US2358572A

US2358572A - Grinding apparatus

Info

Publication number: US2358572A
Application number: US472696A
Authority: US
Inventors: Alfred E Hamilton
Original assignee: Individual
Current assignee: Individual
Priority date: 1943-01-18
Filing date: 1943-01-18
Publication date: 1944-09-19
Anticipated expiration: 1961-09-19

Description

Sept. 19, 1944. A. E. HAMILTON GRINDING APPARATUS Filed Jan. 18, 1943 9 Sheets-Sheet l Sept. 19, 1944.- A. E. HAMILTON GRINDING APPARATUS Filed Jan. 18, 1943 9 Sheets-Sheet 2 Sept. 19, 1944. A. E. HAMILTON GRINDING APPARATUS 9 Sheets-Sheet 3 Filed Jan. 18, 1 943 INVENTOR B a L M M M: pm n 7k Sept. 19, 1944. A. E. HAMILTON GRINDING APPARATUS Filed Jan. 18, 1943 9 Sheets-Sheet 4 INVE [\ITOR Sept; 1944. a HAMILTON 2,358,572

GRINDING AP PARATUS Fi-led Jan. 18, 1943 9 Sheets-Sheet 5 .52 I I I v KNVEN QB I 9 sheets sheet 6 Filed Jan. 18. 1943 IHVENTQ W Sept. 19, 1944. HAMILTON 2,358,572 GRINDING APPARATUS Filed Jan. 18, 1943 v 9 Sheets-Sheet 7 I I L I III ululllnllulh N u lll l hunngllllnlhfll ril llll uJ IIII I ill .lllll w IIIL IIIPLL.

Sept. 19, 1944.

A. E. HAMILTON GRINDING APPARATUS Filed Jan. 18 1943 9 sheets-sheet 8 P A. E. HAMILTON GRINDING APPARATUS Filed Jan. 18, 1943 9 Sheets-Sheet 9 Patented Sept. 19, 1944 UNITED STATES PATENT OFFICE GRINDING APPARATUS Alfred E. Hamilton, Pittsburgh, Pa.

Application January 18, 1943, Serial No. 472,696 10 Claims. (01. 51 40) My invention relates to apparatus for the surfacing of materials of various kinds, such as strips or sheets of steel, transparent plastic sheets, etc., by grinding and polishing.

Oneobject of my invention is to provide grinding and polishing apparatus comprising surfacing rolls and an improved mechanism for supporting them and moving them into and out of engagement with the materials to be surfaced.

Another object is to provide an improved arrangement of work-feeding apparatu in conjunction with surfacing rolls.

Another object of my invention is to provide an improved manner for initially shaping surfacing rolls to accurate cylindrical contour and. to thereafter grind them, as occasion may arise.

Still another object of my invention is to provide an improved arrangement of splash guards for rolls that are mounted for swinging movement to and from operative position.

A further object is to provide an improved arrangement of surfacing roll element and an improved means for assembling them in detachably connected relation.

Figure 1 is a side view of apparatus embodying my invention; Fig. 2 is a rear end view thereof, looking in the direction of the arrows III-II of Fig, 1; Fig. 3 is a plan view of a portion of the apparatus of Figs. 1 and 2; Fig. 4 is a perspective view schematically showing the arrangement of .certain of the parts of the apparatus, including mean for adjusting the surfacing rolls; Fig. 5 is an end view of a portion of the apparatus of Fig. 4; Fig. 6 is an end view of the feed rolls at the.

entrance end of the machine shown in Fig. 1, with certain parts added thereto; Fig. '7 is'a sectional plan view of the structure of Fig. 6; Fig. 8 is'an enlarged view of a portion of the structure of Fig.

' 1, showing the mannerin which the water-spray Fig. 13 is an inverted plan view of a portion of.

the structure of Fig. Fig. 14 is a projected view showing one of the abrasive strips that are wound on the drum; Fig. 15 is a face view of one of the drums showing the abrasive strip helically wound thereon; Fig. 16 is an enlarged sectional view showing the manner in which an abrasive strip is wound thereon, and Fig. 17 is a fragmentary view, partly in longitudinal section, showing the manner in which air i supplied to the surfacing 5 rolls and maintained therein at a desired pressure.

The apparatus is adapted for the surfacing of sheets or strips indicated by the numeral 2, and

comprising a stationary base or foundation 3 .that fixedly supports upstanding frame members 10 4 and 5 at the rear or delivery side of the machine and an intermediate frame member 6 that serves as a slideway for a reciprocable base' member I that carries

surfacing rolls

8 and 9 that are I journaled in arms I0 and II respectively, that are 15 supported by rods l2 and I3, on upstanding bracket members l5 (Fig. 2) which are mounted on the slidable base member I.

The uprights 4 and 5 at the rear end of the machine (Fig. 1) have arms 11 formed thereon 20 that serve as supports for bearing housings I8 and I9 for pair of pinch rollers 2fl--2I and 22.23 V respectively, that are employed in feeding the sheets 2 through the machine.

The base member 1 carries bracket members 24 -25 that support cross-beams 25 and 26 upon which are adjustably supported

bases

21 and 28 for

motors

29 and 30 respectively. Threaded adjusting rods or screws 32 are rotatably supported in the beams 2526, and have threaded engagement 30 with lugs 33 projecting. downwardly from the

bases

21 and 28, this adjustment being provided for shifting the motors, to tension thebelt drives,

to be hereinafter explained.

At the front end of the machine (Figs. 1 and. 6) 35 a slideway '35 is secured to the stationary base 3, for supporting a slide member 36. This member 36 has depending lugs 31 through which an adjusting screw 38 extends and has threaded ensr. gagement. The screw 38 is journaled on the slide- 40 way 35 and is provided with a hand wheel 39 by which'it may be rotated to shift the slide 36 forwardly and rearwardly with respect to the surfacing rolls 89. The member 36 has upstanding bracket elements 4| at its ends that carry

guides

42 and 43 for pairs of pinch rollers 44-45 and 464| that are employed to advance the sheets to the surfacing rolls 89. The bearings for the

lower feed rolls

45 and 51 are normally fixed in their

brackets

42 and 43 respectively, but the bearings for the upper roll 44 and are vertically movable in their

guides

42 and 43 and are yieldably urged downwardly by.

springs

48 and 49 respectively at each end. These springs at their upper end have engagement with through a portion of one of the surfacing drums, 5 blocks 50 and 5| respectively which have thrust engagement with adjusting

screws

52 and 53 respectively, that have threaded engagement with the guides 42-43, so that when the screws are turned in one direction, the spring-seating blocks 50 and 5I will be forced downwardly to compress 5 the springs and thus cause the upper rolls 44-46 to bear more tightly on the sheets 2 or on the lower rolls 45-41.

The tension on the

pinch rolls

20 and 22 heretofore referred to, is adjusted in like manner, by

their tensioning screws 55 and 56ithat correspond? to the screws Hand '53. f r

The slidable base I is oscillated or reciprocated transversely of the path of the sheets 2 to effect"! reciprocations of the

surfacing rolls

8 and 9, and

work of. the machine: and: at its upper end has a 25 link connection at 59: with the reciprocabl'e slide' J I thatcarries the surfacing rolls 8 -9,; so that as the lever is-' oscillated oniitsshaft. 60;- the slide member and the surfacingrons: will be 'reci'j rocated transversely: of the path of T travel of the sheets: A link'liiI (Fig; 27-- thatlfuncti'ons as a-n eccentric rodis connected to thelowerend of the" lever 58 "and' h'as eccentric corn'ie'c'tion at 8 2 w-ith a' driving wheel or disc '63 which is 'driven from a motor 64, through a Rieeves drive B4a, aldrivingi.

belt fi 5," bevel gearing at 68 and wormgearing at{ 66a. As "the eccentric disc 63 rotate the SI will be reciprocated and-thuseifect reciproca tions of the surfacing rolls as heretofore explained; together with the" motors 29' and 30 40 which are carried by the basef 1.5. Thisreciproca tion Will 'eXtendover -a;range' of only a:few inch'es.-

Thelnotor 64' is mou ted 011 3 13945961 thats'at 88 is pivotally supported upon a bracketB'SE adjusting "screw I'I is rotatablysupport'ed by the bracket 69 and has threaded engagement with the base 61 ofthe motor-,to raise and lower itg so th'at as the screw is rotatedj the' 'Reeves drive 'will be Variedto chail ie the speed of the d-i'sc" 63 The motor 2 S 'through a belt drive 13 drives a 0 Pulley 14 that issecurd to; the shaft which carriesfi the-r0119, whilethe motor39; through a belt":- drive 15 clriV'es-a' pulley 16 thatis securedtotne shaft that carries the surfacirf'g roll fi" The roll-supporting arr'nfs II! that are pi votally suppo'rted'upon the rod I 2 and; the roll-supporting arn'is' I I-that are'pivotally supported 'th'e rod I3 arerespectively adjustable aboutithe axesof said rods for the pu'i'pose of varyiiig the pres-'- sure whichthey exert upon the sheets to be sur- 5o faced, and to adjust-the roll pass to sheets of" variousthicknesses. To thisend-1inks T8? are connected to the innerends of the arms I01 an'd links 19 to'the'innerendsof the arms II. Leversthese leversare rigidly secured to a shaft 82; that is carried by upstanding brackets on the slidablev base I. v

A-worm' gear 84 is secured to the shaft 82- and is retatably adjusted by aworin- 85' that is--journale'd in a housing 8'6Ewhich secured to'a disclike or wheel member 8 'I"thatis loosely supported on'the shaft 82 butha-s latched engagementat 88" with a bracket-like cit-tension 89 on the slide T.

For ordinary adjustments of surfacinggten'sion Since this feature. does-' or for variation in roll pass spacing, the worm will be rotated by its hand-wheel 98 to effect shifting of the links I8 and I9 to rock the arms I9 and II, thus moving the rolls 89 closer together or farther apart as the case may be. Where quick separation of the surfacing rolls is required, the latch at 88 may be tripped and the Wheel 81 swung, thereby rotating the worm gear 84 more quickly than it could be turned through rotation of the worm 85.

The-,pincharollssor feed rolls heretofore referred to. aredriven (Figs. 1 and 2) by a motor 9| through a belt 92, the motor being mounted upon a shiftable base 93, which is adjusted by a hand. screw 94 to change the'reduction rate of the Reeves "pulley 91a. The belt 92, through a pulley 95 and suitable reduction gearing in a gear case 96 drives a sprocket chain 91 that passes around a sprocket wheel 98- (Fig. 3) on the shaft 99 which carries-the pinch roll 2|. The upper pinch roll 28 that cooperates with the roll 2| is idlingly driverrethroughits contact with the lower'pinch roll 'orwith:the sheets; The shaft 99 also carries asprockettwheel 'll!Ifiaround which achain I02 passes for transmission of driving force to a sprocket-iwheel103 that is mounted on a shaft: I04, thatacarries 'the loweripinch roll 23'. The shaft IE4: carries: a second sprocketI05 for a drive chain lflfilthatdrivesla sprocket: wheel IOI' on a shaft NIB-that carries the lower pinchroll 41 A second" sprocket wheel= I89? on the shaft I08 drives a'sprocket chain IIOthat passes around a sprocket wheel III onthe shaft which carriesthe remaininglower pinchrol'." The four lower pinch 'ro1ls 2 I, 23, 4 1 and 45': are therefore all' driven from'the motor 9 I;

By provid'in'g'adjustment for the base member 36ithatsupports the pinch rolls at. the entrance endiofithe=machinegthey can be shifted to a position close to the-surfacing rolls, so as to properly feed sheets into the roll pass, and can be withdrawn from-the-roll's a-suflicient distance so as notitosconstitutean obstruction to easy access to theroll'sfor the purposeof changingthem or for applying fresh abrasive material to the rolls, as: hereinafter explained.

hil 'ig. 5Ishow a means-forpreventing chat teririg-of the surfacing rolls

ordrums

8 and 9; while= surfacing-a sheet or strip. To this end, nuts IJI4: that have'swivel mounting on the arms I I' atieachside of the machine have threaded engagementwith: screws H5 that extend loosely through-guides I I6 that have swivel mounting on the arms I81 The screws II5 each carries a nut IIl'thatlservesasaseat fora spring I I8. The upper en'd of the spring seats against the guide H6; so that'whenthe rolls8i and 9 are swung towa'rd one another through operation 0f the wormlgearin'g 84-'85', the springs I I8'wil1' be compressed, thus providing tension that will prevent vibration: orchattering of'the rolls 89 during a surfacing operation; Thetension of the springs can be adjusted by turnin'g the screws H5 in the nuts I14, or by. adjusting their nuts I I1.

Referring now to Figs. 6 and '7', I show means whereby-'the ro-

lls or'drums

8 and 9 can be ground or surfa'ced to 'true cylindrical form, particularly where pneumatic drums of rubber or the like are employed, it being understood, however, that the apparatus could be employed in truing up solid surfacing drums. It is difficult to make rubber drums ofexactly cylindrical contour, owing to the elastic or yieldable nature of the material. Again, after a drum has been in use for some time, certain'portions thereof may stretch slightly or it may become somewhat out of round through other causes. The apparatus of Figs. .6 and '7 serves as a convenient means for either ,truing the drums when first installed in the machine, or for restoring them to cylindrical contour after they have been in use.

A bracket member I20 is secured to the front of the stand for the feed rolls 44 to 41, this bracket member having a dove tail formed thereon to slidably support a block or carrier I2I that carries a bracket I22 in which an abrasive roll I23 is journaled. A screw I24 is journaled'in the bracket I20 and has threaded engagement with the carrier I2I, so that when the screw I24 is turned, the roll I23 will be shifted along the faces of the rolls8 and 9. The bracket I22 is slidable in vertical guideways in the carrier I2I and has threaded engagement with a screw I25 that is journaled in the carrier I2I, so that when the screw I25 is turned, the abrasive roll I23 will be raised and lowered, to surface the roll 8 or the roll 9. The abrasive roll I23 can be frictionally held in its bearings, so that it will not rotate freely when in contact with the surfacing rolls and will, therefore, grind away protuberant areas on the surfacing rolls, or it could be rotated in a suitable manner counter to the direction of the rotation of the surfacing rolls. During such a grinding operation, the screw I24 will be operated to move the roll I23 along the faces of the surfacing rolls. The slidable mounting of the feed roll support 4| permits it to be moved away from the surfacing rolls far enough to allow convenient placing and removing of the grinding roll bracket I20.

In Figs. 8 and 9, I show the manner in which spray shield members I21-I28 and I29I30 are mounted. These spray shields are for the purpose of confining loose grit and water spray, the spray being applied adjacent to the grinding zone, to prevent overheating of the surfacing rolls. The spray shield section I21 has arms I3I welded or riveted thereto, and these are secured I by bolts or to the roll-supporting arms screws, at I32. The shield section I21 also has arms I33 secured thereto, which are bolted or screwed to the lower side of the arms I0. Similarly, the shield section I29 is provided with arms I34 and I35 that are secured to the upper and lower sides respectively of the arms I I.

An angle bar I36 is disposed beneath the rock shaft I2 that carries the roll-supporting arms I0, and at each end carries arms I31 and I38. At their outer ends, the arms I31 are connected to the shield section I 28 by bolts I39 that extend through the end wall of the shield and have threaded engagement with nuts I 46 that are welded to the inner sides of the shield end walls. Similarly, the outer ends of the arms I38 are connected to the lower-portion of the shield I28 by bolts or screws. I4I. When these bolts I39 and MI are removed, the shield section I28 may be 7 taken off, or it can be tilted backinto the shield section I21.

An angle bar I42 is placed above the rock shaft I3 which carries the roll-supporting arms II,

and such bar I42 carries arms I43 at its ends,

or bolts I44 will permit the shield section I30 to be removed or to be swung back into the shield section I29.

The shield sections I21 and I29 have inturned flanges at I41 and I48 respectively, to form a groove into which the inner edges of the shield sections I28 and I respectively extend. The shield section I21 has lugs I50 welded thereto in position to rest on the shaft I2 and thereby support the shield section against sagging,

A scraper or deflector element I52 is pivotally supported between the arms I38 and is angularly disposed crosswise of the sheet 2, :below a deflector plate I5I for the water and grit, to serve as a scraper or deflector bar, and thus deflect from the sheet 2 the grit and water that are carried to the forward part ofthe shield by the surfacing roll 8. Detritus is thus prevented from entering the surfacing roll pass. A spring I53 yieldably holds the scraper bar I 52 against the sheet.

The shield section I29 has a trough-like portion I54 to receive detritus from the lower surfacing roll 9, the shield being open at one end of the trough I53 for convenient disposal of the detritus.

Spray pipes I55 and I56 are positioned alongside the shafts I2 and I3 and have water spray openings discharging through holes I51 and I58 in the shield sections I21 and I29'respectively, to direct water against the rolls and the sheet, at the roll pass.

Clips I60 carried by the bars I36 and I 42 are firmly held against the shafts I2 and I 3. When such shafts are turned during rocking of the arms I0 and II in opposite directions to separate the rolls, the upper and lower shields will also be moved away from one another.

Guide bars I 6I are secured to the arms I38 and I43 by screws, to prevent the strips or sheets being bulged or buckled between the surfacing rolls and the pinch rolls 2223, as explained in my application Serial No. 461,121, filed Oct. 7, 1942.

In Figs. 10 to 16 I show details of one ofthe surfacing rolls of the other figures, it being usual to have both the upper and lower rolls of the same form. A roll shaft I62 has rigidly mounted thereon a metal hub: I63 that carries a pneumatic drum I64 of rubber or other suitable material, air pressure being supplied to the annular space I65 within the drum, through a pipe I66, as hereinafter explained. An abrasive strip I61 is helically wound upon the drum I64, This strip may be of waterproof sandpaper, emery cloth or the like. The ends of the strip I61 are tapered as at I68, so that the end turns thereof will overlie a flange I69 that is formed on the hub, without projecting beyond the flange. The turns of the strip have an overlapping area at HI, and the outer wall of the drum I 64 is helically grooved or depressed to accommodate the double thick ness of strip at I1I, thereby providing for a substantially smooth and continuous abrading surface.

The ends of the strip I61 are detachably secured to the annular flanges I69 at'the ends of the hubs by metal straps or hoops I12. The tapered ends I68 of the strips are wrapped around the flanges I69 and the straps I12 placed over the same. The flange I69 is broken and has inturne ends at I13 between which a portion of the strap is passed and extends around the shaft I 62. and through a yoke I14. A pin I15 extends through the legs of the yoke for supporting an eyebolt I16 that extends loosely through a bracket member I11 which is screwed to the end of the hub I63. Nuts I18 are provided onthe bolt I16, so that the yokes I14 can be drawn to-' wardthe bracket members I to tighten the st aps, I12 .on', the endsfof the abrasive strips and thus maintain the abrasive strip's firmlyinplace during surfacing operations. An extension arm I 'I9 carried by the bracket lllsurrounds the shaft I62 andfserves as a brace to resistradial thrusts en the bracket member I", when'the' nuts are turned to tighten thestrap I'I2. Cliplike elements I8Iare'welded to the edge of. the

strap I12 and are provided with elongated holes; I82 through'which screws I83 extend, the inner while theelongated holes allow the necessary slight circumferential movement or sliding ofthe strap I12 during 'thetightening thereof.

Referring now to Fig. 17, I show a manner in which air pressure is maintained within the drums I64 so that they will have sufficiently snug fit with their hubs to maintain them against turning on the hubs under grinding friction, and to maintain the helically-wound abrasive strips taut thereon. Also, the pressure can be controllably varied to suit various grinding conditions. For example, 'a high pressure will be employed when an intense surfacing action is required on a strip or sheet, and lower pressures for lighter grinding or surfacing operations. The pressure in the rolls may suitably vary from lbs. to 20 lbs. per square inch, depending upon the grain size or, nature of the working being operated upon. I The roll shafts I62 and I62a each has a passageway formed therein that communicates with one of the pipes I66, the said pipes, of course, rotating with the shafts. On the shaft I62, stuffing boxes I85 are mounted to seal a header sleeve I 86 in which the shaft rotates. A hose or pipe I81 communicates through the sleeve I85 with the passageway inthe shaft I62. A swivel joint I 88is provided at one end of the shaft I62a so that air flow can be maintained to the passageway in said shaft from a pipe I 89, while the shaft is rotating.

A reservoirv I90 is supplied with air under pressurethrough a pipe I91, from a suitable compresso (not shown). When it is desired t at the pressures in the rolls be identical, air issupplied from the reservoir I90v past a pressurereducing valve I92 and through a pipe I93 to the upper drum, while such supply will be through a pipe I94 to the lower drum, If pressures of different degrees are required in the upper and lower drums, a valve I95 in the line I94-will be closed, and a valve I96, in a line I91 will be opened. Thereupon pressure to the lower drum will be through. a pressure-reducing valve I98 and through pipes I97 and I89, to the lower shaft H5211. I

The pressure-reducing valves may be of any conventional form and can be adjusted by their handles I98 and I99, to automatically effect supply of air at a desired pressure to the drums, which pressure will ordinarily be somewhat less than the pressure in the reservoir I90. In order to prevent an excess of pressure being developed in the drums, as a result of heat through grinding friction or increase of atmospheric temperatures, I, provide pressure relief valves 2IlI and 292 that are adjustable to permit exhaust of air fromthe drums at pressures above that at which the air is being supplied past the regulator valves I92 and I99. These valves 20I 202 may be of conventionalform and. adjustments are'made therein by turningtheir adjustingscrews 2l l3 a nd a heli'cally-wound abrasive strips I 61 will be maintained in proper position upon the drums. Some strips will be wider than other strips that, may

be used onthe 'drums and will, therefore, be

wound on a different helical pitch than narrower ,,;strips.' Again, some strips will have greater stretch under the expansive force of the air than otherstrips, and. this stretching tendency will vary", with the helical pitch at which astrip is wound on the drum. The pneumatic pressure ,must, ofcourse, be sufiicient to prevent displacement of the strip on the drum during grinding operation and must, nevertheless, not be so'great as to rupture the strip. Reinforcing cords of fabric 5 are preferably providedin the rubber drums to control the expansion'thereof and to A assist in maintaining the cylindrical contour of the'drum.

I claim as my invention: 1. Grinding apparatus comprising a, pair of surfacing rolls positioned to engage opposite faces of a sheet, pivotally mounted arms supporting the rolls, a rock shaft, link connections between" the said arms and the rock shaft, so arranged that upon oscillation of the shaft the rolls will bemoved toward and away from one another,

a spring yieldably resisting movement of the rolls toward one another, and means movable to oscillate the rock shaft, and serving to maintain the rock shaft at anyposition to which it has been turned, the said means comprising a worm and worm gear. 2. Grinding apparatus comprising a pair of surfacing rolls positionedto engage opposite faces of a sheet, pivotally mountedarm 'supporting the rolls, a rock'shaft, link connections'b'etween the? said arms and the rock shaft, so arranged that upon oscillation 'of the shaft the rolls will be moved toward and away from one another; means m'ovable' to oscillate'the rock'shaft, and means for 'tensioning the said arms against vibra tory'movements when they are in positionto hold therolls againstasheet. 3. Grinding apparatus comprising a pair of surfacing rolls'positioned to engage opposite faces of a sheet, pivotally mounted-arms supporting the rolls, a rock shaft, link connections between the said. arms and, the rock shaft, so arranged that upon, oscillation of the shaft the rolls will be moved toward and away from one another, means movable to oscillate the rock shaft, and a spring in position to be stressed by said arms when theyare moved toward one another to bring the rolls into engagement with a sheet;

4. Grinding apparatus comprising a'pair of surfacing'rolls positioned to engage oppositeface's of a "sheet, pivotally mounted arms supporting the rolls,'a rock shaft, link connections between 5. Grinding apparatus comprising a pair ofv surfacing rolls positionedto engage'opposite'faces of. a sheet, arms pivotally supported intermediate their ends and carrying the rolls at their outer en s a o k sha t. a i crank ms extendi g in opposite directions, a link connectiqnbetween each crank and the inner end of one of the firstnamed arms, whereby rotative movement of the rock shaft in one direction will bring the rolls toward one another for engagement with a sheet, and rotative movement of the shaft in the opposite direction will efiect separation of the rolls, and a spring yieldably resisting movement of the rolls toward one another.

6. Grinding apparatus comprising a pair of upper and lower surfacing rolls positioned to engage opposite faces of a sheet, a pair of pivotally mounted arms supporting one roll at its ends, a pair of pivotally mounted arms supporting the other roll at its ends, a rock shaft having crank arms extending in opposite directions, the crank arms that extend in one direction being connected with the supporting arms of the one roll and other crank arms being connected to the supporting arms of the other roll, means for rocking the said shaft to move the rolls toward and from one another, and a spring interposed between the roll arms at each end of the rolls, for yieldably resisting movement of the arms toward one another.

7. Grinding apparatus comprising a pair of upper and lower surfacing rolls positioned to engage opposite faces of a sheet, a pair of pivotally mounted arms supporting one roll at its ends, a pair of pivotally mounted arms supporting the other roll at its ends, a rock shaft having crank arms extending in opposite directions, the crank arms that extend in one direction being connected with the supporting arms of the one roll and other crank arms being connected to the supporting arms of the other roll, a worm gear mechanism for oscillating the rock shaft, to move the rolls toward and from one another, and a spring interposed between the roll arms at each end of the rolls, for yieldably resisting movement of the arms toward one another.

8. Grinding apparatus comprising a pair of surfacing rolls positioned to engage orpposite faces of a sheet, pivotally mounted arms supporting the rolls, a rock shaft, link connections between the said arms and the rock shaft, so arranged that upon oscillation of the shaft the rolls will be moved toward and away from one another, a spring yieldably resisting movement of the rolls toward one another, means movable to oscillate the rock shaft and serving to maintain the rock shaft at any position to which it has been turned, the said means comprising a worm and worm gear, and a latch device for releasably retaining the worm gear in position to hold the rolls in cooperative relation with a work piece, whereby upon tripping of the latch, the rolls will automatically be moved to inoperative positions, under the influence of the said spring.

9. Grinding apparatus comprising a pair of surfacing rolls positioned to engage opposite faces of a sheet, pivotally mounted arms supporting the rolls, a rock shaft, link connections between the said arms and the rock shaft, so arranged that upon oscillation of the shaft the rolls will be moved toward and away from one another, means movable to oscillate the rock shaft and serving to maintain the rock shaft at any position to which it has been turned, a spring arranged to yieldably resist movement of the rolls into work-engaging position, and a latch device for releasably holding the rock shaft in position at which the rolls will engage a work piece, whereby upon tripping of the latch, the spring will move the rolls to inoperative position.

10. Grinding apparatus comprising a surfacing roll mounted for engagement with a work piece, means for moving the roll toward and from its operative position, a spring arranged to resist movement of the roll to its operative position, and a latch for retaining the roll in its operative position, whereby upon release of the latch, the roll will be moved by said spring to inoperative position.

ALFRED E. HAMILTON.