US3461617A - Methods and apparatus for lapping workpieces - Google Patents

Description

Aug. 19, 1969 3,461,617

METHODS AND APPARATUS FOR LAPPING WORKPIECES D. W. WRIGHT 3 Sheets-$heet 1 Filed Aug. 18, 1965 INVENTOR. Da/e W Whig/71 BY QTTORNfiXQ Aug. 19, 1969 o. w. WRIGHT 3,461,517

METHODS AND APPARATUS FOR LAPPING WORKPIECES Filed Aug. 18, 1965 5 Sheets-Sheet B INVENTQR. Dq/e W. wry/J7 M MVMQW United States Patent '0 3,461,617 METHODS AND APPARATUS FOR LAPPING WORKPIECES Dale W. Wright, Saginaw, Mich, assignor to Miles Machinery Company, Saginaw, Mich. Filed Aug. 18, 1965, Ser. No. 480,574 Int. Cl. B24b 7/02, 9/00 U.S. Cl. 51-121 17 Claims ABSTRACT OF THE DISCLOSURE A lapping machine having a rotatable, annular lapping wheel and a workpiece support for holding a workpiece against the wheel, the workpiece support including driving means for rotating the support relatively to the wheel in such manner that the workpiece traces a path relative to the wheel which is selectively circular or sinusoidal.

This invention relates to a machine tool construction and more particularly to apparatus and methods for lapping workpieces having flat surfaces.

Lapping machines of the general class to which the invention relates have been proposed heretofore, but not all of them have been altogether satisfactory for a number of reasons. For example, some of the known machines are so constructed that successive workpieces move relatively to a lapping wheel in a uniform circular path, thereby rather rapidly forming a groove in the lapping wheel and necessitating frequent dressing of the wheel. The task of dressing the lapping wheel of some of the known machines often requires substantial dismantling of the machines, resulting in considerable loss in the productive use of the machine.

In those machines that are so constructed that each workpiece follows the identical path with respect to the lapping wheel, the grooving of the wheel not only results in the problems stated above, but frequently causes the grooving of many workpieces, particularly those workpieces that are lapped just prior to dressing of the wheel. Such workpieces must either be scrapped or subjected to further lapping operations, either of which is undesirable.

A particularly important object of the invention is to provide lapping apparatus and methods which overcome the disadvantages hereinbefore described.

Another object of the invention is to provide lapping apparatus which requires but infrequent dressing of the lapping wheel and wherein the dressing of the wheel may be accomplished rapidly without necessitating any dismantling of the machine parts.

A further object of the invention is to provide lapping apparatus in which the part to be lapped is caused to traverse the lapping wheel in a circuitous path so as to enable each part to be presented to the lapping wheel from a number of different relative positions, thereby providing a smoother or flatter surface finish on the part.

Another object of the invention is to provide lapping apparatus of the character described and in which the path of a part relative to the lapping wheel may be adjusted so as to achieve the optimum movement of the part relative to the wheel.

A further object of the invention is to provide lapping apparatus wherein the speed of relative movement between the lapping wheel and the part to be lapped may be adjusted within wide limits.

Another object of the invention is to provide lapping apparatus wherein the force by which a part is held against the lapping wheel may be adjusted simply and quickly.

Patented Aug. 19, 1959 Other objects and advantages of the invention will be pointed out specifically or will become apparent from the following description when it is considered in conjunction with the appended claims and the accompanying drawings, in which:

FIGURE 1 is a fragmentary view partly in side elevation and partly in section of lapping apparatus constructed in accordance with the invention;

FIGURE 2 is an enlarged, vertical sectional view taken on the line 2--2 of FIGURE 1;

FIGURE 3 is a sectional View taken on the line 33 of FIGURE 2;

FIGURE 4 is an enlarged sectional view taken on the line 44 of FIGURE 2;

FIGURE 5 is a fragmentary, enlarged sectional view of adjusting apparatus forming part of the construction;

FIGURE 6 is a reduced, somewhat diagrammatic, top plan view of the apparatus;

FIGURE 7 is a diagrammatic view of hydraulic apparatus which may be incorporated in the apparatus; and

FIGURE 8 is a fragmentary, enlarged, diagrammatic view illustrating the path that a typical workpiece may take with respect to a lapping wheel.

Apparatus constructed in accordance with the disclosed embodiment of the invention is adapted for use in conjunction with a base 1 of any suitable construction and having a horizontal bed or table 2 that may be supported by means of suitable frame members 3. Fixed on the upper surface of the bed 2 is a support 4 in which a drum 5 is joumaled by bearings 6 for rotation about a vertical axis. Secured in any suitable manner to the drum 5 is an annular lapping or grinding wheel 7.

The drum 5 and the wheel 7 are adapted to be rotated by means of an electric motor 8 that is connected by belts or the like 9 to the input shaft 10 of a variable speed reduction drive unit 11 of known construction, the output shaft 12 of which may be connected by belts or the like 13 to a drive shaft 14 that is fixedl to and rotates the drum 5, and is journaled in bearings 15 supported in the base 1. Preferably, the wheel 7 is located within a cupshaped shield 16 that is secured to the bed 2 and which prevents the splashing of coolant. The apparatus described thus far is conventional and forms no part of the invention per se.

At the rear end of the table 2 is mounted a base or pedestal 17 in which is fixed an upstanding tubular mounting post 18 (see FIGURES l and 5). A supporting frame or arm member 19 is mounted at its rear end on the post 18 for both axial and rotary movements. A vertical opening 20 is provided at the forward or free end of the member 19 and the latter has a flat top wall 22. Bearings 23 and 24 are carried by the arm 19 and accommodate the mounting member 18 therein. As is best shown in FIG- URE 5, the post 18 extends completely through the member 19 and is received within a cylinder 25 that is fixed to and extends above the top wall 22. The upper end of the cylinder 25 is sealed by a cap 26 which is fixed to the member 19 by means of bolts 27.

Manually operable means 28 is provided to effect vertical adjustment of the member 19 relative to the bases 1 and 17 and comprises a shaft 29 having a smooth shank portion 30 that extends through a sealed opening formed in the cap 26 and terminates at its lower end in a threaded portion 31 that is received in the correspondingly threaded bore 32 of a plug 33 which is fixed in the upper end of the mounting member 18. On the shank 30 is a flange 34 that bears against a wear ring 35 carried by the plate 26, and the threaded portion 31 terminates in a reduced end extension 36 on which is secured a thrust ring 37. The upper end of the shaft 29 preferably has a handwheel 38 secured thereto. The construction and arrangement of the adjusting means 28 are such that rotation of the shaft 29 in one direction will cause the arm 19 to move upwardly axially of the mounting member 18, and rotation of the shaft 29 in the opposite direction will cause the member 19 to move downwardly.

The apparatus also includes power means designated generally by the reference character 40 (FIGURE 7) for effecting vertical movement of the member 19 relative to the base 1. The power means includes a preferably hydraulic pump 41 that is adapted to pump fluid from a reservoir 42 through a line 43 leading to a manually operable valve 44 so as to direct fluids selectively to a return line 45 or to a line 46. The line 46 extends through the mounting member 18 and communicates with a port 47 (FIG- URE that extends through the plug 33. The arrangement is such that, in one position of the valve 44, fluid may be pumped through the line 46 and through the port 47 into the cylinder 25 so as to move the member 19 vertically upwardly with respect to the mounting member 18. When the member 19 has been moved upwardly the desired distance, the valve 44 may be adjusted so as to lock the member 19 in its adjusted position. To lower the member 19, the valve 44 may be adjusted so as to permit fluid to drain from the cylinder 25, under the influence of the weight of the arm 19, into the reservoir 42 via the lines 46 and 45.

As is indicated in FIGURE 1 and in full lines in FIG- URE 6, the member 19' projects forwardly of the base 1 so as to overlie the lapping wheel 7. The longitudinal axis of the member 19 should lie on the diametral plane of the wheel 7 and to assure such a relationship when the member 19 is in a lowered, operative position, the member 19 carries at its rear end a guide and latch plate 47 that is adapted to fit snugly against a companion abutment 48 that is carried by the support 17. The plate 47 is adjustable vertically with the member 19 so as to be engageable with and disengageable from the abutment 48, and to assure snug fitting of the parts without interference, the upper surface of the abutment 48 may be chamfered as at 49. To minimize the risk of injuring a workman, a three-sided guard 50 may extend around the parts 47 and 48 and be secured to the support 17.

At the forward end of the arm member 19 is mounted a workpiece-engaging member 51 comprising a disk or spider 52 of a diametral size such as to correspond substantially to the diametral size of the lapping wheel 7. The member 52 is provided with a plurality of circumferentially spaced openings 53 (see FIGURE 8) having a configuration corresponding substantially to the configuration of a workpiece 54 that is adapted to be accommodated therein.

Radially inwardly of each opening 53 is a mounting bracket 55 on which is pivotally supported an angular arm 56 which, at its outer end, carries a presser plate 57. Each presser plate 57 is pivoted as at 58 to a ring 59 that is slideably and rotatably mounted on its associated arm 56, thereby enabling the plate 57 to be substantially universally adjustable. Each plate 57 is adapted to bear against a workpiece that is accommodated in the associated opening 53 so as to press the workpiece against the upper surface of the lapping wheel 7. A vertically adjustable stop 60 is associated with each arm 56 so as to limit the force with which the plate 57 bears against the workpiece. Although only two of the arms 56 and their associated devices are illustrated in FIGURE 1 for purposes of clarity, it will be understood that a larger number of such devices may be utilized.

The workpiece-engaging member 52 i mounted on the supporting frame 19 for rotation about an axis which may either coincide with the axis of rotation of the lapping wheel 7 or which may move in an orbital path about the axis of rotation of the lapping wheel. The mounting means for the workpiece-engaging member is best illustrated in FIGURES 2 and 3. The mounting means comprises a hollow support or carrier 62 that is rotatably journaled in the opening 20 of the arm member 19 by bearings 63 and 64 for rotation about an axi that coincides with the axis of rotation of the wheel 7. The lower end of the carrier 62 extends below the lower surface of the member 19 and is threaded to accommodate a nut 65 which functions as a bearing retainer. The lower bearing 64 is protected by a seal 66. As is best illustrated in FIGURES 2 and 3, the carrier 62 has an eccentric bore 67 extending therethrough.

Rotatably mounted within the support 62 i a sleeve 68. The upper end of the sleeve 68 projects above the upper end of the carrier 62 and is provided with an enlarged flange 69 in wedging relation with the upper end of the carrier 62. The lower end of the sleeve 68 extends below the lower end of the carrier 62 and is threaded to accommodate a wedge-shaped locking nut 70 which may be adjusted so as selectively to enable and disable relative rotation of the carrier '62 and the sleeve 68. The sleeve 68 also has an eccentric bore 71 extending completely through the sleeve, and the eccentricity of the bore 71 corresponds to the eccentricity of the bore 67.

A spindle 72 is journaled for rotation about its own axis in the sleeve 68 by means of bearings 73 and 74 and includes a lower, enlarged portion 75 that extend below the sleeve 68 and is fixed to the workpiece-engaging member 52. The upper end of the spindle 72 extends above the sleeve 68 for a purpose that hereinafter will be explained.

The apparatus includes means for rotating the members 62 and 68 conjointly and comprises an electric motor 77 to the armature shaft of which is fixed an adjustable diameter sheave 78 of known construction. The sheave 78 is connected by a belt 79 or the like to a similar adjustable diameter sheave 80 and which is fixed to a shaft 81 that is rotatably journaled in the arm member 19. Fixed to the shaft 81 is a worm 82 that meshes with a driving worm gear 83 which is fixed on the support or carrier 62. The adjustable diameter sheaves 78 and 80 have manually operable adjusting knobs 84 and 85, respectively, by means of which the diameters may be adjusted so as to vary the speed at which the members 62 and 68 are rotated. Upon rotation of the worm 82, the gear 83 rotates about a fixed axis and the carrier 62 rotates about the same axis. This axis coincides with the axis of rotation of the lapping wheel 7 and is indicated in FIGURE 3 by the reference character X.

When the carrier 62 and the sleeve 68 are in the positions of adjustment shown in FIGURES 2 and 3, the axis Y of rotation of the spindle 72 is in its maximum position of eccentricity to the axis X. Accordingly, rotation of the members 62 and 68 about the axis X will cause the spindle 72 to move in an orbital path about the axis X and such movement of the spindle 72 will cause the workpiece-holding disk 52 also to move in an orbital path about the axis of rotation of the lapping Wheel 7.

The eccentricities of the bores of the members 62 and 68 are such that rotation of the member 68 relative to the carrier 62 through from the position shown in FIGURE 3 will cause the axis Y of the spindle 72 to coincide with the axis X. Such relative rotation of the members 62 and 68 may be accomplished by loosening the nut 70. When the axes X and Y coincide, rotation of the member 62 will cause corresponding rotation of the workholding disk 52 about the axis of rotation of the lapping wheel 7. The members 62 and 68 may be so adjusted relatively to one another as to provide any desired degree of eccentricity of the axes X and Y between the maximum and zero eccentricities.

Apparatus constructed in accordance with the invention includes drive transmitting means 86 for rotating the spindle 72 and the disk 52 about the axis Y of the spindle, regardless of the eccentricity of the axes X and Y. The drive transmitting means is located in a square, hollow housing 87 having a bottom wall 88 fixed to the arm 19 and to which are secured upstanding side walls 89. The

bottom wall 88 has an opening 90 therein which is coaxial with the opening 20. A cover 91 is removably secured to the walls 89.

The drive transmitting means 86 includes an intermediate planetary gear train 92 comprising a sun gear 93 fixed to a block 94 that is secured to the sleeve 68 for rotation with the latter. Both the gear 93 and the block 94 loosely receive the spindle 72. The gear 93 is in mesh with three idler gears 95 that are fixed on stub shafts 96 journaled in a three-armed spider member 97 that is keyed or otherwise suitably fixed to the upper end of the spindle 72. At the upper end of each shaft 96 is secured a gear 98 which meshes with the teeth 99 of an additional, ring-type gear 100. The body of the gear 100 is square in plan, but has a size smaller than the interior size of the housing 87.

The gear 100 is slidably supported atop an open, square frame 101 that is supported on a shelf 102 on the walls 89 so as to lie about midway between the top and bottom walls of the housing 87. Slidably supported on the frame 101 and overlying the gear 100 is a rectangular guide frame 103 comprising two spaced apart, parallel bars 104 and 105 joined at their opposite ends by bars 106 and 107. Each of the bars 104 and 105 is provided with a downwardly projecting guide flange 108 between which is received the gear 100. Neither of the bars 106 and 107, however, is provided with such a flange. Accordingly, the gear 100 is capable of reciprocating movement between the guide flanges 108. The guide frame 103 itself is slid able relatively to the housing 87, but in a direction normal to the direction of sliding movement of the gear 100 relative to the frame 103. The frame 103 is guided in its sliding movements by a pair of guide surfaces 109 and 110 carried by the cover 91 at opposite ends thereof. As is indicated in FIGURE 2, the lower ends of the guides 109 and 110 terminate at a level above the gear 100. The construction and arrangement of the parts are such that, although the gear 100 is incapable of rotating about the axis of the spindle 72, it is capable of sliding movements in either of two normal directions in the same plane and, therefore, is capable of moving orbitally about the axis X.

The drive transmitting means is so constructed that rotation of the carrier member 62 is imparted via the sleeve member 68 to the sun gear 93. Rotation of the sun gear 93 imparts rotation to the idler gears 95, and rotation of the gears 95 is imparted via the shafts 96 to the planetary gears 98. Since the teeth of the planetary gears 98 mesh with the teeth of the ring gear 100, and since the latter is restrained against rotation by its engagement with the guides 108, 109 and 110, rotation of the gears 98 effects rotation of the spider member 97 and, consequently, rotation of the spindle 72 about its own axis Y. The speed of rotation of the spindle 72 about its own axis will depend on the ratio of the gears in the drive transmitting mechanism, the speed of the driving motor 78 and the ratio between the diameters of the pulleys 78 and 80, but the member 62 should be rotated several times the speed of rotation of the spindle 72.

When the apparatus is conditioned for operation, the frame member 19 will be in the position shown in FIG- URE 1 and in full lines in FIGURE 6 so that the axis X coincides with the axis of rotation of the lapping wheel 7. This relationship is assured by the cooperating latch parts 47 and 48. The handwheel 38 may be so adjusted as to locate the workpiece-carrying disk 52 at the desired clearance above the upper surface of the lapping wheel. The motors 8 and 77 then may be started so as to effect concurrent rotation of the lapping wheel 7 and the workpiececarrying member 52 in opposite directions and at different speeds.

When the members 7 and 52 attain the desired speeds of rotation, workpieces 54 may be inserted in the cavities 53 of the member 52 so as to locate the lower surface of each such workpiece in engagement with the upper surface of the lapping wheel. To facilitate introduction and removal of workpieces to the cavities 53, each of the arms 56 may be provided with a radially inner extension 111 which lies in the path of a cam 112 supported at the forward end of the arm member 19 and which cooperates with the extension 111 to lift momentarily the presser plate 57 so as to permit access to the cavity 53.

If the carrier member 62 and the sleeve 68 are so adjusted relatively to one another that the axis Y of the spindle 72 coincides with the axis X of the member 62, each workpiece 54 will be moved in a circular path about the axis of rotation of the lapping wheel 7. It is preferred, however, to adjust the members 62 and 68 in such manner that each workpiece 54 will move in a circuitous path about the axis of the lapping wheel.

When the members 62 and 68 are in their maximum positions of eccentricity, as is indicated in FIGURES 2 and 3, operation of the apparatus will cause a workpiece 54 to traverse an orbital path about the axis of rotation of thelapping wheel 7. Thus, as is indicated in FIGURE 8, each workpiece 54 will traverse the surface of the lapping wheel along a path in the form of a sine Wave so that each workpiece moves first radially outwardly and then radially inwardly of the wheel 7, simultaneously with its movement circumferentially of the wheel. The amplitude of radial movement of each workpiece relative to the lapping wheel may be adjusted by adjustment of the eccentricity of the axes X and Y, and the number of cycles of such movement will depend upon. the difference in speeds of rotation of the carrier 62 and the workpiececarrying member 52. Inasmuch as the speed of rotation of either or both of the members 62 and 52 may be adjusted, the relative speed may be selected to provide the best results for the particular workpieces being lapped.

When it becomes necessary to dress. the upper surface of the lapping wheel 7, the hydraulic pump 41 may be started and the valve 44 adjusted so as to introduce pressure fluid to the chamber between the plate 26 and the upper end of the mounting tube 18, thereby effecting upward displacement of the arm member 19 relative to the base 1. When the arm member 19 has been adjusted to a height such that the workpiece-carrying member 52 may clear the shield 16, the latch members 47 and 48 will be disengaged, whereupon the arm member 19 may be swung about the axis of the tube 18, as is indicated in dotted lines in FIGURE 6. A wheel dresser (not shown) then may be utilized to resurface the dressing wheel.

Following the dressing of the lapping wheel, the arm member 19 may be swung back to its original position and the valve 44 adjusted to permit the arm member to return to its lowered, operative position, whereupon the latch members 47 and 48 will latch the arm in the previously described position. In the event it becomes necessary to make a further vertical adjustment of the workpiececarrying member 52 such as to compensate for the removal of material from the lapping wheel, the handwheel 38 may be rotated in the appropriate direction.

The disclosed apparatus and methods are representative of presently preferred forms of the invention, but are intended to be illustrative rather than definitive thereof. The invention is defined in the claims.

I claim:

1. A machine tool construction comprising supporting frame means; carrier means mounted on said frame means for rotation about an axis; drive means connected to said carrier means for rotating the latter about said axis; sleeve means eccentric to said axis carried by said carrier means for rotation about said axis in response to rotation of said carrier means; spindle means; means journaling said spindle means on said sleeve means for rotation relative thereto about the axis of said spindle means; and rotatable and bodily displaceable gear means drivingly interconnecting said sleeve means and said spindle means for rotating said spindle means about its own axis in response to rotation of said carrier means about its said axis, whereby said spindle means is enabled to move in an orbital path about the axis of said carrier means.

2. The construction set forth in claim 1 wherein said eccentric means is adjustable relatively to the axis of said carrier means; and including means for maintaining said eccentric means in a selected position of adjustment relative to said axis.

3. The construction set forth in claim 2 wherein said eccentric means is adjustable relatively to the axis of said carrier means from a position in which the axis of said spindle means coincides with the axis of said carrier means to a position in which said axes are spaced from one another.

4. Apparatus for use with a lapping machine having an annular grinding wheel presenting a fiat face of predetermined radial width, and means for rotating said wheel about an axis, said apparatus comprising supporting frame means; a tubular carrier member having an eccentric bore therethrough; means mounting said carrier member on said frame means for rotation about an axis coincident with the axis of said wheel and eccentric to said bore; drive means connected to said carrier member for rotating the latter about said axis; a sleeve member rotatably supported within the bore of said carrier member and having an eccentric bore therein complementary to the bore of said carrier member; a spindle rotatably mounted within said sleeve member for rotation about its own axis; means on said spindle for holding a workpiece against said face of said wheel; adjustable means reacting between said carrier member and said sleeve member for maintaining said members in a selected position of relative angular adjustment between a first position in which the axis of said spindle coincides with the axis of said carrier member and another position in which the axis of said spindle is spaced from the axis of said carrier member; and drive transmitting means interconnecting said carrier member and said spindle for rotating the latter about its own axis solely in response to rotation of said carrier member.

5. The apparatus set forth in claim 4 wherein said drive transmitting means comprises a planetary gear train.

6. The apparatus set forth in claim 5 wherein said planetary gear train comprises a sun gear on said carrier member, planetary gearing on said spindle, and ring gear means on said frame, said planetary gearing being in mesh with said sun gear and with said ring gear means.

7. The apparatus set forth in claim 6 wherein said ring gear means is movable relatively to said spindle in either of two mutually normal directions in the same plane.

8. Driving apparatus comprising driving gear means; means mounting said gear means for rotation about a fixed axis; a spindle; means mounting said spindle for rotation about said fixed axis and about its own axis; intermediate gear means in mesh with said driving gear means; an additional gear means in mesh with said intermediate gear means; means mounting said additional gear means to preclude rotation thereof and to enable linear movements thereof in either of two mutually normal directions in substantially the same plane; and means connecting said intermediate gear means to said spindle for rotating the latter about its said own axis in response to rotation of said driving gear means about said fixed axis.

9. The apparatus set forth in claim 8 wherein said spindle is mounted eccentrically of said fixed axis.

10. The apparatus set forth in claim 8 wherein the mounting means for said spindle is adjustable relatively to said driving gear means for adjusting said spindle from a position in which said axes coincide to a position in which said axes are spaced apart.

11. Driving apparatus comprising driving gear means rotatable about an axis; driven gear means in mesh with said driving gear means and adapted to be driven by the latter; linearly displaceable and nonrotatable gear means in mesh with said driven gear means; and rotatable means connected to said driven gear means for rotation in response to driving of said driven gear means by said driving gear means.

12. The apparatus set forth in claim 11 wherein said rotatable means comprises a spindle; and means mounting said spindle for rotation about its ownaxis and for rotation about the axis of said driving gear means.

13. The apparatus set forth in claim 11 wherein said nonrotatable gear means is movable in two mutually normal directions in the same plane.

14. A method of lapping a workpiece comprising holding a workpiece against a lapping wheel having an annular surface; moving said workpiece in a circumferential path relatively to said wheel; and sequentially moving said workpiece radially at a uniform rate inwardly and outwardly relatively to said wheel as said workpiece is moved in said path and with such frequency and amplitude that said workpiece traverses a sinusoidal path about said lapping wheel.

15. A machine tool construction comprising a lapping wheel; means mounting said wheel for rotation about a first axis; support means for holding a workpiece against said wheel; means for rotating said support means about a second axis parallel to said first axis; means mounting said support means for movement toward and away from said wheel and for rotary movements relative to said wheel about a third axis parallel to said second axis for moving the axis of rotation of said support means into and out of a fixed predetermined relationship with said first axis; and releasable latch means acting on said support means in response to movement thereof toward said wheel when said support means is in said predetermined relationship for releasably maintaining said support means fixed in said relationship relative to said axis.

16. A machine tool construction comprising a lapping wheel; means mounting said wheel for rotation about a first axis; support means for holding a workpiece against said wheel; arm means mounting said support means for rotation about a second axis; means mounting said arm means for movements toward and away from said wheel and for rotation about a third axis to and from a fixed position in which said first and second axes are coincident, said third axis being parallel to said first axis; and releasable latch means on said arm means operable in response to movement thereof toward said wheel to latch said arm means in said fixed position and operable in response to movement of said means away from said wheel to release said arm means.

17. The construction set forth in claim 16 including means connected to said arm means and operable to effect movement of said support means toward and away from said wheel.

References Cited UNITED STATES PATENTS 2,225,826 12/1940 Duifens 51124 1,151,785 8/1915 Hitchcock 5l133 1,561,107 11/1925 Parsons 51-133 1,577,137 3/1926 Maynard 51-133 1,610,527 12/1926 Indge 51133 1,739,961 8/1929 Wentz 51-131 X 1,874,920 8/1932 Dehufl.

2,272,974 2/ 1942 Indge 51120 2,740,237 4/1956 Day 51-120 X 3,172,241 3/1965 Habenicht 51120 HAROLD D. WHITEHEAD, Primary Examiner US. Cl. X.R.

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