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INSTRUCTIONS AND SAFETY REGULATIONS
3.5
Maximum rotation speed
The maximum rotation speed in revolutions/minute (r.p.m.) is one of the
main technical features of each power chuck. It is specified in all catalo-
gues and is engraved on the front of each power chuck (N max - r.p.m.).
The system to calculate the max speed is specified in the Proposal regu-
lation EN 1550 according to the following formula:
2
.
n max=
3
where:
n max [r.p.m.] = Maximum r.p.m.
Fsmax [N]
= Max. static gripping force
m
· r
[Kg·m] = Mass moment of 1 jaws,"T" nut and screws
1
1
m
· r
[Kg·m] = Mass moment of 1 gripping jaws
2
2
Z
= Number of chuck's jaws.
THE MAXIMUM SPEED is the one at which the power chuck looses 2/3
of "maximum static clamping force" due to the "theoretical centrifugal
force" using standard hard top jaws in reversed position (high slot
outwards) in an external position but within the diameter of the power
chuck.
THE MAXIMUM SPEED is not an absolute value, but can be
reached only under the following conditions:
A)If the "maximum static gripping force " (Fsmax) acts on the workpiece.
B)If the standard hard top jaws (or soft top jaws with equivalent weight
moment) are positioned within the outside diameter of the chuck.
If the "Maximum draw pull" is not applied (Ftmax) and the
"Maximum static clamping force" (Fsmax) is not achieved, or if heavier
jaws are used in a more external position, it is necessary to reduce the
rotation speed according to the following formula:
2
.
n=
3 (m
Example: on a 260 APD-3 jaw chuck, with Fso = 120kN (120000N) veri-
fied; with m
· r
=0.10 (see schedule at point 3.3); with m
1
1
(weight of 1 jaw by its baricentric radius), the maximum speed (according
to ISO and DIN standards) is the following:
2
Fso
.
n=
. r
. r
) . Z
3 (m
+ m
1
1
2
2
4.
CLAMPING JAWS AND T-NUTS.
The clamping jaws are among the most important components in the
workpiece gripping operation. It is ESSENTIAL to know exactly how to
use them.
Any type of jaw used, must be positioned so that the clamping of
the workpiece is in the middle of the radial stroke of the master jaw.
CONCENTRICITY: Concentricity is the value of the difference from the
theoretical rotation axis of the external surface of a round workpiece
clamped between the jaws of a power chuck; usually it is measured with
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.
4.0
TOP JAWS for models AP-RD AP-RC NT-RD NT-RC
These top jaws are mounted on the master jaws by means of an inclined
T-nut instead of the conventional T-nut and bolts (see the drawing on the
lower side of pag. 15). When mounting the top jaws for a new compo-
nent, the inclined T-nut must be tightened with a torque wrench set to
the torque indicated in the table at page 15.
Caution: always keep the seat of the T-nut perfectly clean; to do that, just
dismantle the assembly following the instructions of page 21, par. 5.2.1.
Fsmax
30
.
. r
. r
) . Z
(m
+ m
1
1
2
2
Fso
30
.
. r
. r
) . Z
+ m
1
1
2
2
2
120000
30
.
.
=
(0,10+0,085) . 3
3
4.0.1 In the operation of the radial positioning of the top jaws for chuck AP-RD
and NT-RD, always be sure to have complete contact between the incli-
ned T-nut and the top jaw. With standard reversible hard top jaws, it's
tollerable to reduce the contact lenght to 5/6 of the total length l2, but
never less than this (see drg. 4.1)
4.0.2 In the soft top jaws boring opera-
tion, beside all other precautions,
note that machining below the
"NO TURNING ZONE" line is not
permitted (see drg. 4.2). Turning
below the "NO TURNING ZONE"
line will damage the top jaws and
the inclined T-nuts (reducing their
mechanical strength).
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-
· r
=0,085
ted concentricity tolerances.
2
2
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.
30
≅ 3600
.
The clamping surfaces on the chuck are turned, taking up the play and
r.p.m.
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 or ISO 3442-2) 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).
drw. 5
fig. 4.1
fig. 4.2
19
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