Bicycle Mechanics - Tourque wrench questions...

Does 12 in-lbs = 1 ft-lb?

Can anyone officially answer this...not just a "yeah, the math seems right" answer. You know that in electricity 2 110 circuits can't be put on one 220 breaker even though the math equals.

Thanks,

PJBAZ

The answer is yes. 12 in lbs = 1 ft lb.

To derive inch lbs from ft lbs multiply by 12.

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That's what I thought as well...then I thought some more and really complicated the idea in my head.

Has it been tested somewhere on a guage? The reason I ask is this...

If you torque a bolt to 120 in-lbs and then use a foot pound wrench on the same bolt set to 10 ft-lbs the only way to know if it was more would be if the bolt turned and the wrench didn't click over. However, if the force was less it would click over and couldn't be known.

Although, it could be tried the other way but the same principle applies...

PJ

That's what I thought as well...then I thought some more and really complicated the idea in my head.

Has it been tested somewhere on a guage? The reason I ask is this...

If you torque a bolt to 120 in-lbs and then use a foot pound wrench on the same bolt set to 10 ft-lbs the only way to know if it was more would be if the bolt turned and the wrench didn't click over. However, if the force was less it would click over and couldn't be known.

Although, it could be tried the other way but the same principle applies...

PJ

You don't need to test this one.....it's a matter of the definition of the units. Torque is measured by the length of the lever arm, and the force applied to the arm. So, if you accept that 1 foot = 12 inches, then it goes without saying that 120 in-lbs = 10 ft-lbs, just like 120 inches = 10 feet.

You can measure torque in one unit, like in-lbs, and convert it to many different units, with conversion factors. For example, in the metric system, newton-meters is commonly used. To convert from ft-lbs to newton-meters, you multiply by 1.355. So, 120 in-lbs = 10 ft-lbs = 13.55 nt-m's. Guaranteed!

Sweet! an actual scientific answer...that's what I wanted.

As I've said, I always thought it was the proper conversion but it was "one of those things" where it could Not make sense. i.e. the 110-220 electricity reference from earlier.

Thanks.

PJ

However, it depends on how precise you want to be. If you need 16 inch pounds you will have to use an inch pound wrench. There is also a fair chance that your foot pound wrench, when torqueing 2 foot pounds may torque between 22 and 26 inch pounds. The variance may be even bigger depending on the quality of the wrench, how it is used, and how long it has been since it was last calibrated. You can purchase a calibrator from Snap-On for around $50,000 ;)


Edited for bad math,020104

An inch-lb is a force of 1lb acting on a lever at a point 1 inch from the fulcrum (the bolt in this case). Thus 12 inch-lbs is 1lb acting 12 inches from the bolt, which is the same as 1lb acting 1 foot from the bolt. As long as the force unit doesn't change, you can change the distance to any unit you normally would (but a metre-lb is a useless unit. Best stick to all metric or all imperial).

So how much is that in furlong-stones?

To get furlong-stones divide foot-pounds by 9240.

TO quote one of my favorite movies

Mona Lisa: If you will look in the manual, you will see that this particular model faucet requires a range of 10-16 foot pounds of torque. I routinely twist the maximum allowable torquage.
Vinny: How can you be sure you used 16 foot pounds of torque?
Mona Lisa: Because I used a Craftsman model 1019 Laboratory edition, signature series torque wrench. The kind used by Cal Tech High Energy physicists, and NASA engineers.
Vinny: In that case, how can you be sure THAT'S accurate?
Mona Lisa: Because a split second before the torque wrench was applied to the faucet handle, it had been calibrated by top members of the state and federal department of weights and measures, to be dead on balls accurate. Here's the certificate of validation!
Vinny: Dead on balls accurate?
Mona Lisa: Its an industry term.
Vinny: I guess the ****in thing is broken then!

Regards the two 110vac circuits on a single 220vac line. Every main breaker box that I've worked with in my personal experience, does exactly what you've said can't be done. The utility supplies anywhere from 204 up to 220vac. We all call it "220" when it most often isn't. This line has two "high" sides and a neutral.
The two high sides are 180 degrees out of phase with eachother. The breaker box splits this into many 110vac (102-110) circuits. Each of the two high sides measured to ground will be approximately one half of whatever the utility company is providing to the house (204-220).

My high school physics teacher made a big deal about distinguishing between torque and work, both of which have the same dimensions of length times force. We generally spoke of meter-newtons or foot-pounds of torque, but newton-meters or pound-feet of work.

I didn't mean to say it can't be done...what I was saying is that you can't safely wire two seperate 110 circuits into a panel and use one 220 breaker to control them.

It would need too much juice before the breaker pops that way...same idea as throwing a 50 amp fuse in a 10 amp line.

PJ

See also for torque http://www.parktool.com/repair_help/torque.shtml

and for basic thread concepts http://www.parktool.com/repair_help/thread.shtml