I might have electro-mechanical problems, jitter in cuts

LightBurn Hardware Compatibility
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This is gonna be a long one.

Several days ago i received my cutter. Giddy as all hell.
Machine specs:
Yellow/Gray round front case, controller set in at 45deg angle.
Ruida RDC6442s controller
CDWG 80W tube (replacement to EFR 100W pending shortly)
PSU MYJG100W (non-LED)
M415 stepper drivers, Nema17 motors, Y dualshaft thicker than X head one. Will get specs later (if there are stickers on them somewhere)
Air assist pump, water bucket/pump for start.
No idea about lens/focal length at this point. 7.7mm focusing stick.

So, i’m trying to cut thick paper, card more like (180+gsm?) and thats where i get problems. Whenever i cut round shapes i get wobbly lines all over the place.
I figured, maybe belts loose. Tightened belts a bit. No change.
Gantry/head moves freely by hand, doesnt appear to be binding or sticking.
Gantry motion (Y) runs on 12mm chrome rods on either side (not LM rails/bearings), X motion has a linear rail with a linear bearing. It was a bit of a surprise, i expected Y to be linear block/bearing as well as X. Go figure.

At the time i suspected air pump induced case vibration, as it was sat on the top of the machine. Put in on the floor - no change.

Also, my machine sits on foam insulated wood effect floor, it is a bit spongy. So, with a lot of effort, i moved the machine temporarily to other room with tiled floor, to completely kill any external vibration problems - got better but only by a hair - still prominent wavy lines in cut test circles.

Tried varying speeds from 400mms to 75mms (remember, were cutting paper, hence high’ish speeds) On both floor types - no change. At 400mms lost steps.

Acryllic cuts fairly well at 20mms/60%, didnt play much with it for now as i dont have much material to hand. Made maybe 8 oval shaped keyrings with 400mms engraving, no problems there (not that i know any better to discuss this at this moment). But seeing that cutting motion speed is WAY down same problems may not apply.

It is true that cutting paper is one of most difficult things to do on a cutter. And it appears its a good way to pull all the problems out into the light, fast…

When it comes to my experience working with XY machines, i used to run vinyl cutters back in the day, still have one in the house (Summa D60-R-FX). Also, more recently i got and learned ins and outs of 3d printing, by building and tuning/modding my plywood framed ebay special 3d printer. Thats where my stepper/driver knowledge comes from. But as i’m wading into unknown waters with big(ish) XY gantry bed, i must accept my ignorance in diagnosing problems. I’ve no experience in flatbed CNC other than 3d printers.

Attaching load of pictures. Notice red/white card design waviness, its NOT the design itself. Cutter is doing that. (biggest amplitude of the wave seems to be in Y direction). Thats why i just thrown out design and just drew 75mm circle in LB, offset inside by 15mm each to see how it would cut.

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Lens loose in housing?

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Nope. Checked that. That has already been brought to my attention in earler short post i made in Ruida controller forum (yeah, wrong place).

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That really does look like a loose lens. It could also be a loose mirror in one of the mounts, or wobble on the X gantry itself, though the wobble looks left to right, not up & down, which is what I’d expect if the gantry had vibration.

Check to make sure your X belt isn’t too tight. If it “twangs” like a strummed guitar string, it can resonate and cause vibration as it moves over the pinion teeth.

1 Like
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Definitely not loose lens, but will have to check mirrors.
Belts ring very very low, were much slacker before i tensioned them, but it didnt change anything tbh.

I dont get those wobbles. My first cuts were mostly exclusively Y wobbly. Look at floral design i cut on slack belts. Decided to switch to circle test pattern, thats where all the ringing moved more towards X.

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Here we go again. I definitely have mechanical problems.
Tried spiral bowl today.
Cutting from 2mm ply. Dialed cutting speed/power to 50mms and 50% (80w tube). Test squares fall out nicely (15x15mm), no charring.
Now the bowl spiral, will not cut at certain head travel angles. Resonance, vibration.
Absolutely repeatable, did 4 tries, ALL of them came out with defects in exact same place.

Thoughts, people…





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Did line engraving on the durface of the same plywood to see the wobbles coming through. Here they are:

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Have you tried running the job in different places on the bed to see how that affects things? I would do the extreme upper left corner and then the extreme lower right corner (or all four extreme corners if you have cheap testing material). It might be give you a clue in terms of troubleshooting. Just a thought.

What are your acceleration settings? Have you tried lowering them?

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Good advice. Will do swirl test and bialy100k backlash test in all four corners.
When i first noticed all this i was running on top-left. Yesterday i realigned mirrors to be able to use all of the bed and issues persist on top-right as well. Will have to check bottom as well. Btw, my home is TR, but the only guide rail for Y is on the left.

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Here’s the test, material moved to all four corners, constant speed of 100mms:








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That is interesting. A bit more intense on the right side tests than the left side and it radiates versus a pure horizontal/vertical pattern.

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It does radiate towards centre of any arc or on slanted straight cuts at certain angles.
Bialy100’s backlash test shows that i cannot even cut straight lines that are not strictly X or Y oriented.

Also, this problem is irrespective of speed at all. Tried all the way down to 10mms, its still there, but much more closely packed, which makes fat line and thats why spiral bowl wouldnt cut through on certain travel angles.

I’m completely at a loss. Short of changing motors/drivers i’ve no idea what to do.

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Since you just received it, what has the seller advised? Is this an ebay special? Did you pay via PayPal and/or credit card. File a dispute NOW if you bought via ebay and are getting near the end of the 30(?) day return period. Do all correspondence via the ebay communications function so it is recorded for ebay customer service to see.

You might post this information and pictures over at RDWorksLab forums. There are some guys over there who are good at helping with these issues.

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Thank goodness i bought it from UK dealer. Its been difficult dealing with them as they’re not really that well technically versed apparently. All support goes through china manufacturer. Takes forever. Makes me frustrated.

No paypal, but there are other avenues to pursue if it comes to that.

All correspondence goes through email, so everything is recorded.

On a side note, where does one purchase dual-shaft nema17 motor in UK ?

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