relieving method, showing the relative movement which takes place between the relieving tool and the hob blank during the relieving of the hob; and 7 I Figure 7 is an axial sectional view of a taper hob relieved according to the method of. this invention.

The cutting edges of a hob are'arranged in a helical thread, the teeth ofthe hobbeing formed by gashing and relieving this thread. After a hob is sharpened the new cutting edges have changed positions in the thread helix, that is, they have different angular and axial positions from the positions previously occupied by the cutting edges. The prior practice has been to relieve the teeth of a hob so that the side faces of the teeth are of the same pressure angle from front to rear. It will be clear that when such a hob is sharpened the new cutting edges will have axial andangular positions di'fl'erent from the axial and angular positions of the original cutting edges, and that consequently the cutting action of the new cutting edges will be different from the cutting action of the original cutting edges. While the pressure angles of the original cutting edges were correct for producing a gear of a desired pressure angle, the pressure angles of the new cutting edges would not be correct for producing the same gear.

One of the purposes of the present invention is to provide a method whereby a gear cutting hob may be relieved so that its cutting action will be just as correct after sharpening as it was before sharpening. To this end, in manufacturing a hob according to this invention, the relieving tool is tilted continuously during the relieving of each tooth of the hob so as to vary continuously the inclination of the cutting edge of the relieving tool relative to the tooth face being relieved, thus varying the pressure angle of the side face of the tooth continuously from front to rear of the tooth. This variation in pressure angle of the tooth from front to rear is just enough to insure that when the hob is sharpened, its cutting edges will have pressure angles exactly suited, by reason of their changed positions in the helix, to produce the required pressure angle on the teeth of the gear to be cut.

one of the teeth of In a further aspect, the present invention has for its purpose to provide a method for relieving taper hobs whereby taper hobs, such as are employed in the cutting of spiral bevel gears, may be produced which are much stronger than taper hobs of previous constructions. This purpose is achieved by tilting the relieving tool continuously as it moves from the large to the small end of the hob so as to provide teeth on the hob of continuously increasing pressure angle from the large to the small end of the hob. Thus, the teeth of the small end of the hob, being of greater pressure angle than corresponding teeth in prior constructions, will be correspondingly stronger. The pitch of the hob thread can be maintained constant, if desired, on its root, pitch, top, or any other surface by rotating the blank at a uniform velocity and moving the tool longitudinally of the hob at a uniform velocity and by tilting the tool during its longitudinal movement about points lying in one or other of these surfaces.

The two features of this invention may be used separately or in combination. Thus, a hob may be relieved so that it has teeth with side faces of changing inclination from front to back or so that it has cutting edges of changing pressure angle from one end of the hob to the other or the hob can be relieved in such a way as to have both cutting edges of changing pressure angle from one end of the hob to the other and teeth with side faces of changing pressure angle from front to rear.

This invention relates only to the relieving of the side faces of the hob teeth. The tips of the teeth may be relieved in any usual or suitable manner.

In the embodiment of the invention illustrated in the accompanying drawings, the relieving movements are imparted to the tool and as the tool reciprocates, the hob blank is simultaneously rotated on its axis and the tool moved lengthwise of the blank to relieve the successive teeth correctly and in accordance with their helical arrangement. These motions are usual in hob-relieving machines.

The invention is illustrated in connection with the relieving of a taper hob. In the relieving of such a hob, it is required to feed the relieving tool toward the hob blank continuously, as the tool moves from one end to the other of the hob, in order to maintain the tool in operative relation to the hob. This feed motion is preferably effected in a direction perpendicular to the cone surface of the hob to prevent slippage between the side of the tool and the sides of the teeth being relieved.

Where the hob is tapered, it is desirable not only that the side faces of the hob teeth be relieved so as to be of changing pressure angle from front to rear so that the hob can be sharpened without altering its accuracy, but

also that hob have cutting edges of continuously increasing pressure angle from the large to the small end of the hob so as to get increased strength at the small end of the hob. The first of these objects is accom- 4 plished in the embodiment of the invention illustrated by using the relieving motion of the tool to tilt the tool continuously during the relieving of each tooth of the hob and the second of these objects is achieved by using the motion required to feed the tool relative to the hob in accordance with the taper of the hob, to tilt the relieving tool continuously as it moves from one end of the hob to the other.

In the drawings, the invention is illustrated as embodied in an attachment for a usual form of relieving lathe and the mechanisms of the lathe ordinarily provided for rotating the hob blank, producing the relieving movement and feeding the relieving tool lengthwise of the hob are employed for the same purposes in the present invention.

Referring first to Figures 1 to t inclusive, 10 indicates the work-piece, the hob to be relieved, in this case, a taper hob such as might be employed in bobbing spiral bevel gears. The hob blank is mounted between the centers L0 and 41 carried by the head stock 4:2 and the tail stock 43, respectively, of the 43 is slidably adjustable. The construction of the head and tail stocks and the adjustment of the latter form no part of the pres ent invention and may be of any usual or suitable type.

The work is rotated continuously, during the operation of the machine, being driven from one of the cone pull ys 4&6 by means of the driving dog designated generally at d7.

The relieving tool is designated by the numeral 34-. It is mounted, in a manner to be described more particularly hereinafter, upon a carriage 50 which slides on the horizontal ways or guides 51 provided upon the top of the bed or frame The table or carriage 50 is moved longitudinally of the bed or frame 45 in time with the work rotation, by means of a screw 52 which threads into a nut 53 securedto the carriage 50.

The screw 52 is driven from the head stock spindle 54 through the gears 55, 56, the shaft 57, the

gears

58, 59, 60, the shaft 61, and the

gears

62, 63, 64 and 65, the last named gear being secured to the screw shaft 52.

l/Vhere a taper hob is to be relieved, it is preferred, as stated above, to mount the relieving tool 34 so that it moves in its reliev ing movement in a direction perpendicular to the cone surface of the worlr whereby, as described in my co-pending application No. 202,695, filed June 30,1927, any tendency gularly adjustable plate 67.

of the relieving tool to slip sidewise, during relieving, due to the conical nature of the plate 67 which is angularly adjustable on "the carriage 50 and which is provided with an annular flange 68 that seats in a circular grooveor socket 69 provided in the uppe 3 face of the carriage 50. The relieving tool is carried on this plate 67 and, hence, by adjusting the plate 67 to the required angle, the relieving tool can be positioned to move in a direction perpendicular to the cone stir-- face of the hob 10.

7 moves longitudinally of the work-piece 10,

to maintain the tool at all times in operative engagement with the conical hob blank. For this reason, the carrier 70 is provided. This is mounted for sliding movement on the an- This carrier 70 is guided in its movement on the plate 67 by means of the ways 71 which engage a dovetailed guide surface formed on. the plate 67.

The mechanism for feeding the carrier 7 and with it the relieving tool, toward the hob blank during the movement of the carriage will now be described. Secured to. one side of the bed or frame 45 of the I machine is a bracket 73 and on this bracket is mounted an angularly adjustable guideplate 74. The guide-plate 74 is provided with a stud 75 that engages in a suitable socket or recess formed in the bracket 7 3 and 1,1,. it is about the axis of this stud 75 that the guide-plate 74 is angularly adjusted on the bracket 73. This adjustment of the'guideplate is made manually and the guide-plate can be secured in any adjusted position on f the bracket 73 by means of bolts 76 which pass through arouate slots 7 7 formed in the guide-plate concentric with the stud 75 and thread into the bracket 7 3. Graduations 78 are provided on an arcuate flange formed j at the edge of the bracket 73 and the guide-j plate 7 4 has an index mark 79 scribed on its upper face at its periphery to assist in setting the guide-plate accurately to an angle corresponding to the angle of taper of the ,1 hob 10.

There is a dove-tailed guide-rail 80 formed on the upper face of the guide-plate 74 and this guide-rail 80 is engaged by correspondlngly shaped surfaces of a slide or follower 81. The follower 81 is connected through the relieving tool 34 mounted thereon will be fed in toward the work as the carriage 50 moves longitudinally on the bed or frame 45. Thus, the relieving tool will be maintained automatically and continuously in operative engagement with the hob 10 despite the taper of the cone surface of the hob. Due to the angular setting of the plate 67, this movement of the carrier 7 0 will at the same time take place in a direction perpendicular to the cone surface of the hob 10.

Mounted-on the carrier 70 for reciprocable movement relative thereto is the relieving slide 85. This slide 85 is reciprocated by means of a snail cam 87, such as is ordinarily employed in a relieving lathe. This cam acts to feed the relieving tool 34 toward the hob as each tooth of the hob rotates beneath the relieving tool and then allows the relieving tool to return quickly to starting position ready for the succeeding relieving operation on the next tooth of the hob. The snail cam 87 is secured to the vertical shaft 88 which is ournaled in the extension 83 of the carrier 70. The cam engages a contact member or. follower 89 which is secured to the slide 85. A pair of springs 90, which are mounted upon rods 91 secured to the part 83 and slidable in the slide 85, serve to maintain the surface of the cam 87 at all times in contact with the contact member 89 and to return the slide 85 quickly to initial position after each tooth of the hob has been relieved.

The relieving cam 87 is driven continuously during the operation of the machine and in timed relation with the rotation of the work-piece 10 and the movement of the carriage or table 50 so that the proper relieving operation is imparted to the successive teeth of the hob. The mechanism for so rotating the cam 87 will now be described.

Mounted on the shaft 61 (Figure 1) at its inner end is a spur gear 95' forming one of a set of change gears 95, 96 and 97 which transmit the rotation of the shaft 61 to the shaft 98 suitably journaled in the bed or frame 45 of the machine. Thus, through the gears 95, 96 and 97, the shaft 98 is rotated in timed relation with the rotation of the work 10. This shaft 98 carries at its inner end a bevel gear 99 forming one of a set of differential gears of which the planet members 100 are mounted upon a spider 101 which is secured to the shaft 102 journ aled in the base or frame of the machine 45 in alignment with the shaft 98. The other side gear 103 of the differentia-l is journaled on the shaft 102 and is rotated in timed relation with the rotation of the lead-screw 52, being driven from the leadscrew 52 by means of the change gears104, 105, 106 and 107, the shaft 108, the bevel gears 109 and 110, the shaft 111, the worm 112, and the worm wheel 113 which is secured to or formed integral with the side gear 103. From the construction described, it will be seen that the shaft 102is driven continuously in timed iio . 121 (Figure 4).

relation with the work rotation and table movement.

The shaft 102 carries at its outer end a spur gear 115 which forms one of a set of change gears 115, 116, 117, and 118 whlch serve to transmit the motion of the shaft 102 to a shaft 120 which extends longitudinally of the machine between the sides of the bed or frame 45 and to which is keyed a bevel gear This bevel gear 121 meshes with and drives a bevel gear 122 on a vertical shaft 123 which is journaled in the table or carriage 50 co-axial with the flange 68 of the plate 67.

Secured to the shaft 123 at its upper end is a bevel gear 124 which meshes with a bevel gear 125 that has a splined connection with the shaft 126. The bevel miter gear 125 is suitably journaled in the plate 67 while the shaft 126 is suitably journaled adjacent its outer end in the carrier 70. Keyed to the shaft 126 at its outer end is a bevel gear 127 which meshes with and drives a bevel gear 128 that is secured to the cam shaft 88. Through the mechanism just described, it will be seen that the cam 87 is rotated continuously during the operation of the machine in timed relation with the work rotation and carriage movement.

So far, the means for rotating the work, the means for moving the carriage or table 50, the angular adjustment of the relieving tool, the means for imparting a feed movement to this tool in a direction perpendicular to the cone surface of the Work and the means for imparting the relieving movement to the too]. have been described. I shall now describe the means for continuously tilting the tool during the relieving of the teeth of the hob and as the tool moves longitudinally from one end to the other of the hole.

The relieving tool 34 is secured by means of straps 130 and bolts 130 to an angularly movable plate 131. This plate 131 is mounted upon a slide 132 for pivotal movement about the axis of the stud 133 which is journaled in the slide 132. The slide 132 is adjustable by means of the screw 135 upon a second slide 136 which, in turn, is adjustable by means of a screw 137 upon the relieving slide 85. The ustments effected by means of the screws 135 and 137 are in directions at right angles to each other and permit of adjusting the relieving tool for relieving hobs of different diameters and of different pitches.

The plate 131 is provided with an extension or arm 138 and this extension or arm is provided on its upper face with fine clutch teeth adapted to be engaged by similar clutch teeth on the lower face of an arm 139. This arm 1.39 is provided with a slot 140 in its outer end and in this slot is adjustably mounted a roller 141. The roller 141 engages a guide rail 142 (Figures 1 and 3) which is secured to the carriage 5O. By engaging the clutch teeth of the arm 138 and the arm 139, the arm 139 can be connected to the plate 131.

The guide-rail 142 is straight in the machine shown and extends parallel to the axis of the work. As the guide-rail is inclined to the path of movement of the relieving slide 85, it follows that during the relieving of each tooth of the hob, the support 131 and the relieving tool 34 carried thereby are moved angularly on the slide 132 thereby tilting the relieving tool relative to the side face of the hob tooth being relieved as the hob tooth rotates past the cutting edge of the relieving tool. Thus, the pressure angle of the side face of the tooth of the hob is changed constantly from front to rear of the tooth and so the hob is relieved in such a manner that it will always have the same cutting action on the tooth of a gear.

It follows, also, that as the guide surface of the rail 142 is inclined to the path of movement of the carrier 70, the support 131 and relieving tool 34 will be given a continuous angular movement as the relieving tool moves from one end of the hob to the other thereby producing on the hob cutting edges of changing pressure angle from one end of the hob to the other. By adjusting the slide 136 so that the axis of the stud 13.3 lies in the pitch surface of the hob, the angular tilting movement of the relieving tool 34 will take place about points lying in the pitch surface of the hob and consequently the hob will be of constant pitch from one end to the other measured on that surface. In like manner, the hob might be made of constant pitch on the root surface or any other surface thereof.

A spring 143 secured at one end to the arm 139 and at its other end to the guide-rail 142 serves to maintain the roller 141 at all times in contact with the guide-rail.

Figures 1, 3 and 4 show the relieving tool 34 positioned for relieving one side of the hob thread. The opposite side of the thread may be relieved by substituting an appropriate relieving tool and by disconnecting the arm 139 from the plate 131 and connecting instead with the plate 131 another arm 145 shown in dotted lines in Figure 3. This arm 145 extends beneath the hob to the other side of the machine and like the arm 139 is provided with a slot 140' in which is adjustably mounted a roller 141 which is adapted to engage the inner face of a guide-rail 142 that is secured to the carriage or table 50 in a manner similar to the guide-rail 142. A coil-spring 143' may be employed to maintain the roller 141 in engagement with the guide-rail 142. Through the guide-rail 142', the roller 141, the arm 145 and the plate 131, the proper tilting movements can be imparted to the relieving tool to relieve the other side of the hob thread to produce side cutting edges on that side of varying pressure angle from one end of the hob to the other and relieved side tooth surfaces of varyingpressure angle from front to rear of the hob teeth.

The action of the relieving tool is clearly illustrated in Figures 5 and 6. As the hob rotates on its axis, the relieving tool is moved continuously toward and away from the hob, moving toward the hob during the passage of each tooth 11 of the hob under the tool and being moved quickly away from the hob again after the tool has cleared a tooth so that the tool will be in position to engage the follow ing tooth of the hob. As the relieving tool 34 is fed into the tooth of the hob, it is simultane ously tilted through the engagement of the

roller

141 or 141, as the case may be, with the guide 142 or- 142'. Thus,.the angle of inclin ation of the cutting edge of thetoolto the axis of the hob will be changed as the tool moves from front to rear of the tooth 11. Hence, the sides of the teeth of the hob will be of changing inclination or pressure angle from front to rear. By suitably locatingithe guide surface 14.2 or making it of proper curvature, therefore, teeth, can b'eproduced on the hob having side surfaces so inclined to the axis of the hob that the pressure angle of the cutting edges after sharpening, will be changed just enough from the pressure angles of the original cutting edges to compensate for the changed position of the cutting edges 7 place about points 37, 37', etc., lylng on the due to sharpening.

Figure shows in full lines and in dotted lines two positions assumed by the relieving tool 34 as it relieves the sidetooth surface 36 of the tooth 11 of the hob 10. The movement of the tool toward the blank provides the necessary side. clearance for cutting and the tilt ing of the tool during this movement provides the tooth face 36 with a continuously varying pressure angle from front to rear of such amount that after the hob tooth is sharpened, the new cutting edges will have pressure angles varied just enough from the pressure angles of the original cutting edges .to compensate for the changed position of the cutting edges in the helical surface of the hob thread.

As the carrier 'ZO moves continuously in a direction inclined to the

guidesurface

142 or 142, as the case may be, during the relieving of the hob, the tilting motion imparted to the relieving tool will be continuous from end to end of the hob. Hence, the inclination of the sidecutting edge 35 of the relieving tool relative to the side faces of the hob teeth being relieved varies continuously as the tool moves longitudinally of the hob. In this way side tooth surfaces are produced on the hob which are of continuously varying prlessure angle from one end of the hob to the ot 1G1.

In producing a taper hob for the purpose of cutting spiral bevel gears, the pressure angles of the cutting edges are preferably in creased from the large to the small end of thehobso as to provide teeth at the small end ofthe hob of-increased strength. ,In Figure,

the cutting edge 35 of'the tool to the hob;

thread has been increased with the conse-, quence'that the tooth 21 of the hob will have, a side cutting edge 19 of increased pressure;

angle as compared with the pressure angle of the sidecutting' edge 16 of the hob tooth 17 For'the pur'poseof comparison, the position of the tool relative to the blank when relieving the tooth l7z-is shown in dotted lines at 34 i at, the right hand side of Figure 5 to indicate how the tool has been tilted continuously to the postion 34', shown in full lines, which is the position it has assumed when it reachesthe tooth 21. As will be understood, the tilting motion of the tool is continuous as the tool moves longitudinally of the hob' from one end to the other so that the pressure angles of cor.- responding side cutting edges of the hob vary continuously from one-end of the hob to the other.

As stated above, if the tilting motion takes pitch surface 15 of the hob, the pitch 79 of the hob can be made uniform on this surface as shown. So a hob relieved'according to the present invention may be employed for cut ting spiral bevel gears according to the processof the Trbojevich Reissue Patent No. v

16,17 3" of September 22, 1925, or the process of the Taylor Patent No. 1,618,240 of February 22,1927, etc. v

As stated above, the guide surface of the

rails

142 and 142 are straight and extend parallel to the axis of the work. When the" guide-rail is set at the correct distance from the axis of the work, it has been found that this straight guide surface will impart the correct tilting movement to the relieving tool to properly change the pressure angles of the cutting edges of the hob during the relieving of the hob teeth. The guide surface may, however, be curved or inclined to the axis of the hob as may be determined by the'distance' of the guide surface away from the axis of the hob and by the amount of movement required to impart suflicient tilting movementto the tool as it moves from endto end of the hob to vary the pressure angles of'the cutting edges the desired amount.

In the case of a cylindrical hob for cutting spur gears, there would ordinarily be no object in changing the pressure angle of the cut ting edges from one end of the hob to the other and in relieving such a hob, neither the Plate 6 01 hecarrier 70 would have any an i gular adjustment. The relieving tool would move perpendicular to the pitch surface of the hob, namely, perpendicular to the axis of the hob. In this case, the tilting movement of the tool required to properly relieve each of the teeth of the hob according to this invention would be obtained by selecting a guide member 1 12 or 142 which has its guiding surface inclined at the proper angle to the axis of the hob. Thus, such a hob could be relieved so that each of its teeth would'have side faces of changing inclination to the axis of the hob from front to rear but the cutting edges of the hob would be of the same pressure angle from one end of the hob to the other. The hob would, therefore, be suited to cut spur gearsand would be of the same accuracy after sharpening as when new.

Figure 7 shows a taper hob relieved accord- 2 ing to this invention where the two features of changing inclination of the side faces of the hob teeth from front to rear and of changing pressure angle of the cutting edges of the hob from one end of the hob to the other are combined. Such a hob would be relieved with the attachment shown in the drawings and with the plate 67 and carrier adjusted at an angle to the axis of the hob determined by the cone angle of the hob. 14: designates the axis of the hob, 15 its pitch cone surface, and 13 is a pitch cone apex. Due to the method of relief, the pressure angles of the hob teeth will vary continuously from one end of the hob to the other. Thus, the pressure angle a of the cutting edge 16 of the hob tooth 17 will be less than the pressure angle a of the opposite side cutting edge 18 of the same tooth and these two pressure angles in turn will be less than the pressure angles a and a of the corresponding side cutting edges 19 and 20, respectively, of the hob tooth 21 at the small end of the hob. The pressure angles of the cutting edges of the

teeth

22, 23, 2 1 and 25 intermediate the

teeth

17 and 21 will be greater than the pressure angles of the cutting edges of the tooth 16 and less than the pressure angles of the cutting edges of the tooth 21, the pressure angles of the cutting edges of each of the

teeth

22, 23, 24 and 25 depending upon their position along the length of the hob, the cutting edges of the hob increasing continuously by reason of their relief from one end of the hob, to the other. Each tooth of the hob will have side faces of varying pressure angle, that is, of varying inclination to the axis of the hob, from front to back, as already explained with reference to Figure 6 and as already ex plained, the pitch of the hob can be made constant from one end of the hob to the other on any surface of the hob, such as the pitch surface 15.

It will be understood, also, that the present invention is not limited to the formation of hobs of constant pitch, as with the present in vention it is possible to change the pressure angles of theside faces of the teeth of a hob of varying pitch from front to rear so that the hob will always have the same cutting ing from one end of the hob to the other so that it increases towards the small end of the hob, it is possible to use a conical grinding wheel with which to relief-grind. The increase in pressure angle of the teeth at the small end of the hob permits of relieving the successive teeth of the hob with a grinding wheel without danger of interference with other teeth. I

While the invention has been described in connection with a particular embodiment and in connection with a particular use for that embodiment, it will be understood that the invention is capable of various further modi fications and uses without departing from its scope and this application is intended to cover any adaptations, uses, or embodiments of the invention following, in general, the "principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which it pertains and as may be applied to the essential features hereinbefore set forth and as fall within the scope of the invention or the limits of the appended claims.

Having thus described my invention, what I claim is:

1. The method of relieving a hob which comprises effecting a relative relieving movement between a relieving tool and hob blank for each tooth of the hob while rotating the hob blank on its axis and moving the relieving tool and blank relative to one another longitudinally of the blank and tilting the relieving tool as it moves from one end of the hob to the other to cause the tool to produce teeth on the hob having side cutting edges of changing pressure angle from one end of the hob to the other.

2. The method of relieving a hob which comprises effecting a relative relieving move ment between a relieving tool and the hob blank for each tooth of the hob while rotating the hob blank on its axis and moving the relieving tool and blank relative to one another longitudinally of the blank and simultaneously changing the inclination of the side cutting edge of the relieving'tool to the axis of thehob blank continuously during the relieving of the side faces of each tooth of the hob and as the relieving tool moves from one end of the hob blank to the other.

his

- dinally of the hob to present successive teeth of the hob to the action of the relieving tool, and while relieving the side faces of each tooth of the hob, tilting the relieving tool continuously to produce side faces on 'the hob teeth of changing inclination from front to rear.

4.. The method of relieving a hob which comprises rotating a hob blank on its axis at a uniform velocity while producing a relative movement between the blank and relieving tool longitudinally ofthe hob at a uniform velocity topresent successive teeth of the hob to the action of the relieving tool, and

while relieving the side faces of each tooth of the hob, tilting the relieving tool continuously to produce side faces on'the hob teeth of changing inclination from front to rear. v

5. The method of relieving a taper hob which comprises tilting the cutting edge of the relieving tool continuously during the relieving of the side faces of. each toothfof the hob and as the relieving tool moves from one end of the hob to the other whereby to produce teeth on the hob having side faces of continuously changing pressure angle from front to rear and having side'cutting edges of continuously changing pressure angle from one end of the hob to the other. 6 The method of relieving a taper hob i Whichcomprises producing relative relieving movements between the hob blank and the relieving tool to relieve side faces of successive teeth of the hob while rotatingthe hob blank on its axis and simultaneously producing ar-elative movement between the blank and relieving toollongitudinally of the blank to present successive teeth of the hob to the action of the relieving tool, and simultaneously tilting the'relieving tool con tinuously as it moves from one end ofthe hob to the other to produce side cutting edges ofcontinuously changing one end of the hob to the other.

7. The method of relieving ajtaper hob which comprises producing relative relieving movements"betweenthe hob blank and the relieving tool to relieve the side faces of successive teeth of the hob while rotatingthe blank on its axis at a uniform velocity andsimultaneously producing a relative movement between the blank and relieving tool lon'gitudinallyof the hob at a uniform velocity to presentsuccessive teeth of the hob to .the action of the relieving tool, and simultaneously tiltingthe relieving tool continuously as it moves from one end ofjthe hobto the other to produce side cutting edges of continuously" changing pressure angle from one end of the hob to the other.

i 8. The method of relieving a taper hob pressure angle from which comprises producing relative relieving movements between the hob and relieving tool to relieve the sides of successive teeth of the hob while rotating the hob blank on its axis at a uniform velocity and simultaneously producing a relative movement between the hob blank and the relieving tool longitudinally of the blank at a uniform velocity to present successive teeth of the hob to the action of the relieving tool and changing the inclination of the side cutting edge of the relieving tool to the axis of the hob continuously during the relieving of side faces of successiveteeth of the hob and as the tool moves from one end of the hob blank to the other.

v9. The method of relieving'a taper hob which consists in producing relative relieving movements between a relieving tool and the hob blank while rotating the blank on its axis continuously at a' uniform velocity, producing a relative movement between the tool and blank longitudinally of I the hob blank at a uniform velocity and feeding the relieving tool relative to the blankin accordance with the taper ofthe hob, and simultaneously varying the inclination of the side cutting edge of the relieving tool relative to the axis of the hob blank whereby to produce cutting edges on the hob of varyingpressure angle from one endof the hob to the other.

10. The method of relieving a taper hob which comprises producing a'relative relieving'movement between a relievin'g'tool-and the hob blank while rotating the blank on its axis continuously, simultaneously producing a relative movement between the hob blank 7 and the relieving tool longitudinally of the blank to present successive teeth of'the blank to the action of the relieving tool and simultaneously producing a relative feeding move inentbetween the relieving tool and the blank in a direction perpendicular itothe'con'e sur face of the blank continuously while the tool is moving from one end of the blank to the other, and changing the inclination of the side cutting edge of the relieving tool to the axis ofithe blank continuously asit moves from one end of the blank'to' the other.

support, a rotatable work support, a car-' r age upon which one of said supports is mounted, means for moving the carriage lon 11. In apparatus for relieving hobs, a tool .115

ments, and means for varying the inclination of the side cutting edge of the relieving tool relative to the axis 'of'theworkj continu ously during the relieving of the side faces of each'hob tooth.

12; In apparatus for relieving taper hobs,

atool support, arotatable"work'support, a

carriage upon which one of said supports is mounted, means for positioning the tool support so that it will move in a plane perpendicular to the cone surface of the work, means for moving the carriage longitudinally of the work, means for rotating the work support on its axis, means for simultaneously producing a relative relieving motion between the tool support and the work in timed relation with the work and carriage movements, means for imparting a relative feed movement between the tool support and the work in a direction perpendicular to th cone surface of the work as the carriage moves longitudinally, and means for changing the inclination of the side cutting edge of the re lieving tool to the axis of the work continuously during the relieving of the side faces of each tooth of the hob.

13. In apparatus for relieving hobs, a tool support, a rotatable work support, a carriage upon which one of said supports is mounted, means for moving the carriage longitudinally of the work, means for rotating the worl support on its axis, means for imparting a relieving motion to the tool support in timed relation with the work and carriage movements, and means actuated by said relieving movement for changing the inclination of the side cutting edge of the relieving tool relative to the axis of the work continuously during the relieving of the side face of each tooth of the hob.

14. In apparatus for relieving taper hobs, a tool support, a rotatable work support, a carriage upon which one of said supports is mounted, means for moving the carriage longitudinally of the work, means for rotating the work support on its axis, means for imparting a relievingmovement to the tool support in timed relation with the work and carriage movements, means for simultaneously producing a relative feed movement between the tool and work in accordance with the taper of the cone surface of the hob, and means actuated by the said feed movement for changing the inclination of the side cutting edge of the relieving tool to the axis of the work continuously as it moves from one end of the work to the other.

15. In apparatus for relieving hobs, a bed, a reciprocable tool slide, a rotatable work spindle, a carriage upon which the tool slide is reciprocable, said carriage being movable on the bed in a direction longitudinal of the work, a tool support rotatably mounted on the slide and adapted to carry a relieving tool, means for moving the carriage longitudinally of the work, means for rotating the work spindle on its axis, means for imparting a relieving movement to the tool slide in timed relation with the work and carriage movements, and means actuated by the movement of the tool slide, during the relieving of each tooth ofthe hob,for moving the tool support on its axis to change the inclination of the side cutting edges of the relieving tool relative to the axis of the work continuously during the relieving of the side faces of each tooth of the work.

16. In apparatus for relieving hobs, a bed, a reciprocable tool slide, a rotatable work spindle, a carriage upon which the tool slide is reciprocable, said carriage being mounted on the bed for movement in a direction longitudinal of the work, a tool support rotatably mounted on the slide and adapted to carry a relieving tool, means for moving the carriage longitudinally of the work,.means for rotating the work spindle on its axis, means for imparting a relieving movement to the tool slide in timed relation with the work and carriage movements, a guide secured to the carriage, and a follower carried by the tool support adapted to engage said guide, said guide being so formed that the relieving movement of the slide causes a movement of the tool support on its axis to change the inclination of the side cutting edge of the relieving tool continuously to the axis of the work during the relieving of each tooth of the hob.

17. An attachment for a lathe provided with a bed, a rotatable work spindle, a slidable carriage movable on the bed in a direction longitudinal of the work, means for moving the carriage, means for rotating the work spindle, and a shaft driven in timed re lation with the work spindle and carriage movements, comprising a reciprocable tool slide, a tool support rotatably mounted on said slide, means driven from said shaft for reciprocating said slide, and means adapted to be actuated by movement of said slide for moving said tool support on its axis to change the inclination of the side cutting edge of the relieving tool relative to the axis of the work continuously during the relieving of each tooth of the work.

18. An attachment for a lathe provided with a bed, a rotatable work spindle, a slidable carriage movable on the bed in a direction longitudinal of the work, means for moving the carriage, means for rotating the work spindle, and a shaft driven'in timed relation with the work spindle and carriage movements, comprising a reciprocable tool slide, a tool support rotatably mounted on said slide, means driven from saidshaft for reciprocatingsaid slide, and means adapted to be actuated by the movement of said carriage for moving said tool support continuously on its axis to change the inclination of the. side cutting edge of the tool continuously relative to the axis of the work during the relieving of the side faces of each tooth of the worl 19. In apparatus for relieving taper hobs,

a bed, a reciprocable tool slide, a rotatable work spindle, a carriage movable in adiupon which one of rection longitudinal'of the work, a tool sup port rotatably, mounted on the slide and adapted to carry a relieving tool, a, carrier uponwhich the slide is-reciprocable, a plate uponwhichthe carrier is movable, said plate being mounted on said carriage for angular adjustment thereon to position the tool slide -and carriage for movement in a direction perpendicular to "the cone surface of the work, means for rotating the work spindle on its axis, means for imparting movement to the carriage, means for moving the carrier, means for reciprocating the tool slide, a guide on the carriage, and a follower carried by the tool support adapted to engage said guide whereby movement of the tool carriage acts to move the tool support continuously during movement of the carriage to change the inclination of the side cutting edge of the relieving tool continuously relative to the axis of the work as the tool moves from one end of the work to the other.

20. In apparatus for relieving hobs, a tool support, a rotatable work support, a carriage upon which one of said supports is mounted, means for moving the carriage longitudinally of the work, means for rotating the work support on its axis, means for imparting relieving movements between the tool and work supports in timed relation with the work and carriage movements, and means for changing the inclination of the side cutting edge of the relieving tool to the axis of the work as the tool moves relatively from one end of the work to the other to produce teeth on the hob having cutting edges of changing pressure angle.

21. In apparatus for relieving hobs, a tool support, a rotatable work support, a carriage said supports is mounted, means for moving the carriage longitudinally of the work, means for rotating the work support on its axis, means for. imparting relieving movements between the tool and work supports in timed relation with the work and carriage movements and means for changing the inclination of the side cutting edge of the relieving tool to the axis of the work both as the tool relieves each tooth of the hob blank and as the tool moves relatively from one end of the work to the other whereby to produce teeth having side faces of changing pressure angle from front to rear and side cutting edges of changing pressure angle from one end of the hob to the other.

22. In apparatus for relieving hobs, a tool support, a rotatable work support, a carriage upon which one of said supports is mounted, means for moving the carriage longitudinally of the work, means for rotating the work support on its axis, means for imparting re-f lieving movements between the tool and work supports in timed relation with the work and carriage movements, and means actuated by movement of the carriage for changing the hobs,

the work support on its axis, meansfor imparting relieving movements between the tool and work supportsqln timed relat on with the work and ;C11T1tg6 movements,

meansoperative on movement of the carriage forproducing a relative feed movementubetween the tool and work to maintain the. tool in operative relation with the conical. blank as it moves relatively from one end thereof to the other, and means operative during'feed movement for changing the inclination of the side cutting edge'of the tool to the axis of the work during relieving of= difierent teeth of the hob whereby tovproduce teeth on'the hob sure angle from one end thereof to theother'.

24;. In apparatus for relieving taper hobs. a tool support, a rotatable w'orksupport, a carriage upon which one of said supports is mounted, means for moving thecarriage longitudinally of the; work,-means for rotating the work support'onlits axis, means forim: parting relievingmovements between the tool and work supports in timed relation with the work and carriage movements, means for a;

producing a relative-feedmovement between the tool and work to maintain the tool'in op,- erative relation with the conical blank as the tool moves relatively from one end of the work to the other and'means for. changing the inclination of the side cutting edge of the tool to the axis of the work during relieving ofdifierent teeth-of the hob blank whereby to produce teeth on thehob having side zcutting edges of varying pressure angleirom g one end of the hob tothe other. 1

25. In apparatus'afor relieving hobs,"a tool support, a rotatable work support, a carriage upon which one of said supports is mounted,

means for moving the carriage longitudinal- 1y of the work, means for rotatingthe work support on its axis, means for imparting re lieving movements between the tool and work supports in timed relation with the workand carriage movements, means whereby the relieving movement of: the tool operates to tilt thBliOOl continuously during relieving of each tooth of the hob blank, and meansactuated 'bymovement of the carriage for fur-f 'ther tilting the relieving tool continuously as it moves relatively. from one end ofthe work to the other,

7 26,111 apparatus for relievingtaper'hobs, a tool support, a rotatable work support,-a-

carriage upon which one of said supports'fis having side cutting edges-of varyingpresmounted, means for moving the carriage longitudinally of the work, means for rotating the work support on itsaxis, means for imparting relieving movements between the tool and work supports in timed relation with the work and carriage movements, means for producing a relative feed movement between the tool and work supports to maintain the tool in operative relation with the conical blank as it moves relatively from one end of the blank to the other, means whereby the relieving movement of the tool operates to tilt the relieving tool continuously during the relieving of each tooth of the blank, and means operative during the feed movement for further tilting the relieving tool during relieving of different teeth of the hob whereby to produce teeth on the hob having side cutting edges of varying pressure angle from one end of the hob to the other.

27. In apparatus for relieving hobs, a bed, a carriage mounted on the bed for movement longitudinally thereon, a rockable tool support and a work support, one of said supports being mounted on the bed and the other on the carriage, means for rotating the work support, means for effecting movement of the carriage, a guide mounted on the bed, and

means operatively connecting the guide with the tool support whereby on movement of the carriage, the tool support is rocked on its axis to change the inclination of the side of the tool to the axis of the work to produce .v cutting edges of different pressure angle on different teeth of the hob.

' 28. In apparatus for relieving hobs, a bed, a carriage mounted on the bed for movement longitudinally thereon, a slide reciprocable on the carriage, a tool support rockably mounted on the slide, a work support rotatably mounted on the bed, means for effecting movement of the carriage, a guide mounted on the carriage, means for reciproeating the slide to impart relieving move- 4.5

ments to the tool and means operatively connecting the guide with the tool support whereby on movement of the slide, the tool support is rocked to produce side faces of changing pressure angle from front to rear on the teeth of the hob.

29. In apparatus for relieving taper hobs, a bed, a work support rotatably mounted on the bed, a carriage mounted on the bed for movement axially of the work support, a plate angularly adjustable on the carriage, a carrier reciprocable on the plate, a slide reciprocable on the carriage, a tool support rockably mounted on the slide, a guide angularly adjustable on the bed, means operatively connecting the guide to the carrier to produce a feed movement of the tool support relative to the work support to maintain the tool in operative relation with the conical blank as it moves relatively to one end thereof to the other, a guide mounted on the carriage, means work. ERNEST C. HEAD.