US2829471A - Machine for correcting screw threads - Google Patents

Description

April 8, 1958 v. L. Pr-:lcKu 2,829,471l

MACHINE FOR CORRECTING SCREW THREADS Filed oct. 27, 1954 v @sheets-sheet 1.

LULU

E- if INVENTOR.

BY 'MM/44. qu@

April 8, 1958 v. PElcKu MACHINE FOR CORRECTING SCREW THREADS 5 Sheets-Sheet 2 Filed Oct. 27, 1954 T IIIIFIP Je. m WP April 8, 1958 v. L. PElcKn MACHINE FOR CORRECTING SCREW THREADS 3 Sheets-Sheet 5 Filed OCT.. 27. 1954 NVENTOR. yasdfz'e Fez.' W7/ZL BY l 1 Mafvu MACHINE FOR CORRECTING SCREW THREADS Vaisalie L. Peickii, San Mateo,iCalif.,'assignor to Micromatic Hone Corporation, Detroit, Mich., a corporation i of Michigan `Application October 27, 1-954,` Serial No. 464,999

` Z Claims. (Cl. 51--95) One object of the invention is to provide a simple,l

accurate means for correcting deficiencies in the lead,

thread-wobble and pitch-diameter occasioned by the previous matchining operations or heat treat deformation.

Another object is to provide `a means whereby the workpiece may be mounted for rotation about the generative axis of its helix, inspected for the locale and de gree of error; corrected, and re-inspected without del mounting therefrom in the interim.

Another object is to provide a means whereby the vhelix of threaded components may be ground or otherwise rna-` chinedwithout the use of a lead-screw, sine-bar or other conventional means to procure the desired helix.

The overall invention consists of the principles shown and described herein and in the co-pending application, Serial No.' 465,000, liled October 27, 1954, and assigned to the assigneeof the present application, and the combination of elements and arrangement of parts as shown in the attached drawings; wherein:

Figure 1 is a plan view of a grinding or lapping machine embodying the features of the present invention;

The machine as illustrated in the drawings consists of l a base plate 1 on the rearward surface of which a precision grinding assembly generally indicated at 45 is xedly mounted. The grinding assembly consists of a pair of parallel head frames 2 atlixed to a supporting plate 1a which is mounted on base 1 for pivotalmovement about a center pin.2a. Adjustment of screws 2b, which extend through arcuate slots in the supporting-plate 1a, permits positioning of the grinding assembly so that the axis of grinding wheel 7 is at right angles to the workpiece helix. A forwardly extending wheel arm 3 and a rearwardly extending stabilizer arm 4, formed as a unit, are pivotally mounted between the head frames 2 on trunnions 5. The trunnions 5 ride on bearings 8 housed in the head frames 2 so as to afford a free tipping motion to the wheel arm 3. A grinding wheel 7 is rotatably mounted on the forward end of the wheel arm 3 so as to be driveable by a drive motor 9 mounted on the wheel arm. A spring 6, bearing against the under surface of the stabilizer arm 4 adjacent its rearward end, serves to force the grinding wheel 7 in a downward direction. The downward movement of the grinding wheel 7 is limited and may be regulated by a feed-adjusting screw 13 which is mounted on a xed bracket 10 and bears against a block 11 mounted on the upper surface of the stabilizer arm 4. A dial indicator 14, carried by an arm 12 iixedly secured to the bracket 10 above the stabilizer arm 4, registers the movement of the grinding wheel 7 as the feed-adjusting screw 13 is backed oi.

United States Patent It may be seen that the grinding assembly above described provides the dressing tool for correcting threaded parts which may be precisely operated. The grinding wheel 7 may be raised or lowered to grind oi any desired amount of material. The dial indicator 14 being the same distance from the trunnions 5 as is the working surface of the` grinding wheel 7, the amount of moving of the stabilizer arm 4 below the dial indicator 14 will be identical to that of the wheel 7.

A block 15 is xedly mounted onthe base 1 below the grinding wheel 7 and isprovided with a transversely extending dovetail groove. A supporting block 16 having a dovetail base portion is mounted on the block 15 with its dovetail base disposed in the dovetail groove of block 15. A set screw 17 threaded into the supporting block 16 allows the block 16 to be secured in any desired longitudinally adjusted position along the block 15. A supporting member 18 is mounted in the top of the block 16 and adjustably houses an upwardly extending followerlinger 19, the follower-linger 19 lying directly below the axis of the wheel 7. The linger 19 has a tip 20 which conforms to the flank shape of the threads of the workpiece, but is suciently truncated at its end to clear the root of the helix. The tip 20 is iinely finished so as to closely iit the Hank faces of the threads of the helix upon the pitch-diameter thereof. Finger 19 is vertically adjustable in its supporting member 18 bymeans of set screw 21 to accommodate workpieces of varying size. Furthermore, the linger 19 may be rotated toconform to threads of varying pitch. e

A V-block 22 is tixedly mounted on the base 1 in parallel relation to the axis of the wheel 7, and has a` plurality of balls 23 mounted therein which form a frictionless guideway for a workholding carriage, generally indicated `at 40. The workholding carriage is formed as a separate unit and includes a supporting bar 24 and two `is movable along the generative axis. of its threads past the grinding wheel.

The workpiece is provided with pivot ends 30 and 30a, preferably formed integrally with the workpiece, and centered onthe generative axis of the threads of the workpiece. The workpiece is mounted with its pivot ends 30 and 30a disposed in the work centers 27 and 28 so as to be freelyu rotatable therebetween about the generative axis of its threads.

One pivot end 30a is provided with a pinion 31 which is dogged thereto for mutual rotation with the workpiece. A motor 32 is mounted on transverse arm 26 and is provided with a gear 33 fast on the end of its drive shaft. The gear 33 engages an intermediate gear 34 rotatably supported on the transverse arm 26, which in turn en gages the pinion 31 whereby the workpiece may be rotated. As will be apparent to those skilled in the art, any suitable driving means such as belt and pulley may be used to drive the workpiece in rotation.

It may be seen that the preponderance ofweight is on the ends of the transverse arms adjacent the grinding wheel and therefore the entire workholding carriage will tend to tip downwardly at that end. However, the follower-linger 19 which engages the threads of the workpiece supports the workholding carriage in an upright position. As the motor 32 is driven, the rotation of the workpiece will feed thethread onto the fixed linger V19, moving the workpiece along its axis. Because the supporting bar rests freely on the balls 23 the entire workholding carriage is free to move with the workpiece. It should also be noted that the workholding carriage, along with the workpiece, forms an integral unit which may be freely removed from the rest of the machine in order to examine or inspect the workpiece. The workpiece itself need not be removed from the carriage on which it is xtured. This integral unit is common with that shown in my copending application above described and has utility therewith.

In the operation of the machine the block 16 is adjusted so that the finger 19 is disposed in a thread groove slightly in back of the grinding wheel and is adjusted in height so that the transverse arms 25 and 26 lie in'a substantially level plane. Since the purpose of the machine is primarily to correct error in a machined or ground helix of the workpiece, it is desirable vthat the pitch diameter of the latter be provided slightly oversize prior to this operation. In this manner the helix can be exactly nished to its proper specications. The feed-adjusting screw 13 is adjusted so as to bring the wheel 7 into proximity with its adjacent thread groove. The follower-finger 19 is then adjusted to center the peripheral edges of the wheel in a neutral portion of the thread groove; that is to say, to a position where there is similar clearance between the thread flanks of the workpiece andthe two grinding surfaces of theV wheel.

In an operation where extremely precise dimensions are required, a magnifying glass or microscope may be used, as is shown schematically at 36. This facilitates observations during the above-described adjustments. The motors 9 and 32 are then started and the feed screw 13 is further adjusted to lower the grinding wheel into its adjacent thread groove. The degree of infeed of the wheel is indicated on the dial gauge 14 which maybe set at its zero point at any time by the operation of screw 37 which is threaded through the block 11 into engagement with an extensible rod 38 which form part of the gauge 14. As the workpiece is rotated the threads are caused to advance by the finger 19, which feed the entire length of thread past the grinding wheel 7. At the end of each .pass of the complete screw length, the feed motor 32 may be reversed to conveniently repeat the grinding operation by movement of the workpiece in the opposite direction. However, it is usually found advantageous to check the condition of the workpiece after each grinding pass, This procedure requires the retraction of the grinding wheel, the removal of the carriage from the machine and its transfer to the companion inspection instrument covered by my copending application mentioned above.

This periodic removal of the carriage, with the workpiece intact, enables convenient and precise checking of the condition of the helix and the determination of where additional corrective treatment may be needed thereon. In practice, it has been found that by adjusting the grinding wheel and follower-finger as the need is indicated by my checking device, this machine has produced screw threads, and other helical forms, of extreme precision, even when manipulated by a relatively unskilled operative.

It will thus be seen that this invention provides a simple, economical and effective means for correcting the geometry of screw threads and the like helices; and that the method herein described, of periodic inspection of the workpiece while still fixtured on its generative axis, avoids the need for taking into account the probability of error usually present whenever refixturing is required.

What is claimed is:

l. In a machine for dressing a thread on a workpiece, a base, a support on said base, a lever pivotally mounted on said support between the ends of said lever, one portion of said lever having a dressing tool mounted thereon, the opposite portion of said lever having adjusting means thereon by which said lever is rocked, ball means supported on said base, a carriage mounted on said ball means having on the portion thereof adjacent to said dressing tool supporting means for the workpiece, the preponderance of weight of said portion causing said carriage to tilt downwardly away from the dressing tool, and a finger adjustably mounted on said base engageable with a portion of the thread engaged by said tool for tilting the carriage and adjusting the workpiece toward said tool, said carriage and workpiece forming a unit which is removable as a unit from the finger and ball means on said base.

2. In a machine for dressing a thread on a workpiece, a base, a support on said base, a lever pivotally mounted on said support between the ends of said lever, one por-V tion of saidflever having a dressing tool mounted thereon, the opposite portion of said lever having adjusting means thereon by which said lever is rocked, ball means sup,- ported on said base, a carriage mounted on said ball means having on the portion thereof adjacent to said dressing tool supporting means for the workpiece, the preponderance of weight of saidA portion causing said carriage to tilt downwardly away from the dressing tool, a\ iinger adjustably mounted on said base engageable with a portion of the thread engaged by said tool for tilting the carriage and adjusting the workpiece toward said tool, and driving means for said workpiece which produces the rotation thereof and also the longitudinal movement due to the engagement of said finger with said thread portion.

References Cited in the tile of this patent UNITED STATES PATENTS 1,782,154 Thomas Nov. 18, 1930 2,088,538 Solomon July 27, 1937 2,122,184 Scrivener June 28, 1938

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