I have taken a long covid break with Lightburn and I am having a problem burning through wood. In March of last year I would easily burn through 3mm birch plywood in order to cut using Speed of 15 and 75% power. I have tried it for the past two days and had to run the path 3 times.
Any advice on what I am doing wrong? Same wood and same device…
Either your plywood is not the same or your laser tube is about to be replaced.
You write that it is the same wood, is it from the same piece / batch as the one you used before or the “same” material bought again ?, I have bad experiences with “the same” type of plywood, even though I only buy it from it same dealer.
Also try to see the color of your laser beam into the tube itself, is it violet, pink or more colorless white? (it should preferably be pink / violet)
Ive just had to run a pass three times on 6mm MDF that last week I ran one pass and it cut beautifully.
On closer inspection, it’s not the same as I was cutting last week - it’s the last of my stock from early in the year and is significantly harder to cut.
The stuff I bought last month I can cut at 50mm/s at 85%. The old stock, visually identical, 30mm/s at 85% with a final pass at 150mm/s and 75% to ensure a clean cut, and even then I needed to run the whole job again. Luckily it’s the last of that batch and I won’t be using it again.
I also have some 2.4mm ply that will cut great over most of the sheet, but then I hit somewhere with excess glue or occlusions and it needs to be cut through by hand.
Plywood, by its nature, is different every sheet.
Use something like thin MDF or heavy card to test on.
Or, try and source ‘laser ply’ or ‘solid-core’, which is two thin wood veneers with a thin sheet of mdf at the core. That is consistent across sheets.
Without a laser power meter, you will only be guessing, anyway.
And I’ll add to the already great information provided. Your machine’s optics should be checked. Ensure your mirrors are aligned well and cleaned. Evaluate the condition of your lens and determine if it is in need of being cleaned or replaced.
Jumping in here just with a personal peeve: “15” is not a speed, but just a number. 15 mm/minute and 15 inches/sec are both speeds, but the latter is about 1500 times faster than the former - please include units. 
Also worth mentioning, if cutting at or below the ‘Start Speed’ setting in your controller, which is 10mm/sec by default, but sometimes higher, the only power value used will be Min Power, so if you aren’t setting both, you should. That has bitten more than a few people who’ve forgotten to set it, and had them wondering, like you are, why they weren’t getting enough power to the material. Worth a look, just in case.
And to add something that has caught me out, and that is the cleanliness of the lens. You only need to have forgotten to turn the air assist on for a few seconds on a previous job and the effective power to the job is drastically reduced. I now know that if a project doesn’t work that once was fine, I check and clean the lens. Comments on the variability through out a sheet of ply are absolutely true!
Cheers
David
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