Getting High Torques Right

[Newland]

I have very little mechanical experience but now that I own a tractor, I want to learn enough to properly maintain it. The first thing I read about my rotary cutter was the blade bolts should be torqued to 300 ft pounds and there are other bolts at 400 foot pounds. I'm guessing an air driven impact wrench can take the nuts off but how do you accurately get the torque back where its supposed to be when you put the nuts back on. The impact wrenches I saw had no calibrated torque settings and the torque wrenches I've seen with the torque needle don't go up that high. What should be used and where do you get it.

Also can anyone recommend a good book relative to tractor maintenance that would cover the sort of thing that any 12 year old who grew up on a farm would know.

Thanks,
Newland

 

[Darren]

Look for a torque multiplier on Ebay. They're made in different ratio. You'd use one of those in conjunction with a lower rated torque wrench.

For example, using a torque wrench rated at 100 ftlbs. driving a torque multiplier geared for 1:4 would give you 400 ftlbs output. A torque multiplier will also remove fittings that an air wrench won't budge.

 

[RoyJackson]

Look for a torque multiplier on Ebay.

You'll probably want to find a length of pipe that fits the handle of your torque wrench too. 400 Ft Lbs, even with a torque multiplier, is going to be a tough pull. You'll need leverage (when I weighed about 150 lbs, I could dern near do chin ups on a torque wrench set for 300 ft lbs.).
Please make sure your cutter cannot move when you're doing this task. It's gonna want to rotate in the direction you're torquing.

 

[justractors]

With a torque multiplier you only "pull" the amount of torque produced by the torque wrench not the multiplier. So to produce the 400 foot pounds in the above example you only need to pull the 100 foot pounds.
Bill

 

[RoyJackson]

With a torque multiplier you only "pull" the amount of torque produced by the torque wrench not the multiplier.

This is correct...there was a sentence left out of my post that stated the price of multipliers may be cost prohibitive for an individual.

However, here's a <A target="_blank" HREF=http://www.tristarindia.com/multi.htm>link to one site</A>.

However, you may be able to rent one...

 

[Darren]

Roy, that's why I suggested eBay. As you said a new torque multiplier is expensive. They run several hundred dollars to thousands new depending on the multiplier. With a little patience a guy should be able to snag one for much less. Sweeny and Proto multipliers show up on eBay frequently enough that you just have to keep checking and not get carried away with the bidding.

You may also need a 3/4" or 1" drive socket for the output end in the size for whatever your torquing. That's the thing about tools. One always necessitates another. With luck you can fill the whole garage, the barn and the basement before the lady of the house catches on.

 

[kevinro]

Just for kicks, I thought I would point out what a ft/pound is, and that might help you with your question. Torque is a measurement of rotational force around a center point. Its units are foot/pounds. The measurement is exactly the way it sounds. 1 foot pound is the amount of torque exerted by a 1 lb weight connected to a 1 foot long stick.

A key point is that torque is a linear measurement. If you use a 2 foot stick, you can use a 1/2 lb weight. So, if you are in a bind and need a good guess at how tight something is, you can try this sort of stunt. If you need 400 foot pounds, and you are lucky enough to weigh 200 pounds, in theory you can stand on the end of a 2ft breaker bar. The breaker bar needs to be roughly parallel to the ground for the measurement (at 3 or 9 o'clock).

I say in theory, because torque specifications are usually stated for a moving system. In other words, as the bolt tightens. When you use a torque wrench, you start with a bolt that is known to be 'not tight enough', and turn the wrench up to the maximum torque point. DON'T JUMP OR BOUNCE ON THE BAR! You would be amazed at how much force you can generate by doing that. F = 1/2 M V^2 => Force = 1/2 mass x velocity squared. That faster you move, the much more force you create. Its quite easy to double or quadruple your weight by jumping or bouncing too hard!

Kevin
Kevin

 

[RoyJackson]

That faster you move, the much more force you create. Its quite easy to double or quadruple your weight by jumping or bouncing too hard!

Hey Kevin...now you can explain inertia too!

I wonder if we can get an ME degree from TBN...the way some of these posts are going...

 

[kevinro]

I wonder if we can get an ME degree from TBN...the way some of these posts are going...

Whoops, I must have put my nerd glasses on. /w3tcompact/icons/cool.gif Amazingly enough, they look fine with my new TBN hat.

 

[Egon]

Kevin:

There's also the post jump pain factor when the broken end of the wrench cracks your shin. [ experience ]

Egon