Torque Wrench Extension Calculations?

My question is what actually determines the length (wrench length not extension) we use for torque wrench extension calculations? Is the length (the figure we use for the calculations) a set figure unrelated to the physical length of the wrench but the wrench is usually calibrated in a way which means the theoretical length of the wrench we use for the calculation is the same as a physical length of the handle? Or do I have this all wrong?

The only reason for the length is to be able to convert the torque (Nm) into the force that needs to be applied at a right angle at that distance from the center of rotation in order to produce the required torque. If you double the length (by using an extension), you have to apply only 1/2 the amount of force at twice the distance to achieve the same torque.

If you are using a calibrated force (say 9N) applied at 1/3m, the torque applied is 3Nm (9N x 1/3m). If you extend the handle and apply the same 9N force at 2/3m, the applied torque is now 6Nm (9N x 2/3m).

If instead you have an automatic torque wrench, one that clicks or releases when the setpoint torque is achieved, then the length of the handle makes no difference. If you have the torque wrench set at 3Nm, then at 1/3m distance, you will have to apply 9N of force to make it click (9N x 1/3m = 3Nm). If you use a handle extension to double the length, you will have to apply only 4.5N at 2/3m to make the wrench click (4.5N x 2/3m = 3Nm).

Does that clear it up?

A look at what is currently available on eBay

1/2" drive torque wrench and extension by BERGEN AT676 US $45.84

7 TORQUE EXTENSION Bar IMPACT WRENCH STICK MAG WHEEL US $79.95

Neiko 5 pc 1/2" Dr. Torque Wrench Extension Bar Set US $69.99

1/2" Torque Wrench Micrometer Adjustable SAE Click Stop W/ Adapter & Extension US $39.95

Norbar Insulated Torque Wrench HF Insulated Socket Extension Battery String Tool US $25.99

Torque Wrench 150 ft. lbs. with extension *FREE SHIP* US $40.00

Caterpillar Torque Wrench 26" Extension Bar P/N 8F-4677 US $75.00

TORQUE WRENCH SNAP-ON TORQOMETER 1" DRIVE WITH 4FT EXTENSION POLE US $800.00

CDI TORQUE WRENCH, DIAL TYPE, 3/4" DR, 0-600Ft/Lb's, WITH EXTENSION ARM, 6004DF US $259.00

UTICA TORQUE WRENCH, DIAL TYPE, 0-600 FT/LB's, MODEL DA4600F, WITH EXTENSION US $189.00

Applied Materials 0021-77926 TORQUE WRENCH EXTENSION AMAT US $160.00

Neiko 8 pc 1/2" Dr. Torque Wrench Extension Bar Set US $94.99

Caterpillar Tools CAT 8H8548 8" Socket Extension for 3/4" Torque Wrench US $74.99

Snap On 3/4" Torque Wrench TE-352-FU TE352FU w/ Extension TorqueoMeter US $209.99

Utica DA-3250-F 250 F + Lb 1/2" Drive DA3250F Dial Torque Wrench Extension US $169.99

3 Pc Reverse Click Micrometer Torque Wrench 1/2" Dr SAE/Metric Adapter Extension US $37.99

SNAP ON 3/4" DRIVE RATCHET EXTENSION AND TORQUE WRENCH 100-500 US $349.95

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