US3221447A

US3221447A - Device for grinding and resharpening gear-cutting hobs

Info

Publication number: US3221447A
Application number: US268400A
Authority: US
Inventors: Riebel Felix
Original assignee: Individual
Current assignee: Individual
Priority date: 1962-03-29
Filing date: 1963-03-27
Publication date: 1965-12-07
Anticipated expiration: 1982-12-07
Also published as: GB1033677A; DE1427501B1

Description

Dec. 7, 1965 F. RIEBEL 3,221,447

DEVICE FOR GRINDING AND RESHARPENING GEAR-CUTTING HOBS Filed March 27, 1963 5 Sheets-Sheet 1 WIIIIIIIIIII/ Dec. 7 1965 RIEBEL 3,221,447

F. DEVICE FOR GRINDING AND RESHARPENING GEAR-CUTTING HOBS Filed March 27, 1963 5 Sheets-Sheet 2 Dec. 7, 1965 F. RIEBEL DEVICE FOR GRIND ING AND RESHARPENING GEAR-CUTTING HOBS 5 Sheets-Sheet 5 Filed March 27, 1963 Dec. 7, 1965 F. RIEBEL 3,221,447

DEVICE FOR GRINDING AND RESHARPENING GEAR-CUTTING HOBS Filed March 2'7, 1963 5 Sheets-Sheet 4 Dec. 7, 1965 F. RIEBEL 3,221,447

DEVICE FOR GRINDING AND RESHARPENING GEAR-CUTTING HOBS 5 Sheets-Sheet 5 Filed March 27, 1963 United States Patent Claims The invention relates to a device for grinding and resharpening gear-cutting hobs, particularly hobs for cutting spur gears having a concave back. The device operates with a profiled grinding wheel, whereby the backs are ground by plunge feed in a dividing process.

Hitherto known hobs are resharpened by regrinding the tooth face. Hereby the whole back wear must be eliminated in peripherical direction. From this results a tooth which is relatively long in peripherical direction; or, in other words, a long tooth pitch results. This tooth pitch means a low number of teeth of the hob which limits the speed of feed when cutting gears. The speed of feed does not only depend on the number of the teeth of the gear being cut, but also on the number of teeth of the hob. Furthermore, the number of resharpenings is relatively small in spite of the considerable tooth pitch. Both facts result in a low economy of cutting gears.

The purpose of the present invention is to provide a novel device suitable both for manufacturing hobs of the kind described, and for sharpening said hobs; a greater number of teeth are realized in this manufacturing method while a greater number of resharpenings are achieved by means of the same device.

The purpose of the invention is attained by providing hob backs formed as surfaces of rotation which are concave with respect to the hob axis and are generated by a plunge feed by means of a profiled grinding wheel in a dividing process.

In the known relief grinding process the hob rotates while it is ground so that very small grinding-wheel diameters only are possible. The relief grinding process is, therefore, uneconomical for resharpening.

The improved method used with the device according to the invention, however, admits grinding-wheel diameters which are greater, in most instances, than the diameters of the hobs. The grinding wheels may be given diameters which are multiples of the respective hobs. These grinding wheels have a long dressing life and make it possible to employ the same process for resharpening as for the original manufacturing of the hob back. When resharpening the back, the short side of the back wear is eliminated in radial direction. This gives to 6 times more resharpenings per unit of length and when resharpening the tooth face.

By resharpening the hob back in radial direction an improved hob is achieved, the novel feature of which is that the teeth are so short in peripherical direction as safety considerations against breakage will allow. These improved hobs have 60 to 100% more teeth than the known relieved hobs.

A device according to this invention, adapted for grinding and resharpening the improved hobs, comprises means by which the profiled grinding wheel plunges into or attacks the hob or, the hob is made to plunge into the wheel. The device further comprises a dividing attachment coordinated with the hob, and a swivelling base by which the hob axis can be inclined with respect to that of the profiled grinding wheel in correspondance with the helix angle of the hob. The device may also comprise a carriage combined with means for generating a lead, the motion of which is derived from the dividing attachment so that every dividing motion of the hob results in a translation between the hob and the grinding wheel.

It is particularly economical if all teeth lying at the same flute are ground simultaneously with a multi-profile grinding wheel.

The inventive device is adapted to provide a novel hob, for example for cutting spur gears, which shows improved features when compared to conventional relieved hobs having a constant tooth profile. It will be understood that in the present specification spur gear is mentioned in an exemplary fashion only and is meant to represent any gear adapted to be machined by means of the cutting hobs here described.

The new device according to the invention provides a method of manufacturing hob backs by respective plunging of the profiled grinding wheel into the hob or vice versa, the axis of the grinding wheel being inclined with respect to that of the hob by an amount corresponding to the helix angle of the hob.

The invention also provides a device for resharpening the hobs made according to the above-mentioned method, performed by the same process so that the hob-back wear is eliminated in radial direction while a grinding on the tooth face only serves for the smoothing thereof. After two or three resharpening processes an amount of material is removed which is smaller in peripheral direction than the back wear in the same direction.

The invention provides a device adapted for making hob backs, and alternately for resharpening them, according to the methods outlined hereinabove, so as to obtain novel hobs as described hereinabove.

The invention will now be more fully explained, together with other objects and many of the attendant advantages, as the same becomes better understood by reference to the following detailed description, when considered with the accompanying drawings, in which:

FIG. 1 shows a gear-cutting hob in lateral view and the generating process of the hob back;

FIG. 2 shows the cooperation of the profiled grinding wheel and the hob on an enlarged scale;

FIG. 3 is a modification of the arrangement shown in FIG. 2;

FIG. 4 shows the grinding of a hob by means of a multiprofile grinding wheel;

FIG. 5 shows on an enlarged scale, a hob tooth and schematically the method of resharpening;

FIG. 6 is the view of the tooth face of the hob shown in FIG. 5;

FIG. 7 shows a hob-grinding device according to the invention in a side view;

FIG. 8 shows the device of FIG. 7 in a top view;

FIG. 9 shows the hob carriage in a top view and the dividing spindle stock in section; and

FIG. 10 shows the dividing plate and the change gears of the dividing spindle stock (view taken upside down from the side of the device opposite that shown in FIG. 7).

While the inventive device for grinding and resharpening gear-cutting hobs will be fully described with reference to FIGS. 7 through 10, the improved hobs, as well as some of the considerations that apply in their processing, are being explained first, with reference to FIGS. 1 through 6.

FIG. 1 shows, as an example, a gear-cutting hob 10 having teeth 11 which are gound at their backs 12 by means of a profiled grinding wheel 13. This wheel is used both during the first production and during each resharpening. The grinding wheel may perform a plunge feed in different directions, e.g., as shown by the arrows 14$, 15, 16. The extreme direction 14 is parallel to the tangent plotted against the back 12 at the outermost sectional point A of the tooth edge. The outer extreme direction 15 is determined by the top K of a neighboring tooth 11a. Between these two extreme values all directions lying within an arc 17 are possible, such as, for example, shown at 16. The direction 16 is the base for the construction of the grinding device shown in FIGS. 7-10. The inclination of the profiled grinding wheel is indicated by a projection 18 of the grinding wheel axis in the plane of FIG. 1.

FIGS. 2 and 3 show in partial sectional views, as a matter of example, two types of cooperation between

hobs

21, 31 and

respective grinding wheels

24, 33. According to FIG. 2, the root of the hob tooth has a groove at 22 and the grinding wheel 24 is formed so that only the flanks 23 and the head 25 of the same tooth are machined with the grinding wheel 24. In the example according to FIG. 3, the flanks 32 of a space between two hob teeth are ground simultaneously with the tooth root 34 and the tooth heads of an appropriately profiled grinding wheel 33.

FIG. 4 shows the machining of a hob 41 with a multiprofile grinding wheel 42. Hereby a resharpening time is attainable which is even shorter than the time needed for the conventional resharpening at the tooth face. This method, however, can be employed only with relatively short hobs and with a small helix angle. Otherwise the difference between the clearance angle of a tooth on one end of the flute becomes too great as compared with that on the other end, because of the inclination of the grinding wheel. In this case, the dressing of the grinding wheel must be performed with a template and a diamond; the dressing plane must have the same position with regard to the grinding wheel as the tooth faces of the teeth being ground simultaneously.

With FIG. the method of resharpening is described. AC and GH are the traces of the hob back in the respective planes YY and X-X of the cutting points A and G (FIG. 6). The wear of the back appears in FIG. 5 as the triangle ABD. If this hob were resharpened on the tooth face, the amount DB would have to be ground away, which is not economic. By the resharpening method exercised with the device according to the invention, however, only the small amount AD is to be ground away in radial direction, and the above-mentioned lines AC and GH which are to show the back appear as dotted lines EF and IL.

The tooth face may be smoothed by a slight grinding. Mostly it is sufiicient to grind the tooth face at every second or third resharpening of the hob back. OMNP is the tooth at the end of the hob life span. Regrinding of the tooth face will maintain the length of the tooth head (AC-MN) while the flute becomes deeper.

Both FIGS. 1 and 5 show clearly the difference in the constructional features between the improved hobs processed with the device according to the present invention and the known, relieved hobs having a constant tooth profile; i.e., the pitch (arc AK) which is very short as compared to the cutting-profile depth (AG in FIG. 5) and the hob diameter; the teeth which are short as compared to the flute; and the backs which are concave surfaces of rotation (AC and GH in FIG. 5).

The improved hobs with a pitch similar to FIGS. 1 or 5 always out with at least two teeth simultaneously in one thread, one behind the other. Contrary to the chattering manner in which a known hob with a long pitch works, the short pitch of the improved hob results in very smooth cutting. The cutting edges are spared so much that, for example, if an improved hob with twenty teeth is made to cut with double the fed as a known hob with only ten teeth, the number of workpieces being cut per resharpening is greater than that with a known hob, and mostly amounts to the double in case of stable workpieces.

In FIGS. 7-10 the inventive grinding device is shown which is adapted both for the manufacturing and the resharpening of the improved hobs. The feed means by which the profiled grinding wheel 13 plunges into the hob It), is a carriage slide 53 which is supported by rollers, as shown at 57. By a tension spring 58, carriage 53 is pressed hand against a stop 59 during grinding so that the hob will have a good run-out. The plunge feed motion is provided by an eccentric disc 60.

An adjusting slide 52 is connected with carriage 53, which carries an attachment 49 for the grinding wheel 13. By means of a hand wheel 77 and spindle screw 78, the grinding wheel 13 is set into the grinding position as shown in FIG. 7 or into the opposite direction away from the hob 10, Where it is profiled by means of a crushing roll 54, the attachment 55 of which is directly mounted on the bed 56. For the crushing process, belts '75 and 76 for grinding wheel 13 and disc 60, respectively, have to be inactivated, e.g. by disconnecting one end thereof. If conventional steel crushing rolls are used, wheel 13 does not have to be rotated because it is entrained by driven roll 54.

Motors

85 and 86 are provided for driving the grinding wheel 13 and the eccentric disc 60, respectively, through the afore-mentioned belts. FIGS. 7 and 8 also illustrate a belt 76' for driving roll 54 from motor 86.

FIGS. 8-10 show that the hob 10 is set up on an arbor between a tailstock center 79 and a dividing spindle 69. The dividing motion is executed as soon as the carriage 53 gives an impulse, upon reaching the back dead center. This is accomplished by a switch 62. which closes a circuit (not shown) so that a solenoid 63 retracts an indexing finger 64 from a notch of a dividing plate 65. A motor 66 turns the dividing spindle 69 and the plate 65 by means of a drive comprising a worm 67 and a worm wheel 68. As soon as carriage 53 leaves the back dead center, solenoid 63 is de-energized whereupon finger 64 is urged by a spring (not shown in detail) against the outer diameter of the dividing plate 65, and it falls into the next notch.

By means of change gears 70 the rotation of the dividing spindle 69 is transmitted to a lead screw 72 which displaces a top carriage Stl with respect to a carriage rest 73 from one tooth to the next in accordance with the lead of the hob 10.

By means of a swivelling base 71 (see FIG. 9), the axis of the hob 10 can be inclined in relation to the axis of the grinding wheel, corresponding to the helix angle of the hob.

To adjust the clearance angle, the hob can also be adjusted with regard to the grinding wheel 13, perpendicular to the direction of the plunge feed (performed by carriage 53), by means of a vertical slide 74 and a spindle screw (FIG. 7).

The grinding device may also be employed for grinding and for resharpening of profile cutters and other similar tools.

It should be understood, of course, that the foregoing disclosure relates only to a preferred embodiment of the invention and that it is intended to cover all changes and modifications of the example described which do not constitute departures from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. A device for manufacturing and sharpening gearcutting hobs in a dividing process by means of profiled grinding wheels, the hobs having a plurality of cutting teeth arranged in a helical pattern around the hob periphery in at least two substantially adjacent rows and tooth backs forming concave surfaces of rotation with respect to the axis of the hob, comprising, in combination, support means for a hob to be machined, dividing attachment acting on said hob support means for rotating the same tooth by tooth, support means for a profiled grinding wheel, swivelling means acting on said hob sup port means for tilting the axis of said hob with respect to that of said grinding wheel, feed means acting on said wheel support means for producing plunge feed between said hob and said grinding wheel, and means for generating a lead acting on said hob support means for displacing the same longitudinally from one row of teeth to the other.

2. A device according to claim 1, further comprising drive means for said dividing attachment, the motion of said lead generating means being derived from said drive means.

3. A device according to claim 1, wherein said hob sup port means comprises a movable carriage, a tailstock center and a dividing spindle, the latter being operatively connected with said dividing attachment.

4. A device according to claim 1, wherein said dividing attachment comprises gear means and indexing means operatively connected therewith.

5. A device according to claim 4, further comprising electrical means for actuating said indexing means depending on the position of said lead generating means.

6. A device according to claim 5, further comprising contact means adapted to disengage said indexing means in the position of said wheel support means remotest from said hob support means.

7. A device according to claim 1, wherein said wheel support means comprises a movable attachment for rotatably supporting said grinding wheel, biasing means for urging said attachment toward said hob support means, and adjustable stop means for limiting the movement of said attachment in the position of said wheel support means closest to said hob support means.

8. A device according to claim 1, wherein said swivelling means comprises a carriage rest and a carriage movable thereon for inclining said hob with respect to said grinding wheel by an amount corresponding to the helix angle of said hob.

9. A device according to claim 1, wherein said feed means comprises an eccentric drive operatively connected to said wheel support means for producing plunge-type reciprocation with respect to said hob support means.

10. A device according to claim 1, wherein said lead generating means comprises a lead screw the motion of which is derived from said dividing attachment, every dividing motion of said hob resulting in a translation between said hob and said grinding wheel.

11. A device for grinding and resha-rpening gear-cutting hobs in a dividing process by means of profiled grinding wheels, the hobs having a plurality of cutting teeth arranged in a helical pattern around the hob periphery in at least two substantially adjacent rows and tooth backs forming concave surfaces of rotation with respect to the axis of the hob, comprising support means for a hob to be machined, support means including a movable attachment for rotatably supporting a profiled grinding wheel,

the diameter of said wheel being approximately twice that of said hob, feed means for producing plunge feed between said hob and said wheel, biasing means for urging said attachment toward said hob support means, and adjustable stop means for limiting the movement of said attachment in the position of said wheel support means closest to said hob support means.

12. A device for grinding and resharpening gear-cutting hobs in a dividing process by means of profiled grinding wheels, the hobs having a plurality of cutting teeth arranged in a helical pattern around the hob periphery in at least two substantially adjacent rows and tooth backs forming concave surfaces of rotation with respect to the axis of the hob, comprising support means for a hob to be machined, support means including a movable attachment for rotatably supporting a profiled grinding wheel, the diameter of said wheel being approximately twice that of said hob, feed means for producing plunge feed between said hob and said wheel, dividing means for rotating said hob tooth by tooth, and means for generating a lead for displacing said hob longitudinally from one row of teeth to the other, said dividing means and said generating means acting both on said hob support means.

13. A device for grinding and resharpening gear-cuttin-g hobs in a dividing process by means of profiled grinding wheels, the hobs having a plurality of cutting teeth arranged in a helical pattern around the hob periphery in at least two substantially adjacent rows and tooth backs forming concave surfaces of rotation with respect to the axis of the hob, comprising Support means for a hob to be machined, support means including a m-ovable attachment for rotatably supporting a profiled grinding wheel, the diameter of said wheel being approximately twice that of said hob, feed means for producing plunge feed ber tween said hob and said wheel, and means for journaling said wheel and said hob with their respective axes arranged substantially parallel to one another.

References Cited by the Examiner LESTER M. SWINGLE, Primary Examiner.

Claims

13. A DEVICE FOR GRINDING AND RESHARPENING GEAR-CUTTING HOBS IN A DIVIDING PROCESS BY MEANS OF PROFILED GRINDING WHEELS, THE HOBS HAVING A PLURALITY OF CUTTING TEETH ARRANGED IN A HELICAL PATTERN AROUND THE HOB PERIPHERY IN AT LEAST TWO SUBSTANTIALLY ADJACENT ROWS AND TOOTH BACKS FORMING CONCAVE SURFACES OF ROTATION WITH RESPECT TO THE AXIS OF THE HOB, COMPRISING SUPPORT MEANS FOR A HOB TO BE MACHINED, SUPPORT MEANS INCLUDING A MOVABLE ATTACHMENT FOR ROTATABLY SUPPORTING A PROFILED GRINDING WHEEL, THE DIAMETER OF SAID WHEEL BEING APPROXIMATELY TWICE THAT OF SAID HOB, FEED MEANS FOR PRODUCING PLUNGE FEED BEBTWEEN SAID HOB AND SAID WHEEL, AND MEANS FOR JOURNALLING SAID WHEEL AND SAID HOB WITH THEIR RESPECTIVE AXES ARRANGED SUBSTANTIALLY PARALLEL TO ONE ANOTHER.