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T–3
Belt Technical Information
1-2 Making Measurements
Belt installation tension is generally measured in the following ways:
Force/Deflection: Belt span tension can be measured by deflecting a belt span 1/64" per
inch (0.4 mm per 25 mm) of span length at midspan, with a known force (see Figure 1). This
method is generally convenient, but not always very accurate, due to difficulty in measuring
small deflections and forces common in small synchronous drives. The force/deflection method
is most effective on larger drives with long span lengths. The static (or installation) tension (Tst)
can either be calculated from Equation (1-1) or Equation (1-2), or selected from Table 1 or
Table 2. The deflection forces can be calculated from Equation (1-4) and Equation (1-5). The
span length can either be calculated from Equation (1-3), or measured. If the calculated static
tension is less than the minimum Tst values in Table 1, use the minimum values.
PD – pd 2
t =
Ö
CD2 – (––––––––)
(1-3)
2
where:
t
= Span length (in)
CD = Drive center distance (in)
PD = Large pitch diameter (in)
pd
= Small pitch diameter (in)
t
Tst + (––) Y
L
Deflection force, Min. = –––––––––––– (lbs)
(1-4)
16
t
1.1 Tst + (––) Y
L
Deflection force, Max. = ––––––––––––––
16
where:
Tst
= Static tension (lbs)
t
= Span length (in)
L
= Belt pitch length (in)
Y
= Constant, from Table 1
Shaft Separation: Belt
installation tension can be applied
directly by exerting a force against
either the driver or driven shaft in a
simple 2-point drive system (see
Figure 2). The resulting belt tension
will be as accurate as the force
applied to driver or driven shaft. This
method is considerably easier to
perform than the force/deflection
method and, in some cases, more
accurate.
Fig. 1 Force/Deflection Method
Deflection 1/64" per inch of span
Fig. 2 Shaft Separation Method
Fig. 3 Single Tension Vector Force
