US2888858A - Hobbing machine - Google Patents

Description

June 2, 1959 A. D. F. MONCRIEFF HOBBING MACHINE 5 Sheets-Sheet 1 Original Filed March 28, 1951 INVENTOR; flfsrd/riarfl 2774441727 75 7 MFA/75,

A. D. F. MONCRIEFF 7 2,888,858

June 2, 1959 HOBBING MACHINE 3 Sheets-Sheet 2 Original Filed March 28, 1951 June 2, 1959 'A. D. F. MONCRIEFF 8 HOBBING MACHINE Original Filed March 28, 1951 v 3 Sheets-Sheet 3 United States Patent HOBBING MACHINE Alexander D. F. Moncriefi, Bloomfield Hills, Mich., as-

signor to Michigan Tool Company, Detroit, Mich, a corporation of Michigan Original application March 28, 1951, Serial No. 217,999, no w Patent No. 2,769,375, dated November 6, 1956. and this application June 25, 1953, Serial No.

2 Claims. (Cl. 90-4) This invention relates to new and useful improvements in gear-bobbing machines.

This is a division of my copending application Serial No. 217,999, filed March 28, 1951, now Patent No. 2,769,375.

An important object of the present invention is to provide a gear-hobbing machine wherein a gear blank is moved across and in mesh With the hob and wherein both the blank and the hob are rotatably driven in timed relation.

A further object of the invention is to provide a gearhobbing machine having novel means for adjusting the hob angularly in accordance with the helix angle of the gear being acted upon to assure proper meshed engagement of the hob with the gear blank.

Other objects and advantages of the invention will be apparent during the course of the following description.

In the drawings forming a part of this specification and wherein like numerals are employed to designate like parts throughout the same:

Fig. 1 is a front elevational view of a gear-bobbing machine embodying the invention and showing the hob carrier inclined from the vertical to position the hob for a helical gear blank;

Fig. 2 is an enlarged, fragmentary, vertical sectional view through the headstock and associated mechanism which rotatably drives and axially moves the work;

Fig. 3 is an enlarged, fragmentary, vertical sectional view taken on the line 3-3 of Fig. 2;

Fig. 4 is an exploded perspective view showing the stationary and movable guide elements which control angular or rotary displacement of the gear workpiece during reciprocation thereof in accordance with the lead of the gear teeth;

Fig. 5 is a vertical, sectional view showing a fragmentary portion of the headstock and illustrating a modified means for controlling rotary movement of the work during reciprocation thereof in accordance with the lead of the gear teeth;

Fig. 6 is a fragmentary, horizontal, sectional view taken on the line 6-6 of Fig. 5; and

Fig. 7 is a fragmentary, vertical, sectional view taken on the line 77 of Fig. 5.

Reference is first had to Fig. 1 which illustrates the general construction and operation of the machine. In the general form of the invention shown, the machine is provided with a suitable base 28 having a horizontally movable slide 22 thereon. A hob carrier 24 is mounted on the slide 22 for angular adjustment about a horizontal axis. Also mounted on the base 28 and in front of the slide 22 are headand tailstocks 26 and 28 which suitably clamp a workpiece 30 and operatively support the same for engagement with a hob 32 on the hob carrier 24.

In operation, the slide 22 is adjustable on the base 2% to move hob 32 to and from the workpiece 30. Prior to a hobbing operation the slide 22 is advanced to position the hob 32 for proper engagement with the gear blank 30. Means is provided for rotating the hob 32 and ice gear blank 30 in proper timed relation, and it is a feature of the invention that the hob carrier 24 is adjustable angularly in order to position it for proper engagement with the gear blank without disturbing the rotary drive to the hob. In this manner, the machine is readily adaptable for use either with spur gears or helical gears. In Figs. 1 and 3 I show the hob carrier 24 near one limit of its adjustment to position the hob 32 for proper engagement with a helical gear blank, whereas in Figs. 2, 4, and 5 I show the hob carrier positioned vertically and approximately midway between its adjustment limits for operation on a spur gear. In its initial position, the workpiece 30 is disposed at one side of the hob 32, and, in the operation of the machine, means associated with the headstock 26 operates to push the gear blank 30 axially and across the face of the hob 32. After the gear blank 30 disengages the hob 32, slide 22 retracts to move the hob out of the way of the workpiece and the latter is then returned to its initial position preparatory to removal from the machine.

A special feature of the invention resides in the provision of means for controlling angular or rota-tive displacement of the gear blank 30 during axial movement thereof in the hobbing operation. Of course, no rotative displacement occurs in the case of spur gears but helical gears must be rotatively displaced angularly during the hobbing operation to compensate for the lead of the gear teeth. This operation has been accomplished in a novel and efiicient manner by incorporating uniquely con structed and coactive guide elements in the headstock 26. The particular arrangement afforded by this invention permits the machine to be readily adapted for either spur gears or helical gears and for helical gears having different leads. Further, the arrangement of the guide elements is such that the rate of advance of the gear blank 30 can be changed at any place in the operation of the machine while the machine is in operation and without stopping the machine. This is highly advantageous in many instances.

With the foregoing as a general introduction to the construction and operation of the machine, attention is now directed particularly to the remaining drawings which illustrate details of construction. Reference may also be had to said co-pending application, Serial No. 217,999, now Patent No. 2,769,375, from which the subject matter of the present application has been divided out.

Attention is now directed particularly to Figs. 1-4 which show the construction and arrangement of the headstock 26. It will be observed in this connection (Fig. 1) that the operating parts of the headstock 26 are contained primarily in a housing 212 disposed on the base 29 opposite the tailstock 28.

As specifically shown in Fig. 2, the headstock 26 comprises a tubular shaft 214 which is supported for rotation in the housing 212 by front bearings 216 and rear bearings 218. Two front roller bearings 216 separated by a spacer 220 are here shown, and the bearings are held against an internal radial shoulder 222 of the housing 212 by a collar 224 which is detachably fastened to the front of the housing by an annular series of screws 226. The shaft 214 is formed with a radial flange 228 which is held against the inner bearing 216 by a nut 230 threaded on the forward end of the shaft. Also, the instant construction embodies two ball bearings 218 received within a bearing carrier 232 and held against the spacer 234 by a nut 236 threaded on the rearward end of shaft 214.

A rotatable drive is provided for shaft 214 by a worm gear 238 which surrounds and is rotatably fixed to the shaft by a key 240. Gear 238 is held against axial movement on shaft 214 by a spacer 234 and a radial shoulder 242 both on the shaft. The particular gear 238 here shown is a split gear of conventional construction having separate toothed sections 244 and 246 that are relatively displaceable circumferentially by a cam 248 to take up backlash between the worm gear and a worm 250 which meshes with and rotatably drives the worm gear. Manifestly, rotation of gear 238 rotatably drives the shaft 214 through key 240.

Within the tubular shaft 214 is a. sleeve bearing 252 which slidably supports the headstock spindle 254. A face plate 256 bolted to the collar 224 confines a slinger ring 258 to prevent loss of oil normally maintained in the housing 212 to lubricate the bearings and moving parts contained therein. The spindle 254 here shown is tubular in form, and a plug 260 is fastened in the forward end of the spindle by screws 262. The plug 260 has a tapered hole 264 which receives the correspondingly tapered shank 266 of a conventional driving dog 268. A rotary drive is established between the plug 260 and the dog 268 by inner engaging teeth 270 thereon, and the dog extends into an opening 272 in the side of the gear blank 30 to establish and maintain a rotary drive between the dog and the gear blank.

The spindle 254 has a rearward extension 274 which is detachably fastened thereto by screws 276, and a collar 278 is keyed to the rearward end of the extension and held against a radial shoulder 280 on the extension by a threaded nut 282. Spindle 254 is reciprocated back and forth in the rotary drive shaft 214 by a pair of fluid motors 284 and 286 disposed on opposite sides thereof and suitably supported by the housing 212. The two piston rods 288 and 290 of the fluid motors 284 and 286 respectively are connected to opposite ends of a cross link 292, and the latter carries a relatively short shaft 294 which is rotatably supported by bearing 296 confined by a bearing retainer 298. At the inner end of shaft 294 is a radial flange 300 which aligns with the collar 278 on the spindle extension 274 and is detachably fastened thereto by screws 302. By reason of this construction the fluid motors 284 and 286 act through the crosss link 292 and connecting parts to move the spindle 254 axially back and forth during operation of the machine so as to move the gear blank 30 across the hob 32 to the end of its forward stroke and then to retract the gear blank to its initial position after the hobbing operation has been completed. Also, it will be apparent that the spindle 254, spindle extension 274, and shaft 294 are free to rotate independently of the reciprocatory actuating mechanism.

According to the present invention rotation is transmitted from the driving shaft 214 to the spindle 254 through a novel guide mechanism which also serves to effect angular or rotative displacement of the spindle and consequently of the gear blank 30 during reciprocal travel thereof. When the workpiece 30 is a spur gear, the guide holds the spindle to a rectilinear path of travel, whereas if the workpiece is a helical gear, the guides cause the spindle 254 and workpiece to corkscrew or be angularly or rotatively displaced in accordance with the lead of the gear teeth. The guides of course are adapted for the particular gear being acted upon and it is necessary to replace the guides whenever the machine is adapted for a different type gear. It is a feature of the invention that the guides are readily accessible and easily replaceable.

More specifically, the above mechanism comprises a guide bushing 304 which fits snugly within the rearward end of shaft 214 and is detachably fastened thereto by screws 306. Within the bushing 304 is an axially fixed guide member 308 and an axially movable guide member 310. The axially fixed guide member 308 is generally tubular in form, fits snugly around the spindle extension 274, and is connected thereto by a key 312 for mutual rotation therewith. Approximately half the guide member 308 is cut away at the outer surface thereof to provide a portion 314 of reduced thickness and to define radial guide walls or cams 316 and 318 (Fig. 4). The relatively movable guide member 310 fits in the cutout portion of the companion guide member 308 and snugly between the radial guide surfaces 316 and 318. As shown in the drawings, the guide member 310 is relatively thin so as to lie flush with the outer surface of the guide 308 when the parts are assembled together. Thus, when the two guide members 308 and 310 are assembled, they, in effect, form a complete cylinder, although the guide member 310 possibly is considerably shorter than the relatively fixed guide member 308. The guide member 310 here shown is made in two parts, 310A and 310B, having diagonal mating edge surfaces 320 and 322 so that the parts can be moved axially relative to each other to adjust the width of the member so that it fits snugly in the cutout portion of guide member 308 and flatly engages both of the radial guide surfaces 316 and 318. Since the guide surfaces 316 and 318 control angular or rotative displacement of the spindle during axial movement thereof, it is desirable to eliminate any play or relatively rotational movement between the two guide elements 308 and 310. This is accomplished in a highly efiicient manner by making the guide member 310 in two parts as shown. Both parts of guide member 310 are fastened to the guide bushing 304 by screws 324 which extend inwardly from the bushing and into the guide parts. The holes in the bushing 304 which receive screws 324 are made sufficiently oversize to permit the slight relative movement that is required between the two guide parts 310A and 310B to assure a snug fit between guide surfaces 316 and 318 and for any adjustment that is required from time to time to compensate for wear taking place between the two guide members 308 and 310.

From the foregoing it will be apparent that the bushing 304 is fastened to the rotary drive shaft 214 and that the guide element 310 is fastened to the guide bushing so that all of these parts operate in unison. The guide member 310 in turn acts through radial faces 316 and 318 to rotatably drive guide member 308 and the latter acts through the key 312 to rotatably drive spindle 254. At the same time that the spindle 254 is being rotatably driven, fluid motors 284 and 286 are free to move it axial- 1y. During such movement the guide bushing 304 and guide member 310 remain axially fixed while the companion guide bushing 308 moves axially with the spindle. Since relative axial motion occurs between the guide members 308 and 310 it is apparent that radial cam faces 316 and 318 guide the spindle 254 in its axial travel. As suggested, these cam faces 316 and 318 are straight or rectilinear when the workpiece 30 is a spur gear and they extend in a helical path when the workpiece is a helical gear. The latter form of guide is shown in the drawings and perhaps is best illustrated in Fig. 4. In practice the helix angle of the guide is a function of the lead of the gear blank. It will be apparent, however, that the helix angle of the guide will not be the same as the helix angle of the gear except when both the guide and the gear are the same diameter. Actually the helix angle of the guide is greater than the helix angle of the gear whenever the gear is smaller in diameter than the guide. Conversely, the helix angle of the guide will be less than the helix angle of the gear whenever the gear is larger in diameter than the guide.

In order to facilitate removal of the guide members 308 and 310 the upper end of cross link 292 is made in the form of a hook (not shown). Thus, when nut 332 and the screws 302 are removed, the link 292, together with the stub shaft 294 carried thereby, can be swung about the piston rod 290. Nut 282 can then be removed and collar 278 pulled off of the shaft extension 274. This operation exposes the guide members 308 and 310 which usually are disassembled, together with the guide bushing 304, merely by removing screws 306. The entire guide assembly can then be pulled out of the drive shaft 214 and necessary repairs or substitutions made. Manifestly, the parts are reassembled in converse order.

The common drive which assures operation of the work 30 and hob 32 in proper timed relation is shown and described in co-pending application 217,999, now Patent No. 2,769,375.

In Figs. 5-7 I have shown an alternative mechanism for adjusting the gear blank 30 angularly or rotatively during the hobbing operation and in accordance with the lead of the gear teeth. If desired, this mechanism can be used in place of the mechanism particularly shown in Figs. 2, 3, and 4 and hereinabove described in its essential details.

In Figs. 5-7 all parts which are identical to or are equivalent in all essential details to corresponding parts, in Figs. 24 are identified by the same reference numerals. Those parts which are different and which op crate differently in the modified construction have their own identifying reference numerals.

In the modified form of the invention now being described, the spindle 590 preferably is formed in one piece. Adjacent its forward or inner end the spindle 590 is supported for rotation by a sleeve bearing 592. The outer end of the spindle 590 is supported by the roller bearings 218 as in the form of the invention first described.

Spindle driving gear 238 is mounted on the sleeve member 214 as in the form of the invention first described and the sleeve member surrounds and retains the sleeve bearing 592. In the instant construction, however, the guide bushing 304 and its adjuncts are replaced by a bifurcated retainer 594 which embraces the spindle 590 behind or rearwardly of the gear-carrysleeve 214. In the particular construction here shown, the retainer 594 has an inner hublike portion 596 that fits snugly around the spindle 590 and extends into and internally supports the sleeve 214. Screws 598 fasten the retainer 594 to the sleeve portion 214.

As perhaps best shown in Fig. 5, the bifurcations of retainer 594 are disposed on opposite sides of and spaced from the spindle 590. Since the retainer 594 is fastened to the sleeve 214 it rotates with the sleeve.

In order to transfer rotation from the retainer 594 to the spindle 590 a sine bar 600 is fastened to one bifurcation of the retainer 594 by screws 602. The sine bar 600 has a rearwardly or outwardly extending journal 604 supported for rotation in an opening 606 provided in the retainer 594. On the inner face of the sine bar 600 is a groove or way 608, and the sine bar is angularly adjustable about the axis of journal 604. Screws 602 operate in arcuate slots provided in the supporting bifurcation of retainer 594, and the screws can be tightened to hold the sine bar in a selected rotatably adjusted position. Thus, screws 602 not only hold the sine bar 600 fastened to the retainer 594 but they also hold it in a selected rotatably adjusted position. As will be hereinafter apparent, the particular angularly adjusted position of the sine bar 600 is a function of the lead of the gear teeth on the gear blank 30. Thus, the modified construction here shown has the advantage over the construction previously shown and described in that it is not necessary to replace any part or to substitute one part for another when it is desired to adapt the machine for cutting a helical gear blank having teeth of different leads. It is merely necessary to adjust the sine bar 600 angularly in accordance with the particular lead of the gear to be acted upon.

Mounted to travel back and forth in the way 608 is a guide 610, and surmounting the guide is a rack 612 having a rearwardly extending pin 614 journaled in the guide. The rack 612 extends transversely with respect to the spindle 590, and the rack teeth 616 mesh with gear teeth 618 formed on the periphery of the spindle 590.

From the foregoing it will be readily apparent that rotation of the retainer 594 rotatably drives the sine bar 600 and the rack 612 carried thereby; and, since the rack teeth are rotatably interlocked with the teeth 618, the rack and spindle 590 are forced to rotate together. As long as the spindle 590 does not move axially, the retainer 5'94 and the spindle rotate in unison. However, when the spindle 590 begins to move axially relative to the retainer, the guide 610 moves in the way 608, and when the way is disposed at an angle with respect to spindle 590 as shown in the drawings, the guide has a lateral component as well as an axial component of movement. This lateral component of movement moves the rack 612 transversely of the spindle 590 so that the rack teeth 6116 act against the teeth 618 to adjust the spindle 590 angularly independently of and simultaneously with rotation of the spindle. As suggested, the extent of angular adjustment is a function of the lead of the teeth on the workpiece 30 carried by the spindle 590.

Having thus described the invention, I claim:

1. In a hobbing machine, a rotatable and reciprocable work spindle, a rotary drive mechanism for the spindle comprising a demountable guide assembly including a guide bushing and coactive guide members in said bushing, one of said guide members being connected to said spindle and movable axially and rotatably therewith, the other of said guide members being connected to said bushing for mutual rotation therewith and held thereby axially fixed with respect to said one guide member, said guide members having interengaging cam surfaces which cooperate to guide the spindle during reciprocatory travel thereof, and means for reciprocably actuating said spindle comprising a pair of fluid motors on opposite sides of said spindle having piston rods extending in the direction of and beyond the end of said spindle, and a cross link pivotally attached to one of said piston rods and detachably connected to the other of said piston rods and lying athwart the mentioned end of said spindle, and a coupling rotatably supported by the cross link detachably fastened to the spindle.

2. In a gear-bobbing machine, the combination including a spindle adapted to hold a workpiece, a tubular support, said spindle being mounted in said support, a retainer fastened to said support surrounding said spindle, a multi-element guide mechanism for imparting helical movement to said spindle, said multi-element guide mechanism being carried by said retainer around said spindle, said guide mechanism including at least one element mounted for rotation about the axis of said spindle, said one element being generally tubular in form, a part of the outer surface of said one element defining radial cam faces arranged in a helical path, the helix angle of said faces being a function of the lead of the teeth on a gear blank to be acted upon by said machine, a second element axially fixed relative to said spindle and coaxially rotatable therewith, said second element being connected to said retainer and held thereby fixed axially relative to said one guide element, said second element comprising two parts which coact with said radial cam faces to cause predetermined helical movement of said spindle, said two parts having mating surfaces adapted to be adjustable relative to each other.

References Cited in the file of this patent UNITED STATES PATENTS 1,755,916 Eberhardt Apr. 22, 1930 2,125,304 Miller Aug. 2, 1938 2,481,974 Bradner Sept. 13, 1949 2,484,856 Purvin Oct. 18, 1949 2,528,242 Praeg Oct. 31, 1950

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