My MPCNC Primo with Makita spindle ran fine for the last weeks but a couple of days ago a got time-greedy, lowered the travel security distance of the Z-axis and worked through a metal clamp. Since then, the Z-axis is making jumps when being lowered very deep.
Thought that the lead screw might have bent or the grub screws somehow are not in perfect position any more.
So I took of spindle and dissembled lead screw and the feathery aluminium thingy above it from the z-stepper motor.
Found out, that the lead screw does not rotate completely centered when doing so manually. It’s not bent though. The aluminium thingy was a little stretched to one side, pressed it tightly together, seemed fine again.
Put everything back together and wanted to lower the Z-axis tubes in the core element but now the lower front bear rings won’t let the tubes through. When I force it by manually spinning the lead screw hard, the aluminium thingy above the lead screw stretches a lot and I am afraid to break it. Please see this video of the problem: MPCNC z-axis trouble - YouTube
It appears as though your lower z bearing clamp wedges are too tight, or the z tubes are out of parallel. I would first verify the tubes are parallel, then loosen the lower bearing wedges to reassemble the core. After it’s all together, repeat the squaring/tightening process on the z tube clamps to ensure proper operation.
On a sidenote, your lower z bearing mount looks too low (big gap between the bearing and the springy thing). Ideally, the bearing should be touching your z coupler with the slightest amount of pressure. Having any gap there allows the router to be lifted by milling forces. This may not be that noticeable for some things, but it will be a problem if you ever use a downcutting bit, or higher downward z acceleration sometimes used for 3d operations.
Hi Kev,
Many thanks for your advice and observation regarding the lower bearing mount.
I will check parallelism of the z tubes first and report the results. Further I will increase the height of the lower z axis bearing mount to slightly touch the spring thingy.
To describe the potential cause of the failure, I should add, that before the crash into the metal clamp, the z axis tubes two times went into the metal clamps until I learned, that I need far lower clamps on the far y side of the working piece with this kind of machine setup.
First time, I didn’t notice but the milling path was far off and the resulting piece of wood looked tragically.
Second time (same job), I was aware but thought, something else caused the problem, I could react fast though. Because of observing, I saw, that the z tubes rammed the screwd down clamp which put a lot of force on the whole machine. What do you pros’ think might have got damage by that else than z tubes and lead screw?
I pushed the upper tube holder back to its original position, slightly touching the feather thingy. Thanks for mentioning.
The tubes are still parallel.
Truglodite, I didn’t get your recommendation “then loosen the lower bearing wedges to reassemble the core.” Aren’t the lower bearing wedges the little wedge shaped printed parts through which the screw goes that holds the lower z bearing? If so, what do they have to do with the core? If I loosen them, the core is still completely intact. Do you recommend to take it apart and reassembling + squaring/tightening it?
I realized that when manually rotating the lead screw, it’s lower end circulates in a wider circle than it should. Please see this video:
But the lead screw itself seems super straight, no funny appearance when rolling down a plane surface. Could it be fixed a bit skewed by the grubing screws hitting the thread of the screw and is totally normal?
Wow Kev, you were right from the beginning. I read this sentence like “the wedges are too tight. The wedges are faulty”. And I thought that’s a result of the accident. But actually, I just tightened the screws too much. I relaxed them one rotation and everything works smoothly again.