US2171892A - Apparatus for grinding - Google Patents

Description

p 5, 's. G. RICHARDSON 2,171,892

V APPARATUS FOR GRINDING Original Fild Oct. 14,, 1936 ads-74743 Patented Sept. 5, 1939 UNITED STATES PATENT OFFICE APPARATUS FOR GRINDING Substituted for abandoned application Serial No.

105,552, October 14,

1936. This application March 29, 1938, Serial No. 198,783

6 Claims.

The invention relates to machines for and methods of producing smooth and flawless surfaces, and with regard to its more specific features to machines and methodsfor producing a mirror finish on a metal object, for example on a cylindrical surface thereof.

One object of the invention is to achieve a very smooth mirror-like surface on a metal object. Another object of the invention is to enable the manufacture of steel rods, shapes and plates to produce such things with a smoother surface. Another object of the invention is, in the manufacture of steel, to avoid flaws, cracks, incipient fractures and the like. Another object of the invention is to provide for the manufacture of parts with a mirror finish in a grinding machine. Another object of the invention is to achieve a smooth flawless surface.

Another object of the invention is to provide a machine which will grind and also produce a finish as good as or better than a lapped finish. Another object of the invention is to eliminate the hills and valleys on a metal object, due to grinding. Another object of the invention is to The invention accordingly consists in the features of construction, combinations of elements and arrangements of parts, as will be exemplified in the structure to be hereinafter described, and

the scope of the application of which will be indicated in the following claims.

In the accompanying drawing in which is shown one of various possible embodiments of the mechanical features of this invention,

Fig. 1 is a plan view of a machine constructed in accordance with the invention;

F g. 2 is a fragmentary view, partly in elevation and partly in section, along the line 2-2 of Fig. 1, showing the first reduction gear unit, the clutch and the second reduction gear unit, the casings being omitted;

Fig. 3 is a fragmentary view, partly in elevation and partly in section, along the line 33 of Fig. 1, showing the second and third reduction gear units, the casings being omitted in this View; and Fig. 4 is a fragmentary sectional view, taken approximately on the line 4-4 of Fig. 1, show ng a section through the wheel spindle illustrating the brake and combined with a wiring diagram to show the interconnection between the wheel driving motor and the brake.

Referring first to Fig. 1, I provide a machine base III of any suitable type for the support of awork table I I on ways 12 and I3 for reciprocatory traverse. The base In and the tableit may be of the type found in grinding machines and, when the invention is applied to the production of a mirror finish on large, heavy rolls for steel rolling mills, the base l0 and the table II will preferably be of the character found insocalled froll grinders.

Any suitable mechanism for traversing the table II may be provided. Such a mechanism is not shown herein in detail because many types of traversing mechanisms are well known in the art. However, in so much as a mechanism for traversing a work piece relative to the wheel I4 is to be deemed part of the invention, so far as certain features are concerned, I have illustrated the .usual reversing lever l5 pivotally mounted on the. base I0 by means of a hub 16 and a shaft l1 and in position to be contacted alternately by table actuating dogs l8 and I9 which are adjustably mounted in a T-slot 20 on the front of the table II so that a long or a short traversing stroke may be given to the table II and, by means of a suitable control mechanism, at any desired speed within wide limits. The lever l5 may control any desired translating mechanism, as by means of a valve 2| connected by pipes 22 and 23 to opposite sides of a cylinder 24 having therein a piston 25 connected by a piston rod 26 to the table II. I provide a source of fluid under pressure, for example a pump 21, connected by means of a pipe 210. to the valve 2|; an exhaust pipe 28 is also connected to the valve to discharge the fluid from the exhaust side of the system.- The valve 2| is not illustrated in detail as many types of reversing valves are well known for the operation of a traversing table for a grinding machine- Associated with the reversing lever i5 is a suitable load-and-fire device, otherwise known as a snap-overmechanism, not shown.

The foregoing constitutes means for reciprocating the table I I relative to the base It and any other suitable type of reciprocating mechanism, such as the screw feed type with reversing clutch control, may be provided. The speed of reciprocation may be controlled in any suitable manner, for example in the illustrative embodiment by means of a throttle-valve 29 controlled from the front of the machine by means of a lever 30 which is connected to the valve 29 by means of a shaft 3l.-

With a mechanism of the type described, a reciprocatory traverse may be achieved at any speed between two inches per minute and thirty feet per minute. The table II has mounted thereon a headstock 33 and a footstock 34 which are adjustably mounted on ways 35, 36 on the table II. Thus the headstock 33 and the footstock 34 may be moved toward or away from each other and clamped in the desired position for the support of rolls to be ground of varying lengths. Mounted on the headstock 33 is a driving motor 31 operating a suitable driving face plate 38 through reduction gearing in the casing 39. Coaxial with the face plate 38 is a center 40 which is in line with a footstock center 4| which may be advanced and retracted by means of a screw 42 operated by a hand wheel 43. I further provide massive work supporting journal rests 44 and 45 for the support of the work piece to be ground in so much as, for the grinding of large rolls of rolling mills, it has not heretofore been possible to provide strong enough head and foot centers to hold the work piece satisfactorily. These work supporting journal rests may be mounted on the same ways 35-and 36 upon which are mounted the headstock 33 and footstock 34. Many variations may be made of these features and special adjustable steadyrests may be provided if desired or, in case of grinding a light shaft of short length compared to its diameter, work supporting journal rests and steadyrests may be dispensed with altogether.

The work piece 46 (a fragment only of which is shown in order not to obscure the machine mechanism) has a pair of journal portions 41 and 48 resting in the work supporting journal rests 44 and 45 and a cylindrical portion 49 to be polished and also driving grooves 50 at one end at least. By means-of these grooves 50, the roll is driven in' the rolling mill and one or more massive lugs adjustable in a diametral slot 52 in the face plate 38 are provided to drive the roll 46 in the machine. The roll 46 is'first centered by means of the centers 40 and 4| but the load is taken by the work rest journals 44 and 45 and any suitable expedient for adjusting the journals 44 and 45 may be adopted, as for example the use of shims.

The foregoing constitutes a mechanism for holding, rotating and traversing the massive rolls, such as used in a rolling mill for the rolling of steel, and' as is known in grinding machines. However, instead of reciprocating the work piece, the grinding wheel I4 may be reciprocated in a manner, such as that shown in the prior United States patent to C. H. Norton, No. 1,096,188, dated May 12,1914. The latter type of machine is old and well known in the trade and is commonly known as the grinding wheel traverse type cylindrical or roll grinding machine. Although the portion 49 has been referred to as a cylinder, suitable known roll crowning attachments may be provided within the scope of this invention to polish a crowned roll.

The grinding wheel |4 may be of many different types, but for producing a mirror surface of very fine quality on steel, such as for example steel used in a massive roll for rolling mills, or ordinary cold rolled steel, I prefer to use a wheel bonded with one of the organic bonds, for example rubber, shellac and synthetic resins, and. I- prefer to use one of the synthetic resins, for example phenolformaldehyde, that is, a type of bond which has been known as Bakelite. However, so far as the broad features of this invention device 61.

cause it is desirable that the grinding wheel |4 are concerned, any type of grinding wheel may be employed, for example one bonded with vitrified ceramic material or a cement bonded wheel or a silicate bonded wheel.

The grinding wheel II, which may also be referred to as a polishing wheel or'even a honing wheel, as it is preferably of very fine grit size as specified, is mounted on a suitable spindle 55 which is journaled in a bearing 56 mounted in a cross slide 51. The cross slide 51, in this illustrative embodiment of the invention, is. of comparatively large area and rests upon a rearward extension 58 of the machine base I0. Suitable V and flat ways, not shown, are provided for supporting the cross slide 51 on the extension 58 of the base I. I further provide means or mechanism for moving the cross slide 51 transversely in the direction of reciprocatory traverse of the table II, preferably perpendicularly or normal thereto. This may be embodied in a feed screw shaft 60 journaled in suitable bearings, not' shown, in the machine base I0, the front end of which extends to the front of the machine and is pro videdwith a suitable hand wheel 6|. A nut or half nut 62 is fixed to the cross slide 51 and receives the screw 60, whereby the cross slide 51 may be slowly advanced or retracted and brought to an adjusted position with accuracy. It should be understood that any known cross feeding apparatus may be used for advancing or retracting the cross slide 51 but, in the preferred manner of practicing my invention, there is substantially no relative cross feed between the wheel and work during the polishing action, the cross feed mechanism being simply employed to perform a previous grinding operation and to bring the parts to the desired adjusted position which involves simply a light pressure between the Wheel and work piece, enough to insure a steady contact.

I further provide, for example in connection with the footstock 34, a suitable grinding wheel dressing tool 55 which may be embodied in a cylindrical member having a diamond 56 at one end and adjustably mounted in the footstock and slidably clamped therein, as by a clamping This dressing device is provided bebe so far as possible absolutely cylindrical when the polishing operation is performed. The wheel may be dressed or trued by traversing it in front of and in contact with the diamond 66, by the power traverse already described with the valve 29 closed to provide a very slow relative movement or, if desired, manual means may be provided for moving the table It even more slowly for the dressing operation.

For rotating the wheel I4, I provide an electric motor which is connected directly to a suitable speed reduction transmission, such as the unit which is on the market under the name "Transitorq. In so much as the Transitorq may be purchased in the open market and the ing disks 11. The driving disks 11 may be swung so that they take the position represented by dotted lines "a, Fig. 2, and they may also be moved to position represented by dotted lines IIb, Fig. 2, and may be placed in any intermediate position. Thus the driving ratio between the driving race I5 and the driven race 18 may be varied within wide limits. I

Referring to Fig. 1, the Transitorq is controlled by a control wheel'80 which is associated with a dial, not shown, giving the actual number of revolutions per minute of the driven element. Referring to Figs. 1 and 2, keyed to the driving way-I6 of the Transitorq is a driven shaft 82 upon which is rotatably mounted a multiple groove V pulley 83. This multiple V pulley has clutch teeth 84 at one end adapted to be engaged by corresponding clutch teeth 85 on a shift the shafts 82 and 90 are coupled together but the pulley 83 is free on the shaft 82.

The shaft 90 is journaled in a suitable casing SI and, as shown in Figs. 2 .and 3, has a worm 93 meshing with a worm wheel 94 which is secured to a shaft 95 also suitably journaled in the casing 9|. The shaft 95 is coupled by means of a coupling 96 to a shaft 91 having a worm 98 formed thereon. The Worm 98 meshes with a worm wheel 99. A shaft I00 to which the worm wheel 99 is secured and also the shaft 91 upon which the worm 98 is formed, are journaled in a. suitable casing IN. The shaft I00 projects from the casing IM and has secured to it a multiple groove V pulley I02. A plurality of V belts I03 connect the pulley I02 with a multiple groove v pulley I04. The V pulley I04 is mounted on the end of a shaft I05 which is journaled in a bearing I06. As shown in Fig. 1, the shaft I05 has mounted on the left-hand end thereof a slidable clutch member I0! which is keyed to the shaft I05 and which has teeth positioned for engagement with a clutch member I08 mounted on the right-hand end of the wheel spindle 55.

Also mounted on the wheel spindle is a multiple groove V pulley I09 which is connected by means of a multiple V belt IIO to the V pulley 83. A control lever Il2 mounted on a pivot stud II3 has a yoked portion II4 engaging the clutch member 86 and another yoked portion II5 engaging the clutch member I01. When the control lever H2 is in its right-hand position, as shown in full lines in Fig. 1, the clutch teeth 84 and 85 are in engagement, thus connecting the pulley 83 to the shaft 82, and disconnecting clutch teeth 81 and 88 so that the worm 93 is not ro-' tated. Furthermore, the clutch members I01 and I08 are disengaged when the control lever H2 is in the full line position of Fig. 1. As the pulley I09 is fastened to the spindle 55, the motor 10 drives the wheel I4 at a relatively high speed which is controlled by the control wheel of the Transitorqh' Such speed may, by adjusting the Transitorq, be a grinding speed, for example of the order of between 5000 and\8000 surface feet per minute.

When, however, the control lever is shifted to the lefthand position indicated in dotted lines in Fig. l, clutch teeth 81 and 88 are connected, and the clutch teeth 84 and 85 are disconnected, whereby the worm 93 is driven and the pulley 88 is free'of the shaft 82. In this position of the parts, theclutch member I0! is in engagement with the clutch member I08, and thus the spindle 55 is driven at a very slow rate of speed, which may also be varied by means of the Transitorq" control wheel 80, it being possible to achieve a speed as slow as, for example, one revolution in four minutes. 1

with a pivotal Transitorq and motor unit, a speed range between 3600 R. P. M. and 360 R. P. M. may be achieved. Considering now the maximum speed of the wheel I4 for grinding, in so much as the pulley I09 is approximately twice the size of the pulley 83, the maximum number of revolutions of the spindle 55 will be, in this particular embodiment of the invention, in the neighborhood of- 1800 R. P. M. With a wheel 20" in diameter, for example, this makes a surface speed, when the wheel is new, of approximately 9420 S. F. P. M. However, this is the maximum speed in the illustrative embodiment of the invention and a slower grinding speed, for example of the order of 6000 or 7000 S. F. P. M., may be desired, but the "'I'ransitorq control permits the speed in revolutions per minute to be increased as the wheel wears to a smaller diameter in order that the speed in surface feet per minute may be maintained constant, if desired.

Considering now the slowest speed of the wheel I4, the gear ratio between the worm 90 and wheel 94 is shown as 27 to 1, and the gear ratio between the worm 98 and the worm wheel 99 is shown, as the same, and the pulley I04 has ap-' proximately twice the diameter of the pulley I02. Accordingly, with the Transitorq set to reduce the speed of the shaft 82 to the low rate of 360 R. P. M., the wheel spindle 55 will be rotated at approximately one-quarter of a revolution per minute.

The roll 46, in this illustrative embodiment of the invention, may be driven at in the neighborhood of 25 to 50 R. P. M. Assuming a diameter of the roll of 10 inches, this involves a peripheral speed of the roll of in the neighborhood of 65 to feet per minute. It may be desired in certain instances to introduce another reduction gear unit to cause the wheel I4 to rotate still more slowly. Furthermore, the speed in rev olutions per minute will vary with the size of the work and the size of the wheel. While the invention has been described in connection with a grinder for grinding heavy rolls, it may be applied to any cylindrical grinding machine, for example to a machine for grinding small shafting and the like, and so far as certain features of the invention are concerned, the invention may be embodied in a surface grinder in which the speed of travel of the wheel over the work or relative thereto is of the same order of magnitude as herein indicated for the surface speed of the roll 45, and in which the grinding wheel rotates to give a speed in surface feet per minute of the order of that herein specified.

Returning now to the illustrative embodiment of the invention, the operator may place the lever H2 in its right-han d-position to cause the wheel I4 to rotate at a grinding speed, and he may then grind the roll 45 in the customary manner which need not be described herein in detail. When the roll 45 is ground to the desired size, the operator may shift the control 'lever II2 to the left and change the setting of the Transitorq control wheel 80 and proceed to polish the work piece 45 to a mirror-like finish. In certain instances, a grinding wheel of a particular grit size and grade may be used for the grinding operation, which grinding wheel may be replaced with the wheel I4 of characteristicsv such as hereinbefore indicated when it is desired to polish. It is an advantage to have a machine which may be reasonably quickly set up for either grinding or polishing. Furthermore, by using a single machine to grind and to polish, I avoid the cutting and marring of the work piece during the polishing operation. This may result from the use of two machines when inaccuracies ofalignment are involved. A true mirror surface is achieved by merely wiping out the grinding lines in the polishing operation. For polishing I may reduce the wheel speed down to any figure, and in the preferred form I may stop the rotation and hold the grinding wheel stationary (non-rotatable) during the polishing operation.

Considering now the stationary non-rotatablewheel I4 (Fig. 4)for a polishing operation, the wheel is held against rotation by a mechanism such as a manually operated brake. As illustrated in the drawing, the pulley I09 is provided with an internal brake drum surface II9. Inside of the brake drum surface H9 is a brake band composed of two semi-circular brake members I20 and I2I which are supported by and held against rotation by a stud I22 which is fixed to the wheel slide 57. During the grinding operation the two brake members I20 and I2I are held in a collapsible or non-braking position by means of the tension of a spring I23. A cam I24 pivotally mounted on a stud I25 serves to expand the brake members I20 and I2I into engagement with the brake drum surface H9 to hold the pulley I09 against rotation, thereby holding the wheel spindle 55 and the grinding wheel I4 stationary (non-rotatable) for a polishing operation. The cam I24 may be actuated in any suitable manner, such as by means of a manually operable lever I25. In the position of the parts as illustrated in Fig. 4, the lever I 25 and cam I24 are shown in a braking position with the brake members I20 and I2I expanded against the brake drum surface IIS to hold the wheel I4 stationary.

It is .desirable to provide an interconnection between the grinding wheel driving motor 10 and the braking mechanism so that when the lever I25 is thrown into a braking position (Fig. 4), the motor will beautomatically stopped. The motor I0 is connected to a suitable source of power, as indicated by the power lines in the drawing. A starting mechanism, as indicated by the push button I26, is provided to facilitate starting and stopping of the motor 10. In order that the motor may be stopped when the brake is applied, a limit switch I2! is connected in the circuit in series with the motor 10 and the push button I26 and is arranged so that a cam I28 carried by the lever I25 engages a'roller I29 on the limit switch I21 so that when the lever I25 is moved toward the position shown. in Fig. 4 to brake the rotation of the wheel, the limit switch I21 will be opened, thereby breaking the circuit and stopping the motor 10.

The limit switch I21 also serves to prevent starting rotation of the motor I0 or the wheel I4 until the brake has been released. In starting up the machine the operator pushes the button I 26 to startthe motor 10. While the brake is in the position illustrated in Fig. 4, namely in a braking position, the rotation of the motor cannot start since the limit switch I2! is open, thereby preventing completion of the circuit. The operator may then move the brake lever I25 in a counterclockwise direction (Fig. 4) to release the brake bands I20 and I2I and at the same time the movement of the cam I20 relative to the roller I29 allows the limit switch I21 to close and thereby to complete the electric circuit to start the rotation of the motor 10.

Further considering specifically the illustrative embodiment of this invention, and particularly in connection with the grinding of heavy rolls for rolling mills and the like, the roll 49 may be placed in position between the centers 40 and M and a coarse wheel of any type which is customarily used or which is desired may be placed upon the spindle 55. By a coarse grinding wheel, I mean a grinding wheel having abrasive grains appreciably larger than the 500 mesh size hereinbefore referred to, for example of the order of 80 mesh size or perhaps larger. The grinding wheel may be aluminum oxide bonded with a vitrified bond, or it may be of any other suitable type. With the machine so set up and with the lever H2 in its right-hand position to rotate the grinding wheel at a grinding speed, the rough operation involving the removal of a substantial amount of metal may be performed. This operation, assuming there will be a considerable amount of stock to remove, will consume a considerable amount of time. Then the machine may be stopped and the wheel I4 of the type heretofore described may be placed on the spindle 55. Relative to the time consumed in rough grinding, a change of wheels can be made on the spindle 55 in a very short time.

With a fine wheel I4 on the spindle 55, the speed control lever H2 is still maintained in its right-hand or moved to its left-hand position and the finish grinding operation is performed at either a grinding speed or a slow finishing speed. This involves some cutting and is a true grinding operation but is distinguished from the previous operation in that light cuts are taken and the roll is reduced to its final diameter to high precision limits with regard to size and also roundness. When this has been achieved the brake lever I25 is shifted in a clockwise direction (Fig. 4) to break the circuit and stop the wheel drive motor 10 and to apply the brake and stop the rotation of the grinding wheel I4 and hold it stationary (non-rotatable) during the polishing operation.

,The relative reciprocatory traverse for rough grinding may be relatively fast; for finish grinding it may be relatively slow; and for the polishing operation it may be relatively slow, for ex ample of the order of a few inches per minute, or in the preferred form the grinding Wheel may be stopped and held against rotation during the final or finish polishing operation.

The action of a stationary (non-rotatable) wheel on the work piece when polishing accord ing. to the present invention is quite substantially different from the action of the same wheel when rotating at a normal grinding speed. A work piece examined under the microscope after being operated on according to the invention has a very smooth mirror-like finish characterized by the absence of grinding lines, particularly circumferential grinding lines, assuming the work piece is a cylinder or a shaft. This polish may be achieved upon a work piece over a large area thereof by employing the mechanism hereinabove described to effect a reciprocatory traverse of the wheel and work. The table traversing mechanism may be operated to produce a table traverse of approximately the same speed as' would be used in a grinding operation, such as traverse speeds which are variable within wide limits, and therefore I do not specify any particular range.

This invention, as above described, is applicable to a grinding machine in which a coarse or rough grinding wheel is utilized first to grind the roll or work piece to the approximate size and then the grinding wheel is replaced with a finer or finish grinding wheel which may be rotated either at a normal grinding speed or at a reduced slow polishing speed, after which the rotation of the wheel may be stopped and a brake applied to hold the wheel stationary for a final polishing operation. It may be desirable, however, to utilize two machines in carrying out this method of grinding, viz. one machine set up with a coarse or rough grinding wheel, and a second machine set up with a fine or finish grinding wheel. In the second grinding machine the work piece would be finish ground either with the wheel rotating at a.normal grinding speed or at a much reduced, slow polishing speed, after which the rotation of the wheel is stopped and the wheel held stationary while the work is rotated and traversed longitudinally relative thereto to produce a final polishing action. Or, if desired, a machine may be set up and used merely as a polishing machine, utilizing a stationary wheel which is held against rotation while the work is rotated and traversed relative thereto.

If, after a polishing operation with the stationary non-rotatable wheel a flat spot has been produced on the periphery of the grinding wheel, the wheel may be readily trued by rotating the same and traversing it across the face of the truing tool GB'which has been described above. This truing operation, however, would not be stopped in identically the same position for successive polishing operations.

Besides being useful in obtaining a surface characterized by extreme smoothness and lack of grinding lines on heavy rolls for rolling mills and the like, as heretofore indicated, the invention has particular applicability in connection with the grinding of ball and roller races. Any irregularities of surface in the race of a ball or roller bearing results in some wear and for such purpose no surface can be too smooth. Furthermore, it has been found that a brake band or brake drum is very more efficient and lasts much longer if it has a smooth or mirror finish characterized by lack ofdeep grinding lines or scratches. A brake band or a brake drum mates with another element, in some cases both being of metal, with a smooth flawless surface on each part, such as may be produced according to the present method. The friction between the parts is bound to be greater for a given pressure and,

the wear is found to be less.

In almost all machines there are many cylindrical, conical or other surface of revolution parts which fit in mating parts. An example is any part which is journaled in another part or 2 cylinder or piston or a shaft which slides in a bearing. It has been customary, especially in automobile practice, to set up the various mating and relatively moving parts to a certain pressure when the machine is new, and thereafter when a certain amount has been worn to tighten the bearings, etc. With the present method of finishing parts no such adjustment after the initial period of wear need be undertaken. As the hills and valleys are smoothed off there is not that excess initial wear which has heretofore been experienced. It will be seen thatthe achievement of this result is of greater importance in the auto.- mobile field and also in connection with other machinery. From the foregoing, it will be appreciated that the method is specifically applivention and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawing is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. In a grinding machine, a rotatable grinding wheel and a rotatable work support, a longitudinally reciprocable table supporting one of said elements, a transversely movable slide supporting one of said elements, a driving mechanism for said grinding wheel to rotate it at a grinding speed for a grinding operation, means to disconnect said driving mechanism,.and means to hold said grinding wheel stationary for a polishing operation.

2. In a grinding machine, a rotatable grinding wheel and a rotatable work support which are movable longitudinally and transversely relative to each other, a longitudinally reciprocable table supporting one of said elements, a transversely movable slide supporting one of said elements, a driving mechanism for said grinding wheel which is arranged torotate the wheel at a grinding speed for a grinding operation, means to disconnect said driving mechanism, and a brake to hold said grinding wheel stationary for a polishing operation.

3. In a grinding machine, a rotatable grinding wheel and a rotatable work support which are movable longitudinally and transversely relative to each other, a longitudinally reciprocable table supporting one of said elements, a transversely movable slide supporting one of said elements, a driving mechanism for rotating said grinding wheel which is arranged to rotate the wheel at a grinding speed of the order of three thousand surface feet per minute, or above, means to dis- "connect said driving mechanism, and means including a brake to hold said grinding wheel stationary for a-polishing operation.

4. In a grinding machine, a-rotatable grinding wheel and a rotatable work support, a longitudinally reciprocable table supporting one of said elements, a transversely movable slide supporting one of said elements, means including a driving mechanism to rotate the grinding wheel at a rough grinding speed of the order of more than three thousand surface feet per minute for a rough grinding operation, or at a finish grinding speed of the order of less than three thousand surface feet per minute for a finish grinding operation, means for connecting'either one of said drives to rotate the grinding wheel, and means to hold the grinding wheel stationary for a polishing operation.

5. In a grinding machine, a rotatable grinding, wheel and a rotatable work support which are) movable longitudinally and transversely relative to each other, a longitudinally reciprocable table supporting oneof said elements, a transversely movable ,slide supporting one of said elements, a driving mechanism for rotating said grinding wheel which is arranged to rotate the wheel at a grinding speed of the order of three thousand surface feet per minute, or above, for a grinding operation, a driving mechanism for the grinding wheel to rotate it at a slow speed of the order of less than three thousand surface feet per minute for a finish grinding operation, means for connecting either one of said drives to the wheel, and

ried by said work support, and means to hold the grinding wheel stationary during rotation of the work and the relative longitudinal movement between the wheel and work for a polishing operation.

SYLVESTER G. RICHARDSON.

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