Axle Nut Torque-To-Angle Method?
 

Since the cost of a sufficiently large torque wrench is prohibitive for such an infrequently used tool, I was wondering if there is a way to calculate an angle for the final torque value, from a lesser preset torque, that would allow use of a "normal" torque wrench, say 100 ft-lbs. I am imagining torquing the nut to some value within the wrench's range that would then allow a simple large breaker/socket to be turned, say 90 degrees, to arrive at the final torque.

Any reason this wouldn't work? I suppose it would require the angle to be determined by actually using a torque wrench capable of the final value once. Then subsequent trials could use the breaker bar.

Assuming steel materials in the stud/nut one would need to know at a minimum the thread size and pitch, some idea of the thread friction used in the original torque calculation and the grip of the joint.

Here we go...
http://www.cncexpo.com/TorqueAdapter.aspx

Good stuff, Zef, but calculating the torque with an extension isn't what I'm after. What I want to know is whether I can torque the axle nut to a value within the range of my current torque wrench, say 95 lbs, and then use a larger breaker bar to turn the nut a specific number of degrees further that corresponds to the final torque value required? It seems like it's doable if the angle can be determined. Can't the angle be determined by using a large (borrowed or rented) torque wrench, which can then be used for all future torques?

In theory, using the "high level capacity torque wrench once" method would work. One problem may be measuring the number of degrees of rotation going from the baseline torque to the final torque especially if it turns out to be a small angle. Your method would likely work better with fine pitch threads and longer grips (like cylinder studs). Look up "turn of the nut" torquing method.

Will do. I was thinking that it could be reverse calculated to use a specific angle like 90 degrees, which is easy to do quickly. The variable would then be the initial torque value required, and whether it was within the wrench's range.

Zoanas, I don't think it would be all that accurate, if you're trying to save the cost of a more expensive wrench, the easiest way to do it is using your weight and braker bar, calculate where you need to stand on it to get the correct torque. EG 200 lbs at one foot = 200 ft lbs, Much more accurate IMHO.. ( just remember not to jump)

Zoanas, here is what I would do.

Find an extension about 3 feet out from the nut. Find a digital bath room scale and stand on it while you are torquing the nut. Let's say you need 300 lb-ft or torque, you would push down on the end of the extension, standing on the weighscale, until your weight is 100 lbs less (meaning you have applied 100 lbs on the end of the extension bar). 100 lbs * 3 feet = 300 lb-feet.

no need to buy anything expensive. I even used that method to calibrate my 150 lbft torque wrench (using smaller weights).

9dreizig, I use that method now, but I'm certain that the torque-to-angle method is more accurate. Especially if the preload torque value is known. Achieving a specific angle is easier than balancing my weight on a breaker bar.

Yelcab, sounds like a good idea, but a little cumbersome. What I envision is determining the angle I need, and then being able to just set the preload torque value and then crank the breaker bar by 90 degress or whatever. Although, I suppose I could use your method to determine the angle I need.

9dreizig/Todd is right. Weigh yourself and figure out how far away from the socket you need to step to produce N foot x lbs. (Your weight divided by desired torque = distance in feet.Edit, OK I was a little quick on the math there. Distance from socket (in feet) = torque / your weight
) Put the wrench on the big nut so the wrench handle is horizontal, step on the wrench (don't bounce!) and you're done.
Torque is simply force times moment arm length T = weight * length of lever.

If you could use a long wrench handle and a weight hung at the exact distance from the socket you would have a more accurate torque than what you'd get with a torque wrench I bet. Factor in the weight of the unsuspended end of the wrench (like weighing a con rod end) and now you are looking at a setup that you could probably calibrate a torque wrench with.

You need to remember how crude torque measurement actually is. People worry about how accurate their torque wrench is when they should be worrying about the real causes of torque inaccuracy - friction.

-Chris

So, if I weigh 190 lbs, I need to stand on the bar at 190/339=.56' or 6.73" from the nut to achieve 339 ft-lbs? Doesn't seem right.

I think it's the reciprocal of that. 339/190=1.78' or 21.41" from the nut. That might be easily repeatable with a permanent mark on the breaker bar.

Two major points here 1) like anything else in life Lubrication is important
2) did Chris really say "9dreizig/Todd is right" can we get a sticky on that ??
But I agree with Chris I think the distance/weight method is the most acurate, doing an angle calculation is really open loop and in addition to the friction variable it would also depend on how many times the threads had been previously stretched ( fatigued).
On a side note, damn I love your boobs man....

I'm just trying to make a small difference... :)

The world is a better place because of people like you...

190??? who are you kidding? :D

Ha HA!

Watch it, I still wear a 34/32 Levi, brother. :)