Uneven burns at edge of fill


What is the causing the uneven burns at the beginning of the scans? I’m trying to tune for bi-directional scanning but this definitely makes it harder.

Hello Austen,

Assuming this is your CO2?

You might need to go over this document,

You’re looking at the turn-on time of the laser tube, which will be on the order of a millisecond or two.

Squinting at the scale, the blurs look to be about 0.5 mm long and, at a layer speed of 500 mm/s, that’s about right.

@gilaraujo it is a co2

@ednisley so you’re saying this is within normal tolerances? Is the best solution to just slow down? Maybe a better power supply?
it was at 400mm/s on a 16001000mm sized machine (if that matters)

Hey, pretty close! :grin:

IMO, that’s as good as it’s going to get, because the response time of the HV power supply is on the order of a millisecond or two. Going faster smears that millisecond out over a longer distance and makes it more noticeable, slowing down crowds it into a smaller space where maybe it’ll be overlooked.

We got into some speed-vs-pretty tradeoffs in a parallel discussion:

As far as a better power supply goes, looking at the guts of three power supplies on my shelf may be instructive:

AFAICT, more expensive machines (for a given size) tend to have better components, but it’s not at all clear how much better they are, because the published specs largely gloss over their shortcomings and often omit chunks of useful information.

Basically, you gotta work within the limitations of what you have, because any improvements will be marginal, at best.

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Going faster smears that millisecond out over a longer distance
This makes complete sense.

thanks for the very detailed reply. I’m going to dive into those when I get some time and figure out if I want to do anything about it.

If you do the math… it’s got to be pretty fast to make any real difference… it’s just slow, so to speak.


if I mainly intend on doing dithered images with a focus on quality, how should I approach the smear at higher speeds?

Should I line up the edges to where the laser begins to fire but not fully on? Or should I over compensate and tune to make the solid parts after the laser has full turned on where the 2 rows meet up?

I’m sure this is subjective but I think my main worry is if I tune for when the laser fully turns on the image lines will be shifted away from each other and reduce photo quality even though the edges look better.

If you must run at high speed, you live with the smear.

If you must run faster, then trade it in for an RF excited or metal tube co2.

Good luck


Exploring Dot Correction may take you deep into another rabbit hole:

Note that the effect is small, symmetric, and best applied after you nail down everything else contributing to poor results.

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that is exactly what I was looking for. Thank you for sharing that link!

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I’m doing scan interval tests and I noticed that there seems to be some inconsistency between the distance of the lines.

This is on MDF so maybe it’s just because of the material? Is what I’m seeing to be expected? Any insight will be appreciated!

btw, it appears the interval test doesn’t work with dual laser machines. I’m trying to run the test on my 2nd laser and it’s just not possible from what I’ve tried. I even went into machine settings, set it as a single tube machine and turned off tube 1.

A machine with dual laser tubes tends to be on the really big end of the size range along the X axis. If those units are mils and the scale graduations are (half) millimeters, then the “1.2” lines are 0.03 mm apart and it has a nicely focused spot.

So you’re looking at the limit of the machine’s accuracy in positioning that huge gantry after each tiny Y axis motion.

Using the same assumptions, the horizontal offsets in the digits look to be 0.3-ish mm. At 300 mm/s, that’s 100 µs.

Without knowing how Ruida controllers handle two data streams, I’m unsurprised. The two power supplies aren’t matched for response time (or anything else, for that matter), so the two parallel data streams would require separate timing adjustments with nanosecond resolution, which seems unlikely.

Getting two HV supplies with response times only 100 µs apart is surprising, because that’s definitely not in the spec. :grin:

IMO you are once again expecting too much from the machine.

Given your extremely tight timing and positioning expectations, an affordable machine large enough to live in can’t do what you want, no matter what the seller may have promised.

Sorry I should have clarified.

I’m not currently not using the 1st laser at all for any of these tests. I was merely pointing out that the test only uses the laser 1 and there is no way to enable it for laser 2 for my understanding.

These tests were ran at my minimum power for a 75W laser and 160mm/s. Any slower and it seems to leave burn marks on the mdf which isn’t great for tight intervals

What are my options for more sensitive materials?

EDIT: The image you see above was a file that I made to test the interval heights. It was not the built in interval test within lightburn. I couldn’t get that to work because I’m trying to test laser 2

Doesn’t matter: the gantry weighs the same and moves the same no matter which beam is active, so the mechanical accuracy will be the same.

As far as the scan offset goes, I don’t know how LightBurn generates & the Ruida applies timing corrections, which means everything I think is likely wrong. I suspect the entire chain has been developed / optimized / tested / verified for only the Laser 1 path, with the expectation Laser 2 will just tag along and be Close Enough™ for all purposes.

IMO you don’t have many.

If I understand what you have, it’s a big machine intended for high-rate cutting production, with a side order of Good Enough™ engraving for most purposes. If you were slamming out signage or display cases, you’d never look back.

A mechanically large machine has (relatively) low mechanical accuracy, so it cannot achieve the precision you expect. However, it’s not clear to me a smaller machine will be significantly accurate to meet your expectations, as the design / build of machines in the few-kilobuck range seems optimized for low cost, rather than precision.

For example, here’s my OMTech 60 W 700×500 mm machine after scan correction from 100 to 500 mm/s in edge-lit acrylic:

Those are 1 mm squares and it’s not overwhelmingly better than your results.

A high-power CO₂ laser cannot be throttled down enough to reduce the damage (= produce the results you want) in “delicate” materials, because it will not fire below maybe 15% of its rated current. Higher power requires higher speeds to deposit “little enough” energy in the material, which causes the problems you’ve seen.

A machine combining large area, tight accuracy, and specific results in particular materials may push you into one of those custom-hardware corners where you must design & build the machine of your dreams … which introduces a whole 'nother level of complexity.

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