I just replaced the screen on my resin printer and I suspect it ended up lower than it should have, because now there is a gap (something around 0.2mm to 0.5mm) between the screen and the FEP even when I screw the vat down firmly. Could this be the reason for some warping in my prints? Should I move the screen up so it touches the FEP?
Photo of print done despite the gap:
(done directly on the build plate, should have even thickness with little regular nobs)
The FEP should sit flush against the screen when the build plate is raised in order for your build plate to be properly homed and levelled.
To overly simplify things:
The Zero position of the build plate is the top of the screen + the thickness of the FEP.
This means that if your FEP isn't touching the screen then one of two things will happen.
The build plate will push the FEP down until it touches the surface of the screen, and stretch it out, in order to reach its zero position. So the tension of the FEP will be incorrect (and will possibly damage the FEP), when it comes to releasing each layer
The build plate's zero position will be the surface of the FEP, not the surface of the screen + the thickness of the FEP. So your resin will be cured further away from the screen than it should be.
In your case, you have warping rather than under exposure or light bleeding, so 1) is the most likely.
In short, screen too low = FEP tension is wrong = warped print.
