I was about to torque up all my bigend and mains bearings (hopefully heads this afternoon) when I thought "How accurate is this torque wrench I had had for 35 years?" It has undergone a lot of abuse over the years but was a expensive tool when I bought it.
So I thought about calibrating it a came up with an easy method. I anchored the sq flats of the 1/2" drive in my vice and had the torque wrench sticking out at 90 deg away from the bench. There is a steel ring in the end and I measured from the centre of the sq drive to the ring, it was exactly 18" (1.5 ft). I thenset our digital bathroom scales to 'lbs' and put iton the floor directly under the ring, set the torque wrench to the 1st calibration point of 40ftlbs (sorry wrench is only has imperial settings).
I then stood on the scales the scales read my weight (205lbs) and then progressively pressed down on the ring until the wrench 'clicked' and recorded the weight shown on the scales. I did the measurement 3 times for each setting then repeated it for settings up to the max. By taking the difference between my weight and the weight the scales showed when it clicked and multiplying by 1.5 (effective length of wrench) I got the actual torque being applied.
Results were surprisingly accurate at top end but quite a long way out at the lighter settings. Calibrating the wrench this way allows me to compensate for the inaccuracy when torquing bolts to the lighter range.
- Alan
So I thought about calibrating it a came up with an easy method. I anchored the sq flats of the 1/2" drive in my vice and had the torque wrench sticking out at 90 deg away from the bench. There is a steel ring in the end and I measured from the centre of the sq drive to the ring, it was exactly 18" (1.5 ft). I thenset our digital bathroom scales to 'lbs' and put iton the floor directly under the ring, set the torque wrench to the 1st calibration point of 40ftlbs (sorry wrench is only has imperial settings).
I then stood on the scales the scales read my weight (205lbs) and then progressively pressed down on the ring until the wrench 'clicked' and recorded the weight shown on the scales. I did the measurement 3 times for each setting then repeated it for settings up to the max. By taking the difference between my weight and the weight the scales showed when it clicked and multiplying by 1.5 (effective length of wrench) I got the actual torque being applied.
Results were surprisingly accurate at top end but quite a long way out at the lighter settings. Calibrating the wrench this way allows me to compensate for the inaccuracy when torquing bolts to the lighter range.
- Alan
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