US2897634A

US2897634A - Method and apparatus for producing helical gears

Info

Publication number: US2897634A
Application number: US394645A
Authority: US
Inventors: Wildhaber Ernest
Original assignee: Individual
Current assignee: Individual
Priority date: 1953-11-27
Filing date: 1953-11-27
Publication date: 1959-08-04
Anticipated expiration: 1976-08-04

Description

war- I D Aug. 4, 1959 E. WILDHABER 2,897,634

METHOD AND APPARATUS FOR PRODUCING 'HELICAL GEARS Filed Nov. 27, 1953 e Sheets-Sheet 1 I l l i I INVENTOR. 43 E- WI LDHABER FIG. 6

A t'l'ame 1959 WILDHABQER 2,897,634

METHOD AND APPARATUS FOR PRODUCING HELICAL GEARS Filed Nov. 27, 1953 6 Sheets-Sheet 2 IN VEN TOR.

BY q

Afforrmf f E- WILDHABERV 4, 1959 E. WILDHABER 2,397,634

METHOD AND APPARATUS FOR PRODUCING HELICAL GEARS Filed NOV. 27, 1953 6 Sheets-Sheet 3 6 so '3 I00 I I2 35 I22" I s? I97 |2o' IN V EN TOR:

E- WILDHABER Aug. 4, 1959 E. WILDHABER 2,897,634

METHOD AND APPARATUS FOR PRODUCING HELICAL GEARS Filed Nov. 27, 1953 Y 6 Sheets-Sheet 4 7T6? i no FIG. 0

INVENTOR: E WILDHABER BY Z Attorn y Z Aug. 4, 1959 E. WILDHABER METHOD AND APPARATUS FOR PRODUCING HELICAL GEARS Filed NOV. 27, 1953 6 Sheets-Sheet 5 2 r w G H w R E mB l Y F/Q E FIG.27

Aug. 4, 1959 wlLDHABER 2,897,634

METHOD AND APPARATUS FOR PRODUCING HELICAL GEARS Filed Nov. 27, 1953 s Sheets-Sheet 6 2| 276 Z, 2?? 23l\. 277 252' 220 4 y -27? KW my 28l 284 28 Q) 282 285 METHOD AND APPARATUS FOR PRODUCING HELICAL GEARS Ernest Wildhaber, Brighton, N.Y.

Application November 27, 1953, Serial No. 394,645

25 Claims. (Cl. 51-52) The present invention relates to the production of helical teeth and more particularly to the production of helical teeth on gears which are to run either on parallel or non-parallel axes, and to the production of helical threads on worms and screws, especially helical threads of substantial lead angle. In a more specific aspect, the invention relates to the production of helical teeth and threads with rotary tools having formed cutting profiles, either milling cutters or grinding wheels. Still more specifically, the invention relates to the production of helical teeth and threads with milling cutters or with grinding wheels that have concavely curved side profiles and which produce convex tooth profiles on the work.

Because a grind wheel is a cutter with an infinite number of cutting edges, and because the invention is especially useful in grinding, we shall describe it hereafter in reference to its particular application of grinding helical gear teeth, but it is to be understood that this is intended in no way to limit the scope of he claims.

In a form-grinding operation the profile shape of the grinding wheel depends on the profile shape of the teeth or threads to be produced, but with helical teeth or threads the profile shape of the wheel is not a direct counterpart of the profile shape of the teeth or threads to be produced. This is because the contact between a grinding wheel and the helical teeth it grinds extends obliquely across the grinding surface and is not contained in a plane normal to the teeth and containing the axis of the grinding wheel. For this reason the wheel profile in that plane is less curved than the tooth pro file. The wheel profile depends also on the diameter of the grinding wheel. The larger the wheel diameter the larger becomes the curvature radius of the wheel profile at a given mean point. For very large wheels, the wheel profile approaches a straight line, when the wheel is intended to grind involute helical teeth, which are the usual helical teeth.

The dependence of the wheel profile on the wheel diameter is one of the difiiculties of grinding helical gears or threads with a formed wheel. Another difliculty lies in dressing the wheel to the desired shape.

These difliculties with grinding helical gears or threads are magnified where an attempt is made to grind opposite sides of the teeth simultaneously. The customary practice is to adjust the grinding wheel to the helix angle at the pitch circle; but then one side of the wheel is apt to run out of grinding contact before the other, at the ends of the tooth spaces. This occurs especially where he teeth have long or lengthened addenda, which is often the case with pinions; and it occurs even with teeth of standard addenda. When grinding continues on one side and ceases on the other side, the grinding pressure becomes unbalanced so that the grinding wheel tends to spring away from the surface still being ground and to leave more stock on the back end of the tooth. This little extra stock may result in gear noise and reduced gear life.

atg

. of a .tooth .space of the work.

A further object of the invention is to provide a 7 method of cutting or grinding helical teeth in which both "ice With previous methods of producing helical gears and threads, moreover, it has not been practical to produce the localization of tooth bearing or evase ofi at the ends .of the teeth that is desirable to render the teeth less sensitive to displacements and deflections under load, and less sensitive to manufacturing inaccuracies and tolerances. 7

With ease-0E of the tooth surfaces at the tooth ends, the tooth contact does not sweep the entire working surface of the teeth in any given mounting position under a light load, but only a portion thereof. The tooth bearing is localized and is confined to a restricted area.

The desired form of this bearing area is bounded by something like an ellipse or oval, whose major axis extends in the direction of the teeth. No grinding method has heretofore been known which can actually achieve this form of tooth bearing on helical teeth of cylindrical gears. Nor is there any cutting method known to achieve this shape on helical teeth with a formed disk milling cutter.

One object of the present invention is to provide a process in which both sides of a tooth space can be cut or ground simultaneously while maintainingthe opposi-te cutting or grinding pressures in balance during cutting or grinding of the full length of opposite sides sides of a tooth space are cut or ground together and in which cutting or grinding contact ceases nearly simultaneously on the two tooth sides.

Anothere object of the present invention is to provide a method and means for producing localized tooth bearing or ease-off on helical gear teeth, and broadly tocontrol the shape of the tooth bearing area. I

Another object of the invention is to provide a method and means for cutting or grinding helical teeth in which localization of tooth bearing or ease-oflf at the tooth ends can be attained and controlled both and as to shape.

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

In the drawings: a

Fig. l is a side elevation of ahelical gear, illustrating diagrammatically the conventional procedure in grinding a helical gear with a formed wheel, and showing the two zones of grinding engagement of the wheel with sides of a tooth space of the gear;

Fig. 2 is a side elevation of a helical gear, but illustrating one embodiment of the present invention and showing how the two zones of grinding engagement of the wheel with opposite sides of thetooth space are aligned with each other axially;

Fig. 3 is a fragmentary view taken perpendicular to the axis of the gear and further illustrating the process of the present invent-ion, the gear being'slrown in sec tion and the grinding Wheel being shown partly in section Fig. 5 is a side elevation of a helical tooth, and illus trating the form of ease-off or localization of tooth bear ing desired lengthwise of the tooth;

Fig. 6 is a View similar to'Fig. 5 showing the desired shape of the localized tooth bearing obtained through,

ease-oiflengthwise and profilewise on a tooth;

Fig. 7 is a fragmentary normal section through the tooth space of a helical gear, illustrating a somewhat modified procedure;

Figs. 8 to 11 inclusive are diagrammatic views repreas to amount opposite sition nearthe tooth end with one side in grinding con- E s- 11 is e ra n a y. ew ta en at rialit' sl s t l qn 9f the te t .shn iu exa e a d y th p tion o v e r n i swh la j ce t hericpt .e d;

ias fii a disa m f r er.ex l n toryn it en Qt. f

obtaining a desired forrn of tooth ease-elf in accordance with the present invention;

F s- :14 i a m a y ir i g l i g h h" a grinding Wheel h adb ltt a e tir thenr s ti r tion, the section being taken at right angles to the axis of the grinding wheel; I d I A p FigflS is an axial section through the grinding wheel andits mounting;

Fig. 16'is a cross section threu uja' modified ltor rn of wheelhead, and taken "at rightangles to the axis at the grinding wheel; d

Fig. 17 is an axial section of the wheel head shown'in Fig. 16;

Fig. '18 is an end view of the wheel head ofFigs. 16 and 1 7 with the dust seal and dust cover removed therefrom; r,

Fig. 19 is a fragmentarytransversesection through the wheel head of Figsflfi to 18 and showing particularly a cylindrical slide used in displacing the wheel transversely of its axis; I d

Fig. 20 is a more or less diagrammatic plan view of one form of grinding machine constructed in accordance with the present invention;

, Fig. 21 is a drive diagram of the machine shown in 2 V Fig. 22 is a View showing a partial axial section of a grinding wheel, and illustrating the principle of operation of the" wheel dresser constructed according to the present invention; d I

Fig, 23 is a fragmentary normal section along the line 23-43015 Fig. 22, looking in the direction of the arrows;

Fig. 24 is an axial section of a wheel dressing or truing device-constructed in accordance with one embodiment of my invention, the section being along the drawing plane of Fig. 23;

Fig. 25 is an end view taken from the left of Fig. 24 and J showing the adjustable part ofthe dresser which holds the diamond; V i

Fig. 26 is a fragmentary section similar to Fig. 24 illustrating a modified construction;

Fig. 27 .is a development to a plane of a part of the circumference of a cam used in dressers constructed 'ac-' cording to my invention, and showing this cam in contact with an abutment. or follower;

Fig. 28 is a diagrammatic sectional view of a device constructed according to the present invention'for dressing or truing opposite sides of a grinding wheel simultasly;

Fig. 29 is a diagrammatic view, partly in section, of a modified form of dressing or truing device, for dressing or truing both sides of a r eiand. a. r a Fig; 30 is a diagram corresponding to Fig 29 illustrating an operative connection.

grinding wheel of curved axial Referring now to the drawings by numerals of refer;

encef35 denotes a helical gear; and 36 denotes the axis of this gear. In conventional practice, the grinding Wheel,"

the two opposite tooth normals which pass through the,

point 38 are what is known as contact normals. They contain the points of

contact

39 and 40 between the grinding wheel W and the profiles of the

opposite sides

41 and 42 of the helical teeth 43 of the gear. The

points

39 and 40 are low onthe tooth profiles '41 and 42, lower than the pitch point" 38, that is, closer to the tooth bottom. This low position causes the two

oblique lines

45 and 46 of grinding contact to have different axial positions. Line 45 is closer to the upper end 47 of the gear 35 than the line 46. v a

Ingrinding'a tooth space, the work 35 and the grindingwheel W move in ahelical path about the axis 36 relative to eachother' as the wheel rotates on its own axis. Asregards relative positions and grinding contact, the helical motion can be considered performed entirely. by the work 245. ,Atfonefltime, then, the. gear end 47 will be ina position as shown by dotted lines 47 In thisv end position only a small end portion of the grinding line 45 remains on the work while most of the grinding line 46 is still on the work. It is seen then that grinding contact ceases on tooth side 41 long before it ceases on the opposite side 42. In the middle regioniof the teeth, the grinding pressure on one side provides some direct bal ance to the grinding pressureon the opposite side.

tooth space with the end of grinding contact on the opposite side of the tooth space. The wheel tends to spring Inaccordance with one. phase of the present'inventionthis deficiency is remedied by setting thefgrinding wheel W (Fi'gs. 2 3 and 4) to a diiferen't angular position and by modifyingits shape accordingly. The grinding wheel is set toa larger helix angle than the'helix ,angle-atthe pitch radius of, the gear. ,In thejembodiment illustrated. in Figsf2and'3 it is so set"that thegririding'lines45" 46 lpassthrough mean-points 50', 51 of the tooth profiles in a transverse section, that is, in a section perpendicular to the Work axis as'indicat'ed in Fig;: 3. l In this Way the grinding lines 45 46 have substantially equal axial positionslf When the upper end 47 bof the pinion is intheposition ,47' (Fig, '2), then, one halflof each grinding line 45' "46" remains onthe Work; Contact ceases s'ubstantially at thesanieitimeon bothfsides, There is no unbalanced pressure between the two sides.

, Helix angle setting Thedet'ermination of the angular setting of the "grind-J ing wheel will now be described so that the grinding lines The tooth surface normals 52, saga: points 50,51 arefirst determined. On involute gears they are tangent to the base circles (not shown), as 'well'known, and areinclined "to the plane of rotation, that is, to the drawing plane of Fig.

pass through meanpoints 50, 51.

3, at an angle equal to the known base helix angle. Next their. intersection points 55, 56 with the, plane 57 are determined. This plane contains the wheel axis 60 and is parallel to the axis 36 of the work.

The axis 60 of the grinding wheel W is the straight line connecting the intersection points 55, 56, for the t 7. the tooth ends however, this balance is disturbed. The H balanced support for the wheel ceases on one side of the The crest of this wave projects normals to a, surface of revolution all pass through its axis. By fulfilling this condition as described, the

normals

52, 53 are made contact normals, namely, normals which are common between the work and the grinding wheel.

The working surface the grinding wheel The working surface of the wheel is best determined by first determining the line of contact between the working surface of the wheel and a helical tooth side of the Work 35. After the line of contact is determined, with all the contact normals along it, these contact normals and contact points are turned about the axis of the grinding wheel into a single axial plane of the grinding Wheel. The contact points are then points of the grinding profile in this position, and the turned contact normals are normals to the grinding profiles.

As shown in Fig. 2 the

contact normals

52, 53 do not intersect. However, there is one pair of contact normals which intersect. They intersect on a radial line 59 at a point 61 (Figs. 3 and 4). This point is located at such a radius 3661=r' (Fig. 3) that the helix angle 1/1 at said radius is equal to the helix angle setting of the grinding wheel determined above.

r can be determined from the well known equation for the helix angle 1,0:

L. tan ,0

Like all normals of a surface of revolution, the surface normal at each point of the line of contact intersectsthe axis of the grinding wheel or rotary cutter. To determine the contact position at a given radius of the helical tooth surface, the surface normal at that radius is moved in a helical path along the tooth surface until it intersects said axis. In this imaginary displacement along and about the axis of the helical surface, the original normal continues to be a tooth surface normal; and the point where it intersects the tooth surface in its final position is a point of contact between the tooth surface and the working surface of the grinding wheel. Other points, corresponding to different radii are similarly determined, to obtain a series of points defining the line of contact.

The line of contact can also be considered the normal projection of the wheel axis to the tooth surface. It can be demonstrated mathematically that it can also be con sidered the normal projection to the tooth surface of another straight line, which is located nearer the tooth surface and is more convenient for determining the line of contact. The contact normals all pass through this other line 62 (Fig. 2). It connects points 61 and 63 (Figs. 2 and 3). The latter point is obtainable by spacing a unit distance (1 inch) from point 61 on a line drawn through this point parallel to the gear axis 36, to point 65 (Fig. 2); From point 65 the distance u defined below is measured oif on a line 6563 parallel to the wheel axis 60. It is measured on the same scale as said unit distance.

Herein R denotes the radius of the grinding Wheel to point 61, that is, center distance, G minus r (C -r').

The axial profile of the grinding wheel can bedeter mined from the points and normals of the line of contact I along oblique lines, the grinding wheel profile in the normal section (Fig. 4) is less curved than the convex 6. tooth profile. The said normal section is perpendicular to the direction of the teeth and contains the axis of the grinding wheel. It is also an axial section of the grinding wheel.

.The difference between the profile curvatures of the grinding wheel and the work in the normal section can best be illustrated by the centersof curvature of the two profiles. 66, ,66' (Fig. 4) denote the contact normals which pass through the point 61. The

centersof curvature

67, 67', 68, 68 of the contacting profiles of this normal section lie on these normals. The tooth profile curvatures and the location of their curvatures centers 67, 67' are known. The curvature centers 68, 68' of the wheel profiles can be obtained from the wheel profiles as determined above. The distances of the curvature centers of the wheel profiles, from the curvature centers 67, 67' of the tooth profiles depend on the wheel radius R to point 61, on the helix angle setting 1/, and on inclination p of

normals

66, 66 to a plane 69 perpendicular to radius 59. Distance Ap is equal to 67-68 (6768') can be shown to amount approximately to:

Ap R tan 4/ sin This distance A increases with increasing wheel radius. The larger the wheel, the more its profile approaches the profile of a rack which in the involute gear system is straight.

In the drawings, the wheels are shown small enough to keep them within the drawing space provided. Larger wheels are preferably used in practice.

Instead of aligning the axial positions of the grinding lines 45', 46' completely, it is also possible to align them only partially. Thus, the mean points of contact 50', 51', may be assumed in a normal plane (Fig. 7) rather than in a transverse plane perpendicular to the work axis 7 as was done in Figs. 2 and 3. V

On the larger member of a gear pair with corrected tooth proportions, that is, with shortened addendum and lengthened dedendum, the two grinding lines are often sufficiently aligned in the conventional procedure so that they do not require my special procedure just described. In general, the special procedure described results in an improvement of the gear pair by improving either one or both members. It represents the preferred procedure and can be practiced without any change in machine structure.

Another and very important feature of the present invention is the procedure to attain the desired form of tooth ease-off or localization of tooth bearing. The

teeth are eased ofi near their boundaries, lengthwise and profilewise, so that they bear over a localized area when run at light load in their exact position. Slight changes in the mounting, deflection under load, inaccuracies even within tolerances, displace the bearing area on the tooth surface, but with properly eased-off teeth, the teeth will never hear hard at their ends. Without ease-off this may occur. Tooth ends are then more apt to break off under fatigue and noise is more apt to develop. The result is that eased-off teeth are stronger and better.

Referring first to the lengthwise ease-0E only, without profile ease-off, a generally square or rectangular hearing area is desired. This is shown at 70 in Fig. 5. It is the area between the straight lines 71, 71'. 45" is the line of grinding contact inthe mean position.

Dotted lines

45 and 45 are lines of grinding contact on opposite sides of line 45" and are generally similar to line 45".

In the known methods of grinding ease-0E the wheel is moved slightly depthwise adjacent both ends of the teeth. There is no depthwise motion at the middle of the teeth. This procedure is satisfactory on straight teeth; but on helical teeth it produces a form of ease-off different from the one intended. The ease-01f follows 7 the line or grinding contest; At end profile assess, the e localized tooth bearingfobtaindfin this known rmethod is an area likethe onbofifided .bylines45 and45 It Q is at a bias. Too much ,stock has been removed at the diagonal corners 73, 73',and not enoughat the diagonal 5 commune. v

We can plot, the ease-ofijat the various points of jthejf tooth surface'iby connecting points iof equal e se-on thereby obtaining a geodetic mapofthe'ease ofi surface Line 45", is a line of zero ease-elf. If line's 45 a'ndi4S are"consider'ed lines of constant andequal ease-oft, then their inclination'or slant depends to'soniegfexte'flt onthe curvature or the wheel profile. But in "any averaged "slant is substantially equal to'th'eTsl v 45". Heretofore, there has been no' knewmway of '15 avoiding the bias condition. I p v v The p esent invention, however, permits "of, attaining a localized bearing'are'a as boundedhy lines 71, 71"when; only-lengthwise ase-offis consideredjfandjan ovalfareafj 75 such as shown'in Fig. '6 whenfprofile ea fij is add Further, any form of bearing area maybe attained, what" ever may be held desirable. *The methodof the present invention provides full control of thebearing area. It can be kept free of slant as normally desired,: or it can be slanted one way or the other. 7 The present invention enables full control as to where to pIacYhecas'e Sfi'; and how much of it to provide. 7

Principles of controlled tooth 'eizs-ofi The explanatory diagrams' Figs. 8 to ll can 3 sidered a partial development to a plane ofi a cylindrical mid-section laid through the gear teeth. The axis open cylindrical sectional surface coincides with the'gear axis; 36. The section may be taken along the pitch c ylinder j' of the gear. In other Words, the figuresshow developed portions of the peripheral surface of the gear. For clarity, the sections have not been cross-hatched. p

In Fig. 8, 77 denotes the grinding wheel section in the mid-position of the grinding wheel. Its axis is parallel to line 78 and above it. If no ease-ofi were provided,. the considered cylindrical surface would intersectjthe tooth sides in helices. These show up in the develop ment as straight lines 79 in Fig. 8. With ease-o ffl the developed intersection lines with the tooth sides are convex curves 80 tangent to lines 79. Their curvature is very much exaggerated. At the tooth ends, the curves 80 have a normal separation z from their mean tangents 79,, which on gears of the size, of automotiye transmis sion gears, amounts to something in the order Qf 0.00 l

inch. This is at a distance s from thepoint of tangency with a line 79, which distance depends upon the length of face F and on the helix angle of the gear.

"'2 cos g0 At the "small mean: at z considered; instantiated? and distances are tied up with the radiusR or 'cui'vature radius like the ordinates era parabola,naniely,

. ,sL, Z and a This determines radiusR Each are 80 has a vary ing'inclination to the direction of -its tangent 79. Q It is zero at the middle 'and' increases toward the ends; At the'tooth ends the inclination t' of a curve 80 to its mean tangent 79 amounts to:

Are tin radians teetert. .s f This can be transformed into:

The wheel position for generating the eased-off tooth end will nowbedeteiniined, first for'grinding a single side. For this reference will be made to Figs. 9 and 10. The dotted section 77 again represents the grinding wheel position for grinding truly helical .tooth sides 79 without ease-off. At the upper end of the tooth space contact has shifted in the directionof the gear axis 36 from a mean position" 81 to end point 81. To obtain satisfactory eased-0E teeth We must kee the pressure angle constant along each side'ofa tooth space from end to end of a tooth.

To form the eased-oil tooth ends, the'grindi ng' wheel:

is, as in conventional practice, vfeddepthhris intothe work as it travels from a central position lengthwise of. the work to either end of a tooth space. But as indi cated by section 77.,, the wheel should contact curve 80 immediately adjacentpoint 81". Only then will it bepossible to retain the same inclination of the tooth sur face normal to the cylindrical surface as on the true .helicoid. The preservation of this inclination or pres tion immediately adjacent point 81 as curve 80. 'This object could be attained in dilferent ways if the'wheel were grinding only one side of a tooth 'space at jatime'. The wheel could for instance, be slightly turned about any axis passing through 81' and contained in the normal plane perpendicular to the tooth direction. None of these turning adjustments would affect the'pressureangle.

:In other words; an infinitesimal turning adjustment of this kind would cause a pressure angle change whichjis infinitesimal in the second order, and is entirely negligible.

One position of the turning axis fits both sides of the .tooth space equally well and results in simplicity besides'f' This axis is parallel to the axis of the grinding wheel, and may also pass through point 81.

Fig. 9 shows its effect. The tooth surface normal 81"-82 before ease-off is inclined to the drawing plane of Fig. 9 at what'may be called the normal' pressure angle at 81' so' that the endpoint 82 'is below the drawl ing plane. The turning axis 85 lies in the drawingplane.

As normal 81'82 is turned about axis' 85 its point 82 describes a circle which is projected as a straight line in i 'Fig. 9. Point 82 thereby moves to a position 82' so. 7 that normal '81'82' is perpendicular to curve 80. In

this new position of the normal its inclination to the drawing plane has not changed at all. Through this a turning adjustment the grinding wheel is now capable of contacting curve 80 immediately adjacent pointSl' as required. The turning displacement on axis 85 moves the wheel axis to a position 60',

In addition to this turning displacement a linear displacement of the wheel with respectto the'work is re- :quired to advance the wheel outline a distancez over point 81'. In the present case'this advance'is best ob-: tained by a depthwise displacement z which depends on thei'inclination of the tooth normal, or the normalpre's sure angle (,0 at point 81', as follows! Thus at the tooth ends, the grinding wheel should bc relatively advanced depthwise an amount'z and it should be relatively turned on an axis 85 through an angle which produces the required helix angle change I, and which amounts to:

Both of these displacements move the wheel further into the work so that the outline 77. of the wheel in the drawing plane of Fig. 9 becomes larger.

The same is true for the opposite side of the teeth which is referred to in Fig. 10. The points 81 82 82,,, and the line 85 in Fig. 10 correspond to the

points

81, 82, 82 and the line 85, respectively in Fig. 9, but relate to the opposite side of the tooth space. The described conditions apply also when both sides of the tooth space are ground simultaneously. This desired case is illustrated in Fig. 11 where the grinding wheel is also shown near one of the two end positions.

The distance b of the projected wheel axis 60 from turning axis 85 in Figs. 8 to 10 amounts to the product of the wheel radius R to point 81' and turning angle t It is:

i in radians This is further shown in Fig. 12 which is a View along the axis of the grinding wheel. Dotted line W shows the grinding wheel periphery in a position to grind teeth without ease-off. Full line position W shows the actual grinding position. The wheel is fed in depthwise a distance z so that the wheel axis is displaced from position 60 .to position 60 Simultaneously it is turned on axis 85 through the above defined angle t whereby the wheel axis is displaced from position 60 to 60'. It has then a distance b from the plane 6085. Its depthwise distance z from the initial position 60 is made up of a distance z and of the depthwise elevation of position 60 over position 60'. The latter is:

/zt R After transformation the total amounts to:

e ztzzd l+ R tan 50) These two displacements b and z can be obtained in accordance with my invention by moving the grinding wheel axis 60 about an axis 87 (Fig. 12) parallel to axis 60. Radius r ='6087 and the turning angle 0 about axis 87 has to fulfill the equations:

Zt= /20 r b=t9r By'division and 22 b Hence, also,

This determines pivot, 87 and the point of swing 0 about it.

The swing is in one direction at one end of the tooth space and in the opposite direction at the other tooth end. As the wheel goes through a grinding path from one tooth space end to the other, the swinging motion about axis 87 is continuously in one direction. The swinging position moves from an angle (-0) to zero and to (+0). It is proportional to the stroke. Some overtravel should be had.

The above described procedure produces the desired bearing without bias providing the grinding Wheel and the work are very rigidly mounted.

Bearing changes can be made by altering the data z}; or b, and determining r and 6 over again. A reduction in b tends to slant the tooth bearing toward the direction of the line of contact 45" (Fig. 5 An increase in b tends to slant it in the opposite direction.

There may be an occasional demand for an ease-01f which starts only adjacent the tooth ends, and which leaves the middle portion of the helical teeth entirely unaltered and Without ease-off. The curve 80 (Fig. 8)- would then be composed of a straight middle portion coinciding with the tangent 79 and of curved end portions. This kind of ease-off can also be attained in accordance with the present invention. In this case the swinging motionof the wheel on axis 87 (Fig. 12) is not proportional to the stroke distance. Instead it stops at the middle of the stroke. The swinging motion is interrupted by a dwell at the middle portion.

Fig. 13 shows diagrammatically the gist of the method of obtaining a controlled tooth ease-01f in accordance with the present invention. It comprises feeding the wheel in relative to the work substantially in proportion to the square of the distance s from the mean point, and in also changing the grinding wheel position so that grinding contact with the lengthwise tooth curves 80 can be effected immediately adjacent a line parallel to the gear axis 36. The two end points of the curve 80 are then ground in positions displaced from one another in the direction of the gear axis. While this is true for the grinding points themselves, the corresponding point of the wheel axis moves differently. This point will be referred to as the wheel center. It will be defined as the intersection with the wheel axis of a plane perpendic ular thereto and containing the mean point of the grinding profile, the point which produces the mean point of the gear tooth profile.

This definition applies to grinding wheels for grinding one side of the teeth. On wheels for grinding both sides of the teeth the wheel center is the average of the two individual centers as above defined. The wheel center 89 in Fig. 4 then lies in the plane 90 of symmetry of the wheel, and is its intersection with the wheel axis 60.

In the diagram Fig. 13 the grinding wheel is defined by its plane of symmetry 90, by its axis 60, and by its wheel center 89. 91 denotes the middle of the grinding area on the gear 35 defined by its outline and its axis 36. T he projected distance 89-91 equals the distance b inthe end positions above referred to.

As the middle of the grinding contact area moves from 91,, to 91 and to 91 in the axial direction of the work, the wheel center moves from 89,, to 89 and to 89 along a line 92 inclined to the direction of the gear axis 36. In the preferred embodiment the swinging motion of the grinding wheel on axis 87 is continuous during a grinding pass.

In accordance with the present invention the wheel center moves relative to the work in a direction inclined to the direction of the work axis, while describing a curve concave toward the work, and while the work turns on its axis. The direction 89 89 lies between the direction of the work axis and the direction of the teeth. The

latter coincides with the direction of the plane 90 of sym- Structure for attaining controlled ease-ofi Figs. 14 and 15 illustrate one embodiment of a wheelsupporting and wheel-actuating mechanism for carrying out the method just described.

vided in the wheel head 133. While the bearings'showns.

wheel W' is h eresiecured to a shaft" 95 in conventional manner." This shaft; is iotatably mounted in a holder 96 which is radially adjustable in a pivot member 97. This member is adapted to swing in time with the working stroke by means such as shown in the Part 122, which has the rectangular opening, is -made--' V embodiment of Fig. 16. It is split lengthwise into two up of two component parts 122', 122" (Fig. 16) rigidlyhaIves 97', 97" which are bolted together by bolts 98.. secured together by means not shown. .v Part 122' con It is'pivotally mounted in a wheel head 99 in two spaced tains a cylindrical outside surface 134 which during the

bearings

100, 100 which may be anti-friction bearings grindingpasses is engaged by a stop135 (Fig.16) Inif desired. this position the cylindrical surface 134 is coaxial with- Holder radially adjustable in pivot member 97, spaced screws 101 being provided for this purpose. These screws thread into nuts formed integral with the bevel are plain bearings they may also be made anti-friction bearings if desired. The wheel head 133 is adjustable angularly for helix angle about axis 111.

theaxis130 of the pivot member 118. Rocking motion on the pivot axis 130 then leaves the position of the cylindrical surface unaffected. It doesnot move in, nor

gears 102. These gears are journaled in the pivot member 97, and are turned simultaneously by pinions 103 which are rigid with a common shaft 104. The two end screws lfll are rigid with slidable holder 96. The middle screw 101 bears against an elastic disc 105 and serves to secure the radial position of the holder resiliently so that all the screws are under load always and do not tend to shake ereby the

gears

116, 117 roll on their racks.

does it moves out through the rocking motion. Part 122 -is slidable in {a transverse cylindrical-hole- 136 provided in the pivot member 118. The hole -13-; extends in the direction of the pitch planesof the racks As the part 122 moves to theright in hole 136 it carries-.theholder 115 and the grinding wheel--with it'g- The loose, The shaft ,104 is journaled in projections of the lower half of the pivot member. It is secured in a desired turiiing position by known means (not shown) and is accessible from the outside through a hole 107.

grinding wheel then recedes depthwise from the work, and gets clear of the work. The reverse occurs before the start of a grinding pass.

The. periodic advance and withdrawal of the grinding Thehdjustment of holder 96 is to offset the wheel axis Whfielio and f WOYkhlg P05111011, The pp n 60 from the axis 37 to secure the desired localization of fected y a cam This ham is rigidwhh Shah-141 tooth bearing. The wheel head 99 is adjustable for helix Whch is mounted in the Wheel head and Whivh angle on ways 110 about an i 111 (Fi 15), W s geared. to perform one complete turn between succes- 110 are curved about this axis, sive grinding passes. This cam engagesthe cylindrical-' Flexible dust seals 112 are used to protect the inside s f e except during g g gag nt i s f of thewheel head from grit. Shaft 95 and the grinding wheel .W' mounted thereon are rotated by a V-belt acting on pulley 113.

A further embodiment of a wheel head is shown in Figs.

where there is a very slight clearance between said surfaceand the cam. The position of part 122 is then determined by stop 135 (Fig. 16).

Engagement between part 122 and stop 135 part.

16 to V 7 V j 122 and theca n 140 is maintained by a spring 142 (Fig.-- .1 Here the adjustment of the holder in the pivot mem- This spring s on alever 143 rotatably yber is made use of for withdrawing the wheel from the. mg a roller Rohef 144 bears against cyhhdhcal work. The wheel is preferably withdrawn from the work. hf 145 Provided P In the forward after each grinding stroke, and it is advanced to working. Posmoh, w the P 122 engages the'stcp 135,

position again prior to each grinding stroke. In accord- 4O face 145 15 coaxial with the P i ance with the present invention this advancement and The P 122 is Prhssed against stop 135 during grind withdrawal, the clapping, is preferably made in the same The P exefts Pressure which is Substantially direction as the adjustment of the holder for eccentricity nqrmal 9 the cyhhdrical Surface 134 and which to the pivot axis, and is made with respect to the pivot tams large downward component The P3115422 member 7 made suflieiently free or loose in the cylindrical bore- The Shaft 95 of the grinding Wheel is here rotatably 136 so, that the downward pressure is transmitted to the mounted in a holder 115 which has two spaced gears 116 holder 120 rather than to the how Thereby the gear and 117 rigid with it. These gears are coaxial with shaft teeth of the holder Pressed tightly into teeth of 95 Gear 117 is seen also in Fig 18 The tooth profiles their racks to keep the whole unit rigid during grinding. of the two gears are alike. The teeth may be helical, and Shaft 141 rotated by Worm Wheel 146 a they are then of opposite hand on the two gears. Each of of a W Y Passe? t q the adjustment axis 111 the two gears meshes with a rack rigidly secured to a pivot and which 17 q sd by a dotted line 147'- member one such rack is seen in Fig 18 and The required tuned rocking motion on pivot axis 130 denoted at V for localization of tooth bearing is efiected by a cam Intermediate the two

gears

116, 117 the holder rotata- 150 secured to shaft 141 one This same shaft bly carries a sliding block 120 made up of two parts 120, holds can lts Opposite 150 engages a '(Fvig 1.6) rigidly secured together Sliding roller 151 (Flg. 18) mounted on the pivot member 118. block isrotatable on the holder 115 on an axis coincid- Ehgagement between 5 roller 151 main; ing with the axis of shaft 95 and of grinding Wheel tamed by the spring 152 indlcated m dotted lines in Fig. It is adjustable radially in a rectangular opening 121 pro- 150 easlly accesslble and can be changed vided in a-part 122 which during grinding is fixed relareadily tive to the pivot member 118. Adjustment is. made by General structure turning the square end of a screw 123 which is rotatably Either a vertical or a horizontal disposition of the. held in said opening. In this adjustment the axis 60 of work axis may be used. In Fig. 20 I have shownas an shaft 95 is rad ally offset from the. axis 130 of the pivot example a vertical disposition. The work 35 is ro- I member 118. In this radial adjustment the two gears tatably mounted on a slide 156 which is radially ad- 7 116,117 rollontheir respective racks 119, and because justable along ways 157 provided onthe base 158. This 7' ofthe r ample axial distance from one another they mainadjustment is to bring the work into and out of optam the holder 115 exactly parallel to its initial position erative engagement with the grinding wheel. and parallel to the axis of the pivot member. Backlash The grinding wheel W is mounted in a holder radially 7' is avoided during the grinding passes by pressing the adjustable in a pivot member, as described, which is... gearsdepthwise into their racks as will further be dedisposedinside of awheel head 133. It is driven from scribed. j r t a motor 160 mounted on the wheel head 133 on the op- The pivot member 118 is mounted for oscillation on posite side of the grindingwheel. The drive is by '"a its axis 130 in two spaced bearings 131, 132 (Fig. 17) probelt 161 to a pulley 162 secured to a counter shaft 163 also mounted in bearings rigid with the wheel head. Another pulley 164 on shaft 163 drives the pulley 113 (Fig. 15) of the wheel spindle through a belt 165. This belt is shown in this diagrammatic view as a plain belt rather than a V-beltr The belt 165 passes over a tension pulley 166 which is movable about shaft 163 and is kept pressed against the belt by spring means not shown. In this way a safe drive to pulley 113 is effected from a shaft with a fixed axis even though the pulley 113 partakes of a small rocking motion.

The wheel head 133 is mounted on a slide 167 for adjustment about an axis 111 in accordance with the helix angle of the work. The slide 167 is vertically adjustable in the direction of the work axis along guides 170. This adjustment is to locate the position of axis lllrelative to the work. The slide 167 may also be used for reciprocation if desired.

Preferably grinding is effected during the stroke in one direction only and the work is indexed between successive grinding strokes. Whether the linear stroke along the work axis is performed by the Wheel or the work is a matter of choice. On large gears the wheel is preferably reciprocated axially of the work.

One simple way of grinding helical teeth is by rotating the work at a uniform rate during the whole of the grinding process. The work turns through a integral number of teeth between successive grinding passes. To avoid complications this integral number is preferably kept prime to the number of teeth of the work.

Fig. 21 shows a drive diagram of the feed motions. Motor 172 imparts rotation to a sleeve 173 through change gears 174. The sleeve 173 drives a shaft 175 mounted on the slide 156 shown in Fig. 20. Shaft 175 drives worm 176 through change gears 177. The worm 176 meshes with a worm wheel 180 coaxial with the work.

If the linear strokes are imparted to the grinding wheel then the dotted rectangle 181 represents a known stroke mechanism which is driven from the sleeve 173 through gears 182. The gears 182 further operate through other gears 183, 184 to impart motion to a shaft 185 mounted in the wheel head. Shaft 185 imparts motion to the cam shaft 141 (Fig. 17) through a worm 186 and wheel 146 to turn it at a rate of one turn between successive passes. Shaft 141 thus turns around completely as many times as there are strokes. Thus the pivotal support for the wheel is oscillated once per stroke of the wheel through cam 150; and the wheel is moved into engagement with the work prior to a grinding stroke and withdrawn from engagement with the wheel at the end of each grinding stroke by operation of cam 140.

Dotted rectangle 190 represents a known indexing mechanism. With such a mechanism it is possible to grind straight teeth on a given grinding machine and thus extend its range. An indexing mechanism also has use on helical teeth in modified procedures. If the stroke is to be performed by the work then the rectangle 190 also represents a known stroke mechanism in addition to an index mechanism. Of course, there is only one stroke mechanism. If the work is reciprocated there is no need for reciprocating the grinding wheel. My described method and means for applying controlled tooth ease-oif can be used with any one of heretofore known methods of grinding helical gear teeth with a grinding wheel of curved, or even straight, axial profile. The ease-01f may be applied to either one or both members of a gear pair.

The wheel dressing and truing device The wheel dresser has not been shown onthe diagrammatic drawings of Figs. 20 and 21. A; preferred form of wheel dressing and truing mechanism -'will now be described. Its'principles are illustrated in Figs. 22 and 23.

The end diamond 200 merely serves to dress off the periphery of the wheel W. If the tooth space bottomis left unground a straight dressing pass is suflicient. Otherwise the corners of the wheel profile should be rounded off in known manner.

The

sidedressing diamonds

201, 202 have to dress the

curved side profiles

204, 205 of the wheel. These profiles usually have varying curvature, being more curved adjacent the point of the wheel than further back. This is illustrated by the circle 206 which is the circle of curvature at the mean point 207 of the active grinding profile. The profile 204 hugs the curvature circle 206 very closely adjacent point 207, then extends outside of it further back on the wheel, while more toward the point of the wheel it tends to reach inside of the curvature circle. Non-circular curve 204 has an evolute 208 (Fig. 22) and is generally similar to an involute. 209 denotes the surface normal at point 207. The tangent plane at point 207 to the wheel surface is perpendicular to the surface normal.

In accordance with my invention the diamond point, which in one position coincides with the point 207, is turned about a dresser axis 210 (Fig. 23) inclined at an acute angle to the wheel surface and to said tangent plane and passing through the mean normal 209. The axis 210 lies in the drawing plane of Fig. 23 and is so positioned that at point 207 the diamond moves in the direction of the axial wheel profile. point 207 lies in an axial plane of the wheel.

As the diamond turns on dresser axis 210 it describes a circle about said axis. This circle shows up as a straight line 211 in Fig. 23. Shown with exaggeration the diamond moves from a position 207 to a position 212.

As the described circle does not lie exactly on the desired surface of the grinding wheel, the dresser is advanced along its axis 210 to compensate for the difference. The diamond thereby moves from a position 212 to a position 213 (Fig. 23) which corresponds to a point 213' of the grinding wheel profile (Fig. 22). When the diamond motion is tangent to an axial plane at point 207, as described, the dresser axis 210 intersects the surface normal 209 at the curvature center of the axial profile that would be produced on the grinding wheel without motion along the dresser axis. This can be demonstrated mathematically.

In accordance with my invention the dresser is so adjusted that its axis 210 intersects the surface normal 209 in the center of curvature 215 of the required grinding wheel profile. Without any axial advance of the dresser the diamond would then produce a substantially circular wheel profile which has the same curvature radius 207- 215 as the wheel profile requires. Then the axial motion of the dresser has to make up only for the slight difference between the profiles of the same mean curvature radius.

To attain a curvature center 21 5, the dresser axis 210 is set to pass through this center. Should a curvature center 215' be required, then the dresser axis is set to the dotted position 210' where it passes through point 215'.

The axial motion of the diamond is controlled by means of a cam and follower, one of which is held stationary,

. and the other of which is rigid with the diamond carrier.

In the embodiment specifically illustrated the cam is the stationary member. It is a face type cam. As the swing of the diamond carrier is limited, only a fraction of the entire circumference of the cam is swept by the follower. It is therefore feasible to put several cam profiles on the same cam member.

Fig. 27 is a partial development of the cam. Follower 220 contacts the cam profile 221 at a point 222 which corresponds to the position of the diamond at the mean point 207 of the active grinding profile. As the dresser is set to dress the required profile curvature at point 207 even without axial motion, the cam 221 has to provide very little axial motion in that region. 222 is a point of inflection on the cam profile. When the follower 220,

The direction of the motion at l l o.

turns from right to left in engagement with the cam profile it moves up-or forward axially until it reaches the proximity of point 222. There its axial motion stops briefly, and then gradually continues in the same forward direction. More broadly its minimum axial motion is at the mean point 222,'and it moves in the same direction axially on both sides of this point, as it swings over the cam profile from one end of swing to the other end;

The above characteristic of the cam profile can be expressedin mathematical terms using the profile tangent at point 222 as one axis of a coordinate system, and the verticaldirection as the other axis, point 222 being the origin. -The ordinate y is then the distance of a given profile point from the profile tangent at the point of inflection 222. And the lateral distance of the profile from origin 222 is the abscissa x. It is measured in the direction of-the profile tangent at the origin 222.

The cam profile can then be expressed by the following equation: y=Cx where C is constant. 1 This omits possible higher orders, that is,terrns where x appears at a higher power than the cube.

In accordance with the present invention, the profile curvature is automatically changed very gradually as the wheel diameter changes through repeated dressing and truing. As pointed out, a concave'wheel profile should become more curved as the wheel diameter is reduced to produce a constant profile on the helical teeth. This is done by tying up the turning position of the cam 221v with-the diameter of the grinding wheel, that is, with the position of the dresser slide which is adjustable radially toward the grinding wheel.

It will now be shown that small changes of the turning position of the cam result in small changes of the curvature radii produced on the wheel profile. sumed that the cam is so set that a point of the cam profile with abscissa dx contacts with the follower 220 while the diamond is at the mean point 207 as before. The-abscissas correspond to turning angles from the new mean position on the cam. Theynow amount to:

ligible as compared with the terms in dx. Thus we obtain:

at the small amountsof dx considered. 1

As will be recognized, the term in 1: results in'a change Let it be asin curvature .of the path described by the diamond, and of the curvature produced on the wheel profile. It is seen then that a small change in the cam timing effects primarily a curvature change on the wheel profile.

Structure of the dressing mechanism Referring particularly to Fig. .24, diamond 201 is provided in a pivoted part 251. For adjustment, a tool 1 may be used which engages a threaded hole 232 provided. in. the holder. The holder is secured in any adjusted position by a screw 233 with a square end. This screw. threads into. the threaded holeprovided in the pivotedpart 231and acts on the holder through a cylindrical pin 234 with an inclined plane end 235. This end contacts -the=adjacent plane side. 236 (Fig. 25) of the holder. An elastic disc"237iis interposed between the screw 233 and pin 234 to maintain pressure at all times and to thereby secure screw 233 against accidental rotation.

Part 231'has a pivot axis 210 inclined at an acute angle to the holder 226' and tothe line of'adjustment 230.

Axis 210-intersects the line. 230. The pivoted part 231 is mountedfor oscillation about and motion along its axis 210 in a housing 240, being journaled on two spaced bearings 241, 242'. Thefront bearing 241 extends around the holder 226. Thisbearing is cut oif in front at an angle so-thatthe' bearing portion around its periphery has varying axialpositions. The upper portion 241 is farther advanced axially. The other bearing 242 is a more conventional bearing' It is disposed at the rear. By using a front bearing 241 which extends partly beyond holder 226 a sufiicient spread of the two bearingsis obtained'lfor mounting the pivoted part 231 rigidly in a confined space. i v

A sleeve 245 is threaded onto a stem 246 of the pivoted part 231 and fits about the cylindrical portion 247 of this stem... Sleeve 245-contains a cam follower 220, and its cylindrical-outside surface 250 serves as a bearing surface in bearing 242. A coil spring 251 is inserted between a shoulder 240 ofhousing 240 and an opposed shoulder on the outside surface of sleeve 245. This spring presses the follower 220-against the cam 252 whose cam profile has already been described.

After partial assembly, the sleeve 245 is secured again turning motion on the stem 246, for instance, by a pin extending through coaxial holes- 253 of the stem and sleeve, or in any other suitable known way.

' Pivoted part 231 contains helical teeth 254. They engage rack teeth rigid with a hydraulic piston not shown in Fig. 24 so that thepivoted part may be oscillated by such conventional hydraulically actuated means.

Face cam 252 contains teeth 255 on its outside, which are engaged-by matching teeth provided internally in a ringmember 256. These teeth serve for coupling, that is, rigidly connecting the cam and ring member 256.

The ring member is maintained stationary in the grinding operation; but it is turned when the dresser slide (not shown in Fig. 24) is advanced toward the wheel axis. To this end it is mounted on the housing 240 by means of a ball bearing257 with double contact. The ring member further contains the worm.- wheel teeth 260 for engagement with a worm not shown in Fig. 24. An end plate .261 is rigidly secured to the ring member 256 and holds the cam member axially.

The dresser or truing apparatus obviously will be protected from .dustby conventional dust seals. I have shown, however, a seal-262 at the front because of its more unusual-construction. It is a flexible seal made for instance of synthetic rubber bonded to the conical front end 263 of part 226. At its other end it is secured ingrooves 264 provided on housing 240 by a clasp 265 of known construction.

Even without the provision for changing the cam timing, this dresser has merit. It is simple and it maintains the diamond at a nearly constant angle to the grinding wheel-surface. This makes it possible to use diamonds other than those lapped to a single sharp point.

The'dressenshown in Fig. 26 has no adjustment for changing the cam timing. Here the cam is formed on the hub 270 of a flanged member 271 which is bolted directly to the housing 240. I have shown here a square projection 272 on the stem'246 of pivoted part 231. It permits hand operation with a suitable tool should such hand operation be .desired. The preferred operation is howeverby hydraulic means as in'the dresser of Fig. 24.

One way of arranging a pair of dressers is indicated in Fig. 28. The dressers are of the type described but are more diagrammatically shown than in Figs. 24 and 26.

Each holder 226 is adjustable toward and away from the grinding wheel in a pivoted part 231, preferably along the mean surface normal 275. The pivoted part contains a cam follower 220 engaging a face cam 252.

The pivoted part 231 is mounted in a housing 240 formed integral with or rigid with a slide 276. This slide is here mounted on a circular slide 277 for adjustment in the same direction 275 as the holder 226. The circular slide can be adjusted angularly for pressure angle about a pin 280 whose axis is perpendicular to line 275 and intersects the pivot axis 210 at an acute angle. The circular slides 277 of the two opposite dressers are adjustable about their pins 280 on a common slide 281, to which these pins are secured. This common slide is adjustable in a straight line to move the pair of dressers radially toward or from the axis of the grinding wheel.

In this illustrated embodiment a ball linkage effects a change in the cam timing as the wheel diameter is reduced. The stationary ball joints 282 are located on a slide 283 adjustable in the same direction as the slide 281 but held stationary after initial adjustment. These joints are indicated by their external spherical portions only. Each cam contains another ball joint 284 at a given distance from its axis. The connecting link is indicated by the straight line 285. It is adjustable for length.

To effect an angular adjustment of each cam 252 upon adjustment of their common slide 281, the two joints of each link have to be at different vertical levels with respect to the drawing plane. If they were at the same level a moderate adjustment of the slide 281 would leave the cam timing practically as it was. The larger the inclination of the link axis to the drawing plane, however, the more adjustment of the cams will result at a given displacement of the common slide 281. The said inclination at the middle position of the common slide 281 can be set to the desired amount by adjusting slide 283, and then looking it.

Instead of the shown linkage I may also use the cam timing control described below.

The dressing and truing device illustrated in Figs. 29 and 30 differs from the dresser of Fig. 28 in that the pivoted parts 231 are set at a fixed inclination on a common slide 286 which is adjustable to move the dressers toward or from the wheel The housing 240 is shown here merely by slide 287 with which it is rigid. The two opposite slides 287 are adustable at right angles to the adjustment of the common slide 286, that is, in a direction parallel to the wheel axis. They are so adjustable directly on the common slide 286.

Fig. 29 shows diagrammatically one way in which the device may be operated hydraulically. The hydraulic cylinders 288 are rigidly secured to the common slide 286. A pair of pistons 289 formed in one piece are adapted to reciprocate therein. They act on a bar 290 through a joint 291. This bar is pivoted at its opposite end in a ring 292, which engages a sleeve 293. The latter contains internal threads. The thread on one side is a right hand thread. On the other side it is a left hand thread. The internal threads are engaged by the threaded ends of the racks 294 which engage helical teeth 254 (Fig. 24) provided on the pivoted parts 231. When the pivoted parts are locked, turning of sleeve 293 will move the opposite slides 287 equally in opposite directions at the same time.

Intermediate the ring 292 and joint 291 the bar 290 passes through another joint 295 which is similar to joint 291. This joint 295 is stationary and adjustable along the guides 296 in the general direction of bar 290. It serves as a fixed pivot for the bar but permits lengthwise movement of the bar.

Each of

joints

291 and 295 comprises a cylindrical pivot 297 which is slotted to receive the bar 290. The outside surface of this pivot is rotatable in the cylindrical inside surface of abearing portion (the bearing portions 18 of pistons 289 in the case of joint 291, for instance), which is recessed at both ends to clear said bar.

In the described construction the amount of swing of both pivoted parts 231 is simultaneously adjustable. To shorten the swing, joint 295 is adjusted toward ring 29 2. To lengthen the swing, said joint is adjusted away from ring 292. The position of the swing is also adjustable. After locking the slides 287 in their desired positions and leaving the pivoted parts free to turn, a turning adjustment of the sleeve 293 in one direction swings both pivot parts down. In this way the mean position of swing may be altered as desired.

The end diamond 200 (Fig. 22) may be made to move with ring 292 if desired.

As indicated in Fig. 24, the cam 252 is adjusted by means of the teeth 260 provided on a worm wheel rigid with the cam. Each Wonn wheel 260 meshes with a worm 298 (Fig. 30).

The worms 298 are rotatably mounted on the respective slides 287 and their shafts have splined connection with a worm wheel 299 having a long hub 300. A worm 301 meshes with the worm wheel 299. It is driven from the spindle 302 by means of change gears 303 indicated by their pitch circles only. This spindle is mounted on common slide 286 in an axially fixed position. It contains a screw (not shown) for adjusting slide 286 through engagement of said screw with a stationary nut.

As the common slide 286 is adjusted by turning spindle 302, the worms 298 are also turned in time therewith. They turn worm wheels 260, and thereby the cams 252 so that the dressed wheel profile becomes more curved as the wheel diameter is reduced in the amount required for grinding helical teeth.

The two worms 298 like the two cams 252 are of opposite hand to obtain the desired result simultaneously on both side dressers by rotating both worms in the same direction. I

The described method of automatically changing the wheel profile with the wheel diameter permits of obtaining a constant product with a practical range of wheel diameters before a new set-up is required. It eliminates a defect of the conventional process.

While the invention has been described particularly with reference to grinding, it is understood, as previously stated, that the invention is applicable also to cutting of gears. The term gear as used herein is intended to include all forms of helically toothed members including worms.

Having thus described my invention, what I claim is:

l. The method of producing helical side tooth surfaces on a gear which comprises engaging a disc type rotary tool with a gear blank, and rotating the tool in engagement with the blank, while effecting a relative helical motion between the tool and blank about and in the direction of the blank axis, and while simultaneously effecting a further relative motion between the tool and blank in a plane which is perpendicular to the tool axis and which is inclined to the blank axis and in which the tool center travels in a path which is concave toward the blank.

2. The method of producing helical side tooth surfaces on a gear which comprises engaging a disc type rotary tool, that has opposite side working surfaces that are of curved profile in axial section and that are symmetrical to a central plane perpendicular to the tool axis, with a gear blank so that said plane is inclined to the axis of said blank, and rotating the tool in engagement with the blank while eifecting a relative helical motion between the tool and blank about and in the direction of the blank axis to elfect working passes of the tool longitudinally of the workpiece, and while simultaneously effecting a further relative motion between the tool and blank in said inclined plane which is continuous in one direction and without reversal during each working pass.

3. The method of producing helical side tooth surfaces on a gear which comprises engaging a disc type rotary tool, that has oppositeside Working portions that lie, respectively, on opposite sidesof. a mean plane perpendicularto the tool'axis and that lie, respectively, in separate surfaces of;revolution coaxial with. the tool, with opposite side tooth surfaces of a gear blank so that said plane, is inclinedto the axis of said blank, and rotating the tool in engagement with the blank while, effecting a relative helical motion between the tool and blank about and in the direction of the blank axis, and while simultaneously effecting a further relative motion between the tool and blank in a direction approximately lengthwise of the engaged side tooth surfaces and about an axis which is ofiset from but parallel to the tool axis and which is offset from the tool axis in a direction approximately radial of the blank.

4. The method of producing helical surfaces on a workpiece which comprises engaging a rotary tool, that has working portions disposed in a'surface of revolution extending about the tool axis, with thelworkpiece,.so that a plane, which is perpendicular to the'tool axis, is inclined to the axis of the workpiece, and rotating the tool in engagement with said workpiece while effecting a relative helical motion between the tool and rworkpiece about and in the direction of the axis of the workpiece, and while simultaneously effecting a further relative motion between the tool and workpiece inthedirection of a mean helix of the engaged helical tooth surfaceto be produced on the workpiece and, about an axis. perpendicular tosaid main helix, the tool axis being offset from the last-named axis in a direction approximately radial of the workpiece.

5. The method of producing helical side tooth surfaces on a gear which comprises engaging a disc type rotary tool, which has opposite side working surfaces that are symmetrical with respect to a mean plane perpendicular to the tool axis, with a gear blank so that said plane is inclined to the axis of the blank, and rotating. the tool on its axis in engagement with the blankjwhile eliecting a relative helical motion between the tool and blank about and in the direction of the blank axis, and while simultaneously effecting a further relative motion between the tool and blank in a plane, which is inclined to the blank axis, in time with said helical motion and in which the tool center travels in a path which is concave toward the blank.

6. The method of producing helical side tooth surfaces on a gear which comprises engaging a disc type rotary tool which has opposite side working surfaces that are disposed at opposite sides of a mean plane perpendicular to the tool axis and that are of curved profile in an axial plane, with a gear blank so that said plane is inclined to the blank axis, and rotating the tool in engagement with the blank while eifecting a relative helical motion between the tool and blank about and the direction of the blank axis, and while simultaneously effecting a further relative motion between the tool and blank about an axis, which is perpendicular to the general direction of the engaged tooth surfaces, in time with said helical motion and in which the tool center moves in an arcuate path concave to the blank.

7. The method of producing helical surfaces on a workpiece which comprises engaging arotary tool, that has working portions disposed in a surface of revolution extending about the tool axis, with the workpiece, so that a plane, which is perpendicular to the tool axis, is inclined to the axis of the workpiece,-'and rotating the tool in engagement with said workpiece while effecting a relative helical motion between the tool and workpiece about and in the direction of the axis of the workpiece, and while simultaneously effecting a further relative motion between the tool and workpiece about an axis parallel to the tool axis and offset therefrom in a direction approximately radial of the workpiece, in time with and substantially in direct proportion to, said helical motion L 8; The method of producing helical side tooth surfaces on a gear which comprises engaging a disc type rotary tool, which has opposite side working surfaces of curved axial profile symmetrical with reference to a mean plane perpendicular to the tool axis, with a gear blank with the tool inclined to'the blank axis at an angle larger than the helix angle at the pitch radius of the blank, and rotating the tool in engagement with the blank, while simultaneously effecting a relative helical motion between the tool and blank about and in the direction of the blank axis.

9. The method of producing helical side tooth surfaces on a gear which comprises engaging a disc type rotary tool, which has opposite side working surfaces of curved axial profile symmetrical with reference to a mean plane perpendicular to the tool axis, with a gear blank with the tool inclined to the blankaxis at an angle larger than the helix angle at the pitch radius of the blank, and rotating the tool in engagement with the blank, while simultaneously effecting a relative helical motion between the tool and blank about and in the direction of the blank axis, and while simultaneously effecting a further relative motion between the tool and blank about an axis which is perpendicular to the general direction of the engaged tooth surfaces in time with said helical motion and which is offset from the tool axis in a direction approximately radial of the blank.

10. The method of producing helical side tooth sur faces of convex profile shape on a gear which comprises engaging a disc type rotary tool, which has opposite side working surfaces that are of concave curved axial pro file but less curved than the profiles of the tooth surfaces which are to be produced, with a gear blank with the tool inclined to the blank axis at an angle large than the helix angle at the pitch radius of the blank, and rotating the tool in engagement with the blank, while simultaneously efiecting a relative helical motion between the tool and blank about and in the direction of the blank axis, and while simultaneously effecting a further relative motion between the tool and blank about an axis parallel to but offset from the tool axis and in time with said helical motion.

11. In a machine for grinding helical gear teeth, a rotatable tool support, a rotary disc-shaped grinding wheel having a curved axial profile secured to said tool support to rotate coaxially'therewith, a rotary work support, a pivoted carrier on which said'tool support is mounted, said carrier being oscillatable about an axis parallel to the axis of said tool support and displaced from the axis of said tool support in a direction approximately radial of the axis of said work support, means for adjusting said tool support on said carrier to offset the axis of said grinding wheel from the axis of said carrier in said direction, means for turning said carrier on its axis in time with rotation of said work support, and means for effecting a further relative motion between the tool support and work support in the direction of the axis of the work support and in time with the rotation of the work support.

12. In a machine for grinding helical gear teeth, a rotatable tool support, a rotary disc-shaped grinding wheel, having a curved axial profile, secured to said tool support coaxially thereof to rotate therewith, a rotary work support, means for effecting a,relative helical motion between the tool and work support, about and in the direction of the axis of the work support in repetitive strokes, a pivoted carrier on which said tool support is mounted, said carrier being oscillatable about an axis parallel to the axisof said tool support, means for ad-' justin'g said tool support in said carrier to offset the axis of the grinding wheel mm the axis of said carrier in adirection approximately radial of said work support, means for rotating said tool support, and means for oscillating said carrier on its axis in time with said strokes so that one complete oscillation corresponds to one complete stroke and thecnds of said oscillation oc- 21 our at about equal distances from the middle of said stroke.

13. In a machine for grinding helical gear teeth, a rotatable tool support, a rotary disc-shaped grinding wheel, having a curved axial profile, secured to said tool support coaxially thereof to rotate therewith, a rotary work support, means for effecting a relative helical mo!- tion between the tool and work supports about and in the direction of the axis of the work support in repetitive strokes, a pivoted carrier on which said tool support is mounted, said carrier being oscillatable about an axis parallel to the axis of said tool support, means for adjusting said tool support in said carrier to offset the axis of said grinding wheel from the axis of said carrier, means for rotating said tool support, means for oscillating said carrier in time with said strokes so that a complete oscillation of said carrier occurs for each said stroke and the ends of said oscillation occur at about equal distances from the middle of said stroke, and means for withdrawing said grinding wheel from working position at the end of each said stroke and for advancing the grinding wheel into working position again prior to each working stroke.

14. In a machine for grinding helical teeth, a rotatable tool support, a rotary disc-shaped grinding wheel, having a curved axial profile, secured to said tool support coaxially thereof to rotate therewith, a rotary work support, means for eflecting a relative helical motion between the tool and work supports about and in the direction of the axis of the work support in repetitive strokes, a pivoted carrier on which said tool support is mounted, said carrier being oscillatable about an axis parallel to the axis of said tool support, means for adjusting said tool support in said carrier to offset the axis of said grinding wheel from the axis of said carrier, a head in which said carrier is mounted, means for rotating said tool support, a shaft journaled in said head, means for rotating said shaft once for each stroke cycle, and means actuated by said shaft for moving said tool support in opposite directions at opposite ends, respectively, of said strokes to move the grinding wheel, respectively, into and out of operative position, and means actuated by said shaft for oscillating said carrier in time and approximately in proportion with said strokes so that a complete oscillation of said carrier occurs for each stroke.

15. In a machine for grinding helical teeth, a rotatable tool support, a rotary disc-shaped grinding wheel secured to said tool support coaxially thereof to rotate therewith, a rotary work support, means for effecting a relative helical motion between the tool and work supports about and in the direction of the axis of the work support in repetitive strokes, a head adjustable about an axis perpendicular to the axis of the tool support, a carrier mounted in said head for oscillation about an axis parallel to the axis of said tool support, means for adjustably supporting said tool support on said carrier for adjustment thereon to offset the axis of the tool support from the axis of said carrier, means for rotating said tool support, a shaft journaled in said head, means for driving said shaft at the rate of one full turn for each stroke cycle, a cam secured to said shaft and operatively connected to said carrier to oscillate said carrier, and a second cam secured to said shaft and operatively connected to said carrier to move said grinding wheel into and out of grinding position in time with said strokes.

16. A machine for producing helica'l side tooth surfaces on a workpiece, comprisinga rotary tool support, a rotary disc-shaped tool secured to said tool support coaxially thereof to rotate therewith, a rotary work support, means for adjusting the tool support angularly to incline a mean plane perpendicular to the axis of the tool to the axis of the work support, means for rotating the tool support, means for rotating the work support, means for effecting a relative feed movement between the tool support and the work support in the direction 22 of the axis of the work support and in time with the ro-" tation, of the work support, and means for effecting a continuous relative movement without reversal between the tool and work supports, in said mean plane in time with said feed movement.

17. A machine for producing helical side. tooth sur= faces on a workpiece, comprising a rotary tool support, a rotary disc-shaped tool secured to said tool support coaxially thereof to rotate therewith, a rotary work sup port, means for adjusting the tool support angularly to incline a mean plane perpendicular to the axis of the tool to the axis of the work support, means for rotating the tool support, means for rotating the work support, means for effecting a relative feed movement between the tool support and the work support in the direction of the axis of the work support and in time with the rotation of the work support, and means for effecting relative movement between the tool and work supports in said mean plane in time with said feed movement and approximately longitudinally of the engaged tooth sides, and in which the center of the tool travels in a path concave toward the work.

18. A machine for producing helical side tooth surfaces on a workpiece, comprising a rotary tool support, a rotary disc-shaped tool secured to said support coaxially thereof to rotate therewith, a rotary work support, means for adjusting the tool support angularly relative to the work support to incline a plane perpendicular to the tool axis to the axis of the work support, means for rotating the tool support, means for rotating the work support, means for effecting a relative. feed movement between the tool support and the work support in the direction of the axis 'of the work support and in time with the rotation of the work support, and means for effecting relative movement between the tool and work supports in time with said feed movement and approximately in proportion to said feed movement and about an axis parallelto but offset from the axis of said tool support in a direction approximately radial of the axis of the work support. I I

19. A machine for producing helical side tooth surfaces on a workpiece, comprising a rotary tool support, a rotary disc-shaped tool secured to said support coaxially thereof to rotate therewith, a rotary work support, means for adjusting the tool support angularly relative to the work support to incline a plane perpendicular to the tool axis to the axis of the work support, means for rotating the tool support, means for rotating the work support, means for effecting a relative feed movement between the tool support and the work support in the direction of the axis of the work support and in time with the rotation of the work support, means for effecting relative movement longitudinally of the helical side tooth surfaces between the tool and work supports in time with said feed movement and about an axis parallel to but offset from the axis of said tool support, and means for effecting further relative movement between the tool and work supports in a direction perpendicular to said parallel, offset axis at opposite ends of said feed movement to move the tool in and out of engagement with the work, respectively.

20. In a machine for producing tooth surfaces on a cylindrcal workpiece, a rotatable tool support, a rotary disc-shaped tool secured to said tool support to rotate coaxially therewith, a rotatable work support, a pivoted carrier on which said tool support is mounted, said carrier being oscillatable about an axis parallel to the axis of said tool support, means for effecting a relative feed motion between said carrier and said work support in the direction of the axis of the work support, and means for turning said carrier on its axis in time with said feed motion and approximately in proportion thereto.

21. The method of producing essentially helical tooth surfaces on a rotatable cylindrical work piece which comprises engaging a disc-type rotary tool with a work lation whose mean direction is inclined to the axis of the work piece, while the tool axis is 'maintained at a constant angle to the axis of the workpiece.

22. The method of producing essentially helical tooth surfaces on a rotatable cylindrical work piece, which comprises engaging a disc-type rotary tool with a work piece so that the axis of said tool is angularly disposed to the axis of the work piece, rotating said tool in engagement with the work piece while turning the work piece on its axis and while effecting a relative feed motion between the tool and the work piece across the face of the work piece, said feed motion being a translation in a plane inclined to the axis of the workpiece, while the tool axis is maintained in a constant angular position, the relative path described in said plane being curved to produce a different tooth thickness at the ends than at the middle of the teeth; a

23. In a machine for producing tooth surfaces on a cylindrical workpiece, a rotatable tool support, a rotary disk-shaped toolsecured to said tool support to rotate coaxially therewith, a rotatable work support, a pivoted carrier on which said tool support is mounted, said carrier being oscillatable about an axis parallel to the axis of said tool support, means for effecting relative feed motion between said carrier and said work support in the direction of the axis of the work support, and means for turning said carrier on its axis in time'with said feed motion to move said tool in an are extending approximately in the longitudinal direction of the tooth surfaces engaged by said tool. 7 V

24. In a machine for producing tooth surfaces on a cylindrical workpiece, a rotatable tool support, a rotary disc-shaped tool secured to said tool support to rotate coaxially therewith, a rotatable work support, afpivoted carrier on which said tool supportis mounted, the pivot axis of said carrier and the axis of said tool support being arranged in parallelism, adjustment means for changing' the distance betweensaid two axes, means for effecting a relative feed motion between'said carrier and said work support in the direction of the axis of the work support, means for turning said carrier on its pivot axis in time with 'said feed motion in one direction only during the operative feed motion in one direction, and means for changing the ratio of said turning motion to said feed motion.

25. The method of producing tooth surfaces on a cylindrical workpiece, which comprises providing a disktype rotary tool having working portions disposed in a surface of revolution of concave'axial profile and of convex profile in peripheral direction, rotating said tool on its axis in engagement with a cylindrical workpiece, efiecting a relative feed motion between said tool and work piece in the direction or the axis of said Work piece, elfecting a distinct additional motion between said tool and workpiece by which the tool axis is moved relative to the workpiece in an arc in an' average direction lengthwise of the tooth sides engaged by said tool while maintaining the tool axis and the axis of the workpiece each in a fixed direction, said additional motion being in one direction only during the operative part of the feed motion in one direction, and repeating said motions on other teeth of said workpiece. 1

References Cited in the file of this patent UNITED STATES PATENTS Griflin Oct. 21, 1 952