US2950493A - Polishing machines - Google Patents

Description

1960 L. ROSOLIA ETAL 2,950,493

POLISHING MACHINES 3 Sheets-Sheet 1' Filed Nov. 20, 1957 21 mum' ATTORNEYS 1960 L. ROSOLIA ETAL POLISHING MACHINES 3 Sheets-Sheet 2 Filed Nov. 20, 1957 IN VEN TORS lay/ls 30501122 BY P zer fie Maura A- 4m M 1- 4 Q-L AT TO R N EYS Aug; 30, 1960 1.. ROSOLiA ETAL 2,950,493

POLISHING MACHINES Filed NOV, 20, 1957 3 Sheets-Sheet 3 FIGJO FIG. I2

.31 E I l 5 i4 43 4] {FD A! r 1N VEN TORS ATTORNEYS Unite ttes Patent PGilSlfiNG NiACHINlES Louis Rosalia, Brooklyn, and Peter De Mauro, Whitestone, N.Y., assignors to Globe Lighting Products, inc, Brooklyn, N31, a corporation of New York Filed Nov. 20, 1e57, Ser. No. 697,564

6 lairns. (Ci. 15-21) This invention relates to polishing apparatus and in particular to apparatus for polishing articles of various shapes, especially articles of irregular shapes.

Machines heretofore and currently used for polishing articles of various irregular shapes are complex in con struction and operation, and, moreover, are very expensive not only as to initial cost and maintenance but also as to cost of operation. Such machines are also objectionable because of the comparatively long time required for the polishing operation and the time and labor required for setting up the machine for the polishing operations.

More particularly, certain machines currently available on the market for polishing irregularly shaped objects are provided with a plurality of polishing heads for polishing difierent parts, respectively, of the same object and a plurality of jigs or work holders are employed and must be constructed and arranged to hold objects of the same irregular shape in a plurality of difierent positions, respectively, so as to present different surface portions to the series of polishing brushes of the respective polishing heads.

The above and other shortcomings of such machines are obviated by our present invention pursuant to the principal object thereof.

More specifically stated, one object of this invention is to provide a new and improved polishing apparatus, which requires only a single brush for polishing objects of irregular shape or surface contour.

Another object of the invention is the provision of polishing apparatus having a polishing station to which a plurality of work holders are movable in succession md at which each Work holder is automatically connected upon arrival at said station to means for bringing the work into engagement with the polishing means and for moving the work in relation to the polishing means during the polishing operation.

A further object is to provide actuating means at or in predetermined relation to the polishing machine which may be continuously operated for actuating the work holders, respectively, while they are at the polishing station and to provide each work holder with means automatically engage-a is with and disengageable from said actuating means upon movement of each work holder to and from said station, respectively.

Another object is the provision of means to start the operation of the work holder, for moving the work during the polishing operation, before the work is brought into contact with the polishing means and to continue said operation while the work is in contact with the polishing means.

Another object of the invention is to provide polishing apparatus with means for maintaining optimum brushto-work contact pressure and to prevent excess pressure between the brush and the work polished thereby.

A further object of this invention is to provide polishing apparatus having a novel means for moving the work into and out of engagement with the brushing means while rotating the work relative thereto.

I new A yet further object is generally to provide a new and improved polishing apparatus of simplified design construction, and operation.

F or a better understanding of the present invention and of the above and other objects thereof, reference is had to the following description considered in connection with the accompanying illustrative drawings.

Referring to the drawings in which like reference characters designate corresponding parts through the several views;

Fig. 1 is a top plan View of a polishing apparatus embodying the invention in a particular form, the polishing brush being omitted;

Fig. 2 is a perspective side View of the apparatus, the polishing brush being shown, for illustrative purposes at right angles to its correct position which is illustrated in Fig. 10;

Fig. 3 is a top plan view, on a larger scale, of a work support including a jig containing the work separably attached thereto;

Pig. 4 is a sectional view, on a larger scale, on the line of Fig. 3;

Fig. 5 is a sectional view on the line 55 of Fig. 1;

Fig. 6 is a sectional view on the line 66 of Fig. 2 illustrating the indexing mechanism in engagement;

Fig. 6A is a plan view of a manually operated indexing mechanism;

ig. 7 is a sectional view similar to Fig. 6 but showthe indexing mechanism prior to engagement; lg. 8 is an enlarged fragmentary sectional view on the 88 of Fig. 2;

lin

= i 9 is a horizontal sectional View on the line 99 g. 8; i ig. 1G is a view of parts of the apparatus showing the raised position of a work holder and the work thereon in engagement with the polishing brush;

Fig. 11 is an enlarged view of the lower part of a work holder and the upper part of the piston rod of the motor for raising the work holder and for supporting it in the raised position illustrated by Fig. 10;

Fig. 12 is a perspective view of part of a lamp fixture, illustrating an article of irregular shape; and

Fig. 13 is a circuit diagram illustrative of an electrical control system for the apparatus.

Referring to the drawings in detail and first to Figs. 2 and 5, the polishing apparatus 20 embodying the present invention includes a base 21 supponting an upright sta tionary shaft 22 on which the carrier or turret 29 for the work holders 37 is mounted for rotation in a horizontal plane. A collar 23 provided with a thrust bearing 24 is attached to the shaft near its upper end which extends through roller bearings 27 fixed to the hubZS of carrier 29. A plurality of radially extending horizontal arms 31 are carried by hub 28 and are provided with brackets 31:! on which the work holders 37 are mounted.

The work-holder carrier 26 may be turned by hand for moving the work holders to and from the station at which the polishing operation is performed, but as illustrated by Fig, 2 and also by Fig. 1, provision is made for the controlled power operation of said carrier for turning the latter intermittently with intervening dwell periods for the polishing operation. For this purpose a driven gear 32 is fixed to hub 23 and is rotated by a driving gear 36. As indicated in Fig. 1, an electric motor 33 is connected to driving gear 36 by a slip clutch 34 and is effective to rotate carrier 29 except when the latter is held against rotation, as hereinafter described, during the dwell periods of the Work holders at the polishing station. It will be understood that when the carrier 29 is thus held against rotation, the provision of the slip clutch 34 between the motor shaft and the driving gear 36 enables the electric motor 33 to operate without interruption, and without overloading, so that the 7 carrier 29. is actuated as soon as it is released upon completion of the polishing operation on the work at the polishing station for automatically moving the work holder from said station and for bringing the next work holder to said station.

Each work holder 37 comprises a horizontal table 37a upon which the work is held by means of a suitable jig 38 (Figs. 2 and 3,). Referring to Figs. 3 and 4, there is shown a removable jig 38, which carries the article or articles to be polished. The object to be polished, here shown as part of a lamp fixture, is referred to hereinafter as work 41. A quick-releasable clamp 39 is provided for removably securing the work in the jig.

Each work holder 37 is provided with a shaft 46 which is rotatably. and slidably mounted in a vertical sleeve bearing 42 fixed to the bracket 31a,j on carrier arm 31. In its retracted position illustrated in Fig. 2, work holder 37 normally rests on stop 45. On the lower end of shaft 40 is attached a gear 43 for rotating work holder 37. Rigidly attached to the underside of gear 43and concentric therewith is a part 35 made of hard steel.

There is represented in Fig. 1, three equally spaced Work stations, a loading station A, a polishing station E, and an unloading station C. These stations are designated in Fig, 1 by the broken line circles and the movement of the work holders to these stations is in the indicated counter-clockwise direction. As here shown (-Figs. 2 and the polishing means at station B comprises a rotary brush 46 actuated by a power-operated shaft 46a journalled for rotation in stationary support 46b. Adjacent to the polishing brush 46 is an applicator for periodically applying a polishing medium to brush 46. The applicator is of well known construction and operation and is not per se part of our invention. It includes an air cylinder 47 and an electrically operated valve 48. When a work holder 37 arrives at the polishing station B valve 48 is operated as described hereinafter for admitting compressed air to the motor from a source (not shown). The piston rod 49 of air cylinder 47 is moved towards the rotating brush and thereby brings a stick of a polishing substance 51 attached to its outer end into contact with brush 46. At the conclusion of a predetermined interval the air in cylinder 47 is exhausted to the atmosphere by valve 48 and spring 50 returns the piston to its retracted position thereby disengaging the polishing medium 51 from brush 46. This operation is repeated at intervals under the control of a timer during the polishing operation.

The shaft 40 of work holder 37 is actuated for moving the work holder 37 to move the work into and out ofengagement with brush 46 and relative thereto during the polishing operation. To perform this last-mentioned operation the polishing station B includes an electric motor 52 mounted on base 21 and connected through have a loose meshing engagement initially when the work holder 37 is in its lower position as illustrated in Fig. 2 at station B and this enables the gear 43 to be brought into proper relation to driving gear 54 without substantial clashing of the gears. Similarly, this con struction provides for the disengagement of the gears 43 and 54 when the work holder is moved from station B to the unloading station C following the lowering of the work holder upon completion of the polishing operation.

For moving the work holder vertically to bring the work 41 thereon into engagement with brush 46 a doubleacting air cylinder or pneumatic motor 58 is suitably mounted on base 21 at polishing station B immediately under the axis of rotation of gear 43. In typical double type action air is admitted into the cylinder 58 on either side of the piston therein, 'while air on the side is exhausted to the atmosphere. In this manner piston rod 59 may be positively raised. and lowered vertically to: raising the work holder and for controlling the lower-. ing thereof. Compressed air is admitted to air cylinder 58 from a source of compressed air (not shown) through an electrically operated valve 61. The piston rod 59 of air cylinder 58 terminates in a ball bearing 60 on which the wear plate 35 of shaftv 40. is engaged. A transverse finger 63 is fixed to the piston rod near its upper end for closing amicroswitch 62 positioned ad-.v jacent tow the travel path of piston rod 59 for initiating the operation of a timer (subsequently referred to) which controls the operations of valve 48 of'the polishing applicator-motor 47 described above..

The polishing apparatus 20 includes means for index! ing the movement of carrier 29 to each station and for preventing the rotation of carrier 29 until the polish.- ing operation is completed. The releasable mean comprises an air cylinder or motor 64 mounted on base 21. The piston rod 65 of cylinder 64 projects vertically through a spring-mounting housing 66 mounted on base 21 above air cylinder 64. Air cylinder 64 is controlled by an electrically operated air valve 67. Piston rod 65 is normally biased upward by the action of spring 68 (see Fig. 6) upon a collar 69 on said piston rod. The upper part 70 of rod' 65 provides a releasable detent member which is releasably engageable with a companion. detent member 72 carried by each arm 31 of the work holder carrier 29. Said detent member 70' is in the path of circular movement of members 72 so that it is depressed by the inclined cam portion 74 by member 72 by the movement of the work holder 37 to station A. When this work holder is at station A, detent 70 is projected by spring 68 into recess 73 of member 70 for arresting the movement of the carrier 29 either manually or by motor 33 and the work holder at the polishing station is correctly indexed at said station and is rea speed reducer 53 and sprocket chain gearing 53a to the. shaft of gear 54. Gear 54 is continuously rotated by motor 52. When carrier 29 carries a work holder. 37 to polishing station B, gear 43 at the lower end of'shaft 40 engages. gear'54 thereby causing the work holder to rotate about a vertical axis, transversely of the axis of brush 46. In the movement of a work holder, to the polishing station B, the gear 43 moves bodily in a. circular. path and upon arrival of the work holderat said station gear 43 is positioned for meshing engagement with gear 54, while the latter is being rotated. To enable this engagement to take place-without clashing of the gears, end portions of said gears are modified and specially designed in accordancewith the. present invention. As illustrated by Figs. 8 and 9, end. portions 55 of gears 43 and 54 are of reduced radial extent 'or depth and are of reduced thickness and are rou d. t h r. o t r en s. hus, h e s .3 d

leasably held at said station during the dwell period for the polishing operation, Upon completion of the dwell period, valve 67 is operated to admit air to cylinder 64 above the piston thereon for lowering rod 65 against the force of spring 68 and thereby retracting detent 70 from detent member 72 and releasing carrier 29 for movement either by hand or motor 33, as the case may be, for moving the work holder at the polishing station B to the unloading station C and for moving the work holder at the loading station A to the polishing station B.

A microswitch 71 is mounted on housing 66 in position to be closed by collar 69, when detent 70 is in restraining engagement with detent member 72, for closing a circuit for. operating the valve 61 of motor 58 to admit air for raising rod 59 and'thereby raising the work holder at the polishing station B to brush engaging position.

It will be observed that gear 43 is moved vertically in relation to driving gear 54 for effecting a normal drive meshing of said gears forinitiating rotation of the work before the work holderis raisedsuificiently to engage the Fl L work with brush 46. Accordingly, at the time the work is moved up against the brush for the polishing operation, the work is rotating and this eliminates the possibility of stalling motor 52 or subjecting it to overload operation and likewise this eliminates stalling or overloading of the motor 78 (Fig. 13) which drives the shaft of brush 46.

As illustrated diagrammtically by Fig. 13, the apparatus is preferably operated under the control of electrically operated timers Stl, S1 and 82. In Fig. 13, the motors 33, 52 and 78 are connected to the electric supply lines L1 and L2 through a disconnect switch 76. The timers and the electrically operated valves are conventional and readily available on the market. Said timers are adjustable for time control and are of the self-resetting type. Timer 81 controls the operation of valve 61 of the pneumatic motor 58 by which the work holder is raised and lowered and held in raised position for the polishing operation during the dwell period according to the setting of said timer. The operation of timer 31 is initiated by the closing of switch 71 when detent member 7%) is projected by spring 68 into holding engagement with detent member 72, as described above, and this results in the operation of valve 61 to admit compressed air below the piston of motor 58 for moving the work holder to its raised position and for holding it in said position for a predetermined period of time according to the setting of the timer. Upon expiration of said period of time for the polishing operation valve 61 is operated to discharge air from beneath the piston of motor 58 and to admit compressed air above said piston for moving support rod 59 rapidly downward to allow the work holder 37 to move by gravity out of brush engaging position and to its retracted position illustrated in Fig. 2. Timer 8% is set to operate valve 67 to admit compressed air above the piston in pneumatic motor 64 for actuating rod as to disengage detent 7% from the carrier detent 72. This operation takes place almost immediately after the lowering of rod 59 and the substantially simultaneous lowering of the work holder to the retracted position illustrated in Fig. 2. Upon release of the detents 72, carrier 29 is auto matically turned by power operated gear 36 to move the lowered work holder from station B to the unloading station, to advance the work holder from the loading station A to station E, and to advance the third work holder from the unloading station to the loading station. Upon arrival of the last-mentioned work holder near the loading station and as the carrier continues to turn, the cam 74 carried by the supporting arm 31 of said work holder engages the detent 79 and prevents the immediate upward movement of rod 65 by spring 63 and thus prevents closing of switch 71 until the work holder moving in the meantime from the loading station to the polishing station arrives at the polishing station. it will be understood that timer Sii is set so that valve 67 is operated to cut ofi the supply of air to motor 64 to open exhaust port for the previously admitte air as soon as the detent 72 of the work holder approaching the loadin station is in position to engage at its cam 74 the det 78 for temporarily holding switch actuating co ar 63 f moving into switch closing position. As p iously explain=d, the polishing applicator niotor 3-7 o vated only when the work holder at the polishi r raised by the pneumatic motor which also I operadon of closing of switch Timer 82 controls th, val e 43 as as s.. tab 62 is closed it is to operate valve 48 intermittently to admit and exhaust air from motor 47 so that the latter is effective to mo e the polish 51 into and out of engagement with brush It will be understood that timer controlled electrically operated valves for Lhe pneumatic motors 47, 58 and 64 are well known devices and do not per se form part of our invention and hence do not require any specific description or illustration.

Thus, it is seen that the workholder carrier 29 and the work holders are operable automatically under the 5 control of timers and 81, respectively, and that timer 81 is operable under the control of switch 71 which is operated under the control of timer 8% and the work holder carrier. However, if this fully automatic operation is not desired, timer Ed is not used, and instead detent 68 may be manually retracted or, as here shown in Fig. 6A, a foot operated pedal 85 connected to rod 65 may be provided for withdrawing the detent 73 from detent '72 and for controlling the operation of time switch 71. Further, in such case, control switch 71 for timer 81 may be omitted and the timer may be operated directly without automatic switch control.

it will be understood that the rotation of the work in the plane of brush contact therewith results in the accomplishment of an important feature of this invention, for this operation is effective to present to the brush all surface portions of the irregular shaped article, except of course the surface portions which lie against the work supporting sui ace of the jig. In the practice of this invention, two polishing operations are performed on each article of the illustrated type; that is, after the article is polished on one side, it is removed from the work holder and placed in a stand-by receptacle at the unloading station together with other or similar articles of the same days or other run of the apparatus, and thereafter, on a subsequent ru these articles are polished on their other sides oy positioi 'ng them on the work holders, at the loading station, with their unpolished sides uppermost. it will be understood that articles of different shapes car be polished in the same run of the machine, it being merely necessary to provide an appropriate holding jig accor ing to the shape of the article. it is to be noted, however, that only a single' polishing station is needed pursuant to present invention and that the work holding jigs are simple and easily attached to and removed holder support 37a.

from too Among the other advantageous features of the abovedescribcd apparatus is the pneumatic motor 58 for supporting the work holder in its raised position for the polishing operation. This pneumatic motor provides a yieldable support which is efiective to hold the work firmly and with a desired predetermined pressure against the brush for effective polishing action and yet is effectively resnent so tmt the work support can move do nwardly small distances when high parts are brot t against he brush during th rotation of the work holder, or if for some other reason there is excess pressure between the work and the brush during the polishiz ation. it will be understood that th resiliently 3 action derives from the compressibi ty and expa sis ..ty of the air under the piston of motor 58 in response to significant changes in contact pressure between the work and the brush.

While we have shown and described the presently preferred embodiment of our invention, it will be understood that the invention may be embodied otherwise than as here shown or described and that in the specific embodiment herein illustrated or described certain changes in the details of construction and in the form and arrangement of parts may be made without departing from the underlying idea or principles of the invention. Also, it will be understood that certain features of the invention may under some circumstances be used without one or more other features. Further, although the present invention was developed for the provision of a polishing machine at least certain features thereof are applicable to other machines in which analagous operations are performed. Accordingly, we do not wish to be limited to the invention or use thereof specifically described or illustrated except as may be required by the scope of the appended claims.

Having thus described our invention, what we claim and desire to secure by Letters Patent is:

l. Polishing apparatus, comprising a polishing station, work-polishing means at said station, a plurality of work holders, a carrier for said work holders for moving them in succession to and from said polishing station, means mounting each of said work holders for movement for bringing the work thereon into and out of engagement with said polishing means and for moving the work thereon relatively to said polishing means in engagement there with, said mounting means comprising a bearing carried by said carrier, and a shaft projecting from said Work holder and slidably and rotatably mounted in said bearing, means operable for moving the work holder vertically, relativeto the carrier from a retracted position for moving the work into operational engagement with the polishing means, and means for rotating said work holder in relation to the polishing means for the polishing operation, comprising driving gear means at said station and driven gear means on each work holder shaft automatically engaged with said driving gear means upon movement of the work holder to said station and automatically disengaged from each other upon movement of the work holder from said station, said driving and driven gears being relatively slidable and in driving engagement during the upward movement of the work holder shaft for engaging the work with said polishing means and while the work is engaged with said polishing means, and said means for moving the work holder vertically comprising means vertically yieldable to permit limited relative sliding movement of said gears while the work is in engagement with said polishing means.

2. Polishing apparatus, comprising a polishing station, work-polishing means at said station, a plurality of work holders, a carrier for said work holders for moving them in succession to and from said polishing station, means mounting each of said work holders for movement for bringing the work thereon into and out of engagement with said polishing means and for moving the work thereon relatively to said polishing means in engagement therewith, said mounting means comprising a bearing carried by said carrier, and a shaft projecting from said work holder and slidably and rotatably mounted in said bearing, means operable for moving the work holder vertically, relative to the carrier from a retracted position for moving the Work into operational engagement with the polishing means, and means for rotating said work holder in relation to the polishing means for the polishing operation, comprising driving gear means at said station and driven gear means on each work holder shaft automatically engaged with said driving gear means upon movement of the work holder to said station and automatically disengaged from each other upon movement of the work holder from said station, said driving and driven gears being relatively slidable and in driving engagement during the upward movement of the work holder shaft for engaging the work with said polishing means and while the work is engaged with said polishing means, and said means for moving the work holder vertically comprising means vertically yieldable to permit limited relative sliding movement of said gears while the work is in engagement with said polishing means, said driving and driven gears having gear teeth portions, respectively, having a loose meshing engagement with each other when the work holder is in said retracted position at said. station.

3. Polishing apparatus, comprising a polishing station,

work-polishing means at said station, a plurality of work holders, a carrier for said work holders for moving them in succession to and from said polishing station, means mounting each of said work holders for movement for bringing the work thereon into and out of engagement with said polishing means and for moving the work thereon relatively to said polishing means in engagement therewith, said mounting means comprising a bearing carried by said carrier, and a shaft projecting from said work holder and slidably and rotatably mounted in said bearing, means operable for moving the work holder vertically, relative to the carrier from a retracted position for moving the work intov operational engagement with the polishing means, and means for rotating said work holder in relation to the polishing means for the polishing operation, comprising driving gears means at said station and driven gear means. on each work holder shaft automatically engaged with said driving, gear, means .upon movement of the work holder torsaid station and automatically disengaged from each other upon movement of the work holder from said station, said driving and driven gears being relatively slidable and in driving engagement during the upward movement of the work holder shaft for engaging the work with said polishing means and while the work is engaged with said polishing means, and said means for moving the work holder vertically comprising means vertically yieldable to permit limited relative sliding movement of said gears while the work is in engagement with said polishing means, said driving and driven gears having gear teeth, portions, respectively, hav-i ing a loose meshing engagement with each other when the work holder is in said retracted position at said station, said work holder carrier being mounted for rotation about a vertical axis spaced from and parallel to the axis of rotation of said driving gear and said gear teeth portions of the driven gear being brought into said loose meshing engagement with said gear teeth portions of said driving gear automatically upon movement of the work holder to said work station by rotation of said carrier relatively to said driving gear.

4. Polishi g apparatus, comprising a polishing station, work-polishing means at said station, said work-polishing means including a polishing brush and an applicator for applying polishing medium to said polishing brush, a plurality of work holders, a carrier means for said work holders for moving them in succession to and from said polishing station with a dwell interval at said polishing station, means mounting each of said work holders for movement for bringing the work thereon into and out of engagement with said polishing means and for moving the work thereon relatively to said polishing means While in engagement therewith, time controlled means for moving the work holder relative to the carrier, for moving the work into and out of operationalengagement with the polishing brush, said time controlled means comprising a timer activated at the start of the dwell interval for controlling the duration of said operational engagement during the dwell interval, second time control means comprising a timer activated at the start of the operational engagement for controlling the operation of the applicator during the operational engagement, and rotational means for rotating said work holder in relation to the polishing means while in engagement therewith for the polishing operation.

5. Polishing apparatus, comprising a polishing station, work-polishing means at said station, said work-polishing means including a polishing brush and an applicator for applying polishing medium to said polishing brush, a plurality of work holders, a time controlled carrier for said work holders for moving them in succession to and from said polishing station with a dwell interval at said polishing station, said time control comprising a timer, and means for moving said carrier, said timer being releasably coupled to said moving means for controlling the duration of alternate moving and dwell intervals, means mounting each of said work holders for movement for bringing the work thereon into and out of engagement with said polishing means and for moving the work thereon relatively to said polishing means while in engagement therewith, other time controlled means for moving the Work into and out of operational engagement with the polishing means, said other time controlled means comprising a second timer activated at the start of the dwell interval for controlling the duration of said operational engagement during said dwell interval,

second time control means comprising a timer activated at the start of the operational engagement for controlling the operation of the applicator during the operational engagement and rotational means for rotating said work holder in relation to the polishing means while in engagement therewith for the polishing operation.

6. Polishing apparatus, comprising a polishing station, Work-polishing means at said station, said work-polishing means including a polishing brush and an applicator for applying polishing medium to said polishing brush, a plurality of work holders, a time controlled carrier for said Work holders for moving them in succession to and from said polishing station with a dwell interval at said polishing station, said time control comprising a timer, and means for moving said carrier, said timer being releasably coupled to said moving means for controlling the duration of alternate moving and dwell intervals, means mounting each of said work holders for movement for bringing the work thereon into and out of engagement with said polishing means and for moving the work thereon relatively to said polishing means while in engagement therewith, other time controlled means for moving the work into and out of operational engagement with the polishing means, said other time controlled means comprising a second timer activated by said time controlled carrier means at the start of the dwell interval for controlling the duration of said operational engagement during said dwell interval, second time control means comprising a timer activated by said other time control means at the start of the operational engagement for controlling the operation of the applicator during the operational engagement, and rotational means for rotating said work holder in relation to the polishing means while in engagement therewith for the polishing operation.

References Cited in the file of this patent UNITED STATES PATENTS 615,383 Ellis Dec. 6, 1898 1,832,190 Doane Nov. 17, 193-1 1,938,278 Connor Dec. 5, 1933 2,070,322 Sperry Feb. 9, 1937 2,177,898 Leguillon et al. Oct. 31, 1939 2,194,780 Andersen Mar. 26, 1940 0 2,493,206 Okey Ian. 3, 1950 FOREIGN PATENTS 338,058 Great Britain Nov. 13, 1930 512,297 Great Britain Aug. 31, 1939

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