Quote Originally Posted by michaelhigh View Post
Probably about $40 in parts (the scope example was to simplify explaining hi-impedence). In addition to backlash, it could also be used for more accurate limit switches, and home positioning. 1 pulse from it should equal 0.000125" worth of travel, and ive yet to see a mechanical "home" switch have that accuracy. Also, it would simplify realigning after an e-stop, for example if the servos trip during a high speed jog, or power failure it would allow you to resume from the exact position where it tripped. Also, in addition, if it works, would be able to provide realtime info on the backlash over time, ie in its simplest form, a led lights up when it gets over "x". Electrically I know its sound,, the point of the post was to ask what I dont know, for example is the mill always 8000 pulses per inch, or can that change over time, (also, the pulses on the encoders match the steps in the motor, as I bought the all in package from taig). That said, it did just occur to me, it wouldn't work for backlash, as I thought about if the locknut wasn't tightened down.

Backlash is the mechanical difference between the leadscrew (ballscrew) and the actual table position when measured in both directions. In other words, there might be enough mechanical looseness in the system where reversing the direction of the leadscrew does not instantly move the table the expected amount. Normally you would measure this with a dial indicator, but it can be done electronically also.

A combination of linear scales and the rotary encoder on the motor shaft would be needed to read this difference. This allows you to compare the actual table position to the leadscrew position.

Without some serious mechanical issues, if 8000 pulses per inch is correct today, then I would expect it to also be 8000 PPI 10 years from now.

There are some high precision mechanical switches available that are supposed to be repeatable to 0.0005mm (0.00002'') https://www.automationdirect.com/adc...eat_accuracy)# But this kind of repeatability would be way overkill in a normal home shop.