Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a conically clamping collet for
the mechanical handling of workpieces with a circular profiled clamping
surface.
- Automatic lathes or milling machines for the machining of solid
cyllndrical parts, for various reasons,are frequently fitted with special
chucks which are adapted to the particular workpiece concerned. Collets
which are driven hydraulically, pneumatically or electrically and are
opened and closed by the axial movement of a conical bushing are widely
used. Por the proper operatlon of such collets it is important for
10` their clamping surfaces to present a circular clamping profile in the
closed state.
This requirement leads to difficultles,in that workpieces with
diameters which may deviate from the norm will not be uniformly clamped
over their entire circumference,and pressure against the workpiece
becomes concentrated at a few clamping points. In order to remedy this
to a certain extent, collets having six or nine finger chucks are used,
departing from the usual three-member chuck. However, the basic diffi-
culty described above, cannot be overcome in this way.
Another disadvantage of such collets has now become evident in
the machlnlng of delicate artlcles such as deep-drawn sheet metal parts.
When such parts do not meet the correct tolerances of roundness in the
deep-drawlng process, subsequent machlning is necessary. The parts have
to be clamped in a collet to effect this. In doing 80, however, elastic
alteration of the profile occurs in adaptlng to the cylindrical clamplng
surface of the collet. In consequence, notwithstanding the machining,
the flnlshed parts show considerable departures from the ideally round
profile upon removal from the machine.
The present disclosure meets the problems presented by the prior
art and enables the construction of a reliable accurately clamping collet
which 18 simple in operation.
More particularly in accordance with the invention there is
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provided, a collet for articles having a generally circular surface to
be clamped, comprising,
a chuck, clamping fingers to said chuck providing a generally
circular clamping surface for operatively clamping 6aid article surface,
means for ving said fingers for clamping said article surface,
a circumferentially disposed groove in said chuck formed in sait
fingers,
an elastomeric ring received in said groove,
said groove being formed with a depth less than the thickne6s
of said elastomeric ring, said ring thereby being enabled for protruding
out of said groove beyond said clamping surface of said fingers. At least
a pair of grooves may be provided in the clamping surface of the chuck,
each with its elastomeric ring. Preferably, the elastomeric rings are
toroidal 0-rings and the bottom of each groove has 8 rectangular cross
section.
Specific embodiments of the invention will now be described
having reference to the accompanying drawings in which;
Figure 1 shows,partially in section, an externally clamping
collet with a six-finger chuck; and
Figure 2 shows, also partly in section, an internally clamping
collet.
The collet of Figure 1 comprises basically a tapered chuck 1,
with six fingers 6 cooperating tapered clamp ring 2 and adJustlng ring 3.
The design of the chuck is not restricted to a six-finger form; and a
three-, nine- or more-finger embodiment may be chosen instead, if
desired.
The chuck has grooves 4 in the clamping surfaces of the fingers 6,the
bottoms of which preferably have a rectangular profile and the depths of which
are less than the diameter of 0-rings 5 therein received.
In general, in order to obtain a satisfactory seat for the work-
pieces to be clamped, it is sufficient for the 0-ringg to protrude above the
clamping surface by about 0.5mm in the unloaded state. This figure, however,
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should only be taken as a guideline, and may be greater or less, depending
on the specific properties of the pieces to be held and on the clamping
diameter. The best protrusion for the particular circumstance can, if
necessary, be determined by simple testing, and offers no difficulty to
the man skilled in the art.
The axial positioning of the 0-rings relative to the chuck will
not be described in detail since this i8 detèrmined directly from the form
of the workpiece to be clamped, and is merely arranged so that the
clamping is effective.
Figure 2 shows an embodiment of the new collet, which is intended
for internal clamping of suitable workpieces. It functions similarly to
the device in Figure 1, but the clamping surface is formed by the outer
diameter of chuck 10. Chuck 10 is operated by the axial displacement of
tapered shank 12, which is in direct sliding contact with the conical
inside face of the chuck. The chuck 10 is retained in axial position by
engaging sleeve 13. As in the previous embodiment, here again the chuck
may have three-, 8iX-, nine- or more-fingers.
The arrangement and function of grooves 14, which receive 0-rings
is similar to that of Figure 1. Here, however, it must be kept in mind
that the protrusion of the 0-rings above the clamping surface in the
unloaded state should be greater than in the case of the outside-clamping
chuck of Figure 1, since,unlike the compression occurring there during
the clamping process, there is a stretching of the rings with consequent
decrease of their thickness diameter.
Basic advantages of the new collets are that the clamped work-
pieces are held in an extremely reliable way while avoiding any undesired
deformations or damage, and especially important, is that a circumfer-
entially symmetrical clamping is assured even with workpieces whose profile
is not exactly circular.
