US2324918A - Abrading device - Google Patents

Description

July 20, 1943. B. W. ENGLE I ABRADING DEVICE Filed March 11, 1942 1 "muil" l i l IN VEN TOR. 7n Q/g Patented July 20, 1943 ABRADING DEVICE Bruce W. Engle, West Burlington, Iowa, assgnor to Foster-Johnson Reamer Company, Chicago,

' Ill.

Application March 11, 1942, Serial No. 434,161

is claims.

The invention relates generally to an abrading l i tremely difficult operation requiring great prev cision, and is usually performed by highly skilled mechanics only. Heretofore, a specially made file has been used which is comparatively expensive and, even so, can be employed'a short while only before it becomes so worn or so filled with the fillings as to necessitate cleaning with acid f or complete disposal. More'often than not, the file is, after but a short use, thrown away. It is a general object of the invention, therefore, to provide a new and improved abrading hand tool of the character describedmaking possible a better result in a shorter time, and even a satisfactory result by one not so highly skilled in One of the more particular objects is to provide a new and improved abrading hand tool which obviates the present necessity of throwing away the entire tool after but short usage there- Another object is to provide an abrading h'and tool having a removable and replaceable abrasive surface retained on the tool in a new and improved manner.

Still another object is to provide an abrading tool having a hollow, main portion with an ex'- ternal, flat, master lappedsurface, means for tautly holding over the surface an abrasive strip, and additional means for holding the strip truly and uniformly on the surface.

Other objects and advantages will become apparent from the following detailed description taken in connection with the accompanying drawing, in which:

Fig. 1 is a top plan View of an abrading tool embodying the features of my invention, the tool being shown in actual size but with a portion broken out intermediate the ends thereof.

Fig. 2 is an end view taken from the left in Fig. l.

Fig. 3 is a longitudinal sectional view taken approximately along the line 3--3 of Fig. 1.

Fig. 4 is aA transverse sectional view taken approximately along the line 4-4 of`Fig. 3.v

Fig. v5 is a View like Fig. l, but of a modified form of the invention.

Fig. 6 is a longitudinal sectional view taken along the line 6-6 of Fig. 5.

Fig. '7 is a transverse sectional view taken along the line I-'I of Fig.6.

Fig; 8 is a transverse sectional view taken along the line .8-8 of Fig. 6.

Fig. 9 is a fragmentary front elevational view of the right end only of the tool as shown in Fig. 5.

While the invention is susceptible of various modifications and alternative constructions, it is shown in the drawing and will hereinafter be described in two embodiments. However, it is not intended that the invention is to be thereby limited to the specific forms shown. On the contrary it is intended to cover all modifications and alternative constructions falling within the spirit and scope of the invention as defined in the appended claims. Y v VTurning first to the form of the invention shown in Figs. l to 4, it will be seen Ythat the abrading device or tool is comparatively long and slender, having an intermediate portion l5, which is the effective or abrading portion of the tool, and somewhat `reduced portions I6 and I1 at either end forming hand grips for the mechanic using the tool. In the main, the tool is composed of but two parts I8 and I9, with the part I8 forming the main, effective, or abrading portion I5, and the reduced portion I6. The part I8 may be formed in any desired manner,

vbut it has been found that for convenience in manufacture the part I8 is preferably initially of solid stock, rectangular in cross section. For the size of tool here shown, by way of example, the part I8 is preferably of square cross section, as clearly shown in Fig. 4, and is then narrowed at one end and on two sides only by suitable means to produce the rectangular (see Fig. 2), reduced portion I6, leaving two sides 20 and 2| of the same width as the main portion I5. At the extreme left end of the tool the reduced portion is further turned down to form a tubular extension 22 for the reception of an air hose, the purpose of'which will laterbe made known.

The main portion I5 of the tool is made hollow, preferably by drilling from the end opposite the reduced portion I6, thereby forming a bore 23 of comparatively large diameter and having walls 44 of varying thickness. Extending axially of the tool from the bore 23 through the reduced portion I6 and the tubular extension 20 is a reduced bore 24, so that the bore 23 may be in communication with the air hose attached over the tubular extension 22.,v At least one face of the main portion i5 of ne tool is made absolutely nat with the surface ground and spotted to portion Il and terminates a bifurcated end- 21 the prongs or fingers '2S of which extend over the sides of the main portion i5 not bearing the lapped surfaces 25 and 2G. The part 9 is rigidly Y attached to the part i8 by ineans of a plurality of screws 2S carried in the fingers 28 and engaging the main portion i5. The base 30 of the bifurcated end 2? is spaced from the end of the main portion l5 to provide 'the necessary room for operation a tensioning device presently to be described, and the reduced portion I1 is preferably knurled to improve the grip that may be had by the mechanic.

The abrading means or surface of the tool is herein made removable and replaceable, in order that a clean sharp abrading surface may be had without the effort heretofore required in cleaning, or the expense of an entirely new tool as has been the case heretofore. This abrasive is in the form of a strip 3| either of emery cloth or paper which is adapted to overlie both surfaces 25 and .26. Means is provided herein for holding such a strip 3l of abrasive material removably and at the same time tautly and firmly in position over the faces 25 and 25. This means includes gripper plates 32 mountedfone on each of the sides 20 and 2I and retained in position by a screw 33 extending therethrough and threaded into the re'- duced portion I5. Each gripper plate is, along the edge adjacent the main portion I5, bent slightly inwardly to form a knife edge 34 by means of which the plates are capable, when the screws 33 are turned in, of firmly and uniformly gripping the strip 3i over its entire width.L Each plate 32 is held against rotation about its single screw 33 by means of a threaded peg 35 projecting into a notch 3S formed in the edge of the plate opposite the knife edge 34.

The strip 3I is always held taut and thus caused to lit flat over the surfaces 25 and 25 by r means of a plunger 31 slidable in a tube 38 inserted into the open end of the bore 23. This tube 38 is closed at its inner end and near its outer end is provided with an annular flange 39 threaded to be screwed into the end of the bore 23 in air-tight relationship to form of the bore a chamber. At its outer end the plunger 31 carries a rounded head 40 over which the strip 3l runs. The plunger 31 is constantly urged outwardly by means of a compression spring 4I interposed between the closed end of the tube 38 and the plunger 31.

Because of the extreme precision required in the refacing of the slide valves and their seats, it is essential that the abrasive strip 3l be as true as the master lapped surfaces 25 and 26. While this is substantially accomplished by the means herein provided for securing the strip in position, additional means is provided for holding the Y strip firmly and uniformly against the surfaces 25 and 26 throughout the entire area of those surfaces. To that end, the walls having the surfaces 25 and 26 are made perforate with a large number of uniformly arranged perforations 42. Herein the perforations are arranged, as best seen in Fig.

1, in rows with the perforations in adjacent rows staggered. In order that the very edges of the strip 3I may be held tightly against the surfaces 25 and 26, the end perforations 43 of alternate rows are slanted outwardly from the bore '23, as best seen in Fig. 4, in order that they may terminate very closely adjacent the longitudinal vedges of the surfaces 25 and 26. When in use, the tool is,l throughr the tubular extension :22 and the air hose attached thereto, connected to vacuum so that the air is exhausted from the interior of the tool and, as a result of the differential in pressure, the abrasive strip 3l is firmly and uniformly, throughout the entire areas of the surfaces 25 and 25, pressed against those surfaces, thereby holding the abrasive strip just as true and uniform as the lapped surfaces 25 and 26 themselves.

It will be apparent from the foregoing that the strip 3| must be continuous at the end passing over the head Il and that. therefore, the tool will have the same grade of abrasive surface on both sides. In Figs. 5 to 9. there is disclosed a modified form of abrading device constructed so that abrasive strips of different grades may be provided on the opposite faces of the tool. Basically, this tool is the same as that closed in Figs. 1 to 4. The tool has a main intermediate portion I5 and reduced portions I6 IE at the extremities, forming hand grips for the mechanic using the tool. The main portion I5 and the reduced portion I6" are formed from a single part I8 with the intermediate portion square in transverse cross section and provided with opposite walls 44 having true lapped surfaces 25 and 26 formed with perforations 42 opening through the walls to the bore 23. The portion I6 is reduced in thickness to result in a rectangular, transverse cross Section providing 'sides 2U and 2I of the same width as the main portion I5. Extending through the reduced portion IS is a bore 24 communicating at its inner end with the bore 23 and threaded at its outer end to receive a threaded nipple 56 for the attachment of an air hose (not shown). Gripper plates 32 constructed in identical manner with the plates 32 are secured by screws 33 on the sides 2% and 2|.

Means` is provided at the opposite end of the tool for tautly holding individual strips 5I and 52 of abrasive material. This means comprises a basic and preferably initially solid member 53 (see Fig. 9) which, throughout a major portion of its length is generally rectangular in transverse cross section (see Fig. 8) with its major dimension equal to the width of the main portion I5 so as to provide two flat sides 54 and 55 equal in width to the width of the main portion I5. At its inner end. the element 53 flares outwardly from the sides 54 and 55 to form a square base 56, which in turn is turned to a round portion 51 of the diameter of the bore 23 and threaded to be received threadedly in the open end of the bore 23. The base 56 inwardly of the threaded portion 51 is provided with a further reduced portion 58 so as not to block the apertures 42 opposite the reduced portion 58.

The element 53 has extending longitudinally thereof two bores 59 terminating short of the inner or left hand extremity of the element and opening through the outer or right hand extremity of the element. Reciprocable in each of the bores 59 is an elongated plunger 60 constantly urged outwardly by a compression spring 6I inserted in the bore between the closed end thereof and the plunger. Each plunger 60 may, if desired, be at its inner end formed with a reduced and centered projection 52 for holding the end of the spring `(il bearing against the plunger-in position. Each plunger 60 is at its inner end formed with 'a flat area 63 (see Figs. 6 and 7), and secured to this surface is a plate 64 approximately square and approximately equal to the width of the sides 54 and 55.' Herein the plate is secured by a screw 65 and by a threaded peg 66, both ex'- tending through the plate 64 and threaded into the plunger 60 through the flattened area 63. Mounted over and cooperating with each plate 64 is a gripper plate 61 of identical construction as y the gripper plates 32 and 32', having a knife edge 68 atv its inner end and a notch 69 at its outer end for the reception of the peg 66. The plate is retained and adjusted tov releasing or gripping position by means of a screw I ythreaded into the plate 64 and the plunger 60.

In order that the plungers with the plates 64 secured thereon may have a limited movement under the influence of the spring El, the sides 54 and 55 of the element 53 are out away at H and the plungers- 60 are so proportioned as to terminate short of the outer end of the bores 59 when the abrasive strips 5I and 52 are drawn taut. The outer ends of the bores 59 are closed by an end plate 12 removably secured by screws 13. To facilitate application of the abrasive strips 5I and 52, means is provided for holding the plungers B9 in their inner positions against the action of the springs 6l. To that end, there is threaded through the end plate l2 an ladjusting screw 14 having a large knurled head l5.

The end of the screw 14 bears against a disk 16 which partially Y overlies the ends of the plungers B0 and which movesin a third bore T1 formed in the end of the element 53 concentric with the screw M (see Fig. 8 in particular). Thus by turning the adjusting screw 14 inwardly it will bear against the disk 16, which in turn will bear against the ends of the plungers 6i), thereby forcing the plungers inwardly against the action of the compression springs 6I. In this inner position of the plungers the strips 5l and 52 of abrasive material may conveniently be inserted underneath the gripper plates Vl'l and the screws 10 turned inwardly, causing the plates securely to grip the endsV of the strips 5I and 52 which have already beensecured at their other ends by the gripper plates 32. The screw 'M is then again-turned outwardly releasing the plungers B0 to the action of their respective springs Bl, whereupon each plunger will be forced outwardly individually until its respective abrasive strip is drawn tautly over "1 the lapped surface of the abrading tool. It is believed apparent that with this construction the strips 5| and 52, being independent and being independently secured, may, of course, be of different grades of abrasive, so that one surface of Vthe tool may be employed for the roughing cuts,

while the other surface may be employed for the finishing cuts. to 4, it is intended, of course, that the tool during operation will be connected to vacuum so that the air within the tool will be exhausted, causing the difference in pressure firmly and uniformly to press the abrasive sheets onto the lapped surfaces 25 and 26 throughout the entire area thereby making the abrasive as true and uniform as the lapped surfaces themselves. n

It is also believed apparent from the foregoing that I have perfected a tool adapted for abrading generally, but especially adapted forrresurfacing slide valves and their seats in-air brakes, which Like the tool disclosed in Figs. 1`

permits the employment of an inexpensive abrading surface that-may be replaced at frequent intervals to -keep the tool constantly in proper condition. `With my construction, the abrading surface may when worn be discarded and replaced at very slight cost, thus providing a great economy over the present practice of requiring the entire tool to be reconstructed or thrown away. Such replacement of the abrading surface is with my constructions readily and quickly accomplished so as to take little of the mechanics time and willY thus enable the tool to be kept in prime condition, enabling the mechanic to perform better work more quickly. Most important of all is the combination of the taut holding of the abrasive strip plusthe applicatiornby the employment of vacuum, of a uniform pressure on the outer surface of the strip throughout the entire area of the working surface so that, though the abrasiveV surface is separate and removable from the tool, it nevertheless is held so firmly and uniformly as to provide a true surface.

I claim as my invention: l

1. AV hand-held abrading device comprising a first elongated part providing a main portion and a reduced portion forming a hand grip at one end, said elongated part having a chamber in the main portion formedy by .a bore opening through the end remote from the reduced portion, walls with opposed flat working surfaces on the exterior of the main portion extending longitudinally thereof and a plurality of perforations in each of said walls opening through the working surface and communicating with said chamber, aV tubular member threaded into the open end of the bore to close the same, vsaid tubular member being closed at one end and open at the other, a plunger reciprocable in the tubular member and projecting through the outer end thereof, a compression spring constantly urging the plunger outwardly, a bore vin the reduced portion communicating with the chamber in the main porti-on and opening at the other endthrough the end of the reduced portion, said'reduced portion terminating in means adapted for connection to an exhausting device for exhausting the air in the chamber during use of the device, means on Opposite sides of the reduced portion for releasably gripping the ends of a strip or abrasive material overlying both working surfaces and engaged intermediate its ends by said plunger to draw the abrasivemat'erial taut and smooth to permit the pressure differential further to hold the material truly on the working surfaces, and a second part having a reduced portion forming a hand grip and means adapting it for attachment to said first part opposite the reduced portion of said rst part.

2. A hand-held abrading device -comprising an elongated part providing a main portion and a reduced portion forming a hand grip at one end, said elongated part having a chamber in the main portion formed by a bore opening through the end remote from the reduced portion, walls with opposed flat working surfaces on the exterior of the main portion extending longitudinally thereof, and a plurality of perforations in each of said walls opening through the working surface and communicating with said chamber, a tubular member threaded into the open end of thebore to close the same, said tubular member being closed at one end and open at the o-ther, a plunger v reciprocable in the tubular member and projecting through the outer end thereof, a compression spring constantly urging the plunger outwardly, a bore in the reduced portion communicating with .the chamber in the main vportion and opening at the other end through the end of the reduced portion, said reduced portion .terminating in means adapted for connection to an exhausting device for exhausting the air in the chamber during use of the device, and means on opposite sides of the reduced portion for releasably gripping the ends of a strip of abrasive material overlying both Working surfaces and engaged intermediate its ends by said plunger to draw the abrasive materal taut and smooth to permit the pressure diierential further to hoid the material truly on the working surfaces.

3. A hand-held abrading device comprising an elongated body having a hollow intermediate portion and reduced end portions forming hand grips, means communicating with the hollow intermediate portion terminating in means adapted for connection to a device adapted to maintain the hollow intermediate portion below atmospheric pressure during operation of the abrading device, said elongated body having at least one wall with an elongated and iiat working surface on the exterior of the intermediate portion and a plurality of apertures in said wall opening through the working surface and communicating with the hollow interior of the intermediate portion, and

means for detachably holding an abrasive strip in smooth and uniform contact with the working surface .in hiding a gripper plate having knife edge extending fully across the abrasive strip to hold the same ilatwise over the working surface, and means at the other end oi the working surm face engaging the strip of abrasive material tc draw the same taut.

4. A hand-held abrading devi-ce comprising an elongated body having hand grips at each end thereof, a hollow intermediate portion adapted to be maintained below atmospheric pressure during operation of the device, walls with oppositely disposed worlzing surfaces on the exterior of the intermediate portion and a plurality of apertures in each of said walls opening through the working surface and communicating with the interior of the intermediate portion, means communicating with the hollow intermediate portion terminating in means adapted for connection to a device for maintaining the hollow intermediate portion bcloiv atmospheric pressure, and means for detachably holding an abrasive strip tautly in overlying relation to the working surfaces comprising a pair of means each adjustable to grip or release an end of a strip of abrasive overlying both surfaces, a tube disposed largely within the hollow intermediate portion closed at its inner end and opening through its outer end, a plunger reciprocable in the tube carrying a head for engagement with the inner' side of a strip of abrasive material, and a compression spring constantly urging said plunger outwardly to draw the abrasive strip taut and tightly against the working surface.

5` A hand-held abrading device comprising an Velongated body having hand grips at each end thereof, a hollow intermediate portion adapted to be maintained below atmospheric pressure during operation of the device, walls with oppo` sitely disposed working surfaces on the exterior of the intermediate portion and a plurality of apertures in each of said walls opening through the working surface and communicating with the interior of the intermediate portion, means communicating with the hollow intermediate portion terminating in means adapted for connection to a device for maintaining the hollow intermediate portion below atmospheric pressure, and means for detachably holding an abrasive strip tautly in overlying relation to the working surfaces comprising a pair. of means each adjustable to grip or release an end of a strip of abrasive overlying both surfaces, and means engaging the strip of abrasive intermediate its ends yieldably drawing the abrasive strip taut to cause the same to lie fiat and smooth over and in Contact with the Working surfaces.

6. A hand-held abrading device comprising an elongated member having a chamber therein adapted to be maintained below atmospheric pressure during operation of the device, a wall with a working surface on the exterior of the member extending longitudinally thereof and a plurality of apertures in said wall opening through the working surface and communicating with the chamber, means in communication with the chamber adapted for connection to pressure reducing means, and means for detachably holding an abrasive strip tautly in overlying relation to the working surface comprising a stationary means atone end of the working surface adjustable to grip or release one end of va strip of abrasive, and yieldable means at the other end of the working surface engaging the strip of abrasive for drawing the same taut.

'7. A hand-held abrading device comprising an elongated member having hand grips at each end thereof, a hollow intermedia-*c "ortizn adapted vto be maintained at below atmo pressure during operation of the device, a wall with a working surface on the exterior of the intermediate portion and a plurality of apertures in the wall opening through the working surface and comcating with the interior of the intermediate portion, means communicating with the hollow intermediate portion terminating in means adapted for connection to a device for maintaining the hollow intermediate portion below atmospheric pressure, and means for detachably holding an abrasive strip tautly in overlying relation to the working surface.

8. A hand-held abrading device comprising a member having at least one hand grip and a main portion having a chamber therein adapted to be maintained at below atmospheric pressure during operation of the device, a wall with a working surface on the exterior of the main portion and a.

plurality of apertures in the wall opening through the working surface and communicating with the chamber, means in communication with the chamber adapted for connection to pressure reducing means, and means for detachably holding an abrasive sheet tautly in overlying relation to the working surface.

9. A hand-held abrading device comprising an elongated body having a main portion with a bore therein, a wall with a flat surface extending longitudinally of the main portion and a plurality of apertures in the wall opening through the flat surface and to the bore, said apertures being disposed in rows with the apertures in alternate rows staggered and the end apertures in each second row inclined outwardly from the bore to the surface to open through the surface clc-ely adjacent the longitudinal edge thereof, a reduced portion forming a hand grip having a bore therein communicating with the bore in the main portion and adapted to be connected to an exhausting device during use of the abrading device to reduce the pressure in the bore of the main portion, and means for replaceably holding a strip of abrasive material tautly in overlying relation to the fiat surface sea-ling the apertures therein.

10. A hand-held abrading device comprising an elongated body having a main portion with a atmospheric pressure during use ofthe device,

'a'wall with a flat surface extending longitudinally of the main portion and a plurality ofapertures in the wall-opening through the surface and communicating with the chamber, means in communication with the chamber adapted for connection to pressure reducing means, a hand grip portion atone end of said main portion having a fiat side offset inwardly from the surface, said side having a width equal to the width of the surface, and means for removably holding a strip of flexible abrasive flat on the surface including a gripper plate cooperating with the flat side to hold the strip on a line across its entire width.

11. A hand-held abrading device comprising an elongated member having a chamber therein adapted to be maintained below atmospheric pressure during operation of the device, walls with diametrically oppositely disposed working surfaces on the exterior of the member extending longitudinally thereof and a plurality of apertures in each wall opening through the working surface and communicating with the chamber, means in communication with the chamber adapted for connection. to pressure reducing means, and means for holding independently and detachably an abrasive strip tautly in overlying relation to each working surface.

12. A hand-held abrading device comprising an elongated member having a chamber therein adapted to be maintained below atmospheric pressure during operation of the device, walls with diametrically oppositely disposed working surfaces on the exterior of the member extending longitudinally thereof and a plurality of apertures in each wall opening through the working surface and communicating with the chamber, means in communication with the chamber adapted for connection to pressure reducing means, and means for holding independently and detachably an abrasive strip tautly in overlying relation to each Working surface, comprising a stationary means at one end of each working surface adjustable to grip or release one end of an abrasive strip, and independent means at the other end of each working surface adjustable to grip or release the other end of the abrasive strip and yieldably urged outwardly to draw the strip tautly in overlying relation to the working surface.

13. A hand-held abrading device comprising an elongated member having a chamber therein adapted to be maintained below atmospheric pressure during operation of the device, walls with diametrically oppositely disposed working surfaces on the exterior of the member extending longitudinally thereof and a plurality of apertures in each wall opening through the working surface and communicating with the chamber, means in communication with the chamber adapted for connection to the pressure reducing means, and means for holding independently and detachably an abrasive strip tautly in overlying relation to each working surface comprising a stationary means at one end of each working surface adjustable to grip or release one end of an abrasive strip, independent means at the other end of each working surface adjustable to grip or release the other end of the abrasive strip and yieldably urged outwardly to draw the strip tautly in overlying relation to the working surface, and a common means for said independent means adjustable to hold said independent means in an inner positi-on for convenience in attaching the abrasive strips.

14. A hand-held abrading device comprising an" elongated member'having a main intermediate portion with a chamber therein adapted to be maintained below atmosphericy pressure during .operation of the device and reduced end portions forming hand grips, walls with diametrically'oppositely disposed working surfaces on the exterior ofv the main portion lextendinglongitudinally thereof and a plurality of apertures in each wall openingI through the working surface and communicating with the chamber, means incommunication with'the chamber adapted for connection to pressure' reducing means, and means for holding independently and detachably an abrasive strip tautly in overlying relation to each working surface comprising stationary means on opposite sides of one reduced portion corresponding to the working surfaces on the Amain portion adjustable to grip or release one end of the abrasive strips, and independent and movable means for holding the other ends of the strips comprising parallel longitudinally extending bores in the remaining reduced portion closed at their inner ends, a plunger reciprocable in each bore, a compression spring in each bore interposed intermediate they closed end thereof and the plunger to urge the plunger outwardly, and means carried by each plunger for releasably gripping an abrasive strip.

l5. A hand-held abrading device comprising an elongated member having a main intermediate portion with a chamber therein adapted to be maintained below atmospheric pressure during operation. of the device and reduced end portions forming hand grip-s, walls with diametrically oppositely disposed working surfaces on the exterior of the main portion extending longitudinally thereof and a plurality of apertures in each wall opening through the working surface and communicating with the chamber, means in communication with the chamber adapted for connection to pressure reducing means, and means for holding independently and detachably abrasive strip tautly in overlying relation to each Working surface comprising static-nary means on opposite sides of one reduced portion corresponding to the working surfaces on the main portion adjustable to grip or release one end of the abrasive strips, and independent and movable means for holding the other ends of the strips comprising parallel longitudinally extending bores in the remaining reduced portion closed at their inner ends, a plunger reciprocable in each bore, a compression spring in each bore interposed intermediate the closed end thereof and the plunger to urge the plunger o-utwardly, each plunger having a attened area near the inner end thereof, said reduced portion being cut away on opposite sides to expose the plungers at their flattened areas, a plate secured to each plunger on its flattened area to provide a flat; surface equal vto the Width of the working surfaces, and a gripper plate mounted over said firstv mentioned plate and cooperable therewith to grip an abrasive strip.

15. A hand-held abrading device comprising an elongated member having a main intermediate portion with a chamber therein adapted to be maintained below atmospheric pressure during operation of the device andireduced end portions forming hand grips, Walls with diametrically oppositely disposed working surfaces on the exterior of the main portion extending longitudinally thereof anda plurality of apertures in each wall opening through the working surface and communicating with the chamber, means in com- Amunication with the chamber adapted for con- 10 sive strips.

pression spring in each bore interposed intermediate the closed end thereof and the plunger to urge the plunger outwardly, means carried by each plunger forvreleasably gripping an abrasive strip, and means including an adjustable screw operable when turned in to engage bot-h plungers and force the same inwardly against the action of their compression springs to hold the same in an inner position during attachment of the abra- BRUCE W. ENGLE.

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