Chucks or sockets – Radially reciprocating jaws – Lever actuated
Patent
1988-11-17
1990-07-03
Howell, Daniel W.
Chucks or sockets
Radially reciprocating jaws
Lever actuated
279 1L, 279121, B23B 3116
Patent
active
049384910
DESCRIPTION:
BRIEF SUMMARY
Field of the Invention
The present invention relates to devices for centering and securing workpieces in a machine-tool, and more particularly it relates to four-jaw self-centering chucks.
Background of the Invention
There are widely known three- and four-jaw self-centering chucks wherein the clamping jaws are brought together by equal distances from the axis of the chuck. However, when workpieces having either flaws in the shape of their reference surface or a cross-sectional shape symmetrical about its centre are secured in such chucks, the axis of the workpiece becomes displaced from the axis of the chuck (V.S.Korsakov "Osnovy konstruirovaniya prisposoblenii", 2d rev. ed., Mashinostrojeniye /Moscow/, Ch. 2, Para. 3, pp. 33-35).
There is know a four-jaw self-centering chuck including a housing having mounted therein radially movable clamping jaws interacting with a self-centering mechanism operatively connected with a drive (SU, A, 234826).
The self-centering mechanism in this know chuck includes two double cranks having a common axis of rotation. Each double crank is intended for synchronously actuating a pair of claimping jaws. The drive includes two coaxial gears meshing with the third gear having a "floating" axis. A belical groove is cut in the end face of either one of the two coaxial gears.
Synchronous actutation of the two pairs of clamping jaws is effected as follows. With the third gear being rotated, the two coaxial gears rotate in opposite directions, one of the clamping jaws of each pair cooperating with the helical groove in the end face of the respective one of the two coaxial gears and moving in the radial slot of the housing, while actuating the other clamping jaw of the pair through the respective double crank. As the clamping jaws of one of the two opposing pairs close on the surface of the workpiece being clamped and are arrested by the engagement with this surface, one of the clamping jaws of the other pair engages the workpiece and begins displacing it relative to the closed clamping jaws into alignment with the axis of the chuck, i.e. until the workpiece engages the fourth clamping jaw. However, as the forced interaction of the opposing pairs of the clamping jaws takes place through the gear with the "floating" axis, a rising effort applied to the clamping jaw displacing the workpiece results in the effort applied to the already closed pair of jaws also rising, so that when the workpiece is being clampled, the distribution of the clamping effort among the jaws is non-uniform. Moreover, if the flaw of the reference surface of the workpiece is such that the movment of the workpiece towards the centered position requires that the spacing of the already closed pair of clamping jaws should be increased, the workpiece would become centered only by three clamping jaws. This is explained by the fact that the workpiece is being centered and clamped, the engagement of one of the clamping jaws with the helical groove in the end face of the gear would not allow to increase the spacing of the clamping jaws of the pair already closed on the workpiece. Furthermore, the maximum possible differential of the spacings of the opposing pairs of the clamping jaws is limited by the length of the slot of the third "floating" gear.
Thus, the hitherto known four-jaw self-centering chuck of the prior art would not provide for relatively high accuracy of the centering and reliability of the clamping of workpieces having a cross-section symmetrical about its centre.
Summary of the Invention
It is an object of the present invention to create a four-jaw self-centering chuck wherein the self-centering mechanism should be of a design providing for relatively high accuracy of the centering and reliability of the clamping of workpieces, while extending the applicability of the chuck for clamping workpieces having a cross-section symmeterical about its centre, as well as workpieces having flaws in the shape of their reference surface.
The essence of the present invention resides in a four-jaw self-centering ch
REFERENCES:
patent: 2828134 (1958-03-01), Buck et al.
patent: 2921796 (1960-01-01), Ernest
patent: 2932524 (1960-04-01), Pealer
patent: 4103915 (1978-08-01), Zdanovsky et al.
Kiknadze Nikolai A.
Sumenko Vladimir I.
Taniashvili Teimuraz S.
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