Laser isnt cutting throught on same wood

I’m having issues with my laser will stop cutting through the wood…i thought it was the wood itself which has been the case in the passed but cutting the same wood…i was running at 15 speed and 90 power now i have to go 5 and 95 and 3 to 4 passes on the same wood…ive cleaned everything double check focus and alignment and i still cant figure out what is going on…can someone help

Hi Ryan,

Running through your focus and alignment are great initial diagnosis steps. Did you clean every lens from the focus lens all the way back to the laser’s first mirror? I’ve personally had some variation sheet to sheet that’s doubled cut time when wood density changed dramatically, but quadrupling the pass count is very odd, and could be a sign of a laser tube on the way out. There have been some recent reports of Omtech tubes failing in as little as 250 hours.

Ouch!! Yeah ive check all of them…and thats what im afraid was happening…got any recommendations on a different tube was gonna go from this 55w to an 80w

I’d check what @Colin advised before swapping out parts, especially expensive parts.


Running in the 90% range is usually pretty ‘hot’ for the tube generally speaking.

What kind of current are you running?

Do you have a proper chiller?


You can also check the resonance of the tube to ensure TEM0 operation.


This thread is typical of problems with higher power tube upgrades, so keep it in mind. A new tube might not be as simple a swap as imagined, especially if it’s an higher power tube.

https://forum.lightburnsoftware.com/t/laser-isnt-cutting-throught-on-same-wood/79934/28

Good luck

:smile_cat:

Yes, upgraded everything from chiller to exhaust…did a test yesterday power at 1,20,50, and 90 and my MA was 0ma at 1, 3ma at 20, 11ma at 50 and 21ma at 90

If you have a 40W tube it’s a little high, if you have a 150W tube, it’s a little low… :thinking:


How was the resonance?

:smile_cat:

I have a 55w

IMHO, what makes this difficult is there is virtually no power control. And that’s complicated by the fact you’re trying to use it at the low end of it’s intended operating range.

When your tube lases it does so at 22mA, which should be ok for a 55W tube.

If the 22mA gives you 55W then the material is hit with 55W when it lases, no matter where the percentage is set …

50% pwm is 100% power for 50% of the time.

With thin material, your only real control here is speed… You will have to experiment …

Do you know what the lowest percentage that it will lase?

Good luck

:smile_cat:

No, i can tell you better in about an hour ill be home and have it right in front of me and if possible to have you walk me through making sure i didnt mess it up

But remember that’s not how a CO₂ laser power supply behaves. The digital PWM input to the HV power supply sets the analog current output: 50% PWM means the tube is lasing at half the full-throttle current for the duration of the output pulse.

The power supply in my 60 W OMTech looks like this at 50%:

The tail end of that 50% PWM green pulse is about 12 mA, half of the power supply’s 25-ish mA maximum output at 100% PWM, with no trace of the 20 kHz PWM signal.

OK so how do you run, whats you feeds and speeds…right now we are cutting quarter inch birch and to get it to cut is 5 speed and 90% at 3 to 4 passes…ive upgraded everything and was told when i got home that the lens in the tub could be cracked thats why its not cutting…i really need someone who could take the time and walk through this with me to make sure i havent done something

Just to see what happened, I cut squares out of random wood from the stockpile:

They’re all considerably slower than you’re running, so it maybe a matter of slowing down to make things work.

Crank up the exhaust fan!

Ive done the square test at all different speeds and power but seems to have to be ran with every kind of wood we run with…but right now its the wrose ive seen it where i cant seem to get anything to cut unless its slow slow and multiple passes at top power

And exhaust fan at top along with air assist

Cuts out pieces but not the whole thing and at 5 and 90% with 4 passes

This is 2 passes on whatever the setting say


We’ll have to agree to disagree as my eyes tell me differently.


A small box ‘fill’, with a 1mS period at 50% pwm.

At 500mm/s it’s a brown line.

At 1000mm/s it’s a dashed line, you can see where the it’s on and off.

There is also no ‘halving’ of the burn appearance, color is very close to 500mm/s.

At 1500mm/s dashes spread out more …

If it’s working as you say, why not a continuous line?

Can’t run fast enough to dump the period, but what I see and what you say don’t seem to jive…


The old lps you are using is, by your own diagnostics, broken. It fires when there is no signal to fire. If the ‘new’ one is identical on the scope, I’d say you have two broken lps modules…

Mine doesn’t and never has had the ‘speckles’ from it lasing abnormally.

IMHO… :thinking:

:smile_cat:

I guess im not sure what your talking about i cant run 500mm or 1000mm and im not sure what you mean by halving it this whole post has completely confused me what brown line what dash line whats turned on or off …all my layers are lines

Sorry, it was a response to @ednisley

:smile_cat:

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