Scotty -

Good explanation.... <img src="/forums/images/graemlins/kewl.gif" alt="" />

Frank

I have come to the conclusion that the size of the fastener is also a variable. All that 6" extension is is a 12" socket, right? That means every torque wrench is incorrect except if applied on the fastener size it was calibrated on, because you are measuring the torque on the axis of the bolt head. I suspect that they use a 1/2 or 9/16 as a standard, but somebodywith access to a calibrator can check the gizmo. It may well be just a 1/2" square drive orfice.

This means that your 24mm crank bolt is not torqued correctly, because it's roughly twice the size of the standard. It also means that you need a seperate torque wrench for each fastener size if you want the most accuracy possible. I become a greater fan of degree of rotation wrenches all the time...

One more "certainity" in this world exploded. I should have been ready for it - almost all the others are already gone poof.....

Oh boy, Eddy - this horse will never run again, will he? <img src="/forums/images/graemlins/lol.gif" alt="" /> -

I think you're partly correct - but I'm not sure it's for the right reason. <img src="/forums/images/graemlins/lol.gif" alt="" />



I believe that's true - but primarily because of difference in thread pitch and friction loading (more on larger diameter fasteners). I think at least some torque wrenches are calibrated with a set coefficient of friction assumption of .14 to .16. If you notice in this next paste, there is a reference:



The strange thing to see on the CDI site is that when you consider that clamping force is what the purpose of torquing a fastener is all about, it seems hard to believe that about 90% of the applied force is used to overcome friction - 50% head friction/40% thread - and only 10% results in clamping force. I still don't understand all of that, but I suppose I'll accept it until I see something different.

I do think (but I could be wrong) that the diameter of the fastener matters (particularly the diameter of the nut) but the difference between sockets is very little as a percentage of the overall handle length, so the wrench may very well be calibrated using a mid-range size socket. I'd have to do some more research on that before I'd come close to understanding the possibilities I'm considering.

I did ask the engineer at CDI about my hypothesis (maybe someone else's rule?) that mechanical advantage could be found by using the Ratio of Circumferences between the handle length and either bolt diameter or perhaps mean thread diameter as a method of determining applied torque without benefit of a torque wrench. He said he thought it probably could be done, but wasn't certain which base number reference should be used.

As luck would have it, one of my torque wrenches just blew up - can't read the number in the window any more - so I'm now off to Sears for a replacement (I hope). The warranty says they repair AND recalibrate within 3 months, but only repair (no free re-calibration) for the next 9 months. I don't think it'd be worth much without a calibration - maybe not even with one..... <img src="/forums/images/graemlins/lol.gif" alt="" /> so I'm off to argue for a replacement.

Frank <img src="/forums/images/graemlins/cheers.gif" alt="" />

If everyone's lost on the torque wrench theory, how about using angle of twist. That's the way we do it on the Shuttle Booster nozzles. OOps, hope I didn't open another can of worms! <img src="/forums/images/graemlins/shocked.gif" alt="" /> <img src="/forums/images/graemlins/nana.gif" alt="" /> <img src="/forums/images/graemlins/smile.gif" alt="" />

If you want to calculate exact preload on the fastener, friction and the nut size will come in to play. But, if you're just applying a torque to a nut or fastener, size doesn't matter. Torque is just a rotational force around a point. Or, how about lubricating everything first to reduce friction. That's why there are usually two different torque values; one for a lubricated fastener and one for a dry one.

Ahhhhh - there's the explanation for the difference. As usual, it's something simple made over-complicated. <img src="/forums/images/graemlins/lol.gif" alt="" />

Well, that would mean that fastener size and frictional forces are taken into consideration in the recommended torque value as published by the engineer to create the proper clamping force on the material..... well, that's so simple it's comical, eh? <img src="/forums/images/graemlins/lol.gif" alt="" /> <img src="/forums/images/graemlins/lol.gif" alt="" /> Of course they are.. <img src="/forums/images/graemlins/lol.gif" alt="" /> <img src="/forums/images/graemlins/lol.gif" alt="" /> I think I'll go back to sleep now. <img src="/forums/images/graemlins/sleeping.gif" alt="" />

Frank

I follow all that. It's only about clamping force, and torque is how you measure it. If you have to know, get data on measured and "true" torque with varying length extensions, and apply multiple linear regression or multivariate analysis to see which formula really fits. I'm sure there's a learned engineering paper out there on setting recommended torque ranges to accomodate the widest range of wrench error using statistical analysis of true vs indicated.

I'm going to do it just like always, 95% of the bolts I tighten I do by touch, stuff I want to feel good about I torque wrench (mainly heads, mains, and rods), based on learned bolt break points mostly, I guess.

Eddy, I have to disagree on your conclusion and assumption. Whoops....those definitive statements can get me in trouble. A 6" extension WOULD be like a 12" socket IF said socket had it's square drive centered over the circumference of the socket. You weren't trying to catch me were you, cause I'm kinda paranoid about posting these days. <img src="/forums/images/graemlins/baby.gif" alt="" /> <img src="/forums/images/graemlins/lol.gif" alt="" />

As for as the size of the fastener is concerned, it has many effects but they relate to clamping force,maximum clamping force,amount of torque needed to achieve a given clamping force and many others.The size of the fastener doesn't have an effect on the torque applied to it.IT JUST REACTS TO IT. Engineers take into account tensile strength, thread diameter,thread pitch, application and God knows what else when setting torque specifications, we just need to know how to plug the variables into a conversion formula and read a torque wrench scale. <img src="/forums/images/graemlins/cheers.gif" alt="" />

Scotty

P.S. I hadn't read LeeN's or Frank's post before composing this one, I swear. I could just delete it but I'm not. <img src="/forums/images/graemlins/smile.gif" alt="" />

If ya'll ain't careful, some folks might get to actually understand this here thing they call torque...... scary, ain't it?

The simplest things can become so complicated when you stick something into the equation that doesn't belong..... and unfortunately the only way to resolve it is to admit that it doesn't belong there - but to do that, you first have to understand why - and to do that is where the problem sometimes lies... (personal experience) <img src="/forums/images/graemlins/cheers.gif" alt="" />

Frank

"Understand".

Christ, I don't understand "understand".

Scotty, I don't set traps. I just make mistakes, sometimes. Say what you think. Either I'm starting to like your style, or your style is mellowing, but that's Relativity for you.

Since this is already verging on the mathematico-philosophical, here's my final observation. You can't be sure of anything. I had this adolescent dream of finding out how to calculate anything. One by one all the golden promises evaporated. Every calculation is a guess. Even the math we use is just a set of arbitrary rules we made up that seem to describe certain aspects of the real world, sometimes, with the following exceptions....
Engineering turned out to be gross overestimates of (you name it) built into the design, and called a safety factor. "Pure" science turned out to be politics and intellectual snobbery. Many of my generation became obsessed with saving the world, and are still at it today. I have all I can do to save my little part, and I'm not "sure" of anything I'm doing...

You make the best guess you can on the best data you can get, and you keep a bolt hole handy, and trust that hunch. I love "The Prince": "God we thank you for your gift of free will and thus that share of the glory that is ours"

Eddy,I was joking about you setting a trap, see my emoticons following the question. I just thought it was some kind of reverse segue to my description of a Rube Goldberg type socket that would technically fit your statement. Between that and my recent public embarassment, I found a little humor in it, at my expense I might add.Your Forum Friend, Scotty <img src="/forums/images/graemlins/cheers.gif" alt="" />