Testing the precision of Elegoo Mars – Volume 1: Z-axis

I have recently bought a new SLA printer – Elegoo Mars. For 250 € it is a wonderful device (I have to admit there are some minor flaws, but for the price).

I am interested in making precise mechanical components with it. Small teaser – you can make herringbone gears with module M0.5 or even M0.3. Wonderful. However, during my experiments, I have found a strange behavior regarding the height of the components. It seems like the first 5 layers have a wrong height. Therefore, I prepared a test piece and performed some measurements.

The test piece is simple – it is a staircase with steps of 0.2 mm in the Z-axis and 1 mm in the horizontal plane. Then I printed the piece several times and measured the height of the steps.

Numbers 1, 2 and 4 were printed directly on the bed. Piece number 4 was printed on supports (3 mm height). See, that pieces 1, 2 and 4 seem to have a thin beginning. My measurements confirm that (direct link to the table):

As you can see the printer is quite precise, however, there seems to be something wrong with the first 1 mm of the Z-axis – once I lift the model on the supports, the problem disappears. Note that I sanded the bottom of the lifted model, as the overhangs are always a little bit convex. I examined the sliced files with Photon File Validator and they seem fine. Therefore there has to be something wrong in the printer – either buggy firmware or hardware error.

I haven’t found the cause of the problem yet – do you have any ideas what could it cause? Does your printer feature the same behavior? Test it and let me know. Here is the Fusion model: https://a360.co/2NlHemW.

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