43
5 Design Hints, Dimensions and Tolerances
5.1 Allowances, length tolerances
Table 5.1: Allowances to be provided for installation and tensioning
≤ 305 ± 0.14
> 305 ≤ 390 ± 0.16
> 390 ≤ 525 ± 0.18
> 525 ≤ 630 ± 0.21
> 630 ≤ 780 ± 0.24
> 780 ≤ 990 ± 0.28
> 990 ≤ 1250 ± 0.32
> 1250 ≤ 1560 ± 0.38
> 1560 ≤ 1960 ± 0.44
> 1960 ≤ 2360 ± 0.52
> 2360 ≤ 3100 ± 0.61
> 3100 ≤ 3620 ± 0.73
> 152.4 ≤ 254.0 ± 0.22
> 254.0 ≤ 381.0 ± 0.23
> 381.0 ≤ 508.0 ± 0.26
> 508.0 ≤ 762.0 ± 0.31
> 762.0 ≤ 990.6 ± 0.33
> 990.6 ≤ 1219.2 ± 0.38
> 1219.2 ≤ 1524.0 ± 0.41
> 1524.0 ≤ 1778.0 ± 0.43
> 1778.0 ≤ 2032.0 ± 0.46
> 2032.0 ≤ 2286.0 ± 0.49
> 2286.0 ≤ 2540.0 ± 0.51
> 2540.0 ≤ 2794.0 ± 0.54
> 2794.0 ≤ 3048.0 ± 0.56
> 3048.0 ≤ 3200.4 ± 0.59
> 3200.4 ≤ 3556.0 ± 0.61
> 3556.0 ≤ 4064.0 ± 0.66
> 4064.0 ≤ 4318.0 ± 0.69
> 4318.0 ≤ 4572.0 ± 0.71
L
wSt
(mm)
L
wSt
(mm)
a
LTol
(mm) a
LTol
(mm)
y
1
(ZRL)
y
1
y
2g
(ZRL)
y
2g
y
2k
(ZRL)
y
2k
y
3
(ZRL)
y
3
xx
(ZRL)
on small
pulleys
i
eff
= or
=
1
on large
pulleys
i
eff
=
1
0.6 + 0.002 · a
nom
0.8 + 0.002 · a
nom
1.5 + 0.002 · a
nom
3.5 + 0.002 · a
nom
2.4 + 0.002 · a
nom
6.0 + 0.002 · a
nom
4.2 + 0.002 · a
nom
6.7 + 0.002 · a
nom
|
a
LTol|
+
0.002 ·
a
nom
a
LTol
on
Table
5.2
|
a
LTol|
a
LTol
on
Table
5.2
Table 5.2: Length tolerances, for standard belts see Table 5.6,
page 48
For a two pulley drive with and without flanged pulleys Table 5.1
gives the allowances to be provided for installation y and for
tensioning x. For both installation and tensioning, one pulley must
be free to rotate.
y
1
The allowance y
1
permits belt installation on two pulleys, each with
standard flanges.
y
2
The allowance y
2k
ensures installation on two pulleys where the
drive ratio i is not equal to 1, or the smaller pulley is provided with
two standard flanges or on the installation-side with one standard
flange (see Figure 5.1, page 44). The drive ratio i = 1 is also taken
into account in the allowance y
2k
.
The allowance y
2g
refers to a similar installation-side flange
arrangement on the large pulley.
y
3
The minimum allowance y
3
for installation assumes that there are
no flanges on either pulley. It takes into account only the maximum
possible length minus the centre distance tolerances.
The table values y
1
and y
2
are guide values and refer to the most
unfavourable drive configuration. Dependent on the tooth depth h
t
of the section, the diameter difference D
b
– d
a
between flanges and
pulleys, the drive ratio i
eff
and the centre distance a
nom
, the values
y
1
and y
2
of Table 5.1 may be considerably lower.
x
The allowance x to be provided for tensioning of the timing belt
within the permissible elastic stretch. The correct tension setting
should be taken from the information on page 28 (ZRM/ZRP) or
page 40 (ZRL).
ZRL
Length tolerance for
ZRL timing belting:
± 0.5 mm per 1000 mm length
The allowances x and y specified do not apply to timing belts (open-
ended or joined endless) which are provided with a precisely
specified number of teeth z
R
for use with welded-on cleats (see
page 11).
Type of allowances Allowances for installation, y Allowances for tensioning, x
Section Provision for installation Provision for tensioning
0.6
0.8
1.5
3.5
2.4
6.0
4.2
6.7
on neither
pulley
on both
pulleys
MXL 11 12 9 10 5 6
T2.5 16 17 12 13 7 8
XL; T5; AT5; 5M 17 18 13 14 8 9
L; H; T10; AT10 22 25 17 20 10 13
8M 24 27 19 22 11 14
T20; AT20 32 38 25 31 15 21
14M 48 52 37 41 21 25
XH 48 55 37 44 21 28
ZRM ZRP
Timing belt
length
Centre
distance
tolerance
Timing belt
length
Centre
distance
tolerance
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