Anybody here know about strain sensors and the like?

I don't think you'll find anything for $100 that'll last long in a machine shop.

But that's just me being dismal.

You may be able to toss something together from parts for that much, without the wireless part.

It's fun to think about one device with two orders of magnitude dynamic range at low cost. Heck, let's make it wireless.

Do you REALLY need all that? How much accuracy do you really need? Wonder if you can't get the job done by monitoring the motor current?

I don't know exactly what I need and maybe two sensors are required. But this is for tap sizes from 2-56 t0 1/4-20. I think I already have the wireless part figured out. Do you know of any sensors that would work for any part of the range? Can you at least point me in the right direction? Current monitoring might work but I need to be able to measure the tapping torque on several different machines. Thanks, Eric

Do you actually need strain sensors, on the few occasions I've looked at them they looked like trouble unless you were doing them frequently. In the past I work for a company that made force and torque testing equipment and under $100 doesn't seem reasonable.

I'm wondering in this case if you could use something like a power steering sensor idea where you have a bar transmitting the torque and measure the angular displacement due to the torque transmitted with a simple potentiometer. You might have to make and calibrate it but that's half the fun.

Even easier would be using two "tone" wheels or encoders at the top and bottom of the torque bar. One wheel generates both RPM and angular position data, the other wheel generates position data. with the rpm known and the relative change in the angular position as a function of time it should be easy to calculate the torque load and calibrate the time offset using dead weight testing.

The usual method is to physically bond a couple pieces of carbon to a "window" that's been machined into your test link so that whenever the link is stretched they will change resistance a little, another two resistors are added that do not get stretch and the whole works are wired together making up a circuit that's called a "wheatstone bridge"

HTH

It is a solved problem for sure. They put a set of four strain gauges around the diameter, connected in a bridge, with gauge long axis at 45 degrees to the length. When the rod is twisted, one set of gauges lengthen, the other set shortens.

If the rod is rotating, one find a wireless way to get drive onto the rid and torque signals off the rod, because the strain gauges are spinning with the rod.

There are many books on how to use strain gauges.

Joe Gwinn