Patented Jan. 3..1939 2pl42 285 UNITED STATES PATENT OFFICE 2,142,285 HOB AND METHOD OF MANUFACTURE Harry Pelphrey Detroit Mch., assignor to Mchigan Tool C;@ipany, a,, corporation of Delaware AppHeation April 2,@ 1936, SerW No. 72,239 11 Claims. (Cl. 51-278), The Present invention relates to gear cutting tools, and in Particular. Provides an improved method and means for forming and sharpening hobs of the globoidal or Hindley types. . ObJects of the present invention are to provide an improved method and means for manufacturing or re-sharpening hobs of the globoidal 6r Hindley 'type; to provide such a method and means whereby the cuttirig edges of the teeth 10 of a globoidal or Hindley hob. may be accurately cut to correct form by a single pass, or a plurality of duplicate passes, of a tool along the leading faces of the hob teeth; to provide such a methoct and means i@hereby in@- resharpening the hob, the machining or,grinding action nray be conflned to the leading face of the hob teeth no grinding of the &nks of the hob teeth beIng necessary; to provide such a method and means whereby the tool may be inoved in a con20 tinuous path nlong the flutes between adjacent hob teeth, to thereby grind the leading faces of adjacent hob teeth and dress a cxitting edge thereon. Further objects of the present invention are .25 to provide a method for fluting 'a hob to form a plurality of spaced cutting teeth thereon, and/or for re-sharpening the teeth so formed, which comprises machining or grinding the hob(flutes to thereby dress a cutting edge on the lead30 ing face of each tooth, utilizing a tool, a 6utting edge of which Is disposed as a tangent to the base circle of the hob and lies in the mid-plane thereof; to provide such a method iri which the tool Is bodily,moved relative to the hob in the 35 mid-Plane of the hob along an arcuate paththe center@of which arci-Tate path coinc-ides with the center of the base circle of the worm; to provide such a inethod izx which the arcuate bodily movement of the tool relative to the hob is accom40 parged by a rotation of the hob about the axis theieof, so that the h6b 4.tut.es are heucally dispidsed about the hob; and to provide 'such a method In which the helix of the hob fluting is so related to the heux of the hob teeth that the angle between one flank. of each tooth Eind. the leading face thereof Is equal to or less than 00 degrees. Further objects of the present Invention are to provide an improved fixture for machining and 50 grinding the leading faces of the teeth-of a.hob of the globoidal or Mndley type embodying -means to support the bob, and further embodyIng means to move a tool in the mid-plane of the hob along an arcuate path of which coincides with the center of the base circle of the hob; to provide such a flxture in which the nia6hining or grinding tool is so suppo#ed that at each point in said movement, said tool coincides with a tangent to the base circle of the hob; to provide such a fixture enibodying means to effect a rotative movement of the hob In timed relation to said tool movement; to provide such a flxture -in which the, machining or grinding tool may comprise a pencil wheel and, embodyling improved ineans to drlve the pencil wheel le in rotation during.said movement thereof. With the above and other objects in view which appear In the following description, and in the clatms appende d hereto, a preferred biit inustrative embodiment of the present invention ia 15 shown in the accompanying drawings, throughout the several views of wl,.Ich corresponding reference characters are used to designate corresponding parts and In whi@h: Flg. 1 is a view of a hob constructed in accord- ze ance with the present invention; Fig. 2 is a view In end elevation taken along the line 2-2 of Fig. 1; Flg. 3 Is a view in vertical, section, taken along the line 3--4 of Fig. i; 25 Flg: 4 is a view in elevation of a preferred constkucti on of the flxture of the present Invention; Fig. 5 is a view in top plan of the machine In Fig. 4; pig. 6 is,a fragmentary view of a fixtiire for 30 dressi ng ihe grinding tool which nisy be used with the machine of Flgs. 4 and 5; and Plg. 7 is a rletafled view taken aIGng the line 7-7 @ o! Pig. - 6. in its broader aspects, the present invention relate s generally to the manufacture as weR as to the resharpening of hobs of the globoidal or Mndle y types; that is, hobs designed for use In the cutting of the worm wheels or worm gears of gear sets embodying the Mndley or globoidal 40 princi ple. In a narrower sense, the present inventio n is directed prInciPally to the provision of an im r6ved method and flxture for re-grindp ing or sharpening the cutting edges of the teeth of hobs designed to cut worm wheels' for such 45 gear sets. United State@., Paterit No. 2,026,215 grante d Dec6mber 31, 1935, to Samuel I. Cone descri bes and claims a globoidal hob to which the improvements of the present Invention are partic ularly appli6able. be As described in detail In the Cone patent, globoidal hobs for forming globoidal worm wheeis are characterized in that in the mid-plane of the hob each tooth face Is redtuinear, and that lines &awn in the mid-plane as extensions of the tooth

2 .2,142,285 faces of the helical thread of the hob all lie tangent to a common circle, which circle may be, called the base circle of the hob and the axis of Q@hich circle coincides with the axis of a worm .5 wheel of mating capacity with and positioned at c6rrect center distance from the hob. In accor&nce with usual practice,..the hob thread Is fluted at i plurality of points around the circumference to the hob, to thereby form a plurality 10 Of spaced cutting teeth, a leading edge of each of which is dressed to provide a cutting edge. Preferably also as disclosed In the Cone patent, the flanks of the hob teeth are, relieved rearwardly from the leading face there6f, the relieved 15 surface being a hehx of lesser pitch than the helix of the thread, but preserving the above stated rectilinear and tangential relation to the base circle. An Improved machine for providing the helical relief to the hob teeth Is described 20 and claimed in Patent No. 1,980,444 granted November 13, 1934., to George R. Scotlt. In further accordance with the disclosure of the above Cone patent, the hobbing Is preferab]Y gccomplished in two steps, Including a roughing 25 step and a finishing step. The I.enti.re flwshing step Is effected while the hob and worm wheel are on c6rrect center distances, and any feeding between the hob and the worm wheel during the finishing Is accomplished by rotatively advancing, 30 the hob relative to the worm wheel. To accommodate the Initial movement of the finismng hob to correct center distance from the worm wheel, the teeth of the finishing hob are thinner than required for full mating capacity with the worm 35 wheel., One leading edge of each hob tooth thus remains Inactive. The two hobbink steps are Preferably also employed in the practice of the present invention, the present' hob being particularly designed to 40 effect the flnishing st6p, although, as will appear from a complete understanding thereof, it may, elso be used for the roughing step. Thus, the hob teeth are thinner than required for fuH mating contact with tiie wheel. 45 In the preferred practice of the present Invention one edge only of each hob tooth is dressed to a cutting edge, the other edge, being inactive, not being required to be so dressed. A complete fiWsMng operation is thus conducted in two steps, 60 the llrst step serving to flnish one flank of each wheel tooth and,the tubsequent step, effected by Inverting the hob, serving to finish the remaining flank of each wheel tooth. FAther edge may be selected as the cutting edge, and the Improved fixture hereinafter.described Is selectively adjustable to correspond to the cutting edge sel.ected. R,eferring In detail to Mgs. 1 to 3, the hob 10 may be' supported upon an arbor 12 in the =way, is provided with a plurality of dutting 60 teeth 14, which are helically disposed abou . t the hob body and which are separated by h@elically extending flutes I S. The lefthand flank a of each tooth 14 Is generated In, helically relieved relation to the main thread helix, in accordance with the teachings of the above Identified. Cone patent, that is, -so thait extensions thereof lying in the mid-plane of the hob &R fall tangent to the base circ.le of the hob. Such tangents are indicated In dotted Unes.in lMg. I and designated b. The OXbthand.tooth faces.c are preferably similarly generated although this relation Is not essential since,,as dewri@ea above hob 11-is speci:dcally de-:aig@ned for the flnislhing step, and, as clearly ap-pem In the sectionally illustrated ndd-plane on of Fig. 1, the hob teeth 14 are each someporu what thinner than the spacing between the teeth IO of the worm wheel. Being inactive, the form of the righthand faces c Is not important, it being only necessary to provide sufficient clearance between them and 6 the adjacent faces of the worm wheel teeth. -Th@ cutting edges df the hob teeth 14 are designated d, and are formed by the junction between the leading faces e thereof anti the lefthand flanks a thereof. 10 In accordance with the present invention all cutting operations are effected entirely by machining or grinding away the leading tooth faces e, no cutting being re4Wred on the flanks a. For this reason the cutting edges d after eilch sharp- 15 ening operation ar@- progressively moved rearwardly of the associated tooth as indicated by the dotted lines d, d", etc. In thus r@tiring the cutting edge d, however, it is necessary that each new cutting edge d',,d", etc. conform in config- 20 uration to a corresponding part of the main helilx of the hob thread. Sinc6 the working flanks a are relieved along a helix of lesser pitch than such main helix, this conformation occurs only if the cutting edges d, d' and cl" are radially dis- 25 posed, it being characteristic, as previously noted, that the main and re)Jeved helices are radiahy rectilinear. Each hob tooth 14 is thus characterized ag hav'mg a rearwardly helically relieved flank a and a linear radially disposed cutting, 30 edge d. As further disclosed In the above identified Cone patent, It is desirable that the flutes 16 which space the respective teeth 14, be helically disposed about the hob in order to avoid the for- 35 mation of interior angles at the cutting edges d which exceed 90 degrees. Preferably the helix angle of flute 16 is such that the angle included within each tooth between the forward face e thereof and the main thread helix of the hob is substbtltially 90 degrees. The relief angle is preferably of the order of 10 degrees, so that the resultant angle Included within each tooth between the relieved flank a thereof and the leading face e thereof is of the order of 80 degrees. 45 In.accordance with the present invention, the initial cutting of the flutes I 6, as well as the cutting away of the leading faces e to effect a re-sharpening of the cutting edges d of each row of teeth may be. and -preferably is effected in a 50 single continuous pass, or a plurauty of duplicate Passes, across the leading faces e from one end of the hob to the other of a tool having a reetiliriear cutting @ surface. The, 6utting: surface pf the tool Is preferably co-extensive in length with 55 each cutting edge, and the tool is so disposed that the cutting edge is radial to the hob. To pre.! serve the radial relation of the tool cutting edge to the hob, the movement of the tool axially of the h6b Is accompanied by timed relative rots- 60 tion between the hob and the tool. To preserve the rectilinear form of each cutting edge, the tool Is so disposed relative to the hob that at each point in its movement aidaly of the bob, It coincides with a tangent to the base circle of'the e5 hob. Thus, In moving along each flute 16, the Mear cutting edge of the tool, cuts a Unear cutting edge d, d', dl', etc. on each hob tooth 14, which is linear and is tanaential to the hob base circle. TO Referring now to PIP. 4 and 5, the fixture com prises generally a base structure 21, upon which a head stock 22 and a taU stock 24 are disposed. The hob II to be sharpened is carried upon the arbor 12 between the- driving center 26 and the 7ii

dead-center 28 associated with stocks 22, and 24 respectively. The tool 30 is iiiustrited as a rotatably mounted abrasive peneff wheel; it will, however, be understood that the pe4cil wheel is illustraiive oply of -,any of a-variety of different types of tools which may be utilized to suitably form or dress the leading tooth siiifaces by.a grinding, cutting, or, other suitable action. It will further be understood that the t@6rm "tool" 10 in the present specification- and in the claiins Is used in a correspondingly generic sense. The wheel 30 is carried in a bearing member 32, which beaiing member is &djustably suported within a split bracket 34. Bracket 34 in tum is'pivotally 15 secured in adjustable relation upon a post 36, which is carried by a stide 38. Slide 38 rides lri suitable, ways formed in a second sude 40 and Is adjustable therealong by conventional lead screw mechanism 42. Slide 40 rides in ways 44 formed 20 in a rotatable table structure 46, and Is adjustabletherealong by conventional lead@ierew mechanism 48. Table 46 is provided with a downwardly extending drive spindle 49 provided with suitable bearings 50 formed in the machine 25 frame 20, and is suppoited In swtably el6vated relation to table 20 by one or more bearing washers 52 wmeh are disposed between the underside of the rotatable table 46 and an upwardly extending frame boss 54. Rotation of table 46 thus ;3( causes bodily movement of the slides 40 and 38 and consequently of the pencfl wheel 30. Spindle 49 is so located, that the center of the Just stated bodily rotation of wheel 30 coincides with the center of the base circle of the hob 10. This 35 center is designated g in Fig. 5. The radial spacing between the center g of boduy,rotation of wheel 30 and the axis of axiw. rotation thereof is accurately adjustable by suitable adjustment of the position of slide 38, and by rotation of 40 bracket 34 about post 36, to correspond exactly to the radius of the base circle of the ' hob I 0. Wheel 30, accordingly, coincides at all points in its bodily rotation to a tangent to the base circle. The active end of wheel 30 is tal*red, and to 45 render the upper tapered surface theireof radial with respedt..to hob 10 wheel 30 Is supported with@the tapered ed-ge s;icientiy below the aids of hdb I 0 to compensate foj7 thie taper. The tapered portion -of pencil wheel 30 Is sufficiently 50 long that an entire leading face e of a hob tooth may be dressed thereby durlng operatidn. With this arrangement, it will be appreciated that as wheel 30 is bodily rotated by table 46 and thus travels from the one end of hob 10 to the 55 other, the active working face of wheel 30 is always disposed radially of the hob and in each bodily rotative position of wheel 30, it coincides with a tangent to the base, circle of- the hob. As the pencil wheel travels along and engages a 60 cutting edge;of a hob tooth, the cutting edge li engaged simtltaneously from end to end and the resultant new edge cut by the pencil wheL-1 is also a straight line. The axial rotation of wheel 38 is effected by 65 a motor 60, also adjustably suoported upoii the previously mentioned post 36, through a belt 62, which is trained around motor puhey 64 and a second pulley 66 secured upon the outer,end of the shaft of wheel 30. 70 In order to effect the bodily rotation of wheel 38, the lower end of spindle 49 is provided with a worm wheel 70, which meshes with and Is driven by a worm 72, the shaft 74 of which is suitably supported In the machine frame. At its' 75 outl-r end sbat '74 carries a pinion 76, which meshes with and Is driven by an idler gear IL Idler gear 78 in turn meshes with and is driven by a gear 80. Gear 80 in turn meshes, with end is driven by a pinion 82 supported in@.the machine frame upon a shaft 84, which may be driven 5 in any suitable way, a crank handle 86 being illustrated. -Gear 80 is loosely carried upon the spindle 90 associated with the driving center 26 fbr hob I$. and is provided with a hub 92 which Is selectively 10 connectible by a detent 94 carried by a hub bracket 93 to an Indexing wheel 96. Indqxing wheel @ 96 is removably secured by a nut 08 upon the outer end of the spindle 90 in driving rel&Uon thereto. Indexing wheel 96 Is provided with a plur&Hty of notches 100 on its periphery, equi-angularly spaced from each other and the number of which correspond s to the number of !lutes on the hob 10. Detent 94 is retractible against the force of 20 a biasing spring 102 associated therewith, and so may be retracted from any of the notches 100, to permit free rotation of. ixidexing wheel 96 with. respect to gear 80. With the above described driving relation, it 25 will be understood that rotation . of shaft 84 rotates hob 10 through spindle 90, Index wheel 96, detent 94 and gears 80 and 82. Such rotation effects corresponding rotation of table 46 and consequent ly causes bodily rotation of wheel 30 30 through gears 82, 78, 78 and 70. It wiU be understood that the gearing retation Is such that a rot@tion of hob 10 in a clockwise direction as viewed in Flg. 4 is accompanied by movement of the wheel 30 from the lefthand end thereof to- 35 wards the righthand end of liob II as viewed in Fig. 5. It will also be understood that the gearing relation is such that the helical path traced by wlieel30 acrdss the hob IO corresponds to the helix of the flutes. 40 Consider ing the operation of the machine as a whole, after preliniinarily L ftposing a hob I#. requiring either to be initiary dressed or to,be resharpened, between the ce'nters 26 and 28, the crank. 86 may be turned until the pencil wheel 38 '46 is slightly to the left (Flg. 5) of the position to be occupied by the lefthand tooth of a given rd* on hob I 0. Hob I 0 may then be disposed between centers 26 and 28 with the edge d of such tooth below the level of the upper surface of pencil $$. 50 a distance determined by the amount of stock which it Ls desired. to remove from the face of the tooth. Follo wing the abov6 described preliminary adjustment s, motor 60 may be started Jn any suit- 55 able way, placing wheel 30 in a3dal rotation at a relatively high rate. Crank 86 -may then be operated to cause hob 10 to rotilte,a)dally and to cause the linear grinding face@l' of wheel 31 to move bodily in an arcuate path, sweeping 60 across the successive forward filces e of the teeth 14 of hob 10, the combined rotation of hob Is and translation of wheel 30 resulting in a heRcgll movement of wheel 30 with respect to hob 10. Since each tooth 14 presents a straight line 6,5 which may be extended to form a tangent to the base circle and since the cutting surface of wheel 30 Is radi;l 'Df hob 10 and tangential to the base circle, it will be appreciated that as wheel 31 advances and - engages the - ;teeth 14. an points 76 along each such straight lin-e are engaged simultaneously, and the grincling action is not affeeW--L- 7by the helical travel of wheel 39-relative to hob 10. The new cutting d, d', d", etc. thus formed Is a true stra*hV-Me. =dial of the hob and tm- IS