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What the "Z=0" function really does...
#1
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:

[Image: AlignFromManual-00.jpg]
[Image: AlignFromManual-01.jpg]

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...
-cliff knight-
[Image: 816-20120803-wide800.jpg]
paladinmicro.com
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#2
I found this post very useful, but I still have one question.  Do you need to do this every time you repower the printer?  In other words, is this a one time setup that is remembered after the printer is turned off?  I have found that I can keep the printer running and do multiple prints with the same height calibration (including removing the bed and reinstalling), but I haven't tried printing without doing a height calibration after powering the printer on.
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#3
(09-13-2020, 12:24 PM)TomWS Wrote: I found this post very useful, but I still have one question.  Do you need to do this every time you repower the printer?  In other words, is this a one time setup that is remembered after the printer is turned off?  I have found that I can keep the printer running and do multiple prints with the same height calibration (including removing the bed and reinstalling), but I haven't tried printing without doing a height calibration after powering the printer on.

The "Z=0" setting is stored in non-volatile memory, there is no need to repeat the adjustment at each power-up.
-cliff knight-
[Image: 816-20120803-wide800.jpg]
paladinmicro.com
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#4
Nice post. I have been running z0 off of the sheet of paper and not raising it then zeroing. I haven't had any problems doing this.

I suppose this raising the height method could maybe be used to cure the elephants foot if some material is going to be removed off the bottom of the model anyway. Idk?
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#5
(09-19-2020, 11:54 AM)NeSs7or9 Wrote: Nice post. I have been running z0 off of the sheet of paper and not raising it then zeroing. I haven't had any problems doing this.

I suppose this raising the height method could maybe be used to cure the elephants foot if some material is going to be removed off the bottom of the model anyway. Idk?
Using "Z=0" without manually raising the trolley just sets the logical zero position to coincide with the mechanical zero--I.e. it does nothing that the firmware does not do by itself.

I have never used it ("Z=0") so I cannot comment as to it's effects. I have not found the mechanical alignment process to be so bothersome as to prevent my doing it periodically.
-cliff knight-
[Image: 816-20120803-wide800.jpg]
paladinmicro.com
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#6
"I have never used it ("Z=0") so I cannot comment as to it's effects. I have not found the mechanical alignment process to be so bothersome as to prevent my doing it periodically. "

Curious reply. I've used your advice from above on how to use Z=0 and, along with the information that the setting is non-volatile, my practice has been:
Home with 2 sheets of paper.
Adjust 0.1mm up until paper will slip out with slight tension (typically one 'up' pulse).
Set Z=0.

I've done this once and then have done multiple prints with multiple power cycles over several days and every print was fine (other than other parameters I might have messed up on the print). So, to me, the process works and hasn't required realignment yet.
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#7
I have only realigned the platen a few times, after replacing the FEP or the LCD. I found Elegoo's specification of "a sheet of paper" to be a bit ambiguous ("sheet of paper" is not a standard unit of measure) so I found a piece of paper that was 0.15 mm thick (30 lb vellum) same as the OEM FEP. Using that as a spacer I adjust the platen mechanically so as to provide the stated "snug fit"¹ I have played with the "Z=0" setting, but never found any need for it.

------------------------------------
¹- Still a less than precise specification, but better than "sheet of paper". BTW, a sheet of plain ol' common 20 lb bond copy/printer paper is 0.097 mm, some 53 microns thinner than the FEP.
-cliff knight-
[Image: 816-20120803-wide800.jpg]
paladinmicro.com
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#8
Nice work man, I had not had time to look into it all. 

Like you , Ive never used the thing and never had issues either printing.
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