Z-Wobble but everything seems tight


I have build my MPCNC a few month ago and already had some good success with it. I only have one problem I can’t really solve. When slotting semi hard materials like wood, aluminum and plastics the Z-Azembly randomly starts vibrating. If I don’t immedeatly dampen this vibration by grabbing the running router with my hand, it usually gets worse for some seconds until it vibrates massively (sometimes I guess more than 1cm), the bit snaps and the part is ruined.This only happens when milling slots. When the tool is only used on one side it’s working perfectly and with pretty good accuracy.

For some materials I found a way to eliminate this by reducing the stepdown to 0,3mm, but with other materials this doesn’t help. To me it seems like the problem is that when doing multiple stepdowns the tool starts rubbing along the walls until one flut catches and throws the tool to the other side of the slot and from this point on it never stops without grabbing it.

Has anyone else this problem? Or does anyone know what could be the issue? One way I found to minimize this, is by increasing the rpms to the maximum and going slower. But this doesn’t always work, because for example in plastics the will start melting when doing this. Looking forward to any ideas.


Kind Regards,


Is you bit perpendicular to the work? If it’s at an angle, it can be grabbing a full length cut when it gets deeper. Ryan had a 3D printed part for the 660 collet that would help you see any problems eith perpendicularity. It was just a bolt extended 4" or so away from the collet and when you rotated it, it would touch in the low spots.

In materials like aluminum, there are milling strategies like trychoidal milling or adaptive clearing to never do just a slot when cutting out a part.

You didn’t mention a speed, but you could also try fewer, deeper passes but slower. That stuff gets into the dark arts part of milling a bit more.


Thanks for the tips. I will try to also print such a thing and test it my perpendicularity.

Going deeper and slower is also an idea I will definitely try out. I’m changing my speeds alot while also trying differnt doc. That’s why didn’t mention them. For carbon fiber I usually go with 0,3mm doc and 600mm/min. I never had issues with these numbers in carbon fiber. Only softer materials seem to be a problem.

I use Fusion360 CAM and unfortunately there is no trochoidal strategy as far as I know. I could use adaptive, but then I would have to model my stock with slots in it instead of just the part I need. I never really wanted to do this but if its the only possibility I will try that.