View Full Version : dropping Z axis

02-22-2015, 04:36 PM
Hello guys, Im pretty new to this cnc mechanics. I have been getting a Z error when i power down but didnt think anything of it, cause i couldn't see anything physically moving, But the last time i used my machine it dropped in the middle of a toolpath. so i brought my spindle up and powered down, then noticed that the spindle was dropping alot this time. so i was wondering if they are both connected somehow.

02-22-2015, 05:14 PM
Sounds like you have two separate problems.
#1: when you power down the stepper driver the z axis lowers and hits the table? - It means you have enough weight on your z axis to overpower the powered down stepper motor resistance, and gravity just takes over from there. Best way to overcome that is counter balancing the z assembly using some type of pulley system, air assist, or gas struts are the common ones. This will also effect problem 2

#2: If you find the z axis slowly drifting down throughout your cut, its possible your loosing steps , meaning everytime the z move up it doesn't go as far as it thinks. usually caused by too fast of motor acceleration, mechanical binding in the drive screw, under powered motor for the carriage weight or slippage in the motor to screw coupler. If the z axis just dropped a large amount at one time its probably a loose grubscrew on one of the couplers causing slippage.

Counter weighting the z carriage will help with problem 2 as with the right system you can get the z assembly to near weightless which will allow higher speeds and accelerations.

02-22-2015, 08:27 PM
ok thanks for the feed back. the dropping when the power is off is a new thing. ive been using the table for a few years now. and its never dropped before, a few days ago.

02-23-2015, 09:42 AM

If this is one of our machines, feel free to send us a note and we can help you out directly. If you have a Dumpster ACME nut, you may need to re-tighten the plastic nut into the aluminum body and tighten the jam nut and set screw.

The Dumpster nuts will wear with time and can get to the point where you can back-drive the axis with enough weight. A counter-balance system can definitely help (and can speed up your axis on up moves), or there are some other tweaks we can help you with.

Best regards,

CNCRouterParts (http://www.cncrouterparts.com)