80W CO2 laser - Line Engraving Quality question

Although this isn’t quite comparable, here’s a row of much nicer dots from a 60 W (claimed) laser:

Those were done in Dot Mode:

Dot Mode layer parameters:

  • 2 ms pulses
  • 0.25 mm spacing
  • 20% power
  • set speed 100 mm/s, actual around 5 mm/s

I don’t know if yours were done with Dot Mode, but, if not, it’d certainly be worth trying to see if it looks better. Then we can compare results and maybe reach some conclusions.

Some background and other power variations on my blog:

Hi Ed, thanks for the image. Those marks a far more consistent than mine. I’m just checking into all the information that Jack provided regarding the limitations that the laser firing speed imposes.

Thanks Jack. The thread has been moved. I understand your thinking on the laser firing speed. Just taken the machine to bits so I can see all the various components and get some specs. It is an Oculus 6040 (600mm x 400mm bed) from OPUS CNC based up in Durham, England. It’s a bench top, but you need one heck of bench, it weighs more than 300kg. Thanks for pointing me to what will clearly limit potential resolution. The speed for the dot test was 100mm per second. Do you think the 0.05mm diameter dots indicate that the 6040 can resolve a 0.05mm dot and retain a 0.05mm gap, but obviously not consistently? In the manual it recommends a line interval setting of 0.035 for raster engraving images on acrylic. Thanks again.

You can’t really tell what kind of a dot you can make if the machine isn’t operating correctly. Yours is clearly got an issue with it’s optics/source…

The ramp test isn’t bad, but the output of these dots look unfocused.

Don’t know where you got your source… or how it’s configured… but here is a dot test from Russ Sadler and how to interpret it… It’s under the heading Interpreting The Dot Size Test results

dotSize.lbrn2

When you load this, use the zoom to frame selection zoom-to-frame-selection to see it… :face_with_spiral_eyes:

Are you running in pass through mode on the layer?

:smiley_cat:

It turns out the power supply puts a rather low limit on the overall response time, on the order of 250 Hz for PWM input. That’s not the PWM carrier frequency, which is typically 20 kHz for Ruida controllers, but the rate at which the laser power can change.

The overall risetime is around 1.5 ms, so the dots can’t be much less than 4 ms “wide” to have reasonably steep sides and a flattish top. That means a 0.05 mm dot requires a scanning speed around:

12.5 mm/s = 0.05 mm / 4 ms

Which is sufficiently lethargic to incinerate anything you’re likely to be engraving and so slow you’re likely to not believe it.

I didn’t believe it, either, so here are the measurements & pix:

The linkies there take you to the background on the test setup & suchlike; it took me a while to work around to those conclusions.

So a CO₂ laser can produce high resolution images and run at high speeds, just not both at the same time.

Hi Jack and Ed and thanks for your help.

I have run Gareth’s dot test. Seems like this device is producing a dot size of 0.2mm.

OPUS are also running test on another 6040, same material same test files. Should hear from them a bit later.

I’m using Lightburn Ed, does this have ‘dot mode’? I can’t seem to find that. It does provide ‘Threshold’ which is either on or off for black or white.

I’ve checked the laser power supply, Model: HY-T80 so Response Speed is ≤1ms to 90% of set power. Should be able to run at 200mm/s by Gareth’s info, maybe up to 400mm/s.

The Ruida Controller is model RDC6442G-B.

Going see what some slate engravings look like at 127dpi.

Thanks again for your input.

It applies to vector lines, rather than image engravings:

It’s a good technique for producing controlled burns (or dotted lines!) at much lower power than a normal vector can achieve, at the cost of running around 5 mm/s no matter what speed the layer calls for.

Got you, thanks for that. Another thing learnt:-)

Are you running the test with pass through enabled on the layer?


:smiley_cat:

Hi Gentlemen. These are my latest results. Having read your suggestions Jack, I thought I would check everything. The laser tube was not secure in its mounts, so sorted that and ended up with better alignment from Tube to M1 anyway, it was always slightly high. Then a I recalibrated M1, M2 & M3. The first result is the is Gareth’s dot test run on card. The second is a grey scale test run at a line interval of 0.15mm.

Clearly the non secure tube was an issue. Using Gareth’s guidance would you say that a line interval of 0.15mm is the best resolution on this device? I’m thinking the dot size and therefore line interval is less than 0.2mm but more than 0.1. My only other thought is that the lines are defo not touching on the greyscale test, which would indicate slightly higher resolution would be available on the anodised alloy business cards. Also, do you think the burn marks are about right for a CO2 gantry laser? The diode Galvo seem far better and more consistent.

I don’t know who this is… So can’t really comment.


What line interval are you using here?

With the proper line interval it should be just touching… or you will have gaps in the scan lines.

My machine with a stock lens, 1.5", can do about 0.10mm line interval with the compound I can get at least 0.05mm or less…

You need to solve the Y wobble problem before you’ll have a good functional machine.


I circled a few lines that wobble, this should not happen… You can see it on all of the output you posted… it’s not straight.

Since it’s doing it where it should be going straight along the X axes, its going up/down… indicative of Y axes issue.

I would think this is evident of issues with the Y axes (assuming X is horizontal) being lose or incorrectly adjusted… It could be a grub screw coming lose or some other mechanical anomaly.

Better output… keep adjusting :thinking:

:smiley_cat:

Or a loose lens, as happened with somebody else in recent memory. You’d never notice anything along the X axis, but any motion in Y would produce those worms.

If it’s traveling in the X direction, I wouldn’t expect any wobbles in the Y direction…

Or is that what you are saying…?

:smiley_cat:

If the lens is wobbling around while traveling parallel to the X axis, any motion in the X direction will be pretty much invisible: if the beam goes backwards or forwards, the trace will be marginally lighter or darker.

But if it wobbles in the Y direction, then the beam will burn to one side or the other of the center line where it should be, which could produce those worms.

Come to think of it, in Dot Mode a wobble in the X direction could produce irregular dot spacing, which is kinda-sorta what appears in the bottom track.

I’m not convinced, but it’s certainly worth checking all the doohickies on the laser head for a snug fit.

You and I know the first thing to check is mechanics… :thinking:

Much more likely a mechanical failure than an electronic one.

:smiley_cat:

Hi Jack and Ed,

You guys are great.

The line interval on these latest results was 0.15mm. Gareth must have been from the previous thread, he has an interesting website https://laseruser.com/how-to-laser-engrave-slate/

I’m so glad you guys have raised the worm issue. I have no experience with lasers at all and don’t know what I should be expecting in terms of results. To give perspective the laser was £6k Sterling and it was new March 2022. However, I have not started using until about 4 weeks ago and was immediately struck by lack of quality on attempting to picture engraving.

I will investigate the mechanical setup further. There’s no way I would have know that the wobble you refer to should not be an expected result. I would have put it down to units limitations. Really appreciate your input. Thanks.

These are two different types of slate… Notice one engraves light the other dark… These were done with the 2" lens.

This one was done on the fiber… this has a smaller dot, but the material, is generally the what sets the dpi limit … in the end it will be laser dot size and material that will decide the best dpi.

You are running the dot test in pass through mode, correct?

Hang in there… I’m sure we’ll get you going…

:smiley_cat:

Given a loose tube rattling around in the back, it should be awful.

With that snugged down, the results look pretty good and we’re quibbling about details.

The scan interval depends on the width of the surface damage in the target: 0.15 mm is an itsy too wide for the grayscale material, but might work fine in a different material.

At some point you should explore Dot Width Correction for images; I don’t have a lot of experience, but it’s apparently the ticket for crisping up the contrast:

This laser everything video talks to the Lightburn developer of dot width adjust at about 20:18 into the video… good explanation… also a very good video on how to set up the proper dpi for a any given material/laser.

:smiley_cat:

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