US2705004A - Forming means for profile grinding wheels - Google Patents

Description

March 29, 1955 H. s. HALLEWELL 2,705,004

FORMING MEANS FOR PROFILE GRINDING WHEELS Filed Sept. 6, 1952 3 Sheets-Sheet l m nwra/e A. s. HAM/P144624 March 29, 1955 H. s. HALLEWELL FORMING MEANS FOR PROFILE GRINDING WHEELS Filed Sept. 6, 1952 5 Sheets-Sheet 2 JQuba March 29, 1955 s, HALLEWELL 2,705,004

FORMING MEANS FOR PROFILE GRINDING WHEELS Filed Sept. 6, 1952 I 3 Sheets-Sheet 3 United States Patent FORMING MEANS FOR PROFILE GRINDING WHEELS Harold Stuart Hallewell, Hillingdon Heath, England Application September 6, 1952, Serial No. 308,210

Claims priority, application Great Britain September 10, 1951 Claims. (Cl. 125-11) This invention relates to a pantographic wheel dressing device adapted to be attached to a grinding machine and employed for forming on the grinding wheel thereof a profile reproduced from a template, the device being of the kind having a base adapted to be mounted on the grinding machine, means for mounting the template in a plane, a template-follower member rockable about an axis perpendicular to the template plane and mounted in a bearing in a first member, a dressing-tool holder rockable about an axis perpendicular to the template plane and mounted in a bearing in a second member, a pantograph connection between said first and second members, and a connection supplementary to the pantograph connection for constraining the template-follower member and the dressing-tool holder to rock in unison.

In devices of this kind at present in use the dressingtool is usually of the diamond-tipped chisel type, mounted in the dressing-tool holder so that the axis of its tip, which is radiused, lies on the rocking axis of the holder. In operation, the grinding wheel being dressed is set tangentially to the rocking axis of the dressing-tool holder.

Grinding machines are often used in the production of profiled toolssuch as lathe tools. Such a tool usually has the face in which the cutting edge is formed relieved by at least a few degrees so that, except for the cutting edge, the face clears the work. Therefore, when grinding a profile on the tool, it is set in the grinding machine with its cutting face inclined at the relief angle to a tangent to the grinding wheel surface. It will be apparent that the profile (hereafter called the first profile) which is formed on the grinding wheel differs from, and is a distortion of, the profile (hereinafter called the second profile) which the tool forms on a workpiece. It will be apparent that the said first profile must also be distorted when the tool is raked, since otherwise an accurate second profile is not obtained.

When the sum of the relief and rake angles is about 10 or less (account being taken of the relative senses of the two angles) the first profile can be produced on the grinding wheel, using a template profile of the same form as the second profile, without introducing serious errors, by displacing the dressing-tool a predetermined short distance along the said rocking axis. This displacement is usually made in the direction in which the adjacent portion of the grinding wheel periphery -is moving, since if it were made in the reverse direction the dressing-tool might be drawn into the wheel and damaged or destroyed. The required magnitude of the displacement can be calculated using well-known formulae.

For rake and relief angles, the sum of which is greater than 10, the errors introduced by the above-mentioned method of producing the first profile become appreciable, and therefore the distortion must be compensated for by modifying the template profile. Even if the second profile is simple in form, the calculation of the modified form of the template profile to give the required first profile can be a tedious and lengthy operation.

An object of this invention, therefore, is to provide a pantographic wheel-dressing device of the kind specified with which the said first profile can be formed on the grinding wheel of a grinding machine by using a template profile of the same form as the said second profile.

According to this invention, the above object is attained by providing that in a pantographic wheel dressing device of the kind specified, the part of said means for supporting the template and to which the template 2,705,004 Patented Mar. 29, 1955 "ice can be secured is tiltable about an axis which is disposed in parallelism or approximate parallelism to the plane of the template, and which is adjustable to be capable of being set parallel to the axis of rotation of the grinding wheel.

A typical operation for which grinding machines are used is the production of dies which subsequently are used for generating rolled screw threads on bar stock. The dies may consist of flat rectangular plates and, during the rolling operation are moved relatively to one another in two spaced parallel planes with the member being rolled disposed between them, the direction of movement being parallel to one of the sides of the dies. With the abovementioned rectangular form of die, the ridges and grooves constituting the die profile are inclined at the helix angle to its longer sides. During the grinding operation, the die blank is so disposed that the grinding wheel traverses it in a direction parallel to the said ridges and grooves. It will be apparent, therefore, that the profile (hereinafter called the first profile), which must be formed on the grinding wheel by the dressing tool differs from, and is a distortion of the thread profile (hereafter called the second profile) which the dies form on the bar stock. This is due to the fact that the grooves are oblique to the sides of the die. This obliquity slightly affects the angularity of the sides of the grooves and requires the angles of the sides of the grooves to be compensated therefor so that in a direction of the sides of the dies the angles of the grooves will be proper for the threads being rolled. The angles of the sides of the threads in a direction normal to the direction of movement of the die must be 55 or 60 for standard screw threads. As these grooves are ground longitudinally the angles on the sides of the grooves on the wheel must be slightly less than these standard thread angles.

Therefore, with the apparatus known hitherto, before such an operation can be begun it is necessary to calculate the form of the first profile, i. e. the form which the second profile takes when rotated through the helix angle about an axis in the plane of the profile and perpendicular to the grooved face of the die. The template profile has the same form as the first profile. Even if the second profile is simple in form this calculation can be a tedious and lengthy operation.

Another object of this invention is to provide a pantographic wheel-dressing device of the kind specified with which the last-mentioned first profile can be formed on the grinding wheel of a grinding machine using a template profile of the same form as the last-mentioned second profile.

Also according to this invention, the last-mentioned object is attained by providing that in a pantographic wheel-dressing device of the kind specified, the part of said means for supporting the template to which the template can be secured is rotatable about an axis, which is disposed approximately parallel to and adjacent the plane of the template, and which is capable of being set pehrpelndicular to the axis of rotation of the grinding w ee An embodiment of this invention will now be described, by way of example, with reference to the accompanying drawings wherein:

Figs. 1A and 13 together show a front view in elevation of the complete device,

Fig. 2 is a side view of part of the device, the view being partly in vertical section and partly in elevation taken on broken line 2-2 in Fig. 1A, and

Fig. 3 is a plan view of the part of the device shown in Fig. 2 with the template and the template-follower member removed.

Referring now to Figs. 1A and 1B, the device includes a baseplate 10 to which are fixed plates 11 adapted to be engaged by the magnetic chuck of a grinding machine (not shown). The pantograph connection comprises a link parallelogram constituted by two short and two long links. The first long arm of the link parallelogram comprises a more or less horizontal H-section link 12 pivoted to a more or less vertical short link 13 about a horizontal axis 14, which is fixed relatively to the base 10 and thus constitutes the fixed point of the pantograph connection. The short link 13 constitutes the second arm of the link parallelogram and is pivoted about the axis 14 to a mounting 15 on the base plate.

A tubular lever 16 parallel to the short link 13 is pivoted to the free end of the long link 12 at 17 and carries a template-follower pin 18 at its upper end. A light alloy casting 19 (Figs. 1A and 1B) constitutes the third, long arm of the parallelogram extending parallel to the long link 12, the casting being of inverted channel section with boxed-in ends and serving to protect the bearings of the link parallelogram from rust, etc. The casting is pivoted to the lever 16 about an axis 20 and to the short link 13 about an axis 21. The portion of the lever 16 between the pivots 17 and 20 constitutes the fourth, short arm of the parallelogram.

The supplementary connection comprises three steel tapes 22, 23 and 24, the two tapes 22 and 23 both passing round and being pinned to the periphery of a rotatable drum 25 coaxial with the axis 20, and each passing round and being pinned to the periphery of a different one of two drums 26 and 27 coaxial and rotatable with a dressing-tool holder 28 and a shaft 29 (Fig. 2) respec tively. The third tape 24 passes round and is pinned to the peripheries of two drums 30 and 31 coaxial and rotatable with the shaft 29 and the template-follower pin 18 respectively. Each tape is provided with a tensioning spring 32.

A bracket 33 (Fig. 2) rigid with the base 10 extends parallel to the lever 16 and carries a support to which a template can be fixed. The support is formed in three separate parts, a part 34 rigid with the bracket 33, a part 35 hinged to the part 34 about a vertical axis AA, and a part 36 hinged to the part 35 about a horizontal axis BB. When the device is in position on a grinding machine the said rigid part 34 lies with its front reference surface 34A in a vertical plane, the hinge axis AA lying vertically and the rocking axes of the templatefollower pin 18 and the dressing-tool holder 28 lying horizontally. A template 37 is secured to the part 36 and thus to the part 35 by countersunk screws 38 (Fig. 1A), the template being located accurately by means of two straight edges 39 and 40. The axis AA is thus disposed vertical, and perpendicular to the axis of rotation C-C of the grinding Wheel 41, and parallel to the template plane. The part 35 is retained in the position to which it has been rotated by means of two lock- nuts 42 and 43 fixed to the rigid part and frictionally engaging the part 35. A mark 44 on the part 34 co-operates with a scale 45 fixed to the part 35 to show the angle between the planes of the template 37 and the surface 34A.

Similarly, when the device is in position on a grinding machine, the axis B-B lies horizontally, parallel to the axis of rotation C-C of the grinding wheel 41, and close and parallel to the plane of the template on the side of the template support remote from the template follower pin 18. The part 36 is retained in the position to which it has been tilted by means of a lock-nut 46 fixed to the part 36 and frictionally engaging the part 35. A scale 47 fixed to the part 34 and a pointer 56 fixed to part 36 show the angle between the planes of the template 37 and the surface 34A.

The template follower member is V-shaped and is constituted by the pin 18, which engages the template profile, and two side wings 48 The member is pivoted freely between a pin 49 and a rod 50, and is constrained to rotate with the rod 50 without backlash by means of a pin 51 on the member engaging in a slot in an arm 52 which is rotatable with the rod 50. The rod 50 is in turn rotatable with a shaft 53 on which are fixed the drum 31 and an operators hand-wheel 54. The pin 49 is carried by a sleeve 55 mounted in a forked part 16A of the lever 16, the end of the sleeve which projects beyond the part 16A being ground truly fiat and engaging the surface 34A of the part 34. Thus, the link parallelogram cannot be distorted by a careless operator pushing the lever 16 too hard in the direction towards the template support.

The length of the template-follower member, in a direction perpendicular to the plane of the surface 34A, is sufficient for its mounting in the lever 16 not to foul the template when the latter is rotated through its greater angle to the plane of the surface 34A. The edge forming the tip of the V-section has the same shape as the top of the dressing tool. its radius being equal to that of the dressing-tool tip multiplied by the mechanical advantage of the pantograph connection. The edge of the template 37 engaged by the pin 18 is bevelled, as shown at 37 in Fig. 2, to ensure that the pin 18 will engage the correct profile and to obviate errors in the profile produced on the grinding wheel which might be due to the thickness of the template.

The scale 45 is graduated in degrees and minutes from zero to the value of the maximum required helix angle of the threads to be formed (usually from zero to about 15). The scale 47 is preferably graduated in degrees from zero to 35. If the angle required lies between 35 and 45 degrees, the dressing tool is first displaced along its rocking axis, as mentioned above, to take account of the excess over 35, and the template 37 is then tilted the full amount of the scale 47.

Two springs 56 (only one shown) are provided to take the weight of the pantograph linkage, so that the weight does not have to be supported by the operator whilst manipulating the handle 54.

I claim:

I. A pantographic wheel dressing device for attachment to a grinding machine and for forming on the grinding wheel thereof a profile reproduced from a template, the device comprising a base for mounting on the grinding machine, a grinding wheel rotatably mounted on said machine, a template support for angularly adjustably mounting the template thereon, said support comprising a first part rigid with the base and a second part pivotally mounting the template on said first part about a fixed axis parallel to the axis of rotation of the grinding wheel, a first member mounted on said base, a bearing in said first member, a template-follower engageable with the template mounted in said bearing and rockable about the axis thereof, a second member mounted on said base, a bearing in said second member, a dressing-tool holder mounted in the last-mentioned bearing and rockable about the axis thereof, a pantograph connection between said first and second members, and a connection supplementary to the said pantograph connection constraining the template-follower member and the dressing-tool holder to rock in unison about an axis normal to the axis of the wheel.

2. A pantographic wheel dressing device as claimed in claim 1, wherein the said pantograph connection comprises a link parallelogram.

3. A pantographic wheel dressing device as claimed in claim 1, wherein the said first member comprises a forked lever and two coaxial bearings, each disposed in one arm of the forked lever, and the template follower extends between and is mounted for rotation in the two coaxial bearings.

4. A pantographic wheel dressing device as claimed in claim 1, wherein the said first part of the template support includes a reference surface and the template follower comprises a bearing surface engaging the said reference surface.

5. A pantographic wheel dressing device for attachment to a grinding machine and for forming on the grinding wheel thereof a profile reproduced from a template. the device comprising a base for mounting on the grinding machine, a template support for adjustably mounting the template thereon, the said support comprising a first part rigid with the base and a second part for pivotally mounting the template on said first part about two mutually perpendicular axes, one of said axes being capable of being set parallel to the axis of rotation of the grinding wheel, a first member mounted on said base, a bearing in said first member, a template-follower engageable with the template mounted in said bearing and rockable about the axis thereof, a second member mounted on said base, a bearing in said second member, a dressingtool holder mounted in the last-mentioned bearing and rockable about the axis thereof, a pantograph connection between said first and second members, and a connection supplementary to the said pantograph connection constraining the template-follower member and the dressingtool holder to rock in unison.

6. A pantographic wheel dressing device as claimed in claim 5, wherein the said pantograph connection comprises a link parallelogram.

7. A pantographic wheel dressing device as claimed in claim 5, wherein the said first member comprises a forked lever and two coaxial bearings, each disposed in one arm of the forked lever, and the template follower extends between and is mounted for rotation in the two coaxial bearings.

8. A pantographic wheel dressing device as claimed in claim 5, wherein the said first part of the template support includes a reference surface and the template follower comprises a bearing surface engaging the said reference surface.

9. A pantographic wheel dressing device for attachment to a grinding machine and for forming on the grinding wheel thereof a profile reproduced from a template, the device comprising a base for mounting on the grinding machine, a template support for adjustably mounting the template thereon, the said support comprising a first part rigid with the base, a second part, and a third part for mounting the template, the second part being pivoted to the first part about a first axis and the third part being pivoted to the second part about a second axis mutually perpendicular with the first axis, one of the said axes being capable of being set parallel to the axis of rotation of the grinding wheel, a first member mounted on said base, a bearing in said first member, a template-follower engageable with the template mounted in said bearing and rockable about the axis thereof, a second member mounted on said base, a bearing in said second member, a dressing-tool holder mounted in the last-mentioned bearing and rockable about the axis thereof, a pantograph connection between said first and second members, and a connection supplementary to the said pantograph connection constraining the template-follower member and the dressing-tool holder to rock in unison.

10. A pantographic wheel dressing device for attachment to a grinding machine and for forming on the grinding wheel thereof a profile reproduced from a template, the device comprising a base for mounting on the grinding machine, a template support for adjustably mounting the template in a plane, the said support comprising a first part rigid with the base, a second part, said second part being pivoted to the first part about a first axis, means for retaining the first and second parts in predetermined angular relationship relative to one another, a third part for mounting the template pivoted to the second part about a second axis mutually perpendicular with the first axis, one of the said axes being capable of being set parallel to the axis of rotation of the grinding wheel, means for retaining the second and third parts in predetermined angular relationship relative to one another, a first member mounted on said base, a bearing in said first member, a template-follower engageable with the template mounted in said bearing and rockable about the axis thereof, a second member mounted on said base, a bearing in said second member, a dressing-tool holder mounted in the last-mentioned bearing and rockable about the axis thereof, a link parallelogram pantograph connecting the said first and second members, and a connection supplementary to the said pantograph constraining the template-follower member and the dressing-tool holder to rock in unison.

References Cited in the file of this patent UNITED STATES PATENTS 731,066 Nye June 16, 1903 790,172 Benton May 16, 1905 1,302,540 Hanson May 6, 1919 1,424,196 Fowler Aug. 1, 1922 1,594,607 Engelmann Aug. 3, 1926 2,225,489 Tessky Dec. 17, 1940 2,452,509 Victory Oct. 26, 1948 2,469,844 Porter May 10, 1949 FOREIGN PATENTS 643,240 Great Britain July 24, 1951

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