Tarkin's #3 mirror got a little hot

Wow, that was still cutting “ok”, but that mirror pretty much went to hell and back.

Not sure when. It looked dirty from the side, but when it didn’t clean up I pulled it and discovered this. #2 mirror is fine, this had to be contamination. Gold plating over silicon, the plating blistered all over

Replaced with a molybdenum mirror to see how that goes. Moly is slightly less reflective but has a higher thermal conductivity and melting point than silicon, making them extremely damage-tolerant if contaminated.

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What’s your guess as to root cause?

Those speckles make me think of acrylic.
At the start of a class I found the cone’s outside
covered with a white condensation of acrylic vapor.

There’s a bit of a leap in my thinking but it’d be good to know what happened.

This is after cleaning

The speckles are actually blistering in the gold plating. It doesn’t appear limited to where the beam hits, so most likely the entire thing got quite hot due to soot that turned a bunch of wattage into heat at the lens. I have cleaned the mirror periodically, I’m not sure when this happened but I think I would have noticed this if it was before Saturday.

Crud on the outside of the air assist cone doesn’t automatically suggest a problem. That’s fairly normal. However, anything which infringes into the nozzle orifice is a prob and needs to be cleaned asap.

Interesting, so sounds like we need a pretty regular lens cleaning schedule for Tarkin.

IMPORTANT NOTE - no one should clean any laser lens unless they have been explicitly trained and authorized by @dannym. If you see a lens problem, be sure to post here on Discourse and tag him.

We did some 3/8" acrylic cutting a few weeks ago and had a really inconsistent cut across the bed. Danny happened to be there and checked the bed level, was pretty spot on. Strangely we had stuff on one side cut completely through cleanly and stuff on the other side only cut like halfway through in some places. I wonder if these was at play there as well.

I noticed on sustained, full-power cutting, the chiller was not keeping up with the heat load. It’s more of a factor when it’s vectoring slow in thick material, but not cornering through fine detail, because that automatically throttles back the laser output when the head slows down for corners and tight curves at higher speeds. If so it’s readily apparent on the chiller’s temp readout. The coolant slowly crept from the 20C target to 25C over 5-10 minutes at continuous full power. This isn’t anywhere near overheating the laser, but CO2 output does drop at about 1% per degC so it can cause this.

Cut order optimization naturally starts in one place, does everything in one area and gradually moves to other parts of the bed later. This pattern can give the misleading impression that the bed location is the problem, whereas it’s actually chronological.

The chiller is rated for 125% of the max heat load. But it was pretty full of dust that crept in from the main shop. Filters and the condenser core itself. I’m not certain if that explains the problem, but Zach and I did clean it last night. Had to move it to do that, and had a coolant loss situation we tried to clean up but if you see evidence of water that’s why, not an ongoing leak. It was just distilled water.


That’s super informative and totally makes sense on the bed location red herring! Thanks for taking the time to explain :slight_smile: I’ll pay attention to the chiller temp next time and watch for changes there.

With the chiller condenser core cleaned out, it seems to be doing just fine for cooling now at full power with no temp rise. The dust is too fine for the mesh filters on the sides of the chiller. They had plenty of dust on them but most went through, and it was still unable to keep the cooling up when I just took the side filters off for a few minutes to see if clogged filters were doing this.

If it was the dust buildup on the core, I’m surprised it was that detrimental to cooling performance, but that seems to be the case. It didn’t look bad from above, but from the inside, I could see that yes there was certainly a lot of buildup. And that’s all after it was moved into the laser room.

So, this is something that needs to be done monthly or so, at least until the doors are closed off.