Setting Torque on Torquing Screwdriver

[Mark L]

I recently bought a CDI 4-40 in.lb. torque screwdriver, the torque can be adjusted with a allen wrench through the butt end of the driver. A torque tester is recommended for setting the desired torque. Of course, I may use this tool in a way that I will often change the torque breakaway. A torque tester is an expensive piece of calibration equipment (~$1000 or more). Wondering if anyone has ever used a calibrated torque wrench to set the breakaway. The range or variance is 3-4 in lbs on the driver. Any thoughts?

[DaAV8R]

Why not build a simple little calibration tool. Use a horizontal lever arm on a pivot point. Fixed length arm, say 4". Place a 1# weight on the end of the arm and the screwdriver at the pivot. Start at the low end of torque and slowly sneak up on the 4 in/lb. When the screwdriver can just rotate the arm, you have 4 in/lbs. Add weight as needed to adjust the torque or moment. Weight x Arm = Moment. Nothing more accurate than a lever and a little weight.

[rubber314chicken]

Originally Posted by DaAV8R

Why not build a simple little calibration tool. Use a horizontal lever arm on a pivot point. Fixed length arm, say 4". Place a 1# weight on the end of the arm and the screwdriver at the pivot. Start at the low end of torque and slowly sneak up on the 4 in/lb. When the screwdriver can just rotate the arm, you have 4 in/lbs. Add weight as needed to adjust the torque or moment. Weight x Arm = Moment. Nothing more accurate than a lever and a little weight.

If you use an arm of any significant mass, you are gonna have to include the arm in the torque calculations as well. As long as its homogeneous, you can just use the center and the overall mass of it as the arm and the force, respectively. With this setup you'll also have to make sure that it is vertical and you don't turn the screwdriver too fast because then you'll set the torque on it too high (this setup will have a large moment of inertia, especially compared to what you'll be torquing)

A setup that might work a bit better would be to put the arm on a workbench and a fish scale at the other end. Then you turn the screwdriver slowly and see what it measures on the scale. Would be easily to control IMHO. Just make sure again that you don't turn it too fast (again, you'll set the torque too high)