US2968135A

US2968135A - Lapping machine

Info

Publication number: US2968135A
Application number: US726753A
Authority: US
Inventors: Stephen A Boettcher; Jack C Page
Original assignee: ABRADING SYSTEMS Co
Current assignee: ABRADING SYSTEMS Co
Priority date: 1958-04-07
Filing date: 1958-04-07
Publication date: 1961-01-17
Anticipated expiration: 1978-01-17

Description

Jan.17, 1961 Filed April '7, 1958 2 Sheets-Sheet 1 i I 423 if 56 56- v| 'h 1- l 2 70 66 Il 278. .62 l1 70 A J" I I "l: l' 56" 85. '71 36 35 f--45 v /M n @a N -51 ill 32 j? 18 2 kLg L66 f 761 j! Q'. Ze 85 @0 /68 6% INVENTORS.

ifzen//.oe'c/zev: ,r wfaclc .Pa e, 35 "i 71, 6@ wm gm f ,Al/M4 Jan. 17, 1961l SQA. BOETTCHER ErAL LA'PPING MACHINE 2 Sheets-Sheet 2 Filed April 7, 1958 INVENTORS. Si@ zen/ Coei''c/e wc/ QP e,

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United States Patent LAPPING MACHINE Stephen A. Boettcher, Evanston, and Jack C. Page, Palatine, Ill., assignors to YAbrading Systems Company, Skokie, Ill., a corporation of Illinois Filed Apr. 7, 1958, Ser. No. 726,753

7 Claims. (Cl. 51129) This invention relates to lapping machines and particularly to improvements in machines for lapping fiat and parallel surfaces on machined, ground, or precisioncast work pieces. In general, such machines comprise a horizontal lapping wheel or plate which is rotated about a vertical axis and which has an annular lapping surface on which the Work pieces are placed, in confined positions, so that movement of the lap surface relative to the work pieces brings about abrasive wear of the latter at their surfaces in engagement with said lapping surface. Of paramount importance in all such machines of this class is the maintenance of the lapping surface in planar condition. It is well known that the lapping sur face of the wheel tends to wear unevenly in the lapping operation, which, if not corrected, renders the lapping wheel ineffective for its intended usage.

The present invention is particularly directed to an improved means for maintaining the lapping surface corrected to a true planar condition and for accomplishing such function substantially simultaneously with the lapping operation which creates the need for the correction.

In brief, a lapping machine embodying this invention may comprise a drum-like base or pedestal at the upper end of which is supported a horizontal lapping wheel rotatable about a vertical axis. A horizontal staging table surrounds the lapping wheel to provide an area for accommodating Work pieces as the same are fed to and taken from the lapping wheel. A bridge structure is provided over the lapping wheel, carrying a plurality of vertical spindles, each of which, at its lower end, centers a circular weight plate resting on work pieces on the wheel, such weight plate, in turn, loosely centering a surrounding retaining ring also resting on the wheel. As the wheel rotates, so do the rings on their own axes, and so do the weight plates (by way of the work pieces); the retaining rings are truing elements for the lapping surface, the combined wear effect of the bottoms of the rings and the work pieces beneath the weight plates being relied upon to maintain the surface of the lapping wheel in a planar condition. The spindles are fixed, but are vertically adjustable for the purpose of applying Vpressure to the work pieces in addition to the weight of the weight plates. Importantly, the present invention provides braking means for controlling the rotational velocity of the retaining rings and the group of work pieces on the lap, the braking means, in the form shown, being interposed between the fixed spindle and the weight plate and being adjustable for varying the amount of its brak ing effect, thus to control the wear effect of the work pieces and the ring on the lapping wheel.

Figure 1 is an elevation, with parts shown in crosssection, of the upper portions of a lapping machine vembodyingthe improvements of this invention.

Figure 2 is a partial cross-sectional View, on a larger scale, taken substantially on line 2 2 of Figure 1, looking in the direction of the arrows;

Figure 3 is a partial plan view on the line 3-3 of Figure l; and

Figure 4 is a view on the line 4-4 of Figure 2, looking downwardly.

The machine villustrated has a cylindrical supporting pedestal 11 having a door 14 for access to the interior.-

AS seen in Figure l, cylindrical collar 17 is mounted in the upper end of pedestal 11 by means of an inclined drip pan 18 for receiving, for return, abrasive and carrier mixture used in the lapping operation.

A motor mount 25 pivotally carried on a verticalaxle 26 is positioned within pedestal 11 for carrying a main drive electric motor 27. Sheave wheel and belt drive means 28 serve to interconnect motor 27 with a.l conventional gear reducer unit 30, mounted within ring;

17 and held to an internal flange 17 on the said ring by

bolts

31, 31. Output shaft 32 of the gear reducer unit is keyed or otherwise affixed to a hub portion 33 of ro-` tatable lapping wheel 35.

As best shown by Figures 3 and 4, lapping wheel 35 comprises a circular wear resisting metallic alloy disc` having a central depression or well bore 36, thus defining an annular lapping surface 40. A plurality of

radial sots

41, 41 are cut in the wheel to the depth of the center well bore, according to conventional practice, which slots receive and carry away abrasive and oil mixture, fed to the lapping wheel from a drip supply line 43.

Surrounding the lapping wheel 35 is a ring 44 on which is mounted a planar staging table 45. Said table45 hasV The lower end of each spindle is fitted into a ballY bearing 65 (Fig. 2) mounted in a shouldered well bore 66 formed into the upper face of the related Weight plate 68 of dz'sc formation.

Each weight plate is surrounded with slight clearance, by a truing-retainer ring 70. The periphery of the Weight plate and the inside surface of the ring 70 can be knurled.

Work pieces, indicated at 71, are positioned freely on theY lapping wheel within the confines of ring 70 for retention in the circular area defined thereby. There may, of course, be but one work piece.

In operation, as the lapping wheel rotates on its vertical axis, driven by the motor 27, the ring 70 and the weight plate 68 (the latter by way of the Work pieces 71) are made to rotate on their Vertical axes, as indicated by the arrows in Figure 3, abrasive and carrier mixture be-Y ing fed thereto from the drip spout 43, the action resulting in the Vlapping of the under surfaces of the workV pieces and the simultaneous dressing of the annular lap-` ping surface of the wheel 35. t

It is, of course, known that the pressure applied to the interfacial contact between the rings or the work pieces, on the one hand, and the lapping surface, on the other, is a factor in the wear of the lapping surface.

Relative movement between the twocontacting-surfaces' is also a factor, and that assumes particular importance here because of the characteristic arrangement fof.y the truing retainer rings and the group of work pieces-confined therein and the weight plate on the annular-lapping surface; each such assembly lies entirely to one" side of the axis of the lapping wheel, and the rings and their APatented Jan. 17, 1961vr contents rotate about their axes in the same direction aS the lapping wheel rotates about its axis, clockwise or counter-clockwise as the case, may be; the result is that, at the periphery of the lapping annulus, the ring assembly moves in the same direction as the lapping annulus, and that, centrally, the ring, assembly moves oppositely to the lapping annulus; We have discovered that, the lapping wheel rotating at a constant velocity, if means is provided to retard the ensuing rotation of Ithat assembly and making such means adjustable, such means enables effective selection of the area of wear of the annular lapping surface; the wear is normally to concavity of the lapping surface, and if the rotation of the assembly is retarded, the wear approaching the periphery will'be increased, thus counteracting the tendency to concavity and maintaining the desired planar condition of the lapping surface. If the tendency should then be toward convexity, that can be met by permitting a speeding-up of the assembly.

As previously stated, we provide a braking means interposed between each of the fixed spindles and its related weight plate, adjustable for varying its braking effect, to regulate the rotational velocities of the weight plate and the truing-retainer ring and the wear effect of the work pieces and the ring on the lapping wheel.

We apply the braking means to the weight plate as indicated at 62 in Figure 1 and as shown in detail in Figures 3 and 4. The construction embodies a plurality of friction disc elements 75 which are keyed to the spindle 56, as by mating key projections 76 and a vertical keyway in the spindle 56. Alternating with the friction disc elements 75 are brake plates 78 which fit freely about the spindle 56 so that they are rotatable with respect thereto. Plates 78 are of a larger diameter than the disc elements 75, and` are attached to the weight plate 68, as by stud bolt 80 received in the threaded opening 81 in the weight plate. A clamping cap 82, having threading engagement with threads 83 on the spindle 56, engages the uppermost of the disc elements 75, with a spring washer 84 intervening. An annular recess 86 in cap 82 accommodates the heads of the bolts 80. By threading the clamping cap 82 on the threads 83, said cap being knurled at S7, variations in the braking effect of the

brake members

75 and 78 may be had inorder to retard or free the rotation of the weight plates 68 andthe related wear rings.

A protecting shroud ring 85, fitted into annular slot 86 in the weight plate 68, surrounds the several friction discs and

plates

75 and 78.

In routine, the rings 70 are on the staging table and the work pieces are disposed therein, such assembly being then moved onto the lapping annulus to position where the spindle 56, braking means 62 and weight plate 68 are lowered into the ring and onto the work pieces and pressed downwardly to the desired pressure, then tightening the set screws 60. Periodically, the plane of the lapping surface may be checked; and, if concavity appears, the knurled clamping cap 82 is manipulated to counteract it. When that particular lapping operation is Completed, the set-screws 6l) are released, the spindles, braking means and weight plates are lifted out of their rings, and the rings, still containing the work pieces are` moved onto the staging table for removal from the machine.

We claim:

l. In a lapping machine, a rotatably operated lap having a planar lapping surface, truing means frictionally engaging said surface and thereby being rotatably driven about a fixed axis transverse to said surface, and means acting laterally against said truing means for adjustably retarding rotational velocity of said truing means independently of downward pressure on said lapping surface to regulate abrasive wear of said surface.

2. In a lapping machine, an operating lap having a planar, annular lapping surface, a truing ring engaging4 said lapping surface and rotating relative thereto, fixed spindle means and a circular weight plate within said ring defining the rotational axis for said ring, and means including a friction brake means on said spindle means, to selectively adjust rotational velocity of said ring independently of downward pressure on said lapping surface, thereby to control Wear of said lapping surface.

3. In a lapping machine, a rotatable lapping element having a planar lapping surface, said lapping element comprising a wheel rotatable on a vertical axis, retaining and truing ring means engaging said lapping surface on one side of said axis, said ring means being restrained to rotate about a vertical axis and being frictionally driven by said lap, and brake means acting laterally against said ring means for regulating the rotational velocity of said ring means independently of downward pressure on said lapping surface, thereby to control the velocity thereof relative to said lapping surface for the purpose of maintaining the latter in planar condition.

4. In a lapping machine, a disc rotatable on a vertical axis and having a horizontal annular planar lapping surface, retaining and truing ring means resting across said surface, a weight plate within each ring means with close clearance and adapted to rest on work pieces confined in said rings and resting on said lapping surface, vertical spindle means defining fixed rotational axes for said weight plate and ring means, and means for selectively regulating the rotational velocity of said weight plate and ring means independently of downward pressure on said lapping surface to selectively regulate wear of said lapping means to maintain the same in planar condition.

5. In a lapping machine, a disc rotatable on a vertical axis and having a planar lapping surface, a retaining and truing ring resting on said lapping surface, a weight plate in said ring and adapted to rest on grouped work pieces confined within said ring and resting on said lapping surface, fixed axis means centering said plate and ring so that they are rotatably driven by frictional engagement with said lapping surface, and means independent of downward pressure on said lapping surface for selectively braking the rotation of said weight plate, ring and work-piece group to regulate wear of said lapping surface.

6. In a lapping machine, a disc rotatable on a vertical axis and having a planar lapping surface, a retaining and truing ring resting on said lapping surface to one side of said vertical axis, a weight plate disposed with slight clearance in said ring and adapted to rest on work pieces resting on said lapping surface within said ring, a vertical spindle centering said weight plate and being vertically adjustable to regulate downward pressure on said weight plate, and adjustable braking means interposed between said spindle and said weight plate to regulate the rotational velocity of said weight plate, said braking means comprising a set of friction discs keyed to said spindle and a set of alternate friction discs fixed to said Weight plate to rotate therewith, and means for adjustably clamping said sets of friction discs together.

7. In a lapping machine, a disc rotatable on a vertical axis and having a planar lapping surface, a retaining and truing ring resting on said lapping surface on one side of said axis, said ring being held on its own fixed axis and being rotatable thereon by its frictional engagement with said lapping surface, and means acting laterally against said ring for adjustably braking its said rotation.

References Cited in the file of this patent UNITED STATES PATENTS TJUA