US1698213A - Method of truing gears - Google Patents

Description

Jan. s, 1929.

A. w. coPLAND ET AL mmo'n OF TRUING GEARS Filed April 10. 1922 ATTOPNEK Patented Jan. 8, 1929.

v I 1, 9 ,213 UNITED STATESPATENT OFFICE.)

ALEXANDER w. COPLAND nn MAXWELL I. MATHEWSON, or DETROTT, MICHIGAN, ASSIGNORS To DETROIT AND SECURITY TRUST COMPANY, or DETROIT, MICHIGAN,

A. CORPORATION OF MICHIGAN.

' METHOD or 'IRUING GEARS.

The invention relates to the art of truing gears and more particularly to that part of it which is generally known, as lapping.

The lapping of gears has heretofore been effected by running two ormore gears in meshwith each other and with an abrasive material between the engaging surfaces or by similarly running a gear in-mesh with a rack. Where the only movement given to the gears is that of rotation about their respective axes, the results obtained are not satisfactory. This is for the reason that the grinding is only produced where there is a slipping or sliding of one surface over another,,and inasmuchas the sliding upon each other'of the teeth of rotating intermeshing gears with the commonly employed involute teeth is zero at the pitch circle and progressively increases on each side of said circle with a maximum at the crown of each tooth, it is evident that the grinding produced has a tendency to change the tooth from its true involute form. With certain lapping methods a relative axial reciprocation has been imparted to the intermeshing gears, or to the gear and the rack in case a rack is employed, in addition to the relative rolling, but this is also defective and inevitably results in distortion of the true involute tooth form because the effect includes that incident to the rolling as above described.

In such a lapping or grinding operation as last referred to, the amount of grinding or abrading of a surface sliding in contact with another is dependent first, on the character of the abrasive material used; second, on the area of abrading surface that-is moved over each unit area of the surface to be ground or trued; and third, the amount of pressure per unit area of contact. Accordingly, to pro duce uniform grinding on all portions of a surface contacting with the abrading surface there must be uniformity in abrasive mate improvement, the principles underlying the same are illustrated diagrammatically in the accompanying drawings, in which:

Fig. 1 is a iagranimatic View showing the ntermeshing teeth of a spur gear and a lap in the form of a second spur gear and indicat-' mg by the diagonal shadin the relative widths of zones of surface W ich are trav-, ersed by the mating tooth during equal angu' lar movements.

Fig. 2 is a view similar to Fig. 1 showing the tooth of a spur gear in mesh with the teeth of a lap, the lap in this instance being 1n the form of aracli having straight sided teeth; f

7 Figs. 3and 4 are respectively a sectional elevation and a side elevation of a gear in mesh with a rack surface forming a lap therefor, the section shown by Fig. 3 being taken on the line 3-3, Fig. 4.

Fig. 5 is a view similar to Fig. 3 showing a modified construction. 4

In Fig. 1 is shown a portion of a spur gear 1 having teeth 2, 2- of involute form-in mesh with correspondingly shaped teeth 3 of a lap 4:, which in this instance is in the form of'asecond spur gear. The relative widths of zones traversed by the mating tooth for equal angular movements of either the gear or the lap are indicated by diagonal shading on the body of each tooth. It will be observed that these zones vary in thickness from the roottowards the crown of each tooth. It will also be observed that when two teeth are in mesh that the smallest zones on one are adjacent the largest on the other. As, forinstance, zones at and b on the gear 1 are adjacent zones at and b on the lap 4. As the zones indicate the amount of surface traversed by the mating tooth for equal angular movements, the zones will have to traverse each other during a unit amount of such movement, which, dueto the difference in width of the contacting zones, will result in a relative sliding between the contacting surfaces. It will also be observed that the intermediate zones are more nearly equal. This means that the relative sliding becomes progressively less as the point of engagement approaches the mid portions of the respective teeth. with zero sliding at the pitch line.- It will thus be seen thatthis relative sliding of the tooth surfaces is greatest at the extremities of the intermeshing teeth and gradually decreases to zero. at the pitch line.

%s the grinding away of the tooth surfaces occurs only where there is relative sliding it follows that during tlie relative rotation of a spur gear in mesh with a lap in the form of a 5 second spur gear the .contacting surfaces will .be ground away more at their extremitles than at the pitch line. Asstated, it has been proposed to combine an axial reciprocation of either the gear or the lap simultaneously 1 with the relative rotations, but this is also .defective as the sliding which is incident. to

the relative rotation above noted, is still present. J

In Fig. 2 we have shown a portion of a: spur I6 gear 5 with a tooth 6 of involute form in mesh with the teeth 7, 7 of a lap 8 which 1n this case is in the form of. an involute rack having straight sided teeth. The relative widths of thezones traversed by the mating teeth for 2 equal angular movements of the ear to be und are indicated by diagonal s ading, as

inthe previously described case. It will be observed however that the zones on the rack tooth are equal in width, The relative s1id 2 ing between the contacting teeth will be zero at the pitch line, as in the first instance but the variance in the relative slidin between i the contacting surfaces above and elow the pitch line is not the same as in the previously described exam le; however, it canbe readily ascertained y comparing the widths of the zones on the adjacent surfaces of the intermeshing teeth. It has also been proposed -'to combine a reciprocation of the rack parallel to the gear axis (or an axial reciprocation of the gear) simultaneously with their rela: tive rotation; but, as in the previous case, .there will still be a difference in the grinding effect due to the above noted sliding action inco cident to the rotating movement.

If, during the relative rotation and simultaneous reciprocation of the intermeshing gear and lap, the length of the reciprocation of the lapping surfaces could be varied-in inverse proportion to the amount of sliding incident to the rolling action, the area of abrad-- ing surface moving over each unitarea of the surface to be ground could be made uniformthroughout. This supposed variable .50 reciprocation is not feasible, but if, in place of a continuous surface on the lap tooth, this surface is interrupted or cut away with the width of the interruptions varying in direct proportion to the amount of relative sliding,

5 the samecompensation ma be made for the unequal width of zones wit uniform lengths of mi rocation.

As i ustrative of some of tli difierent ways in which the effective grinding area of the lap 00 can be varied, we have shownjn Figs. 3 and 4 a-lap with its teeth modified in one way, and in Fi 5 a co'rresponding'lap with a distinctl erent modification.

gear wheel and 11 a lap in the form of a rack shown in' Figs. -3 and 4, 10 represents a relation to which the gear wheel is reciprocated axially while rolling in mesh therewith.

Any suitable means may be employed for pro- 11, 192&,to W. E. Hoke. In this modification, I

the teeth of the rack are interrupted or cut away by the V-shaped channels 12. Obviously a lap of this form will have agrinding effect on the gear tooth to be lapped that pro-v gressively increases from'the root of the gear tooth toward its crown.

In Fig. 5 the arrangement of lap 21 and gear 20 is similar to Figs. 3 and 4, the difi erence being that the interruptions or cut-away portions 22 of the lap in this instance are dove-tailed in shape with the width of interruption greater. at the base of the rack tooth than at the crown. Obviously this construction has an opposite effect to that shown in Figs. 3 and 4. In utilizing our invention one first prede termines the amount of relative sliding occurring between the contacting surfaces ofthe particular 'form of'gear and lap teeth in-' volved incident to their relative rotation, and

- then forms the lap so that the width of the interruptions or cut-away portions will-in suitable roportion be greater at the point where the argest amount of sliding occurs and smaller where the lesser amount of sliding ocours; It will thus be seen that through the use of our method the contacting areas of the tion to the amount of relative sliding etween --the contacting gear and lap surfaces incident to the relative rotating movement, to com ensate for that variable-sliding. Otherthings rotating movement, ut in practice this strict roportionality may .bemodified somewhat v y the fact that variation of the contacting areas tends to affect the other two determinmg factors, namely, the pressure per unit incident to the relative area and the effect of the abrasive, and it is desirable to take this into account in determmmg the proper variation of the contact areas, as can readily be done if on first tr ifi 'III the desired compensation is notfull secured.

In considering the action of the m 'fied lap, it is to be borne inmind that the abrasive action is mutual, afiecting the lap as well as the gear.

is applicable in instances where it is desired to produce a uniform ofthe gear tooth surfaces. is desira le when the Themethod as specifically' described'above original contour of the geartooth is substantially correct, and all that is needed is. a smooth finished surface. "However, our invention is also the originaltoo surface not atplplicable where lapping surface are varied in suitable tpropor-e rectly formed, asfor instance where there interruptions or cut-away portions of the lap tooth would be so formed as to compensate for the relative slidin referred to above and at the same time so ormed as to grind away more surface at the point'where the excess material occurs. In order to produce this combined action of compensating for the relative sliding and the difierentlal grinding the width of interruptions at the base of the lap toothwould be relatively smaller so as to present a larger area of abrading surface ing comp to contact with the crown of the tooth and thus correct the original defect in the tooth form, while at the same time, the-lapping produces the smoothly finished surface desired. Thus by properly formingl the interruptions in the lap any desire grinding efiect may be; roduced,'siich for instance, as uniform grin ing where the tooth form is originally correct or differential grinding where the original tooth form needs modification. v

While we have described our method as applied to the grinding of gears, it is obvious that it is equally ap licable to the grinding d circular bodies; also, that it is equally applicable to the grinding of internal and externalsurfaces.

What we claim is:

1. In a method of grinding gears by imparting simultaneously relative rotation and axial reci rocation to a gear and a 1a ;l havementary intermeshing teet the provision and use of a lap so formed that its abrasive area which is brought into contact with the gear teeth said reciprocation varies during the relative movement of the gear and lap in suitable proportion to the amount of relative sliding between the contacting gear and lap surfaces incident to the relative rotation of the gear and lap to compensate for said sliding.

' 2.. In a met 0d of grinding gears by imparting simultaneously relative rotation and axial reciprocation to a gear and a lap having complementary intermeshing teeth; the provision and use of a lap so formed that its abrasive area which is brought into contact with the gear teeth by said reciprocation varies during the relative movement of the gear and lap in suitable proportion to the amount of relative sliding between the contacting gear and lap surfaces incident to the relative rotation of the gear and lap and to 1 the amount of excess material to be removed to compensate for said sliding and for the saidexcess material.

3. The method of finishing surfaces of gear teeth to predetermined contours which consists in lmparting simultaneously relative rotation and axial reciprocation to the gear and a lap having tooth-like lapping surfaces which are in abrasive contact with the gear and .formed to have their surface areas which are brought into abrasive engagement with the gear teeth by .the said reciprocation varied by the combined rotation and reciprocation in suitable proportion to the amount of relative'slidin' between the contacting gear and lap sur aces incident to the sai rotation to compensate for said sliding.

4. The method of grinding toothed bodies teeth of the body with a toothed a rading tool, causing between the body and-tool a rel-.

ative an ular motion in the plane of the gear body and also a relative transverse motion in an axial plane of the gear body and by the combined angular and transverse motion varying the area of abrasive contact of the radial faces of the tool with the teeth of the gear incident to said transverse motion in a predetermined proportion to the slip or relative sliding between the teeth of the body and the too'i due to the said angular motion.

In testimony whereof we afiix our signatures.

ALEXANDER W. COPLAND. MAXWELL I. MATHEWSON.

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