US3411492A

US3411492A - Apparatus for truing grinding wheels

Info

Publication number: US3411492A
Application number: US540408A
Authority: US
Inventors: Henry E Merritt
Original assignee: Merritt & Co Engineering Ltd
Current assignee: Merritt & Co (engineering) Ltd; Merritt & Co Engineering Ltd
Priority date: 1965-04-10
Filing date: 1966-04-05
Publication date: 1968-11-19
Anticipated expiration: 1985-11-19
Also published as: GB1125181A; DE1577414A1

Description

Nov. 19, 1968 H. E. MERRITT APPARATUS FOR TRUING GRINDING WHEELS 5 Sheets-Sheet 1 Filed April 5, 1966 I nvenlor Henry E. Merritt y W Mttomey;

Nov. 19, 1968 HEMERRWT 3,411,492

APPARATUS FOR TRUING GRINDING WHEELS Filed April 5,195 5 Sheets-Sheet 47 Inventor Henry E. Merritt y M MW I WA Nov. 19, 1968 H. E. MERRITT 3,411,492

APPARATUS FOR TRUING GRINDING WHEELS Filed April 5, 1966 5 Sheets-Sheet 5 Inventor Henry E. Merritt A ttorney;

United States Patent Ofiice 3,411,492 APPARATUS FOR TRUING GRINDING WHEELS Henry E. Merritt, Warwick, England, assignor to Merritt & Co. (Engineering) Limited, Warwick, England, a British company Filed Apr. 5, 1966, Ser. No. 540,408 Claims priority, application Great Britain, Apr. 10, 1965, 15,335 65 Claims. (Cl. 125-11) ABSTRACT OF THE DISCLOSURE In apparatus for truing the profile of a grinding wheel the truing tool is adjustably mounted on a gimbals arrangement which is connected by a universal joint to the follower of a cam and follower arrangement which generates the form of the desired profile. Movement of the follower is transmitted to the truing tool by the universal joint so that, in use, the tool is maintained normal to the profile of the grinding wheel, and the size of the profile reproduced by the truing tool may be varied by virtue of the tool mounting being adjustably carried on the gimbals arrangement. Grinding wheels for cutting internal and external gear teeth may be trued by the apparatus.

This invention relates to apparatus for truing grinding wheels, especially but not exclusively involute gear grinding wheels.

According to the present invention, there is provided apparatus for truing grinding wheels to a desired profile, said apparatus including a base, a carrier rotatably mounted on the base about a carrier axis, a first gimbal member rotatably mounted on the carrier about a first gimbal axis, a second gimbal member rotatably mounted on said first gimbal member about a second gimbal axis, said first and second gimbal axes and said carrier axis intersecting at a point fixed relative to said base, a tool holder on said second gimbal member for holding a grinding wheel truing tool, and profile generating means including a guide fixed relative to said base, and a follower adapted to co-operate with the guide so as to generate the form of the desired profile, and a connection between the second gimbal member and the follower, said connection being adapted to transmit movement of the follower to said second gimbal member so that the latter moves about said point, and the tip of a grinding wheel truing tool, when held on the tool holder, moves in a path which substantially corresponds with the desired profile.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a sectional side elevation of apparatus according to the invention;

FIG. 2 is a plan corresponding to FIG 1, and

FIG. 3 is an end elevation corresponding to FIG. 1.

The apparatus shown in the drawings consists in general of a tool carrying assembly connected to a profile generating assembly by a universal type joint.

In the tool carrying assembly, a carrier 10 having spaced upwardly extending arms is mounted on a stationary base 11 for rotation about a vertical axis 12. At the upper ends of the arms of the carrier 10 there is mounted a rectangular frame 13 which is rotatable on the arms about a horizontal axis 14 which intersects the vertical axis .12 at a gimbal point 15 which is stationary.v

As can be seen in FIG. 2, the axis 14 is normal tothe length of the frame 13.

A movable member in the form of a bar 16 fits neatly 3,411,492 Patented Nov. 19, 1968 into the frame 13 and has a crank 17 at each end. The bar 16 is parallel to the long side of the frame 13 and is journalled on the frame 13 for rotation about an axis 18 which passes through the gimbal point 15 and which is the longitudinal central axis of the rectangular frame 13. The relative sizes of the bar 16 and the frame 13 are such that the bar 16 may be rotated through 360 on the axis 18.

The bar 16 is rotatably mounted on the frame 13 by means of crank pins 19, 20. The crank pin 20 extends through the frame 13 and has a control ball 21 on the end out with the frame 13. The centre of the control ball 21 lies on the axis 18. A guide ball 22 is connected to the pin 20 and is spaced therefrom by an arm 22A so that a line joining the ball centres is normal to the axis 18. Thus rotational movement of the guide ball 22 about the axis 18 is transmitted to the bar 16 and transverse movement of the control ball 21 relative to the base 11 is transmitted to the bar 16. A tool holder 23 is s'lidably and adjustably mounted on the inside of bar 16 and holds a tool 24 having a diamond point 25. The axis of the tool 24 is normal to the axis 18. The tool holder 23 can be secured in any position along the length of the bar 16 between the end cranks 17, and the tool 24 can be adjustably positioned in the tool holder 23 so that the diamond point 25 lies on the axis 18.

The tool holder 23 is. on the opposite side of axis 18 from the arm 22A so that the axis of the tool 24 is parallel to the line joining the ball centres.

Profile generating means for moving the bar 16 and hence the diamond point 25 consists of two

guide plates

26, 27 bolted to the base 11. The

guide plates

26, 27 are slightly greater than semi-circular, are of the same diameter and are mounted in a parallel spaced upright manner with their common axis 28 parallel to and directly below the axis 18. A straight follower in the form of a rocking plate 29 rolls on the curved surfaces of the guide plates and is attached to said plates by means of taut steel tapes 30. Each tape 30 is attached at one end to one of the

guide plates

26, 27, contacts the curved surface of a guide plate, leaves the curved surface at the point of contact between the rocking plate 29 and the guide plate and thereafter contacts the rocking plate, the other end of the tape being attached to the end of the rocking plate.

There are four tapes 30 (two for each guide plate) and adjacent tapes 30 are oppositely attached to the relative parts. The tapes 30 thus constrain the rocking plate 29 to roll truly on the

guide plates

26, 27.

A. T-shaped swivel arm 31 is positioned upright and a leg 32 of the T passes through a longitudinal slot 33 in the rocking plate 29 and the upper cross pieces 34 of the T arm carry rollers 35 which are engaged in longitudinal grooves 36 in the rocking plate 29.

The lower end of the leg 32 is rotatable about a dowel pin 37 joining the

guide plates

26, 27. The dowel pin 37 passes through a hole 38 in the leg 32. The hole 38 is of larger diameter than the dowel pin 37. Below the dowel pin 37, the leg 32 has a bore 39 in which there is a spring-urged plunger 40 which has a concave end face corresponding to the curvature of the dowel pin 37. The plunger 40 bears on the dowel pin 37 and by reaction maintains contact between the rocking plate 29 and the

guide plates

26, 27. Thus, regardless of the angular position of the T-shaped arm 31, the rocking plate 29 and

guide plates

26, 27 will be spring-urged towards each other.

In order to roll the rocking plate 29 on the

guide plates

26, 27 there is provided a rotatable crank 41 mounted on the guide plate 27, and this crank 41 has a roller 42 which neatly engages a longitudinal slot 43 in the leg 32 of the T arm 31. The crank 41 is keyed to a worm wheel spindle 44 rotatable by a worm 45 and Wormwheel 46 contained in a gearbox casing 47. The worm 45 may be rotated, manually or otherwise, by means of a square end 48 on the worm shaft 49 and which projects from the casing 47.

A connection between the two main parts of the apparatus is established by an adjustable setting block 50 releasably secured to a swivel head 51 attached to the rocking plate 29 at the side remote from the worm and wormwheel casing 47. The swivel head 51 had a guideway extending parallel to the rocking plate and on which the setting block 51 slides; the setting block 50 has a cylindrical socket 52 in which the control ball 21 neatly fits so that it can slide in the direction of the axis of the cylindrical socket 52. The guide ball 22 is located in a slot 53 in the setting block 50. The length of the slot 53 is greater than the diameter of the guide ball 22, and the width of the slot 53 is equal to the diameter of the ball 22, so that the line joining the ball centres remains parallel to the guideway on the swivel head 51. The swivel head 51 comprises two relatively rotatable discs 54, 55 so that the guide ball 22 and the bar 16 may be set at 180 relative to the position shown in FIG. 2.

The position of the apparatus in the drawings is the datum position and the axis 18 passes through the tangent point between the rocking plate 29 and the

guide plates

26, 27. If it is desired to true an involute gear grinding wheel, the wheel is placed with the lower end of its profile touching the diamond point and with its axis of rotation normal to the axis 18. The wheel is rotated relatively quickly and then the worm 45 is also rotated. Thus the swivel arm 31 pivots from the vertical position and the rocking plate 29 is induced to roll on the curved surfaces of the

guide plates

26, 27. Therefore, in end elevation, FIG. 3, the control ball 21 describes an involute to a base cylinder of radius equal to that of the

guide plates

26, 27. As the gimbal point 15, which is on the axis 18, is fixed, all points on the axis 18, in end elevation, describe involutes to base circles of varying radius. The base circle radius at the gimbal point is zero, and the base circle radius increases progressively as points on the axis 18 move further from the gimbal point 15. The guide ball 22 maintains the line joining the ball centres tangential to the base circle at all times, and, therefore, the axis of the tool 24 remains normal, in end elevation, to the profile of the grinding wheel.

As the swivel arm 31 rotates, the diamond point trues the gear profile on the grinding Wheel, and the involute reproduced by the diamond point 25 is reduced in relation to the involute of the control ball centre by the ratio of the relative distances of the control ball centre and the diamond point 25 from the gimbal point 15.

In order to true a corresponding profile on the other side of the grinding wheel the bar 16 is rotated through 180 and the swivel arm is rotated in the opposite direction by the worm and wormwheel 46.

Inverseinvolutes may be trued by moving the tool holder 23, with the diamond point 25 to the other end of the frame from that shown in the drawings in order to true grinding wheels for producing internal teeth.

Dependent upon the characteristics of the gear to be produced by the grinding wheel being trued, the position of the setting block may be adjusted relative to the guideway on the swivel head 51, in the direction of the rolling surface of the rocking plate 29. This adjustment provides a means of varying the tooth thickness in the final cut gearwheel.

Appropriate data for the grinding wheel will govern the position of the diamond point 25 on the axis 18 relative to the gimbal point 15.

The apparatus may be mounted on an extension of the bed of a grinding machine so that the axis of the workpiece, the axis of the base cylinder and the gimbal point will all lie in the same vertical plane.

Whereas any point on the rocking plate 29 moves in a plane, the diamond point 25 moves on the surface of a sphere the centre of which is the gimbal point 15. In practice, however, the error due to the spherical movement of the diamond point 25 is negligible.

It will be realised that for a particular curvature of the guide plates 26, 27 a limited range only of involutes may be generated. This can be overcome by providing a series of differently sized guide plates.

In a modification of the invention, not shown, the frame 13 is open-sided in that it is U-shaped in plan and is rotatably supported on a single carrier arm for rotation about horizontal axis 14. In this case the bar 16 would be rotationally displaced to a position below the plane of the frame 13. The diamond point 25 would, of course, remain on the axis 18. The shape of the tool holder would have to be slightly modified. Also, the inner ends of the pivot pins 19, 20, may be used for the purpose of mounting a device for setting the diamond point to the required position.

The apparatus may be used to true grinding wheels other than gear grinding wheels, for example milling cutter grinding wheels and spline grinding wheels.

The invention need not necessarily be limited to truing involute profiles, and may be used to true any gear grinding wheel profile. For example, a profile generator may be used which produces circular arcs or other profiles dependent upon the shape of the guide and the manner in which the follower moves on the guide.

I claim:

1. Apparatus for truing grinding wheels to a desired profile, said apparatus including a base, a carrier rotatably mounted on the base about a carrier axis, a first gimbal member rotatably mounted on the carrier about a first gimbal axis, a second gimbal member rotatably mounted on said first gimbal member about a second gimbal axis, said first and second gimbal axes and said carrier axis intersecting at a point fixed relative to said base, a tool holder on said second gimbal member for holding a grinding wheel truing tool, and profile generating means including a guide fixed relative to said base, and a follower adapted to co-operate with the guide so as to generate the form of the desired profile, and a connection between the second gimbal member and the follower, said connection being adapted to transmit movement of the follower to said second gimbal member so that the latter moves about said point, and the tip of a grinding wheel truing tool, when held on the tool holder, moves in a path which substantially corresponds with the desired profile.

2. Apparatus according to claim 1, in which the tool holder is position-adjustably mounted on the second gimbal member.

3. Apparatus according to claim 2, in which the tool holder is selectively positionable on either side of the plane containing the carrier axis and the first gimbal axis.

4. Apparatus as claimed in claim 3, in which the connection between the second gimbal member and the follower includes a universal joint comprising a first balland-socket element for rotating said second gimbal member about the second gimbal axis and a second balland-socket element for causing displacement of said second gimbal axis relative to said base.

5. Apparatus as claimed in claim 4, in which the universal joint is position-adjustably mounted on the follower.

6. Apparatus as claimed in claim 4, in which the balls of said ball-and-socket elements are in fixed mutual relationship and are connected to said second gimbal member.

7. Apparatus as claimed in claim 6, in which an imaginary line passing through the ball centres of the first and second ball-and-socket elements in parallel to the axis of a grinding wheel truing tool when the latter is held in the tool holder.

8. Apparatus according to claim 7, in which the guide References Cited has a cam surface and the arrangement is such that the UNITED STATES PATENTS follower ma roll on said cam surface.

9. Apparatus according to claim 8, in which said guide 1912410 6/1933 shotfsy 125 11 has a cylindrical cam surface and the follower is a fiat 5 1988895 1/1935 Godzlewskl 125-11 plate. FOREIGN PATENTS 10. Apparatus according to claim 9, in which said fol- 1,045,823 7 /1953 France lower is constrained to roll on said cylindrical carn sur- 253,089 5/1926 Great Britain.

face by yieldably tensioned flexible tie means connected to the follower and t0 the guide. 10 HAROLD D. WHITEHEAD, Primary Examiner.