US2655769A - Lapping machine - Google Patents

Description

Oct. 20, 1953 T. a; Lewis LAPPING MACHINE 4 Sheetg-Sheet l mm an mm Q 9w Filed May 22, I950 {I an QM ThomasGLewis ATTQRNEY T. G. aims 2,655,769

Get. 20, 1953 I MACHINE 4 Sheets-Sheet 2 Filed May 22, 1950 rm z Thomas G.Lewis ATTORNEY INVENTOR.

Oct. 20, 1953 'TJG. LEWIS LAPPING MACHINE 4 Sheets-Sheet 3 Filed May 22, 1950 INVENTOR. Thomas G. Lewis ATTORNE Y Patented Oct. 20, 1953 UNITED STATES the? OFFECE LAPPING MACHINE Application May 22, 1950, Serial N0. 163,561

17 Claims.

This invention relates to machines for lapping metal articles with suspensions of particulate abrasives in liquid vehicles, and particularly to an improved machine for the lapping of cylindrical shaped articles.

Previously, it has been the practice to employ lapping tools having a relatively high inherent retentivity for the abrasive materials when lapping metal articles with abrasives suspended in liquids. Under these conditions, a large proportion of the abrasive particles become embedded in the laps, where they effect their abrading action on the work by a shearing or tearing motion somewhat resembling that of a conventional lathe tool. A varying quantity of the abrasive remains in a more or less free condition for one or more transverses of the tool past the work and, therefore, a non-uniform movement of the particles ensues, resulting in an uneven distribution of the abrading burden among the particles, and scratching of the surface of the work. In addition, particles of surface material removed from the work in the course of abrading tend to aglomerate into larger masses, which eventually deface the work surface as lapping continues.

I have now found that an improved abrading action is secured when the abrasiv particles are rolled freely between the Working surface of the lapping tool and the Worked surface of the article being processed as relative movement is maintained between the lap and the work. This rolling movement of the abrasive particles is depend ent on a number of factors, including the physical properties of the lamp material itself, the pressure with which the abrasive is forced into contact with the work, the viscosity of the liquid ve hicle in which the abrasive is suspended, the pattern of movement preserved between the lap and the work, and other variables. 1

An object of this invention is to provide an improved lapping machin for cylindrical objects which is capable of imparting a superior surface finish to the work with accompanying economies in time and labor.

Another object of this invention is to provide an improved lapping machine for cylindrical objects which is largely automatic in operation and which may be attended by unskilled personnel.

Another object of this invention is to provide an improved lapping machine for cylindrical objects which is capable of reproducing a predetermined quality of surface finish to a high degree.

These and other objects of this invention will become apparent from the description of the'following illustrative drawings in which:

Figure 1 is a side elevation of one embodiment of this machine employed for the surface finishing of a relatively large diameter cylindrical roll, such as those used for the casting of film-forming materials;

Figure 2 is a front end elevation of the machine shown in Figure 1 with the driving motor and driving belts for the lapping head shown by broken line representation;

Figure 3 is a front elevation of the lapping head,

Figure 4 is a longitudinal section through the double eccentric driving mechanism for the lapping head, with a rough lapping head attached,

Figure 5 is a fragmentary front end view of the double eccentric driving assembly shown in Figure 4,

Figure 6 is a vertical central section through a lapping head employed for fine lapping,

Figure 7 is a partially fragmentary perspective View of a rough lapping head, and

Figure 8 is a perspective View of a lapping head employed for the fine lapping operation.

In general, the objects 'of this invention are attained by providing an apparatus for rotatab-ly supporting the work and forcing particulate abrasives suspended in oil applied to the work. 7

against the surface with a self-aligning tool shaped to conform to the surface, while maintaining ahigh degree of-random movement between the working' surface of the tool-and the worked surface of the piece treated. According to a specific embodiment of the in vention, these objects are accomplished by flexibly supporting a lapping head in parallel relation to the rotatably supported work, with resilient force applying means bearing against the lapping head, comprising a double eccentric (e. 23 and All) and self-aligning bearing rods (e. 42, 42) mounted in parallel relation with the double eccentric, thus forming three principal reference axes so as to produce substantially free, threedimensional movement of the lapping head while still retaining the longitudinal surfacing elements of the lapping head parallel to the axis of rotation of the cylindrical object being surfaced.

Referring to Figure 1, the apparatus comprises a base structure I consisting of a heavy I-beam frame resting on the building floor, which frame is preferably strengthened by one or more cross pieces 2 welded to the insides of the webs. To the top of frame I are secured sub-frames 3 and 4, which may also be conveniently fabricated from channel irons or I-beams, sub-frame 3 providing support for th lapping head while sub-frames 4 support a pair of self-aligning split pillow block bearingspone-oi which is indicated at-5. Sub- =3 frames 3 and 4 are assembled upon base I with bolts 6 and 7, respectively. Bearings are assembled upon sub-frame 4 with bolts 8.

The cylindrical work piece 9, the integral annular shell ill of which is to be surfaced, is fixedly secured to shaft H by keys or other means and shaft I I is journaled in bearings 5, sufficient lateral clearance between the I-beams constituting the side members of base i being allowed so that cylinder 8 is freely rotatable within bearings The upper flanges of base members I are provided with a series of drilled holes to permit adjustment of sub-frames 4 at var ing distances from the lapping head to accommodate work of different diameters. Pinion l2 driven by shaft I3 connected to a suitable gear head motor, not. shown, turns shaft 5! by engagement with bull gear is keyed to H at one end, rotation being in a counterclockwise direction as indicated by the arrow. tween the surface to be worked and the lap should not exceed about 180 ft./minute for rough lapping about 175 ft./minute for fine lapping, therefore, cylinder 9 is revolved at a slow speed. In a typical case where a roll 24" in diameter with a face 24" wide as processed, a rough lapping speed of 1.6 R. P. M. and a fine lapping speed of 2.0 R. P. M. were entirely satisfactory.

As shown in Figures 1 and 2, sub-frame 3 supports uprights l5 carrying flanges at their lower ends for the reception of bolts l6 passing through drilled holes in the upper flanges of 3. The forward edge of the flange of sub-frame 3 is provided with strip I! securely welded thereto which is drilled and tapped across its length for the rcg2;

thereto for the support of the front and rear bearings 2| and 22, respectively, which carry the outer shaft 23 of the double eccentric which drives the lapping head 24. Bearings 2i and 22 are preferably of the one piece pillow block type, incorporating integral shaft locking elements, and are secured to pad by bolts 25.

The upper ends of uprights l5 are provided with hearing boxes 25, secured theretoby bolts 21, within which freely rotatable shaft 28 is journaled. The central portion of shaft 28 is enlarged to a square cross section as indicated at 29 for the reception of the forked ends of the two hanger arms 30 which are fixedly secured thereto. Attachment is accomplished by rear plates 3| which complete the enclosure of portion 29 when assembled to the forked ends of hanger arms 3!! with hexagonal-headed bolts 32 engaging with tapped holes in the hangers. The forward ends of hangers 30 are provided with vertical slots 33 (Fig. 1) for the reception of the upper ends of the turnbuckle type ball bearing supporting members indicated generally at .34 which are attached thereto by bolts 35. Members 34 may be commercially available, self-aligning bearing rods. The lower balls of members 34 are attached to the end lugs 35 of lapping head 24 by bolts 31 which engage with internal threads in the balls. Within limits, this flexible supporting arrangement maintains or efiects the free vertical, horizontal and transverse movement of lapping head 24, while always maintaining its longitudinal axis parallel to the axis of rotation of the work 9, the upper and lower balls of members 34 being restrained against movement but their mating bearing parts being freely movable It is preferred that the relative speed be- 4 with respect to the balls, to facilitate the threedimensional movement.

Referring to Figures 3, 4 and 6, the front side of lapping head 24 is provided with a recessed seat for the reception of a self-aligning antifriction bearing 38 which incorporates an integral sleeve element 39. The bore of 39 is sufficiently large to accommodate the crank end 40 of the double eccentric with a sliding fit, so that head 24 is free to move axially with respect to the double eccentric during operation of the latter. In setting up the machine, a clearance of about 1%" minimum is preferably allowed between the end of 40 and the adjacent side of the working face of the head, so that the lapping elements of the head will always conform to the profile of the work as the head is oscillated by the double eccentric. Head 24 is also provided with two selfaligning bearing receiving recesses 24a located approximately one-fourth of the distance in from each end of the head for the loose reception of the hemispherical heads of spring-actuated, force-applying members 42. The rear ends of members 42 are threaded to receive adjusting nuts 43 which bear on the rear ends of compression springs 44, the forward ends of which abut backing members 19. Thus, the force exerted by the springs 44 against head 24 can be increased by turning nuts 43 in a forward direction or decreased by adjustment in the opposite direction to maintain any desired contacting pressure of head 24 against work 9. The forward ends of members 42 are steadied loosely within holes in members [9, a total clearance of the order of about 1% being allowed, so that the hemispherical heads of members 42, seating in recesses 24a are maintained free to assume a position on the same horizontal line as the center of crank end 40 during its rotation, thereby avoiding the development of force couples which would tend to throw the longitudinal axis of lapping head 24 out of parallelism with the longitudinal axis of the work 9. The forward ends of members 42 may be freely slidable within the holes in members H), as shown in Figure 1, or may be provided with conventional latching devices for complete longitudinal retraction from head 24 for'facility of adjustment.

It will be seen, therefore, that with the selfaligning means suspended as indicated, with the ends of force-applying members 42 bearing against the head 24 in recesses 24a and in parallel relation with force-applying member 44 of double eccentric 23 also bearing against head 24, to effect three-dimensional movement of said head, lapping head 24 is thereby maintained in position to produce substantially free movement along each of the three principal reference axes of elements 42, 40, 42, while maintaining the longitudinal elements of the lapping head parallel to the axis of rotation of the object being surfaced, as heretofore described;

In the assembly arrangement of the several parts of the machine, it is preferred to dispose the points of connection of the lower balls of members 34 with head 24, the center of rotation of bearings 38, and the self-aligning-bearings 24a in head 24 receiving the ends of force-applying members 42 all on a common horizontal line passing through the center of gravity of head 24. With this organization, the development of inertla force couples which impose nonuniform loads on the work at the top and bottomof the oscillation cyles isavoided.

Referring to Figures 4 and5, the anti-friction bearing retainers 45 and 46 of front bearing 2!: and rear bearing 22, respectively, rotatably support the outer 23 of the eccentric drive for head 24. The bore of shaft 23 is provided with the greater eccentricity of the pair of eccentrics constituting the drive, the degree of eccentricity of the bore of 23 being chosen so that the maximum radius of oscillatory movement to be applied for lapping head 24 will be produced when the eccentricity of the second member of the pair is added, while the minimum radius of oscillatory movement to be applied will be produced when the two ecoentricities are opposed to one another. In practice, an eccentricity of 3 for the bore of shaft 23 has proved entirely satisfactory. inner shaft 4! is supported in freely rotatable relationship within the bore of 23 by the two end bearing bushings 48 and 49-. The second eccenti'icit'y of the drive is provided by the offset of crank: end 40 of shaft 41, which, for the typical case described, may be 3 Shaft 23 is turned at a relatively high speed by V-belt sheave 59 fixedly secured thereto by set screw 5|. Shaft 41 is turned at a slow rate with respect to shaft 23 by V-belt sheave 52 secured to collar 53 by one or more screws 54, collar 53 being mounted in freely rotatable relationship on the outside of shaft 23. To secure the differential speed necessary to turn 41 at a constant rate with respect to 23, the diameter of sheave 52 is made slightly greater than the diameter of sheave 50, a difference of about referred to pitch diameter sheaves operating with ordinary belt slippage resulting in a lag of one complete revolution of shaft 41 with respect to shaft 23 once every two minutes when shaft 23 is revolved at 600 R. P. M. Sheaves 50 and 52 are driven from a common V-belt pulley 55, secured to the shaft of motor 56, through V belts 51 and 58, respectively'. Driving connection between sheave 52 and shaft 41 is accomplished through collar 59 provided with crank pin fill which engages with a radial slot 6! formed in the forward face of collar 53. Collar 59 is fixedly secured to shaft 41, in slidable relationship with the forward end of shaft 23, by drive pin 62, collar 59 thus securing sheave 52 against outward movement along shaft 23. The opposite end of shaft 41 is provided with with a counterweight 63 fixedly attached to shaft 4'! in slidable relationship with the adjacent end of shaft 23 by set screws or any other suitable means, not shown. It will be understood that counterweight 63 is proportioned and mounted so that its unbalanced mass will oppose and counteract the unbalanced forces produced by the complex movement of lapping head 24. The double eccentric mechanism hereinabove described causes a point on the lapping head to describe a high non-repetitive path, the diameter of the lapping circle varying continuously from about k" to 1" every two minute for the specific conditions detailed. It will be understood that the paths described by individual abrasive particles between the working surface of head 24 and the worked surface of cylinder 9 are even more random and complicated due to the superadded continuous rotation of the work 9 within bearings 5.

The foregoing is a highly important feature of this invention, and this pattern of movement makes it possible to eliminate pits or depressions from the surface of the work without concurrently cutting grooves, or so-called comet tails, transverse the lower peripheral edges of the depressions. The pits or depressions referred 6 to are sometimes cylindrical in form. with their axes normal to the work, while at other times they may be concave or more or less conical in shape, and apparently are caused by non uni form deposition of metal, or the inclusion or minute gas bubbles, where the surface of shell in is electroplated, as is the usual practice. In the course of lapping, abrasive particles collect within these depressions and, as the surrotmding' metal is abraded away, and eventually forced out by the lapping head. The paths taken by these escaping particles have an important bearing on the formation of comet tails. If the movement of the lapping head is pure reciprocatory and the work is simultaneously turned, the lower edges of the depressions are grooved out between lines generally defining a sector having a center coinciding with the center of the depression. The continually expanding and contracting oscillatory pattern imparted to the lapping head 5y the double eccentric mechanism hereinabo've do scribed appears to remove abrasive particles from the pits by a rotational or cratering movement, urging the particles along paths distributed around the full peripheries of the pits and more nearly concentric therewith. The result is that the formation of the comet tail defects is ractically completely avoided and the surface quality greatly improved.

The rough lapping head shown in Figures 4 and 7 and the fine lapping head shown in Figures 6 and 8, are identical in all respects, except as regards the working elements and thei'nanne'r in which these elements are attached to the heads, and are completely interchangeable in their mounting on the machine. The rough lapping head elements consist of straight lengths of tool steel or other hard material 64, slightly longer than the width of work 9, seated "within recesses in the head 24 and retained in place'by socket-headed bolts 65. The working surface of strips 64 are shaped to a curvature conforming to the periphery of shell Ill, the surface of which it is desired to lap. For best results, it is preferred to limit the length of elements to the.

length of the cylindrical work piece plus about twothirds of the length of the maximum stroke of crank 40, thus compensating for excessive edge lapping effects byre'stricting lapping action in the end zones to only a portion of each cycle of oscillation. The width ofelements 64 should be limited to values where the total pressures applied to the worked area are not so great as to deflect the work to such a degree that dimensiohal control is lost Excessively wide elements also develop on wedges between their working surfaces and the work, which reduces cutting eificiehcy, since the oil film then attains a thickness greater than about two-thirds the average abrasive particle diameter and the particle are thereby cushioned from effective contact with the work. In the typical case where a 24" diaiheter roll of 24" face width wassu'i'faced ac cording to this invention, elements 64 havinga width. of 1 2" and a length of 24%;," with center-to-centr spacing of about 29 proved entirely satisfactory. v

The fine lapping element consists of a full tetrafiuoroethylene, such as that disclosed in my copendingapplicatioh, Ser. No. 163,562, filed May 22, 1950. The fine lap is secured to the working face of head by metalretaining stripsiil attached to the rearwardly inclined edges of 24 with cap screws 68. It will be understood that, if springs 44 are regulated to the same compression as during the rough lapping operation, the total pressure applied to the work during fine lapping will remain unchanged; however, the pressure per unit area will be reduced in the direct proportion in which the working area of the fine lap exceeds the combined working areas of the two strips 64. The length of the fine lapping'element is preferably limited to the width of the work plus about two-thirds the maximum stroke of crank 40, as hereinabove described for the rough lapping elements, to compensate for the somewhat more rapid lapping which occurs in the end zone regions.

The fine lapping element 66 is backed with a relatively thin canvas bag 69 filled to a thickness of about to /2" with pitch or a material of similar properties, the pitch having a plasticity at operating temperatures and pressures sufficient to permit strip 66 to conform to the surface of shell l0, while still providing support for the strip and distributing pressure evenly over its entire area. 'The pitch backing bag is secured in place on head 24 by tucking the loose edges beneath retaining strips 61 and punching holes through the edges for the passage of screws 68.

Where an impervious material, such as polytetrafluoroethylene, is employed as the fine lap,

the working surface of strip 65 is preferably broken with a uniform square pattern of slit lines having a depth of 0.040" to 0.060", as indicated at in Fig. 8, each unit of which measures about 0.015" to about 0.125" on a side, with one diagonal'of the square approximately parallel to the axis of head 24 and work 9. It will be understood that the lap is not weakened appreciably by the surface roughening imparted by the slitting, and a polytetrafluoroethylene lap thick may be treated as described without sacrificing much of its useful strength. The primary purpose of the slit lines is to relieve pressure built up in the abrasive-suspending liquid vehicle film, particularly when very fine abrasives such as diamond dust are employed, so that the thickness of the liquid film will not exceed a value ofabout twothirds the average abrasive particle diameter, where abrading action is considerably reduced or even entirely halted, An additional effect of surface slitting is that the flexibility of the lap isthereby somewhat improved, so that the formation of hard spots resulting from non-homogeneities in the lap material is largely avoided.

H In operation, the full face width'of the work is lapped by applying suspensions of abrasive of progressively decreasing particle size in sequence to the surface to be worked. This may be accomplished by either dripping the suspensions on the work at a point above the lapping head, or applying the suspensions manually with a paint brush. The work may be turned in either direction as viewed in Fig. 1; however, it is pre-' ferred to operate with counterclockwise movement, for the reason that the recovery of suspended abrasive escaping from the edges of the work is thereby somewhat facilitated. The compressions of the springs 44 are adjusted so that an average contacting pressure of below about 18 lbs/sq. in., preferably about 10 lbs/sq. is applied by the head to the work. The lapping is accomplished in two stages, the rough lapping being effected at a relatively rapid rate by the tool steel head after which the fine lapping head is substituted, and the fine lapping conducted at a somewhat slower rate until the final quality of finish is obtained. It is preferred to reverse the direction of oscillation of the lapping veniently accomplished by providing the apparatus with a conventional reversible type motor 56 for driving the double eccentric mechanism.

It will be apparent from the foregoing dis-- closure in detail that this invention may be modified in various ways including the manner in which the lapping heads are supported, andpressed against the work and oscillated, without departing from the scope and spirit of the invention; it is not the intention to be limited in the scsope of the disclosure except to the extent indicated in the following patent claims.

I claim:

1. In a lapping mechanism including means for rotatably supporting and drivingly rotating a cylindrical work piece, a base structure, a lap-' ping head having a con-cave surface to conform substantially to the external surface of the cy1in-' drical work to be surfaced, supporting means for maintaining the lapping head in parallel relation and substantially in the same horizontal plane with the axis of the work piece, said supporting means comprising upright supporting members mounted in spaced relationon the base structure,

shaft having its ends rotatably journaled insaid upright members and positioned substantially in spaced, parallel relation with the lapping head, hanger arms supported at one end on said shaft with the other ends free, self-aligning supporting means depending from the free ends of said hanger arms and engaging the outer ends of the lapping head for supporting the lapping head parallel with the axis of the work,-

eccentrically operated means also mounted on the base structure for oscillating the lapping head, and auxiliary means positioned in spaced rods for producing vertical, horizontal and trans-, verse movement of the lapping head, in parallel relation to the axis of rotation of the work piece, eccentrically operated means positioned to oscillate thelapping head against a rotating cylindrical object, powered means for oscillating the lapping'head past the surface of a rotating cy-. lindrical object, and a self-aligning connection.

between the powered means and the lapping head for controlling the oscillations.

3. The invention of claim 2 in which the eccentrically operated means comprises an inner shaft, and an outer shaft having a bore with greater eccentricity than the inner shaft, an offset crank end on the inner shaft for producing the second eccentricity of the drive, and a counterweight mounted on the inner shaft having an unbalanced mass opposing and counteracting the acumen 9 unbalanced forces produced by the complex movements of the lapping head.

4. The invention of claim 2 in which the eccentric drive comprises a double eccentric in-- cluding an inner shaft and an outer shaft and front and rear bearings for rotatably supporting the outer shaf, said outer shaft having a bore with greater eccentricity of the pair of eccentrics constituting the drive, while the inner shaft is supported in rotatable relationship within the bore of the outer shaft, so that the maximum radius of oscillatory movement for the lapping head is produced when the second member of the pair is added, while the minimum radius of oscillatory movement is produced when the two eccentrics are opposed to one another.

5. The lapping machine of claim 2 in which the powered means for oscillating the lapping head past the surface of the object to be lapped comprises a first rotatable shaft having an eccentric bore, a second shaft mounted in substantially free, independent, rotatable relationship within the eccentric bore of said first shaft, said second shaft having an eccentrically disposed pin forming a longitudinal extension of said second shaft and positioned for oscillating said lapping head when eccentrically operated, means eliminating relative movement between said shafts in a direction parallel to the axes of said shafts, a first powered means for turning said first shaft at one predetermined speed, a second powered means mounted in independent, rotatable relationship to said first powered means for turning said second shaft at a predetermined speed differing from the speed of said first shaft, said second powered means having a driving slot, a collar carried by said second shaft and freely movable with respect to said first shaft, said collar having an eccentrically disposed driving pin for engagement with said driving slot of said second powered means, a common powered means for driving said first and second powered means, and a self-aligning connection positioned to move axially with respect to the longitudinal, eccentrically disposed pin of said second shaft and in engagement with said pin.

:6. In :a lapping apparatus including means for rotatably supporting and drivingly rotating a cylindrical work piece, a base structure, a lapping head having a concave surface to conform substantially to the external surface of the cylindrical Work to be surfaced, means for dependently supporting the lapping head in working position'comprising upright members in spaced relation mounted on said base, an oscillating shaft rotatably journaled in said fupright members, hanger arms supported at one end by said shaft with their opposite ends free, supporting means dependent from the free ends of said arms and engaging opposite ends of the lapping head to support the lapping head in parallel relation with the work to be surfaced, powered mean for oscillating the lapping head past the surface of the cylindrical object to be surface, a self-aligning connection between the aforesaid ,powered means and the lapping head, and a pair of force applying means in spaced parallel relation with said oscillating means and with each other, positioned to urge the lapping head in the direction of the axis of the work to be surfaced during said oscillations.

'7. The invention of claim 6 in which the supporting means depending from the hanger arms comprises self-aligning bearing rods with one set of elements at one end attached to the hanger 10 members and the corresponding movable ele-' ments at the opposite end afiixed in spaced relation to the lapping head.

8. The lapping mechanism of claim '6 in which the centers of the dependent supporting means, the ends of the force applying members, the center of rotation of the self-aligning connection between the powered means oscillating the lapping head and the lapping head, and the center of gravity of said lapping head, when placed in operation for surfacing a cylindrical work piece, are all positioned to be maintained substantially upon a common horizontal line parallel to a line drawn through the axis of rotation of the cylinder to be surfaced.

9. In a lapping apparatus including means for rotatably supporting and drivingly rotating a cylindrical work piece, a base structure, a lapping head having a concave-curved working surface to conform substantially to the external surface of the cylindrical object to be surfaced, and in parallel relation therewith, an eccentric driving means positioned for oscillating the lapping head at its center portion, means to urge the head to-- ward the axes of the cylindrical Work piece, .supporting means effecting vertical, horizontal and transverse movement of the lapping head while maintaining the longitudinal axis of said head parallel to the axis of rotation of the work piece, comprising self-aligning bearing rods which in combination with said driving means constitute three principal references axes with substantially free movement of said lapping head along each of said axes to produce three-dimensional movement of the lapping head during oscillation while still retaining longitudinal elements of said head in parallel position to the axis of the cylindrical object when rotated.

10. In a lapping apparatus including means for rotatably supporting and drivingly rotating a cylindrical work piece, a base structure, a rotatable shaft supported on said base structure, hanger arms in spaced relation having one end of each supported on said shaft with their free ends in position to support a lapping head, a lapping head dependently supported by the free ends of said arms, a. double eccentric means for oscillating the lapping head axially with respect to the eccentric means, comprising an inner shaft and an outer shaft, a crank end on the inner shaft and a sleeve bearing mounted on the lapping head for accommodating the crank end, powered means for driving each of said shafts at different speeds to oscillate the lapping head, force applying means mounted on said base structure in parallel relation and on opposite sides of the double eccentric with their ends bearing against the lapping head in self-aligning relationship to urge the lapping head towards the axis of the cylindrical work piece.

11. In a lapping apparatus including means for rotatably supporting and drivingly rotating a cylindrical work piece, a base structure, a mechanically actuated, self-aligning lapping head having a concave-curved surface to conform to the cylindrical surface of the work piece, a double eccentric driving means positioned to operate the lapping head comprising an inner shaft and an outer shaft mounted to be driven at different speeds, spaced bearingssupporting said double eccent c a freely rotatable shaft supported at right angles but in spaced relation to the eccentric driving means, hanger arms extending horizontally from said rotatable shaft and supporting said lapping head, means positioned to maintain the lapping 1 1 head against the cylindrical work piece including a crank end of the double eccentric in position to oscillate the lapping head, spring-actuated, force-applying means in spaced parallel relation with said eccentrically operated shafts, positioned to urge the lapping head toward the axis of the work piece, and self-adjusting means depending from said hanger arms capable of maintaining said force-applying means and lapping head in coordinating relationship.

12. In a lapping apparatus including means for rotatably supporting and drivingly rotating a cylindrical work piece, a base structure, a mechanically actuated, self-aligning lapping head mounted on said base having a concave-curved surface adapted to conform to the cylindrical surface of the work piece, a rotatable shaft supported by said base in spaced parallel relation to the lapping head, hanger arms extending horizontally from said rotatable shaft and positioned to support said lapping head, a double eccentric driving means for oscillating the lapping head comprising an inner shaft and an outer shaft, powered means positioned to drive each of said shafts, with one at a speed differing from the other, a pair of spaced bearings supporting said double eccentric, a counterweight mounted on the inner shaft at the end opposite to the driving means, having an unbalanced mass opposing and counteracting unbalanced forces produced by the complex movement of the lapping head, means for maintaining the lapping head in lapping position comprising a self-aligning bearing in the lapping head, and a crank end of the double eccentric positioned therein to apply oscillating action thereto, spring-actuated means in parallel relation with said eccentrically operated shafts and positioned to urge the head in the direction of the axis of the work piece, with one end of each shaft bearing against said lapping head in self-aligning relationship, and selfadjusting means dependent from said hanger arms for maintaining the lapping head in oscillating position.

13. The method of lapping a cylindrical work piece of substantial dimensions comprising rotatably supporting and drivingly rotating the cylindrical work piece while dependently supporting a lapping head in horizontal, parallel relation therewith having a surface adapted to conform to the surface of the cylindrical work piece, applying double eccentric action to the lappinghead while urging the lapping head towards the axes of rotation of the cylindrical object by forces in spaced, parallel relation with and independent of the eccentric movement, and moving the lapping head in vertical, horizontal and transverse directions with respect to the cylindrical object while maintaining the longitudinal elements of the lapping head parallel to the axis of rotation of the cylindrical object.

14. The method of claim 13 in which two independent eccentric movements of differing ro tational speed are applied simultaneously to the lapping head to oscillate the lapping head past the surface of the work to be lapped, and produce the maximum radius of oscillatory movement of said lapping head when the eccentricities of saidtwo movements are added, and producing the minimum radius of oscillatory movement when the eccentricities of said two movements are opposed.

15. In the lapping of cylindrical objects of substantial dimensions, rotatably supported and drivingly rotated, in which a suspension of particulate abrasives in liquid vehicle is applied to the surface of the cylindrical object and to the lap of a lapping head dependently supported in horizontal, parallel relation with the axis of the cylindrical object and in position to provide vertical, horizontal and transverse movement of the lapping head while maintaining the longitudinal axis of the head parallel to the axis of rotation of the cylindrical work piece, the steps comprising oscillating the lapping head by a pair of eccentric movements applied to the head while its surface is maintained in conformity with the profile of the cylindrical work surface, and urging the head in the direction of the axis of the cylindrical work piece by forces parallel to each other and independent of and parallel with the pair of eccentric movements and maintaining the centers of application of the parallel forces and the point of application of the pair of eccentric movements in a common horizontal plane to eliminate development of force couples tending to throw the longitudinal axis of the lapping head out of parallelism with the longitudinal axis of the cylindrical work piece.

16. The invention of claim 15 in which one of the pair of eccentric movements is greater than the other so that the maximum radius of oscillatory movement applied to the lapping head is produced when the eccentricity of the second movement is added, while the minimum radius of oscillatory movement is produced when the two eccentric movements are opposed to one another.

17. The invention of claim 15 in which different speeds are applied to each of the pair of eccentric movements, while counterweighting one of the eccentric movements to counteract the unbalanced forces produced by the complex movement of the lapping head during oscillation by the pair of eccentric movements and the superadded continuous rotation of the cylindrical work piece, to cause a point on the lapping head to describe a highly non-repetitive path to eliminate surface irregularities from the work surface.

THOMAS G. LEWIS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 512,012 Delano Jan. 2, 1894 960,188 Nichols May 31, 1910 1,039,514 Gladhill Sept. 24, 1912 1,142,146 Combs June 8, 1915 1,227,775 Friess May 29, 1917 1,316,506 Pitter Sept. 16, 1919 1,593,212 Hart July 20, 1926 2,195,047 Wallace Mar. 26, 1940 2,195,049 Wallace Mar. 26, 1940 2,195,053 Wallace Mar. 26, 1940 2,195,065 Wallace Mar. 26, 1940 2,402,340 Parmenter June 18, 1946 FOREIGN PATENTS Number Country Date 220,986 Germany Apr. 14, 1910 393,668 Germany Apr. 5, 1924

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