US2360504A - Method and apparatus for grinding or polishing metal sheets - Google Patents

Description

Oct. 17, 1944. T. J. MASSE 2,360,504

METHOD AND APPARATUS FOR GRINDING OR POLISHING METAL SHEETS Filed July 28, 1959 5 Sheets-Sheet l Fig.5

LNV E N T 0 RV THOMAS JEROME MA 575E SATTOTZNEYS Oct. 17, 1944. J, ss 2,360,504

METHOD AND APPARATUS FOR GRINDING OR POLISHING METAL SHEETS Filed July 28, 1959 s Sheets-Sheet 2 l NVE NTO R THOMAS JEROME MA SSE ATTORNEYS 3 Sheets Sheet 3 E m M 5 R M k H w 4 m m N x 9 w m m E R 6 a 6 V O 2 .M 3 7. 8 i! 7 N M W 5 5 6 5 8 4 7 l 5 w 6 v w 7 o 7 L o m A a N 5 w r N w II I I III l I ||l.| I 7/ A z 1/ 1 \M\ .7//////lln\\ B 1| If} Hun F. HHHHHHHHHH MHHHHH I MHHHH HHMM A .m 0 u 2 6 O i 6 v G L 00 8 5 7 w 6 H w 6 w 6 8 METHOD AND APPARATUS FOR GRINDING 0R POLISHING METAL SHEETS I "f Filed Jilly 2a, 1959 roll.

Patented Oct. 17; 1944 UNITED STATES PATENT OFFICE METHOD AND APPARATUS FOR GRINDING OR POLISHING,METAL SHEETS .Thoinas Jerome Masse, Alexandria, near Sydney, New South Wales, Australia, assignor to The Edes Manufacturing Company, 7 Plymouth, 7

Mass, a corporation of Massachusetts Application July 28, 1939, Serial No. 286,953

In Australia March 29, 1939 23 Claims.

This invention relates to a new method and apparatus for grinding or polishing the surfaces of metal sheets.

In the usual method of grinding sheets of zinc,- copper, and other hard metals to produce thereon a smooth surface, as in the manufacture of photoengraving plates, the grinding is effected by'trav-' ersing each sheet repeatedly under a felt roll which rotates on'a horizontal axis and distributing an abrasive powder onto the surface of the sheet as it passes under the roll.

In the practice of this usual method it is impossible continually to produce sheets with a uniform smooth surface finish. The rotary pad soon becomes more worn at some places along its length than at others, so that the pressure and I grinding action of the pad on the sheet is not nomi'cal recovery of metal values which are removed from the surface of the sheets during the grinding operations. The metal particles are so intermingled with the grinding powder that the trouble and expense of effecting a separation are not warranted.

The present invention has been'devised with the object of avoiding these defects which are incident to the known sheet surface grinding methods and machines, and this invention provides a new method and apparatus by which the grinding and polishing of metal sheets may be carried out more uniformly and more efficiently than heretofore; and with the production ;of ground and polished sheets of improved quality.

According to the method of the present invention, the surface of the metal sheet or sheets to be ground is subjected uniformly to the grinding or polishing action of a small abrasive-surfaced pad or pads which rotate at high speeds in circular'swaths or whorls on thesheet surface, about an axis substantially vertical to the sheet. The

- abrasive is fixed to the pad, so that there is subit is impossible to ensure uniform distribution of the powder over the sheet surface, and this introduces further irregularities and non-uniformities in the surface finish.

Moreover, as metal particles are ground from the surface of the sheet, some of the metal sticks in the pad face and clogs it or is overtaken by the pad in its continued rotation and caught under it. The clogging of the pan with metal results in metal-to-metal contact; when this occurs the metal seizes, and scratches are produced on the surface of the sheet. In the use of the conventional grinding method, therefore, the pad soon becomes inefficient, losing its optimum grinding or polishing action and producing scratches on the surface of the sheet. When detectable scratches appear the grinding must be prolonged until the scratches have been worked out. The grinding sometimes must be carried on for so long a time that the sheet is diminished in thickness and is thereby rendered unsatisfactory for use by photo-engravers or by other artisans in whose work sheets of great accuracy in thickness and substantially perfect in surface finish are required.

A further objectionable feature of the usual grinding method is that there can be no ecostantially no free abrasive on the sheet. During the grinding of the sheet by the revolving pad the sheet is moved to and fro in a linear path beneath the pad, and at the same time the revolving pad is moved bodily to and froover the sheet in a. cross-wise linear path. These movements are controlled so as to ensure uniform coverage of the entire sheet by the abrading means. The pressure of the revolving pad on the sheet surface is kept constant by mounting the same for movement in vertical direction and applying a constant pressure to the same during such manner as to pick up and flush aw'ay'partia cles of metal immediately after they have been removed from the sheet by the abrasive held on the pads. The application of the flushing liquid has the further important function of maintaining a protective liquid film'between-the abrasive and the sheet surface, which allows theiabrasive to actupon the metal to the desired extent but keeps it from digging freely into the metal or producing comparatively deep scratches" which might interfere with the useof the finished sheets in photo-engraving work. This continuousfiushing of the free metal particles away from the grinding zone essentially involves an operation in which the flushing'liquid is flooded onto the sheet, from a point inside the circular path or orbit of the grinding pad or pads, so as to flow path of movement of the pads. The surface of the sheet where the grinding is being carried out is kept clean and free of metal particles to such an extent that the pads do not pick up metal particles and become clogged but, instead, continue to give uniform and highly satisfactory grinding or polishing effects over long periods of use.

The particles of metal ground from the sheet are carried away from the sheet in the flushing liquid, and the liquid is then filtered or otherwise clarified to separate and recover the metal, which may be reused or disposed of as desired to effect an important saving over the usual practice. The clarified flushing liquid may be recirculated and reused in the same cycle of operation.

The flushing medium employed in this method may be kerosene, stearine oil or any other suitably mobile non-corrosive liquid which allows the abrasive to perform its function without damaging the sheet surface and at the same time picks up and removes the particles of free metal abraded from the sheet. Kerosene is the preferred flushing liquid in the grinding or polishing of zinc sheets, while stearine oil is preferred in the case of copper sheets.

The apparatus of the present invention is an eflicient and practical apparatus for carrying out the grinding or polishing of metal sheets according to the above-mentioned method. In general, the apparatus includes a horizontal movable work table upon which the sheets are held during the grinding operation, one or more vertical spindles, each having a rotary grinding head at its lower end on which an abrasive-surfaced grinding pad or pads are fastened, means for revolving the spindles at high speed, means for traversing the work table to and fro beneath the revolving pads in a rectilinear path, and means for traversing the revolving spindles and pads to and fro across the work table in a rectilinear path at an angle to the path of the table. Each spindle is mounted for revolution at high speed about a vertical axis, and means are provided for holding the abrading means against the surface of the sheet under constant pressure while permitting variations in the vertical position of the spindle and the horizontal plane of the grinding pad during the grinding operation. The apparatus also comprises means for continuously supplying a stream of flushing liquid onto the surface of the metal sheet at a point disposed inside the grinding path or orbit of each grinding pad, such means preferably including a hollow. spindle for the grinding head, an openin'g allowing passage of liquid from the spindle onto an underlying sheet, and means for feeding the liquid into and through the spindle during rotation thereof at high speed.

iThe spindles are provided with means for effe'ctingpositive movement thereof in a vertical direction, while either revolving or not revolving, in order to raise the grinding pads off the surface of a sheet or sheets on the work table.

of the table I0.

The machine is constructed so that the spindles may be driven at high speeds; e. g. by belts, without imposing transverse strains thereon and without restricting the ability to move the spindles and pads in vertical direction while they are being driven.

A pair of abrasive pads preferably are mounted in spaced relation on each rotary grinding head of the apparatus, there being an open space between the pads to allow for the flooding of the flushing liquid onto the sheet from the outlet of the revolving spindle.

An illustrative embodiment of apparatus for use in accordance with my invention is shown in the accompanying drawings and described more fully hereinbelow. In the drawings,

Figure l is a longitudinal sectional elevation of the apparatus.

Figure 2 is a transverse sectional elevation.

Figure 3 is a side elevational view of one of the grinding spindle, head and pad assemblies.

Figure 4 is a vertical section through the assembly of Figure 3, and

Figure 5 is a plan of the chain and sprocket arrangement for driving the table.

Figure 6 is a horizontal section along the line 66 of Figure 4.

Referring to the drawings for illustrative details, the machine table In is traversible lengthwise on a pair of horizontal rails H which are fixed to the machine bed 12.. Flanged runner wheels l3 are secured to the under side of the table to run on the rails II. A gutter I4 is fixed around the sides and ends of the table to collect liquid flowing off the table.

Traverse motion is applied to the table through a pair of continuous chain belts [5 which are carried over end sprocket wheels l6 and H which are driven by the motor 2| through gears 23, a

chain belt 22, sprockets 24 and chains 25 (see Figures 2 and 5). straddled between and secured to chains I5 is a spindle l8 which carries a slide block l9. Block I9 is fitted to slide in a driver fork 20 which is fixed to the under side The slide block I9 is carried along with the chain belts l5. Working in the fork 20, it applies longitudinal to and fro movement to the table along the rails II at a slow rate.

As shown in the drawings, the slide block [8 is fitted closely in the driving fork 20. In practice, a clearance of an inch, more or less, may be provided between the block and the fork, in order I to cause a pause in the longitudinal movement of the table at each end of its stroke. Such a pause may be desired to ensure that the degree of grinding in the immediate vicinity of the ends of the sheets will be the same as the degree of grinding on the intermediate area of the sheet. It is important that the reversing of the table movement shall be gradual and not rapid, and this slowing down and slow restarting of the tables movement is provided for in the illustrated embodiment by the continuous chain drive transmitted through the block or pin carried by the chains, since the longitudinal component of the movement of the block or pin I9, when making its circuit around the sprockets l6 and I1, diminishes gradually to zero and increases gradually from zero.

Rails 30 on a transverse bridge 3| above the table I0 carry a carriage 32 on which two grinder spindles and associated mechanisms 33 and 34 are mounted. To and fro traverse movement is applied to the carriage 32 through a pair of chain belts 35 and a slide block 36 working in a fork 31. The chains 35 run over and between sprockets 39 and 40.

For the same reason as described in reference to the longitudinal movement of the table I0, it is important that the movement of the carriage 32 with respect to the table shall be slowed up gradually and re-started gradually. The weight of the carriage is considerable and its rate of slide movement is relatively rapid, so that the importance of obviating rapid reversals of its movements is accentuated. If the reversals were rapid, vibration would .be caused and mechanical injury would result. For these reasons the carriage 32 is driven by the continuous chain arrangement 35, or by some other equivalent arrangement. In that form of drive, the longitudinal component of the movement of the block 36 in passing around the sprockets 39 and 40 gradually slows up to zero and gradually re-starts from zero in the opposite direction. The traverse-movements of the carriage 32 are therefore gradually commenced and gradually terminated at zero and are therefore quite smooth. One pair of the end sprockets over which the chain belts 35 run is driven by an electric motor 44 through a reducing pulley 43 and chain belts 4 I.

As shown in Figure 1, a drain tube 46 depends from the gutter I4 and serves to drain liquid and powdered metal into a sump tray 41. From the tray 41 this mixture of metal powder and liquid passes to a clarifier chamber 48, in which the liquid is separated from the metal. The clarified liquid runs from ,the chamber 48 into a pump suction chamber 49, whence it is pumped for recirculation to the spindles lby operation of a pump 45. The same liquid (subject to replenish-, merit) may be used repeatedly on the table. Pump 45 is driven by motor 44.

As seen in Figures 1 and 2, the mechanisms 33 and 34 include vertical transmission shafts I which are driven by an electric motor 58. The transmission shafts 5| for the spindles are both belted to. the motor 50, and they run in ball bearing 52 and 53 which are mounted on fixed yokes 54. (Figures 3 and 4.) Driving pulleys for the shafts 5| are shown at 55. Both shafts 5| are hollow. The bottom end 56 of each shaft 5I is telescopically connected to the top end of a hollow spindle 51, and is fitted with fork arms 58 which carry leaf springs I69 in spaced relation to their lower extremities. Springs I39 coact with cross trees 68 which extend laterally from a head piece 59 fixed on the top end of the spindle 51. Leaf springs I69 bear against the trees 68 and drive the spindle 51. Fork arms 58a. act as stops for the cross trees 68.

It will be understood that this construction and arrangement of the driving means and spindle permit the spindle 51 to be moved vertically with respect to the lower end portion 56 of shaft 5I while the spindle 51 is either revolving or at rest, and also that the spindle 51 is free from constraint by the driving belt.

bearings 66 and 61. The carrier 69 is splined for vertical movement in the bore 65a. It is pressed downward by a. pair of adjustable helical springs 18 in tension. The lower ends of those springs 10 are hooked onto cross arms H which .project laterally from the member 65, and their top ends are hooked onto cross arms 12 which project laterally from a head piece 13 which is screwed onto the top end of the carrier 69. A flexible dust collar 14, of leather or fabric, is clamped by rings 15 to the head piece 13 and the casing member 65. A similar flexible collar 16 connects the bottom end of the casing member 65 with a foot collar 11 on the carrier 69. The tubular socket 83 of the grinding head 80 is screwed onto the bottom end of the hollow spindle 51, which projects down through the foot collar 11.

Th grinding head 80 comprises a cross head bar 8I secured by screws 82 to a flange portion of the socket 83. A spring clip 84 is fixed to each side of the bar 8|. Felt pads 85 having curved faces are set up against the bottom face of the bar 8I. Strips of abrasive fabric 86 are stretched over the felt pads 85 and are held thereby the spring clips 84. The abrasive strips 86 are narrow (in practice less than an inch in width), and they are spaced apart so that the intervening space is substantially over an inch in width. These measurements are not critical and may be varied as desired. There is clearance between the bar BI and the surface of the metal sheets heldon the work table, so that only the abrasive surfaces of the pads contact the sheets during rotation of the spindles. The abrasive fabrics 86 carry a fine grit, which may consist of alumina particles or other suitable abrasive material secured to the fabric by suitable adhesive. Several A valve 60 is located in a liquid supply pipe 6I.

A pipe 62 depends from valve 68 and is telescoped into the top end of the hollow transmission shaft 5|, whereby to supply flushing liquid into the hollow spindle 51.

Lubricators for bearings 53 and 52 are indicated at 60 and SI.

Casing members are fixed on the carriage 32, and each of these members 65 has a vertical bore 650. which houses a double end tubular carrier 69 having upper and lower ball bearings 66 and 61. The hollow spindle 51 runs in those ball different fabrics are used in a complete grinding and polishing operation on a sheet. The work begins with fabric carrying the coarsest grit in the range used, and as the work proceeds other fabrics carrying successively finer abrasives are used. In the finishing of photo-engraving plates, for example, the coarsest grit may be No. in the recognised trade usage, and the finest may be No. 320 in that usage. Pressure is applied to the grinding heads during rotation of the spindles by reason of the weight of spindle section 51, carrier 69 and the associated parts, supplemented to the required degree by the tension of the springs 10. The pressure is varied according to the nature of the sheet metal which is being ground. In the case of zinc, a satisfactory total downward pressure on each grinding head is about 15 lbs.

It will be noted that the bar 8I on each grinding head is bored axially at 8Ia so as to communicate with the bore of the hollow spindle 51 and to open onto the metal sheet between the abrasive pads on each head. By means of the pump 45, kerosene or other appropriate flushing liquid is forced up into an overhead tank (not shown), and from the tank the liquid fiows in a steady stream at constant pressure down through the pipe BI and thence through shaft 5I, spindle 51 tubular socket 83 and opening 8Ia. of the grinding head to a location on an underlying metal sheet between the abrasive elements on the revolving head.

In practice, as in the grinding and polishing of photo-engraving plates, thegrinding'pads on heads 88 are equipped with abrasive fabrics of the desired gauge after telescoping carrier 69 and spindle 51 upwardly against the tension of the springs 10. For effecting this movement of the spindles, a cam roller 92 is secured to each head piece 13, and a cam bar 93, having for each roller stepped surfaces 94 and 95 connected by an inclined cam surface 96, is mounted for reciprocation back and forth beneath the rollers.

The metal sheets to be finished are placed on the work table I while the pads are raised. The spindles and grinding pads are rotated at high speeds, for example, about 2200 R. P. M., although higher or lower speeds than this may be used. While the pads are raised, the carriage 32 and the table ID are started in motion in their crosswise rectilinear paths at speeds such that the paths traversed by each set of rotating pads will overlap repeatedly during the course of the operation. The revolving grinding pads are then lowered to their normal positions bearing on the sheets, and the continued rotation of the pads and movement of the table l0 and carriage 32 result in a grinding of the whole surface of the sheet in overlapping swaths in a manner which ensures .equality and evenness in the surface finish. During all of this grinding, a stream of flushing liquid is continuously fed through each spindle and is flooded onto the surface of the sheet from a point inside the circular path of the pads. The heavy flush of liquid thus flooded onto the sheet surface, aided by centrifugal force imparted by the rapid rotation of the grinding pads, sweeps away free metal immediately as it is rubbed off the sheet surface. The liquid, together with the particles of metal, flows into the gutter l4, and thence to the clarifier chamber 48. Pump 45 returns the clarified liquid to the same cycle of operation.

When a grinding operation has been completed, the pads should be raised from the sheet before their rotation-or the movement of the table or carriage is stopped.

The flushing liquid fed through each spindle is thrown into the path of the pads, where it is overrun by the rapidly revolving abrasive. Metal particles removed by the abrasive are held in liquid under the pad, and the spinning of the pad causes this liquid and the free metal to be thrown outwardly and away from the grinding swath. When the pads approach a portion of the sheet on which used liquid and free metal may have collected, the continuous outward sweep of liquid from the swath of the pads brushes away this used liquid and free metal and clears the sheet surface, so that danger of overtaking and overrunning metal particles that have already been removed is avoided.

Thus, the described method and apparatus are exceedingly effective for maintaining a clear surface on the metal sheet throughout the grinding operation. Clogging of the abrasive fabric with metal dust is avoided, and scratching of the plate surface is consequently obviated. The grinding time is shortened, and a uniform smooth finish is obtained on the-sheet surface.

It'is important that the grinding pads shall not be subject to mechanical disturbance by the driving equipment. Such disturbance is avoided since the spindle 51, the parts which are carried by it and the carrier 69 in which it is housed are not constrained in lateral direction by belt pull on the pulley 55, and the spindle 51 is free to rotate steadily on its own gyrostatic center,

unaffected by the drive coupling through the ly, the respective machines beingv armed with abrasive fabrics of appropriate gauge. The number of to and fro movements of the machine table and the number of traverse movements of the spindle assembly will necessarily vary according to the nature of the metal of which the sheet is composed and the type of surface finish desired to be attained.

In the grinding or polishing of engravers sheets, which should have a uniform thickness and uniform surface finish over their entire surface, the path of movement of the table I0- and the carriage 32 should be coordinated so that the circular swath of the grinding pads will extend somewhat beyond the edges of the sheet but not to a point where the weight of the spindle assembly would not be borne entirely by the sheet.

It will be understood that a grinding fabric or paper coated'with fine abrasive tends to clog or load up with metal more easily than in the case of coarse abrasive, because there is less free space for movement of liquid and metal particles. For a constant rate of flow of kerosene or other flushing liquid onto the sheet, the Width of abrasive material in contact with the sheet, in the direction of movement of the pad, is preferably less in the case of a fine abrasive than when using coarse abrasive. In thisway the effective flushing action of the liquid is increased to compensate for the greater difficulty in flushing away the free metal.

In the finishing of accurately planed zinc sheets, such as produced according to the disclosure of my copending application, filed March 29, 1937, now United States Patent No. 2,216,538 to meetthe requirements of high grade photoengraving work, it is found in practice that about ten minutes grinding is effective for a complete grinding and polishing operation on a sheet measuring 20 x 40 inches. The grinding pads operate with clean surfaces because of the immediate clearance of the removed metal from their path, so that in practice comparatively large amounts of metal may be removed from each sheet per minute in the grinding operation, without diminishing the accuracy of the planed surface of the sheet.

It will be understood that many details of construction and operation which have been described in reference to the illustrated embodiment of the apparatus are set forth merely for clarity of disclosure, and that numerous variations and modifications may be made without departing from the contributions of the invention, as intended to be set forth in the appended claims.

I claim:

1. The method of producing a uniform smooth surface finish on a metal sheet which comprises rotating a yieldable pad surfaced with abrasive fabric on a surface of thesheet at high speed about an axis constantly at right angles to the sheet, while effecting relative movement between the sheet and said axis whereby to traverse the rotating pad in overlapping swaths uniformly covering the entire area of said surface. yieldably holding the abrasive surface of the rotating pad under constant pressure against said sheet surface during said movement, and simultaneously flooding a constant stream of gritfree flushing oil onto the said surface from a point adjacent said axis of rotation.

2. The method of producing a uniform smooth surface finish on a metal sheet which comprises" starting rotation of a yielding pad surfaced with abrasive at high speed about an axis at right angles to the sheet, starting relative movement between the sheet and said axis such as to traverse the rotating pad in overlapping swaths uniformly covering an entire surface of the sheet, thereafter applying the rotating pad against said surface, pressing the abrasive surface of said rotating pad uniformly against said sheet surface during said relative movement between the sheet and said axis, and throughout the grinding operationafiooding a constant stream of grit-free flushing oil onto said sheet surface from a point adjacent said axis of rotation to cause the abrasive to overrun av film of the oil and the oil to hold and flush away freemetal immediately after the same has been abraded from the sheet.

3. Apparatus for grinding or polishing the sur faces of metal sheets comprising continuously operating means for reciprocating a sheet in one linear path, means for repeatedly traversing abrasive pads over a surface of the sheet in a crosswise linear path and means for rotating said pads at high speed in a plane parallel to the sheet, said last-recited means including a,

tubular vertical spindle having a pad-holding head fastened to its lower end, said head having an axial bore communicating with said spindle, a tubular transmission shaft fixed against vertical movement and telescoping into said spindle, means mounting said spindle to permit vertical movement of the same while rotating, cooperating means secured to said transmission shaft and said spindle for transmitting rotation to said spindle without restraining it freedom xto move vertically, and means for supplying a and means for supplying liquid into said spindle;

for delivery to a point between said pads during rotation thereof.

5. In an apparatus for grinding or polishing the surfaces of metal sheets, a vertical hollow spindle. a transverse block secured to the lower end of the spindle and having an opening there through communicating with the spindle, spaced yieldable pads fixed to the bottom of said block on opposite sides of said opening, means on said block for fixing an abrasive fabric over each v of said pads. means including a hollow transmission shaft telescoped into said spindle for rotating said spindle, block and pads, means for supplying liquid into said shaft to flow through grinding head having abrasive-surfaced yieldable grinding pad secured to the lower end of said spindle and adapted tobear upon the surface of a sheet on said table, continuously operating means for reciprocating said table in a linear path beneath said spindle,,continuously operating means for reciprocating said cross-head and spindle in a cross-wise linear path above said table, means for rotating said spindle and head athigh speed While said table and cross-head are in motion, and means for raising or lowering said head with respect to said table while the spindle is rotating.

7. Apparatu for grinding or polishing the surfaces of metal sheets comprising a sheet-holding table, a cross-head mounted above said table, a plurality of hollow vertical spindles secured to said cross-head, a grinding head having abrasivesurfaced yieldable grinding pads secured to the lower end of each spindle and adapted to bear upon the surface of a sheet on said table, continuously operating means for reciprocating said table in a linear path beneath said spindles, continuously operating means for reciprocating said cross-head and spindles in a cross-wise linear path above said table, means for rotating said spindles and heads at high speed while said table and cross-head are in motion, means for feeding a continuous stream of flushing liquid through each hollow pindle and onto a sheet inside the path of rotation of the pads while the spindles and heads are rotating, and means for simultaneously raising or lowering said heads with respect to said table while the spindle are rotating.

8. In an apparatus for grinding metal surfaces, a rotary spindle having abrading means fastened to its lower end, a non-rotary carrier sleeve surrounding said spindle and having bearings on its upper and lower ends holding said spindle in a fixed and coaxial relation thereto, means mounting said carrier for free ,sliding movement in axial direction, said means including a housing fixed against axial movement, and spring means connected with said carrier and said housing for pressing the carrier and said spindle downwardly in axial direction and thereby yieldably holding said abrading means under constant pressure against a surface to be ground.

9. In an apparatus for grinding metal surfaces, a vertical hollow spindle having abrading means fastened to its lower end, a non-rotary carrier holding said spindle in a fixed coaxial relation thereto, means mounting said carrier for floating movement in axial direction, said means including a fixed housing supporting said carrier for vertical sliding movement relative thereto and springmeans connected with said carrier and said housing for pressing the carrier slidably toward a surface to be ground, a hollow transmission shaft telescoped inside the upper end of said spindle, cooperating means connected to said shaft and said spindle for rotating the spindle, respectively, with the shaft while permitting vertical movement of the spindle, and means for driving said transmission shaft at high speed.

10. Apparatus for grinding metal sheets comprising a horizontal work table, a vertical spindle mounted above said table, said spindle having abrading means fastened to its lower end and adapted to bear on the surface of a sheet on said table, means for rotating said spindle at high speed, continuously operating means for reciprocating said table in a linear path beneath said spindle and continuously operating means for reciprocating said spindle in a crosswise linear path above said table, said means for reciprocating said table being operative to move said table at a constant rate intermediate the extremities of its path of movement and including means for delaying appreciably the restarting of the table movement at each end of said path whereby to obtain uniform abrasion of the entire surface.

11. Apparatus for grinding metal sheets comprising a horizontal work table, a vertical spindle mounted above said table, said spindle having abrading means fastened to its lower end and adapted to bear on the surface of a sheet on said table, means for rotating said spindle at high speed, continuously operating means for reciprocating said table in a linear path beneath said spindle and continuously operating means for reciprocating said spindle in a crosswise linear path above said table, said means for reciprocating said table and spindle each being operative to move the respective table or spindle at a constant rate over substantially all of its linear path of movement, but each including means for delaying appreciably the restarting of the respective table or spindle movement at each end of its path.

12. The method of grinding or polishing the surfacesof metal sheets so as to produce thereon a uniformly smooth surface finish which comprises rotating spaced yieldable pads surfaced with abrasive fabrics at high speed in an annular path about a common axis at right angles to the sheet surface, simultaneously moving the sheet to and fro in a fixed linear path beneath said pads, simultaneously moving said pads bodily to and fro over the sheet in a fixed linear path transverse to the path of the sheet, yieldably holding the abrasive surfaces of said rotating pads under constant pressure against said sheet surface during the aforesaid simultaneous movements whereby to abrade the sheet surface uniformly by overlapping circular swaths of said pads, and simultaneously flooding a constant stream of grit-free oil onto said sheet surface from a point inside the path of rotation of said pads so as to keep the abrasive working through films of oil and continuously to flush oil and any free metal particles away from the abrasive.

13. The method of grinding or polishing the surface of a metal sheet which comprises rotating a grinding pad surfaced with abrasive at high speed in progressively overlapping annula swaths on said surface, simultaneously flooding a stream of grit-free flushing oil onto the surface and across said paths from a point inside of said paths to keep the abrasive working through oil and flush away free metal immediately after the same has been abraded from the sheet, collecting used flushing oil flowing from the sheet and treating the same to separate free metal therefrom, recirculating and reusing the treated grit-free oil as aforesaid, and recovering the separated free metal.

14. The method of grinding or polishing the surface of a non-ferrous metal sheet which comprises rotating a yieldable pad surfaced with abrasive fabric at a high speed in progressively overlapping annular swaths on said surface and continuously flowing across the path of said pad a stream of mobile, non-corrosive oil containing yieldable pad having a surface composed of abrasive alumina particles and continuously flowing across the'path of said pad a stream of mobile, non-corrosive oil containing kerosene oil.

16. The method of grinding or polishing the surface of a zinc sheet which comprises rotating a yieldable pad surfaced with abrasive fabric at a high speed on said surface and simultaneously flowing across the path of said pad a stream of kerosene oil.

1'7. The method of grinding or polishing the surface of a copper sheet which comprises rotating a yieldable pad surfaced with abrasive fabric at a highspeed on said surface and simultaneously flowing across the path of said pad a stream of mobile, non-corrosive oil including stearine oil.

18. In an apparatus for grinding or polishing metal sheets, a vertical hollow spindle having a grinding block fastened to its lower end, diametrically opposed, abrasive-covered pads secured to the underside of said block, a passage extending through said block from said hollow spindle and opening at a point between said pads, a non-rotary carrier holding said spindle in vertical position, means mounting said carrier for free sliding movement in axial direction, a hollow transmission shaft telescoped inside the upper end of said spindle, cooperating means connected to said shaft and said spindle, respectively, for rotating the spindle with the shaft while permitting free vertical movement of the spindle, tension spring means connected with said carrier and said mountin means for yieldably holding said pads against a work sheet under constant pressure, means for driving said transmission shaft at high speed, and means for introducing flushing liquid into said transmission shaft.

19. The method of producing a uniform smooth surface finish on metal work which comprises rotating a yieldable pad covered with abrasive fabric in progressively ,overlapping annular swaths on a surface of the work so as substantially uniformly to abrade the entire surface, while flowing a stream of grit-free film-forming liquid on to said surface from a point inside of said swaths and yieldably pressing said pad against said surface with a force suflicient for the abrasive to work through the resulting liquid film and abrade said surface, thereby maintaining protective liquid between the pad and said surface and causing liquid and any free metal particles constantly to be swept away from said pad.

20. The method of producing a. uniform smooth surface finish on a metal sheet which comprises holding thereagalnst a yieldable pad covered with abrasive paper and rotating said pad bodily in an annular path about an axis perpendicular to the sheet while traversing the rotating pad progressively and substantially uniformly over the entire sheet surface, and simultaneously flowing a stream of grit-free oil on to the surface and across said path from a point inside of said path so as to maintain a film of oil between said pad and the surface and cause oil and any free metal particles constantly to be swept away from said pad.

21. The method of producing a uniform smooth surface finish on a plane metal surface which comprises rotating thereon a yieldable pad faced with adherent abrasive at high speed and in progressively overlapping annular swaths traversing the entire surface, while flowing a stream of gritfree oil on to said surface from a pofmt inside of Saidswaths, thereby causing the abrasive conaseasos tinuously to work through the oil fllm'and centriiugally expelling oil and any free metal particles away from the abrasive.

22. The method of producing a uniform smooth surface finish on metal engraving sheets which comprises holding against a surface of each sheet a plurality of spaced yieldable pads covered with abrasive fabric and rotating said pads bodily in a common annular path about an axis perpendicular to the sheet while traversing the rotating pads progressively and substantially uniformly over the entire sheet surface, and simultaneously flowing a stream of grit-free oil on to the sheet and across said path from a point inside of said path so as to keep the abrasive working through the oil and constantly to sweep oil and any free metal particles away from the abrasive.

23. In an apparatus for grinding metal sheets. a rotary spindle having abrading means fastened to its lower end, a non-rotary carrier sleeve surrounding said spindle and having ball bearings at its upper and lower ends holding said spindle in a fixed and coaxial relation thereto, a fixed housing surrounding said carrier intermediate the end portions thereof, cooperating means on said carrier and said housing to permit free axial movement but prevent rotation of said carrier, spring means connected with said carrier and said housing for yieldably pressing the carrier and spindle axially toward a surface to be ground and flexible dust collars extending between the end portions of said sleeve and the respective end portions of said housing.

THOMAS JEROME MASSE.

CERTIFICATE OF CORRECTION. Patent No. 2,560,5oh. October 17, 19%.

moms JEROME MASSE.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, first column, line 5, claim 2, for the word "yielding" read -yieldable--; and second column, line 614., claim 9, strike out respectively," and insert the same after "spindle" in line 65, same claim; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 16th day of January, A. D. 19LL5.

Leslie Frazer Acting Commissioner of Patents.

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