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Operating Instructions • Warning Information
How to Compute Torque (cont.)
Load must be applied at center of knurled grip when using
ex ten sion.
The letters in the formula have the following meaning:
A = length of torque wrench
B = length of adapter
C = torque wrench setting
D = desired torque at end of extension
Here is a typical problem. You have an adapter that adds 6 inches to a
torque wrench. You are using a torque wrench. What should the setting
be to obtain 90 pounds of torque at the end of the adapter?
A = 14" *SEE NOTE
B = 6"
D = 90 foot pounds
C = unknown
A
C = D x
,
C = 90 x
( A + B )
C = 90 x .7 = 63 ft. lbs.
Your answer is a setting of 63 foot pounds on the torque wrench will
give 90 foot pounds of torque at the bolt.
By using the above figures in the formula for dimension "A", an
accuracy of ± 2% of the desired torque at the end of the adapter will
result.
*NOTE: For illustration purposes only. Actual measurements will vary
with each model torque wrench and extension length.
Operating Instructions...
It is important to understand the following when using adapt ers or
extensions on torque wrenches.
1. The formula given apply only to torque wrenches.
2. Load should be applied at center of hand grip.
3. Length of adapter should be measured from the center of adapter
opening to center of square drive opening. Measure only distance
that is parallel to torque wrench.
4. If your torque wrench reads in inch pounds, then measure in inches.
If it is calibrated in foot pounds then measure in feet. Or if it is more
convenient change everything to inches.
Conversion Formulas
It is often necessary or helpful to change torque readings from foot
pounds to inch pounds or inch pounds to foot pounds. To convert from
one specification to another it should be remembered that there are
twelve inches in a foot and one foot pound of torque equals 12 inch
pounds of torque. From the above, the following formulas may be used:
Foot pounds x 12 = inch pounds.
Inch pounds ÷ 12 = foot pounds.
Cm. – Kgs. ÷ 13.8 = foot pounds
Cm. – Kgs. ÷ 1.15 = inch pounds.
M/kgs. ÷ Ft. lbs x .1383
Ft. lbs. = M/ kgs. x 7.2329
Cm. – kgs. = inch pounds x 1.15
Cm. – kgs. = foot pounds x 13.8
9701A/9702A/9703B: Operating Manual
14
( 14 + 6 )
Testing accuracy of a Torque Wrench
It is impossible to check the accuracy of a torque wrench by using
another wrench.
For example: A wrench is used to tighten a bolt to 90 foot pounds.
Another torque wrench is used to loosen the bolt as an accuracy test for
either wrench. This is a test or comparison that is frequently performed
and invariably re sults in an assumption that one of the torque wrenches
is not calibrated correctly.
What is generally not known or understood is that the break-loose
torque is considerably less than the applied torque. This means that the
torque required to loosen a bolt previously tightened to 90 foot pounds
would be con sid er ably less than the 90 foot pounds of applied torque.
In view of the above, it is easy to see why one of the torque wrench es
could be considered inaccurate. A torque wrench should be tested on a
torque wrench testing machine to determine its true accuracy.
Owner/User Responsibility...
Always follow the manufacturer's specifications when ev er possible.
Look for footnotes that might indicate under what conditions the torque
values were established.
Any assembly held together by a number of fasteners should be
tightened down a little at a time going to each fastener in turn until
specified torque has been reached. A good practice to follow is to
torque in three steps. First ap ply 3/4 of specified torque all around, then
reset wrench and apply the specified amount of torque. Third step is to
retorque all bolts to be sure none were missed.
Never use a torque wrench on a nut already tightened with a standard
wrench or socket. For accurate torque the final turn of the nut must be
done with a torque wrench.
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04/05/16
