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Anyway, if you put a 1 ft extension straight off the end of a torque wrench and you measure 75 ft-lbs on the wrench you are apply 150 ft-lbs to the fastener.



It's called ft-lbs because thats how much weight in lbs is being applied 1 foot from the fastener.

Lets say for example that you don't have a torque wrench, just a 12 inch ratchet. You could bring out your bathroom scale and stand on it while tightening the fastener. However much of your weight is not on the scale, is on your 12 inch ratchet. Ft-lbs

If your ratchet is twice as long, you'll need 1/2 the weight.

That's the way physics work.

Using a crows foot type extension is in no way different than adding a cheater bar to make the handle longer. Either way, you're adding distance between the fastener and the force (your hand).

You can prove this to yourself by using your torque wrench with a long cheater bar on it to tighten a fastener to any set amount. Then remove the cheater bar and tighten the fastener to that same amount. If the fastener is already tight that would mean the cheater bar did not make a difference. If the fastener has bit to go before it's tight, then the cheater bar Does make a difference.

Another thing that concerns me is an extension between the ratchet and the socket. The length and diameter of this type of extension can make a difference. It will twist like the torsion bars on our mopars. How much of my ft-lbs applied force are absorbed by the twisting motion of this type of extension? The absorbed amount is not applied to the fastener.

Tav



Tav, sounds like you are saying exactly what I said but are disagreeing. If you put a 1 foot cheater bar on the handle of a torque wrench and apply force until the wrench reads 75 ft-lbs it takes 1/2 the strenght in your arm than if you didn't use the cheater bar (thats why we call them cheater bars, more torque with less force). But if you put a 1 foot extension on the other end and pulled on the torque wrench until it reads 75 ft-lbs you have doubled the moment arm so you have doubled the torque applied to the fastner or 150 ft-lbs. In this case your arm will feel the same preceived amount of effort as if you didn't have the extension beacuse you aren't providing leverage to the measurement.

Take your ratchet example. With the ratchet horizontal and you hang a 75 lb weight 1 foot along the handle from the center of the socket you have 75 * 1 or 75 ft-lbs. Now move that same 75 lb weight to 2 feet along the handle from the socket and you have 75 * 2 or 150 ft-lbs.

When it comes to a ratchet extension between the socket and torque wrench. There is no loss of torque between the wrench and the socket. You may have to physically move the wrench more depending on the diameter and length of the extension to get to a give torque reading but no torque is lost along the length of the extension.

Dave Clement Pembroke, MA 03 PT Cruiser GT Turbo 99 Dakota SLT+ CC 4x4 68 Barracuda sport coupe http://home.comcast.net/~dgc333/