US1512657A - Hob - Google Patents

Description

Oct. 21 1924. 1,512, 57

E. WILDHABER HOB . Fil ed June 8, 1922 4 Sheets-Sheet 1 ATTORNEY 21, 1924. 1,512 657 Oct 5. WILDHABER HOB Filed June 8, 1922 4 Sheets-Sheet 3 mvamoR" MVld/iabz,

ATTORN EY Oct. 21. 1924. 1,512,657

E. WILDHABER HOB Filed June 8, 1922 4 Sheets-Sheet 4 INVENTOR MM/WM,-

ATTORNEY Patented Oct. 21, 1924.

UNITED STATES 1,512,657 PATENT OFFICE.

ERNEST WILDHABER, or BROOKLYN, NEW YORK, AssIeNoa'ro NiLnsBmuENr-rom) com-ANY, or NEW YORK, N. Y., A CORPORATION on NEW JERSEY.

HOB.

Application Med June 8,

To all whom it may concern.

Be it known that I, ERNEST WILDHABER, a citizen of the Republic of Switzerland, residing at Brooklyn, in the county of Kings and State of New York,.have.invented certain new and useful Improvements in Hobs, of which the following is a specification.

My invention relates to hobs and particularly to ground hobs for cutting teeth on 1) gear wheels, sprocket wheels, spline shafts and similar articles.

A One object of myinvention'is to provide a hob that shall have only a portion of a number of the teeth ground and that shall finish a piece of Work in the same manner as a hob having the side surfaces of all the teeth completely ground.

Another object of my invention is to provide a hob that shall have ground ribbons projecting from a portion of the teeth, the

ground ribbons being so spirally arranged as toetfect a finishing cut when the hob is operating on a piece of work.

A further object of my invention is to provide hob of the above indicated character that shall have ribbons of ground surfaces projecting froma number of the teeth, the ground surfaces being relieved and so arranged in the form of a spiral as to finish the work which has been roughly cut by the other portions of the hob.

At the present time, it is customary to completely grind the teeth of a hob which is to accurately form a piece of work, such for example, as a gear wheel. The sides and top of the teeth are accurately ground and relieved if a gear wheel is to be cut with precision. It is necessary to grind a hobby reason of the errors which are introduced in the form thereof during the hardening process. The grinding of a hob in such manner is somewhat expensive and takes considerable time.

In a hob constructed in accordance with my invention only a small number of the teeth are ground. Moreover, only a very narrow ribbon of ground surface is formed on any of the teeth. The finishing operation of a helicoidal hob corresponds to the meshing of a spiral pinion with a gear wheel. As is well known, such pinion and gear wheel mesh in a so-called point contact. The surfaces of the gear teeth enga e the teeth on the spiral pinion in only sing e point contacts. In a like manner each out- 1922. Serial No. 566,856.

ting side of each hob tooth comes into contact with the finished surface on a blank in a single point, or in a ,very short line. "Accordingly, there is only one point on the side of each tooth cutting edge which effects a finishing cut. The remaining portions of the cutting edge of each toothare adapted merely to rough out the work being cut. Moreover, the location of the finishing points vary or change according to the tooth being considered. I

Inasmuch as only predetermined points on a helical hob effect finishin cuts, it is unnecessary to completely grim? any of the hob teeth. Moreover, nly a very few of the hob teeth need to be ground at all. Ac-

cordingly, it is" only necessary to grind and relieve the points on thejteeth which effectthe finishing cut in order to obtain a hob adapted to finish work with precision. Thus, it is unnecessary to grind more than half the number of teeth on a hob and, moreover, the teeth, which are ground, have only a small portion of their surfaces ground and relieved.

Ingrinding a hob in accordance with the usual practice, it is necessary to grind the top surfaces and the rounded outside corners of the teeth. Such grinding of the top surfaces and the outside corners of the teeth I requires three settings of the grinding machine and takes somewhat of time. One setting of a grinding machine is required for grinding the. top edges and two settings of the machine are required for grinding the outside corners of the teeth. In forming a hob in accordance with my invention, all such operations are unnecessary.

In order to grind certain points or ribbons of the side surfaces of certain teeth on a hob, it is necessary to have such portions of the side surfaces of the teeth project beyond the remaining portions thereof. The projecting portions are ground and relieved and serv'e'to effect a finishing cut. The remaining portions of the ground teeth and the unground teeth serve to rough out, the work'preparatory to the finishing cut. v

It wouldbe a somewhat complicated o eration to relieve a hob of the above in icated type in accordance with modern ractice. However, such a hob may be relleved efiiciently and quickly by the method disclosed in my application Serial No. 566,855, filed June 8, 1922. In the process disclosed in such application, each tooth on the blank has a coordinate tooth on the master hob and the teeth on the master hob relieve the teeth on the hob blank. Each tooth of the master hob relieves only one tooth on the hob blank. Accordingly, it is only necessary to provide a master hob having corresponding teeth. No change is necessary in the relieving operation and such a hob is formed as simply and easily as an ordinary hob.

In the accompanying drawings:

Figure 1 is a diagrammatic view of a Worm member meshing with an involute gear wheel.

Fig.2 is a. bottom plan view of the worm member and gear wheel shown in Fig. 1.

Fig. 3 is an end view of the worm member shown in Fig. 1.

Fig. t is a side elevational view of a hob formed in accordance with my invention.

Fig. 5 is a sectional view of-the hob shown in Fig. 4

Fig. 6 is an end sectional view taken along the line 66 of Fig. 4.

Fig. 7 is a partial sectional view of a hob showmg the ground surfaces near the end thereof.

Fig. 8 1s a diagrammatic view illustrating the grinding of grooves in the master hob.

Figs. 9 and 10 are sectional views illustrating master hobs which are adapted to form hobs other than those adapted to cut true involute teeth.

Fig. 11 is a diagrammatic plan view of a master hob in engagement with a blank.

Fig. 12 is an end view of the hob and blank shown in Fig. 11.

Referring to Figs. 1, 2 and 3 of the drawings, a worm 1 is shown meshing with an involute. gear Wheel 2. The worm l is assumed to rotate on an axis XX and the gear wheel is assumed to rotate on an axis Y. The gear .wheel 2 is assumed to have straight involute teeth 3. The worm 1 is assumed to correctly mesh with such teeth and to be inclined with respect to the gear wheel at an angle equal to the lead angle at the pitch circle. It is customary to so position a hob with respect to a blank when cutting involute gear teeth on the blank. Although it is customary to so position a hob with respect to the blank, it is in no way essential that such relation between the hob and blank be obtained in all cases.

The lines of action between the worm and the gear wheel are indicated by the lines B0 and BO. The intersection point 0 is the contact point between the pitch circle 4 of the gear wheel and the pitch circle 5 oft-he worm. When a Worm meshes with an involute gear wheel, the line of action is a straight line and must pass through the contact point 0 as above stated.

i The side surfaces of the worm teeth intersect the lines of action, when referred to the worm or hob, in contact points which are arranged in the form of helicoidal spirals. Thus, if all the contact points where the worm engages or touches the tooth surfaces of the involute gear were marked on the sides of the worm teeth, a spiral would be drawn. Such a spiral is indicated by the line 6 iii-Fig. 3 of the drawings.

Referring to Fig. 3 of the drawings, a base cylinder 7, upon which the involute curves of the worm are based, is indicated by a dot and dash line. The line of action between an involute gear wheel and an involute worm is tangent not only to the base circle or cylinder of the gear wheel but also to the base circle or cylinder of the worm. In Fig. 3 of the drawings, the line of action ()B" is a line drawn through the point 0 tangent to the base circle 7. It is also a well known fact that the contact point travels uniformly on the line of action when involute gear wheels are in mesh. The point travels an amount equal to the so-called normal pitch for each revolution of the worm. In the case of involute gear wheels with straight teeth, the so-called normal pitch is equal to the circular pitch of the gear wheel multiplied by the cosine of the pres sure angle. Thus, in the case of a 20 pressure angle the normal pitch P is equal to the circular pitch multiplied by the cosine 520.

Referring further to Fig. 3 of the drawings, the path of the contact Joint between the worm and the gear whee travels uniformly on the line which is tangent to the base cylinder 7 and which rotates at a constant sieed on the axis X.-X. The line OB" which is tangent to the base cylinder 7 may be considered any such line. The distance moved by the contact point along the tangent line to the base cylinder per revolution of the tan ent line is in proportion to the normal pitcl i P in the pro ection shown in Fig. 3 of the drawings. The projection of OB" in such figure is in proportion to the ,actual length of the corresponding part of the line of action. Thus, it may be stated the linear distance covered per revolution is equal to the normal pitch P multiplied by the cosine of the inclination angle of the line of action when considered with respect to a plane perpendicular to the axis XX or to the plane of Fig. 3 of the drawings. In the projection shown in Fig. 3 of the drawings, the contact spiral is very close to an Archimedic spiral. As well known, the Archimedean spiral would correspond to a point moved towards the axis Y--Y instead of tangentially toward the base cylinder 7.

The contact spiral on the worm may also be determined experimentally if so desired. The surfaces of the teeth on the worm may III! be covered with a thin layer of any suitable paint or chalk and then meshed and operated with an involute gear wheel. The paint or chalk will be removed from the sides of the worm teeth at the points of engagement between the worm and 'the gear wheel. By such means a'line is obtained on the sides of the involute teeth. Such line will be in the form of a spiral, as indicated in Fig. 3 of the drawings.

The experimental determination of the.

contact spiral is applicable not only to involute gear Wheels but also to non-involute gear wheels, sprocket wheels and to spline shafts. Such determination of the worm spiral is also applicable to any position of the worm or hob with respect to the gear wheel or blank. In Fig. 1 of the drawings, the worm is shown inclined with respect to the gear wheel at an angle equal to the lead angle at the pitch circle. As heretofore set forth, the positioning of the members at such angle relative to each other is the usual practice but it is not a necessity. The inclination of the worm or the hob may be chosen at will within certain practical limits. It is possible, if so desired, to set the hobor worm with respect to the blank or gear wheel so that the axes of the two members are perpendicularly disposed. The experimental determination of the spiral line of contact on the worm may be used in any of the above cases.

Referring t o Fig s. 4, 5 and 6 of the drawings, a hob 10 is shown constructed in ac cordance with my invention. Teeth 11 are formed on the hob by means of axial flutes. Although axial flutes areshown in the drawings, it is to be understoodthat inclined or spiral flutes may be utilized if so desired. The hob is assumed to cut involute gear teeth and is provided with ground ribbons of relieved projecting surfaces for effecting a finishing cut on the gear blank. In Fig. 5 of the drawings, the lines of action have been indicated by reference characters B0" and B() as in Fig. 1 of the drawings. Contact points of ribbons 13, 14 and 15 are shown on one side of the hob teeth and on the line of action B O. Similarly, contact points 16, 17 and 18 on the other side of the hob teeth are located;' on the line of action B0. The contact spots or ribbon project slightly from the side surface of the teeth in order that such spots may be conveniently ground without grinding the complete side surfaces of the teeth.

Referring to Fig. 6 of the drawings, the spiral arrangement of such spots or. ribbons of ground relieved surfaces is illustrated. Preferably such ground surfaces aswell as the remaining portions of the teeth are radially relieved but if sodesired, axial relief or a combination of axial and radial relief may be provided.

drawings. However, it should be noted the.

round relieved ribbons on the hob shown in ig. 7 are located near one end thereof whereas in the hob shown in Figs. 4, 5 and 6, the ground relieved ribbons are located near the center of the hob.

The hob may be placed symmetrically with respect to the blank being operated on or may be moved longitudinally in either direction so as to have an unsymmetrical position with respect to the blank being operated on. The ribbons of ground surfaces on the-hob, which effect the finishing cut, should be centrally placed with respect to the work being operated on. Thus, in hobs shown in Figs. 4:, -5 and 6 the teeth on one side of the ground ribbons will rough out the hob teeth whereas the teeth on the other side of the ground ribbons will perform no function on the blank. In order to utilize the complete hob, the ribbons of ground surfaces should be located near one end thereof so-that the roughing out of the gear teeth may be effected by all of the teeth having no ground surfaces thereon. In a h'ob constructed in accordance with my invention, it is desirable to accurately set the hob with respect to the blank in order that the ribbons'of ground surfaces may be-so positioned as to effect the finishing cut. Re-

ferring to Fig. ('3 of the drawings, it will be noted the ground ribbons do not extend to the back of the hob teeth. The hob ribbons are so limited in order to obtain a clean end for each ribbon.

Referring to Fig. 8 of the drawings, a

master 1101) 25 is shown which is adapted to form hobs in accordance with my invention when operated by the methods disclosed in my copending application, Serial No. 566,855, above referred to. When operating a master hob in accordance with the methods disclosed in my companion application, it is necessary to form grooves on the master -hob which will form raised or projecting ribbons on the hob blanks; The master hob 25 is shown provided with teeth 26 and on certain of the teeth are formed grooves 27 by means of the grinding wheel 28. The grooves 27 are formed along the lines of action B0 and B'() as in the hobs heretofore considered.

A master hob of the above indicated type may be very simply formed ifan unrelieved hob is used in accordance with the method disclosed in my companion application, So-

rial No. 566,855. If a relieved master hub is provided, arelieving motion must be added to the motions of the grinding wheel and the position of the relief for each tooth must be determined and set separately. Such setting is necessary not only for involute hobs but also for non-involute hobs. How ever, when it is considered the number of hob blanks which may be cut by the master hob, such setting is not considered to' effect the efliciency of the relieving of hob blanks in accordance. with my methods.

In Fig. 9 of the drawings, a hob 30, which is constructed in accordance with my invention, is adapted to cut or shape spline shafts. It will be noted the lines of action B() and B0 are materially different on such a hob from the lines of action shown in Fig. 5 of the drawings. In Fig. 10 of the drawings, a hob 31 is indicated for cutting modified involute gear teeth. In such hob, it should also be noted that the lines of action B0 and BO- are materially changed. The change in the lines of action, of course, changes the positions of the ribbons or spots of ground surfaces.

Referring to Figs. 11 and 12 of the drawings, a master hob 35 is shown operating in enga ement with a blank 36. The master hob 1s provided with teeth 37 which are formed by. axial flutes 38. The blank is provided with teeth 39 and with axial flutes 40 similar to the axial flutes 38 on the inaster hob. A certain number of the teeth on the master hob are provided with ground rooves 41 which are adapted to form proecting surfaces 42 on certain of the teeth 39 on the blank. The blank 36 is assumed to rotate in a counter-clockwise direction as indicated by the arrow a and the master hob 35 is assumed to rotate in a clockwise direction as indicated by the arrow a. The teeth on the hob and the teeth on the blank are shown facing in opposite directions and accordingly, it is necessary to feed the hob and blank towards each other for forming relief on the blank teeth, as set forth in my companion application, Serial No. 566,- 855. Sometimes, however, in forming hobs having ribbons of ground relieved surface on a portion only of the teeth, it is desirable to have the faces of the blank teeth and the faces of the hob teeth face in the same direction in order to obviate the necessity of having the master hob accurately relieved. The arrow E in Fig. 12 indicates the line of action of the cutting point on the master hob. Although the teeth on the master hob and the teeth being formed on the blank mesh somewhat in the manner of gear wheels, it will be noted the master hob is made somewhat larger than the blank. Moreover, although the hob and blank are rotated at the same angular speed, a cutting action is effected by the master hob by reason of the greater peripheral speed of the h'ob teethas compared with the blank teeth. In order to effect a cut across the teeth, suitable means must be provided for angularly advancing the hob with respect tothe blank. For a more complete description of the method of forming a hob in accordance with my invention, reference may be had to my companion application, Serial No. 566,855.

It will be understood that such changes and modifications may be made in my invention as fall within the limits of the appended claims.

What I claim is:

1. A hob, comprising a thread having any predetermined lead, teeth formed in the thread by flutes, and projecting ground ribbons on the sides of a portion of the teeth, said ribbons being so spirally arranged on the sides of the teeth as to effect the finishing cut.

52. A hob, comprising a thread having any predetermined lead, teeth formed in the thread-by fiutes,the surface back of a portion of the cutting edge of a number of the teeth being ground, said ground surfaces on the various teeth being arranged in the form of a spiral and so disposed as to make the finishing cut by the hob.

3. A hob, comprising a thread having teeth formed therein by axial flutes, a portion of the side surfaces of a number of the teeth projecting to form raised-cutting surfaces, the raised portions of the teeth being ground, and serving to effect the finishing cut and the other portion of the cutting edge of the teeth serving to effect the roughing cut.

4. A hob. comprising a thread having teeth formed therein by flutes, and ribbons of ground surface formed on the sides of a number of the teeth, said ribbons being so related as to effect the finishing cut by the 5. A hob, comprising a thread having teeth formed therein, and projecting ribbons of relieved ground surface formed on the sides of a number of the teeth. said ribbons of ground surface being so located as to effect the finishing cut.

6. A hob, comprising a thread having any predetermined lead, tccth formed in said thread by means of axial flutes. the teeth comprising a portion of the thread having narrow ribbons projecting from the side surfaces thereof, said projecting ribbons being ground and relieved and so located as to effect the finishing cut.

7. A hob, comprising athread having any predetermined lead, undercut teeth formed in said thread by means of axial flutes, the teeth comprising a portion of the thread having narrow ribbons projecting from the side surfaces thereof, said projecting rib coids spirally arranged.

bons being ground and relieved and so located as to eflect a finishing cut.

8. A hob, comprising a thread having teeth formed therein, and having narrow ribbons of ground surface back of the cutting edges of the teeth, said ribbons of ground surfaces being in the form ofheli 9. A hob, comprising a thread having teeth formed therein, relieved ribbons projectin from the sides of the teeth, said ribbons %eing spirally arranged with respect to the hob axis and so positioned as to effect the finishin cut.

10. A ho comprising a thread having teeth formed therein, the surfaces back of a portion of the cutting edges of the teeth being ground,'said portions of the cutting edges being so located as to efiect a finishing cut in the same manner as a hob having the sides of the teeth completely ground.

11. A hob, comprising a thread having teeth formed therein, the teeth having side projecting portions, the portions of the cutting edges formed by said projecting portions serving to effect a finishing cut and the remaining portions of the cutting edges serving to eflect a roughing cut.

signature.

12. A hob, comprising a thread having teeth formed therein, said teeth havin nonradially arranged cutting faces an projecting ribbons of relieved ground surface formed on the sides of a number of the teeth, and said ribbons of ground surface being so located as to effect a finishing cut.

13. hob, comprising a thread having teeth formed therein, the cutting faces of said teeth being non-radially arranged and the surfaces of a portion of the cutting edges of the teeth being ground, said portions of the cutting surface being so located as to efi'ect a finishing cut in the same manner as a hob having the sides of the teeth completely ground.

14. A hob, comprising a thread having undercut teeth formed therein by axial flutes, a; portion of the side surfaces of a number of the teeth projecting to form raised cutting surfaces, the raised portions of the teeth being ground and serving to eflect finishing cuts and the other portion of the cutting edge of the teeth serving to effect the roughing out.

In testimony whereof, I hereto aflix my ERNEST WILDHABER.

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