Greg and all,
This was a great explanation done in true engineer style ;-)) and confirms
that what I've been doing when using an extension on a torque wrench. Well
done!
While on this subject, I must relate a short tale about my "clicker" torque
wrench. It is a GREY 3/8" drive (smaller) and of the best quality and paid
a moderate price for it. One of the first times I used it was to torque the
six small bolts holding the clutch pressure plate assembly to the flywheel
on my then 1979 Toyota Celica. This was actually an excuse to use the
wrench for the first time. <G> The manual called for a setting of 15 ft/lbs
which is minimal (the bolts are small) but I stopped when I had twisted the
heads off two bolts! I assumed the manual was wrong. I have been using this
wrench for my torquing requirements since.
Two weeks ago the local (Bedford, N.S.) Canadian Tire had a "junk bin" with
six 1/2" drive "digital" clicker torque wrenches for $49.00 so I picked one
up. I proceeded to compare my old and new wrenches at the same setting on a
bolt I clamped in a vise and the old GREY wrench seemed to apply more
torque just by the feel of it. So I took both wrenches into the mechanical
lab at the Institute of Technology where I instruct and tested them in a
torque testing machine and discovered that the expensive GREY wrench was
applying almost *twice* the amount of torque that it was set for. The
"cheap" Can. Tire wrench was almost bang on.
I guess the lesson here is not to assume these wrenches are calibrated
properly when you buy one new. There is a small set screw on the handle
(sometimes covered by a sticker or label) to adjust the torque when
calibrating them. The only problem is that there are very few places that
have a machine that will calibrate torque accurately. I guess you could use
a spring scale attached at the handle and do it that way - a bit crude but
it would give a ball park figure. Even Weights and Measures Canada couldn't
do it and had no idea where to get it done until I remembered our
mechanical lab.
Carry on torquing!!
Bob
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Bob Hamilton, Waverley, Nova Scotia, Canada
rhamilto@fox.nstn.ns.ca / Compu$erve: 70754,1533 / GEnie: r.hamilton
Toys: 1954 Sunbeam-Talbot 90 MKIIA, 1968 M-B 280 SE, + Motorcycles
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