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TROUBLE SHOOTING GUIDE FOR POWER CHUCKS
Check that there is no alarm signal in the operation system of the machi-
1
ne that could stop the operation of the controls. Carefully check the elec-
tric circuit and the buttons.
Check that the hydraulic circuit is in good working condition and gives
2
the requested pressure; check the following:
A) The oil level in the tank.
B) The proper operation of the pump.
C) The filters must not be clogged.
D) The solenoid valves must not be jammed.
E) The tubes must be properly connected.
Be careful not to reduce the pressure (relative to the starting pressure) all
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at once to 1/3 (or less), this would prevent the operation of the safety
valves and the piston stroke.
One of the two safety valves is jammed in its seat. This could be due to
4
different reasons (dirty oil, over-pressure, water hammering, changes in
temperature, wear of the internal components of the valves).
To solve this problem please refer to the use and maintenance manual
for the cylinder.
5
If, after having checked points 1-2-3 and 4 the problem still hasn't been
solved, it is necessary to dismount the chuck from the machine and verify
that the draw tube makes its full stroke; if not, refer to the use and main-
tenance manual of the cylinder.
If the power chuck is new, check that the draw-bar between the chuck
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and the cylinder has the correct length and is correctly screwed into the
front and back threads.
If the chuck has been in operation for a long time, check that during
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operation the draw-bar has not unscrewed.
Check if the connecting draw-bar between the chuck and cylinder is
broken, or the two threads are damaged.
If the draw-bar is broken, or the threads are damaged, check the hydrau-
lic system for excessive pressure and that the draw-bar is the correct
size
Place the chuck on a bench. Check, if by pushing or pulling the center
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wedge, the wedge moves through its complete axial stroke and this
stroke becomes the radial stroke of the master jaws, if not, there can be
two kind of problems:
- the chuck is dirty and clogged;
- internal parts are broken or jammed;
Disassemble the chuck and perform the required maintenance.
The body of the chuck is out of center or out of planarity and does not
9
turn within the requested tolerances (see point 2.4). Center the chuck.
The clamping jaws and/or the workpiece are not symmetric with the rota-
10
tion axis and therefore cause unbalance. Balance the chuck with the jaws
and the piece clamped.
Insure that the draw tube is not unbalanced, out of center or out of align-
11
ment.
If vibration occurs only in thrust position, this is due to bending of the
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draw bar which undergoes an axial stop.
It is necessary to drive the draw bar radially onto bronze bearings.
Check carefully, removing, in order, the workpiece, the top jaws, the
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chuck, the draw tube, the cylinder, the adapters, until there is no further
vibration. Then balance the part removed last.
14
Check that the shoulder (diam. E) of the wedge of the chuck does not
touch the machine spindle, interfering with the axial stroke of the wedge.
If this occurs, use a thicker adapter.
15
A radial clearance in the master jaws of 0,15-0,25mm is normal and is a
feature of chucks with inclined surfaces. The clearance can reach up to
0,5mm without consequences.
If the radial clearance is more than 0,5mm, the inclined surfaces are worn
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out due to corrosion or lack of lubrication.
The power chuck can still work but it is not accurate. We suggest
dismounting the power chuck and conducting the maintenance as indi-
cated in the appropriate paragraph.
Dismount the power chuck and check that there are no broken internal
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components.
There could be problems in the hydraulic circuit (insufficient tank capa-
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city, clogged filters, throats in the circuit) and/or the cylinder. Please
refer to the instruction manual for the cylinder for all problems of the
hydraulic cylinder.
19
For a number of reasons (see points 4.2 and 4.3) the master jaws deform
on the side blocking their sliding in the body of the chuck; the principal
reasons can be:
a) the top jaw mounting screws are too tight;
b) The top jaw mounting screws are too long and push against the
bottom of the "T" slot.
c) The serrations of the top jaws do not match the serrations of the
master jaws
d) Damaged or worn out "T" nuts.
These problems cause a great loss in clamping force and excessive wear
of the power chuck. We suggest reading point 4, the clamping jaw
section of this manual.
20
The adapter has been incorrectly machined, and the axial reference of
the chuck is made on the external circular crone instead of on the internal
surface of the chuck (see point 2.4).
Modify the adapter and make the axial reference correctly.
21
The chuck is very dirty; the lubrication is not appropriate (unsuitable oil or
grease) or insufficient. Disassemble the power chuck and conduct main-
tenance on the chuck.
22
The draw pull is insufficient. Check the technical features of the power
chuck and cylinder and adjust the hydraulic pressure in order to apply
the max draw pull allowed.
It is necessary to have a static gripping force meter. The SMW- AUTO-
BLOK type 339H grip force meter will measure the effective gripping
force.
23
Check the features of the power chuck and test the static gripping force
when the chuck is not operating (point 22).
To calculate the remaining gripping force at the desired speed it is
necessary to calculate the centrifugal force (Fc) according to the instruc-
tions at point 3.3 of this manual.
To reduce the centrifugal force it is necessary to make the jaws as light
as possible and reduce the baricenter radius, by putting them toward the
rotation center as much as possible.
To measure the "effective dynamic gripping force" it is necessary to use
a rotating dynamometer type SMW-AUTOBLOK DGM 270.
24
The serrations of the soft top jaws have not been machined properly,
have not been used correctly, or they have not been turned in the proper
way (refer to instructions of points 4.2, 4.3, and 4.4).
25
The top jaws are too high or are in an incorrect position, therefore, during
gripping the jaws lift too much. It is necessary to reduce the height of the
top jaws and position them according to instructions of point 4.3.4.
26
The slides of the master jaws could be worn out, causing excessive
deformation during the gripping; it's necessary to disassemble the
chuck, check the clearences and, if necessary proceed to the revision or
substitution of the chuck.
We advise the use of collet chucks for clamping bar stock. If a power
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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.
When clamping raw workpieces with high roundness errors or irregular
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shapes during first operation, we suggest mounting carbide inserts on
the jaws. These inserts increase the friction coefficient and compensate
for the irregular shape of the clamping surfaces.
29
Hard top jaws are designed to clamp raw workpieces on their edges,
therefore an eccentricity over 0,2mm is normal.
30
The concentricity, clamping with turned soft top jaws, depends mainly on
how these jaws are designed and manufactured (refer to instructions
points 4.2, 4.3 and 4.4).
31
Check that the master jaws or the wedge are not broken and that there is
no dirt in the internal mechanism of the chuck.
Dismount the chuck and conduct the maintenance as indicated in the
appropriate paragraph.
32
Check that the axial reference of the workpiece is made by means of
fixed supports on the body or on the front flange and NOT on the clam-
ping jaws (see point 4.3.3).
33
Check that the jaws are positioned correctly in order to reduce the elastic
deformation of the jaws (see point 4.3.4).
34
When clamping components which require high axial positioning accu-
racy, parallelism and orthogonality, we advise against using normal
chucks with standard serrations.
For these applications we recommend TSC series of chucks with an axial
pull down movement against a fixture.
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