US2026215A - Globoidal hob - Google Patents

Description

S. I. CONE GLOBOIDAL HOB Original Filed May 2, 1927 6 Sheets-Sheet 1- WWW. l 6

Dec. 31 1935.

Dec. 31, 1935. CONE GLOBOIDAL nos Original Fiied May 2, 1927 G'ShGtS-SIIBGT. 2

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Dec.3l l935. I s. L coNE 2,026,215

'GLOBOIDAL HOB Original Filed May 2, 1927 6 Sheets-Sheet 3 Jwoem #01.

Dec. 31, 1935.

S. I. CONE 1 GLOBOIDAL HOB Original Fil'e'd May 2, 1927 6 She ets-She'et 4 7 S. l. CONE GLOBOIDAL HOB Dec. 31, 1935.

Original Filed May 2, 1927 s Shets-Sheet 5 S. I. Cams gm S. ONE

GLOBIOIDAL B Original Fil ed May 2, 1927 6 Sheets-Sheet 6 r 4 r I 5- Cami UNITED STATES PATENT OFFICE Samuel I. Cone, Portsmouth, Va.

Original application May 2, 1927, Serial No. 188,214. Divided and this application July 9,

This is a divis 1930, Serial No. 466,798

9 Claims. (oi. 29-103) ion of Patent No. 1,885,686, issued November 1, 1932 and relates to cutting tools, and

particularly to a hob for cutting teeth in worm wheels and more particularly in worm wheels of the globoidal type.

Theoretically and practically the globoid gear is the most eflicient type of worm gear but it has not been extensively used'because of the lack of a rational method of generation. The methods of production heretofore in vogue not only were costly but resulted in gear elements of poor mating capacity because the underlying principles were not sound.

The general practice, heretofore, in making the worm wheel has been to use a hob of the form of the globoidal worm, or to use fly-cutters. In the case of the hob the feed is perpendicular to the axes of rotation by advancement either of the hob or of the work piece. Hence, an out-of-time relationship ensues which, obviously, results in the removal of material which should be retained in order to insure proper mating with the complemental worm. The fly-cutter method suffers the disadvantage that it results not only in the removal of material, the presence of which is necessary for true mating capacity, but in that likewise it fails to remove certain material which not only is calculated to but actually results in interference when the wheel and worm are assembled. It is manifest that the profile of the wheel, but this simply has resulted in the deformation of both Evidently, in order to produce 'a globoidal worm wheel possessed of the maximum contact obtainable, it is necessary to employ an infinite number of cutters. That manifestly is impossible. 0n the other hand, it is possible and practicable to produce a wheel form having such close approximation to the true theoretical design that the globoidal worm, when later co-operating with the wheel, will produce the theoretically correct form without any perceptible increase in the backlash of the mating members. And the objects of my invention are centered on the attainment of this and, more particularly, in a method of hobbing for generating wheel tooth flanks accordin g to my newly discovered principles, whereby there is avoided the disadvantages common to the old established methods.

The nature of the invention consists in producing globoidal worm wheels in such manner that during the entire finishing operation, the I predetermined timed relationship is maintained and the active cutting edges of the hob and the wheel blank occupy the same relative positions that the worm and worm wheel eventually will have in service.

The invention further consists in a method of and means for producing precision worm wheels with a hob, whereof the length is such that none of its active cutting edges lie outside the parallel tangents of a certain base circle which may be ll defined as that produced by extending the flanks of the worm thread inwardly of the wheel when taken in the axis of theworm. In short the cutting edges of the hob lie and operate within surfaces common in form to those of the thread 2. flanks of the worm with which the wheel is to mate, and under operating conditions the opposed flanks of the hob are, in eilect, shifted about its core in such manner as to represent threads thinner than those of the corresponding worm and having a smaller pressure angle but having the property in common with the worm that when its flanks, taken in the axis of the worm, are extended, they become tangent to a common base circle hereinafter more particularly described. The invention further consists in means for effecting a change in the relative angular positions of the hob and blank during the flank finishing operation in such way as to maintain a flxed relationship between the axes of rotation, 3' thereby maintaining,- during the entire flank flnishing operation, the same relative positions as regards mating capacity as will later obtain in the finished gear set.

The invention further consists in the method 4. of and means for insuring the production of worm wheels of increased durability and maximum efllciency and whereof the wearing surfaces of the tooth flanks are initially. formed by agencies having shaping qualities in consonance with the I normal wearing proclivities oi the mating worm threads upon said flanks, and whereof the engaging or wearing surfaces of the teeth and threads maintain their relative forms throughout the life of the gear regardless of incidental loss of material or accumulation of backlash;

In the attainment of the objects recited and in accordance with the invention, it is essential that the tooth flanks be formed under conditions analogous to those existing in the wearing of the II worm and worm wheel when in operation. This precludes the use of a hob having a body formed identical with that of the worm, inasmuch as the variation of axial distance necessary in feeding the hob into the wheel blank results in'the cutting away of considerable material which should not be removed. Hence, one important characteristic of the invention is the forming of tooth flanks in such way as to maintain throughout this operation the same relative positions of the axes oi rotation as will later be utilized in the finished gear set. Merely by way of illustration and not was a limitation, it may be said that a simple and eiflcient way of accomplishing the objects of the invention is to perform the flank shaping operation in two steps;- namely, a roughing cut during which the hob and blank are advanced towards each other and then a flank finishing operation during which the axial distance remains fixed and a slight retarding and advancing of the respective positions oi the elements causes the hob to seat itself into the right and left flanks of the teeth but, nevertheless, under conditions which preserve the predetermined timed relationship.

The invention in its preferred embodiment is illustrated in the accompanying drawings forming a part hereoi, wherein:

Figure 1 is a plan view of worm and wheel elements having their engaging surfaces formed in accordance with the invention, with parts in section at the midplane to disclose the accurate mating.

Fig. .2- is a sectional view on line 2--2'2 of Fig. 1.

g. 8 is a view taken edgewise of the wheel, Fig. 1, and showing the'peculiar tooth characteristic resulting irom the new method.

Fig. 4 is a view similar to Fig. 1 but with a hob substituted for the worm, and showing the mated fit of the parts at the completion oi the first or axial advance step of the cutting operation, some oi the hob flutes being omitted to avoid obscurity.

Fig. 5 is a view taken edgewise oi the wheel, Fig. 4, and showing the tooth characteristic resulting from the first cutting step.

Fig. 6 is an end view oi the hob iorm, Fig. 4.

Fig. '7 is a plan view of a wheel blank and hob properly mounted for carrying out the invention, portions oi the blank and hob being broken away to disclose the mated relation.

Fig. 8 is a sectional elevational view oi the assembly, Fig. 7. I

Figs. 9 and 10 are views similar to Fig. '7, showing, respectively, the wheel mounting shifted clockwise and counter-clockwise, the parts in section being in the axial plane oi the hob and showing the resulting increase oi tooth gap and the reduction of tooth thickness as indicated by the increase oi its angle from c to o, the latter corresponding'to the angle shown in Fig. 1.

Figs. 11 and 12 are, respectively, side and end views oi the hob iorm 8.

Fig. 18 is a side view oi hob iorm 8.

Fig. 14 is a view, principally in diagram, showing in a comparative way the development of the tooth from the ilrst or axial advancing step oi the hobbing to and including the side cutting step, the completed tooth H, Fig, 8, being indicated in iull lines, and the corresponding partly finished tooth J, Fig. 5, being indicated in dashlines.

As will appear upon comparison oi Figs. 1 and 4, like conditions oi relationship obtain during the iorming operation as during the actual periormance oi the worm and its complemental worm wheel in service. In Fig. l the circle i concentric rotation as at It with the axis of the wheel is the controlling factor for all flank cutting operation of worms, hobs and wheels, its diameter being determined by the desired tooth angle when taken at the midplane and as indicated at o. It will be observed that 5 the flanks of the teeth are generated so that the line of projection of each flank in the midplane is tangent to the circle aforestated. It will be also observed that the diameter of the circle also controls the eifective length of the worm and in Fig. 4 it will be noted that the hob as to its length, follows the condition stated and that none of its active cutting edges trespass beyond opposing parallel tangents of the base circle. In short, the cutting instrumentalites of the hob are located 15 within and operate within surfaces common in form to those of the thread flanks of the worm with which the wheel is to mate and in which the opposed flanks oi the hob are in eifect shifted about its core in such manner as to represent threads thinner than those of the corresponding worm.

In the pursuance of my inventive thought and while maintaining throughout the complete cycle of forming operations perfect harmony and 00- ordination as to timed and fixed center relationship, I preferably accomplish the hobbing in two steps or stages, namely; a roughing cut during which the hob and wheel are advanced toward each other, and a second or flank finishing operation during which the axial distance remains fixed, a slight retarding and advancing of the respective positions of the elements causing the hob to seat itself into the right and leftfianks of the teeth and thus maintaining throughout this operation the predetermined time and position relationship. The thread forms of the hob are thinner than those of the worm and this may be accomplished by reducing the angular distance between the opposed flanks of the threads about the hob axis. While the preferential practice is as indicated a two stage hobbing' method, the invention is not so limited and the description is simply for illustrative purposes. It will also be but a continuation of my inventive thought to operate on a wheel blank cast with teeth and finished according to my practice.

Referring to Fig. 7, the hob l is mounted for and I9, and the wheel blank 8 is mounted on a rotatable table II, it being 5 understood that the table and hob spindle are arranged to be driven in proper timed relationship by gearing (not shown) and that means also is provided for advancing the hob spindle with relation to the axis of the table during the first cutting stage. For convenience of illustration one portion of the shaded section shows the hob and wheel blank at the beginning of the first cutting operation and the other portion shows said elements at the close of said operation, the hob spindle having in the meantime advanced through the feed distance 1:. The blank 8 is mounted on the collar I which fits a boss 8 of the table H and the counterbore S of the blank 8. The blank and collar are secured to the table by means of bolt i0, nut ii, washer l2 and ring clamp is, the latter fitting counterbore 9' of the wheel blank. The collar 1 is provided with an arm it which extends between two studs i8 fixed to the table H. The studs i8 are tapped to accommodate adjusting screws it which lie in a common axis, their points facing each other and engaging opposite sides of the collar arm M. By releasing the clamping pressure 0! the nut ii a slight radial shifting may rection by means of the adjusting screws IS. The second step of tooth flank correcting or finishing operation involves continuing the run-- ning of'the hob and wheelas'during the first step and at intervals shifting the wheel angularly by means of the adjusting screws I. It is as regards the details of to be understood that the shifting shown is for the purpose of illustration only and that means other than the parts indicated may be employed for accomplishing the angular shifting of the blank. The slight shifting of the wheel must, of course, be in both right and left directions in turn in order that both sides of opposed tooth flanks may be uniformly finished. Figs. 9 and 10 show the wheel mounting shifted clockwise and counter-clockwise respectively, the shaded portions being taken through the axial plane of the hob and showing the resulting increase of tooth gap and the consequent reduction of tooth thickness as indicated by the increase of its angle from c to o.

The hob forms 4, 5 and 6 are identical except merits of cutting edges, the purpose of which will be presently explained. The hob has a base portion the surface of which is defined by the inner surface of a torus. One or more rows of teeth are disposed on the base portion with cutting edges thereon so disposed that extensions of the cutting edges are tangent to a circle or torus which is concentrically disposed to the said torus defining the surface of the base portlon. All of the cutting edges fall within parallel tangents to the torus or circle to which the teeth of the wheel cut by the hob are tangent. A hob thus constructed will have all of its cutting edges fall-within parallel tangents to a circle which is the base circle of the teeth of the worm wheel, the circumference of which corresponds to the torus defining the face of the hob.

The shaded portion of Fig. 4 is a section taken through the midplane of the engaged hob form and wheel and when compared with the corresponding shaded portion of Fig. 1 shows the relationship of the hob thread blank form to that of the worm, the difference being indicated in Fig. 4 by the gap lines of angles c and o. The

to Fig.2 wherein the inner dash lines and double.

shading indicate the former and the full lines and single shading indicate the latter. The double shaded or inner form is a section taken on line t-t, Fig. 4, when applied to that figure. It will be observed that in Fig. 2 the thread flanks lines of the hob form difier from those of the worm only in position, the shift of each opposed flank about the axis being indicated by the angle to. The ratio of the wheel shift angle v to that of the worm or w. is therefore equal to the number of threads in the worm to the number of teeth in the wheel. From this it is apparent that the second or tooth flank finishing step might be accomplished by the-introduction of means for relatively advancing and retarding the hob spindieinsteadoftbewheelmountingasshownin fluting and arrange- .the arrows at y and z for the right and left flanks respectively, Fig. 14. If a hob having thread form and thickness equivalent to that of the worm had been first fed into the wheel blank the resulting flanks would have the form indicated by the dotted lines and the useful material between the arrows I and g would have been removed, thus initially destroying valuable bearing metal.

In making the thin thread hob form the shift value 20 Fig. 2, is dependent upon the characteristics of the given design and is determined by consideration of the material at f and g as indicated in Fig. 14 the object being to have the 25 thread form, narrowed sufliciently to admit of its entry into the proposed tooth gap without removing said material. The designed tooth gap should be also sumciently wideto admit of the necessary thinning of the hob thread without30 undulyreducing its face, a reasonable width of which is necessary for the formation of the outer cutting edges 23, Fig. 4. It is also desirable in preparing the hob form to allow a slight fullness of body in order that a root clearance may be 35 provided in the wheel for the worm. This is indicated at e in Fig. 4. The desired end clearance for the teeth of the wheel may be provided by slightly reducing its outer diameter. These clearances have been omitted in thedrawings 40 inasmuch as they do not affect the principle in any way and their presence would tend to confusion. In order to simplify the illustration, the hobs are shown only partly fluted. In Figs. 4, 6, 11, 45 12 and 13 hobs l, 5 and 6 are shown each of which has its flutes 20 formed in a different manner, the flutes of hobs l and 5 being arranged rallel to their axes while hob 6 is grooved spirally. In Figs. 6 and 12 the uncut flutes are 50 indicated by dash lines. The cutting edges are certain of the corners resulting from the intersection of the flutes with the threads and consequently all lie within the thread surfaces. The corners or edges selected are those looking in the direction in which the hob rotates in cutting as 22, 23 and 24, Fig. 4, or 25, 26, 21, Fig. 13. In order to provide the necessary relief for the cutting edges the thread surfaces in the wake of the edges are slightly sloped or backed off 60 as indicated by b in-the several views. It will be observed upon reference to Fig. 4 that the thread and flutesurfaces intersect obtusely at the edges 22 and acutely at the edges 24. This difference results unfavorably for the cutting qualities of the former edges and favorably for the latter. In the hob i, Fig. 13, a more satisfactory cutting edge formation results from having the flutes vary in their course in such way as to intersect each thread approximately at right angles to its incidental path, the edges or corners 25 and 21 thus being nearly equal or approximately square. While e latter form of hob possesses superior cutting ualities to those of u the straight fluted hob 4, its accurate production is considerably more difficult. By preference hob 4 is used only in the first or axial advance step in which less accuracy is required,

The second or finishing step may be performed by the reversing of hob 5, Figs. 11 and 12. In this procedure, and by way of illustration, the first step is performed with the aid oi. either hob 4 or 6, as shown in Fig. 7 and thereafter substituting hob in the side cutting or finishing operation, Figs. 9 and 10. It will be noted upon inspection of hob 5 that the acute or alternate edge formations only are used, as at 28, 29, the backing off in each case being towards the obtuse or rejected edges 30. Inasmuch as this hob is used for side cutting only, its face edges 3| are inactive. It further will be noted that in using this hob a reversal of direction of rotation is necessary for finishing the opposed tooth flanks. The use of hobs, types 4 and 6 is contemplated for both roughing and finishing, and of hob, type 5, for finishing only.

In forming the hob cutting edges care should be observed to have at least one cutting edge within or very near each of the opposed planes of the parallel base circle tangents 2|, as at 32, Fig. 11, and 33, Fig. 4; and it also is very im portant that no active edges be permitted to trespass beyond or outside of said planes. In completing the hob forms shown, all unnecessary material or projections, as indicated at 34, outside of saidplanes should be removed or reduced in such way as to be non-interfering.

When the word globoidal is employed in the claims, it is to be understood to refer to that type of worm gear or tool elements known in the art as enveloping, hour-glass, Hindley, or hollow. These terms distinguish the gear and tool elements from the so-called straight or cylindrical gear and tool elements. In other words,

the globoidal worm or hob follows in general the curved periphery of the worm wheel.

.When the expression materially less thickness is employed in the claims in reference to the teeth of the globoidal hob,- it is to be understood as distinguishing such reduction in teeth thickness from that minute reduction in tool dimensions which may be required for effecting clearance between male and female machine parts to permit their interfitting,v

Having described the invention, what I claim 1. A globoidal hob having arranged thereon at least one row of teeth of materially less thickness than the corresponding globoidal worm thread which mates with the worm wheel cut by said hob.

2. A globoidal hob having arranged thereon at least one row of teeth of materially less thickness than the corresponding globoidal .worm thread which mates with the worm wheel cut by said hob and having side cutting edges which are tangent to a circle to which the projection of the flanks of said worm thread in a plane through the axis of the worm is tangent. a

3. A globoidal hob having arranged thereon at least one row of teeth of materially less thickness than the corresponding globoidal worm thread 5 which mates with the worm wheel cut by said hob and having side cutting edges which are tangent to a circle to which the projection of the flanks of said worm thread in a plane through the axis of the worm is tangent, which cutting edges in 10 said plane have an included angle which is less than the included angle between the flanks of said worm thread.

4. A globoidal hob having arranged thereon at least one row of teeth provided with side cutting edges which are tangent to a circle to which the projections on the flank of said worm thread in a plane through the axis of the worm is tangent, said side cutting edges in said plane having an included angle which is less than the included angle between the fianks of said worm thread.

5. A globoidal hob having arranged thereon at least one row of teeth of materially less thickness than the corresponding globoidal worm thread which mates with the worm wheel cut by said hob, said teeth having side cutting edges which in the plane through the axis of the worm have an included angle which is less than the included angle between the flanks of said worm thread.

6. A globoidal hob having arranged thereon at least one row of teeth provided with side cutting edges which in a plane through the axis of the hob have an included angle which is less than the included angle between the flanks of the thread of the worm which mates with the worm wheel cut by the hob.

- '1. A globoidal hohhaving arranged thereon at least one row of teeth provided with side cutting edges which are tangent to a circle to which the projections on the flank of said worm thread in 40 a plane through the axis of the worm is tangent, said teeth being so constructed that the cutting edges thereof when extended fall within parallel tangents to said circle when disposed normal to the hob axis.

8. A globoidal hob having arranged thereon at least one row of teeth provided with side cutting edges which are tangent to a circle to which the projections on the flank of said'worm thread in a plane through the axis of the worm is tangent, 5 said teeth being relieved in the rear of the cutting edges in such manner that the relieved sides of the teeth when intersected by a plane through the axis of the hob produce lines which when extended are tanignt to said circle. v

9. A glo idal hob having arranged thereon at "least one row of teeth, each tooth having two faces and two sides oppcsitely disposed, diagonally disposed cutting edges formed between opposite faces and sides, the sides being relieved in opposite directions.

SAMUEL-I. CONE.

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