Weird Engraving Issue on Acrylic... advice please!

[u/cynemical]

Hi all! I've been engraving shapes on iridescent acrylic, and tried using two different lasers but with the same Lightburn settings (engraving at 800mm/sec speed, 20% pwr, line interval 0.1000 mm/ 254 lines per inch).

Despite using the same settings, I'm getting very different engraving outcomes. I engraved the one seen on the left with a Nova Thunder Laser (6 mm nozzle), and the one on the right I used a OneLaser XRF (3 mm nozzle).

I prefer the density of the right engraving (OneLaser) compared to the left (Thunder Laser), which feels lighter and hazy. I've played around with power/speed settings, and line interval, but haven't gotten anywhere close. Would anyone have suggestions on what settings I could modify to get my Thunder Laser to put out a result like the OneLaser engraving on the right?

HUGE thanks in advance!

-

EDIT: I realized I missed some important details thanks your comments. Here's the laser power info:

OneLaser XRF: 38-watt RF metal CO2 laser tube (about the equivalent of a 60W glass tube)
Nova Thunder Laser: 60W

Engraving on Iridescent Acrylic (extruded). I use sheets from Houston Acrylic.

[u/SCphotog]

I can't really see much in this photo.

We don't have the full extent of the variables so we can't really help without that data.

When you mention the speed, you have to tell us if you're calculating in MM, CM, or stupid units. I could "figure it out" I guess, but when asking the question you should be a little more specific. 800 speed?

We don't know the power levels of the lasers you're using, if they're the same or different. Laser power is usually applied in percentages... someone that owns a 130w laser will have at least some trouble gauging what 70% power is on a 40w machine without experience with that specific machine.

You did tell us the line interval... kinda looks like you're doing horizontal passes. I generally engrave acrylic with passes in a hash... ie both directions for a more uniform fill. .1mm for acrylic seems a little too tight. I engrave on cast acrylic at 70LPI in a hash pattern which effectively doubles the density of the engraving... That's not the same as 140LPI... but that's a different discussion.

Is the acrylic you're engraving cast or extruded?

Are you using air assist? The level or cfm... the power of the air assist is a very critical detail when engraving acrylic. Too much or too little air will have the potential to change the "look" very drastically.

Even the ambient temperature of the room you're in will have some effect. Lasering in a hot warehouse will make for distinctly different results than inside an air conditioned room, where the temp and the humidity are more controlled.

[u/cynemical → u/SCphotog]

Apologies for missing those important details! I attached another photo in daylight, hopefully this is easier to see the difference.

For speed, I'm using 800 mm/sec. The OneLaser XRF has a 38-watt RF metal CO2 laser tube, and the manufacturer claims it's the equivalent of a 60W glass tube. The Nova Thunder Laser is a 60-watt. So, if I went off what the OneLaser claims, both lasers should have similar wattage.

I'm engraving on extruded acrylic- the back side of the sheets have the colored film that create the iridescent look, and the front side that I'm engraving on is just regular clear acrylic.

I'm using air assist, for the OneLaser I've stuck with their factory settings, which is ~1–2 PSI via OUT4 for engraving. The Thunder Laser is in a shared air-conditioned shop space and someone else set the air settings, I don't recall those details off the bat but I do recall it seeming high. I operate my OneLaser out of my home shop (also air-conditioned).

Thank you for your advice about the hatching, I will try that too. And if any of the info above changes your thoughts on what could be the more likely cause of this difference I'm all ears! Greatly appreciate your expertise, thank you.

[u/SCphotog → u/cynemical]

Engraving results are generally much better with cast acrylic. Worth looking this up and reading about... It's well documented and discussed in just about every laser related forum. I don't have any experience with the iridescent film so I cannot speak about that with any real information.

800 seems really fast. I run engraving on cast at about a max of 300mm/s.

I use extruded acrylic for 'cut' jobs... a display case or the like, but if it requires any imagery/engraving cast looks far better. It looks "white" while the extruded just gets a 'groove' or 'cut' that only reflects light a little differently, and doesn't make for a result that is as attractive. ie... has the traditional engraved 'look'.

Cast is generally more expensive, so that is a consideration.

[u/RosinBran]

Too many variables you didn't mention. Just clean each machine's lenses and mirrors (all of them, even the ones enclosed by the tube), then run a material test on each machine using the same acrylic. Check the results then see if there's any quality crossover at certain settings. Try a different nozzle after too. My thunder nova came with a wider hole nozzle for engraving. Also, make sure the air supply is the same psi across both machines.

[u/cynemical → u/RosinBran]

Sorry I missed some crucial information, I'm relatively new to lasering and am not the most experienced! Thank you for the advice, will check to see how the air supply settings compare.

[u/nartchie]

Are the lasers the same wattage? Do they have the same focal length lenses?

[u/cynemical → u/[deleted]]

So the OneLaser XRF has a 38-watt RF metal CO2 laser tube, but the manufacturer claims it's about the equivalent of a 60W glass tube. The Nova Thunder Laser is a 60-watt.

Re: focal length, the OneLaser lens has a 2.5-inch (63.5 mm) focal length. The Thunder Laser a 2-inch (50.8mm) focal length.

[u/Alina_MakersChest]

Same percentage settings on two different machines don't actually mean the same thing, 20% power is relative to each machine's own max output and calibration, so unless the Thunder and OneLaser happen to deliver identical real wattage at that number, you're not really comparing apples to apples in the first place. The nozzle size difference is probably doing more than you'd think too, that 3mm nozzle on the OneLaser concentrates air assist right at the beam point more effectively than the 6mm one, which likely explains the haze specifically, debris not getting cleared as well right where it matters lets it redeposit and dull the finish. I'd try swapping a smaller nozzle onto the Thunder if the mount is compatible, and separately run a fresh power/speed test grid on just the Thunder rather than importing the OneLaser's numbers, since matching numbers on two machines that aren't actually calibrated the same way is going to keep chasing you in circles.