I’ve seem it said that PLA should be squished a bit for the first layer for best adhesion, but don’t do that at all for PETG. I have certainly experienced having perfect PETG prints, then going to PLA and having it just not stick. This would imply that it would make sense to have a filament-specific Z offset in the slicer. I don’t see this in slic3r or prusa-slicer; as far as I can tell, I need to make a different “printer” if I want to do this. Does anyone know of a setting I’m missing? I’m not used to slic3r missing configuration settings; usually the complaint is that it has the kitchen sink full of settings!
I’ll probably do a new “printer” for PLA anyway, because I think I’m going to give up on PLA sticking to the PEI-coated spring steel bed I bought, or the PEI sheet on my second printer. I have plenty of happy experience printing PLA on glass; I can just set a sheet of glass on top and adjust Z offset for the thickness of the glass and go back to what I know for PLA. For PETG, on the other hand, printing on PEI is great.
I don’t use a Z probe; both of my printers are carefully “leveled” (trammed) with kinematic mounts, and they don’t go out of tram. That means I can’t just probe the current surface with (say) a bltouch. (I even own a bltouch; I just bought it right before learning about kinematic mounts, and I never bothered to install it.)
(I’ve made the mistake of trying to adjust my Z endstop for PLA after dialing in PETG, and losing track of my notes and taking longer than I’d like to get it dialed back in for PETG afterward.)