Compression Calibrator

This resin test is a series of steps from 0.05mm to 2mm for measuring Z height and compression.

Underneath there is also a gap test in the middle with distances equal to the 0.05-1mm measurements on the other side. This can be used to measure elephants-foot.

And then next to that at the edge are vertical gaps with the same distances so you can see how much cure through you have on base layers.

I've just updated this to include a LYS file with the 5 part model (needs unzipping) so you can adjust it to fit different build plate sizes.

This also includes a new model, which I'll fully integrate at some point, but at the moment it's just attached to the main step model. This new model has three rows of differently sized square columns under a hood if the base exposure is on the high side all of them will form, if it's on the low side most won't. About half is good. The advantage of this part is that you can use a high base exposure and lower it bit by bit until you can see the small parts failing and being caught by the roof rather than lowering the exposure until a raft fails and then you need to do a vat clean. It's also good to do this test in all corners and the middle because one area could be higher or dimmer so you need to expose for the worst area.

This is intended to be printed at 0.05mm/50um layer height.

If the 2mm height is accurate but the rest is off that means you have a good z height but have compression.

This can be reduced by:
- Heating up resin to make it less viscous
- Using less viscous resin
- Using a more rigid printer (ie one without springs)
- Using a smaller printer or one with holes in the plate, however
that ruins direct prints so not optimal.
- Slower retract speeds (ie 60mm/min or below)
- In actual prints, you can reduce it by reducing the surface area and surface area change throughout the print starting by not using massive rafts and then rotating models to reduce layer surface area, and for big enough models hollow them making sure to add holes on the plate side.
- Most importantly WAIT / REST BEFORE PRINT! Longer wait times allow for the printer to have time to squeeze the resin down to the correct layer height inspite of the high pressure resisting this on layers with high surface area such as the plate it's self, big rafts, big unhollowed models, or even hollowed models without correct holes that flex because of the pressure causing bad surface finish called bloom.

For normal layers usually 2s wait before print is fine on mid-sized printers, however for the base layers without much longer wait times the initial layers will form as much as 300um thicker than intended, which is why you need long base exposure times. With longer wait times you can dramatically lower base exposure to reduce elephants-foot, base cure-through and warping, allowing for direct printing like printing on FDM.

10s wait time on base layers usually gets most of the distance down, you can wait much longer like 60s+ which gets much closer but on the first couple layers that still might not be perfect because there are diminishing returns. But you can test yourself with this model.

If you find a result where the 1-2mm heights are less than 1mm that means you are getting compression ie 0.5=0.7, 1=1.1, 2=1.8.
This can happen from the initial layers forming too thick mainly because of a lack of wait time, causing the overall model height to be higher than it should be and as a result once the raft or plate is far enough away from the fep/lcd that it doesn't cause a lot of pressure then the printer can cure some layers too thin as the overall height normalizes to what it should be. If you have ever printed flat tests these issues have likely given you results I wouldn't trust because the layer heights are varying.
If you have lots of compression this is usually from the printer's Z height being set too low which can be fixed by releveling with a different number of sheets of paper or setting a Z=0 offset on the printer. If you have a lot of compression then using a measurement of 4-5mm can be more reliable for setting Z height than 2mm.

Personally on my elegoo printers because they per layer settings I use UV Tools to apply a 40s wait for the first 0.5mm (raft thickness) and then slowly transition to 2s over the next 1.5mm.