Decreasing power the longer a job takes?

We noticed that the output power of the laser seems to decrease as the job takes longer (or if you run multiple identical jobs in a row)*? Has anyone else seen this? What could be the cause?

The cooler keeps between the set temperatures, waterflow is unimpeded (unlike earlier when I had that kink in the waterline)…

) For example, a few weeks ago my son cut out stair-like structures to build multi-level displays for Skylander figurines. The first 15+ went just fine and were consistently cut, but the cuts seemed a bit less defined as he went on and had some little splinters when removed from the bed, and the last 3-4 were consistently NOT cut all the way through on some parts of the outline. (This is on 4mm birch ply, all from the same batch, sawed in to ~4060cm sheets)

Hi @CescoAiel, I can’t exactly remember if I experienced a power increase or decrease but I’ve had power changes in the past when doing longer batch production. It was when I was laser engraving logo’s on top of cardboard boxes and I would have to change the settings after some initial time. Not sure about the exact timing anymore but something like 15 minutes or 3-4 boxes. I was thinking it had something to do with the low power that I was running at, it was really at the lowest of the power scale, like 1% power.
But in your case it’s ply so you must be running at the top halve of the power range. Could it be smoke building up in the chamber?

Thanks for your reply…

Yes, it is cutting 4mm Ply… It’s not a smoke issue because we have both a pretty powerful extraction fan, and it also happens after a number of repeated jobs, requiring the opening of the cover to place/reposition material…

Interesting, It could also be with the age of your tube @CescoAiel
What is your temp set at? What is the temp range of the chiller? The new FabCool active will the temp within 1 degree. (the new new ones will actually heat the water if its too cold :open_mouth: )
If the temp can vary too much it can affect the output power.

Another consideration is if you are running a lot of long jobs then the gas does not have ample time to “calm down” this can affect the output power, this will likely become worse with age. As the tube gets older the gas mix will deteriorate.

Something which might be simpler and cheaper to try and fix it.
Check your lenses and mirrors, if they are worn or dirty the transmission / reflectiveness will change as they heat up. Meaning less final power. Same goes for the lens in the end of the laser tube.

Kind regards,

The tube doesn’t have that many hours on it yet…

Temperature (IIRC) is set to 12.5ºC with a 1ºC range. I actually have a submersion aquarium heater next to the cooler, set to approx the same temp, for pre-warming the water if it is too cold… :wink:

I regularly clean the lenses and mirrors (including the one on the tube) with IPA.

The thing is that it does get worse the longer you’re working, but try the next day, and it’ll be fine again. So there might be something in the agitated gas theory. Is there something I could do to alleviate that?

Hi @CescoAiel tubes are ratted for hours but those hours in a way are also running from the second the tube is made. With time (like all things) the seals on the tube degrade and the gas can gradually become tainted.
12.5 is pretty cool, we normally operate them at 16-17 17-18. Maybe its worth testing with a higher watercool temp.