US3160041A - Tailstock - Google Patents

Description

E. C. HANNA Dec. 8, 1964 TAILSTOCK Filed March 21, 1961 0% Q0 Q0. NO 09 INVENTOR EDWARD C. HANNA BY 720%4V1-M ATTORNEY5 United States Patent 3,166,041 TAES'IOCK Edward Q. Hanna, Waynesboro, Pa, assimor to Landis Machine Company, tlayneshoro, Pa, a corporation of Pennsylvania Filed Mar. 21, 1961, Ser. No. 97,222 1 (Iiaim. (Cl. 82-31) This invention relates to tailstocks for assisting in holding workpieces between centers in machine tools and more particularly to means for mounting and operating a tailstock center to accommodate changes in the length of the workpiece being held.

In many cold-forming operations such as thread rolling, the length of the workpiece increases a substantial amount as the operation proceeds. When such workpieces are operated upon between centers, the increase in length creates a particularly troublesome problem since the tailstock center must be capable of axial displacement and at the same time must exert a substantial pressure axially of the workpiece to hold it in place. If the tailstock center is not permitted to move axially under such conditions, it will be destroyed in a short time by friction if it is a plain center. If it is a so-called live center, rotating with the work, the life of its bearing will be very short. In. either case, the workpiece will usually bend.

Attempts have been made to solve the problem by mounting the tailstock center resiliently, that is, by employing a spring, air pressure or hydraulic pressure to urge the center toward the work. In either case the pressure required to maintain the work blank in its proper position when it is being formed is considerable. Consequently, when the workpiece length increases, this holding pressure is increased to an excessive amount, resulting in the reappearance of all of the deleterious effects mentioned above.

A known device, intended to accommodate only the slight increase in work length due to heating thereof, employs a hydraulic system to regulate the axial pressure upon the tailstock center at an approximately constant value. In addition to being quite complex and expensive, this system proves to be of little value in situations where a substantial elongation of the work is caused by an operation involving actual deformation of the work, as in rolling threads or other profiles on cylindrical workpieces.

The device of this invention solves the problem simply, efiiciently and economically by providing a fluid motor in the form of a pneumatic cylinder to urge the tailstock center in the direction of the workpiece, together with means to lock the center axially against this air pressure so that the pressure upon the workpiece is limited, regardless of elongation of the workpiece.

Accordingly, it is an object of the invention to provide novel tailstocks having an axially movable center capable of accommodating an increase in the length of the workpiece while it is held between centers.

It is a further object of the invention to provide novel tailstocks as described above in which the axial pressure is supplied by a fluid motor and is regulated by an automatic locking means. i

A still further object is to provide novel tailstocks as described above in which the locking means effectively transforms the axial pressure exerted by the fluid motor into radial pressure against the interior walls of the tailstock.

Further objects and advantages will be apparent from the following description and the accompanying drawing wherein:

FIGURE 1 is an axial section through a portion of a tailstock, illustrating one embodiment of the invention;

3,159,041 ?atented Dec. 8., 1964 ice FIGURE 2 is a transverse sectional view taken along stock frame (FIGURE 1) which may be of any desired construction for mounting the assembly on the machine tool on which it is to be used. In this first embodiment a plain center 22 is shown in contact with a workpiece W and is slidably mounted in horizontal bore 24- in the housing or frame 29. The bore 24 and the center 22 are coaxial with the opposite or headstock center (not shown).

The bore 24 is enlarged as at 26 and the center 22 is provided at its rear end with a shoulder 28 having a sliding fit in the bore 26. The center 22 is also provided with a keyway 3% on one side engaged by the dog point of a set screw32 which is threaded through one wall of the housing Zii, radially of the center 22 to prevent it from rotating.

A screw 34, disposed centrally of the bore 26, is threaded into the rear end of the center 22 and hasa head embedded in the rear end of a piston 36, through which the screw 34 passes with a sliding fit, an annular seal 37 being provided between the screw 34 and the piston 36. The piston 36, provided with a circumferential seal 38 is enclosed in the conventional manner in a pneumatic cylinder 40. As shown in this example, the forward end of the cylinder 40 is formed with a cylindrical boss 42 which extends a short distance into the bore 26 for centering the cylinder 44 and piston 36 with the center 22. The cylinder 46 may be attached to the rear end of the housing 20 by screws or other convenient means (not shown). The cylinder 49 is closed by a rear plate 44 screwed to the rear end thereof. Passages 46 and i8 are provided to conduct air into opposite ends of the cylinder 40 and lead to the rear surface of the plate 44 to which a suitable valve may be attached to admit air into the passage 46 or 48 by manual or automatic operation, as required.

The piston 36 has a integral hollow piston rod 50 extending forwardly in close sliding contact with the bore of the boss 42, with an annular seal 43 interposed therebetween. The piston rod 59 surrounds the screw 34 and terminates a short distance from the. rear surface of the center 22. The forward end of the rod 50 is tapered and is surrounded by a fiber bushing, cut lengthwise, as shown in FIGURE 2, into a number of shoes 52, to provide for radial expansion, the shoes 52 being held in assembled position by a clamping ring 54. I

A compression spring 56, surrounding the rod 50 and pressing against the rear surfaces of the shoes 52 urges the shoes 52 against the rear surface of the center 22. The rear end of the spring 56 is supported against a washer 58 which, in turn, is prevented from moving rearwardly by a small shoulder to on the rod 50.

In FIGURE 1, the tailstock is shown in mid-operation, i.e. with aworkpiece W being held between the center 22 and the opposed headstock center. At the beginning of the operation, with no workpiece present, the center 22 and the piston 36 are withdrawn toward the right to the extremity of its movement. When the workpiece is held in position to be engaged by the center 22, air is admitted through the passage 46 to the head endof the cylinder 40 to force the piston 36 and the center 22 toward the left to hold the workpiece in position to be machined.

As the piston 36 and the piston rod 50 move to the left, the force applied to the piston 36 is transmitted through the washer 58 to the spring 56 which pushes the shoes 52 and the center 22 to the left to grip the workdoes not exceed the force of the spring 56, the shoes 52 and the center 22 are moved toward the left as a unit, but when the center is stopped by its firm engagement with the workpiece and the force effective to move the piston 36 to the left exceeds the force which the spring can transmit without contracting the spring 56, the ex- .cess piston force is expended radially to lock the shoes 52 in axial position against the interior of the bore 26. Then only a force equal to that of thespring 56 is exerted axially upon the workpiece.

Subsequently, 'as the work forming operation proceeds and the length of the workpiece is increased, an increasing counter force from the left toward the right is exerted upon the shoes 52. When this counter force exceeds the force exerted by piston 36 plus the frictional drag of the shoes 52, the shoes 52 and the piston 36 recede toward the rightuntil equilibrium conditions are reached. When the workpiece has ceased to elongate the previous condition is established, i.e. the leftward force of the piston 36 is expended radially to lock the shoes 52 and the force effective to hold the workpiece in place is substantially equal to the load on the spring 56. Thus the pressure upon the center 22 toward the left is always sufficient to retain the workpiece in position but is never excessive ,due to the locking action of the shoes 52.

FIGURE 3 illustrates a second embodiment of the invention and shows how the details of the structure may be varied without departing from the inventive concept.

The tailstock frame 62 has a rearwardly extending inte- 'the rear end of a nose member 82. The member 82 is s slidably mounted in the rear end of a bore 84 in the tailstock frame 62. A nut 86, recessed in the rear end of the member 82, is threaded upon one end of a stud 38 which passes axially through the member 82 and extends forwardly therefrom into the rear end of a socket to which it is attached by a pin 92.

A bushing 94 is mounted in the bore 84- of the frame 62 and serves as a bearing for the limited axial sliding movement of the socket 90. The socket 90 supports a conventional tailstock center. In the example shown this is a live center comprising a tapered shank 96, projecting from the forward end of the socket 90, and a centering member98 mounted on' the forward end of the shank 96 and having a ball bearing 100 and a ball thrust bearing 102 interposed between the center 98 and shank 96. A cover 104 is also provided to enclose the bearings 100 and 102. 7

It will be recalled that in the embodiment of FIGURE 1, a set screw 32 is provided to prevent the center 22 from rotating and screwing itself off the rod 34. In the embodiment of FIGURE 3, such a key is not necessary since the live center 96-104 is not threadedly engaged with the stud 88.

As in the previous example, fiber shoes 106, forming a tapered bore, surround a conical surface 108 on the forward portion of the nose member 82. The shoes 106 are retained in position by annular retaining rings 110.

A further retaining ring 112 may be provided to retain the shoes 106 axially when it becomes necessary to disassemble the socket 90 from the mechanism. Belleville springs 114 are mounted between the shoes 106 and a shoulder on the member 82 to perform the function of the helical spring 56 in the embodiment of FIGURE 1.

The invention may be embodied in other specific forms without departing from the spirit or essential characterto be secured by United which is elongated as it is worked upon comprising a tubular support assembly, a center assembly engageable with said one end of said workpiece and mounted in said tubular support assembly for movement axially of said workpiece, a power'member mounted in said tubular support assembly for movement axially of said workpiece, said power member having a wedging surface, a brake assembly positioned between said wedging surface and the interior of said tubular assembly, said brake assembly having one end in engagement with said center assembly,

a spring positioned between the opposite end of said brake assembly and said power member to normally maintain said brake assembly out of wedging contact With said power member and said tubular support assembly and operable to transmit force from said power member to said center assembly, said spring being compressed when 'the movement of said center assembly is opposed by a References Cited in the file of this patent UNITED STATES PATENTS Muller Oct. 7, 1919 Drummond Dec. 1, 1931

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