ISO/TR 13618:1993
(Main)Code of practice for the safe operation of work-holding chucks used on lathes
Code of practice for the safe operation of work-holding chucks used on lathes
Lignes directrices pour l'utilisation sûre des mandrins porte-pièce de tour
General Information
Standards Content (Sample)
TECHNICAL
IS0
REPORT
TR 13618
First edition
1993-1 1-01
Code of practice for the safe operation of
work-holding chucks used on lathes
Lignes directrices pour l’utilisation sûre des mandrins porte-pièce de tour
Reference number
ISO/TR 13618:1993(E)
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ISO/TR 136181 993(E)
Contents
Page
1 scope . 1
1
2 Chuck grip .
2.1 General . 1
1
2.2 Forces applied to the chuck .
2.3 Change of grip at speed . 9
2.4 Achieving the required grip . 11
2.5 Flexible workpieces . 11
3 Maximum speed of the chuck . 11
11
4 Balancing .
5 Inertia loading imposed on the drive . 13
6 Gravitational and cutting forces: effect on the machine . 15
7 Other aspects ofthe safe operation of lathe chucks . 15
Chuck keys .
15
7.1
15
7.2 Gross overspeeding .
Adaptors .
15
7.3
Mounting bolts for chuck body . 15
7.4
Mounting bolts for jaws . 15
7.5
Jaw materials . 16
7.6
Dissipation of kinetic energy . 16
7.7
16
7.8 Stroke detectors .
16
7.9 End of bar detectors .
(D IS0 1993
All rights reserved . No part of this publication may be reproduced or utilized in any form or by
any means. electronic or mechanical. including photocopying and microfilm. without
permission in writing from the publisher .
International Organization for Standardization
Case postale 56 CH-121 1 Genève 20 Switzerland
Printed in Switrerland
ii
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ISO/TR 13618:1993(E)
8 Summary of the responsibilities of machine tool manufacturer, chuck
manufacturer and . 16
Appendices
A Estimation of power available at the cutting zone . 18
B Radial stiffness and out-of-roundness of ring held in jaws . 18
C Measurement of the inertia of irregular components . 19
D Worked example . 37
E Bibliography . 52
...
III
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ISO/TR 1361 8: 1993(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work of
preparing International Standards is normally carried out through IS0 technical
committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that
committee. International organizations, governmental and non-governmental, in
liaison with ISO, also take part in the work. IS0 collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical
standardization.
The main task of technical committees is to prepare International Standards, but
in exceptional circumstances a technical committee may propose the publication
of a Technical Report of one of the following types:
- type 1, when the required support cannot be obtained for the publication of
an International Standard, despite repeated efforts;
I
- type 2, when the subject is still under technical development or where for
any other reason there is the future but not immediate possibility of an
agreement on an International Standard;
- type 3, when a technical committee has collected data of a different kind
from that which is normally published as an International Standard ("state of
the art", for example).
Technical Reports of types 1 and 2 are subject to review within three years of
publication, to decide whether they can be transformed into International Stan-
dards. Technical Reports of type 3 do not necessarily have to be reviewed until
the data they provide are considered to be no longer valid or useful.
ISO/TR 13618, which is a Technical Report of type 2, was prepared by Technical
Committee iSO/TC 39, Machine fools, Sub-Committee SC 8, Chucks.
This document is being issued in the type 2 Technical Report series of publica-
tions (according to subclause G.4.2.2. of part 1 of the ISO/IEC Directives, 1992) as
a "prospective standard for provisional application" in the field of work-holding
chucks for machine tools because there is an urgent need for guidance on how
standards in this field should be used to meet an identified need. This Technical
Report reproduces practically verbatim British Standard BS 1983-5:1989 and
implements it as an IS0 Technical Report. For the user's convenience, where
possible, references to national standards have been changed to refer to Inter-
national Standards.
This document is not to be regarded as an "International Standard". It is pro-
posed for provisional application so that information and experience of its use in
practice may be gathered. Comments on the content of this document should be
sent to the IS0 Central Secretariat.
I iv
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ISO/TR 1361 8 1993(E)
A review of this type 2 Technical Report will be carried out not later than two
years after its publication with the options of extension for another two years;
conversion into an International Standard; or withdrawal.
Appendices A to E of this Technical Report are for information only.
a
a
V
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ISO/TR 1361 8 1993(E)
Introduction
Lathe chucks operated at any speed are potentially very dangerous. They
have to be suitably guarded in order to ensure that personnel do not come
into contact with a moving chuck and that parts released from the chuck (for
whatever reason) cannot be thrown at personnel either directly or after a
ricochet. Power chuck controls also have to be suitably interlocked such that
workpieces are not inadvertently released. These safety aspects are covered
in IS0 13046.
However, because of the versatility of lathe chucks, it follows that chuck
designers and manufacturers cannot know the full range of uses to which
their chucks will be put (i.e. range of machines on which a chuck may be
mounted, type of jaws to be fitted, type of workpiece to be held). It is
essential, therefore, for the user to take some responsibility for the applica-
tion of a chuck. Further, in order that such duties can reasonably be under-
taken by the user, it is essential that sufficient design data are available and
that methods of calculation and/or of testing are specified. The machine tool
manufacturer will also be involved in certain aspects of these problems.
This Technical Report attempts to outline the duties of, and to provide some
of the necessary information needed by:
a) the machine tool manufacturer;
b) the chuck manufacturer; i
c) the chuck user.
However, because of the large number of chucks already in use, it is necess-
ary also to attempt to recommend the proper course of action regarding the
application of existing chucks for which the required design data were not,
in fact, transmitted from manufacturer to user and which are now unobtain-
able.
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TECHNICAL REPORT ISO/TR 13618:1993(E)
Code of practice for the safe
operation of work-holding
chucks used on lathes
2.2 Forces applied to the chuck
1 Scope
2.2.1 General, The forces and torques applied via the
This Technical Report identifies and describes safe practices for
workpiece to the jaws of the chuck can be represented
design and operation of workholding chucks used on turning
by four terms:
machines.
ZFax the total axial thrust;
The technical aspects covered by this code concern:
ZFr the total radial force;
(a) the adequacy of the gripping force in the chuck;
EMd the total torque (about the spindle axis);
(b) the fact that at excessive speed there may be failure
ZMk the total (tilting) moment (about an axis
of chuck components (fracture or excessive yielding);
perpendicular to the spindle in the transverse
(c) acceptable degrees of lack of balance and consequent
centre plane of the jaws).
vi bration;
Each cutting tool, deadweight force and out-of-balance
(d) the inertia loading imposed on the machine drive
force and torque makes a contribution, usually to two or
both by the chuck and by the workpiece;
more of these total forces and torques, hence each contri-
(e) gravitational forces arising from the mass of the bution has to be calculated or measured.
chuck and workpiece, together in some circumstances
Evaluation of mass induced forces requires values of
with cutting forces, and their effect on the machine;
density (see table 1) unless components can be weighed.
Evaluation of dynamic forces involves also the eccentricity,
(f) other aspects concerning the safe operation of
e (see clause 4).
lathe chucks.
Whilst primarily intended for application to lever and
Table 1. Typical value of density, p
wedge type power chucks, including centrifugally compen-
sated types, this code of practice can and should also be
kg/m3
applied to manual chucks, but in such cases it is necessary
Magnesium alloy 1800
to know the input torque.
Aluminium alloy 2750
NOTE 1. It should be recognized that even when a torque wrench
or power driver is used, the grip is known to a lesser accuracy than,
Iron 7500
say, that of a power chuck having an hydraulically operated
Steel 7850
drawbar.
Zinc 7000
0 NOTE 2. Publications referred to in this Technical Report are listed
Tin 7290
in Appendix E.
Copper 8780
Nickel 8800
2 Chuckgrip
8280 (on average)
Brass
2.1 General
It should be recognized that there will be change of grip as
2.2.2 Cutting forces and torques. There are many elaborate
the rotational speed increases even when the chuck has
methods of calculating cutting forces and these methods
centrifugal com pensat ion.
are not precluded. Nevertheless the following simple
In the case of uncompensated, or only partially compen-
methods are deemed to be sufficiently accurate.
sated, chucks set up for external grip, i.e. the jaws move
(a) For turning, facing and boring:
inwards radially as the chuck is tightened, then an increase
(1) Estimate the tangential cutting force,
in rotational speed causes a loss of grip. However, when set
up for internal grip an increase in rotational speed causes F, (in N), as:
an increase in grip. Over-compensation has the opposite
F, =depth of cut (in mm)
effect, i.e. an external grip increases with speed. However
x feed (in mm)
over-compensation is not recommended in general because
x specific cutting force (in N/mm2)
it may lead to progressive tightening if the speed is cycled
where the specific cutting force is taken from table 2.
up and down repeatedly.
It is essential that the chuck gripping condition is evaluated
by the user or by tooling experts employed by him.
1
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ISO/TR 13618:1993(E)
Table 2. Specific cutting forces, k,, for turning, facing and boring
Material I Tensile I Brinell
strength hardness
number*
0.1 mm 0.2 mm 0.4 mm 0.8 mm
N/mmz N/mmz
N/mmz HB N/mm2 N/mm2
3600 2600 1900 1360
Carbon steels low carbon (0.1 5 % C) up to 490 up to 150
2100 1520
low carbon (0.25 % C) 490to 580 150 to 200 4000 2900
2200 1560
medium carbon (0.4 % C) 580to 680 180 to 250 4200 3000
2300 1640
high carbon (0.55 % C) 680to 830 200to300 4400 3150
3200 2300 1700 1240
Cast steel 290to 490
1900 1360
490to 680 3600 2600
3900 2850 2050 1500
1 680+
4700 3400 2450 1760
Alloy steels 680to 830
5000 3600 2600 1850
830to 970
970 to 1370 5300 3800 2750 2000
5700 41 O0 3000 2150
1390 to 1750
c
Stainless steel I 580to 680 I I 5200 3750 I2700 I
Tool steel I 1460to1750 I I5700 I4100 I3000 I2150 I
Manganese hardened steel 6600 4800 3500 ,2520
1
Cast iron I I 200 to 250 I 2900 I 2080 I 1500 I 1080 1
Cast iron, alloy I I 250to400 I3200 I2300 I 1700 I1200 I
2400 1750 1250 920
Tempered cast iron
1520 1100 800
2100
Copper
I 1900 I 1360
Copper with commutator mica (collectors) I I
Brass I I 80to120 1 1600 I1150
1400 1000
Cast copper
3400 2450
Cast bronze
I 940 I 700 I 560 I 430 I
Zinc alloy Zn-Al IO-Cu2 I I
1050 760
Pure aluminium
Aluminium alloy with high Si content 1400 1000
(1 1 % to 13 %. Si)
Piston alloy AI, Si (toughened) 1400 1000 700 520
I 1250 I 900 I 650 I 480
G AI-Si
I
1150 840 600 430
Other aluminium castings up to 290
1400 1000 700 520
290 to 420
I I I I
Wrouqht aluminium alloys I 420to579 I I 1700 I 1220
580 420
Magnesium alloys
I
480 350 250 I 180
Hard rubber, ebonite
480 350
Rubber free insulating compound
Novotex, Bakelite, Pertinaz
2””l
380 280
Hard paper, cardboard
- -
- 90
Hard graphite (nuclear)
+See IS0 4964.
-
2
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ISO/TR 13618: 1993(E)
NOTE. When surfacing on a lathe, the depth of cut is measured (b) For drilling (and, approximately, for deep-hole
radially and the feed axially but when facing the depth of cut is
boring) :
measured axially and the feed radially.
(1) Estimate the drilling torque, M (in Nam), as:
Alternatively estimate the power, P (in W), available
M= 1.2k x C,
as in appendix A and derive the cutting force as
where:
follows:
k is the work material factor taken from table 3;
Cutting speed,
V (in m/s) = n x cutting diameter (in m)
C, is the torque factor, taken from figure 4,
x spindle speed (in r/s)
for the drill diameter and feed rate in use.
P
(2) Estimate the feed force, Fa (in N), as:
Tangential cutting force, F, = -
V
F=kf x F,,
(2) Increase F, by 1 %for each degree of top rake
where:
less than 10 O, add 10 %to allow for tool wear.
kf is a work material factor taken from table 4;
(3) Usually, feed force x O.6Fs. (For difficult
F,? is a force factor taken either from figure 5 (for
materials at slow speed, e.g. titanium, feed force
drills of all sizes in brass and aluminium and
= Fs.)
for drills up to 12 mm diameter in steel and
The feed force lies parallel to the spindle axis when
cast iron) or from figure 6 (for drills of 16 mm
cylindrical turning or boring, i.e. F, in figures 1
and over in steel and cast iron).
to 3. It lies perpendicular to the spindle axis when
NOTE 1. The information given in table 4 and figures 5 and 6 is
facing, i.e. F, in figures 1 to 3.
based on two separate series of tests and does, therefore, show small
discrepancies in the region of 12 mm to 16 mm drill diameter.
(4) Separating force % O.25Fs and may usually be
NOTE 2. This calculation may be omitted if the workpiece is
neglected. The separating force lies perpendicular
axially located by the chuck.
to the spindle axis when cylindrical turning or boring,
i.e. F, in figures 1 to 3. It lies parallel to the spindle
axis when facing, i.e. F, in figures 1 to 3.
Table 3. Work material factor, k, for drilling (and deep hole boring) torque
Typical specifications k
Description
Steels:
220 M 07 (En 1 a) 4 to 4.5
Low carbon sulphurized (0.1 % C)
240 M 07 (En Ib)
Low carbon low sulphur (0.2 % C) 080 A 22 (En 3)
(0.25 % C) 070 M 20 (En 4)
(0.3 % C) 080 M 30 (En 5) 5 to 5.5
(0.35 % C) 070 M 26 (En 6)
(0.1 %C) 045 M 10 (En 32)
080 M 40 (En 8) 4 to 4.5
Medium carbon (0.4 % C)
High carbon (0.55 % C) 070 M 55 (En 9)
709 M 40 (En 19)
Alloy steels
817 M 40 (En 24) 6 to 6.5
826 M 40 (En 26)
Brass 2 .O
1.6
Aluminium alloy (cast)
Cast iron: grey
Feed rate >0.7 mm/r
2.0
< 0.6 mm/r 3.0
Malleable iron
2.7
Feed rate > 0.7 mm/r
< 0.6 mm/r 3.5
3
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ISO/TR 13618:1993(E)
~~
(c) For tapping:
Table 5. Value of work material factor, k,
(1) Estimate the torque, M (in N.m), as: for tapping
M=k x ct x cd x cm
k
Brinell
Material
where:
hardness
number*
k is the work material factor from table 5;
~
Ct is the tap factor from table 6;
HB
cd is the thread depth factor from table 7;
200 1.8
Grey cast iron
Cm is the thread factor from table 8.
1.9
300
Increase by 50 % to allow for tap wear. 1.6
150
Malleable cast iron
1.8
250
(2) Feed forces when tapping are not easy to
estimate and are, in general small enough to be Stee I s :
ignored. 2 .O
150
low carbon (0.1 5 % C)
2.4
200
low carbon (0.25 % C)
3.1
300
high carbon (0.55 % C)
3.5
400
typical alloy steel
Table 4. Work material factor, kf, for drilling (and deep
0.7
Aluminium alloys
O .4
Magnesium alloys
1.4
Brass
Material
0.7
Leaded brass
O .8
Phosphor bronze
12mm 16mm
*See IS0 4964.
800 180
Low carbon steel (up to 0.25 % C)
(all feed rates)
1100 200
Medium carbon steel (over 0.3 % c)
I
(all feed rates)
Table 6. Value of tap factor, Ct
Grey cast iron
80
460
feed rate > 0.7 mm/r ct
640 100
< 0.6 mm/r
Spiral-point 1 .O
Malleable cast iron
Helical flute RH 1.3
380 90
feed rate > 0.7 mm/r
1.7
Straight flute: in general
500 120
< 0.6 mm/r
but over 40 mm dia. length of
1.3
thread less than one diameter
Brass
170
feed rate >0.7 mm/r
300 1
< 0.6 mm/r
Aluminium
400
feed rate > 0.7 mm/r
< 0.6 mm/r 600
4
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ISO/TR 13618:1993(E)
Table 7. Values of thread depth factor, cd,
for tapping
Depth of Cd
thread
%
55
0.57
65 0.75
75 0.9
80 1 .O
85 1 .I
Basic
major dia
asic
inor dia.
I- =I ;(e;; thread 1
I
hole dia.
A
Percentage depth of thread = - x 100
B
where:
A = basic major diameter - core hole diameter
B = basic major diameter - basic minor diameter
5
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ISO/TR 1361 8:1993[E)
~~
~~
Table 8. Values of thread factor, Cm, for tapping
(a) IS0 metric coarse pitch series
Diameter X pitch
M3 x 0.5 0.1
M4 x 0.7 0.22
M5 x 0.8 0.35
M6 XI 0.63
1.3
M8 x 1.25
M10x 1.5 2.2
MI2 x 1.75 3.5
M16x 2 6.0
M20 x 2.5 11
M24 x 3 19
31
M30 x 3.5
M36 x 4 48
M42 x 4.5 69
M48 x 5 96
M56 x 5.5 133
M64 x 6 179
(b) IS0 metric constant pitch series
Diameter Pitch (mm)
- -
1 1.25 1.5 2 3 4 6
-
mm
Cm Cm
Cm Cm crn Cm Cm
8 0.9 1.3
10 1 .I 1.6 2.2
12 1.3 2 .O 2.7 4.4
16 1.8 3.7 6.0
20 2.3 4.7 7.7
19
24 2.8 5.6 9.3
7.1 11.8 24
30 3.5
8.6 14.3 29 48
36
42 10.0 16.7 34 56
39 65
48 11.5 19
13.5 22 46 76
56
15.5 26 53 88 179
64
72 17.5 29 60 99 202
80 19.0 32 66 111 226
75 256
90 36 125
139 285
1 O0 40 83
45 92 154 315
110
51 105 175 360
125
57 118 196 404
140
160 65 135 225 463
180 73 152 253 522
6
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ISO/TR 1361 8 1993(E)
(c) B.S.W. (e) B.S.P.
Diameter threads Nominal Outside threads
Cm
per inch diameter diameter per inch
in in in
'14 26 0.6 '/8 0.383 28 0.9
5/~6 22 1 .I '/4 0.518 19 2.5
0.656 19 3.2
3/8 20 1.6 3/8
16 3.2 0.825 14 6.8
'/2 '/2
14 5.1 0.902 14 7.5
5/8 5/8
12 8.1 3/4 1 .O41 14 8.7
3/4
14
"/8 11 11 1.189 10
'/8
1 1 1.309 17
10 15 11
1 '/8 9 20 1 '/4 1.650 11 22
9 1.882 11 25
1 '/4 23 1 '12
8 34 2.116 11 28
1 '/2 1 3/4
7 51 2 2.347 11 31
1 3/4
2 7 58 2 '/4 2.587 11 34
2 '/4 6 86 2 '12 2.960 11 39
2 '/2 6 96 2 3/4 3.210 11 43
3 5 161 3 3.4 60 11 46
3 '/2 4 '/2 227
4 261
4 '12
(f) Inch-based constant-pitch series
Pitch (threads per inch)
Diameter
(d) B.S.F.
8 12
16 20
Diameter threads
per inch
in
in
1 11
6.6 4.5
1
20 1 '/8 12.4 7.5 5
'/4
1.5
18 1 '/4 13.8 8.3 5.6
5/16
2.3
16 1 3/8 15.3 9.2 6.2
3/8
5.2
12 1 '12 34 16.7 10.1 6.8
'/2
7.7 40 19.6
11 1 314 11.8 7.9
5/8
10 11 2 46 23 13.5
3/4 9.1
9 16 l/4 52 25 15.2 10.2
"/a 2
1 8 22 2 '/2 58 28 17 11.4
7 32 2 3/4 64 31 19 12.5
1 '/8
35 3 70 34
1 '14 7 '/2 20 13.7
6 56 76
1 '/2 3 '/4
5 91 82
1 3/4 3 '/2
2 '/2 126 3 3/4 88
4
4 175 4 94
2 '/4
4 196
2 '12
3 300
3 '12
402
3 '/2 3 '14
4 3 532
7
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ISO/TR 13618:1993(E)
2.2.5 Inclined slides and multiple slides. When an inclined
2.2.3 Loading on the chuck: overhung workpiece, simple
slide is used the cutting forces act at a different point and
tooling. The loading on the chuck for an overhung work-
in different directions, see figure 3, where they are
piece, using simple tooling, is the easiest case to analyse.
denoted by FSi, F,,, Fpi, for a slide rotated by angle, a,
Referring to figure 1 :
from the 'horizontal' position.
Axially ZFaX = F, +
The forces, torques and moments F,, F, and F, then
become:
axial thrust (drilling)
Axial force, Fv = Fvi
I'
longitudinal feed force (turning)
Radial forces at the axis,
F, = Fsi cosa + F,, sina
andFp=FpIcosa-Fsisina
NOTE 1. These terms replace F, and F, in the equations in 2.2.3.
dz
Torque about the axis = F,i 2
static unbalance torque
(neglect if nominally
dz .
symmetrical workpiece) NOTE 2. This term replaces F, - in the equations in 2.2.3.
2
Moment in a vertical plane"
cutting torque (turning)
I
dz
Radial force ZFr* = = FsIz - Fvi - COS@
2
(F, - WgI2 + (FPI2 + Wo2e
NOTE 3. This term replaces F,/, in the equations in 2.2.3
I I
Moment in a horizontal plane"
Dynamic out-of-balance
(w = 27~ NI60 where N is
dz
= F,I, - Fvi - sina
the spindle speed in rlmin)
2
(neglect if nominally
NOTE 4. This term replaces Fplz in the equations in 2.2.3.
symmetrical workpiece)
In the case of multiple slides, each slide is treated as inclined
and the resultant values are summed as follows, where the
r.m.s. of cutting
I
suffix j indicates the slide:
forces + deadweight
Axially, Fv = ZFvij
Radially, F, = XFsj
Tilting moment * =
and F, = XFpj
Torque = Z: FSii ($)
Moments in Fs plane
Moment in vertical plane*
4 I
Dynamic out-of-balance
Moments in F, plane
(neglect if nominally
symmetrical workpiece)
Moment in horizontal plane*
Non-rotating Rotating
Fpj/zj - Fvij (zi) - sina)
2.2.4 Loading on the chuck: vertical spindle, simple
2.2.6 Requiredgrip. The values of ZFax, ZMd are used
tooling. From figure 2:
as follows to establish the total grip, F,,, needed to
ZFax = Fv + Fvax + Wg
prevent slip:
where p,, is the coefficient of friction given in table 9.
NOTE. When the workpiece is axially located by the chuck XFaX
may be treated as zero provided it has a positive value initially.
in setting safety factors; no numerical criteria are available.
'These items can, at present, be used only subjectively
8
F,,
---------------------- Page: 14 ----------------------
ISO/TR 13618:1993(E)
The choice between tangential and axial values in table 9
2.3 Change of grip at speed
is somewhat arbitrary. When there is no positive axial
It is essential that the chuck manufacturer provides graphs,
location tangential values for psp should be used if the
figure 8 being an example, showing the change of grip at
torque term (2LiMdldsp) is predominant, i.e. for most
various speeds when the chuck is fitted with standard jaws
turning operations. For drilling however when the term
positioned flush with the outside diameter, inwardly
Li Fa, predominates it is acceptable to select a value of
stepped (see figure 9(c)). Supplementary data for outwardly-
psp from the axial column of table 9.
stepped jaws and for smaller radii would be acceptable,
The grip Fsp then has to be increased by a factor, S,,
as additional curves or on separate graphs, as would
in order to provide for:
comparable data for blank jaws. The information may be
calculated or obtained experimentally using a stiff load
(a) a margin of safety to cater for values of LiMk;
transducer, e.g. one having a steel load path. Results
(b) any further margin of safety.
obtained using a flexible load transducer, e.g. of the
(The force of LiFr will cause radial deflection of the work-
hydraulic type, are not acceptable.
piece but no criteria are available, currently, to establish
NOTE 1. The transducer should, preferably, be some 10 times stiffer
I imits.)
than the chuck.
A minimum of S, = 2 is to be adopted, increased as
The chuck manufacturer also has to state the masses of
necessary to cater for large values of LiMk (for which
base jaws and any top jaws supplied and give the location
I, > dsp probably) and other adverse factors, and a factor
of their centres of mass (both being marked, preferably,
S,, = 1.5 is used to provide a margin of safety when
on the jaws).
calculating the required total static grip, (Fspo) given by:
The chuck user has to read off, from the graphs, the change
Fspo = Ssp (FspzSz + Fc) in grip, F, (in N), arising from the change in speed:
for external grip (jaws moving radially inwards to grip)
(a) an increase for internal gripping;
Fspo = ssp (Fsp2 Sz - Fc) (b) a decrease for external gripping. (See 2.1.)
for internal grip (jaws moving radially outwards to grip)
Unless an internal grip has to be limited by the need to
where F, is the centrifugal force on jaws, see 2.3. avoid marking or distorting the workpiece, it is quicker
and preferable to assume F, = O.
2.2.7 Effect of a tailstock centre. If a tailstock centre is
The loss of grip'should not normally be allowed to exceed
used then the loading situation at the chuck becomes
one half of its original value.
complex. Two approximate simplifications are possible.
Where the conditions of use are not covered by the graphs
(a) When the workpiece is not axially located by the
available the chuck user has to calculate the change of grip,
chuck then an overestimate, and hence a safe estimate
F,, of uncompensated chucks as:
of the forces is obtained if the tailstock is ignored and
F, = o2 Li(ml R1)
the calculations made as for an overhung workpiece.
This approach is justified on the basis that should the
where:
workpiece slip in the chuck then it may well slip off
m1,2 etc. are the masses of the jaw components (in kg);
the tailstock centre.
R1,? etc. refer to the radii of their centres of mass
(b) When the workpiece is axially located by the chuck
(in m);
then:
~3 is the angular velocity (in rad/s) = 2nN/60 where
ZF,, = O;
N is the spindle speed in (r/min).
LiFr* is evaluated after applying the multiplying
Figure 10 shows a log-log plot of F, covering the range of
factor given in figure 7 to each component;
chuck speeds, from 10 r/min to 10 O00 r/min, and products
LiMd is evaluated as for an overhung workpiece;
of jaw mass (in kg) x radius of centre of mass (in m) from
LiMk* is evaluated after applying the multiplying
0,001 kg.m to 100 kgam.
factor given in figure 7 to each component.
For example, a 5 kg jaw set at 250 mm radius will have an
Thus the effect of a tailstock centre is to modify the values
mr value of 5 x 0.25 = 1.25 kg.m and when rotated at
of ZFv* and EMk* thus leading to the subjective choice
750 r/min will cause a loss of grip per jaw of
of lower values for the safety factor S,.
(27r x 750/60)2 x 1.25 = 771 1 N.
NOTE. No guidelines are available to deal with this aspect; moreover
NOTE 2. Where the jaw data are not available from the chuck
the values of Zfr* and of ZMk* will usually besmall. Hence,
manufacturer or where the user has designed and manufactured
at present, it is recommended that ZFr* and xMk* be neglected.
the jaw, the user has to determine the required information on the
mass and the position of the centre of gravity by calculation or by
measurement.
at present, be used only subjectively in setting safety factors; no numerical criteria are available.
'These items can,
9
---------------------- Page: 15 ----------------------
ISO/TR 1361 81993(E)
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---------------------- Page: 16 ----------------------
ISO/TR 1361 8: 1993(E)
Compensated chucks have to be operated strictly in
(b) Externalgrip. Initially calculate the required
accordance with manufacturers' instructions. The use of
grip (i.e. Fçpo) as in 2.2. If this grip is acceptable from
other jaws can lead to over or under compensation,
the point
...
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