US1924736A - Method of truing gears - Google Patents

Description

Aug. 29, 1933. R. B. FEHR METHOD OF TRUING GEARS Filed Jan. 15, 1931 3 Sheets-Sheet 1 INVENTOR B y Wu ATTORNEY5 Aug. 29, B EH METHOD OF TRUING GEARS Filed Jan. 15, 1931 3 Sheets-Sheet 2 NVENT f7 v 77 a 4-7 ATTORNEYS Aug. 29, 1933. R. B. FEHR METHOD OF TRUING, GEARS 3 Sheets-Shet 5 Filed Jan. 15, 1931 ATTORN EYS Patented Aug. 29, 1933 UNITED STATES 1,924,736 METHOD or 'r iUiNG GEARS Roy B. Fehr, Detroit, Mich assignor, by mesne assignments, to Detroit Trust Company, Detroit, Mich, a corporation of-Michigan Application January 15, 1931. Serial No. 508,825

4 Claims.

The present invention relates to a method of truing gears or other bodies of similar shape, and is an improvement on the method disclosed in the patent to Copland et al No. 1,683,867 granted September 11, 1928.

My co-pending application Serial No. 508,652, filed January 14, 1931, discloses a method of gear truing in which the gear tooth faces are abraded by means of a lap having a form complemental to that of the gear, and in which the gear is maintained in telescopic engagement with the lap.

throughout the truing operation so that the lap ping operation maybe performed in a machine driven at a relatively high rate of speed, the grinding operation being continuous and uninterrupted.

The object of the present invention is to provide a high speed method of the character above referred to by which a very uniform grinding action is obtained on the tooth faces throughout the length and breadth thereof by rigidly holding both the gear and lap against relative tilting movement while permitting one to have limited lateral movements during the lapping operation. With the above and other objects in view the invention may be said to comprise the method and apparatus as illustrated in the accompanying drawings hereinafter described and particularly set forth in the appended claims together with such variations and modifications thereof as will be apparent to one skilled in the art to which the invention appertains.

Reference should be had to the accompanying drawings form'rg a part of this specification in which:

Figure l is a side elevation of a machine embodying this invention.

Figure 2 is a front elevation of the machine shown in Figure 1.

Fig. 3 is a plan view of the lap and its support, a portion of the support being broken away and shown in section.

Fig. 4 is a section taken on the broken line indicated at 4-4 in Fig. 3.

Fig. 5 is a side elevation showing the machine in which a floating support for the gear is provided.

Fig. 6 is a section taken on the line indicated at 6-6 in Fig. 5.

Fig. '7 is a side elevation support.

Fig. 8 is a section taken on the line indicated at 8-8 in Fig. 6.

Referring first to Figures 1 to 4 of the drawings, the lapping machine is provided with a of the gear arbor disposed vertically. At the top thereof the frame 1 has a laterally projecting portion 6 which overhangs the turntable 3 in which is slidably mounted a vertically disposed spindle 7 which is disposed substantially in axial alignment with the turntable 3 and lap 5. The gear 8, to be lapped, is adapted to be rigidly secured to the lower end of the spindle '7 for telescopic engagement with the lap 5. At its upper end, the spindle 7 has detachably secured thereto a spline extension Slrvvhich is provided with straight or helically disposed ribs or teeth which are engaged by a spline guide 10 which has internal ribs or teeth of 0drresponding form and which is detachably secured to the frame. The helical angle of the spline is such as to impart to the gear exactly the same rotary movement which would be imparted to it by the lap if the gear were moved longitudinal- 1y through the lap with the lap held against turning movements. 1

The longitudinal lead of the spline teeth is exactly the same as that of the gear teeth, and for gears of small helix angle a spline extension and guide having teeth disposed at a small helix angle will be required. When the gear is a spur gear its helix angle ls zero and a spline extension and spline guide having straight teeth will be employed. j The spindle '7 is adapted to be reciprocated axially by means of a lever 11 which is pivotally connected at its forward end to a collar 12 rotatably mounted on the spindle '7 and held against longitudinal movement with respect thereto. The lever 11 is connected intermediate its ends to the frame 1 by means of a floating pivot 13 and is connected at its rear end by means of a connecting rod 14 with the crank arm 15 of a crank shaft 16 journalled in the frame 1. The shaft 16 may be driven by any suitable means to oscillate the lever 11 and reciprocate the spindle 'Z. The floating pivot l3 is mounted on amovable pivot carrier 17 which is pivotally mounted on an eccentric 18 carried by a shaft 19 which is journalled in the frame 1. The shaft 19 is provided with a hand crank 20 by means of which the eccentric 18 may be turned to raise or lower the pivot carrier 17.

During oscillation of the lever 11 the carrier 1'? is free to swing laterally on the eccentric 18 through an angle sufficient to allow the lever 11 to have the bodily lateral movement necessary to permit the forward end thereof attached to the spindle 7 to move vertically in a straight line during the oscillation of the lever. The vertical adjustment of the pivot carrier 17 is sufficient to move the lower end of the spindle carrying the gear 8 from a position within the lap 5 to a position above and clear of the lap to permit a gear to be removed from the spindle and replaced with another gear to be trued. The length of the stroke imparted to the spindle 7 by the oscillating lever ll is such that, when the pivot carrier 1'? is in its lowermost position, the gear 8 remains in telescope engagement with the lap 5 throughout the entire stroke. Since there is no disengagement of the gear and lap during the reciprocating stroke of the spindle, the reciprocating movement may be quite rapid and the grinding action will be continuous.

The lap is preferably of a length several times the actual width of the gear and is preferably composed of a metal as hard as or harder than the metal of the gear. By reason of the hardness of the lap and by reason of the much greater area of the tooth faces of the lap, the rate of wear per unit of area on the lap tooth faces is but a small fraction of the rate of wear on the gear tooth faces, so that a lap tooth face will not be appreciably deformed in the process of grinding off the high spots on a contacting gear tooth face. Furthermore, passing a succession of gears through a lap distributes the minute errors over all of the teeth of the lap. The teeth of the gears which are of correct form except for slight inaccuracies in some of the teeth tend to eliminate inaccuracies in the lap teeth so that the lap toothfaces are maintained substantially true.

According to the present method the lap and gear are rigidly held against relative tilting movement and against turning movements with respectto the members on which they are mounted during the lapping operation, but the lap or gear, one or the other, is so supported that it is free to move laterally in any direction perpendicular to its axis, so that throughout the reciprocating stroke the lap and gear automatically center themselves with respect to each other, so that excessive pressure between the tooth faces during any portion of the stroke is prevented.

As best shown in Figs. 3 and 4 of the drawings, the turntable '3 is provided with upwardly projecting guide flanges 21 to the inner faces of which are secured hardened steel ball races 22 and which serve as guides for a laterally movable intermediate supporting member 23 to which are attached hardened steel ball races 24 which face outwardly and are disposed opposite the ball races 22. The opposed faces of the ball races 22 and 24 are provided with ball receiving grooves which extend longitudinally thereof in'which are mounted the bearing balls 25, which serve to accurately position the supporting member 23 and permit the same to move freely in a lateral direction. The ball races on the supporting member 23 are provided with wedge shims 26 which may be adjusted to adjust the ball races 24 bodily toward or away from the ball races 22 to clamp the balls tightly between the races and take up any play in the bearing members. I

A lapcarrier 2'7 is mounted on top of the intermediate supporting member 23 for movement lateralh in a direction at right angles to the direction of movement of the intermediate supporting member 23. The lap carrier 27 has depending flanges 28 tothe inner faces of which are attached ball races 29 which are opposed to ball races 30 secured to the intermediate supporting member. The ball races 29 and 30 being grooved to receive balls 31 and the ball races 30 being adjustable by means of wedge shims 32 to clamp the balls snugly between the ball races. The balls 25 and 31 are retained in the races 24 and 30 of the intermediate supporting member by means of keepers 33 which are attached to the intermediate supporting member 23 at the outer end of the ball races 24 and 30.

The lap carrier 2'? is provided on the top face thereof with an annular shoulder 34 within which lateral movement only since the lateral movement of these members during the operation of the machine is very slight. The lateral movements of the intermediate supporting member 23 are limited by a downwardly projecting annular flange 3'? which extends into the opening of the annular turntable 23 and the intermediate supporting member 23 is provided with an annular flange 38 at the top thereof which projects upwardly between the side flanges 28 of the lap carrier 27 and an inner annular flange 39 formed on the lap carrier inwardly of the flanges 38.

In order to protect the bearings from abrasive material a sheet metal guard 40 is preferably attached to the marginal edge of the lap carrier 27 and incloses the intermediate supporting member and the upper portion of the turntable 3. The lower end of the guard being of a diameter somewhat greater than the turntable 3 to allow the necessary relative lateral movement. In order to introduce abrasive carrying liquid into the lap a suitable funnel 41 may be attached to the upper end of the lap 5 through which a stream of liquid may be directed into the upper end of the lap and from which the liquid will flow through the spaces between the lap and gear teeth.

In the operation of the machine a gear is attached to the lower end of the spindle 7 while the pivot carrier 1'7 is adjusted to its uppermost position to bring the lower end of the spindle 7 to a position clear of the lap 5, and after the gear has been attached to the spindle, the carrier .17 is shifted to its lowermost position to enter the gear into the lap -5 after which the crankshaft 16 is driven to reciprocate the gear within the lap. Since the stroke of the spindle '7 is such that the gear does not move out of telescopic engage ment with the lap during the reciprocating stroke, the spindle 7 may be rapidly reciprocated to effect a continuous and rapid abrasion of the tooth faces of the gear. After the gear and lap are telescopically engaged the turntable 3 may be adjusted by means of the hand wheel 4 through the small angle necessary to establish abrasive contact between opposed tooth faces of the gear and lap and maintain a torsional pressure between the engaging tooth faces, and after the gear teeth have been ground sufficiently on one side the turntable 3 may be adjusted in the reverse direction to bring the opposite faces of the gear teeth into engagement with lap tooth faces, and the operation may, then be continued until the opposite faces of the gear teeth have been ground down the desired amount.

between the balls and raceways.

To avoid non-uniform grinding action such as -may be caused by inequalities in torsional pressure during the reciprocating stroke which might otherwise be caused by the mounting of a gear .in a position slightly eccentric with respect to the lap, it is desirable that the gear and lap have a limited relative movement in a direction perpendicular to their common axis, so that there is at all times an automatic centering of the lap with respect to the gear.

The mounting for the lap illustrated in Figs. 3 and 4 of the drawings, permits the lap to have a limited lateral movement in any direction per-,. pendicular to its axis but constrains the lap to turning movement with the turntable on which it is mounted. If desired, however, the lap may be rigidly supported and the gear may be so mounted on the spindle that it is constrained to turn with the spindle but is free to move laterally in any direction perpendicular to the axis of the spindle. Such a mounting for the gear is illustrated in Figs. 5 to 8 of the drawings, which will now be described.

In this modification the lap is rigidly supported in the turntable 42 in axial alignment with a vertically movable spindle 43 which is provided at its lower end with a mounting for a laterally movable arbor 44 to which the gear is attached.

As best shown in Figs. 6, '7 and 8, spindle 43 is provided at its lower end with an elongated head 45 which has attached to the opposite faces thereof, hardened steel ball races 46 and which serves as a guide for an intermediatesupporting member 47 which has upwardly extending guide flanges 48 which form a channel between them to receive the head 45. The guide flanges 48 have hardened steel raceways 49 secured to the inner faces thereof opposite the raceways 46 of the head, and the raceways 46 and 49 are grooved to receive balls 50. The intermediate supporting member 47 has downwardly extending guide flanges 51 which extend in a direction at right angles to the flanges 48 and which are integrally joined with the upper guide flanges 48 by corner blocks 52 which lie in the exterior angles of the crossing channels formed by the flanges 48 and 51 of the intermediate member.

Guide flanges 51 are provided on their inner faces with hardened steel raceways 53 and serve as a guide for a transversely elongated head 54 on the upper end of the gear. carrying arbor 44, the head 54 being provided on its opposite side faces with hardened steel raceways 55 opposed to the raceways 53 of the flanges, the raceways 53 and 55 being provided with grooves to receive anti-friction balls 56. The raceways 49 and 53 of the intermediate supporting member are provided with wedge shims 5'7 which may be adjusted by means of bolts 58 to take up any play in the bearings and maintain snug engagement The balls are preferably retained in the raceways of the intermediate supporting member by means of keepers 59 extending across the outer ends of the raceway grooves on the intermediate member and keepers 60 extending across the inner ends of said grooves.

The lateral movements of the arbor with respect to the spindle 43 are limited by means of interengaging members on the spindle and arbor, the spindle being provided with a recess 61 in the lower end thereof, and the arbor being provided with a projection 62 of somewhat less diameter than the recess which projects into the recess.

A cylindrical sheet metal housing 63 is preferably provided to enclose the coupling members joining the spindle and arbor and protect the bearings against the entry of abrasive mav terial. The housing 63 is attached to the spindle 43, having an opening in which the spindle fits and being supported upon the projecting ends of the head 45; The housing may be provided with an annular bottom plate 64 which projects inwardly beneath the projecting ends of the head 54 of the arbor 44. The internal diameter of the annular plate 64 is slightly greater than the diameter of the arbor 44 to permit the necessary lateral play, and the gap between the interior of the annular plate 54 and the arbor may be closed by a flange 65 secured to the arbor and overlying the upper face of the plate 64.

In each of the modifications described, the

gear and lap are held against relative tilting movements about axes transverse to the spindle or lap axis, so that-unsymmetrical crowning of the ends of the gear teeth is avoided. A slightly greater pressure per unit of area may be exerted when the gear is at the ends of the lap which may result in slightly greater abrasion at the ends of the teeth producing a slight crowning effect which is advantageous. By the present method, this crowning eifect is very slight and is alike in all teeth by reason of the fact that the gear and lap are rigidly held against relative tilting movements.

The relative lateral movements permitted between the lap and gear assure correct centering of the gear with respect to the lap throughout the lapping operation, since the movably mounted lap or gear is free to center itself at all times with respect to the gear or lap with which it engages, the position of the gear with respect to the lap being determined by the circumferentially spaced inter-engaging tooth faces of the gear and lap which are held in contact under torsional pressure.

A new lap will have certain minor inaccuracies which should be eliminated prior to the use of the lap in truing of gears. These inaccuracies may be eliminated by lapping a considerable number of gears successively in the lap. The gears employed for the truing,of the lap may be gears which have not previously been trued but which have been manufactured with fair accuracy. The abrasive action of the gear teeth on the lap teeth has the effect of gradually reducing and eliminating the errors in the lap teeth putting the lap in condition for the accurate finishing of gears. The gears which were used for truing the lap may again be lapped either in the same lap or in another previously trued lap. After a lap has once been trued it may be'used continuouslyin the truing of gears until its teeth are worn to such an extent that they do not possess the necessary strength, and throughout the use of the lap the teeth thereof -will be maintained substantially correct incontour and spacing by reason of the substantially uniform distribution of wear over.

the surfaces of the lap teeth and the continual 'which the abrasive action of the gear teeth is substantially uniform throughout the entire surfaces of the gear teeth.

It will further be apparent that the lap and gear will not bind during the lapping operation and that the pressure between the contacting tooth faces will be quite uniform and will be distributed uniformly over the entire area. of the gear tooth faces.

Furthermore, it is to be understood that the particular form of apparatus shown and described, and the particular procedure set forth; are presented for purposes of explanation and illustration and that various modifications of said apparatus and procedure can be made without departing from my invention as defined in the appended claims.

What I claim is:

1. The herein described method of truing gears which consists in telescopically engaging a gear and lap, one of which has the form of an external gear and the other the form of an internal gear, the gear and lap being of the same pitch diameter and complemental in form, imparting relative axial reciprocating movements to the gear and lap, one with respect to the other while maintaining the gear and lap in telescopic engagement, and rigidly holding the gear and lap against relative tilting movements while permitting free lateral movement of one with respect to the other in any direction perpendicular to the axes of the gear and lap and while main- 1 taining a torsional pressure between opposed tooth faces of the gear and lap.

2. The herein described method of truing gears which consists in telescopically engaging a gear and lap, one of which has the form of an external gear and the other the form of an internal gear, the gear and lap being of the same pitch diameter and complementalin form, imparting relative axial reciprocating movements to the gear and lap, one with respect to the other while maintaining the gear and lap in telescopic engagement, rigidly holding the gear and lap against relative tilting movements while per mitting free lateral movement of one with respect to the other in any direction perpendicular to the axes of the gear and lap, and establishing and maintaining a torsional pressure between opposed tooth faces of the gear and lap by relative angular adjustments of the gear and lap,

one with respect to the other about their axes.

3. The herein described method of truing gears which consists in telescopically engaging a gear and lap, one of which has the form of an external gear and the other the form of an internal gear, the gear and lap being of the same pitch diameter and complemental in form, imparting relative axial reciprocating movements to the gear and lap, one with respect to the other while maintaining the gear and lap in telescopic engagement, rigidly holding the gear and lap against relative tilting movements while permitting free lateral movement of one with respect to the other in any direction perpendicular to the axes of the gear and lap, establishing abrasive contact between opposed tooth faces of the gear and lap by angularly adjusting one with respect to the other, and positively controlling relative angular movements of the gear and lap during the relative reciprocation thereof to maintain said abrasive contact.

4. The herein described method of truing helical gears which consists in telescopically engaging a gear and lap, one of which has the form of an external helical gear and the other the form of an internal helical gear, the gear and lap being of the same pitch diameter and complemental in form, imparting relative axial reciprocating movements to the gear and lap, one withrespect to the other while maintaining the gear and lap in telescopic engagement, rigidly holding the gear and lap against relative tilting movements while permitting free lateral movement of one with respect to the other in any direction perpendicular to the axes of the gear and lap, establishing abrasive contact between opposed tooth faces oi the gear and lap by angularly adjusting one with respect to the other, and oscillating the gear and lap, one with respect to the other during the reciprocation thereof, while positively maintaining a speed of relative angular movement between points on the gear and lap lying in the pitch cylinder common to the gear and lap which is equal to the speed of relative axial movement times the tangent of the helix angle of the gear and lap.

ROY B. FEHR.

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