Z Axis Plunging Too Deep (Solved, But I Have a Question)

I was having the issue that is described in several other posts where my z-axis was plunging into the workpiece more deeply than it should have. Upping the stepper driver voltage on the z-axis driver solved the problem for me, but I’d like to make sure I understand why…

Was this a timing issue? Was the z-axis unable to rise to it’s intended height between cuts in time for the next move, causing it to plunge more deeply on the next z-axis move due to the intended height never being reached? Or is it due to motor stalling, where the z-axis stepper is unable to turn the shaft to achieve the intended number of revolutions? If it is the latter, is the stalling due to resistance caused by the tool against the workpiece?

Just for fun, I’ve attached a picture of one of the workpieces where I experienced the unintended deep plunge (Eunice is what I’ve named my machine; machines run better when named).

I think the problem your describing is the load on the stepper motor is too much and causes the motor the skip steps. Steppers do not provide feedback to the controller, so if the controller tells the stepper to move 10 steps, and it only moves 5, the remaining commands are all off. In your case, if the stepper moved 10 steps down, only 5 steps up, then 10 steps down, etc, it will make deeper and deeper cuts. It’s takes more force to accelerate a mass up, than it does to accelerate down, so it’s more likely to skip steps raising.

The problems that cause increased load can be friction in your Z axis, and or the stepper accelerates too fast. To solve this, you can increase the power on the stepper control as you did. The down side is your driver creates more heat so there is a limit before you need cooling. You can also look for something binding in your Z axis, like loosen the anti-backlash nut. The acceleration is set in the firmware and can be reduced if nothing else works.

Hope that helps,

You have all the weight of your spindle helping the motor when it’s trying to go down, but when you want to go up the motor is having to overcome any inherent friction AND the weight of your tool is a detriment.

Also, if you’ve been using the machine long enough - about a month after I first started using mine I had a crash that was caused by the coupler wearing in such a way that when it turned one direction it caught the all thread and made the axis move, but going the other direction (up), the coupler was just rotating around on the shaft of the stepper but not making the all thread turn. Something about the way the threading on the all thread ate into the PLA coupler that caused it.

Thanks guys!