What the "Z=0" function really does...

[cliffyk]

In an effort to fully understand the "Z=0" firmware function I ran some experiments using a dial indicator, with calibrated 0.0005" (12.7 μm) accuracy.

I first mechanically aligned the platen using the procedure from the 07/22/2019 version Mars Users Manual:




Next I "printed"(vat in place, but no goop) a model and observed via the dial indicator the first layer motion of the platen.

What I found was that when executing G-Code the platen first descended to the limit switch defined "end-of-travel" to establish a reference, and then rose 0.002" (50 μm, the layer height defined in Chitubox) to print the first layer.

I then did the "Z=0" logical setting of a "0" reference as shown in this video--in which the "Z=0" button is pressed after raising the platen 0.1 mm (100 μm) from the limit switch restricted "end-of-travel".

"Printing" the same model as above I observed the platen descend to the limit switch "end of travel" but then rise by 0.004" (100 μm)--I.e. when commanded to move to "0" by G-Code it first went to the limit switch "end of stroke" to "get it's bearings", then rose to the logical "0" position set by the "Z=0" function, which of course will make the first layer 100 μm thick.

This is why Elegoo support in their first response stated the "...zero reset function is mainly to compensate for the large Z-axis error of the machine during long-term use of the machine, and the size of the Z-axis method of the model is not accurate." Prior to this exercise I had not really understood what they meant by "...and the size of the Z-axis of the model is not accurate." 

The "Z=0" function allows you to "fine tune" your model's height (upward), however of course only in 100 μm increments with a practical limit of how thick of a first layer can be cured.

I hope some find this analysis to be of assistance, it helped me better understand WTH the "Z=0" function does and why one would utilize it...