Hello,
I have a problem with my MPCNC… I am in love with this machine but also very annoyed, i mean that goes hand in hand with love
So my biggest problem is, that the middle unit shakes/stutter , the speed is irrelevant the mpcnc shakes always, if I go a little bit faster (1000m/min) the MPCNC shakes so bad that the entire table starts vibrating, so i always have little tiny waves in my piece.
The second problem is that the surface is not flat after i tried surface milling a woodpiece. The weird thing is that is always accures after the mpcnc changes the direction. So the first path is high, the second one is lower that the first one, the third is even with the first path and so on…
That “chatter” is caused by the bit grabbing too much, and moving the machine a little, which causes it to grab more, until it overpowers the rigidity and starts wobbling around. Start by sharing some pictures of your machine, and sharing the machine size (especially the size of Z).
That bit also looks pretty large. What sized bit is that? Anything over about 1/4" and it should be really thin passes (like 1mm or less) to completely remove any load. Also keep in mind that the surface isn’t going to be level, so if you start a 1mm pass flush at the ends, it could easily go deeper in the middle, and suddenly, you’re grabbing 3-4mm of material with a 3/4" bit…
The lack of flatness could be two things (off the top of my head). 1. Is the bit perpendicular to the XY plane? There is a perpendicularity tester that could help, but if it is at an angle, then one side will be higher than the other. You can either shim the tool mount so the bit is perpendicular, or choose much smaller stepover.
The second guess is that after you remove a lot of material, the stresses built up in the wood is causing it to bulge. This has happened to be before.
It looks like you’re milling back and forth, like mowing stripes in a lawn. That means the bit is climb milling in one direction and pulled into the work in the other, which will tilt the router slightly in opposite directions each time.
“It looks like you’re milling back and forth, like mowing stripes in a lawn. That means the bit is climb milling in one direction and pulled into the work in the other, which will tilt the router slightly in opposite directions each time.”
That makes sense!
It is not that the mpcnc does not work, actually i have good results, but i like to go a little bit faster than 600mm/min but than the mpcnc starts dancing and shaking… It does not matter wheter I mill or not.
I think that the stepper run smoothly but somehow the middle sections starts shaking…
None the less, I am already very happy! I did not expect to get these results and so fare I really can trust the machine never did something very bad, which was not my fault =)
I’ve also had one twist and warp while surfacing. Absolutely no fun and I’ll never do it again. Even taking passes at 0.5mm screwed it up. No point in a surfacing pass if it ain’t gonna be flat.
Anyway, I guess everything moved smooth before you hooked up the belts and motors? Just checking…
That’s not good, mine is set up to do non-cutting moves 10 times faster than that! IIRC it started to skip steps at about 8000mm/min. There must be some problem we can track down.
I’m too new to have seen any common failures that could cause it (everything seems to be loose pulleys!) but I’ll try some questions that might help the experts:
If you run one axis at a time, do the shakes occur at the same speed?
Is it smooth to push around by hand?
Are your motors wired in series or with individual drivers?
Okay,
I tried to record a Video but it is very diffucult to capture the chatter…
MPCNC chatterTroubleshooting…
I hope you can notice the chatter on the Video, the table is very heavy and stable. The MPCNC chatters even in slow speed! Everything above 800mm/min does not work because it shakes too much =/
Okay, now it should work. I feel a little chatter, even with the steppers off. Can it be the dust on the pipes and the bearings?
I will also add midspan support for more stability, what else can I do?
I wouldn’t worry about that kind of vibration until you get a reason to. The kind that bothers us is the rumbling type during cutting. What you have could even be from small imperfections in the pipe.
Lower the z until the bottoms of the tubes are level with the bottom of the center assembly(where it will be most stiff. Move a little in xy so all the motors will be locked up. Grab the collet and try to wiggle the router. If you have play or flex, it will be easier to track down this way. A little flex is normal, especially on larger builds but it will help you understand the machine a little better.
Also check that all the bearings are touching the tube and not free spinning. If you feel ok after both of these tests, gitterdirty!
