Turning – Lathe – Work rest
Patent
1987-05-01
1989-04-25
Schmidt, Frederick R.
Turning
Lathe
Work rest
82164, 51238S, B23B 2500
Patent
active
048236578
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a self-centering steady rest for machine tools, e.g. lathes, for centering long, circular cylindrical pieces and overhangs, said steady rest comprising two similar, pivoting levers arranged in symmetry relative to a plane of symmetry A--A passing through the centering point, and which at their ends adjacent the workpiece are provided with rotatable supporting rollers, a slide linearly displaceable radially relative to the centering point of the workpiece, said slide being provided at its end in contact with the workpiece with a rotatable supporting roller and being arranged in said plane of symmetry for the levers in such a way that the point of contact of the slide with the workpiece lies on that side of a plane perpendicular to the direction of displacement of the slide and passing through the centering point, which is opposite to the pivot lever contact points symmetrically arranged relative to said plane of symmetry, a guide means in the form of a cam and cam follower, said means coupling the displacement of the slide to the pivot movement of the levers, so that the three contact points with the workpiece are always at the same radial distance from the centering point, and a device for displacing the slide.
Steady rests of this type have been known for quite some time, see e.g. GB No. 1 220 954 (FIG. 5) and are based on the principle known by German Patent Specification No. 422 198. This known steady rest has, however, certain drawbacks. For example, the clamping force of the levers varies considerably when centering workpieces of varying diameters if the same linear displacement force is applied to the slide. The clamping force thus decreases with decreasing workpiece diameters. In order to compensate for this decrease, there are two possibilities with the known steady rest: to either increase the linear displacement force on the slide with decreasing workpiece diameter, or to apply from the beginning such a linear displacement force to the slide that the required clamping force is provided even for the smallest workpiece diameter within the working range of the steady rest.
Neither of these possibilities is really suitable for modern day machine tools. Providing for adjustment of the linear displacement force on the slide by changing the working pressure in a hydraulic cylinder for example, involves an additional installation operation slowing down production, and a constant large linear displacement force can mean that the increasing clamping force with increasing workpiece diameter can deform the workpiece, particularly when machining thin-walled materials.
In a known steady rest of this type the latter solution was selected with constant working pressure in a hydraulic or pneumatic cylinder. Geometric limitations as regards the design of the levers themselves and the total size of the steady rest, the clamping force relationships described above and the permissible clamping force variation, are such that this known steady rest is manufactured in a number of different models for different clamping ranges, i.e. ranges within which the diameter of a workpiece can lie to obtain an appropriate clamping force. Since the variation in clamping force is too great in these steady rests as well, they are not suitable for machining easily deformable materials either, especially turning thin-walled materials.
A steady rest, with a cam follower joined to the slide and cam curves on the ends of the levers, is known by U.S. Pat. No. 4 519 279. In this known steady rest, however, a pneumatic jack is controlled in response to variations in the diameter of the workpiece. They have thus taken a completely opposite approach to solving the problem of clamping force variation than according to the present invention. It is also evident from the weak design of the levers for example, that this known steady rest is intended for much weaker clamping forces than the design according to the invention, which should be able to withstand clamping forces in the order of 20 kN.
Furthermore, the des
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patent: 2459068 (1949-01-01), Eastwood
patent: 3535963 (1970-10-01), Dietl
patent: 4463635 (1984-08-01), Hafla
patent: 4517866 (1985-05-01), Bazuin
patent: 4519279 (1985-05-01), Ruggeri
patent: 4546681 (1985-10-01), Owsen
Schmidt Frederick R.
Shideler Blynn
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