FWIW - Torque Multiplier (Torquewrench Extensions)

[getoffmyinternet]

I've been seeing a lot of stuff on making your own torque wrench extension (such as adding clutches to an r200) and there seems to be a lot of confusion, such as in saying "torque changes," "I used an online calculator," "instructions with my torquewrench," etc. so I searched torque faq and didn't see one. It was somewhat annoying that there was any discrepancy on the matter, but perhaps making a faq will help someone who needs it, so here goes.

 

FAQ

 

Q. What is a torque multiplier?

A. Adding length to your torque wrench and thus increasing it's applied torque versus it's indication.

 

Q. I need to figure out how much the torque will change.

A. Can you phrase that in the form of a question?

 

Q. What if that thing I said?

A. The applied torque is a ratio of the new arm length to the original length:

 

Your torque wrench was calibrated based on it's designed handle length, which is considered to be from the center of the drive to the center of the grip on the end of the handle (where it is properly held). However, we do not care what the torque will actually be when we set it to what we want, rather we have to work backwards to get from what we want it to be to what it will indicate (or what we will set it to in the case of a click type wrench).

 

Example

 

You need 100ft-lbs and you have a 10" torque wrench that only goes to 900in-lbs. So, because you're a genius, you add a 9/16 wrench and use it as a foot, adding 6" to the total length from the drive of the torque wrench to the center of the boxed end of the added wrench.

 

Since your new length is 16" v. the original 10", your applied torque will be 16:10. This means that you will need to set the wrench at the reciprocal of that to get the correct torque -- remember, you are multiplying APPLIED torque so you will need to in effect do the inverse (divide) to get the INDICATED torque. So here's the math. You take 100 ft-lbs, which is 1200 in-lbs. and multiply by 10/16 (or the ratio of your handle length to the total new length). Thus, you will set your torque wrench to 750 in-lbs (62.5 ft-lbs) and because the extension multiplies that torque, the applied torque will actually be 1200 in-lbs (100 ft-lbs.), the correct amount you are seeking.

 

The Formula

 

example: 100 X 10 / 16 = 62.5

 

Desired Torque X Handle Length / Total Length = Adjusted Torque

 

On a side note, if the extension you use isn't set straight out, the multiplier will be diminished. This can be handy in using a crows foot to torque a brake line for example -- by adjusting the crows foot at a right angle to the torque handle, you aren't actually adding any length, and thus do not have to calculate an adjusted torque. It can be invonvenient however if you are using a ratcheting torque wrench for example and the extension keeps clicking off center -- you must keep the extension straight out from the handle or your reading will be inacurate.

[PanzerAce]

Um..............Based on my admittedly old physics classes, I think you're off on this. The TORQUE (in ftlbs) should be a constant, all that is changing the lever length. You have to put less weight or force into the end of a longer wrench for a given torque value, but the torque reading on the wrench will still be accurate.

 

Example:

 

100ftlbs on a one foot wrench = 100lbs on the end of it

100ftlbs on a two foot wrench = 50lbs on the end of it.

 

Different amount of force on the end of the wrench, but the torque value is still going to be the same.

[ckolander]

Ummmmmmm.......Thats what air ratchets were made for.......and mechanics. I don't have the brainpower to do all this thinking anymore

[kiwi303]

My torque wrench works up to the set ft/lb then starts slipping the cluths... doesn't matter how long the leaver is since the friction discs and torque-y bits are in the head. which stays put other than going round and round.

[Evan Purple240zt]

He is talking about adding the lever between the head of the ratchet and the socket, not the handle end.

[Daeron]

He is talking about adding the lever between the head of the ratchet and the socket, not the handle end.

 

THAT would make the difference!!! Thank you for clearing that up, I was scratching my head over how this could ever work... it seemed like the OP was completely misunderstanding what he was saying, but I never caught the fact of the extension bar being between ratchet head and socket!

[getoffmyinternet]

Ah, EVAN! I was wondering why the hell they weren't getting it. Panzer disagreed with me but everything he said made it seem like we were on the same page. Perhaps I'm not the best at explaining it after all.

 

adding 6" to the total length from the drive of the torque wrench to the center of the boxed end of the added wrench.

Yes, the "weight" you are applying to the wrench doesn't need to be as high to torque the same amount when the arm is longer, that's why you put it at a lower setting! I assumed I was clear enough about it being an extension to the ratchet end, when we need "more torque" to tighten a huge nut I hope none of us are talking about welding a big rod on the end of the wrench handle. If you can't get the wrench to torque down to it's setting, you have different problems than I am describing -- you are lacking LEVERAGE, ie. strength.

 

The problem is that if your torque wrench only goes up to 50ft-lbs and you feel like torquing to 500ft-lbs, then no amount of adding to the handle length is going to make the wrench exceed what it was designed to do. In short, adding an extension to the drive end, like my examples (crows foot, line wrench etc.) doesn't make the torque wrench do any more work, it just gains mechanical advantage at the other end of your new lever. The wrench itself is still doing whatever torque you set it to at its drive, the applied torque, the only thing that matters, on the other end of the extension is what goes up.

 

On a side note, I should have said 7/16 wrench instead of 9/16, did that confuse anyone? Of course that is assuming you have a 3/8 drive torquewrench that only goes to 75ft-lbs, which isn't very convenient.

 

Does that make sense?

[cygnusx1]

Speaking of torque....and multipliers.... sorry if I am slightly off topic...

As a senior design project back in engineering skool..I designed a small dual worm gear box that would attach to two lug nuts (adjustable for any wheel). One of the sockets would turn by cranking a small handle on the side of the gearbox, like a jack-in-the-box. You crank the little handle and the socket turns the lug with a 60:1 torque multiplier. The second socket was on an arm, jutting off the gearbox, that hooked to the other lug for anti-torque. I demonstrated it by tightening a lugnut to 120ft-lbs and then having a lovely lady engineer remove the lug nut with ease. It was an expensive tool and would never replace the tools in a Mercedes Benz; the Roadside Assistance Plan. It was purely an exercise in design engineering.

[getoffmyinternet]

Yes, for a gear box the principle is the same, although it would have to be calibrated for all of the torque loss from mechanical inefficiency. Like in the torquewrench, increasing the leverage means you trade off weight for distance, so increasing the length of the wrench means you have to turn it farther but with less force, so it is easier. I assume you had to turn the handle 60 times around to get the same travel on the lug? I'd probably just put the iron on the lug and kick it a few times, but I digress. Sounds like a really cool project though.

[Daeron]

Honestly, I think alot of the blame for the misunderstanding is the widespread knowledge of cheater bar use, and the fact that we all know the physics in why and how THAT works, and nobody thought you were going any farther than that.. WE all jumped to the conclusion that YOU were misconceived and that we were like, 32093 times smarter than you. At least, thats more or less what happened to me.

 

I would be interested in a gearbox that you could attach to all FOUR lugnuts of a car on a free-spinning wheel, and spin something in the center that would spin the wheel and roll all four lugnuts off at once. I've thought about the gear reduction box, but thoughts of that always leap immediately to the multiple lugnuts at a time. (obviously they'd need to be broken loose before doing this)

[PanzerAce]

Ok, I grok what you're saying now

[jasper]

http://www.motionpro.com/documents/pdf/08-0134.pdf