How to calibrate your own torque wrenches at home

[Kevin Criswell]

Hey guys/gals, in this video I show you how to calibrate your own torque wrenches at home. The adapter I am using can be bought at Harbor Freight Tools for $30.00
http://www.harborfreight.com/digital-torue-adapter-68283.html
(In the video I say $70, but looks like the price has gone down a lot since I bought mine).

Hope you enjoy.

Topic

[Peter]

Sorry to dig up an old thread, but I have a question relevant/related to this thread. It’s a question about the torque adapter used in the video:

http://www.harborfreight.com/digital-torue-adapter-68283.html#pr-header-back-to-top-link

I’ve read on this thread that people have used this setup and adapter for calibrating 1/4 in click style wrenches. The product overview on the HF tool states that the torque range on this tool is from 29.5 to 147.6 ft. lbs. 30 ft/lbs isn’t even close to the max 200 in/lbs most cheap 1/4″ torque wrenches max out at.

For anyone who has used this tool for an in/lbs torque wrench: how accurate is the HF adapter for calibrating these style wrenches? If this one definitely won’t work in that low of a range, can anybody recommend a digital torque adapter that is made for use in that range? Thanks!

[Jon]

I just found out my old torque wrench was 20lbft out! So I thought I would dismantle it, lubricate it and then recalibrate it myself.
With a bit of thinking it is possible to do it accurately and for free, without special expensive tools.
I made this video to help others:

[Patrick]

Sorry if it is bad form to reply to such an old thread. First off, thanks for the great tips on calibration. I just picked up the $30 HF adapter and am looking forward to calibrating my cheap Craftsman wrench.

I would also like to calibrate my Dad’s old Snap On, model QJR3200C, but I can’t find any information about how to do it. Anyone know how to calibrate this one?

[Jon]

So it’s obviously a clicky type with an internal spring and screw down end that sets the torque. The position of the screw in end sets the calibration, just like the one in the video of the previous post. You just have to work out how to fully remove the screw on end. It was assembled somehow so it must come apart, you just have to figure it out. Sorry I can’t help more as I couldn’t find any assembly diagrams for this model. After you work out how to disassemble the calibration procedure will then be the same as in the video.

[Dave]

I would also like to calibrate my Dad’s old Snap On, model QJR3200C,

I have seen posts – rumors? – of folks who sent their wrenches back to Snapon or brought it to a truck and the guy re-calibrated it. It was implied that the Snapon Warranty/Guaranty is to the tool – not the owner like everything else.

I’d be real curious to know if that was true.

[Paul]

[quote=”unknownsoldierx” post=154459]Sorry if it is bad form to reply to such an old thread. First off, thanks for the great tips on calibration. I just picked up the $30 HF adapter and am looking forward to calibrating my cheap Craftsman wrench.

I would also like to calibrate my Dad’s old Snap On, model QJR3200C, but I can’t find any information about how to do it. Anyone know how to calibrate this one?[/quote]

An alternative calibration method is to create a table or graph of the measured torque versus the dial setting on the torque wrench. For example, record 5 measurements from the digital adapter at each torque setting on the wrench, and calculate the average. Then, repeat the measurement for 10 or more commonly-used settings along the full scale of the wrench.

It doesn’t require disassembly, but you have to refer to the calibration table/plot each time the wrench is used, which may be a PITA if the wrench is used often. Also, the clicker style wrenches have the best accuracy at the highest setting, and the accuracy decreases as the setting is lowered. The digital wrenches have a fairly constant accuracy over their specified torque range. So, you obtain a better feel for the accuracy (and expected variation) for different settings and learn each wrench’s character.

[Patrick]

[quote=”DaveNewbie” post=154509]I have seen posts – rumors? – of folks who sent their wrenches back to Snapon or brought it to a truck and the guy re-calibrated it. It was implied that the Snapon Warranty/Guaranty is to the tool – not the owner like everything else.

I’d be real curious to know if that was true.[/quote]

I doubt they would calibrate it for free even under warranty. Plus, the warranty details on their website now state that warranties are only good for the original owner.

[quote=”Hanneman” post=154524]An alternative calibration method is to create a table or graph of the measured torque versus the dial setting on the torque wrench. For example, record 5 measurements from the digital adapter at each torque setting on the wrench, and calculate the average. Then, repeat the measurement for 10 or more commonly-used settings along the full scale of the wrench.

It doesn’t require disassembly, but you have to refer to the calibration table/plot each time the wrench is used, which may be a PITA if the wrench is used often. Also, the clicker style wrenches have the best accuracy at the highest setting, and the accuracy decreases as the setting is lowered. The digital wrenches have a fairly constant accuracy over their specified torque range. So, you obtain a better feel for the accuracy (and expected variation) for different settings and learn each wrench’s character.[/quote]

I’d really like to figure out how to calibrate it. Not just to make it more usable, but to know how this one works.

I finally got to take my own pic. There is a grub screw on the lock ring thingy. It’s the only screw on the shaft or handle.

[Author]

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