US1183020A - Gear-tooth-grinding machine. - Google Patents

Description

M. MAAG.- GEAR TOOTH'GRINDWG MACHINE. APPLICATEQN FILED AUG-8, 1913.

"WEI-n01? A ATTORNEY atented May 16, 1916. 4 SHEETS-SHEET! r I d wlriissses M. MAAG.

GEAR TOOTH GRINDING MACHINE.

APPLICATION FILED AUG-3| I913- 1,183,020. Patented May16, 1916.

4 SHEETS-SHEET 2- WITNESSES INVENTOH M. MAAG.

GEAR TOOTH GRINDING MACHINE.

APPLICATION FILED AUG-8|1913.

Patented May 16, 1916.

4 SHEETSSVHEET 3.

' INVENTOR M. MAAG'.

GEAR TOOTH GRINDING MACHI APPLICATION FILED AUG-3| I91 Ponted May 1 4 SHEETS-SH E 4- WITNESSES."

l/I/I/EIVTOR j; ATTORNEY Max MAAG, or ZURICH, SWITZERLAND.

GEAR-TOOTH-GRINDING MACHINE.

To all whom it may concern Be it known that I, MAX MAAG, citizen of Switzerland, residing at Zurich, in the Canton of Zurich, Switzerland, have invented new and useful Improvements in Gear- Tooth-Grinding Machines, of which the following is a specification.

This invention relates to a machine for finish grinding the previously cut teeth of involute gears, according to the intermeshing generating process, the object being to generate theoretically correct tooth surfaces. This high degree of accuracy is obtained by a number of new means, each of which contributes its part toward increasing the accuracy, and which all combine to produce theoretically correct curves.

One distinguishing feature of the machine is the employment, for the simultaneous grinding of a right and of a left side of a tooth or of two teeth, not of a single grinding wheel having the profile of a rack tooth, but of two entirely independent wheels, which can be adjusted, by suitably inclining and separating them, to the angle of indination and to the distance between two opposing -faces of the same or different teeth of the generating rack. This construction might appear, at first glance, as an unnecessary complication, but it is precisely the use of the two independent grinding wheels instead of one which overcomes the principal difliculties heretofore encountered in the generation of accurate tooth profiles. These difficulties consist in the maintenance of the exact form and position of the active grinding surfaces. 1

As is well known, when one wheel having the profile of a rack tooth is used, the cut- 7 rate involute tooth curves.

ting edges of this tooth are formed by the bounding lines of two truncated cones, which gradually lose, by theununifform wear of the grinding surfaces, the straightness necessary for the generation of accu- After finishing one or more teeth, the wheel has to be set up and trued in order to restore its original shape. This truing presents especial difficulties and does not render possible the permanent maintenance of the shape of the grinding surfaces, because the shape of the wheel varies between truings, so that during that time more or less inaccurate tooth profiles will be generated. This defect is obviated by the use of two grinding wheels independent of each other, since it enables Specification of Letters Patent.

Application filed August 8, 1913.

Patented May 16, 1916. Serial no. 783,763.

the active grinding surfaces to be maintained in planes at right angles to the spindle axes. As will be further explained herein after, it is possible so' to form the wheels that the plane form, necessary for the intermeshing rolling action, is net only not affected by wear but, on the contrary, is con-' stantly renewed, so that, to maintain it, no truing mechanism is necessary.

To always obtainteeth of equal width, it is, however, not only necessar that the exact form of the grinding sur aces be ma1ntained, but also that their position, once taken, be not varied. With single wheels of the shape of a rack tooth, this again requires setting them up and truing them and the position of the active bounding lines is determined by the adjustment of the truing diamonds. at these diamonds are themselves subject to wear, 'so that the wheels become slightly thicker ,each time they are trued. This causes a gradual separation of the lines bounding the working surfaces and consequently the teeth finished last are thinner than those finished first. This objection is also overcome by the present invention, because the original position of the grinding wheel plane remains constantly the same. This is obtained by an automatic adjustment or setting-up of the Wheels controlled by the wear itself and in exact accord therewith. A suitable feed; or adjusting mechanism is set in operation by a feeler which, in the correct fiaosition of the grinding surface, rests against the same, but no longer contacts the same after an extremely slight wear. The wheel is then moved toward the feeler, that is, into the correct working position, in which it again contacts the feeler. By suitable construction of the latter, it is possible to render its own Wear practically negligible, so that the position of the working grinding plane will be always -maintained the same. and all the teeth will have exactly the same cross-section, whether finished at the end or at the beginning of the operation.

The substitution of two independent grinding wheels for a singleone has, therefore, as its principal advantage, an independence, not' otherwise obtainable, of the generating grinding surfaces from wear.

A further advantage which results from the use of two wheels consists in their adjustability for any desired thickness of 'tooth, since the two wheels can be used for IOU finishing gears of any desired pitch and thickness of teeth, while, where only one wheel is employed, a special one is needed for each pitch and tooth thickness.

A third, very important advantage of the use of two wheels instead of one is the possibility of generating theoretically correct 1nvolutes on any desired pitch circle, when, as in the present case, the teeth are generated by the inter-meshing rolling process. When working with rolling arcs it is only possible in a very few cases to employ arcs of the correct diameter, since it would require too many of them. Consequently,

manufacturers are usually satisfied to employ a rolling arc of approximately correct diameter, which necessarily results 1n the production of teeth, the curves of which vary more or less from the correct involute.

In my application Serial No. 711,418, filed July 25, 1912, a simple means is disclosed by which, with the employment of rolling arcs of any desired diameter, theoretically correct involutes can be generated on pitch circles of any desired diameter. This consists in forming the angle of the cutting edges of the tool to correspond with the ratio of the pitch circle and rolling are d1- ameters in each case. The cutting angle is easily adjusted, when two independently adjustable wheels are employed, by su1tably inclining the grinding wheel spindles, while, when a single wheel having the outline of a rack tooth is employed, a special wheel is necessary for each variation of.the angle of the cutting edges.

In addition to constantly maintaining correct the form and position of the grinding wheel, the method of producing the relative rolling motion between the tool and the work plays an important role in the production of accurate tooth profiles.

In developing this invention the following basic considerations were held in mind: The number of elements necessary for producing the rolling action should be kept as low as possible, and only such elements should be employed which can be produced with the highest degree of accuracy, and the rolling movement should be the working stroke of the machine, the work being simultaneously fed forward in the direction of its axis. These two conditions are ideally fulfilled, as is well known, by the employment of a rolling arc and band, since it does away with all transmission elements, such as gear trains, feed-screws and the like, and the accuracy of the result depends solely upon the absolute straightness ofthe guides for the transverse feed movement of the work and the circularity of the rolling are, both of which conditions can be practically fulfilled with the greatest accuracy. But in addition to the production of truly accurate tooth curves, there is also the requirement that the rolling movement snouldproceed rapidly and automatically, that is to say, it should represent the actual working stroke of the machine, while the feed of the work toward the grinding wheel, or vice versa, of the wheel toward the work, should take place only slowly and in the direction of the work axis. For only in this way will actually correct involute curves be generated, while, when the working stroke is in the direction of the work axis and the feed in the direction of the rolling movement, which is not the case in the present invention, profiles will be generated which are not smooth involutes but polygons. The profiles then show, throughout the entire length of the teeth, edges or ridges lying more or less close together, which, when the gears are running in mesh, strike against each other and produce a disagreeable noise. These edges, in wheels of Soft material, be-

come indeed rounded-off in a shorter or longer time, so that the profiles can be practically considered as smooth curves, but this is not the case with gears of hardened steel, such as are universally used in automobile and airship practice. Such gears should be noiseless, notwithstanding their high speed, but it has heretofore been impossible to produce them, while, when, on the contrary, the working stroke of the machine takes place in the direction of the rolling movement while the feed is in the direction of the work axis, the profiles are always formed as smooth curves, and the gears are distinguished by their peculiar noiselessness in running.

The production of the rolling movement by means of a rolling arc and band in combination with means for making the working stroke take place in the direction of the rolling movement and the feed in the direction of the work axis, that is, the mutual cooperation of two constructions, old and well known in themselves, gives a new and useful result, whereby the production of accurate and smooth-curved profiles is rendered possible for the first time. Furthermore, when only one grinding wheel is used, that is, when each tooth flank is ground by itself, 115 my invention enables theoretically accurate profiles to be formed, so that my invention is not limited to the employment of two wheels. I

I will now describe a machine for grind- 120 ing the teeth of spur gears, constructed according to my invention.

In the drawings, Figure 1 is a side elevation, Fig. 2 is a front view of the machine, and Figs. 2 and 2" are detail views of the 125 cross-slide actuating means. Figs. 3 and 4 represent the feeler and adjusting mechanism, while the mode of operation of the grinding wheel is diagrammatically illustrated in Figs. 5 and 6.

. 60, carried by the table shaft 27 and a hand wheel end of the machine and drives,

The general construction of the machine is illustrated in Fi 1 and 2. The work-' table 3 runs in gui es 2 on-the bed 1, and is slowly reciprocated b the screw shaft 4, which is driven from the main driving shaft 5 through worms and worm wheels 6, the lat ter being alternately clutched to the screwshaft 4, theclutch being thrown by the do 3, by reversing mec anism 7, of the ordinary construction. 7 Shaft 5 extends transversely across the through bevel gears, a longitudinal shaft 67, on which is slidably keyed a sleeve worm 68, which meshes'with a worm wheel 69 carried on the lower end of a vertical shaft 8, on the upper end of which is a crank disk 9, carrying, in a radial slot an adjustable crank pin 10, which engages in a slot 71 in a cross slide 11, slidably mounted in guides on table 3, whereby the disk 9 imparts a relatively rapid transverse reciprocation to the slide 11.

Integral with the slide 11 is the head stock 61, in which is journaled the spindle 12, which carries the gear 13, to be ground, on its front end. On the rear of the spindle 12 is mounted an interchangeable index ratchet wheel 62, the number of the teeth of which corresponds to the number of teeth of the work, or to a multiple thereof, and which serves to index the work through one or more teeth, after one or more teeth sides have been finished. The pawl 63 is actuated to turn thewheel 62 by any suitable mechanism, which I have not shown in the drawing, as it may be of any usual construction, sald pawl being mounted in a casing 64, on which is bolted an interchangeable rolling are 14 of suitable diameter. With the periphery of said are engage the ends of two bands 15, the other ends of which are secured .to blocks 16, which are mounted, so as to be vertically adjustable in brackets 17 bolted to the table 3. The bands 15 are stretched parallel to the guides of the cross slide 11, so that, when the latter is moved, said bands cause the rolling arc, the index wheel 62 and the work 13 to turn, the latter moving exactly as if it were rolling on a rack. The teeth of this rack are represented by the two grinding Wheels 18.

A cross rail 21 is mounted for vertical ad justment in guides 19 on standards 20. It is also provided with guides 22 in which slide two carriages 23, movable toward and away from each by a right and left hand screw 24. These carriages support in turn rotary plates 25, which can be simultaneously turned in opposite direction by means of right and left hand worms 26, a rooved 28. The p ates 25 carry guideways 29, in which the grinding wheels 18 can be adjusted by means of screws 30 and hand wheels 31. Said grinding wheels are carried on spindles 33, jourfront ends, an

I planation,

rolling,

naled'in carriers82 and driven by electric motors'34,"fiu1leys35 and belts 86. Spindles e ding wheels 18 on theirthe active edges 37 of said wheels lie in planes at right angles to the axes of said spindles. These planes can be ad usted by means of said rotary plates to correspond to the inclination of the cut edges of a rack tooth, so thatthe rinding wheels can be made to form, i'n-e ect, by suitably approaching the carriages 23 and correspondingly moving the cross rail up and down, a tooth of a rack on which the work is rolled. The characteristic form of the rinding wheel is represented in Fig. 5. Its iameter, however, is shown as considerably smaller than it actually is, in order to permit a more convenient representation of the proportions of Fi 6. In practice, of course, the wheel must be of such a size that the work, in its rolling movement, will pass by the oblique wheel spindle. In Fi 5, 37 represents the active grinding sur ace, which lies in a plane at ri ht angles to the spindle axis. This grindm surface is of restricted width and is limite by the outside edge 65 and the inner edge 66. Assuming, for the present, that the width of the grinding surface=0, then the two edges 65 and 66 coincide. In this case, the cutting edge of the rack tooth, constituted by the grinding wheel, is represented by the 33' carry vertical projection E of the grinding edge 1 plane. It will be seen, without further exthat the grinding edge remains always flat as it wears away; for, if a portion of the same should wear more than the rest, said portion, in the ra id rotation of the wheel about its axis, con (1 nolonger take part in the work of grinding, until the other parts had worn the same amount, that is, until the edge became again straight. The plane form of the grinding edge, necessary for the intermeshing rolling action, is constantly renewed by the wear, that is to say is always maintained.

In practice, naturally, the grinding surface 37 will always have a certain width, but it will be shown in what follows that the grinding surface, without prejudice to its shape necessary for made the same width as that of a rack tooth meshing with the gear tooth. For this purpose, the mode of operation of a considerably narrower grinding surface will first be considered. In Fig. 5, I-V are-a number of positions-0f the work relative to a grinding wheel during one rolling motion, thewidth of the grinding surface being about one-third of the height of the tooth. From position I it will be seen that, during the the head line a of the tooth comes first within the working path of the the grinding surface takes part in the finishgrinding wheel, and, in fact, the entire width ofe. The profile points gradual forward edge, wear more than the latter.

the long dotted lines in Fig. 5,

ing of the head edge a in the line a, Fig. 6. In position II, the short section b of the pitch circle I; is being finished, and again the entire width of the grinding surface takes part in the action on the line I). III represents that position in which the tangent to the inner grinding edge describes the ortion 0 of the line 0. Likewise in the formation of the line a, the entire width of the grinding surface takes part. In position IV, the generation of the line d is represented, and it will be seen that only those portions of the grinding surface, which lie outside the circle through the point D, take part, while the portions lying inside D no longer take any part in the generation of line (13. The projection of the line 0 in position V represents the last point of the profile, which still lies in the correct involute. This point is the last encountered by the outer grinding edge and the portions of the wheel, lying within the same, have no efiect in the production of the line lying beneath the point e are formed during the rolling by the outer grinding edge, approximately from the position II-V; for these represent, as is well-known, only the relative path B, (Fig. 5), of the outer grinding edge and no longer lie upon the involute. When, therefore, care is taken, as in the present machine, that this relative path is already so far described that it is no longer contacted by the grinding wheel, then it is obvious that the parts of the active grinding surface, lying outside the inner grinding For the outer parts have not only to grind, like the inner grinding edge, the.profi le section between lines a and c (Fig. 5), but also those between 0 and 0. It will be further seen that the outer grinding edge, in the feed of the work toward the tool in Fig. 6, always comes into con tact with the, as yet, unfinished parts of the tooth profile. The outer edge will therefore wear more than the parts lying farther inward of the active grinding surface. This greater wear can, however, at the most only equal the amount by which the unfinished profile projects beyond the finished one.

In one passage of the wheel through a tooth space, the active rinding surface will therefore assume the orm represented by in which 00 indicates the highest amount by which the unfinished profile projects beyondthe profile finished by the inner grinding edge. It is to be noted here that all the profile parts between the lines a and 0, (Fig. 5,) are ground to the correct involute shape, provided that the plane of the ,inner grinding edge66 has not changed its position and that the forward feed, per each rolling tact with the point Q in the tice,

movement, is maintained small enou h. v The profile parts between the lines a an e (Fig. 5), on the other hand, do not yet have the correct involute shape, since they were finished by a grinding surface difiering somewhat from the plane form, and they project more or form. It is known, from the theory of gear teeth, that the tooth profiles do not come into engagement down to the dedendum circle, but that the active profiles are, under some conditions, considerably shorter 'than the entire profile between the addendum and the dedendum circles. At the foot of the profile there always remains an inactive part of a certain height, which has no effect in the transmission of movement between the wheels; The end point of the active profile can easil be mathematically or diagrammatically etermined, as well as that point of the generating cutting edge which comes into engagement with said end point.

In Fig. 5 the shaded-part represents the active profile P, which extends to the point Q, and Q is that point of the generating rack tooth profile, which comes into conrolling process. When therefore a grinding wheel is employed, the inner grinding edge of which coincides with the point Q, the entire active profile is formed by Q and receives the correct involute shape under the above conditions. The departure of the profile points, lying farther toward the base circle, from the correct involute form, is of no moment for the running of the wheel with its mate as long as the profile points do not extend into the relative path of the tops of the teeth of the mating wheel. This is easily obtained in pracso that by means of a grinding wheel, the inner edge of which does not lie within the point of the curve being generated corresponding to the end point of the active profile, correctly running tooth profiles can be generated in one passage of the grinding wheel.

The described limiting of thewidth of the active grinding wheel edge, is, however, not necessary for the production of correctly running tooth profiles, if the wheel does not merely make one passage only through a space but is passed through several times, which appears from the following considerations:

It will be seen from what has been said that, in the first passage of the wheel, shown in Fig. 5, the active profile parts, lying between the lines e and a, (Fig. 5 depart somewhat from the theoretically correct form. It will now be assumed thatthe two grinding wheels, during the first passage, were set slightly too close, so that the teeth remained somewhat thicker than necessary and that, for the second passage,

less from the correct the inner grinding edge wheel into exactly the correct position, to

a slight adjustment of the wheels toward the correct position had been made. It will be seen that the parts lying outside of the point a, (Fig. 5,) have only t fact on the profile parts between the lines 0 and 6, since, in ronse uence of the heavy wear resulting from tie first passa e, they lie so faigback from the profile, finished by the inner grinding edge, that they can no longer contact the sameeven bya forward movement in the direction of the feed. But, as will be readily seen, the finishing of the profile zone between '0 and d can only be performed by that profile of the grinding wheel which is precisely in the deepest position, for the active grinding surface, no

longer lying in the plane of the inner grinding edge, does not come at all in contact,

in other. ositions, with the already finihouslng 38 1s provided (Figs.

ished toot profile, because only the inner grinding edge is still touching the same. In consequence, that point of the profile portion of the rinding disk, lying between 0' and 6, acts, during one rolling movement, only on the corresponding point of the zones 0. and e of the tooth profile. During a complete passage, the points of the grinding surface, lying on a circular line of the zones 0 and c, act, therefore, only upon the corresponding straight line in the zone of the tooth flanks lying between 0 and e. The circular line of the inner grinding edge itself,

on the other hand, acts, during each rolling movement, upon a curved line of the zone, between a and e of the tooth flanks, that is, on their rolling line, during one entire passage, therefor, over the entire surface between and c, and wears, consequently,

jnuch faster than the arts of the grinding wheel, lying outside t e same, so that the wheel, by repeated gradually decreasing adustments, becomes at each successive passage more nearly perfectly straight again. In this; way, it becomes finally possible, by a last, infinitely small adustment of the grind the profile to the theoretically correct form throughout its entire extent. This progressive automatic restraightening action of the active grinding surface during repeated passages is continued as Icing as the circular line of the inner grinding edge has to work on a surface during the first passage, while the circular lines of the active grinding surface, lying farther out, still act only upon lines, that is, as long as the inner grinding edge lies an infinitesimal distance outside the opposing point a (Fig. 5) of the generating profile. For a gradual correct generation of the profile, therefore, the width of the active rinding surface may be made nearly equa to the width of the active profile of a corresponding rack tooth.

As has already been shown above, it is, however, not at all necessary to grind the ;end of'which; a fee er roller 44 is of passages or strokes of the grinding wheel,

with an accuracy which other machines, I

I will now describe the feeler and setting up or adjusting mechanism.

; In the above description it has been assumed that the plane of the inner grinding edge does not change its position after it is not obtainable by has once beentaken. "This would'not, however, be precisely the'case without further mechanism, which will now be described.

On each of the two rotary plates 25 a 3 and 4), in which a frame 40 is bolt 39. Th1 frame carries a shaft 43, drivenby the rinding wheel motor through a cordffl41 an pulle 42, and on the lower loosely mounted. Shaft-43 carriesfalso a friction roller 46, which can be brought into contact with asecond friction roller 47. The latter remains static-nary when not in contact with the first roller 46, but is rotated by the latter when they are brought together. In the latter case, a worm 48, on the shaft of roller 47 drives a drum 49 which; by means of a shaft 50, a pair of bevel gears 51 and 52, and a shaft 53, drives a disk 54, carried by the latter. On said disk is a radially adjustable bolt 55,*which actuates a pawl 57 engaging with 'a ratchet wheel 56. fhe latter is journaled'in a box 58, (Figs. 2 and 4), rigidly connected with the rotary plate 25 (Fig. 2), and constitutes a nut engaging the threaded spindle 30, which serves to adjust the grinding wheel carrier inthe direction of the spindle axis.

The feeler roller 44 (Figs. 3 and 4)- is always pressed against the active grinding surface by a spring 59 acting on the frame 40,1{50 that it is in contact with the inner edge of said surface. The frame is located so that the rollers 46 and 47 are hot in contact when the grinding plane is in the correct position. Bat as soon as the grinding edge becomes somewhat worn, the frame swrngs toward the same until the rollers 46 and 47 come into contact, whereby 47 is caused to turn and the grinding disk is adjusted or setu in theE manner described, until the rin ing edge has again forced back the j eeler roller sufficiently to move pivotally mounted on a rotates at the same speed as the latter, while,

when not in contact with the wheel, it is ro-v tated by the friction of the shaft in its bore, whereby it has then a rotary speed approximately equal to that of the wheel periphery. in this way, it does not have to be started up from rest when it is brought into contact with the wheel, whichwould likewise cause an injurious wear on the roller.

While the special form of the grinding wheel described, makes any means for preserving the shape required for the rolling, unnecessary, the described feeler and adusting mechanism serves to always maintain the position of the plane of the inner grinding edge when once assumed, so that, as a matter of fact, complete independence of the grinding wheel from wear is obtained.

The operation of the machine is as follows: After a gear 18, the teeth of which have been cut, has been placed on the spindle 12, an index wheel (32, having a corresponding number of teeth, is placed upon the rear end of said spindle, and a rolling are l t of suitable diameter is secured on the casing (54. After the blocks 16 have been adjusted to the proper height and the bands 15 have been secured to the arc and to the blocks, the two grinding wheels 18 are so mounted and adjusted that they represent, as regards their angle of inclination, their vertical position and the distance between the planes of their grinding edges,a tooth of the rack required to generate the desired involutes. It is immaterial whether both wheels work in one and the same space or in two adjacent spaces or, if desired, in

spaces more or less separated from each other. While now the wheels rotate at high speed, the cross slide 11 reciprocates from 20 to 80 times per minute, which causes the work to receive an equally rapid rolling movement through the action of the bands 15. The work is likewise fed forward in the direction of its axis from 0.2 to 2 millimeters, during or after each rolling, so that it passes through under the grinding wheels gradually and while constantly rotating back and forth; according to the separation of the grinding wheels, the flanks of a tooth space, or the right and left flanks of two adjacent or separated spaces, are finished. At the end of the travel of the table 3, determined by the dogs 60, the rotation of the spindle 4L and the movement of the table 3 are reversed by the clutch mechanism 7 andgears 6, whereupon the work is indexed through one division. During the indexing, the work is entirely outside of the working path of the grinding wheels and then begins its return movement, during which two other flanks are finished. Upon the completion of the return stroke, the work is again indexed, and the. operation is repeated, until all the teeth have passed once under the grinding wheels. Accordin to the width of the activegrinding surfaces and to the accuracy required, the wheel is now given a small adjustment and the work again passed under the same. This operation is repeated as often as necessary to give the desired degree of accuracy.

It will be obvious that the work may be indexed through one tooth only after it has passed under the grinding wheels any desired number of times; the inner grinding edges will constantly maintain unchanged, during the entire grinding operation, their form and position, so that the grinding wheels are always ready to start on new work.

The machine described serves for grinding the teeth of spur gears. By a suitably modified construction it can, however, be arranged for grinding the teeth of helical and bevel gears. Also, it will be obvious that the feeler and adjusting mechanisms can be otherwise constructed. The essential features, which must be retained in such modifications, are the employment of two grinding wheels, independent of each other, for

the simultaneous working of a right and a' left flank, the width of the active grinding surface being at the most equal to the active part of the cutting. edge of a corresponding rack tooth; then the feeler mechanism, which always contacts with the inner grinding edge or, when not in contact therewith, causes the grinding wheel to be adjusted or set up until it again contacts the edge, and finally the production of the rolling movement by means of a rolling arc and bands,

while the working stroke of the machine is in the direction of the rolling movement and the feed in the direction of the work axis.

Having thus described my invention, what I claim is:

1. In a machine for finish grinding involute gear teeth by the inter-meshing generating system, the combination of two independent grinding wheels, and means for operatively carrying the same so as to enable them to be adjusted angularly and toward or away from each other, whereby their active grinding surfaces can be caused to represent the two sides of an intermeshing rack tooth and to simultaneously act upon the two sides of a tooth space in the work.

2. In a machine for finish grinding involute gear teeth by the intermeshing generating system, the combination of two grinding wheels, and means for operatively carrying the same so that the active grinding surface of each wheel lies in a plane at right angles to its axis, said active surface being narrower than the active zone of the corresponding rack tooth.

3. Ina machine for finish. grinding involute gear teeth by the intermeshing generating system, the combination of a grinding wheel, the active portion of the surface of which represents a portion of the face of an intermeshing rack tooth and lies in a plane at right angles to its axis, and means controlled by the wear of said surface for automatically adjusting said wheel in the direction of its axis so as to maintain said plane in a constant position.

4:. In a machine for finish grinding involute gear teeth by the intermeshing generating system, the combination of a grinding wheel, the active portion of the surface of which represents a portion of the face of an intermeshing rack tooth and lies in a plane at right angles to its axis, a feeler roller, means to yieldingly press the same against said active surface, and means operatively connected with the spindle of the grinding wheel for feedingthe latter toward said feeler roller, said feeding means being automatically set in operation by the movement of said roller toward said surface as the latter wears away and being automatically stopped by the movement of said surface toward said roller.

5. In a machine for finish grinding involute gear teeth by the intermeshing generating system, the combination of a grinding wheel, the active portion of the surface of which represents a portion of the face of an intermeshing rack tooth and lies in a plane at right angles to its axis, a feeler roller, a driven shaft on which said roller is frictionally mounted, means to yieldingly press said shaft and roller toward said active surface, mechanism to move said wheel axially toward said roller, and means on said shaft to actuate said mechanism when said surface has worn sufficiently to permit said roller and shaft to move toward said wheel a certain amount, whereby said roller is constantly rotated at approximately the speed of said active surface and is not materially accelerated and consequently worn by being brought into contact therewith, and the active surface of the grinding wheel is maintained in the correct plane.

6. In a machine for finish grinding involute gear teeth by the intermeshing generating system, the combination of two independent grinding wheels, means for operatively carrying the same so as to enable them to be adjusted angularly and toward or away from each other,- whereby their active grinding surfaces can be caused to represent the two sides of an intermeshing rack tooth and to simultaneously act upon the two sides of a tooth space in the work, a work spindle, a cross slide supporting the same, a longitudinally reciprocatory table on which said cross slide is mounted, means to slowly reciprocate said table and at the same time to repeatedly traverse said cross slide, and means to simultaneously rotate the work, whereby the intermeshing rolling movement between the tool and work is the working stroke of the machine and the feed movement is in the direction of the work axls.

In testimony whereof I have hereunto set my hand in presence of two subscribing witnesses.

MAX MAAG. Witnesses:

CARL KLAIBER, A. AEPPLI.

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