Calibrating a Craftsman Digitork torque wrench

[GT350Mike]

Does anyone know how to calibrate (adjust) this older model 1/2" torque wrench? Using a hand held scale, I checked to see how far off it was when set at 54 lbs and surprisingly, it's putting out about 56/57 ft lbs of torque which is only off about 2 or 3 ft lbs. I've had this torque wrench since the 90s and would like to keep it instead of wasting money on a replacement. Other than the description on the handle and a number stamped on the side (930539925), I don't much more about it. Any ideas???

 

[bob15]

Why not just send it out and have it calibrated by a certified shop? They can also tell you if it is even fixable......

 

[Cougar]

See if there is a metrology company in your area. They could do it.

 

[EOC_Jason]

According to your numbers, your torque wrench is within ~5% of its setting... That's usually about what the tolerance is from the factory...

As others have said, you can send them out to be calibrated professionally, and not needing any sort of certification papers it could probably cost even less...

Look on the bottom of your torque wrench handle, most have a cap there to remove which I believe is where they get adjusted. However, I really don't recommend fidgeting with it.

What do you mean 'hand held scale'? Do you have one of those testers or were you comparing to an old school split beam torque wrench?

IMO it seems within spec, I would not mess with it...

 

[GT350Mike]

Haven't considered sending it anywhere to have it calibrated because they would probably come to the same conclusion that I have.

The scale is an analog scale used for checking the weight of luggage. Sometime this evening I'll use some 25lb and 35lb gym weights to determine if the scale is accurate. The video link below demonstrates the method I used to test the torque wrench (fast-forward to 3:15). I measured out from the center of the anvil out 17", set the wrench at 54 lbs and mounted it on a socket that was locked in on the vise, then pulled until it clicked. The scale registered 40lbs so I multiplied it times the distance from the anvil (17"), then divided that number (680) by 12. The final number was 56.6 lbs. I used the same method to test my HF 3/8" torque wrench set at 25lbs and initial, the scales were reading about 27lbs. Since I could remove the cap screw and adjust the wrench, it's about as accurate as a $15 torque wrench is going to get.

Assuming the scales are accurate, the Craftsman torque wrench is within 5% of the reading so if that within a normal, acceptable range, then I'm good to go.

On a side note, the next tool purchase will be a 1/4" torque wrench. At the moment, I'm thinking of a digital wrench offered by Summit for about $100 which is about max for what I want to spend. If anyone has any suggestions, I'm all ears.
https://www.summitracing.com/parts/bkm-15-2148

 

[bob15]

On a side note, the next tool purchase will be a 1/4" torque wrench. At the moment, I'm thinking of a digital wrench offered by Summit for about $100 which is about max for what I want to spend. If anyone has any suggestions, I'm all ears.
https://www.summitracing.com/parts/bkm-15-2148

I would look for a new or used 0-300 in/lb or 0-25ft/lb Snap On or Seekonk dial torque wrench. I am not a fan of the digital type......I think a straight dial (or beam-type) is the best, especially when dealing with small torques.

 

[EOC_Jason]

Most torque wrenches will say in their manuals what their "claimed accuracy" is at *at least* one value/range... Some will give two or three ranges and have difference accuracy for each... Most from factory are "claimed" to be within 3-4% usually... You are at 5% after using it for ~20+ years...

I'm sure in your testing there is also some error that gets introduced like if the luggage scale is truly accurate at whatever weight you are testing. Also making sure you are EXACTLY 90-degrees when pulling... Heck even ambient temperature comes into play...

I still don't think something that close is worth messing with. Maybe in another 20 years...

As for the smaller torque wrench, what ft/lb or in/lb range are you looking for?

 

[BillK]

Mike,
How accurate it your luggage scale ? How close are the 25lb gym weights ? I bet that neither one is as close as you think. Unless you have real calibration weights you just dont know.

I would agree with the others that if you are within 2 lbs at 54 lbs that is well within the original accuracy of the torque wrench. I sure would not be worrying about it.

These are the specs for a $500 Snap On wrench:

• Torque Accuracy: +/- 2% CW and +/- 3% CCW, 20–100% of full scale; +/- 4% CW and +/- 6% CCW, 10–19% of full scale; +/- 4% CW and +/- 6% CCW, 10–19% of full scale

 

[GT350Mike]

Looks like I'll have to wait a few days before I can check the accuracy of the scales because my weights are MIA.....seems like everything I own is free game to my sons. When I do get around to confirming the accuracy of the scales, I'll post the results. Since I only paid $8 for the scales, my expectations are pretty low.

Anyway, based the comments I'll be content with what I've got. Thanks everyone for the feedback.

 

[InsanePyro]

Buy this and never look back

https://store.snapon.com/TechAngle-...que-Wrench-12-5-ndash-250-ft-lb--P760213.aspx

 

[m3bs]

I have a similar wrench that I bought in 1978. I had access to a calibrator for many years. Every time I checked it it was off a consistent 4% across the entire range, so I just adjust my settings accordingly. It’s getting hard to read the setting through the little window....

 

[GT350Mike]

Buy this and never look back

https://store.snapon.com/TechAngle-...que-Wrench-12-5-ndash-250-ft-lb--P760213.aspx

I appreciate the recommendation but that's way too good to collect dust in my toolbox. There's an old saying "Buy once, cry once". If I bought that, I'd cry like a baby for days.

I have a similar wrench that I bought in 1978. I had access to a calibrator for many years. Every time I checked it it was off a consistent 4% across the entire range, so I just adjust my settings accordingly. It’s getting hard to read the setting through the little window....

I'm having the same problem.....I think the numbers are getting smaller.

 

[InsanePyro]

I appreciate the recommendation but that's way too good to collect dust in my toolbox. There's an old saying "Buy once, cry once". If I bought that, I'd cry like a baby for days.

I have to admit I don't use it much. Maybe once or twice every few months. But man, when I do, its nice knowing everything is top notch. And it self diagnoses itself everytime you turn it on and will tell you when/if it needs to be calibrated. And it lights up like a christmas tree and vibrates when you hit your desired torque spec so if you over/under torque something I dunno what you were doing.

 

[EOC_Jason]

I just got in one of those Luggage Scales off eBay, I bought this one, a little different than the youtube videos.

https://www.ebay.com/itm/50kg-10g-P...-Luggage-Scale-Electronic-Weight/332118972296

I folded the strap in half lengthwise and used some painter's tape to keep it like that. I wasn't sure what effect having such a wide strap would be on accuracy so that's why I folded it.

I tested it against some weights that I verified with my two postal scales.

Anyhow, took a few measurements on my Husky 1/2"-Drive 50-250 ft/lb, it was around 1ft/lb but that's well within the margin of error from my setup. I have an older Husky 3/8"-Drive I think is 30-120 ft/lb, it was maybe 2ft/lb low at most. And finally my Armstrong 30-250 in/lb... Had to pull real slow but it too was very close.

Overall I'm satisfied for a $7 scale... I was worried my big husky might have been off when I was torquing the tires on my truck it just seemed like it needed a lot more effort than when I was taking them off. Last time the dealership rotated them, so either they didn't torque them to the spec 140ft/lb or they loosened up some.

 

[1redTA]

how accurate does your wrench need to be and to what percentage of deviance is acceptable to you? if you’re going under water or outer space I think it is ok ��

 

[loannbks]

Sorry I wish this response could have come out sooner. I had to recently play with my very old Digitork (model #44546) to find out my way to calibrate it. There are 2 small screws hidden under the outer end of the handle’s rubber cover that need to be taken out before you can pull out the whole torque setting mechanism. The torque reading dial is a metal drum that is held tight on the long adjusting screw by a nut at each end. Calibrate the wrench your own way (e.g., torquing it against another, reliable torque wrench) and readjust the drum to show correct settings at the glass windows. Hope this helps.