When you press E-Stop or power off your machine, it is possible that the Z axis can lower under its own weight towards the machine bed. This is most common on Q-Series machines with the ATC-2200 spindle and on M-Series machines that are equipped with ball screws.

Why does it happen? The ball screw system on the M and Q machines was designed for very smooth operation to allow the Z motor to be very responsive and provide excellent resolution. There is very little friction in the Z axis assembly on a ball screw machine. Because of this, the weight of the spindle can naturally cause the Z-axis to lower under its own weight when the Z-axis motor is not energized.

How do I resolve this? On the M-Series machines, there really is no direct resolution for this. You should make common practice on any CNC system to home all axes when you power the machine on or before you start using your machine on a given day. This way you can always be sure all your axes’ positions are recognized by the software and this is the best way to ensure that you have no issues with your Z height during your jobs.

Additionally, you should make sure you remove the tool holder (on Automatic Tool Changer spindles) before you power the machine down or remove the end mill from non-ATC spindles. Additionally, you can place something to support the Z Axis under it, such as a block of wood to prevent it from falling all the way to the table.

On the Q-Series machines, we have a solution that can resolve this issue as well as increase the performance of your Z axis during rapid Z operations such as when 3D carving. Please contact support@stepcraft.us for more info on this. Outside of this, the same applies to the Q as with the M, you should make it a common practice to home all your axes when you power on the machine or at the start of your work day.