SMW Autoblok AN Manuel D'utilisation page 19

INSTRUCTIONS AND SAFETY REGULATIONS
a dial indicator.
The concentricity depends mainly on the top jaws:
A) The hard top jaws have been designed to grip on sharp edges increa-
sing the friction coefficient and are not suitable to grip on finished surfa-
ces with high concentricity accuracy (0,2 mm TIR is hard to maintain).
B) With ground top jaws for finishing operation the concentricity can be
very accurate if the instructions of points 4.2, 4.3 and 4.4 are carefully
followed.
REPEATABILITY: Repeatability is the constant positioning of a number
of workpieces, clamped between the jaws of a chuck, under the same
clamping conditions. Once a good concentricity has been obtained, by
correctly grinding the clamping areas, it is a good feature of the
power chuck to guarantee good repeatability, that is, to make sure
that all the components clamped in the same conditions are concentric
within a limited tolerance.
4.1 HARD TOP JAWS.
The standard hard top jaws, supplied on request, are designed to clamp
raw workpieces in the first operation.
The clamping areas of the top jaws are ground in order to have sharp
edges which penetrate the workpiece during the gripping, compensating
for the "out of shape" and increasing the friction coefficient and conse-
quently the draw coupling of the power chuck.
These jaws are not suitable when high accuracy is required for limi-
ted concentricity tolerances.
4.2 SOFT BLANK TOP JAWS.
For finishing operations where good concentricity between the clamping
diameter and the turned one is necessary, soft top jaws must be used.
The clamping surfaces on the chuck are turned, taking up the play and
elastic deformations in the same direction of the clamping (see point 4.4).
The use of non-standard top jaws or not them in the correct way
could create a serious safety problem. Please carefully follow the
rules stated below:
4.2.1 For standard applications, use exclusively SMW-AUTOBLOK soft top
jaws. The SMW-AUTOBLOK chuck guarantee is void if original SMW-
AUTOBLOK top jaws are not used. The use of substitute jaws can cause
breakage in the chuck and/or in the clamping.
4.2.2 Before using non original soft top jaws, check that the serrations
have the same pitch and inclination as the master jaws (inch serrations
1/16"x90° or 3/32"x90°- metric serrations 1,5mmx60°).
4.2.3 Check that the serrations of the jaws do not have a sharp point, but
a chamfer of, at least, 0.3-0.4mm (see ISO 9401) so that the contact is
correctly made on the side surfaces of the serrations.
4.2.4 If the mounting screws are replaced, check that they are not too long
and they are not pressing against the bottom of the T slot of the master
jaws. If so, this would overload the two sides of the "T" slot possibly
breaking it.
4.2.5 NEVER tighten the mounting screws too much (with long wrenches
or WORSE with hammer blows on the wrench). The screws must
always be tightened with a torque wrench set according to the clamping
couples shown in the following table.
Minimum class request 12.9
Dimensions of screw Tightening torque (N.m)
M6 12
M8 30
M10 45
M12 70
4.2.6 The clamping jaws should not extend beyond the diameter of the
chuck. In the rare occasions when jaws are used which extend beyond
the diameter of the power chuck, great care should be exercised in CNC
programming and machining, in order to avoid collisions with the tools
and prevent injury to the operator during machine operation.
4.2.7 NEVER use jaws higher than twice the height of standard jaws.
For special applications with greater heights, it is necessary to use
chucks with tongue and groove master jaws.
4.2.8 The maximum height of the component to be clamped must NEVER be
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Minimum class request 8.8
Dimensions of screw Tightening torque (N.m)
M16 170
M20 300
M24 500
M30 950
higher than 3 times the height of the
clamping jaws.
Components with greater heights must
be supported by a tailstock or by a self-
centering work rest.
4.3 SUGGESTIONS ON HOW TO USE TOP
JAWS.
4.3.1 A constant clamping force, the draw
coupling applied to the workpiece increa-
ses with the clamping diameter. Therefore always clamp the component
on the greatest diameter possible.
4.3.2 The clamping force is reduced with the increase of the height to which it
is applied; therefore, reduce the height of the clamping jaws as much as
possible.
4.3.3 When good axial tolerance is necessary, do not reference the workpiece
on the jaws, because they are deformed by the clamping. In this case,
the axial reference of the workpiece must be done by means of fixed
supports on the chuck body or on the front flange ; these points undergo
less axial deformation (fig. 7A). It is also possible to have the axial
support on the top jaws when the clamping diameter is medium-small in
case of internal clamping and medium-large in case of external clam-
ping,anyway, close to the clamping area. (see fig.7B).
4.3.4 IMPORTANT: When positioning the jaws, the first mounting screw
(A) must be positioned as far as possible away from the fulcrum (C) of
reaction at the gripping coupling thereby incresing the arm (b
reducing the draw force (F1) on the screw itself, and consequently its
stress and deformation.
External clamping: The screw (A) must be as close as possible to the
center:
Internal clamping: The screw (A) must be in the most external position
possible.
4.3.5 We advise the use of collet chucks for
clamping bar stock. If a power chuck is
used for clamping a bar, we suggest
mounting carbide inserts with diamond
clamping areas on the jaws. These
inserts increase the friction coefficient
and compensate for the deformation of
the top jaws.
4.4 INSTRUCTIONS TO TURN SOFT TOP
JAWS.
To obtain the best concentricity between the clamping diameter and the
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>b) and
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