Loose core troubleshooting

Hi, I have recently been getting a lot of chatter when cutting outline shapes in 3mm acrylic sheet (held down with lots of screws) with a 3mm end mill, 0.25 DOC, 30mm/s speed, 12krpm approx. No melting but lots of chatter to the extent that the end mill/core jumps several mm off the intended path.
I think its down to a loose core:

What bolts should I be checking/tightening on the core?

Kind regards, Carl.

Having no real experience with this yet but it looks like your leadscrews brass nut (on the top) is fully loose?

Yes, @Carlos is correct. The leadscrew nut screws have either come loose or have stripped out.

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What type of end mill? For my LR3, I normally use single flute carbide upcut for most materials. But for acrylic/polycarbonate I’m finding down cut bit better at helping to hold the work piece down during cuts/contours.

With down cut bits I also ended up reducing Z plunge per sec, and am over drilling hole depth. Down cut seems to take longer/more-force to eat through material than up cut that pulls material towards it. I’ve not tried compression bit yet.

Thank you for your reply. Yes, they are loose in the video because i am lifting up the router to show the wobble. They are normally well seated when the cnc is in operation.

Its a 3mm single flute upcut. But the issue I am trying to fix is the wobble in the core.

I had this issue on my primo. I ended up very slightly tightening each of the 4 clamps along the back. Maybe 1/8 turn each and seeing what that effected. Also I believe I tightened the 4 outer clamps on the core (just either side of the router). again very slight tightening and seeing where I still had wobble and where I didn’t. it took some time but I got it to all stiffen up and work much better without putting anything in a bind.

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Ah, didn’t realize that. Second area would be the core clamps as @Jonathjon stated. I had a similar issue and it turned out that they were cracked. So if their bolts are tight then check for any cracks.

One of the core clamps could be broken or, if not broken, at least not fastened enough. That kind of wobble only happens when those are loose.

Jonathan, Thanks, I shall check the clamps and bolts. Kind regards, Carl.

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Philipp, Thank you, I will check these. Kind regards, Carl.

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I have similar issues periodically. I check all my bearings now as a preflight before running. Make sure all bearings are touching the tubes first. Take your z axis off to gain access to the core bearings easier. You may need to snug them all up slightly, but feel how they are first. Look for cracks, but i have never found any. Contrary to popular belief, nylock nuts do loosen up over time, especially when vibration is involved. Then reinsert the z axis and check the z bearings the same way. Finally check the tool mount to z axis fasteners. I had them loosen up not too long ago too. Last step is to tram it and then make some chips!

Matt, your advice is appreciated along with everyone else’s. I will take onboard what has been suggested, investigate and feedback soon. Kind regards, Carl.

I had some time to investigate today and found that the four Core Z Clamps had become really loose. So I tightened these up a bit (not too tight). Also the four Core Clamps for X and Y needed tightening up a bit along with their tension bolts.
tested and all seems fine now:-)
Thanks all for your suggestions.
One thing I noticed during this maintenance (and have noticed from first building the machine) is that the four inner Z bearings in the centre of the core hardly touch the Z tubes:- they don’t spin when manually lifting and dropping the Z rails. Whereas the four bearings in the Core Z Clamps make good contact on the Z rails. It does not appear to manifest as a problem during use but why is there mis-alignment? Any ideas?

I’m going to have to look closer at mine, but i believe they all touch on the z axis.

Pretty sure the ones you referenced are too tight as all mine touch and turn when z axis moves up and down.

I was having a brain fart last night on the configuration of the z bearings in the core. All should touch and turn. Yours are either too tight or something else is wrong, because they should be touching and turning.

Yes, they should all turn.