US3032935A

US3032935A - Grinding machine

Info

Publication number: US3032935A
Application number: US16853A
Authority: US
Inventors: George H Lockwood
Original assignee: Heald Machine Co
Current assignee: Heald Machine Co
Priority date: 1960-03-22
Filing date: 1960-03-22
Publication date: 1962-05-08
Anticipated expiration: 1979-05-08

Description

May 8, 1962 G. H. LOCKWOOD GRINDING MACHINE 2 Sheets-Sheet 1 Filed March 22, 1960 gm ITTJQQDODQQQQQQQ FIG. I.

GEURGEHLOCKWOOD INVENTOR.

ATTD EY May 8, 1962 s. H. LOCKWOOD GRINDING MACHINE Filed March 22, 1960 2 Sheets-Sheet 2 FIG. 2.

GEORGE H. LOOK WOOD INVENTOR.

A T TORNE Y United States Patent 3,032,935 GRINDING MACHINE George H. Lockwood, Worcester, Mass, assignor to The Heald Machine Company, Worcester, Mass, a corporation of Delaware Filed Mar. 22, 1960, Ser. No. 16,853 Claims. (Cl. 51-103) This invention relates to a grinding machine and more particularly to apparatus arranged to finish surfaces of revolution by abrasion.

It has long been recognized in the internal grinding art that one of the biggest difficultien encountered is that the outside surface may call for a finish tolerance which is much greater than that of the internal bore. When this is true and the workpiece is supported on this outer surface, as is common during centerless grinding, considerable difliculty is encountered in providing an internal surface finished to a very close tolerance. It has also been recognized that a high degree of 0D. compensation (which is the term used to indicate methods used to compensate for variations in the dimensions of the outside diameter of a workpiece) is obtained by using a V-type shoe support so that the center line of the workpiece varies from piece to piece along the vertical line bisecting the V in a vertical direction. This is used, naturally, when the feed of the abrasive wheel into the work is intended to be in a horizontal direction; it can be readily seen that large amounts of vertical movement due to variations in OD. produce with such an arrangement very little lateral motion of the center line. Various difiiculties are encountered, however, when one attempts to put the V-type support concept into a practical application. For one thing, since the pressure of the wheel on the internal surface is in a lateral direction at a point well above the shoes, there is a tendency for the grinding wheel to roll the workpiece out of the support; it then becomes necessary to use a pressure wheel on the side of the workpiece opposite the supporting shoes or to use a third support opposite the grinding wheel, this last method being indicated in the patent to Quimby l t-2,758,427. This patent, however, shows a third shoe which, although it is adjustable from piece to-piece, is fixed, so far as any individual workpiece is concerned. These and other limitations and difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a grinding machine in which automatic compensation is made for OD. variations and the workpiece is suitably supported during grinding.

Another object of this invention is the provision of an internal grinding machine in which a shoe is pressed against the outside surface of the workpiece at a point generally opposite the pressure of the wheel on the internal surface, the said shoe providing a force almost exactly equaling that of the wheel.

A further object of the present invention is the provision of an internal grinding machine in which a shoe presses against the outside diameter and moves toward and away from a predetermined location in accordance with the variations in the outside diameter of the Workpiece.

It is another object of the instant invention to provide a grinding machine including a novel means for bringing about drag on the workpiece which is proportional to the drag caused by the grinding wheel force.

It is a further object of the invention to provide an internal grinding machine having a V-type shoe support including automatic O.D. compensation, having a third 3,032,935 Patented May 8, 1962 ice shoe whose location varies automatically with vairations in O.D., which presses against the external surface of the workpiece with a force exactly equal and opposite to the grinding wheel force.

A still further object of this invention is the provision of a feed-rate grinding machine for internal grinding in which an exterior shoe presses against the workpiece with a force equal and opposite to the force exerted against the internal surface by the abrasive wheel.

It is a still further object of the present invention to provide a controlled-force grinding machine for internal grinding in which a pressure shoe exerts on the outside diameter a force equal and opposite to that presented against the inside surface by the abrasive wheel.

Another object of the invention is the provision of an internal grinding machine in which distortion due to wheel pressure is reduced to a minimum.

Another object of the invention is the provision of an internal grinding machine of the shoe centerless type, wherein the workpiece is maintained inthe shoes by the. use of an eccentric drive plate and wherein means is provided for providing a friction drag on the exterior surface of the workpiece which prevents the workpiece from leaving the shoes when very high grinding forces are used.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, may be best understood by reference to certain of its structural forms, as illustrated by the accompanying drawings in which:

FIG. 1 is a schematic view of the grinding machine. embodying the principles of the present invention; and

FIG. 2 is a schematic view of another grinding machine making use of the present invention.

In general terms, the present invention consists in providing a grinding machine for finishing the surface of a bore in a workpiece in which a base is provided and a workhead is fixed to the base, which workhead is adapted to support the workpiece for rotation about the axis of the bore; a wheelhead mounted on the base is provided for feeding movement transversely of the axis of the workpiece rotation and a wheel is rotatably mounted on this wheelhead for abrasive contact with the surface of the bore; an actuator is provided for furnishing the said feeding movement and a pressure member is provided which is adapted to contact the outer surface of the workpiece in the general area of intersection thereof with a radial line extending from the axis of the bore through the point of contact of the wheel with the surface of the bore; then, means is provided to cause the force on the outer surface of the workpiece produced by the pressure member to be substantially equal to the force produced by the wheel upon the inner surface of the workpiece,

In FIG. 1 is shown a schematic view of a controlledforce grinding machine making use of the principles of the invention. The grinding machine, indicated generally by the reference numeral 10', is of the general type shown in the patent to Hahn No. 2,647,348 in which the controlled element in feeding is the force of the grinding wheel against the surface to be finished, the rate of feeding varying during the process as is required to maintain the predetermined force. The grinding machine is provided with a base 11 on which is mounted a workhead 12 and a wheelhead 1-3. The wheelhead is mounted on a wheelhead table 14, which, in turn, is mounted on the base 11, there being anti-friction elements 15 interposed .between the two to provide for smooth movement of the wheelhead table over the base 11 in a transverse direction. An actuator 16 of the linear type is included in a feed box 17, which forms part of the base 11; the piston 18, which is joined to the wheelhead table 14 by means of a piston rod 19, serves to join the wheelhead table 14 to the base 11 and to provide for relative motion therebetween. The wheelhead 13 includes an electric motor 21 which drives a wheel spindle 22 on which is mounted an abrasive wheel 23. The workhead 12 includes a pair of

shoes

24 and 25 on which are mounted a workpiece 26 having a bore or inside surface 27 which is to he finished by abrasion and an outside cylindrical surface 28 which presumably has already been completely finished. The

shoes

24 and 25 are provided with arcuate surfaces for contacting the outside surface 28 of the workpiece in a manner similar to the shoes shown and described in the patent to Blood, Reissue No. 24,202. Furthermore, means is provided associated wtih the workhead 12 for driving the workpiece, this consisting of a drive plate (not shown) contacting one end of the workpiece, and another means (not shown) for producing a pressure on the workpiece in the axial direction against this drive plate, all in a manner similar to that described in the Blood patent mentioned hereinabove. The drive plate is located eccentrically of the centerline of the workpiece so that there is a component of slip friction force in the direction of the shoes to hold the workpiece in the

shoes

24 and 25.

Mounted in the workhead 12 is a cylinder 29 in which is slidably mounted a piston 31. The piston 31 is provided at one end with a reduced portion 32 and at the other end with a button 33. A cap 34 is bolted over the opening of the cylinder and limits the outward motion of the piston 31. Also mounted on the workhead 12 is a lever 35 which is attached to the workhead at one end by a pivot pin 36 for swinging motion in a plane at a right angle to the axis of the workpiece. At the end opposite the pivot pin 36 the lever 35 is provided with a contacting finger 37 adapted to engage the button 33 on the piston 31. At an intermediate point between the pivot pin 36 and the finger 37, but related more closely to the pivot pin 36, the lever is provided with a finger '38. Fastened at one end to the workhead 12 is a reed 39, at the other end of which is fastened a supporting shoe 41 which lies between the finger 38 on the lever 35 and the outer surface 28 of the workpiece 26. The surface of the supporting shoe 41 which contacts the workpiece is curved in the same manner as the

shoes

24 and 25 so as to have a curvature equal to the average radius of the workpiece. A hydraulic line 42 connects the outer end of the cylinder 29 to the outer end of the cylinder 17 of the linear actuator 16. A hydraulic line 43 connects the line 42 to the output side of a pressure regulating valve 44, which, in turn, is connected by a line 45 to a source of hydraulic pressure (not shown).

The operation of the invention will now be readily understood in view of the above description. Since the grinding machine is of the controlled-force type, the abrasive wheel 23 will be pressed into the inner surface 27 of the workpiece 26 in such a manner that the force only will be controlled. Usually this is done to provide the greatest grinding force commensurate with long life of the wheel and proper finished surface of the workpiece, but at the same time great enough to provide the shortest grinding cycle. By providing oil pressure through the line 45 and the pressure regulating valve 44 into theline 43 and the line 42, hydraulic fluid is introduced into the cylinder 17 and moves the piston rod 19 to the right, thus causing the wheelhead table 14 to move to the right relative to the base 19 and carry the motor 21 and the wheel 23 laterally relative to the workpiece 26. The grinding force, of course, will be determined by the pressure of the oil in the cylinder 17 multiplied by the area of the piston 18.

The workhead 12 drives the workpiece 26 and rotates it,

and the slight eccentricity between the workpiece and the driving plate forces the workpiece downwardly into the

shoes

24 and 25. As variations occur from-piece to piece in the CD. of the .outer surface 28, the workpieces will ride higher or lower in the

shoes

24 and 25, the centerlines of succeeding workpieces moving along a vertical line passing through this centerline. This means that the horizontal distance of the inside surface 27 from the centerline of the workpiece will not vary appreciably and it will be relatively easy to bring about a proper dimension on the inside surface 27. The hydraulic pressure which is felt by the cylinder 17 also passes through the line 42 into the cylinder 29 and presses against the outboard end of the piston 31 moving it to the left. The movement of the piston 31 to the left causes its button 33 to contact the finger 37 on the lever 35, thus rotating it counterclockwise about the pivot pin 36. This causes the finger 38 to press against the outer side of the shoe 41 which is supported by the reed 39 so that the shoe moves toward the workpiece and contacts the outside surface 28. In a practical embodiment of the invention, the location of the finger 37 and the finger 38 on the lever 35 relative to the pivot pin was in the ratio of 5 to 1, thus providing a second degree lever having that force ratio. It can be seen, also, that the pressure of the shoe 41 is in a predetermined ratio to the pressure of the Wheel 23 on the opposite side of the workpiece 26. Actually, the shoe 41 is arranged so that it lies on the same horizontal line with the axis of the spindle 22 and of the wheel 23. It can be seen that the shoe 41 not only moves inwardly and outwardly to compensate for variations in the location of the outside surface 28 of the workpiece, due to variations in OD, but it also changes its force characteristic on that surface as the force changes on the wheel 23. It will be understood that, in the high-force grinding of the type used, the control element in the grinding machine is the grinding force rather than the feed rate. Such a high force between the wheel and the workpiece provides rotation of the workpiece until under certain conditions it reaches almost the same speed as the wheel itself; this has the effect of reducing the relative slip between the driving plate and the end of the workpiece and, therefore, reducing the component of force which tends to press the workpiece downwardly into the shoes. By use of the present invention, the shoe 41 provides a drag on the surface of the workpiece which is proportional and opposed to the driving force on the inside caused by the wheel 23; this has the effect of maintaining the rotation of the workpiece at a speed slower than the driving plate in an amount sufficient to bring about the required force to hold the workpiece in the shoes. This obviates in many cases the need for a roller pressing on the upper periphery of the workpiece to hold it in the shoes. Furthermore, as is well known, it is desirable that the linear speed of the workpiece be substantially less than that of the wheel, but without the drag provided by the shoe 41 the above described tendency of the workpiece in high force grinding to reach the peripheral speed of the wheel provids an incorrect ratio between the peripheral speeds of the two elements so that the abrading action is less efficient. This drag, incidentally, is proportional to the grinding wheel force; this is a desirable feature, since it is not a good idea to have the drag force higher than is needed.

FIG. 2 shows schematically the application of the invention to a feed-rate grinding machine wherein the feeding of the wheel into the workpiece is at a preselected rate of travel and the forces encountered between the wheel and the workpiece fall in an uncontrolled manner in a wide range of values in a given cycle of operation. The grinding machine, indicated generally by the reference numeral 110, is of the feed-rate type which is well known and which is shown in the above-mentioned patent of Blood, Reissue No. 24,202. The machine is provided with a base 111 on which is fixed a workhead 112. Mounted on the base 111 is a wheelhead 113 mounted on a wheelhead table 114; the table, in turn, is mounted on the base 111 for transverse sliding movement, there being anti-friction elements 115 interposed between the two. An actuator 116 of the linear type is mounted in a feed box 117. The feed box is of the type shown and described in the patent application of Lockwood et al. Serial Number 833,204, filed August 12, 1959. The linear actuator, which is hydraulically driven, is provided with a piston rod 118' formed as a rack which engages a gear 119 mounted on a feed screw 120 suitably mounted in bearings in the base 111. The feed screw engages a nut forming part of the wheelhead table 114 and, by its rotation, causes movement of the wheelhead table across the base 111. An electric motor 121 forms part of the wheelhead 113 and drives a wheel spindle 122 on which is mounted an abrasive wheel 123.

The workhead 112 is provided with

shoes

124 and 125 holding a tubular workpiece 126 having an inside surface 127 and an outside surface 128. Also provided in the workhead is a cylinder 129 in which is mounted a piston 131 having at one end a reduced portion 132 and at the other end a button 133. A cap 134 overlies the cylinder and limits the longitudinal motion of the piston 131. Also mounted on the workhead 112 is a lever 135 connected at its lower end to the workhead by means of a pivot pin 136. At its upper end the lever is provided with a finger 137 and an intermediate portion closely adjacent to the pivot pin 136 is also provided with a finger 138 located on the opposite side of the lever from the finger 137. Also mounted on the workhead 112 is a reed 139 which hanges vertically and has at its lower free end a supporting shoe 141. The shoe 141 as well as the

shoes

124 and 125 are suitably arcuately formed to provide contact with the outer surface 128 of the workpiece 126 in the manner shown and described in the above-mentioned reissue patent of Blood No. 24,202. A hydraulic line 142 is connected at one end to the cylinder 129 and at the other end to the output side of a servo regulator 143. This servo regulator may be of the well-known type, such as shown in Patent No. 2,767,609, which provides a hydraulic pressure proportional to an electrical input signal. The regulator is connected by a line 144 to a source of hydraulic pressure (not shown). The servo regulator 143 is connected by an electrical line 145 to a load-sensing control 146. This load-sensing control is of the type shown in the patent to Dunigan No. 2,722,648 and has the attribute of giving a signal proportional to the load in a three-phase alternating current motor similar to the motor 121 used in the machine. The load-sensing control is connected by three-phase lines 147 to the motor 121 and also connected to an electrical power source (not shown). The loadsensing control 146 is connected to the line 145 to supply it with an electrical signal which at all times is proportional to the load on the wheel motor.

The operation of this apparatus is very similar to that described in connection with FIG. 1. Hydraulic pressure provided to the linear actuator 116 is controlled by the elements in the feed box so that feed takes place according to a pre-arranged cycle and, therefore, the feed screw 120 is similarly rotated to move the wheel 123 into the inner surface 127 of the workpiece 126 to provide an abrading action. The grinding wheel is driven by the motor 121 whose load is continuously sensed by the control 146. An electrical signal proportional to the load on the motor 121 passes through the line 145 to the servo regulator 143; the regulator causes the pressure passing from the line 144 into the line 142 to be proportional to the signal received and this pressure, therefore, is proportional to the load on the motor. The load on the motor is also proportional to the pressure between the wheel 123 and the workpiece 126, this pressure being the grinding force, so-called. This means that the pressure in the line 142 will also be proportional to the grinding force and the hydraulic pressure in the line 142 acts on the piston 131. The force is transmitted through the lever 135 on the supporting shoe 141 so that it presses against the outer surface 128 of the workpiece. In this way it can be seen that the pressure on the outside of the workpiece provided by the shoe 141 is at all times equal to the pressure on the inside of the workpiece provided by the abrasive wheel 123, this being the desired result.

Most of the advantages enumerated above in connection with the controlled-force grinding machine are obtained when the invention is used with a feed-rate grinding machine. For instance, at times during the feed-rate cycle, the grinding force becomes quite high and a drag in the opposite direction to the rotating force of the wheel on the workpiece is desirable and is provided in this case by the shoe 141. In the same way, the pressure of the wheel tends to rock the workpiece out of the shoes 124 and and the pressure of the shoe 141 prevents this.

It will be understood, of course, that in the above description the applicant has omitted many necessary or desirable elements of a grinding machine which, however, are not part of the invention. For instance, it is necessary to provide a workhead and driving plate to engage one end of the workpiece; a clamping plate may be provided at the other end of the workpiece or a pressure roll may engage the periphery of the workpiece opposite the shoes. It will also be necessary to provide for axial movement of the wheel into the bore of the workpiece.

it is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent, is:

l. A grinding machine for finishing a surface of revolution of a workpiece, comprising a base, a workhead mounted on the base and adapted to support the workpiece for rotation about the axis of the surface, a wheelhead mounted on the base, means for bringing about feeding movement of the wheelhead and workhead relative to each other transversely of the axis of workpiece rotation, a wheel rotatably mounted on the wheelhead and adapted to contact the said surface, an actuator for bringing about the said feeding movement, a pressure member adapted to contact a surface of the workpiece in the area of intersection of the surface with a line extending from the axis of the workpiece through the point of contact of the wheel with the said surface, and means to cause the force on the workpiece produced by the pressure member to be substantially equal to the force produced by the wheel on the said surface.

2. A grinding machine for finishing a surface of a bore in a workpiece, comprising a base, a workhead mounted on the base and adapted to support the workpiece for rotation about the axis of the bore, a wheelhead mounted on the base for feeding movement transversely of the axis of workpiece rotation, a wheel rotatably mounted on the wheelhead and adapted to contact the surface of the bore, a linear actuator for bringing about the said feeding movement, a pressure member adapted to contact the outer surface of the workpiece in the area of intersection thereof with a radial line extending from the axis of the bore through the point of contact of the wheel with the surface of the bore, and means to cause the force on the Outer surface of the workpiece produced by the pressure member to be substantially equal to the force produced by the wheel on the surface of the bore.

3. A grinding machine for finishing the surface of a bore in a workpiece having an external surface of revolution, comprising a base, a workhead mounted on the base, two shoes adapted to support the workpiece by contact with the external surface, the shoes being arranged to form a V-shaped support for rotation of the workpiece about the axis of the bore, a wheelhead mounted on the base for feeding movement transversely of the axis of the workpiece rotation, a wheel rotatably mounted on the wheelhead and adapted to contact the surface of the bore, a linear actuator for bringing about the said feeding movement, a third shoe adapted to contact the outer surface of the' workpiece in the area of intersection thereof with a radial line extending from the axis of the bore through the point of contact of the wheel with the surface of the bore, and means to cause the force on the outer surface of the workpiece produced by the pressure member to be substantially equal to the force produced by the wheel on the surface of the bore.

4. A grinding machine for finishing a surface of revolution of a workpiece, comprising a base, a workhead mounted on the base, two shoes adapted to support the workpiece by contact with an external surface of revolution, the shoes being arranged to form a V-shaped support for rotation of the workpiece about the axis of the surface of revolution, a wheelhead mounted on the base, means for bringing about feeding movement of the wheelhead and workhead relative to each other transversely of the axis of workpiece rotation, a wheel rotatably mounted on the wheelhead and adapted to contact the said surface, an acutator for the said feeding movement, a third shoe adapted to contact the workpiece in the area of intersection thereof with a radial line extending from the axis of the bore through the point of contact of the wheel win the said surface, and means to cause the force on the workpiece produced by the pressure member to be substantially equal to the force produced by the wheel on the said surface.

5. A controlled-force grinding machine for finishing a surface of revolution of a workpiece, comprising a base, a workhead mounted on the base and adapted to support the workpiece for rotation about the axis of the surface, a wheelhead mounted on the base, means for bringing about the feeding movement of the workhead and wheelhead relative to each other transversely of the axis of workpiece rotation, a wheel rotatably mounted on the wheel head and adapted to contact the said surface, a first hydraulic cylinder for bringing about the said feeding movement, means providing hydraulic fluid under pressure to the cylinder, a pressure member adapted to contact the workpiece in the area of intersection thereof with a radial line extending from the axis of the bore through the point of contact of the wheel with the said surface, a second hydraulic cylinder actuating the pressure member and receiving hydraulic fluid under pressure from the same means as the first cylinder, the second cylinder causing the force on the workpiece produced by the pressure member to be substantially equal to the force produced by the Wheel on the said surface.

6. A controlled-force grinding machine for finishing the surface of a bore in a workpiece, comprising a base, a workhead mounted on the base and adapted to support the workpiece for rotation about the axis of the bore, a wheelhead mounted on the base for feeding movement transversely of the axis of workpiece rotation, a wheel rotatably mounted on the wheelhead and adapted to contact the surface of the bore, a first hydraulic cylinder for bringing about the said feeding movement, means providing hydraulic fluid under pressure to the cylinder, 2. pressure member adapted to contact the outer surface of the workpiece in the area of intersection thereof with a radial line extending from the axis of the bore through the point of contact of the wheel with the surface of the bore, a second hydraulic cylinder actuating the pressure member and receiving hydraulic fluid under pressure from the same means as the first cylinder, the second cylinder causing the force on the outer surface of the workpiece produced by the pressure member to be substantially equal to the force produced by the wheel on the surface of the bore.

7. A controlled-force grinding machine for finishing the surface of a bore in a workpiece having an external surface of revolution, comprising a base, a workhead mounted on the base, two shoes adapted to support the workpiece by contact with the external. surface, the shoes being arranged to form a V-shaped support for rotation of the workpiece about the axis of the bore, a wheelhead mounted on the base for feeding movement transversely of the axis of workpiece rotation, a wheel rotatably mounted on the wheelhead and adapted to contact the surface of the bore, a first hydraulic cylinder for bringing about the said feeding, movement,.means providing hydraulic fluid under pressure. to: the cylinder, a third shoe adapted to contact the outer surface of the workpiece in the areaof intersection thereof with a radial line extendingfrom the axis of the bore through the point of contact ofthe wheel with the surface of the bore, a second hydraulic cylinder actuating the pressure member and receiving hydraulic fluid under pressure from the same means as the first cylinder, the second cylinder causing the force on the outer surface of the workpiece produced by the pressure member to be substantially equal to the force produced by the wheel on the surface of the bore.

8. A feed-rate grinding machine for finishing a surface ofirevolution of a workpiece, comprising a base, a workhead mounted on the base and adapted to support the workpiece for rotation. about the axis of the surface, a :heelhead mounted on the base, means for bringing about feeding movement of the wheelhead and workhead relative to each other transversely of the axis of workpiece rotation, a Wheel rotatably mounted on the wheelhead and adapted to contact the said surface, an electric motor driving the wheel, an actuator for bringing about the said feeding movement, a pressure member adapted to contact the workpiece in the area of intersection thereof with a radial line extending from the axis of the bore through the point of contact of the wheel with the said surface, a hydraulic cylinder actuating the pressure member, a servo regulator supplying hydraulic fluid under pressure to the cylinder, a control which senses the load on the electric motor and transmits a signal indicative thereof to the servo regulator, so that the force on the workpiece produced by the pressure member is substantially equal to the force produced by the wheel on the said surface.

97 A feed-rate grinding machine for finishing the surface of a bore in a workpiece, comprising a base, a workhead mounted on the base .and adapted to support the workpiece for rotation about the axis of the bore, a wheelhead mounted on the base for feeding movement transversely of the axis of workpiece rotation, a wheel rotatably mounted on the wheelhead and adapted to contact the surface of the bore, an electric motor for driving the wheel, an actuator for bringing about the said feeding movement, a pressure member adapted to contact the outer surface of the workpiece in the area of intersection thereof with a radial line extending from the axis of the bore through the point of contact of the wheel with the surface of the bore, a hydraulic cylinder actuating the pressure member, a servo regulator supplying hydraulic fluid under pressure to the cylinder, a control which senses the load on the electric motor and transmits a signal indicative thereof to the servo regulator so that the force on the outer surface of the Workpiece produced by the pressure member is substantially equai to'the force produced by the Wheel on the surface of the bore.

10. A feed-rate grinding machine for finishing the surface of a bore in a workpiece having an external surface of revolution, comprising a base, a workhead mounted on the base, two shoes adapted to support the workpiece by contact with the external surface, the shoes being arranged to form a V-shaped support permitting rotation of, the workpiece about the axis of the bore, a wheelhead mounted on the base for feeding movement transversely of the axis of workpiece rotation, a wheel rotatably mounted on the wheelhead and adapted to contact the surface of the bore, an electric motor driving the wheel, a linear actuator for bringing about the said feeding movement, a third shoe adapted to contact the outer surface of the workpiece in the area of intersection thereof with a radial line extending from the axis of the bore through the point of contact of the wheel with the surface of the bore, a hydraulic cylinder actuating the pressure member, a servo regulator supplying the hydraulic fluid under pressure to the cylinder, 21 control which senses the load on the electric motor and transmits a signal indicative thereof to the servo regulator, so that the force on the outer surface of the Workpiece produced by the pressure member is substantially equal to the force produced by the wheel on the surface of the bore.

References Cited in the file of this patent UNITED STATES PATENTS 2,603,043 Bontemps July 15, 1952 5 2,909,009 Schmidt Oct. 20, 1959 2,923,106 Reusser Feb. 2, 1960