US2316582A

US2316582A - Grinding and polishing machine

Info

Publication number: US2316582A
Application number: US338175A
Authority: US
Inventors: Lad L Hercik
Original assignee: HILL ACME CO
Current assignee: HILL ACME CO
Priority date: 1940-05-31
Filing date: 1940-05-31
Publication date: 1943-04-13
Anticipated expiration: 1960-04-13

Description

April 13, 1943. l., L.. HERclK 2,316,582

GRINDING AND POLISHING MACHINE Filed May 3l, 1940 5 Sheets-Sheet l IMHHh "um x Z /fvl/E/vra@ 5V j A@ ma@ 47- Top/VEP.

April 13, 1943. L, HERCIK,

GRINDING AND POLISHING MACHINE jApril 13, 1943. l.. l.. HERclK 2,316,582

GRINDING AND FOLISHING MACHINE Filed May 5l, 1940 5 Sheets-Sheet 3 ---"'m` 40 40 /I' im f ,f'll I 53 60 i 53 1 s 5@ v I VIII/lll .y @6,5 Y @y ATTO/@wry April 13, 1943. L.. L, HERCIKv 2,316,582 GRINDIG AND POLISHING MACHINE Filed May 3l, 1940 5 Sheets-Sheet 4 v A0 #ERC/K 5%# gaf@ A Tyne/ yer GRINDING AND POLISHING MACHINE Filed May 5l, 1940 5 Sheets-Sheet 5 /M/E/v ro/P.' Ao L /ffPc//f Afro/PMD Patented Apr. 13, 1943 Lakewood, ohio, assignpr to The (lleveland, Ohio, a corpo- Lad L. Hercik,

`Hill Acme Company,

ration of Ohio MACHINE Application May 31, 1940, 1SerialNo. 338,175 17 claims. y rotti- 139) This invention relates to ygrinding V,and/,Q1` polishing apparatus of that Ytype in which the abrading element comprises an `endless flexible ybelt coated with suitable abrasive material. AIn

-apparatus'of this type the belt is usually .mounted on a plurality of rolls, one of `therolls being a driving roll for causing the belt to travel and another ofthe rolls being a pressure or YContact roll which serves to Apress the travelling :belt

lagainst the surface of the work to :be treated in the machine. In this type of apparatus,.the Work is usually mounted on a suitable support and :is moved past the contact roll, proper relative ularly well adapted foruse in machines intended for removing scale ,from or for otherwise 'treating surfaces on relatively thin flexible sheets or strips of material. This invention is accordingly illustrated and described in its embodiment in =a machine adapted for grinding and/or polishing Irelatively thin-sheets or strips of steek-stainless steel, Monel metal, zinc, bronze or other metallic or non-metallic materials either in continuous lengths or in sheets.

As is well known to those skilled in thisrart, it has been extremely difficult to manufacture, under production conditions, ground or polished sheets or strips which are uniformly smooth and free from irregularities.

In machines of this character numerous types of supports for the strips or work have been used including many which Yare adapted to move the workvtoward and from an abrasive belt travelling about a fixed roll. I have found, however, that the best results are obtained in a :strip grinding and polishing machine if the strip is subjected to extremely heavy tension while being ground in order that the surface ofthe stripmay be perfectly flat and free from buckles and in order to prevent the sheets from warping vat the point of grinding as a result of which'heat is generated. When this extreme tension vis applied to the strip, `itis not feasible to support `the vbelt on a moving support or to advance the work toward a fixed abrading element due to the resistance to movement caused by the tension in the strip; .and it ismanifestly impossible to thus advance-the Work toward the abrading beltwith the 4degree of sensitiveness required ,to produce satisfactory surfacing. For this reason I have .found 'it Vessential thatthe Work-support'be relatively fixed and firmly supported on abase.

The usev of a fixed'work support in a machine of Vthis character makes it necessary to provide a movementof the 4abrading element toward and from 'the work. `In those cases Where such a construction, `including a movable abrading belt mounted on a pressure or contact roll, has -been "provided in machines of this type, several short- -comings have developed which have detrimentally affected the work.

In these devices, insofar as I am awa-re, the movingof the'contact roll toward and'from the work has -beenaccompanied by an alternate tensioning'and slacking vofthe abrading belt which causes damage-to the belt. Itfwill be apparent for instance that the abrasivebelt being formed of paper and being of a relatively delicate nature, is necessarily ,sensitive to variations of operating conditions in respectto tension, drivingfriction, and thelike. Variations in the tension, that is conditions which introduce alternate slackand stressing of the belt produce distortion, `in the belt -and ynon-uniform Voperating characteristics. "Variations in the tension of the belt also :produce vvariations inthe friction or slippage betweenthe driving -pulley and-the belt which induce unequal heating of thel belt Vand conseguentwarping'and defective operation and eventual failure of thebelt. The running of a slack belt at a high r rate `of speed also causes theibelt to vibrate :or lapwith consequent loosening of the applied abrading material. It will accordingly-appearthat maintenance of uniform tension in anabrasive beltis essential.

In prior .movable 'contact roll types of construction, 4insofar as I am aware, the structure supporting the roll -Which has served'to advance the abrasive belt toward the Work has-been relatively light -a-nd :not rigid and 'hence subject to vibration-producing Ichatter lfinish or otherwise unsatisfactory surface.

Inthese prior movable contactroll machines, also, it has usually not Abeen possible, to control the pressure lof the abrasive -belt sufliciently sensitivelyto-produce-perfect work and to avoid spoilage. This is especially vital in those instances wherevery-neflnish is required or very thinfstrips Aare'to--beitreatedl As is well known an v insufficient pressure of belt against Work, limits :the production `and an 'excessive pressure produces burning, oxidation, objectionable discoloration, and. even damage to the belt.

In most v.previous .machines of ythe type for and/or to produce a uniform thickness of finished sheet. Y

It is accordingly a primary object of this invention to produce a machine of the character described in which the tension on the abrasive belt is maintained substantially constant in all normal operative positions of the belt as the belt is alternatively advanced into grinding engagement with and removed from thework.

It is a further object of this invention to provide a structure for supporting the movable contact roll in a machine of the type described which is of rigid construction and which is rigidly supported to eliminate vibration of the contact roll and abrasive belt during the abrading operation.

Itis a further object of this invention to produce a machine of thistype inwhich the intensity of pressure with which the contact roll engages the abrasive belt with the work, can be quickly and sensitively regulated while the machine is operating.

It is a further object of this invention to devise a contact roll pressing mechanism for a machine of this type in which a failure of the pressure applying medium will automatically cause the contact roll and abrasive belt to be removed from the work.

It is a further object of this invention to produce a machine of this type in which the finished surface will immediately and readily become visible to the operator as soon as the work emerges from the position of grinding engagement with the abrasive belt whereby it is possible for the operator to immediately detect defects in the finished surface and to reverse the movement of the strip and to adjust the machine to correct the defect before the defective area in the surface has extended to or travelled any considerable distance from the abrading belt.

It is a further object of this invention to associate a micrometer adjustment with the contact roll and the supporting frame adapted to accurately set the abrading belt with respect to the work support and which setting is adapted to be varied during the grinding operation and which permits the belt to be instantly removed from the work and instan ly re-set into the identical predetermined position.

It is a further object of this invention to so arrange acountenbalancing of the contact roll and associated mechanism that the unbalanced load is relatively light and so that the pressure required to shift the contact roll from an inoperative position to an operative position is relatively very small and can be sensitively and accurately controlled.

A further understanding of the construction and operation and of the manner in which the novel features of this invention effect the above and other objects, will become apparent from the following detail description and the annexed drawings which set forth certain means embodying this invention, such disclosed means constituting however, but one of the forms in which the principle of this invention may be applied.

Referring to the drawings:

Fig. 1 is a side elevation of a strip grinding and polishing machine embodying this invention, this disclosed machine being adapted for grinding and/or polishing continuous strips, this View of the machine being taken from the operators side of the machine.

Fig. 2 is an elevational view of the grinding end or head end of the machine illustrated in Fig. 1, this view being partly in section, and being taken on the plane indicated by

line

2, 2 in Fig. l.

Fig. 3 is an enlarged View of a portion of Fig. 2 to more clearly illustrate certain details of construction.

Fig. 4 is a'still further enlarged fragmentary sectional view to illustrate details of certain adjusting mechanism, this view being taken on the plane indicated by

line

4, 4 in Fig. 3.

Fig. 5 is a fragmentary transverse sectional view thru the head or grinding end of the machine, this view being drawn to the same scale as Fig. 3, and being taken on the plane indicated by

line

5, 5, in said figure.

Fig. 6 is a fragmentary view showing a portion only of the parts illustrated in Fig. 5, certain of the parts being in slightly altered position.

Fig. 7 is a fragmentary plan sectional View .thru the head end of this machine, this view showing certain upper link control mechanism, being taken on the plane indicated by line l, 1, in Figures 3 and 5.

Fig. 8 is another fragmentary plan sectional view thru the head end of this machine, this View showing certain micrometer head adjusting devices, and being taken on the plane indicated by

line

8, 8 in Figures 3 and 5.

Fig. 9 is another fragmentary plan sectional view thru the head end of this machine, this View showing certain lower link control mechanism and head actuating mechanism and being taken on the plane indicated by

line

9, 9 in Figures 3 and 5.

Fig.l 10 is a fragmentary, detailed view, corresponding generally to Figure 5, but showing a modification.

Fig. 11 is a more or less diagrammatic, fragmentary sectional View corresponding generally to the views shown in Figures 5 and 6 and showing a modified form of head guiding means.

Inasmuch as this invention is unconcerned with the specific character.` of the work-material or of the work-treatingfbelt, the terms abrasive and the like andv wor and the like used herein and in the appended claims are intended broadly to include within their comprehension any and all materials to which the machine which constitutes the invention can `be applied, as will be understood by those skilled in the art.

Strip supporting mechanism Referring first to Figures 1 and 2 of the drawings, the base of the machine is indicated at I, this base being constructed in any suitable manner as by welding or casting. Upon this base is mounted a stand 2 upon the upper end -of which is mounted a rotatable work support suitably guided on 'the base I to permit this horizontal adjustment. The means for adjusting this stand, as will best appear from an inspection of Figures 1, 2, 3, and 5, consist of a pair of anchor blocks 4 securely xed to the base I and formed with threaded bores engaged by screw members rotatably mounted but axially xed in the stand 2 and pr-ovided adjacent the axially fixed end with a helical gear 6. Rotatably mounted in the stand at a position slightly above the screws 5 is an adjusting shaft 'l provided with a pair of helical gears 8 each meshing with and adapted to rotate one vof the helical gears 6.

The adjusting shaft 1, as will appear in Fig. 3, is provided with a 'square end adapted to engage a crank and it will be apparent, Without further explanation, that a rotation vof the shaft 'I will cause the screws 8 to rotate in the bores of the fixed anchors Yand will thus shift the stand on the base I to the right or left as viewed in Fig. 1, depending upon the direction of rotation of the shaft 1.

The billy roll 3 proper is supported on a pair of bearings one `of which is xed and the other of which is preferably vertically adjustable, the xed bearing being indicated at 9 and the vertically adjustable bearin'g being indicated at IIJ. The means for adjusting the bearing I0, consist, as best shown in Figures l and 3, of a pair of vertical screws II each provided with a gear I2, both gears I2 being actuated by a pinion I3 on a vertical shaft I4 provided with a hub I'5 formed with Spanner openings or with any other 'convenient means for rotating the shaft I4. It will be apparent that the bearing Il) may be accurately adjusted in a vertical direction by the adjusting mechanism just described, and 'that by this means the axis of Vthe billy roll may be vertically tilted at any Adesired angle within the limits ofthe adjustment.

Longitudinally spaced from the stand 2 and on each side thereof are a pair of sub-bases I6, Fig. 1, each vsupporting a pair of brackets I'I and each bracket supporting a bearing I8. Suitably supported `in the bearings I8 are shafts I9 which in turn support idler rolls or strip deiiection rolls 20. Each pair of bearings I8 may be vertically `adjusted by means of an adjusting shaft 2I, vassociated-worin and gearmechanism 22 and vertical screws 23 fixed in the bearings as suggested in Fig. 1 and engaged by thethreaded bores of the worm gears of the'mechanism 22.

A strip to be finished in this Imachine is indicated at 24 and passes over the billy roll'3fand under the deflection rolls 2l), as clearly shown.. This strip 24 is usually continuous in Fig. 1. and may be 'of any desired width 'and `is 'frequently known as a Istrip sheet, Vand may be composed 'of steel, stainless steel, 'Monel metal, bronze, zinc or other metallic or non-metallic materials, which are to be ground,`polished, satin nished, buffed, or otherwise treated kon this machine.

The vertical adjustability of the guide rolls 20 provides for the possibility of varying the Aangle with which the strip '24 is deflected -over the billy roll 3. The adjustment longitudinally of the billy roll makes it possible to position the billy roll tosecure the most advantageous grinding engagement of the strip with a certain abrarding element to be hereinafter described.

The strip v24 is advanced over the billy roll 3 and deflection rolls 2l] under a'very high tension in order that the "strip may be perfectly-nat .at the area at .which it is beingiground. 'The devices for feeding Aand :tensioning the :strip .are well "known and, as they form per se ino Apart of thisinventi'on, are not shown. It is to beunder- General features of grinding machine Also mounted on the base I i-s a Amain supporting `frame 25, upon one face of which is mounted a housing 26 serving to support the mechanism for driving, supporting and controlling the abrasivebelt. Also supported on the main frame isa driving sub base 21 which is preferably adjustably mounted on the main frame 25, .this driving sub base being mounted on the `left end Vof the frame 25 as viewed in Fig. l. Mounted on this driving base is a motor and associated abrasive belt driving mechanism. The motor is indicated at 28 and is provided 'with a driving pulley 29 upon which is mounted a driv- .ing belt 30 driving a pulley 3l, mounted on a shaft 32, which is in turn mounted in suitable bearings on the 'base 2l. The drive sub base 2'! including the motor 28, driving pulley 29, driving belt 30, driven pulley 3l, and shaft 32, may be adjusted to the left or right, as viewed in Fig. l.. by adjusting mechanism of any suitable type and which may include a crank handle '33, chain 34, gear box 35, and. screw 36, suggested in Fig. l.

At the vend of the housing -26 opposite tothe drive sub base 2?, that is at the right end, as viewed in Fig. l, is'mounteda vertically movable and generally vertically disposed head frame indicated in its entirety at 31, this head frame and its mounting constituting an important feature v of this invention later vto be described in detail. Abrasive belt mounting VMounted on kthe drive shaft 32 is .a drive roll 38. -Mounted 'upon' the upper portion of the .housing 26 isa guide roll 39. Mounted upon the upper end `of the .head frame 31 is an upper `head roll 40. Likewise mounted adjacent the lower endof the head frame andin fixed spaced relation from the roll v4I) is a contact orvpressure :roll4I, .which roll is preferably formed of relatively resilient material. Mounted upon and adapted to be tensioned, driven and guided by the

rolls

38, 39, 48 and 4I is an abrasive belt 42, usually formed of thin and relatively inelastic paper.

f his'beltrf42 isa flexible endless element coated with abrading or polishing material of agrade and. .nature Vsuitable for producing the ltype of :finish ldesired on the strip 24. The roll 38,\be 'ing positively driven by the motor at a high rate of lspeed and the belt being tensioned to engage the 1o1l38 with sufficient pressure willfrictional- 1y causethe belt to travel rapidly inthe direction indicated rby the arrows in -the several figures. Duefto Lthe highvelocity of rotation of the pulley `38"it 'is important to -note that any appreciable slipping between the face of thepulley and the `belt'woul'dresult in the rapid generation of heat which would seriously warp or damage the rela- :tively thin and relatively delicate paperabrading belt, resulting either in the complete destruction of the'belt orr in the unsatisfactory-operation of-the belt. It should also be noted that these "belts being necessarily relatively 'delicate Lare-not constructed to standexcessivetensioning :As 'will :be understood,` the proper tension can be :imposed upon the belt bymeans of the adjusting vvdevice "comprising .the crank Ahandle 33, chain I 34,

tween the belt and the roll 39. This guide'roll.

39 is so designated because itperforms the function of guiding the travelling abrading belt, that is, correctively controlling the abrading belt to travel in a predetermined path. The guide roll effects its correcting functions by a slight tilting of its axis with relation to the axes of the

other rolls

39, 49 and 4|, which tilting is automatically initiated in response to any excessive deviation from the desired predetermined path of travel of the belt. For this purpose this guide roll 39 vis provided with a suitable shiftable bearing 43,

Fig. 1, which may be initially adjusted to maintain the belt tracking in a predetermined path. This shiftable bearing 43 is further provided with suitable shifting mechanism actuated by suitable control devices generally indicated at 44 and ncluding nozzles 45, producing air jets adapted to impinge against control levers 46, only one of each of which is shown. The control devices 44 are adapted to actuate the shifting mechanism responsive to an undesired deviation of the belt `from a predetermined path, all of which form no part of this invention, but which apparatus is completely disclosed and described in my copending application, Serial No. 337,326 filed May 25, 1940. n

'The upper khead roll 49 is preferably a rigid idler roll flxedly mounted in the head frame 31. The contact or pressure roll 4| is provided with a relatively soft periphery and serves to press the abrasive belt into suitable abrading engagement with the upper surface` of the strip 24 adjacent the billy roll 3 when the head frame is actuated by suitable mechanism to be hereinafter described. All of the

rolls

38, 39, 48 and 4| for supporting and advancing the belt 42 are preferably formed with straight or substantially straight faces'and the axes of these rolls are normally parallel to each other.

Head frame The head frame 31 is preferably formed of light material so framed together as to produce a rigid structure, the structure of this head frame consisting of a rear plate 41, side plates 48, upper transverse plate 49 and lower transverse plate 59. The rear plate 41 is formed with suitable apertures as best illustrated in Figures 3,. 5, 7, 8., and 9, to permit the passage of certain elements to be described or to provide accessibility for certain interior mechanism in the housing of the machine. The side plates 48 extend slightly upwardly and downwardly beyond the rear plate 41 and the

transverse plates

49 and 50 extend between the side plates and serve to rigidly tie the two side plates together. The rear plate 41, as'is best seen in Figures '7, 8, and 9, extends laterally beyond the outer faces of the'side plates forming a projecting lip 5| adapted to serve as a guide for the head as will be explained.

Mounted on the exterior side faces of the side plates 48 adjacent the upper ends are a pair of

bearings

52, 52 of any suitable construction which support a transversely extending shaft 53 upon which the upper head roll 40 is mounted. The

pressure roll 4 .and are further formed with Ahead frame frame may of the lips upper'head roll is of hollow .light rigid construction and is disposed between the side plates 48 and above the upper transverse plate 49, as will vclearly appear from Figures 3 and 5.

Likewise mounted on the exterior side faces of the side plates 48 adjacent the lower ends are av

pair o'f bearings

54, 54 of any suitable construction which support a transversely extending shaft 55 which in turn supports the contact or This contact rolll is disposed between the side plates 48 and below the lower transverse plate 56. This' contact roll 4| is also of a light hollow construction, but its periphery is formed of 'a `relatively resilient material provided for the purpose of producing a yielding en gagement of the abrasive belt against the surface to be ground, When the contact roll presses the abrasivebelt against the strip.

Mounting of the head frame The head frame or head 31 is mounted for vertical and limited horizontal movement with respect to the housing 26. For this purpose certain guiding and supporting'elements are associated with a transverse end plate 56, Figures 3, 5, 7, 8, and 9, forming an integral part of the housing 26 and which may, as illustrated, be a continuation of one of the side plates of the main supporting frame 25. As willy appear especially from Figures 7, 8 and 9, side guides 51 and 58 are fixed to the end plate 56 adjacent the projecting lips 5| on the head 31. 'I'hese guides 51 and 58 are formed with surfaces'adapted to engage the outer edges of the projecting lips 5| flanges 59 and 6D, respectively, extending over the outer face of the lips 5| and projecting toward the head frame. It is to be noted that the lateral fit of the rear plate 41 between the

guides

51, 58 is relatively free so as to insure an absence of binding of the in the housing guides during vertical movement of the head, even tho the head be slightly tilted out of vertical. While the' drawings show the lip 5| in engagement with the fianges 59 and 66 on the side guides, it is to be noted that there is in practice sufficient clearance to permit a free movement 5| with respect to the

guides

51 and 58. As will also appear from Figures '7 to 9, ample space is provided between the

plates

55 and 41 to permit the plate 41 to move rearwardly toward the housing.

As is best' seen in Figures 3, 5, and 7, adjacently below the upper transverse plate 49 and on the inner faces of each of the side plates 48 are secured upper link brackets 6| which jointly support a pivot shaft 62. Oscillatorily mounted on this shaft 62 are a pair of links 63. The other ends of the links 63 are pivotally mounted on a pair of stationary pivot pins 64 supported in brackets 65 xedly secured in vany desired manner to the end plate 56 of the stationary machine housing 26.

As is best seen in Figures 3, 5, and 9, adjacently above the lower transverse plate 50 and on the inner faces of each of the side plates 48 are secured lower link brackets 66 which jointly support a pivot shaft 61 upony which are oscillatorily mounted a pair of links 68. The other ends of the links 68 are pivotally mounted on a pair of stationary pivot pins 69 supported in brackets 10 xedly mounted on the end plate 5S of the stationary housing 26. The `links 63 and 58 are substantially of the same length in the disclosure and the

pivot shafts

62 and 61 and the pivot 62, links 631'and pivot pins 64 arevsuperposed over the shaft 61, links 68 and pivot pins 6'9 respectively.

housing 26. The engagement of the links' upon pivot pins is a the associated pivot shafts and snug but free lit whereby there is no resistance to the free vertical movement of the head frame. During this vertical movement the rear plate 41 by the engagement of its lips with the

guides

51 and 58 is guided to prevent deviation in a direction laterally with respect to the direction` of the belt travel, andr the links 63' and 68 are required` to perform only the function of shiftingthe head frame toward and from the housing, that is, the links may be said to control or guide the movement of the head in the direction-of the belt travel.

Head frame support Secured to the upper face of the lower transverse plate is a bracket 1I provided with a pivot pin 12, upon which is mounted an upwardly and outwardly projecting adjustable link 13,A as is best seen in Figures 3,5, andv 1. The upper. end of this link is pivoted at 14, to a. substantially horizontal bar or lever 15, extending toward the interior of thevhousing 26 thru suitable openings in the rear plate 41 of end plate 56 of the housing. This bar is fixedly secured to the shaft 16 by means of a key, Fig. 9. This shaft in turn is rotatably Ysupported on a pair of spaced pivot brackets 11 which are secured to the inner face of the end plate 56. Also flxedly secure' lever 18 horizontally spaced from `but preferably in the same horizontal plane with the bar 15 and extendingy into the interior of the housing 26. Adjacent the inner end ofthe bar 18 is a counterweight 19V adjustably secured 'to the bar4 by bolts, screws or other convenient means. As will appear from an inspection of Fig. 5, the weight of the head frame 31 acting on the lever 1.3 will tend to move'the composite bar or

lever

13, 18 in a clockwise direction and the counter.- weight 19 tends to move. the composite bar or lever in a counterclockwise direction. In practice the mass of the counterweightis so4 selected and so positioned on the lever 18 that the counterweight overbalances the weight of the head frame and associated parts and the co'unterweight normally moves the head frame into the upper position as shown for instance in Fig. 5, a suitable stop being incorporated in a diaphragm mechanism to be described, to limit the upward travel of the headframe. It is to be noted that the amount of the overbalancing effect of the counterweight is, in practice, relatively small so that a relatively small force is required'to move the head frame downwardly from a position as shown in Fig. 5 to a position in engagement with the strip 24 as shown in Fig. 6. It will thus -be seen that this differential overbalancingeiectof:l

the counterweight constitutes constraining the head frame 31 yielding 1 means the head frame and in Vthel d to the shaft 16 is a second bar orV and associated.

mechanism to move in a direction from the work support 3..

Mounted uponl and pivotally connected to a bracket 88,.y Figures 1 and 5,which is in turn sey cured inany desired manner to a diagonally upwardly sloping wall 8| of the housing 26 is a diaphragm mechanism indicated` at 82. This dian phragm mechanism is preferablypneumatically controlled land may be of any desired standard constructionA and is provided with an upwardly and downwardly moving plunger 83 pivotally connected `to" the' bar 18 ,at 84. The diaphragm mechanism may be actuated by compressed air or other iluidfrom any s 'table source admitted into-the diaphragm casing thru an inlet 85.

Itwill appear from the preceding description and from an inspection of Figures 1 and 5, that the admission of air under pressure into the diaphragm causing the' plunger 83 to move in an up'- wardly direction causes'the head frame 31 to move downwardly from the position shown in Figures 1, 3 and 5, in which the abrasive belt is spaced from the workto a position as shown for instance in Fig. 6 in which the abrasive belt 1. is in grinding engagement withA the work. It willu be apparent that the intensity of pressure with which the belt isv engaged with the face of thev work is proportional to the intensity of pres- Sure'applied tothe diaphragm mechanismV 82. It will also beevident. in View of the fact that the overbalancing. effect ofthe counterweight tending to hold `the headframe in its upper position is slight, and in View of the fact that the area of the diaphragm isy relatively large, the head frame will quickly andsensitively respond to a slight Variationin the intensity of the applied air pressure. As pointed out -in the introduction to this specification, pressure with whichy the abrasive belt can be engaged with the work is limited, if defective work and damage to the abrasive belt is to be avoided. Suitable pressure control devicesnot shown are accordingly'associated with the piping leading to the" inlet` 85iin the diaphragm in order to protect both the belt andthe work against an excessive pressure.

M icro'met'er adjustment and stop for head -Referringto Figures 3, 4, 5 and 8, a pair of brackets 86 are fixedly secured to the rear plate 41 of the head frame,l each bracket being formed with upper and lower spaced bosses 81 andl 88 respectively. The upper boss 81 is formed with a plain cylindrical'bore and the lower boss is also formed with a cylindrical bore in which, however, a keyV 89 is mounted (see Fig. 4;) These

bores

81 and 88 are each adapted to receive a vertically disposed adjusting or stop screw 98 in sliding engagement, this screw being formed with a keyway indicated at 9i in 'Fig 4. Interposedv between eachV pair of

bosses

81 and 88 is a worm-gear 92 whose hub is formed with al screw threaded bore adapted to engage the threads on the. screw 90. These worm gears 92` are operatively engaged by

worms

93 and 94, mounted on shafts 95 and 956 respectively. As clearly shownV inA Figures 3 and- 8, the

shafts

85 and 96 areeach rotatively mounted in formed ony the

brackets

8,6'. (see Figures 4 and 8). The shaft 35 projects thru one of the side plates 48 ofthe head. frame 31 and is provided at its outer end with a crankhandle 98.y As will appear from Figures 3 and. 8, the shafts 95. and 86 are connected gaty their adjacent endsby a coupling `99 secured to each shaft end by means of the maximum allowable iny each bracket ears 91 a pair of set screws which permit accurate angu-A` lar adjustment between the two shafts.

-The stationary brackets 10 upon which theY lower links 63 are pivotally mounted and which are xedly mounted on the stationary housing 26, are each formed with a forwardly and upwardly projecting portion formed at its upper and outer terminal with a seat ||l| serving as an abutment. As will appear from an inspection of Figures 3, 5, and 6, the screws 90 are alined with the abutments |0| and engage the seats HH when the head frame is in the lowered position as indicated in Fig. 6. It will also appear that the screws may be vertically adjusted by the rotation of the

shafts

95 and 96 by means of the handle 98, these shafts rotating the

worms

93 and 94 which in turn rotate the worm gears 92 and these gears serve as rotatingv nuts to cause the rotatably xed screws 90 to move upwardly and downwardly as desired. These stop screws 90 are preferably so adjusted that when they engage the abutments ||l| the abrasive belt mounted about the contact roller is spaced from the upper face of the billy roll a distance slightly less than the thickness of the material to be surfaced. It will be apparent that the amount of material removed by the abrasive belt from the work can be varied by an upward or downward adjustment of these stop screws. It will also be apparent that, in the event that the head frame is repeatedly lifted or lowered, the. stop screws will always serve to position the head frame and hence the lower surface of the abrasive belt into exactly the same position with respect to the billy roll or work support. It will also be apparent that the stop screws may be adjusted while the machine is in operation, that is, while the screws are in contact with the seats |0| and while the contact roll is maintaining the belt in abrasive engagement with the work. This adjustment, while the belt is grinding, is effected by simply turning the crank 98 in that direction which the appearance of the grinding may indicate to be desirable. The adjustable stop screws 90 and the abutments HH, serving to limit the movement of the head frame 31 and housing 26 with respect to each other, may be designated as relatively adjustable abutment and stop means to space the contact roll in a predetermined position with respect to the work support. It will also be apparent that the interengaging abutment and stop means shown serve as a safety feature to prevent serious damage to the billy roll in the event that the operator inadvertently lowers the grinding head or in the event that the strip breaks or Vin the event that the grinding is continued after the end of the strip has passed the grinding station. In any of these events the abrading belt will be held spaced from the billy roll by the stops. f

It will further be understood that this micrometer head adjusting mechanism is adapted to position the axis of the contact roll in exact parallelism with the axis of the billy roll, this being eected by individually adjustng one or the other of stop screws 90 after the coupling 99 has been disconnected from the shaft 95 and then turning the shaft 95 with the crank handle 98 or turning the shaft 96 with the aid of the coupling 99, as may be necessary. If, after this adjustment has been made, the

shafts

95 and 95 are again rmly coupled together, the contact roll 4| will continue to run in parallel relation with the billy roll 3. As will be understood, the lateral play between the lips 5| and the guides 51 amount of differential adjustment between the two stop screws 90. If a greater amount of adjustment is required to position the

rolls

3 and 4| parallel to each other, this can readily be secured by means of the billy roll adjusting mechanism including the screws and related ,elements previously described.

Operation The operation of this improved grinding and polishing machine will readily appear from the preceding description and from the drawings, supplemented by a brief further explanation, in which particular reference will be had to certain novel features not previously pointed out, with reference particularly to Figures l, 2, 3, 5 and 6.

In the first four of these iigures the parts of the machine are shown in a non-operative position or a non-grinding position. In these views it is assumed that the work or strip 24 has been correctly supported on the billy roll 3 and that it has been properly tensioned and that it has been caused to travel in the direction indicated. In these views it is further assumed that the abrasive belt 42 has been properly mounted on the

rolls

38, 39, 40 and 4|, and that the abrasive belt has been correctly tensioned by adjusting the drive roll 38 and that the motor 28 has been started, causing the abrasive belt to travel in the direction indicated'and that the guide roll 39 has been properly angularly tilted with respect to the other rolls to cause the abrasive belt to travel in the desired path. In these figures it is also assumed that the billy roll 3 and the contact roll 4| have been properly relatively adjusted into parallel relation with each other and that the stop screws have been accurately adjusted to properly space the abrading belt from the billy roll to conform to the thickness desired in the finished strip 24. It is also assumed that the counterweight 19 has been properly adjusted to over-counterweight or overbalance the head frame 31 so that the head fra-me is located in its upper position in which the abrasive belt 42 is spaced a substantial distance from the upper surfaceof the strip 24, this distance preferably being approximately 11/2 to 2" but may be more or less, depending on conditions. It is to be noted that the upper position Vof the head frame is determined by the abutting of the lower end of the diaphragm plunger against the lower portion of the diaphragm housing, which abutment stops the downwardY travel of the lever 18 and the overbalancing counterweight 19. It is also to be noted in these views, see Fig. 5, that links E3 and 68 are in a substantially horizontal position and that the head frame 31 and hence the

rolls

40 and 4| are spaced at the maximum distance in a horizontal direction from the housing 26 and from the

rolls

39 and 38 respectively.

All of the elements of this machine housing having been properly adjusted and set in motion, as pointed out, air under pressure is admitted to the diaphragm mechanism 82 from a source of compressed air thru the instrumentality of any suitable pressure regulating and control valve devices (not shown). As will best appear by reference to Figure 5 and 6, the application of air pressure will counteract the slight overbalancing effect of the counterweight 19 and will cause the plunger 83 to move in an upward direction, causing the

levers

18 and 15 to rotate in a clockwise direction.

This clockwise rotation of the lever 15 permits and 58 is not sufcient to permit any great75`the head frame 31 and the rolls 4o' and 4| to rita message ty aie-1ers is move `dowriwar'dly and this the head 'frame will continue until the stopl screws 90 engage the abutments lOl, this lowermostpof, Fig. 6. The head frame s ition being shown in Y will normally be held in this position against the abutments by the air pressure in thevdiaphragm mechanism. As will appear from an inspection of Fig. 6, the contact roll in the -lowermost posi'- tion of the head frame, is pressing the travelling abrasive belt into abrading engagement with the surface of the strip 24. If the grinding action of the abrasive belt in this position isnot satisfactory, the head frame may be adjusted upwardly or downwardly, as may be necessary,l by correspondingly adjusting the stop screws 90, which may be done without disengaging the abrasive belt from the surface. of the strip.

Further inspection of Figures and 6 will show that, in the downward movement of the headr frame, the

links

63 and 68 have been tilted downwardly at their right or outer ends as indicated by the arcuate arrows in said figures. It'will also be evident that this downward tilting of the links vconstrains the head frame and the rolls 4l] and di to move horizontally closer to the housing 26 and closer to the rolls3 and 39, respectively.

lt will readily be understood from reference to Figures 1 and 5, that a vertically downward movement of the control roll 4I would cause an increase in the distance between the centers of this contact roll 4i and the drive roll 38 and that the tension in the abrasive belt 4oz-would be substantially increased unlessl some compensating adjustment were made. vIt will likewise be evident from these same figures that a vertically downward movement of the upper head roll 40 l would likewise increase the distance between the centers of the ro-ll M and the guide roll 39 and that the tension in the abrasive belt l112 would be additionally increased in substantial amount by such verticaldownward movement, unless some compensating adjustment were Amade. Reference to Figures 5 and Y6 will likewise disclose that the downward tilting of the

links

63 and 68 causes the

rolls

40 and 4| to move in a direction to shorten the distance 4between the

rolls

40 and 38 and il and 39, respectively, and thatl this link mechanism thus affords such a counteracting adjustment in the spacing of the rolls asis necessary to maintain the tension in the abrasive belt constant.

It will also now of the links are suitably chosen and if the links aresuitably positioned in reference to the location of the several rolls, the correctivemovement of the links can be so arranged that it will cause the rolls 49 and M to travel in a path in `which the rolls neither tend to increase or shorten the lineal length of the belt and in whichthe tension in the belt remains constant for all positions of the rolls Ml and 4l withinthe limits set. 1

It will also be apparent that inthe reversal of the above movement of the rolls 40 and itl, that is in av movement from the grinding position tov the non-grinding or idling position of the abrasive belt, a similar result will obtain. In this circumstance a perfectly vertical `movement of the head frame would introduce slack into the abrasive belt but the corrective arcuate shiftingof the head pulleys in a direction away from the housing, supplied by the

links

63 and 63 as the head frame moves up, serves to take up the slack inthebelt. j .i It will. lbe. seen .that the', corrective y,compensae, progressive and downward motion ofv be evident matti me lengthsV automatic as 'lthe'head 'rolls 4I and 40 are moved bythe diaphragm means.

B'y the use of this principle just explained, I have yconstructed machines oiy substantially the proportions shown in the drawings, in which the lineal length of a peripheral line engaging portions of the outer peripheries of the rolls and passing from roll to roll as docs the abrasive belt,does not vary more than three one hundredths of one per cent at any position during a movement of 2" of the rolls lll and 40, toward and from the work, as measured with a steel tape. This variation in the lineal dimension around the rolls is negligible in its effect on the tension of an abrasive beltA and does not perceptibly affect the tension on the belt thruout the range of movement of these head rolls. 'Ihe tension on the belt is thus substantially identical at the two terminal positions ofthe head rolls, that is in the position in which the belt is grind-v ing and in the non-grinding position in which the belt is idling on the rolls.

It will be clear from an inspection of Fig. 1

that the nish produced by the abrasive belt can be immediately and clearly inspected as soon as' it emerges from the grinding area. The 4fact that the abrasive belt approaches the work in a vertically downward direction is a major featurel which contributes to this visibility.

When the grinding of the strip has been completed or when it is desired to interrupt the grinding operation for any other reason it is only.

necessary for the operator to release the air pres-v sure against the diaphragm in the' mechanism 8L whereupon the counterweight '.'9 will again auto-` matically cause the head frame 3l and rolls d!) and 4I to rise to the upper position without any' further attention by the operator.

General 1t win be evident that the herein disclosed machine provides for maintaining the tension on theabrasive belt constant in all normal positions;

`of the belt as it is alternatively advanced into y this invention set forth at the beginning of this specification. It will also be evident from the prece-ding disclosure that there are no obstructions which would in any respect interfere with the removal or the replacement of the abrasive belt sidewise from or upon the rolls' 38, 39, 40

and 4I.

As is believed t0 be evident from the foregoing description, the broad principles' of the invention are not concerned with the specific Vstructural details of the embodiments shown and described in the present examples, since all that is necessary is thateach element or subcombination of the combinations which comprise the invention perform its intended function. Thus,

Vfor example, the function of the diaphragm means `82 is to control the adjustment of the head frame 31, and this function can obviously be as well performed by any other suitable means, without change in the structure or relationship of thecontrolled parts.-Si1fnilarly theweight fof 19a, shown substituted in Fig. l0 for the counterweight 19 of Figs. 1 and 5. Other changes will suggest themselves to those skilled in the art.

Alternatives In the operation of this machine it will be understood that the air pressure upon the diaphragm may be of suilicient intensity to force and rmly hold the head frame against the abutments IUI in which case sufficient material will be removed from the strip to produce a uniform thickness of the strip, or the intensity of pressure on the diaphragm may be limited to that required to maintain the belt in vsufficient grinding engagement with the strip to produce a satisfactorily finished surface, in which case, the stop screws on the head may not be engaged against the abutments and slight and unobjectionable variations in thickness of the nished strip may result.

It will alsol be apparent that the position of the stop screws 90 and the abutments I 0| may be interchanged, that is the screw means may be mounted on the stationary housing and the abutments may be fixedly secured on the movable head.

As will appear from an inspection of Figures l and 5, the upper head roll 4I, the contact roll 40, and the support roll 3 are vertically alined. While this relationship is desirable for some purposes, it is to be understood that it is sometimes advisable to laterally shift the axis of the support roll 3 with respect to the contact roll 4| by means of the mechanism associated with the stand 2, in order to provide a slight resilience in the strip at the line of grinding contact.

While the

links

63 and 68 are substantially identical in length this is not an essential feature of this invention as the links may be of different lengths and may be variously mounted, it being necessary only that the sum of corrective effects of the links during the movement of the head rolls maintain the tension on the belt constant.

Figure 11 illustrates one form of the modification of this invention, referred to above, in which the links controlling the path of movement of the head are of different lengths from those shown in Figures 1 to 9 and in which the lengths of the links are dilerent from each other. Figure 11 is generally similar to Figures 5 and 6, but is principally in diagrammatic form and shows only sufcient of the elements necessary to the understanding of the modication which this figure is intended to illustrate. Many of the parts in this gure, being identical with those shown in -Figures l to 9, are indicated by the same reference characters as previously applied to the corresponding parts.

Figure 11 differs from Figures 1 to 9 however in disclosing head guide links in which the upper pair of links differ in length from the lower pair of links and in disclosing correspondingly altered pivot brackets on the housing 26 for supporting the pins upon which the links are pivoted. As will be evident, the upper links 63h are longer than the previously described links 63 and the brackets 65h project interiorly of the frame in order to accommodate the extra length of the links 63h. Likewise the lower links 68h in this embodiment are shorter than the links 68 and are pivotally mounted on the stop brackets b generally similar to the brackets 10 but slightly modied to permit the support of the pivot pins 69 in adifferent place on the bracket, as is necessitated by the shorter length of links 68h.

Inasmuch as the construction and operation of the apparatus shown in Figure 11 is generally similar to that previously described, it is felt that no further description of either the construction or operation of the modification shown in this gure is necessary. The full line showing in Figure 1l depicts the position vof the parts when the head is in the upper position and the broken line position shows the position of certain of these parts when the head 3l is in the lower or grinding position.

An inspection of Figure 11 will disclose that, due to the guiding action of the links 6317 and 68h and inuenced primarily by the approximately straight arcuate travel of the pins 62 during the vertical travel of the head, the upper head roll 40 and its shaft 53 travel in a path which is substantially vertical and as a result of this substantially vertical travel the lineal length of that portion of the abrasive belt between the

rolls

39 and 40, indicated at 42x in Figure l1, is increased during the downward movement of the head.

As will likewise be seen, the pressure roll 4I and shaft 55 travel rearwardly to a greater extent than shown for the construction in Figures l to 9, this rearward travel being caused by the sharp arcuate travel of the pins 61 upon the short radii of the links 68h. As a result of this rearward travel, the lineal length of that portion of the abrasive belt between the rolls 4I and 38, indicated at 42.?l in Figure 11, isreduced during the downward movement of the head.

The lineal length of the portion 42g remaining substantially the same during the vertical travel of the head, the lengths of the links 63h and 68h are so selected and the links are so angularly and vertically positioned that, in the downward movement of the rolls, the progressive increase in the length of the belt portion 42x is counterbalanced by the progressive decrease of the length of the abrasive belt portion 42e so that the length of periphery of travel of the abrasive belt is substantially constant during the movement of the head 41.

Numerous other arrangements of the links are available for maintaining a constant peripheral length of belt during the travel of the head.

Many other modications of this invention and its application will naturally occur to those skilled in this art and the present disclosures should therefore be considered as typical only, and I clesire not to be limited to the exact construction shown and described.

It is to be noted that certain features disclosed in this application and not claimed herein are claimed in my copending application Serial No. 337,326, led May 25, 1940, issued Feb. 24, 1942, as Patent No. 2,274,268.

What I claim is:

l. In a machine of the character described, in combination, a work support, a relatively stationary housing, a head guided on said housing for swinging movement toward and fromy the work support, means for swinging the head, an abrasive belt, and a plurality of rolls for supporting and driving the belt, at least two of said rolls being mounted on the head, the head guiding mechanism including links pivoted on spaced axes adapted to constrain the head in its swinging movement to move the rolls thereof simultaneously about dilerent centers.

2. In a machine of the character described, in combination, a work support, a relatively stationaryy housing, a. head guided on said housing for reciprocal movement. toward. and from. the work; support', means for reciprocating the head, an abrasive belt, a plurality of rolls for supporting. and driving the belt, at least two of said rolls being mounted on the head, the head guiding mechanism including: stationary guidesV formed on the housing; adapted to: guide the head in a directionv laterally with respect to the direction. of thebelt travel, and including tvvo pairs: ofV axially spacedalinks4 each pivoted at one end on the housing'. and pivotally connected with the head at the otherv end, adapted to guide. the head in the direction. off the belt. travel 3:.. In a machine of the characterV described, in combination, a work support,` a relativelyA station.- ary housing, a head guided on said housing for reciprocal; movement toward and from. the work supportyan' abrasivey belt, a plurality of rolls for supporting and` driving the belt, at least. two of said rollsf being mounted on thev head, the. head Vmechanism. including stationary guides formed on. the: housing adapted to guide the head in a direction laterally with respect to the direc'- tion ofthe belt-travel, and including two pairsv of axially spaced. links each pivoted at one. end on the. housing and pivotally connected with the head at the. other end, adapted to guide the head `in the direction. of the belt travel, and means, separate from. the stationary guides and links, mounted in the housing; and connected to the head forv reciprocating the head.

4. In. a. machine of the character described, in combination,l a relatively stationaryy Work vsupporting. roll, a relatively stationary housing, a khead frame guided on the housing for arcuate movement,anv endless abrasive belt, a, plurality of rolls. for supporting and advancing the belt, at least two othese rolls being mounted on the head, the said two rolls being superposedv and be'- ing substantially vertically alined with each other and with the work support roll, means connected with the housing and head frame adapted to swing the head frame through an. arcuate path toward and from the work supporting roll.v

5. In a machine of the character described, in combination, a Work support, a housing,v an endless abrasive belt,y a plurality of rolls mounted on the housing for supportingl and causing the belt to travel in a given direction, at least one of said rolls being shiitable toward and from the work support, yieldable constant pressure mea-ns for shitting the roll, relatively adjustable abutment and stop means separate from the shifting means and connected with the housing and shitable roll for limiting the shiftable roll to a predeterminedv spacing from the work support, mechanism adapted to relatively adjust the abutment and stop means while the said means are in engagement with each other and means for controlling the shifting means so as resiliently to urge the shiftable roll toward the work support and the abutment and stop means together.

6. In a machine of the character described, in combination, a work support, a housing, an endless abrasive be1t,'a head frame movably mounted with respect to the housing, yieldable constant pressure means for advancing the head frame to- Ward the Work support, a plurality of rolls including a drive roll and a contact roll for supporting and causing the belt to travel in a, given direction, the contact roll being mounted on the head frame, abutment and stop means separate from the advancing means and connected with the housing and movable head frame for limiting the headframe to a predetermined-spacing from the Work support means for controlling the advancing means so as resiliently to urge the contact roll towardl the Work support and the abutment and stop means together, land means adaptedr to relatively adjust the abutment and stop means while the belt is in abrasive engagement withV the work.

7. Iny a machine ofthe character described, in combination, a work support, a housing, an endless. abrasive belt, a head frame guided on the housing for movement toward and from the Work support, a plurality of rollsV for supporting and causing theA belt to travel in a given direction, at least onecf the rolls being mounted on thehead frame, manually controllable mechanism for advancing the head frame towardthe Work support, two pairs of relativelyadjustable abutment and stop means separate from the advancing mechanism and connected With'the housing and head frame for adjustably limiting the head frame to a predetermined spacing from the Work support, mechanismadapted to simultaneously adjust both pairs of abutment and stop means, and means forming part of the mechanism for individually adjusting each of said pairs relative to the other pair.

8. In a machine oi the character described, in combination, a Work support, a housing, an endlessabrasive belt, a head frame mounted for vertical movement toward and from the Work support, a plurality of rolls for supporting and causing the: belt to travel in a given direction, at least one of the rolls being mounted on the head frame andA adapted to cause the abrasive belt to engage the work in abrading relation, counterweight means associated with the head frame and housing overbalancing the weight of the head frame and associated mechanism and tending to maintain the said roll on the head frame in a position spaced from the work support, and fluid means adapted to overcome the differential overbalance of the counterWeigh-t and to advance the said roll toward the work support.

9. In amachine of the character described, in combination. a Work support, a housing, an endless abrasive belt, a `plurality of rolls engaging the bel-t,4 certainvof said rolls having their axes. .fixed on the housing, mechanism for applying yieldable constant pressure to two others of said rolls to shift said two rolls simultaneously toward the work support to abradework thereon, said mechanism including compensating link elements mounting said two rolls on said housing and adapted to maintain substantially constant during such shifting the average lineal length of .belt between the shifted rolls and the next adjacent rolls which have their axes fixed to the housing.

l0. In a machine of the character described, in combination, a work support, a, housing, an endless abrasive belt, a plurality of rolls mounted on the,y housing for supporting and causing the belt to travel in a given direction, at least one of said rolls being shiftable toward and from the work support, yieldable constant pressure means for shifting the roll, relatively adjustable abutment and stop means separate from the shifting means and connected with the housing and shiftable roll for limiting the shiftable roll to a predetermined spacing from the work support and means for controlling the shifting means so as resiliently to urge the shiitable rolls toward the Work support and the abutment and stop means together.

11. In a machine of the character described, in

`tially constant during said combination, a work support, a housing, an Yendthe belt against work on the support and adapted,

when actuated in another direction, to shift the last named rolls simultaneously both in the same general direction away from the work support, means separate from the supporting mechanism for constraining said shifting of the last named rolls to movement in arcuate paths, each about a diierent center, so as to maintain the tension on the belt substantially constant during such shifting, and means to actuate said roll supporting and moving means.

12. In a machine of the character described, in

combination, a iixed base, a work support mounted thereon maintaining work a fixed distanceA from the base, a housing, an endless abrasive belt, a plurality of rolls in excess of two supporting and driving the belt, the belt being interposed directly between one of said rolls only and the work support and said one roll being shiftable to press the belt into abrading engagement with work maintained on said support, mechanism adapted y to retract said one roll from the work and adapted to simultaneously shift another of said rolls, said mechanism including elements constraining said shiftable rolls to travel in arcuate paths, each about a different center, tain the tension on the abrasive belt substanroll shifting, and means for actuating said mechanism.

13. In a machine of the character described, in combination, a work support, a housing, an endless abrasive belt, a plurality of rolls in .eX- cess of two for supporting and driving the belt, mechanism for moving two of the rolls with respect t0 the other rolls and in the same general direction toward and from the work support, means connecting together said -two rolls for movement simultaneously toward the work support and for movement simultaneously away from .the work support, said roll moving mechanism including means for constraining said movable rolls to move arcuately, each about a diierent center, in 'such manner that the lineal length of a peripheral line engaging portions of the outer peripheries of the belt supporting rolls and passing tangentially from roll to roll remains substantially constant during said roll movement, and means for actuating the-roll moving mechamsm.

14. In a machine of the character described, in combination, a work support, a housing, anl endless'belthaving its front face coated with abrasive, means supporting and driving said belt compri'sing a plurality of substantially parallel rolls all engaging the rear face only of said belt and whereby to maini ent centers so that the including a contact'roll adapted to support and advance the belt toward the work support, at least two of said rolls including the contact roll being mounted for movement relatively to the housing in a direction transversely of their axes, mechanism adapted to be actuated in one direction for moving said two rolls simultaneously in the same general direction toward the work support and adapted to be actuated in another direction for moving said -two rolls simultaneously away from the work support in arcuate paths, each about a different center, so that the lineal length of a peripheral line engaging portions of the outer peripheries of the belt supportingrolls and passing tangentially from roll to roll remains substantially constant during said roll movement, and means for actuating said mechanism.

15. In a machine of the character described, in

combination, a work support, a relatively stationary housing, an elongated head supported on said housing for movement toward and from said support, guide means associated with the head'and the housing adapted to constrain the head to move toward and from the support with its opposite end portions swinging arcuately about vdifferent centers, an abrasive belt, and a plurality of rolls for supporting and driving the belt, at least two of the rolls being supported on said end portions of the head and movable therewith.

16. In a machine of the character described, in combination, a work support, a relatively stationary housing, an elongated head Ysupported on said housing for movement toward and from the work support, means for moving the head, an endless belt having its front face coated with abrasive, a plurality of rolls for supporting and tensioning the belt, all of said rolls being engaged with the rear face only of Ythe belt, power means for driving one of the rolls, at least two of said rolls being mounted on opposite end portions of the head, and means associated with the head supporting mechanism adapted to swing the opposite end portion of the head'about different centers during movement toward and from the work support so as to maintain the tension on the belt constant. Y

17. In a machine of the character described, in combination, a work support, a relatively stationary housing, a head supported on said housing for movement toward and from the work support, means for moving the head, an abrasive belt, a plurality of rolls for supporting and tensioning the belt, power means for driving one of the rolls, at least two of said rolls being mounted on the end portions of the head, and head lguid` ing mechanism including a plurality of links connecting the head with the housing ladapted to constrain the axes of the rolls on the head to move arcuately with respect to the other rolls and simultaneously swing about mutually differtension on the supported belt remains substantially constant during said movement of the rolls.

' LAD L. HERCIK.