US2415646A - Method and apparatus for grinding and polishing surfaces - Google Patents

Description

Feb. 11, 1947. LUBQSHEZ 2,415,646

METHOD AND APPARATUS FOR GRINDING AND POLISHING A SURFACE 2 Sheets-Sheet 1 Filed May 26, 1944 Benjamin ELuboshez Feb. 11-, 1947.

' B. E. LUBOSHEZ METHOD AND APPARATUS FOR GRINDING AND POLISHING A SURFACE 2 Sheets-Sheet 2 Filed May- 26. 1944 Benjamin EflLuboshez' INVENTOR V W. ATTORNEQ" Patented Feb. 11, 1947 METHOD AND APPARATUS FOR GRINDING AND POLISHING SURFACES Benjamin E. liuboshez; Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application May 26, 1944, Serial No. 537,410" (Ci. 51-131) 3 Claims. 1

The present invention relates to the grinding.

and polishing of surfaces, and particularly to a method and apparatus which is conducive to automatic operation since uniform wear on all parts of the surface being ground and/or the tool being used is obtained by the use thereof.

When grinding and polishing a flat surface, it is highly desirable that from the moment contact of the surface with a flat tool has everywhere been established, the wear at all points on the surface shall be the same. Of course, in practice, nelther the plane being surfaced nor the tool is absolutely fiat as they both exhibit slight humps and depressions which by an averagingout process are gradually reduced to tolerable values. With this qualification, the above statement expresses one condition which, if fulfilled, would enable flat surfaces, once obtained in rough grinding, to be maintained and perfected during subsequent smoothing and polishing. I

No present-day grinding machine reaches or even attempts this ideal but relies almost entirely upon the averaging-out process to produce the operator is able, y a series of approximations,

to produce a chosen curvature or flat plane. The system is thus in nosense of the word automatic and requires a skilled attendant who knows by long experience how to balance opposing tende'ncies of various uneven wearing conditions to attain the desired end. With even wear taking place at all points, this method of "feeling one's way is not necessary and renders automatic production possible. This question of even wear is notoniy of importance in connection with the production of a plane surface as such, but also is of prime importance in maintaining a desired angle between different plane surfaces on an optical prism or wedge.

One object of the present invention is to provide a method and apparatus for producing surfaces of a desired curvature automatically and with a minimum of adjustment during the grinding and polishing process.

Another object is the provision of a method and 2 apparatus of the type set forth wherein uniformwear is obtained on the work by disposing the work to one side of the axis of rotation of the tool, regulating the sizes of the two so that the work is always covered by the tool, and simultaneousiy rotating the tool and work in the same direction and at the same angular velocity.

Another object is toprovide a method and apparatus of the type set forth by means of which uniform wear on all parts of the tool is obtained by a compensating shoe frictionally engaging the tool and'having an area proportioned in accordance with the grinding action of the work on the tool.

And still another object is to provide a method and apparatus of the type set forth of such a nature that by a simple adjustment in the drive objects and advantages thereof, will best be un- -derstood from the following description of speciiic embodiments when read in connection with the accompanying drawings in which:

Fig. l-is a diagrammatic view showing a block of work engaging a much larger tool entirely to one side of the latter and used in proving that when the work is so disposed on a tool that the wear on the work will be uniform at all points if the tool and work are rotated in the same direction at the same angular velocity,

Figs. 2-5 arediagrammatic views showing how the work is disposed relative to the tool and how the compensating shoe is designed in order to obtain a uniform wear on the tool and work in an automatic manner, and

Fig. 6 shows a grinding and polishing apparatus constructed in accordance with the present invention and incorporating the principles set forth in Figs. 1-5 and fully described in the specification'.

Like reference characters refer-to corresponding parts throughout the drawings.

Briefly, according to the present invention, a regime of equal wear is maintained over the work by making the work holder enough smaller than the tool so that it can be mounted with its axis of rotation to one side" of the axis of rotation of the tool and be covered at all times bythetool.

3 The work and tool are then rotated simultaneously in the same direction at the same speed. Uniform wear of the tool surface is maintained by the use oi a compensating shoe which frictionally engages the tooL and the effective area of which is proportioned so as to compensate for the grinding action of the work on the tool. .Correct angles between two'plane surfaces of a piece of work can be obtained by stopping the work in a given position and continuing to rotate the tool. After the correct angle is obtained, it is maintained constant automatically by again starting to rotate the work in the same directionand at' the same speed as the tool.

Fig. 1 shows diagrammatically a work holding "block I! and'a much larger tool. ll having axes of rotation a and b. respectively. As is well knownin the art. the work to be ilnished is mounted on the block it in any suitable manner,

so that the surface, or surfaces, to be ground and polished is adapted to be presented to the grind- 4 tween the tool and work must be equal at all points and this means applying it at the center of gravity of the area of the block I (and the size of the block I. relative to the y 1 ll must not be such as to never completely uncover all parts 05 the tool. The latter requirement is an important practical one for the sizes and movements must be such that all Parts oi the tool receive equal opportunities of drying since the working ofabrasives is very sensitive to the amount of lubricant present.

.. In order to obtain the correct angular relationship between surfaces of a prism or wedge,

. assuming this is the time or work being ground,

the-rate of wear, must be changed in a linear. manner across the surface of the block .in the direction required and so the conditions of equal ing tool. Suppose block I0 and tool II to rotate in the same direction (shown by arrows in Fig. 1) and at the same angular velocity. Let u be any 'point on the block ll. Then the point it upon block I! will, at the chosen instant, be moving at right angles to line cu with a speed proportional to the length of' an. Likewise, considered from the point of view of the tool ii, a point immediately under it will be moving at right angles to ab at a speed proportional to the length of ab. The resultant velocity of the point u. which is upon block in, relative to the tool II is obtained by the triangle of velocities ate in whichuo represents the velocity of a and is proportional to on and at represents the velocity of a point immediately under u on tool II and is proportional to ub.

To obtain the resultant velocity relative to tool II, the direction of at inFig. 1 has to be reversed. It is clear that this triangle of velocities is exactly similar to the triangle cub turned through a right angle and in which an represents 7 up, ub'represents at and ab represents the resultant vt. But ab is constant for any given separation of centers, and since u was assumed to be any point on block ill, the velocities of all points on block I 0 relative to corresponding points on tool I i below them, must be constant and proportional to the distance between the centers of the block and tool, thedi'rection of this resultant velocity is always at right angles to the line loining the centers. 7

Thearrangement described, in-which a small 'disk is placed upon a large one, and in which both rotate at the same angular velocity and in the same direction, provides a method of obtaining uniform wear at all points of the smaller disk so long as it is at all times completely covered by the larger one.

. Since the magnitude of the uniform wear is dependent upon the separation between the centers, there is every advantage for quick surfacing in making thisseparation as large as possible The "ilgure of the surface requires no regulation since flatness is maintained automatically, but it is easy to provide for correction if necessary. For instance, by rotating the block ll block is con imenced. Surfacing then is continued wear must be temporarilyupset. A convenient way oi tjioing this with the present arrangement; is to stop therotation oi the block Ill in the required position and to continue rotation of tool; ll until the desired angle 'has been obtained. When the block is stopped, more wear is taking place at points on the block remote from the center of the tool than at points .on the blockcloser to the center of the tool in proportion to, their respective distances radially of the tool.

This gives a simple method of controlling the angle of the surface relative to another previously finished surface, and as soon; as the correct value has been obtained, the rotation of the under conditions of uniform wear and the angle is maintained. v

I Oncethe desired condition or uniform wear on the surface being ground has been achieved, at-.

tention' can be turned to the question of main:

l tainingsuniiorm wear at all points on the toolas welLI. The importance of maintaining the flat: ness oi the tool is secondary only to that oi main-"T taining flatness of the work. For automatic production the value of this refinement is obvious and one object of this invention is to maintain the flatness of both the work and the tool automatically. v

In Fig. 2, l0 again represents a work holding block resting upon a tool ll, the'centers of the two being a and b respectively. It is clear that ii the whole of the tool ii were always covered by block l0, the wear upon the tool would be uniform at all points. but in that case. the wear upon the block in would no longer be uniformover those parts not always covered by the tool. The reason why uneven wear takes place onthe tool can be seen from Fig. 2. Consider any, one of the concentric circles drawn with b as a center; -0n the circle ode the arc cd represents the amount of block I. that passes over any point on the tool H (on the circle in question) during one cycle. It is clear that this is not the same asthe lengths at other radial distances from centerb'l In fact, the wear upon the tool ii due to block II is proportional to the length o! the intercept cd of the arccde. Also, the wear due to unit lengths of any are such as cd is inversely proportional to the distance from center b. Thus ii:

R="distance'-bet'ween centers sand I: w=wear at any distance a: from the center b compared to wear at distance R p n==length of arc intercepted by the circle l0 upon a circle of radius a: and center b then, since the wear per unit area is constant under block I0,

=n.R/a: (Eu. 1)

uniform wear at all points of the tool except at the inner circular area, which, in the limit, is

p and this enables N to be calculated for different bounded by a circle whose circumference is equal to the are as or pr. This small area need never be used in practice and could be cut away on the tool. The uniform wear upon tool ll produced by the area pqrs is of course, proportional to the constant length of the arc pr chosen.

Although the wear upon the tool H due to the surface pan is uniform, the wear upon pqrs is by no means uniform and is, in fact, proportional at all points to the distance from the center b.

In Fig. 4 the surface pqrs, which we will hereinafter refer to as a compensating shoe, since as finally developed it is to compensate for unequal wear of the tool due to the grinding action-of the block W, isagain shown touching upon the rotating tool H. The constant lengths pr or as along any arc is made slightly greater than the maximum intercept ed, Fig. 2, of the block of work to be finished. so that room is left within the confines of the area pqrs for cutting out a disk to accommodate block In or the surface to be worked upon. Suppose for the moment that the block I is not rotated about its center and that like the shoe pqrs itis-kept stationary. If

the pressure per unit area upon block I and the shoe is the same and is applied at the centers of gravity at the respective areas, and if the material be the same, the wear at all useful points of the rotating tool will be constant.

In Fig. 4, suppose a circle on tool II at a distance 'a: from-center b to out the circumference of block it at c andd as before, and the figure at e and f.

Let ce plus d! equal N, and,cd equal n.

Then when block iii does not. rotate, we have seen that uniform wear (on tool H) takes place when -n+N=constant N=L-n. where L is a constant values of z in any given case.

Fig. 5 shows the various shapes concerned for the given proportions of block Ill and tool H. N is the original block rotating on tool H. C is the same as area pqrs in Fig 4. D is the shape arrived at by multiplying n (the length of the arc cut off by block ill) by R./.'::. The wear upon the tool I I due to this shape D, (not rotating) is equivalent to the wear upon tool H due to the block it when it is rotating. The final area E (shaded) shows the differences (measured along the arcs having b as a center) between figures C and D. Hen'ca'with a compensating shoe of the shape of E frictionally engaging the tool and made of the same material as the work carried by the block it, and with the pressure applied to the center of gravity of the area, of such an amount as to give the same pressure per unit of area as that upon block Hi, the wear due to both a compensating shoe of shape E and block In (rotating), is uniform at all useful points upon the rotating tool H. I

' It is believed apparent-that the compensatin shoe E and block ill shown in superposed re-' lation on tool II in Fig. 5 merely to show the development of the area. of shoe E, and that in practice the shoe would be spaced circumferentially of the tool with respectto the work, see Fig. 6. In practice, so that the relative movement between the tool and block will not be repetitive, the speeds of rotation of the tool and block may not be exactly identical although very nearly so. During surfacing, the rotating block 10' and the non-rotating shoe E may be moved back and forth in unison over a small distance radially to and from center I; to further prevent repetitive movement between the block and tool. If this be the case, in a practical shape, the end prof the shoe E may be extended beyond the circumference of the tool Ii and the central area around the center b may be filled in.- The shoe E may have the shape shown in Fig. 5 or it may be divided into sections, each section being spaced at different points around the tool in proper radial position relative to the work. By way of example,

the shoe E shown in Fig. 5 may be divided right in half longitudinally or transversely of its length. the two parts then being relatively spaced around the tool at any suitable point so that the combined action of the two is the same as that for the single shoe. Theefiect' of the shoe is the same, regardless of its number of components and 7 their relative dispositions, so long as the lengths along the arcs are correct. Likewise, when severalblocks are being surfaced upon the same tool at the same time, a single compensating shoe can be proportioned to compensate for them all or a separate shoe may be provided for each one.

Since, in practice, the blocks of prisms, or other work, are made up of a number of small prisms, or pieces, of various shapes, the whole circular area of the block It does not necessarily represent glass surface. The average error due to this cause must .be taken into account in designing.

' the compensating hoe, and, although the general shape of the shoe will remain the same, the cor rection will vary for each blocking arrangement used for the work. On the other hand, if the work being finished is a disk placed with its center in alignment with the axis of rotation of the block, the conditions set forth are fully met.

In Fig. 6 there is shown an actual machine constructed .so as to carry out the method of grinding and polishing set forth above.

As shown, the. machine comprises a frame 50 consisting of a base 5|, which is adapted to rest upon 'a bench or-the' floor; an upright 52 and three arms 53, 54, and 55, looking from bottom to top,

extending from the upright 52. Journaled in the base SI and the lower arm 58 is a stub shaft 58, which is adapted to be driven from a motor-driven drive shaft 51 through bevel gears 58 and 59. The grinding tool may be positively connected to the sub shaft 56 to be rotated thereby by having a conical post 80 extending from thebottom of the tool engaging a corresponding recess Si in the upper end of the shaft, the tool being held against rotation by a pin or key arrangement 82.

Rotatably mounted in the middle arm IN, to

one side of the axis of rotation of the tool, is a tubular shaft 63 to which a bevel gear 64 is at tached. Keyed to this bevel gear, to be free to move vertically relative thereto, is a work spindle 65. The upper end of this spindle is further guided against sidewise'play by passing through a bore in the upper arm 55. The work holding block Ill, on which the work W is mounted in a known manner, is fixed to the lower end of the spindle by the ball and socket joint 88 which is of ordinary construction with the exception that The work spindle is adapted to be driven in the same direction and at the same angular velocity as the tool by virtue of the drive including the bevel gear 68 meshing with bevel gear 64 and fixed to a shaft Journaled in the upright of the frame and having a chain sprocket 89 on the other end. This sprocket is connected to a second sprocket l rotatably mounted on the drive shaft .ilgand including a male clutch member H by a chain .12. The sprocket Ill is adapted to be clutched to, and released from, thedrive shaft when the female clutch member H, which is slidably keyed to shaft 51, is moved into and from engagement, respectively, with the clutch member 'II on the sprocket. The position of the female clutch member is controlled by a treadle l2 including a yoke ended arm ll-engaging the slotted collar of the female clutch member, as

is well known, and the treadle is weighted by a weight 14 to normally engage the clutch. To disengage the clutch the treadle is raised by the toe, or hand, and when the "yoke arm I3 passes the dead center position, the treadle is held up I by the action "of a tension spring 15 which is connected at one end to a pin on the yoke arm and. is fastened at the other end to a pin on the base ll located vertically below the pivot point of the treadle and yoke arm. In the lowered position of the treadie shown in Fig. 6, this spring acts to 'j aid the weight M in holding the clutch in engagement. -Should it be desired to prevent nonrepetitive rotation of the tool and work. this 7 can be done by placing one less tooth in the bevel gear M than in the bevel gear 59, or vice versa.

' The work spindle-68 has fixed thereto a handle wheel 16 which may be used to rotate the work relative to the tool to position the work properly 45 for angle control, as mentioned above, or for raising the work from the tool for any reason whatso- 54 and 55. respectively. is a second vertical spindle/so 11. To the'lower end of this spindle the co m- V pensating shoe E is connected by a-ball-and-socket joint, and this joint is so located that downward pressure on the shoe is applied at the center of gravity of the effective area of the shoe so that the pressure will be distributed evenly over the entire effective area of the shoe. The same holds true for the location of the ball-and-socket joint between the block Ill and the work spindle 65. The compensating shoe is refrained from 60 rotation by a stop lever 18 pivoted at 18' to the middle'arm 6| of the frame and the lower end IQ of which is adapted to engage a slot, not shown, in the edge of a shoe. Downward pressure is applied to the compensating shoe E by removable weights M embracing the spindle and resting on a stop 80 fixed to the spindle. Downward pressure is likewise applied to the work spindle 65 by removable weights M. The weights M andM' both the work and the tool wear uniformly and require a minimum amount of adjustment. The irregular wear that would normally occur on the tool is transferred to the compensating shoe E where it can be more readily dealt with. As

the shoe is stationary, the wear upon it is proportional to the distance from thacenter of rotation of the tool and, hence, if the pressure is applied through a universal joint over the center of l gravity of the area of the shoe, the shoe will automatically remain at all points in contact with the tool'in'spite of wear upon itself. This is very important for it means that the compensating shoe also is self-maintaining and requires a minimum amount of adjustment. Actually. there is a tendency for the surface of the compensating shoe E to grind to a slightly conical shape, but to a first approximation, the above statement is true. In any case, further slight complications arise when 20 the shoe is given a to and fro movement as previously explained. These effects. however, are of the order of a correction upon a correction and as soon as they become suillcientiy important. the shoe can be easily resurfaced.

' Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be limited to the precise details of construction shown and described but is intended to cover all modifications' coming within the scope of the appended claims.

Having thusdescribed my invention, what I claim is new and desire to secure by Letters Patcut of the United States is: p

1. In a grinding apparatus the combination of a rotatable circular grinding disc; a rotatable circular block on which the work to be finished is adapted to be mounted, the diameter of said block being less than the radius of said grinding disc; means for mounting said block relative to said disc so that the block lies entirely to one side of the center of the disc and is completely covered thereby; means for rotating said disc and tool at substantially the same angular velocity and in the same direction, whereby the work is subjected to uniform wear throughout its area; and an elongated stationary compensating shoe ,frictionally engaging the grinding face of said disc, said shoe extending radially of said disc and having an area varying longitudinally of the shoe and proportioned so as to compensate for the non-uniform wear of the tool resulting from said arrangement of grinding disc and tool which is conducive to uniform wear of the work.

2. In a grinding apparatus the combination of a tool; of a rotatable block for supporting the work and holding it against said tool, said block being disposed with its axis of rotation to one side of the axis of rotation of said tool and having a work supporting area of a size to be completely covered by said tool at all timesj means for rotating said tool and block at substantially the same angular velocity and in the same direction, whereby all parts of the work are subjected to uniform wear; and stationary means frictionally engaging said tool to continually dress the same during the grinding operation; said lastmentioned means comprising a single friction compensating shoe extending radially from the axis of rotation of the tool to the outer edge thereof those portions of the shoe not covering the annular area of the tool engaged by the-work being made up of a plurality of arcuate sections I concentric to the axis of rotation of the tool, each arcuate section being of the same length and at least as long as the diameter of the working area of said block; said portions of the shoe bein joined by an area reducedin proportion to the rinding. action on the tool by the work.

3. In a grinding apparatus the combination of a tool; of a-rotatable block for supporting the work and holding it against said tool,-said block being disposed with its axis of rotation to one side of the axis of rotation of said tool and having a work supporting area of a size to'be completely covered by said tool at all times; means for rotating said tool and block at substantially the same angular velocity and in the same direction, whereby all parts of the work are subjected to uniform wear; and stationary means frictionally engaging said tool to continually dress the same during the grinding operation; said lastmentionedmeans'comprising a plurality of substantially stationary friction compensating shoes engaging the surface of the tool at points spaced from one another both radially and circumferentially of the tool; each of said shoes having an area proportioned in accordance with its position relative to the block radially of the tool and in on the tool to compensate for non-uniform wear of. the tool by the work.

BENJAMIN E. LUBOSHEZ.

REFERENCES ci'rEn The following references are of record in the file of this patent:

1 Number 25 Number accordance with the grinding action of the work I UNITED STATES PATENTS Name Date I Blood July 4, 1939 Macbeth "-1 Apr. 29, 1890 Kranich May 4, 1937 Bullard July 23, 1940 Jarrett Feb. 24, 1942 Desenberg June 20, 1944- Holman June 27, 19,44 Tillyer et a1 July 27, 1920 Kernp Aug. 31, 1943 Stromgren Aug. 23, 1932 Avery Nov. 8, 1938 Jackson Aug. 3, 1943 FOREIGN PATENTS I Country Date Swiss Sept. 21, 1897

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