Air bubbles and "skin" on prints

Hi there, I have a little problem here with air bubbles on my last prints. The first three prints I made at 25 microns were great and came out fantastic with very clean surfaces and great detail.

However my last two prints were having some real issues, the first one was very similar to the last two I printed before it and the model is similar in orientation and has a big hole at the bottom so the air can escape. The model has formed some sort of thin skin on the outside and I could peel it off, beneath it the resin wasn’t cured at all.
My last print ( several heads in 1/6 scale, so not really small either ) were all having huge issues and I basically can’t use them. All of them have trapped air bubbles or the same skin issue mentioned above or even holes. All of said heads are hollowed out and the air should be able to escape through the necks.

Here are some pics to explain the problem, the circles are the skin bits or air bubbles:

These prints were made with the second resin cartridge but on the same resin tank, should I have exchanged the tank already? It has a few small spots that are not 100% transparent anymore, but they are way smaller than the affected areas and are not all over the tank window either. Did I do something wrong? I’d really like to know as I am wasting a huge bunch of resin on prints I can’t use for the intended purposes like that.

That is an optical problem. When I had that it was due to dust on main mirror and galvos. Typically a clouded pdms will show low quality loss of detail on a print before it gets to a print failure… Look for any dust on your main mirror which will cause that sort of failure on certain parts of the tank.
If that happens no matter where you print your part then dust is probably closer to the laser such as the galvos.

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I just got the printer about two weeks ago, strange that it has dust in it already. I will do some research on how to get to the laser and galvos before I start unscrewing anything. The first printer I was sent did not work at all and was replaced, this one is starting to act up after only two weeks. I am a little disappointed to be honest.

Sounds familiar… I had oil mist on the inside of the optical window that the tray/tank sits over, there was dust on the main mirror, and what looked like swarf from driving self tapping screws in and out of plastic, scattered about. It wasn’t difficult to open it all up and clean it, but like you, it was only a few weeks after delivery… Talk to support, they are excellent. But I’d rather they didn’t get so much practise in the first place!

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Wrote support and apparently it’s the laser not having enough power according to logs. So I will get the third printer in a month. Support is great, yes, but I do agree it would probably be easier and cheaper for them if the printers would work as expected. I chose the forn2 because my friend has been using his for 2 years without any issues at all. Must be my kind of luck…

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