US2452863A

US2452863A - Polishing machine

Info

Publication number: US2452863A
Application number: US619367A
Authority: US
Inventors: Herbert T Nicholas
Original assignee: NICHOLAS EQUIPMENT CO
Current assignee: NICHOLAS EQUIPMENT CO
Priority date: 1945-09-29
Filing date: 1945-09-29
Publication date: 1948-11-02
Anticipated expiration: 1965-11-02

Description

Nov. 2, 1948. H. T. NICHOLAS 2,452,863

POLISHING MACHINE Filed sept. 29, 1945' 5 sheets-sheet 1 INVENTOR. E@ i Hf/PrT/V/cnoms H #menen N0 2 1948. H. T. NlcHoLs 2,452,863

POLI-SHING MACHINE Filed sept. 29, 1945 5 sheets-sheet 2 N0v.` 2,1948 H. T. NICHOLAS 2,452,863

PoLIsHING MACHINE Filed Sept. 29, 1945 5 Sheets-Sheet 5 @da di@ Error/nm 1\1mf.2,`1948. H. T. NICHOLAS 2,452,863

POLIISHING MACHINE Filed sept. 29,. 1945 5 sheets-sheet 4 By Y @22204, vlwf 17T/BIENE Y! FIG. 7

Nov. 2, 1948.

Filled sept. 29, 1945 H. T. NICHOLAS POLISHING MACHINE 5 Sheets-Sheet 5 l INVENTOR. #Emst/ri- TAI/mams liz-roem: y1

Patented Nov. 2, 194.8

POLISHING MACHINE Herbert T. Nicholas, Huron, Ohio, assigner to Nicholas Equipment Company, a partnership Application September 29, 1945, Serial No. 619,367

11 Claims.

This invention relates to an improved polishing or abrading machine, and especially to an improved machine which will be particularly well adapted for polishing knife blades or similar articles. These, therefore, are the general ob jects of the present invention.

A more specic object of the invention is the provision of an improved actuating mechanism for passing workpieces between a pair of coacting polishing or abrading rolls, as well as the provision of an improved mechanism for controlling the number of passes to be made by the workpieces.

Another object of this invention is to provide a mechanism for polishing or abrading work pieces, between a pair of coacting polishing or abrading rolls, including a method of control for the peripheral speed of the rolls, regardless of variations between the rolls caused by wear and the like.

A further object of the invention is to provide an improved polishing or abrading machine, of the type using a pair of coacting rolls between which the work is passed, the mechanism of which will be so arranged as to eliminate, for practical purposes, undesired vibrations and chattering, either of which is apt to blemish the work pieces, as well as result in early deterioration of the mechanism.

Other objects and advantages of this invention;

will become more apparent from the following specification, reference being had to an embodiment of the invention illustrated in the accompanying drawings. The essential features of the invention will be summarized in the claims.

In the drawings, Fig. 1 is a front elevation of an abrading or polishing machine constructed in accord with the present invention; Fig. 2 is an end elevation of the machine, certain parts being broken away to more clearly illustrate the inn ternal construction; Fig. 3 is a horizontal section through the machine, the plane of the section being illustrated by the offset lines 3-3 of Fig. 1; Fig. 4 is a sectional detail of a portion of the mechanism used to control the position of the abrading rolls, the plane of the section being indicated by the lines 4-4 of Fig. 1; Fig. 5 is a diagram of the mechanism used to pass the workpieces between the polishing or abrading rolls, and Fig. 6 is a diagram of electrical circuits used to control the operation of the roll driving motors.

In general, the machine illustrated in the drawings comprises a substantially rectangular frame-like structure ID, provided with a table II. A pair of polishing rolls I2 and I4 are supported with their axes parallel with each other in a horizontal plane beneath the table II and within the frame structure III. These rolls are driven at a relatively high rate of speed prefer- 2 ably by respective combined motor and speed reduction units I and I6 which are mounted on the table II. These units are of a type to facilitate a comparatively iine and individual adjust- 5 ment of the peripheral speed of their respective rolls.

Workpieces A, supported by a workholder I'I, are reciprocated up and down between the rolls by a hydraulically actuated mechanism mounted within a hollow column I8 which rises vertically from substantially the center of the table II. A mechanism driven by a motor IIl atop the table II imparts a substantially horizontal movement to the workpieces as they pass between the rolls I2 and I4. The speed of travel of the workpieces is controlled by a pair of settable knobs and 2| which are carried by an instrument panel 22 at the front of the machine, while the number of passes the workpieces are to make is controlled by a manually operable knob 23 also positioned on the instrument panel.

A feature of the present invention is the method of and mechanism for controlling the peripheral speed of the abrading rolls I2 and I4. A pair of

ammeters

24 and 25 are mounted on the instrument panel and are so connected in the electrical circuit of the machine that the operator may accurately determine when the peripheral speed of the abrading rolls has been equalized. I have found that the peripheral speed is synchronized when the current flowing through each motor is identical.

Suitable handwheels

26 and 21 mounted on respective speed-reduction units |15 and I6 permit manual adjustment of the peripheral speed of their respective rolls.

The frame I0 comprises, as shown in Figs. 1 and 2, a rectangular base 30 having corner posts 3| in the form of angle irons. These posts support the table structure II. Suitable cross braces, some of which are shown in Fig. 2, at 32, serve to give rigidity to the frame structure. The table II has a downwardly extending skirt 33 from which pivoted hangers 34 depend. The rolls I2 and I4 are each mounted between the lower ends of these hangers.

The rolls illustrated are polishing rolls. These rolls are indicated as being built up of a series of fabric discs which are assembled on shafts 35 and which are held thereon by clamping discs 36 and nuts 31. The fabric discs are yieldable and generally have their peripheries impregnated with a polishing rouge, emery or the like, dependent upon the type of polishing or abrading operation to be performed.

The rolls I2 and I4 are journalled in the lower ends of the hangers 34 with their axes parallel with each other in substantially the same horizontal plane, and with their bite at the transverse center of the frame. As shown, the ends of each roll shaft are mounted in self-aligning bearlare embraced by threaded sleeves @-5.

facing sleeves lid.

'ducer unit.

ings 38 which in turn are adjustably positioned in the lower ends of their respective hangers @il by screws 3S). Suitable collars lill prevent axial displacement of the shafts in their bearings.

The upp-er ends of the roll supporting hangers 3d are pivoted as at di to the table l l and are swingable about their pivots to enable the rolls to be moved toward and from each other and thereby adjust their bite. The movement of the hangers is controlled by hand wheels Il? (Figs. l and 4). Each hanger is provided with a threaded rod 43. These rods are pvo-ted as at ed to the respective hangers and extend outwardly therefrom toward the sides of the frame l il where they rhe sleeves 45 for respective rolls are journalled in respective beams 46 (Figs. 3 and Ll) the ends of which are pivoted as at 4l in the frame posts 3l. Hand wheels 42 are secured to the forwardly facing sleeves d5 which are connected by gears i8 and drive chains 49, with the respective rearwardly Each sleeve l5 is prevented from axial movement by an arm '59 carried by a beam i6 and arranged to coact with a slot 5i) in its sleeve. Accordingly, if either hand wheel di! is rotated, its respective roll l2 or ifi will be moved toward or from the other roll, the axes of the rolls remaining parallel-at all times. This provides an accurate adjustment of the pressure lbetween the rolls as well as providing for accurate alignment of the roll bite with the workpieces.

The combined motor and speed reduction units I5 and I6 are best illustrated in Fig. 3. These units are substantially identical, each comprising an electric motor 5i, the armature shaft 52 of which extends into a housing 53 of a speed re- Secured to the shaft 52 is a conY to the hub t5 of which a cooperating cone spIined. The cone 56 is moved to and from the cone 5t by a nut 5l which is restrained from rotation by the housing and which has a lug 5 engagement with a peripheral groove 5@ 'in the hub of the cone. The nut is moved axially by a threaded shaft fill to which one of the hand wheels 26.or 2l is secured.

A V shaped belt El connects the variable pitch .cones 5S, d with a similar pair of vcones 52, (it,

which actuate the driven shaft tlof the speed reducer unit. The cone 62 is splined to shaft iid and has an elongated hub 65 to which the cone G3 is splined. A compression spring 5t is interposed between the cone 63 and a collar el on the hub of the cone S2 and serves to move the

cones

62, 63 toward each other to eliminate the slack in the belt 6l. The construction is such that as the cones lid, 55 are separated, the cones iii, approach each other, thus varying the relative speeds of the shafts 52 and 5d in the usual manner. The speed reducer shafts t4 are each provided with sheaves G8 which are drivingly connected with sheaves (Se 0n their respective roll shafts 35 by driving belts lli, as indicated in Fig.

The workholder il is best illustrated in Figs. l and 2 and as there shown it comprises a plate 'il to which the workpieces A are clamped in suitable manner. The upper end of the plate li is secured to a T rail l2 which is mounted between ya pair of inverted T rails 'i3 carried by a carriage 74. Preferably, the arrangement is such that the workholder may be slid into position on the carN riage. The carriage is pivotally connected by a pair of parallel links 'il and i8 to outwardly eX- tending arms 'l5 of a sleeve lb, which is slidably mountedon the column I8.

The'sleeve 16 is reciprocated on the column i8 by a hydraulically operated mechanism t0 thereby pass the work W vertically between the rolls l2 and ifi. Mounted in the frame it (Figs. 2 and 5) is an oil storage tankiiii from which oil is drawn through a conduit 8i by a pressure pump B2. rihis pump is actuated by an electric motor 83. The fluid passes from the pump 82 through a conduit Sd to a reversing valve 85. In the position of the valve 8.5 shown in Fig. 5, the fluid under pressure passes from the valve through a conduit 85, a, regulating valve Si, and a conduit 38 to the lower end of a cylinder ed, thus raising the piston 9B thereof. The cylinder dii is positioned within and is secured to the column le, while the upper end of the piston rod @i thereof is secured to a bar SE (Fig. 2) by nuts 93. This bar extends outwardly' from the column i@ through slots 9d therein and its outer ends are secured tothe sleeve it.

While the piston and Wcrkholder move upwardly, fluid is discharged from the upper portion of the cylinder 239 through a conduit S5, a regulating valve tifa, and a conduit ill to the reversing valve t5, from which the fluid returns through a discharge or exhaust conduit 93 to the storage tanlr 3d. The reversing of the control member or piston QQ of the reversing valve 65 causes the reversal of the direction of fluidflo-w above escriben'. between the reversing valve- 35 and the cylinder B91 and accordingly lowers the sleeve and ivorkholder il.

As heretofore mentioned, the workpieces are horizontally while they pass between the rolls i2 and lll. The mechanism for accomplishn ing this is -best shown in 3. A motor lili? is mounted on the table ii and is provided'with a speed reducer unit indicated at lili. The driven iil of the unit lili is provided with an eccentric pin M32 which is connected by a link d3 with a slide itil. This slide is mounted in a guideway carried by the table Il l and embraces the parallel linlr li heretofore described as connecting the sleeve "it with the workholder il. This rotation of the shaft it@ causesthe workholder to be reciprocatedaxialiy of the polishing rolls. The amount of this axial movement is small and its frequency great in comparison with the vertical movement. Thus an even polishing action is accomplished.

The frequency of the horizontal travel of the Worlrhclder is determined by the rate of speed'of the speed reducer shaft l The rate of speed and accordingly the frequency of the vertical movement is determined b f the regulating valves 3l and 95. These valves are identical in construction and are diagrammatically illustrated in Fluid under pressure iiovvs from the reversing valve Sii into one of these valves, it enters. the lower chamber lill of the valve and forces a valve member from its seat against the action of spring i te. 'Thereupon the fluid passes, substantially without restriction, into the upper chamber i it of the valve and thence to one end of the cylinder 23E. However, the discharging fluid from the other end of the cylinder t9 passes directly into the upper chamberl i it of the other regulating valve at. The valve member i t8 of this valve is closed due to the action of its spring ills and the absence of pressure in its lower chamber, accordingly this returning iluid must pass through a restricted orifice ill in the wall between the upper and lower chambers. The effective areaof the orifice lli is regulated by an adjustable needle valve l i2 to which the respec tive speed control knob. 2t' or vEiis secured.

l.The controllingofthe rate of-travel of the workholder by controlling the flo-w of fluid from the cylinder 80 provides an accurate regulation of the rate of travel and is independent of pulsating eiects of the pump. Likewise, as pressure is maintained at both ends of the piston, the movement of the workholder is steady and even, thus enhancing the polishing operation. The elimination of gear or cam driven mechanism for passing the work between the polishing rollsassists materially in reducing vibration and chattering of the workpieces. The use of a hydraulic drive system permits infinite variations in the rate of travel of the workpieces and permits adjustments to be made for the purpose of eliminating vibratory eiects which are ordinarily present in machines of this general type.

The length of vertical stroke imparted to the workholder is controlled by a pilot valve |I4. This valve in turn controls the reversing valve 85 and Ais best illustrated in Fig. 5. The pilot valve may comprise a cylinder provided with ports |,I and I I6 which are connected to opposite ends of the reversing valve 85 by conduits and IIB. rThe pilot valve is also provided with two other ports IIS and |20 which are connected by conduits |2| and |22 with the pressure line 84 and exhaust line 98 of the hydraulic system as heretofore described. The pilot valve is provided with a vane I-23 which divides the valve into two chambers. The position of the vane |23 is controlled by a pair of cams |24 which are adjustably mounted on a bar .|25 carried by an arm 'I5 of the reciprocating sleeve 16 heretofore described and which is connected with the piston rod 9|. These cams are arranged to engage and swing a lever |26 which is connected :by a link |21 with an arm |28 of the vane.

The arrangement of the pilot valve mechanism is such that, when the parts are in the position shown in Fig. 5 (with the piston moving upward), the conduits IIB and |2| are in communication with each other, as are the conduits I|'I and |22. Thus fluid pressure is applied to move the reversing valve control member 95 to the left (Fig. 5). When, however, the lower cam |24 strikes the lever |26 the vane will rotate, bringing the conduit II'I into communication with the conduit |2| and bringing the conduit |I8 into communication with the conduit |22. This will cause the control member 99 of the reversing valve 85 to move to the right (Fig. 5) and reverse the direction of ilow of uid to and from the cylinder 89. n The number of passes that the workpieces make between the polishing rolls I2 and I4, is controlled by a valve |30 which is adjusted by the manually operable knob 23 heretofore mentioned as being mounted on the instrument ypanel 22. This valve is best illustrated diagrammatically in Fig. 5 and as there shown comprises a cylinder |3I having an inlet port |32 connected by a conduit |33 with the pressure line 84, and an exhaust port |34 which is connected by a conduit |35 with the exhaust conduit 98. A valve member in the form of a plug |36, having a peripheral groove |31 is rotatably mounted within the valve cylinder. a ratchet |38 and pivotally mounted about the axis of the plug is a lever |39 carrying a springpressed ratchet pawl |40, the ratchet pawl is moved in a step-by-step movement by the cams |24. As the lower cam |24 rises in response to the rising movement of the piston 90, it engages a lever |4I which is connected .by a link |42 with the lever arm |39 which carries the ratchet p'awlA |40.v

Secured to this plug is The arrangement of the ratchet advancing mechanism is such that the ratchet is advanced one tooth at the end of the upward stroke of the piston. A spring |43 acting on ,the lever |4| returns the ratchet pawl and the associated linkage to their normal positions. The usual detent pawl (not shown) is provided to maintain the ratchet wheel |38 in its advanced position. The gap or groove |3I in the plug |36 is arranged to bring the ports |32 and |34 of the valve structure in communication with each other, thus bringing the pressure line 84 into direct communication with the exhaust line 98, whereupon the movementfof the piston will cease due to a loss of pressure in the operating system heretofore described. Thus the number of passes of the wheel and work pieces is controlled by the angular position of a plug |36 of the valve |30.

When the Workpieces are first inserted in the machine the operator grasps the knob 23 and moves it in a counterclockwise direction to a distance equal to that occupied by the number of ratchet teeth equivalent to the number of passes desired. For convenience, the instrument panel is provided with -a dial 23 A to enable the operator to manually move the plug to its starting position.

As heretofore described, synchronization of the peripheral speed of the rolls I2 and I4 is manually controlled by the actuation of the handwheels 26 and 2'| which regulate the speed of the driven shafts of their respective speed reducer units. I have found that by placing an amineter in the motor circuit of each of the roll driving motors, and by using substantially identical motors, the amperage reading indicated by each of these members is the same when the rolls are in synchronization. Thus, the operator may manipulate the handwheels 26 and 2l until the reading on the ammeters are identical, whereupon the peripheral speed of the rolls will be synchronized, thereby preventing undue abrasive wear on the rolls and eliminating the overloading of leither motor.

The peripheral or surface speeds of the rolls I2 and I4 are synchronized while the driving motors are under load conditions, i. e., while the rolls are in working or peripheral contact with each other or the work. Under such conditions the load on the motors, which are identical, will be identical when the surface speeds of the rolls are identical. This is particularly true where the rolls are driven at relatively high speeds as is common in polishing machines. This manner of adjusting the surface or peripheral speeds of the rolls compensates for variations in the diameter of the rolls due to wear or the like.

The arrangement of the meters and the electrical circuit of the motors is best illustrated in the electrical diagram of Fig. 6. In this diagram the motor I5 is shown as being controlled by a relay |50, while the motor I6 is controlled by a relay I5I. Both of these relays include a master switch mechanism |52, provided with contacts orswitch members |53, |54 and |55, which are arranged, when closed, to connect their respective motors with power lines |56, I5'I and |58. One of the switch members of each of the relays |50 and I5I, namely, the switch member |54, is connected with a line |59 which leadsto a transformer unit |60 of its

respective ammeter

25, 24. The meters in turn are connected by lines |6I with the motors, thus placing the meters in series with their respective motors so that at all 7 times they indicate the operating condition of theirrespective motors.

rThe switch members E52 of the relays ld and l! are normally held in an open position by respective springs l and are closed by solenoids |53 and lill respective, These solenoids, in turn, are controlled by a starter relay lill. Whe-n the apparatus lis rst placed in use, the operator depresses a starting switch M5 which completes a circuit from the power line 55% through a normally close'` stop switch it@ and a normally closed testing switch it? to the line M53, thus energizing a solenoid i653 and moving the switch arm llt* of the starter relay lill against the action of its spring lll, thus closing the switch contact of its relay.

As soon as the relay lill is energized, the starter switch may be released, whereupon the solenoid |65) will remain energized through a line il@ which bypasses the starter relay itl' and leads to a switch Contact llll and thence to the solenoid HSS), Simultaneously with the` closing of the switch arm llt, a switch contact l5 or the starter relay completes a circuit between the power line |55 and the solenoids @63 and its, thus closing the relays 65o and iti. The switch contact |75 is connected to the power line E55 at a point between the stop switch tt and the testing switch 59'. by a line llt and is connected by a line lll with the solenoids' M33 and itil, and they in turn are connected to the power line 358 by lines Il'Si. Thus both relays li and Edt are energized t ereby starting the operation of the roll mechanism.

To protect the ammeters 2li and 25, under the abnormally high starting load, the starting relay |87 is provided with a pair of switch members |80 and 53E which are connected by lines lili. and E33 respectively across the lines its and l5! of their respective amineters, thus providing a shunt for the starting c ent and relieving the ammeters of the heavy starting load.

After the roll driving motor units it and lli reach their normal driving operating speed, the operator depresses the button of the test switch |81, thereby opening the circuit to the line i173 and releasing the solenoid lila and opening and starting relay i8?. This places the ammeters in the circuit of the motors l5 and iii, which are held in operation by a switch member ist of the relay IEEE. This switch member is connected by a line E85 with the power line and by a line 86 with the solenoids ltd and iti, thereby holding both relays |58 and la'l closed despite the opening of the switch lill. This placing of the ammeters directly in the series with their respective motors provides a visible indication to the operator to enable him to adjust the speed reducer unit to synchronize the peripheral speed of the rollers 2 and ifi.

When it is desired to stop the machine, it is only necessary to depress the stop switch E65, thus opening the power circuit ld, whereupon the relays iEll and |'.i| will both be released, permitting their springs to return them to an open position. A pressure switch is likewise provided to stop the opera-tion of motor lill) should the fluid pressure driving the reciprocating mechanism at any time fail. This switch mechanism is best shown in Fig. 5 and comprises a pressure cylinder is@ which is in series with the pressure line 84 and is provided with a piston i9 l. |-Ehe arrangement is such that should at any tin e the pressure in the line 84 drop below a predetermined amount, the spring indicated at E92 will open a switch |95 which is in series with the. power line |55 leading to the d stop switch as shown .in electrical diagram in Fig. 6. l

An important advantage of the present invention is the 'ia-ct that l have provided a method for indicating the relative peripheral speeds of the polishing rolls, and for quickly adjusting the speeds to maintain synchronization, regardless of the relative sizes of the rolls. Thus, the wear on rolls is materially reduced and the degree of pressure desired on the work is readily controlled.

claim:

i. A polishing apparatus comprising a polishing roll, a work holder mechanism, means for recurrently moving the work-holder toward and from the polishing roll to move a workpiece across the face of the roll, a iluid pressure system for actuating said mechanism, a control valve in said system, said valve being movable to release lthe :fluid pressure to thereby interrupt the operation thv echanism, means operable during the movein nt of said mechanism for intermittently advancing said control valve toward the releasing r sition, and means for adjusting the distance oi ovemcnt for control valve to become operative whereby the number of passes or" the work across the face of the roll may be controlled.

2. ./l polishing apparatus comprising a pair of polishing rolls, a workholder mechanism for refrently moving the workholder toward and from the bite of the polishing rolls to move a workpiece through the bite of said rolls, a fluid pressure system for actuating said mechanism, a control valve in said system, said valve being movable to release the iiuid pressure thereby to interrupt the operation of said mechanism, means operable during the movement of said mechanism ior inittently advancing the control valve tothe releasing position, and means for controlling the iiow of iluid in the system, whereby the rate oi movement of the workpiecebetween the bite of the polishing rolls may be controlled.

A polishing apparatus comprising a polishroll, a workholder mechanism for recurrently reciprocating the workholder toward and from the roll to move a workpiece across the face of roll, a uid pressure system for actuating said mechanism, said system including a hydraulic cylinder, piston in said cylinder and connected to actuate said mechanism, a source of uid pressure, a valve in said system to alternately connect end of said cylinder with the source of fluid pressure and to exhaust the opposite end thereof,

controlled by the movement of said mechanism for actuating said valve, independent valves in said system for adjustably controlling the of flow of the exhausting iluid from each end. ci `said cylinder to thereby independently control the rate of movement of the workholder in each oi its reciprocating directions, and a pressure release valve in such system operable conseq ent upon a predetermined number of reciprocaticns of said mechanism to release the pressure supply said system.

fi. il polishing apparatus comprising a pair of oacting polishing rolls, a workholder mechanism or recurrently moving the workholdertoward .nd fr .m the bite oi the polishing rolls to move a wor! ece across the coacting faces of the rolls, a duid pressure system for actuating said mechanii i, a control valve in said system, said valve being movable to release the nuid pressure to the interrupt the operation of the mechanism, ratchet means operable by said mechanism for intermittently advancing said control valve toward the releasing position, and means for adjusting the distance of movement for said ratchet to become operative to move the rvalve to a releasing position, whereby the number of passes of the work across the face of the roll may be controlled.

5. A polis-hing apparatus comprising a pair of coacting polishing rolls, a workholder mechanism for recurrently reciprocating the workholder toward and. from the bite of said rolls to move a workpiece across the coacting faces of the rolls, a fluid pressure system actuating said mechanism, including a hydraulic cylinder and piston, said piston being connected to actua'te said mechanism, a source of fluid pressure, a valve in said system to alternatively connect each end of said cylinder with the pressure supply and exhaust the opposite end thereof, means controlled by the movement of said mechanism for actuating said valve, independent manually operable valves in said system for adjustably controlling the rate of flow of the exhausting fluid from the ends of said cylinder to thereby independently control the rate of movement of the workholder in each of its reciprocating directions, a pressure release valve in such system operable consequent upon a predetermined number of reeiprocations of said mechanism to release the pressure supply in said system and means for manually determining the number of reciprocations to be made before the release valve becomes active.

5. A polishing apparatus comprising a pair of polishing rolls, an operating member, a workholder, a pair of parallel links pivotally interconnected between said member and said work holder, a fluid pressure system for moving the operating member to cause the movement of the workholder to and from the bite of said rolls to move a workpiece between the coacting faces of the rolls, independent motors for driving said rolls, means for swinging the parallel links about their pivotal connection with the operating member to move the workholder in a direction substantially parallel to the axes of the rolls, whereby a vibratory movement is imparted of the workholder in a direction transverse to the direction of reciprocation of the workholder, and an independent motor for actuating said last-named means.

7. In a polishing machine, a frame having a table, a pair of coacting polishing rolls suspended beneath the table with their axes in a substantially horizontal plane, a guide mounted on said table, a slide on said guide, a hydraulic ram connected to said slide to reciprocate the slide in a vertical direction on the column, a workholder connected to said slide whereby the reciprocation of the slide may pass the work between the bite of said rolls, means to align the rolls with the workholder, means to move the workholder in a direction substantially parallel with the aXes of the rolls, a fluid pressure system for reciprocating said slide, said system including a pressure release valve, means actuated by the movement of said slide to move the release valve to a pressure releasing position consequentfupon a predetermined number of passes of said work between the polishing rolls, and means in said system to control the rate of flow of fluid to thereby control the rate of speed of said reciprocating movement.

8. In a polishing machine, a frame having a table, a pair of coacting polishing rolls suspended beneath the table with their axes in a substantially horizontal plane, a vertically extending column mounted on said table, a slide on said column, a hydraulic ram connected to reciprocate the slide in a vertical direction on the column, a pair of links connected to said slide, a wcrkholder pivotally connected to the lower ends of said links, whereby the reciprocation of 'the slide may pass the work between the bite of said rolls, means acting on one of said links to vibrate the workholder in a direction substantially parallel with the axes of the rolls, a fluid pressure system for reciprocating said slide and including a pressure release valve, mechanism actuated by the movement of said slide and coacting with said release valve to move the release valve to -a pressure releasing position consequent upon a predetermined number of passes of said work between the polishing rolls, means in said system to control' the flow of fluid to thereby control the rate of speed of such rolls of said reciprocating movement, and a pair of motors drivingly connected to respective rolls to drive the rolls.

9. In a polishing mechanism, a pair of polishing rolls, a workholder arranged and adapted to feed work into the bite of said polishing rolls, a lconstant speed electric motor for each roll, said motors being substantially identical electrically, a manually operable variable speed driving unit interposed between each motor and its respective roll, an electric circuit for controlling the operation of each of said motors, each circuit including an ammeter, a starting switch for initiating said circuits, means associated with said starting switch to cause said ammeters to be shunted out of the motor circuits, a second switch connected to release said shunt and render both ammeters active for causing both motors to cease to function in the event of failure of the electrical circuit for either motor.

10. The method of maintaining identical surface speeds of a pair of coacting polishing rolls of a polishing apparatus, each of which rolls is rotated by an independent electric motor, said motors being substantially identical and operated at substantially the same constant speeds comprising measuring the electrical load on each motor and varying the speed of the rolls to maintain substantially identical flow of current through the motors.

11. The method of maintaining identical surface speeds of a pair of coacting polishing rolls in a polishing machine each of which rolls is rotated by an independent electric motor which is connected to the rolls by a variable speed power transmission device, said motors being substantially identical and operated at substantially the same constant speeds comprising measuring ,the

electrical load on each motor and varying the speed ratio of the power transmission device of one of lthe rolls until the current flow through both motors is identical.

HERBERT T. NICHOLAS.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date `77,646 Norton May 5, 1865 534,394 Johnston Feb. 19, 1895 1,168,858 Coleman Jan. 18, 1916 2,095,501 Johnson Oct. l2, 1937 2,114,349 Johnson Apr. 19, 1938 2,171,799 Kline Sept. 5, 1939 2,338,599 Ridgway Jan. 4, 1944