Cutting transparent acrylic, passes and power

Newbie, getting started on cutting transparent acrylic - I have a 50w co2 China machine.

Q: (cutting) Is it better to do many many passes with less power
less passes more power?

Right now I have it at 9 passes for 2mm transparent acrylic with decent results.

Q: For cutting, why is there a min and max power? Shouldn’t just one value (eg: max) be enough?

Q: For engraving, do you remove the top plastic protective covering before engraving?


9 passes? at what power? A 50W laser should cut through 2mm acrylic like butter in one pass. I run my 80W through 3mm acrylic at 80% power, 25mm/s. For 50W I’d start with 80-90% power and 15mm/s and keep trying faster until it won’t cut through.

For DSP controllers it’s possible to specify min and max because it will take into account the actual speed the laser is moving at the time. Basically, if you tell it to go 25mm/s it has to accelerate up to that speed and deccelerate when stopping. If it just kept firing at the same power you would get darker burns at the beginning and end (if engraving wood or something). So min power tells it the lowest you want it to go when not up to full speed. This generally only matters for engraving. I almost always leave min and max the same when I want to cut.

If the protective coating is plastic, absolutely remove it. It will just melt onto the acrylic and you’ll have a hell of a time removing it later.
But if the coating is plastic you probably have extruded acrylic which is junk for engraving anyways. You want cast which typically has the paper masking. Which you can engrave right through if you want, but depends on the design - it will prevent fogging of the acrylic around the engraving from the hot gasses but sometimes it’s a pain to remove later with a highly detailed engraving.

Plastic vs paper coating isn’t always a tell of if it’s extruded or cast but more often than not that’s the case. Cast acrylic will become opaque on the surface when engraved but extruded doesn’t. See here:

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9 passes does seem wrong. With my 80W tube I’m cutting 6mm acrylic at 20mm/S and 50% power. I’ve not had plastic covered but do leave the paper on when cutting.

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Do you have a mA meter on your machine? Your 50% could be 3mA or 30mA, no way to give a real “power percentage” quantification without knowing how many horsepower you’ve got under the hood. Having said that my bone stock “50 watt” blue and white laser before changing tube, power supply, mirrors and lens (mine is slightly modded), would have done 2mm acrylic at something like 60% power and 12-15mm/sec IIRC. That’s in one pass. With my 1000mm tube I cut 1/4" (6.35mm) at 15mA (45% on my machine) and 7mm/second. If you go below 10mm/second with the stock Ruida controller you’ll have to adjust the cutting start speed in the controller settings, otherwise it’ll default to low power when you get below 10mm/sec.


Q: (cutting) Is it better to do many many passes with less power
less passes more power?[/quote]

I prefer one cut, with air assist.

Way too slow. You should easily cut through in one pass. You should be able to cut 5mm in one pass.

Cornering, mostly.

If you look at a piece of acrylic that hasn’t been cut all the way through, with the same settings on min/max, when it reaches a corner the depth of cut will nearly double,

Having min/max allows it to drop the power as the head slows over the material during cornering.

It’s worth experimenting with - I couldn’t work out why a design wasn’t cutting out when I had power on my 130W at 65% - because my min was only 25% and the design was mostly small circles and other curved shapes, it was spending most of the time on the lower power. Adjusted minimum and it cut great.

For engraving I don’t bother as it gets eaten up. For cutting, depends on how intricate the cut - if it means twenty minutes of weeding, I peel off both sides and lay it on a pin bed

Thanks for replying guys!

I figured I was messing up somewhere as the youtube videos showed the K40s doing a better job than what I was getting… I’ll post pics of my settings in a bit.

I think this is where I screwed up…

Makes sense, and thanks for the link :wink:

Yep, feels like I’m screwing up somewhere. Is that one pass?

Not that I know of, this is my machine:
I bought it after I was advised that these ruida controllers are most compatible with LB…

I have air assist on this…

:kissing_heart: :kissing_heart: :kissing_heart:
That’s what I wanted to hear as thats the main purpose of this buy; 5-6mm cuts!

Going to have to play with these settings a bit…

The Ruida controller is good, but a mA meter is something you’d have to add separately. Without one you really don’t know what your output is (or if you’re over driving your tube to extinction). They’re like $10 on Amazon and are pretty easy to install (there’s YouTube videos for this).


Hi Bryan,
I made this 3 mm acrylic safe with no problems with my K40. (10 mm/s, power 35 = ca. 10.5 mA)

I remove the plastic wrap after cutting out the items, it works very well for me. I try to find the right cutting speed at the lowest possible power so that the material does not weld together afterwards. It is important to find the right focal point, or the edges will not be angular.
I mean I cut everything (acrylic) up to 6mm in a single pass.
The wildest I have tried is 15 mm.

Or… you calibrate the output of your psu using a multimeter and a screwdriver and know that there’s no such thing as ‘overdriving’ your tube ever again.

Why do people always go for the most convoluted answer to a problem?

The adjustment pot is there for a reason. What you’re proposing is like instead of adjusting your mirror, you instead put in auxiliary mirrors to compensate.

Will look into it. Feel free to link to any videos that you think I should watch :wink:

Damn! That’s pretty! :kissing_heart: :+1:
Thanks for the tips!

Nice pic! Passes?

Got a link or vid? :wink:

Sure: enter “ adjust laser psu” into the search field at and choose the ‘videos’ tab.

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I really think it was only 2 passes, but that’s a while ago. On a daily basis I do not often use thick acrylic, the material was included in an 18 kg box with acrylic residue for a little money.
If you are interested in the details, I could do the test again.
By the way, I have not calibrated my power supply, I just use the autput from the ammeter and never exceed 50% (about 16 mA)

Yes, that’s one pass with air assist

Yes, do this if you can. I set my PSU up so that at 99%, my current never exceeds the max ( for full warranty ) rating. This “lower” setting delivers the full 80W expected from my tube ( per the power report I got when I bought it).
So, even though I have a current meter, I still adjust the PSU to not exceed the max current I want to limit to.

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Not all PSUs have an adjustment pot.


If you must buy the most bargain-basement equipment, then you pays the price.

Thanks, thats kind of you :+1:, was just curious as I’m mentally trying to compare what mine should do once I have the settings in…

I actually have 3 PSUs that were supposed to go into computer builds but got cancelled so are free for my use, they are Corsair 800s I think, I can swap them if need be (with help) :slight_smile:

We’re talking laser PSU, not CNC.

You’ve got (at least) two PSUs - one for the laser - the LPSU, one for the CNC - ~24V - 36v - 50v driving the steppers, etc.

The adjustment is for the pot that controls the maximum output of the laser psu and thus limits the psu from overdriving and burning out the tube.

As a general rule, you should run a materials test on every material you lase.

I’ve found this test card to be useful:

Yea, I’m not gonna get into an argument of comparing each others sword lengths. I think the point here was to help the OP who may or may not have an adjustment pot on their PSU. It’s pretty common for folks to add mA meters to their machines and adjust cuts by actual than percentage.



Here’s a link to a youtube video for mA meter install:

And this is same/similar to the ammeter I installed on my 50 watt:


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