Lots of folk seem to have issues with setting the build plate level at Z=0 on the Elegoo Saturn 2 SLA printer. This is really important for successful printing. But I assure you that the Elegoo instructions and spacer don’t work. So here is a simple quick step-by-step guide to making the build plate level with the FEP and at true Z=0.
Before I launch into the procedure I’m going to make a few statements of fact.
True Z=0 is with the build plate in contact with the FEP sitting on the LCD.
Z=0 is not with the build plate at some arbitrary height above the FEP. If you don’t believe me then look at the first layer height of your model in your slicer. It will be at the print layer thickness above the FEP.
Don’t use the spacer card that came with your Saturn 2. It is too thick.
Your FEP is likely somewhere between 0.127 and 0.150 mm thick and may have stretched slightly thinner than the manufacturer’s specified thickness over time. The Elegoo spacer card is 0.32 +/- 0.01 mm thick. So if you use this card your first layer will be between +0.16 and 0.203 mm too thick (additional to the initial layer thickness). The default layer height for the Saturn 2 is just 0.05 mm thick so with the Elegoo supplied spacer card your initial layer is four to fives times too thick.
Ideally the spacer should be the same thickness as your FEP for true Z=0. The only way to achieve this is to level and set Z=0 on an empty resin vat but this isn’t very convenient. You can also use a spare sheet of FEP as a spacer, but this requires that you have a spare sheet, and FEP is somewhat expensive.
A sheet of 80 g/sq m paper is 0.10 +/- 0.01 mm thick. So two thicknesses with be 0.20 mm +/- 0.02 mm. This is still too thick for a spacer but A4 paper is just a few cents a sheet, environmental (in fact really good carbon capture) and our initial layer will be within +0.03 and 0.093 mm too thick. This is approaching the layer resolution on the Saturn 2.
When setting Z=0 and leveling the build plate don’t press down firmly on the build plate. I’ll say that slightly louder.
Don’t press down firmly on the build plate.
This is contrary to Elegoo’s instructions. The build plate is already under spring compression against two thickness of paper. But it is impossible to press down on the build plate without causing it to rotate sightly, perhaps by as little as 0.06 degrees. At the edges of the build plate this rotation appears as a change in clearance of about 0.10 mm.
With the discussion out the way here is the procedure that I use followed by a captioned video.
Remove the resin vat.
Tighten the build plate top screw to secure it to the Z axis.
Loosen the two hex cap clamping bolts on the build platform with the hex key provided and confirm that the build plate is free to rotate and lift without resistance.
Check that the build plate and LCD are clean.
Place a folded sheet of A4 80 g/sq m paper on the LCD (two thickness of paper).
Use the touch screen to home the build plate and rotate it square with the edges of the LCD.
Hold the build plate gently in place without firm downward pressure while progressively tightening the two hex cap clamping bolts, initially finger tight and then using the hex key.
Use the touch LCD screen to set and confirm Z=0.
Now raise the build plate using the touch screen about 10 mm, remove the paper, and re-home the build plate.
Test for level with a single sheet of A4 paper. It should slide freely between the build plate and the LCD across the full area of the build plate. If it does then we’re done. Raise the build plate say 100 mm and refit the resin vat.
If the paper won’t slide between the build plate and the LCD then note where it is jamming. Repeat setting Z=0 but this time apply gentle downward pressure on the diagonally opposite side of the build plate from where it was jamming and repeat the clearance test.
Click on the Image to Link to the Video
A question that comes up from time to time is how often should you set Z=0 and level the build plate?
Level and Z=0 shouldn’t change, even with changes in ambient temperature. But you should repeat the procedure any time:
a model failure causes the stepper motor to skip, or
a model fails to adhere to the build plate, or
you manually rotate the Z axis lead screw, or
the build plate moves under the clamping bolts, or
you replace your FEP.
If my Saturn 2 has been sitting idle for more than a few days I like to filter the resin before I start the next print job to make sure that it’s well mixed and free from any filaments or particles of partially cured resin. Leveling and setting Z=0 take just a few minutes and has no detrimental effects of the printer so I do this at the same time.