Hi,
I am planning to build a 40W DC CO2 laser cutter from components and have a couple of questions: I understand the normal layout is to have the laser tube horizontal and use one fixed mirror and two moving mirrors and a lens.

I have an existing very accurate moving table machine, so the easiest arrangement for me would simply mount the tube vertically pointing straight down through a lens mounted on my z-axis to allow focusing. Does anybody know if the tube will like being mounted vertically. I.e. will the gas discharge be affected by gravity?

If it needs to be horizontal then I will need one mirror. I have seen that the mirror mounting brackets are usually metal. Do the mirrors get hot, or need heat sinking, or can I use plastic brackets? I ask because I have a home-made FDM machine so plastic is easiest for me.