Using crowsfeet wrenches to torque fasteners in tight spots

[bmwpower]

Quite often I've needed to torque a fastener in tight quarters. I'm thinking of getting some crowsfeet to aid in doing this.

How do you calculate the torque when the torque arm length (I think that's what it's called) is longer?

[kartracer55]

Turn the Crowsfoot 90* to the wrench, and the torque will not be affected

[bmwpower]

Turn the Crowsfoot 90* to the wrench, and the torque will not be affected

What if it's not exactly 90*? And what's significant about 90*?

[kartracer55]

Im stupid, so bare with me in my explanation here. :lol_hitti


A torque wrench gives an "accurate" torque if the fastener is directly below the drive square. If the fastener is ahead of the wrench, leverage is being developed due to the extra length. The torque wrench will still click when the drive square is "feeling" X ftlbs, but because the extra leverage is being generated, more than 10ftlbs will be delivered to the fastener.

If the crowsfoot or torque adapter is turned 90* to the drive square, then the fastner is still in line with the drive square. No extra leverage is being developed, the torque wrench is just twisting around a new axis.... Search the Pirate board for a thread that was on this stuff a while back.

Im sure there are more technical terms, if somebody can explain it more clearly please do so, Im lacking the terminology here

Jim

[Charles (in GA)]

If your adapter is 90 degrees to the head of the torque wrench, there is no correction needed to compensate for the length of the adapter. If you turn the adapter in any other position you will need to do some math for the correction.

The formula for calculating the torque with a crowsfoot. E- Effective length of extension - measured along the centerline of the torque wrench. L Lever length of the wrench - center of grip to center of drive. T(W) - Torque set on the wrench. T(E)- Torque applied by the extension to the fastener.

T(W) = T(E)* L/L+E
T(E) = T(W)* (L+E)/L

Charles

[bmwpower]

Ok, that seems to make sense. Thanks.

T(E) = T(W)* (L+E)/L

T(E) = 15 ftlbs * (12in+1in)/12in

T(E) = 16.25 ftlbs

<edit>

Calc'd it wrong the first time. I think this is right.

[Canadian Charlie]

You learn something new everyday

[volvo]

Watch out for lost of accurate torque when using an extension of any length or small diameter. One reason most car manufactures have gone to angle torque, it can be more accurate when all factors are considered...H

[fefarms]

Even on a good day, bolt torque is not a very accurate way to measure what you really want know, which is clamping force. More than 80 % of applied torque goes to overcoming friction, the remaining 20% or less is what you are trying to measure. The equations dealing with this have an interesting term called "the nut factor", which varies considerably depending on type of materials and dry vs. oiled threads.

Measuring bolt stretch, or using torque to yield fasteners is much more accurate.