T8 Brass Nut not staying in place (Raising & Lowering)


This is my first post here. I assembled the MPCNC during the winter and just started working on it again but I’m having an issue I cannot figure out.

During a cut while the MPCNC is raising and lowering the z-axis, the T8 brass nut is not staying in place. When the z-axis lowers, the T8 brass nut raises and pushes the screws up which prevents the MPCNC from cutting at the right depth. I’m not sure why it’s doing this and would appreciate in help in figuring it out.

Should I epoxy the T8 brass nut down to the plastic piece so it cannot move up and down?

Here are a couple videos showing the problem (Caution videos are LOUD):






I think I just put a few lock nuts underneath to keep it from pulling out of the plastic.

I would say a drop of locktight or super glue will fix that. I use 1-2 10mm screws and have cut from wood to steel and never had an issue. I have not seen that yet, if you printed them I would check your printer out. More concerning is it should not have much pressure in that direction, you are backing out 4 very long screws by the force of a spinning blade on soft wood… are you using and endmill that is for plunging (or maybe it is made for a different rotational direction?)?

I’m very new to the CNC world so I don’t really know much about the endmill. Here’s some pictures of the one I was using (these are the only ones I have used so far as well). I just bought a cheap variety pack off amazon and these came with it.

Amazon link:




It seems like the movement is stoppet very precisely.

I would check the lower spacer. Maybe it has turnednand stops the z-rod.

Thanks for the help guys. Some locktight underneath the T8 brass nut and a different endmill solved the problem, I have been running it for a few hours since with no issue.