Offset Torque

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ctwo
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Offset Torque

Post by ctwo »

[thought I posted this, but cannot find it - sorry if a dup]

I am supposed to use a special tool to torque a nut for bearing preload. This tool takes a 1/2" drive that is offset about 3 inches from the nut that I am torquing. Instructions say to torque with the torque wrench at 90° to the special tool.

I am hoping to avoid this tool by using a castelated nut - so I'd like to confirm that the torque spec. will apply the same.

[I suspect that the torque relationship is related to the torque wrench angle as: torque on nut = torque wrench setting + x*cos(theta), where x is 0.25 ft-lbs)]
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SteveM
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Re: Offset Torque

Post by SteveM »

The reason for the 90 degrees is to minimize the change in length of the lever arm. It's an approximation.

Technically, I think that you would want it slightly sharper than 90 degrees, but the difference is probably minimal and they didn't want people having to pull out vernier protractors to get it.

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warmstrong1955
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Re: Offset Torque

Post by warmstrong1955 »

C = (DxA) / (A + (B x COS Ø))

C= Torque wrench setting
D= Desired torque on fastener
A= Center of torque wrench drive to center of puller' grip on torque wrench
B= Length of extension, center to center
Ø= Angle of extension to torque wrench axis

Bill
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ctwo
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Re: Offset Torque

Post by ctwo »

Thanks! I knew my loose reasoning was correct, and that my formula was incorrect.

However, Bill, your formula produces a reasonable graph when sweeping a circle, but different length torque wrenches produce different results. Is the torque wrench setting really the force applied to the wrench, and not the break torque of the wrench (meaning A will always be 1 if using ft-lbs wrench)?
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...
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warmstrong1955
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Re: Offset Torque

Post by warmstrong1955 »

The equation is actually for calibrating a torque wrench with a crow foot using a weight or weights, not so much the actual setting.
If the setting is accurate with a standard socket, the the 'A' dim will not matter much.
So....the equation, will work when using a crow foot, or most any offset adapter, when you know where you want to be. Again, in that case, the 'A' dim, really doesn't change things much.
Been using this for many years. Got it rebuilding rock-drills long agfo, among other things, where you couldn't get onto a side-rod with a regular socket. I even have an excel sheet to stuff in the required numbers....cause I'm lazy, to get to the setting I need.
Some things....need to be more accurate than what the dial or click setting says, and.... you would be surprised how far off many torque wrenches are, even new out of the box. I can tell you stories of failures on components, from axles to cylinders to valves, that were caused by mis-calibrated wrenches.

To calibrate the torque wrench by length & weight:
T = L x W
T= Torque (in/lbs)
L= Length (in)
W= Weight (lbs)

To test the wrench by setting:
L = T / W

I have weird hobbies I guess....

:)
Bill
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ctwo
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Re: Offset Torque

Post by ctwo »

Hi Bill,

Well, you know you're in good company...

I used the simplified approach to verify my torque wrench, since my snap on is 1 foot long, I hung the desired weight (torque) off the handle center point with it clamped horizontal in the vise.

So, you've seen something like this before, huh? LoL
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Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...
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warmstrong1955
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Re: Offset Torque

Post by warmstrong1955 »

Yeah....that's it....that's the ticket....
;)

I tried attach my Excel 'Torque-Wrench-O-Matic', but I converted it to Office 2010 (xlsx) a while ago, and our site is not xlsx friendly.
I can make a converted/perverted copy to 2003 (xls) when I have a chance, and send it later.

Bill
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ctwo
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Re: Offset Torque

Post by ctwo »

I suspect just renaming the file extension to something benign, like .txt, would work.
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Book1.txt
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Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...
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