The invention relates generally to a device for positioning a workpiece along the center line of a lathe, and more particularly to a device for positioning a workpiece along the center line of an open spindle lathe by supporting one end of the workpiece by a spider tool which is capable of centering itself within the spindle.

Accurately centering and securing workpieces in an open spindle lathe is critical to successfully performing such machining operations as turning, boring, grinding, and threading. The task of accurately centering and securing a workpiece in an open spindle lathe becomes difficult when the workpiece is too short to extend through the entire length of the spindle.

Such short workpieces cannot engage both chucks of the lathe spindle, resulting in the potential for the workpiece to rotate off center during

machining.

A number of devices have been developed for centering a workpiece on a lathe tool. These devices are designed for use on a closed spindle lathe and typically have used some variation of a spider tool which is coupled to

the lathe tail stock and engages the interior of the workpiece with a plurality of bolts, which extend radially outward from the spider tool and are

individually adjusted to engage the interior of the workpiece. These tail

stock devices, while suitable for closed spindle lathes, are unsuitable for use on large open spindle lathes. The tail stock devices also have the disadvantage of requiring laborious manual adjustment of the bolts or pins

which engage the interior of the workpiece.

Another class of centering devices known in the art centers a workpiece during machining by compressing a rubbery member inside one end of the workpiece. The rubbery member when compressed, expands to engage the interior of the workpiece thereby stabilizing it during rotation. The use of an arbor with a compressible member for insertion into a tubular workpiece, does not lend itself to applications involving an open spindle lathe where the centering device should engage both the workpiece and the interior of the spindle in order to effectively and accurately center and stabilize the workpiece.

For open spindle applications, machinists have often resorted to a cylindrical arbor which has fixed rods projecting radially outward, and is customized to the particular lathes in the machine shop. The rods are fabricated to press fit into the lathe spindle. However, these custom arbors,

even when superbly machined, can be prone to misalignment. Moreover, because the rods must be sized to press fit into the spindle, insertion and

extraction of these custom arbors is a difficult and dangerous procedure. In

some cases, the custom arbor must be positioned at the opening of the

spindle and rammed into place by a speeding forklift. Such impact loadings

place the forklift operator at risk, and risk costly damage to the interior of the spindle.

The present invention comprises a spider tool for use in centering a

workpiece in the spindle of an open spindle lathe. In a broad aspect the

spider tool comprises a housing which is adapted at one end to engage the

workpiece so as to support the workpiece along a longitudinal axis common

with the housing. The spider tool further comprises a collar surrounding and supported by the housing with legs or pins which are spaced around the housing and are radially moveable. The spider tool also includes a shaft which is supported within the housing, in a co-axial, longitudinally adjustable relation. The shaft includes a surface intermediate one of its ends which serves as a cam to engage the inner ends of the radial pins and to move the pins radially outward in a uniform manner in response to axial movement of the shaft relative to the housing. The spider tool thus serves to couple one end of a workpiece to one chuck of a lathe, while the other end is supported by another chuck or other suitable member of the lathe.

In one preferred embodiment the end of the housing which engages

the workpiece comprises a conical member which supports and centers the workpiece relative to the axis of the housing. The other end of the housing is preferably adapted to directly or indirectly engage the corresponding end of the shaft in a threaded connection such that rotation of the shaft moves

the shaft axially in relation to the housing. Thus, the shaft may be threaded

along that end to engage a threaded nut, bushing, or similar member

attached to the end of the housing. Rotation of the shaft relative to the housing thereby results in axial movement of the shaft relative to the housing, which in turn causes the cam portion of the shaft to act on the pins. The pins are preferably biased by springs or other suitable means to

urge the pins radially inward against the cam.

It is contemplated that the conical end of the housing will engage an opening in a workpiece; however, the housing may be readily adapted to engage other workpieces. Thus, a centering plate or other suitable member may be coupled to the end of the housing and also to the workpiece.

FIG. 1 depicts a partial sectional view of an exemplary spider tool in accordance with the present invention.

FIG. 2 depicts an exploded exterior view of a conical member and plate in accordance with the present invention.

FIG. 3 depicts a partial sectional view of the exemplary spider tool of

FIG. 1 inserted in an open spindle lathe.

FIG. 4 depicts a partial sectional view of a collar in accordance with

the present invention. FIG. 5 depicts an exterior view of a riser pin in accordance with the

present invention.

FIG. 6 depicts a partial sectional view of the riser pin of FIG. 5

installed in the collar of FIG. 4.

FIG. 7 depicts a sectional view taken at section B-B of FIG. 1.

FIG. 8 depicts a sectional view taken at section A-A of FIG. 1 .

Referring to FIG. 1 , the spider tool 10 has at one terminus a centering

member 20. Referring now also to FIG. 2, centering member 20 includes a

conical surface 22 which is adapted to insert into, and engage the interior surface 24 of workpiece 26, as shown in FIG. 3. A generally cylindrical

centering member nipple 28 extends away from centering member 20.

Shaft bore 30 in centering member nipple 28 is adapted to slidably receive bore end 32 of cam member 34. As shown in FIG. 1 , centering member nipple 28 slidably inserts into a generally cylindrical housing 35. Centering member 20 is coupled to a housing annulus 36 by bolts 37 which are inserted into bores 38 which extend through housing annulus 36 and into centering member 20. Housing annulus 36 is preferably coupled to housing

35 by bolts 39 which are inserted into bores 40 that extend through housing annulus 36 and into housing 35. Housing annulus 36 may also be weld connected to housing 35.

As shown in FIG. 2, centering member 20 includes plate bore 41 which is adapted to receive a cylindrical nipple 42 that is coupled to a

substantially circular plate 44. Nipple 42 may be inserted into plate bore 41 until plate 44 is flush with front 46 of centering member 20. Plate 44 is

designed to enable centering member 20 to engage a workpiece 26 which does not have an interior surface 24. Bore 41 may also receive a nose cone

47 which enables the centering member to engage the interior surface 24 of

small diameter workpieces 26.

Conical surface 22 should be able to withstand the wear and stresses associated with repeated insertions into the interior surface 24 of workpiece 26. As a result, conical surface 22 should be fabricated from a heat treatable steel such as 4140 or 4340, and should be treated to a achieve a

Brinnel hardness of approximately 302 to 341 . A preferred method for obtaining sufficient hardness of conical surface 22 is a quench-polish-quench nitride process. Referring now also to FIG. 4, a substantially circular collar 50 slides over housing 35 and is preferably bolt connected to housing annulus 36 by bolts 51 which pass through bores 52 in collar 50 and into bores 53 in housing annulus 36. Collar 50 includes riser nipples 54. Riser nipples 54 are preferably radially dispersed about center 56 at 120° intervals as measured from the center line 58 of each riser nipple 54, though the number and spacing of nipples 54 may be varied. Riser nipples 54 extend radially

away from center 56 and collar 50. A pin passage 60 extends through each riser nipple 54. Pin passages 60 are adapted to slidably receive riser pins

62. Referring now also to FIGS. 5 and 6, pin passages 60 should be sized slightly larger in diameter than the lower end 64 of riser pins 62. Collar 50

need not have the resistance to high stress and wear that is necessary for conical surface 22. Therefore, collar 50 may be fabricated from softer

materials such as low carbon steel or even aluminum.

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Upper end 66 of riser pins 62 should be sized slightly smaller in diameter than lower end 64 to provide an annular volume 68. Pin spring 70

is slid over the upper end 66 of each riser pin 62 and seated within annular

volume 68, and on top of riser pin shelf 72. As riser pins 62 are translated

radially outward, riser pin shelves 72 engage pin springs 70, compressing springs 70 between riser pin shelves 72 and spring retainers 74, which are

preferably bolt connected to each riser nipple 54 by bolts 75.

To prevent riser pins 62 from rotating during radial movement, set

screws 76 are preferably threadably inserted through collar bores 77 to engage longitudinal slots 78 in pins 62. Set screws 76 may be fastened to collar 50 by methods other than threading, such as friction fitting.

Like conical surface 22, riser pins 62 should be fabricated to withstand significant stresses and wear. The upper end 66 of riser pins 62 should be heat treated using the quench-polish-quench nitriding process or

other suitable process that is used to heat treat the conical surface 22 of centering member 20.

Referring to FIG. 3, riser pins 62 are designed to translate radially outward and contact the inner surface 79 of spindle 80 to stabilize spider tool 1 0 after insertion into spindle 80. To enable quick insertion and

stabilization of spider tool 10, riser pins 62 should be adapted to extend and

retract nearly simultaneously. The nearly simultaneous outward radial translation is accomplished by a cam action between cam member 34 and riser pins 62. Referring now also to FIGS. 5 and 6, the bottom 81 of each

riser pin 62 and the cam surface 82 of cam member 34 are beveled at

approximately the same angle to enable cam member 34 to translate riser

pins 62 radially outward as cam member 34 is translated axially toward

centering member 20. As riser pins 62 are translated radially outward, pin springs 70 are placed in compression. When cam member 34 is translated axially away from centering member 20, pin springs 70 translate riser pins

62 radially inward.

To enable smooth operation of riser pins 62 and cam member 34, cam surface 82 and pin bottoms 81 should be manufactured to a relatively tight tolerance preferably in the range of ± 0° 1 5'. Both cam surface 82 and bore end 32 should be suitably lubricated to minimize friction during axial translation of cam member 34. To avoid jamming of cam surface 82, riser pins 62 should be prevented from rotating within nipples 54. Riser pins 62 are prevented from axial rotation by the set screws 76 discussed above. Referring to FIGS. 1 and 7, cam member 34 is operatively coupled to shaft 86. Thrust end 87 of shaft 86 is inserted into cam bore 88 and held in place by shaft pin 90 which is seated in groove 91 in shaft 86. Thrust end 87 has a semi-spherical thrust surface 92 which contacts the conical

end 94 of cam bore 88. Thrust surface 92 is preferably semi-spherical to

enable it to easily seat against conical end 94 without having to closely

match the dimensions of conical end 94.

Referring now also to FIG. 8, shaft 86 is supported through the length of housing 35 by a series of deflection rings 98 which are preferably

connected to shaft 86 by bolts 99. The number of deflection rings 98

depends upon the overall length of housing 35. The deflection rings 98 have

shaft bores 100 which are sized slightly larger in diameter than shaft 86.

Deflection rings 98 are preferably fabricated from a plastic material and may even be fabricated from a low carbon steel. If deflection rings 98 are

fabricated from a material with a potential for developing friction with

housing interior surface 102, a suitable lubricant should be placed between

housing interior 102 and deflection rings 98.

Shaft 86 extends through housing 35 and out housing nipple 103. Housing nipple 103 is preferably coupled to housing 35 by bolts 104 which insert into bores 105 that extend from housing nipple 103 into housing 35. Shaft terminates at hex end 106. The portion of shaft 86 which extends through housing nipple 103 has external threads 107 which engage the internal threads 108 in housing nipple 103. A tool may be attached to hex end 106 to rotate shaft 86. As shaft 86 is rotated, the action of threads 107, 108 translates shaft 86 axially. Lock nut 1 10 is slipped over hex end

106 and tightened down on external threads 107 to enable shaft 86 to be locked in position.

In this embodiment shaft 86 and cam member 34 are shown as

separate, but coupled components, however, they may alternatively be

formed as a single component.

Spider tool 10 operates in the following manner. Referring to FIG. 3, workpiece 26 is inserted through chuck 1 1 2, and into spindle 80, and

secured by chuck 1 1 2. Spider tool 10 is then inserted through chuck 1 16

and into spindle 80 until conical surface 22 of centering member 20 passes

into and engages the interior surface 24 of workpiece 26. Chuck 1 16 is

then tightened to engage and secure housing 35. After spider tool 10 has been positioned in spindle 80 and chuck 1 16 has been tightened on housing 35, shaft 86 and cam member 34 are translated axially by rotating hex end

106 of shaft 86. As shaft 86 and cam member 34 translate axially towards centering member 20, cam surface 82 engages pin bottoms 81 thrusting pins 62 nearly simultaneously radially outward. Hex end 106 of shaft 86 is rotated until cam surface 82 translates riser pins 62 radially outward far enough to contact the inner surface 79 of spindle 80. After riser pins 62 have contacted inner surface 79 with sufficient force to stabilize spider tool 10, lock nut 1 10 may be tightened, and spindle 80 may be activated for machining.

To remove spider tool 10, the process is reversed. Lock nut 1 1 0 is loosened, and hex end 106 of shaft 86 is rotated, to translate shaft 86 and cam member 34 axially away from centering member 20, thereby enabling pin springs 70 to translate riser pins 62 radially inward. Spider tool 10 may

then be quickly removed from spindle 80. Many modifications and variations may be made in the techniques and

structures described and illustrated herein without departing from the spirit and scope of the present invention. Accordingly, the techniques and

structures described and illustrated herein should be understood to be illustrative only and not limiting upon the scope of the present invention.