[TR] torque wrench question

[Randall]

> The wrench will
> measure the same torque whether I choke up 6" or use a 
> cheater bar (yes, I
> do to get that 105ftlb).

If the wrench reads the same, then why bother with the cheater bar?

Answer is, it doesn't read the same.  The wrench responds to the torque it
sees, which is force applied to the handle times the length of the handle.
Your cheater bar increases the length, so the same force at the end of the
cheater bar results in more torque at the fastener and a higher reading on
the torque wrench.

But, when the cheater (extension) is between the wrench and the fastener,
the reading doesn't change even though the torque is greater.  That's why
you need a correction factor, based on the length of the extension vs the
length of the torque wrench.

Maybe a thought experiment would help.  Let's say you have a little bitty
torque wrench, only 1' long and it only reads to 30 ftlb (for 30 lbf on the
handle).  Now let's say there is a 6' extension between it and the fastener;
and you still apply 30 lbf to the handle.  Do you really think it will still
be only 30 ftlb at the fastener?  Or that the torque wrench is magically
going to read 210 ftlb? (30 lbf times 7')

Now imagine you use a 7' long wrench instead, and pull on it with 30 lbf.
How much torque does that apply?

-- Randall