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The first printer I built used direct GPIO input with a NanoDLP shield. This bottom up printer only has an end-stop at the z-max position (the position farthest from the resin vat) and no end-stop at the z-min position. The printer is calibrated by lowering the build plate to just above the resin vat floor and using the Measure Z Axis button in NanoDLP. This button measures the distance from the resin vat floor to the z-max endstop and is the only z-axis calibration that is necessary.
I am now building a new printer using RAMPS instead of direct GPIO input. My initial intention was to build it the same way with only one z-max endstop. However, there is no Measure Z Axis button with RAMPS and it seems like this is because RAMPS firmware has no measuring capability. My understanding is that people who have built bottom up printers with RAMPS instead use a z-min endstop which is triggered when the build plate reaches its zero position, right above the floor of the resin vat.
I would like to confirm that there is no measuring functionality in RAMPS and that a z-min endstop must be used before I change my design.
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You can use M114 to get information on the current position.
Automatic probe is available but as nobody using PDMS anymore, it is not needed to be used frequently once measure it and enter it manually.
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Thank you Shahin! In case it is of use to others, here is the workflow that I have found for calibrating the Z-axis when only using a z-max endstop. Note that this workflow is for a bottom up printer using a RAMPS board.
1) Manually lower your build plate to the desired 0 level (just above the resin vat floor)
2) In the G-Code terminal, run the command [[PositionSet 0]] to identify this as the zero position
3) Manually raise the build plate until it just triggers the endstop
4) In the G-Code terminal, run the command M114 to find the current z-axis height
5) In System -> Machine Settings -> Axis / Movement set Z-Axis Height to the value returned by M114
When the print begins, the homing command G28 will lift the build plate from whatever location it is in to the endstop. Once the endstop is triggered, the printer will set its position equal to whatever position you input in the Z-Axis Height setting. From here it can move to the 0 position and begin printing.
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