SMW Autoblok AND Manual De Instrucciones página 17

INSTRUCTIONS AND SAFETY REGULATIONS
2.4 Mounting the chuck on the lathe spindle.
Position the chuck properly in front of the spindle (the drive button must
be in line with its seat) and attach the chuck by turning the mounting
bolts.
IMPORTANT: The mounting bolts must be tightened properly with
a torque wrench adjusted to the dimension and the class of the bolts
(see table 2-B).
In the case of cylindrical center diameters, it is necessary to center the
chuck on the rotation axis of the spindle.
Check in accordance with the ISO 3442 norm shown below, that the
concentricity of the chuck outside diameter (A) and the flatness of the
face (B) are less than 1/2 of the spec for normal chucks, and 1/3 of the
spec for high speed chucks.
TAB. 2
Object under
Pos.
measurement
Ø a
A Z Concentricity 0.02
B Undulation 0.02
If the chuck is mounted with a special flange, it is critical that the
support face on the flange is the one inside the centering diameter of the
chuck body (where the bolts are) so that the two surfaces fit without
distorting the shape the chuck body.
Supporting on the external circular crone causes distortion of the chuck
body, blocking the movement of the internal parts, resulting in a loss of
gripping force and a faster wear.
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Tab Tightening torque for mounting bolts
2-B of the chucks on the spindle nose
Minimum class requested 12.9 Minimum class requested 8.8
D (mm) M (N.m) D (mm)
M6 12 M16
M8 30 M20
M10 45 M24
M12 70 M30
D = Dimensions of screw
2.5 Connecting the chuck to the draw tube.
For mounting without through-hole see the instructions on page 22.
For mounting with a partial and complete through-hole (see the instruc-
tions on page 22 and 23) two types of ring-nuts are available, a rotating
and a fixed ring nut depending on the mounting chosen.
If the spindle through-hole and the draw-bar are smaller than the stan-
dard thread (F) of the ring nuts, an unthreaded ring nut with a smaller
internal hole is available. This ring nut can be disassembled from the
chuck (by unscrewing the mounting screws on the wedge bar), threaded
to the proper dimension and then reassembled.
IMPORTANT: When reassembling the ring nut it is ABSOLUTELY
NECESSARY to fully tighten the mounting screws with the correct
torque depending on the dimension and the class request (see table 2-C).
3. MAXIMUM DRAW-PULL - MAXIMUM STATIC GRIPPING FORCE -
DYNAMIC GRIPPING FORCE AND CENTRIFUGAL FORCE -
DRIVING TORQUE - MAXIMUM SPEED.
3.1 Maximum draw-pull.
All chucks, due to the sizes of the internal parts, are limited to a
"Maximum draw-pull" (Ft max) at the draw-bar. This value is clearly
shown in the technical features and is inscribed on the chuck face.
The "draw-pull", in case of drawing with a hydraulic cylinder, is the
multiplication of the piston area (A), the oil feeding pressure (p) and effi-
Ø a = chuck diameter (mm.)
Permissible error (mm)
160 160 Ø a 315 315 Ø a
0.03 0.04
0.03 0.04
Tab Tightening torque for mounting
2-C bolts of ring nuts on the wegde
Minimum class requested 12.9
M (N.m) D (mm)
170 M5
300 M6
500 M8
950 M10
M = Tightening torque
ciency (η), which can be considered 0.95.
Example: On a 210 BHD-3 jaws chuck, the "max draw-pull" is 38 kN
(3800 Kg). If the drawing is made with a 140/52 VSNC cylinder (which
has a 138 cm
IMPORTANT: NEVER apply a higher force at the draw-tube than
the rated maximum. Excessive draw-pull can cause breakage of the
internal parts of the chuck.
IMPORTANT. It is necessary to check the hydraulic circuit for
water hammering. This condition could cause breakage of the draw-
bar or the internal parts of the chuck.
3.2 Static gripping force.
Chucks convert the axial stroke of the draw-tube to a radial stroke of the
jaws by means of an inclined plane (wedge) system.
The wedge changes the "draw-pull" into a much greater "gripping force".
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This gripping force is applied to the workpiece, providing the necessary
force to counter the torque created by the cutting tools during the machi-
ning cycle. The "max gripping force" (Fsmax) and the "max draw force"
(Ftmax) are contained in the technical features and inscribed on the front
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of each power chuck. To calculate the "static gripping force" (Fso) for
each "draw force" (Ft) use coefficient "K" typical of every power chuck.
The value of "K" can be easily calculated with the technical features in
catalogues or on the front of the power chuck:
So, at each value of Ft, corresponds a value of Fso according to the
formula:
Example: for a 210 BHD-3 jaw chuck, we determine Fso for Ft=30kN
Fsmax
K = –––––––– = –––––––––––– =
Ftmax
Z
Coefficient "K" has been determined by experiment on a new power chuck,
clean and properly greased with SMW-AUTOBLOK type K 05 grease.
IMPORTANT: Always keep the chuck well lubricated with SMW
AUTOBLOK type K 05 or K 67 grease .
It's important to use an SMW-AUTOBLOK gripping force dynamome-
ter type 339H to check the static gripping force.
M (N.m)
9.5
3.3 Dynamic gripping force and centrifugal force.
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39
Power chucks are used on modern CNC lathes at high rotation speeds.
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When the power chuck rotates, all the parts which are not anchored
radially i.e. the master jaws, T-nuts, the screws and top jaws are subject
to a "centrifugal force" which decreases the gripping force in O.D. clam-
ping (and increases it in I.D. clamping).
For each speed there is a "Dynamic gripping force" (Fsd) which is deter-
mined as follows:
where: Fsd [kN] = Theoretical dynamic gripping force
Fso [kN] = Static gripping force
Fct [kN] = Theoretical centrifugal force
The "theoretical centrifugal force" is determined as follows:
where: M [Kg] = Mass of master jaws + jaws,"T" nuts and screws
R [m]
To complete the calculations it is necessary to determine the "Mass
moment" M.R as follows:
where: m
r
1
m
r
2
Z
The values for m1 · r1 are indicated in the following schedule:
Ft = A · p · 0.95
2 piston area) the maximum oil pressure is:
Ft 3800
p = –––––––– = ––––––––––– ≅ 30 bar
A · 0.95 138 · 0.95
Fsmax Fso
K = ––––––-- = –––––
Ftmax Ft
Fso= Ft . K
110 kN
2,9 ; Fso= 30 . 2,9 = 87 KN
38 kN
Fsd = Fso - Fct
Fct = M · R · 2
= Radius of the gravity center of "M"
[rad/sec] = Chuck's angular velocity
M · R = (m · r + m · r ) · Z
1 1 2 2
[Kg] = Mass of 1 jaws with "T" nuts and screws
1
[m] = Radius of the gravity center of "m
[Kg] = Mass of 1 gripping jaw
2
[m] = Radius of the gravity center of "m
= Number of the chuck's jaws.
"
1
"
2
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