40W (K40) vs 50W (OMTech)


After 3 years and uncountable projects, it was time to upgrade. I was perfectly happy with my K40, but I needed a bigger work area.
I bought a 50W and there are some differences. Some are better, some are worse.
The main issue I’m having is the power.
On the K40 I can cut 3mm MDF with 5mA and 9mm/s, has a very thing gap and almost no smoke on the material.
The 50W needs 14mA at 15mm/s, has a wider gap and a lot of smoke stains. (See pictures in the link : 40W vs 50W laser results - Album on Imgur)
Can someboy explain this? Why does a 50W laser needs more power to do the same?

I tried a lower power with a lower speed, but the result is exactly the same (less mA ofcourse, but the same gap and stains…)


With a wider kerf, my first guess would be either your focal distance is incorrect or the lens is in upside down.

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Hi HalfNormal,

Thanks for the suggestion. I checked both and they are correct. But I found the issue…
One lens had a black spot and was really hot… I assume it absorbed a lot of energy.
After cleaning, I was able to cut 3mm MDF at 35mm/s ad 35% (15mA) and half the amount of dirty edges…
The charring on te edges was also less. Brown instead of black…

Any idea what the max current on a 50W laser is?

Kind regards,

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How many lens’s do you have on that K50? The K40 normally only has one lens.

You can also look at the laser tube divergence. Look at the burn diameter in front of mirror 1 and then look at the burn diameter in front of mirror 3. Post the pictures and hopefully we can see something.

Hopefully @NedMan will chime in. He also just purchased the same laser.

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It usually says on the tube, but it’s usually about the same as for a K40 (16-18mA) . I limit mine at 16mA.

What control software are you using? If it’s Light Burn then min and max power need to be the same at low speeds or it just defaults to the lower number. That threw me for a bit on mine when I got started.

I think he probably means mirrors.

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My ‘test’ page from my machines manufacturer had 21mA max for the tube. I’ve used that as max and keep it down around 18mA for most things. Tube is 880mm and measures 44W with a Mahoney.

Set the lps to 10.5mA at 50% pwm…

Tubes placard, guess they left that out… lol


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ok could be but there are compound lens’s and IIRC it would effect focus. Never heard anything about ramp testing or focus verification as that is always the first thing to look at when charing and often the first thing even seasoned people forget sometimes.

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From what I’ve heard is that the A grade tube suppliers test at the higher rating so they can be run at 100% without excessive wear. So a 50W laser tube is tested and validated at 60W and likewise a 40W tube is tested and validated at 50W. These don’t have the limitations of junk tubes we get with our lasers from the factory and have to under drive them to get them to last very long.

So how much current you run through your tube depends on the quality of the tube.

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You are correct. I meant mirror (no.2).

I think it’s a residu of the tape I used for the mirror allignment.

I use RD Works and keep min and max power the same.

Thanks for all the info.

Kind regards,

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yup, somehow it doesn’t get out there that you do NOT want to put tape in front of the mirrors when doing alignment UNLESS you put something behind it. Before I 3D printed target holders and slide paper targets in, I used tape too but put a dime attached to the back of the tape so it would not melt the glue onto the mirror.

It really should be in every K40/K50 FAQ to not use tape unless backed with something.

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@dougl Want to look through #k40:intro to make sure it covers this?

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@mcdanlj unfortunately the video does tell you to use masking tape… 1:30 in this video - Ep6: Laser Beam Mirror Alignment. The DIY CO2 Laser Cutter / Engraver Build Series - YouTube

OMG the next link is to a PDF and on page 7 it too says put masking tape over the mirror. WTH.

nuts… even the 2nd alignment link says to put masking tape over the mirrors…

Ugh, I don’t want to just ditch those otherwise good resources. I can at least annotate them. Thanks for checking that!

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Ya the process is good but the technique for getting the marks is wrong.

I cut paper targets out of watercolor paper that just ‘fit’ in the hole.

The target is a little more detailed, as to center…

Cut a bunch out of a sheet and keep them around for when I need them.



Too bad your mirrors have to be aligned to make these :slight_smile:

You need to think ahead… You’ll learn that after a few ‘oops’… and that’s why I mentioned it…


You can always print them and cut the old fashion way with scissors. Or use your 2nd laser to cut them out. :wink:


We use thermo paper (from rolls). This way, we can shoot very weak pulses that don’t get through the paper and still see the mark.