BobGPz said:
Now Rich, I know that physics is exact science and all, but how accurate is it compared to the way TQ Wrenches work/set? Give you example.. A "Inch-Lbs" TQ Wrench set at 24In-lbs is not 2Ft-lbs right?
Actually yes it is. 24 in-lb exactly = 2.0 ft-lb.
What happens with the larger wrench is you have less resolution and accuracy so which makes it nearly useless for small bolts.
But, and this is from my mechanics (not auto mechanics, but mechanical forces) class, we (engineers) design for the worst case. So, if an analysis determines that something needs a 100lb fastener, we/they will often spec it with a safety margin at 150lbs. You can see this in the torque spec numbers.. 180-250.. If you do the math, that is a slop range of 70 lbs which is HUGE (40% or so of the base number). You won't need a 5% torque wrench with a 40% error tolerance, a real cheap 10% torque wrench is suitable.
BobGPz said:
So 24 inches is 2 feet, but 24In-lbs is more like what 10Ft-lbs? Basicaly I'm wondering if TQ Wrenches are based on the same physics as-weight on a level scale.
If someone is pulling 10ft-lb for 24in-lb, better stop them. If you are comparing readings between 2 different types of wrenchs, you should pull with the smaller wrench to your test value, then check the results with the larger one. Loosen and repeat. What you will almost universally find is that the larger one varies a lot for small values and isn't very reliable or repeatable. Hence, that's why they made the smaller T wrenchs to begin with... They needed something better than "Umm.. kinda of tight, but not too tight".
BobGPz said:
I think I know how to do a little math/science experiment to prove/disprove this... I will set my TQ Wrench to say 70 Ft-lbs. Stick my 9 year old daughter (assuming she weighs that now) on the premeasured point of the bar, then I'll see if the TQ Wrench pops without any extra turning of the nut. I'll then set the TQ Wrench to my weight (200)
click it, and see if my weight will turn the nut some more. That should prove or disprove it I think..
You can try the same thing on your lug nuts. But be aware that a good reading of final torque has you turning the fastener constantly
until it reaches the final reading with no pause.. Once its set, then you have static friction to contend with and if you check it to the point that it starts to turn again, it will be higher than what you torqued to for both loosening or tightening. That's OK and the difference is acceptable. You can check this out with a lug nut at about 30 lbs also. Just be sure to loosen the thing inbetween tests.
All of this is the
applied part of applied physics 101.
For anyone who wants to know more: here's one link I found
http://www.boltscience.com/