Jitter/Shake LR4

LowRider CNC Troubleshooting
1

Hello!
I’m doing some of my first cuts with the LR4.

Disclaimer, never used a CNC, never used 3D software, never did Gcode or any of that type of stuff, so I’m as green as one can get, everything is a learning process.

So I cut my strut plates first, everything went id say perfect, they were 0.1mm accurate, cant get better than that. I used the post processor that was shared in the forums, so I didn’t know much about pre-setting. The machine ran at 1000mm/min. It had some jitters and shakes but I could only notice it on the belts and not the gantry or router.

So yesterday I got to cutting the torsion box parts. I’m cutting with a 3mm single flute, extra long 18mm OSB, 17k rpm 2000mm/min 1.5mm passes.

It’s cutting pretty darn accurate again, within 0.1-0.3mm accuracy at the full lenght. (Cutting area is 2500/1250) But at this speed and rate I notice jittering/shaking, the gantry and makita move pretty fast but they have a very shaky jittery motion, the cut is clean I don’t notice the quality being degraded but I guess its hard on OSB as its a wavy material to begin with.

Everything was cut perfectly, if I don’t include the part where I went to brush my teeth for 3 minutes and the machine decided to try and derail right at the last piece, I couldn’t really figure what happened, but I guess my dust hose got caught with the X cable and got stuck and started skipping and twisted. After that it fell straight through and the router plunged all the way down to the collet through the table because it derailed, happy I didn’t have the belts too tight as I would probably have had to to some major fixing.

BUT, it’s fine now. I ran a G code for another thing to cut, girlfirend asked for a step on the toilet for ease of pooping, to check if the machine is fine. It cut it pretty well, there was some tight spots but I’ll give it my fault from my 3d sketch and gcode.

Ive tightened the belts the following way, I ran both axes to their furthest lenght so the belt is at its longest, pulled it by hand to remove slack, and tightened it to the point untill the belt became flat, aka all the teeth are facing the wall, however i did not tightenn it as much as so it doesn’t have any droop at full lenght. Id say it droops almost maybe 1.5cm droop in the middle. I just tightened so it didnt touch the table and so it runs flat/straight when you look lenghtwise.

I didn’t find another topic about LR4 for this and or a fix or if its normal so Im writing this one.

I’ve attached a picture close of the curve cut, also some of my fk up where it derailed at 95% done, the cut after that mishap looks smooth but the machine just looks that it will eventually get it’s nuts and screws loose from jittering, it jittered the same way before it derailed, its not something that happened after the crash.

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2

The belts shouldn’t be tight, they are always a bit loose.

A video of the shaking would help. :slightly_smiling_face:

3

Will whip up something to cut after work today. How can I upload a video here though it doesn’t allow me?

4

Youtube, Google and link it. :slight_smile:

5

So I’m unable to reproduce that jitter while cutting replacement parts from the incident, it went away for now somehow. I don’t know if it’s the different material I’m cutting, but I’ll check this week when cutting the table base from OSB. It was doing it on large oval shapes in osb first time it occurred.

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6

the only thing I can think of on an inconsistent basis like that, wiring. Make sure ALL connections are good. While moving, if a connection is loose, it can cause all kinds of chaos.

7

Yup, checked immediately after the derailing incident. All connections seated and ziptied so if even I pull on cables, they won’t move. It’s cutting butter smooth right now as im writing. At first I thought it’s the feedrate, then I thought it’s the belts.

After some more digging around, I found I forgot to set the tolerance on my last code higher. So I don’t know if the very tight tolerance could have given it some data starvation or idk, I’m not well versed in this. Now it’s set to 0.025mm and it doesn’t jitter, on last file I forgot to change it from the default 0.010

8

re what @RockinRiley said , its not always at the connector can be a break min way along wires inside the sheath, causing it to jitter , my X started to gitter, grind yesterday 5 hrs later :frowning:

i found it mid way along the extension cable when i moved it ,X gittered

only way i found it was to run an air job and run along each cable wiggling them as u move along , pain staking task , changed cable prob sorted

9

It seems to be a tolerance thing. When I set it and it was left to 0.010 it starts to stutter, it still cuts about perfectly, however it jitters and vibrates. Just a simple increase to 0.025 eliminated it for me, I don’t know if it’s some data bottlenecking happening, but I don’t need 0.010, not even 0.10 tolerance so all good.

What tolerance do you guys set for your cuts?

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10

Oi, small detail to ask, machine does vibrate again after some time, but when setting the belts, I pulled the machine all the way to the endstops by hand and then tightened the belts on the other end, should I set the belt tightness on it while it’s on actually? My belts might be just too floppy and cause this jitter at 2000mm/min? https://youtube.com/shorts/sh3_9Rvh5Fo?is=kLTnAe2T4SbfIuey

It’s hard to notice it on the video, but the belts flopping and the cable track on X shaking shows it more to the camera, with the eyes it’s more noticeable, and when I touch the gantry I can most definitely feel serious vibration/jitter.

edit: Another observation from today, after Gcode finished, machine moves real fast back to XY-0, it has no jitter or vibrations when it speeds through the air back then. So it does it only when cutting through material.

11

Welp, on it’s 6th sheet, it skipped steps. I tried lowering the rpm a bit, since I started suspecting the bit might have dulled from it’s first oopsie. But I guess lowering it made it skip steps. I’m trying to recover somewhere along the sheet but for now the forecast is it’s going to be firewood :face_holding_back_tears:

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12

Seems I’m over here spamming, but I’ll eventually get to the bottom of it. So today I had Y skip steps, decided to tighten the belts more. Ran it again, X skipped steps, tightened X. No more skips, Jittering was a bit less, but still significant vibrations and jitters.
Then I learned more about cnc, I have the long 3mm bit from V1 shop. I’m currently cutting below the level of the board which the cnc is riding, because I have no spoilboard yet. So I can’t use any of the other bits, since the machine bottoms out way before they can cut through the material. So i Ran the long bit. I don’t remember how I set it up the first time, but it was hanging quite the lenght below the collet. Now I lowered it Untill the machine bottomed out, raised it by 2mm, and tightened the bit at that height while touching the board which will be the bottom of the cut. Now it sticks out 30mm from the collet, still a lot, but a bit less than before, so maybe all this jittering and vibrations came from bending/deflection of the bit back and forth, combined with maybe too loose belts might have caused all the combinations of issues, thats the guess for now. I have 2 more OSB sheets to cut to finish the table and then I’ll be able to run shorter bits as the current setup is so wonky that I physically cannot put a spoilboard as the weight will fold the temporary tables under the machine. Maybe the bit got dull aswell. I have no idea how long I should use a single bit for, I’ll have to ask google.

Basically the table surface is the temporary spoilboard on which a spoilboard will be attached to.

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13

please don’t burn osb, the pollution from the glue is terrible for the environment

14

@WaffenTreager , sorry, I don’t have a LR4 yet so I don’t have much insight. But it seems like your vacuum hose might put a bit too much tension on the router at certain positions. Have you tried running it without the hose? You could manually follow the cutter with a shop vac hose during this test. That would at least rule out the hose.

15

It’s only got very very slight tension but I wouldn’t even call it much at the furthest corners. It jitters when the hose is free aswell. I just chucked a new bit on. Waiting to see how it goes. The previous one seemed gummed up from the resins in the OSB.

16

Seems to have been a combination of many things. 1 and 2 are most definitely the bit becoming dull and also using a very long bit which combined with even the slightest dulling starts to deflect and bounce back and forth. The next thing is resin buildup on the dull bit. And the last thing, which I have no idea if it was contributing or not is loose belts. Although I did successfuly cut three sheets before beginning to have any issues. However even then I did notice the belts flapping up and down and around like a jumping rope. When the jittering and vibrations started, the belt flopping became even bigger. I hope I didn’t overtighten them now… Someone should post a picture or video of belt tightness, and how they look :sweat_smile:

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17

I don’t even have where to burn it, it’s just a metaphor. But I’d still like to share, every sheet I managed to screw up a bit I have not yet scrapped, somehow managed to save it every time. Re-home, tweak the g code to remove the cut parts, run again and it was spot on each time, exept one :rofl: