Can't decrease Z-axis below zero with Marlin v2.1.1 until manual G1 command is given

idontseeit

Hello,

I have a Delta printer controlled with v2.1.1 Marlin firmware that I'm manually calibrating without a Z probe (using a piece of paper between nozzle and bed).

In Marlin I have set the DELTA_HEIGHT to a little under the exact distance between my nozzle (in the home position) and the bed, so that when initiating the bed leveling procedure with G29 the nozzle does not crash into the bed. 

I've noticed that Repetier-Server won't let me decrease the Z-axis below 0, even after sending M211 S0 to Marlin in order to disable software endstops.

Here is the console log from Repetier-Server

1. Line 118-125: after starting G29, I decrease Z axis by 0.2 mm to get down to 0.0 mm
2. Line 128-129: A further Z decrease by 0.1 mm sends the same G1 Z0.00 F6000, ignoring the negative Z value
3. Line 132-135: disabling Marlin software endstops to assure that Marlin can go beyond minimum Z position (0.00 mm)
4. Line 138-139: Same result as before; a decreasing Z button press does not send a negative Z axis value
5. Line 142: Instead of clicking on the decrease Z axis in Repetier-Server, I send a manual G1 placement below Z axis (the printer responds and decreases by 0.1 mm)
6. Line 144-145: Now I click on decrease Z axis in Repetier-Server and the correct G1 command is sent (G1 Z-0.20 F6000)
7. Line 148-166: This then allows me to go above and below the Z axis, after somehow "unblocking" the negative Z axis values

Any thoughts on this?

Repetier

Server does not prevent moves below 0, but since Z=0 is bed height it won't allow it's move buttons in gui to go below. You can still send G1 Z-1 and if firmware allows moving below it will happen. This is to protect printers since it is not wise to crash print head by going outside allowed region. Once calibrated this is also good as you won't crash unintentionally into bed (at least if moving without homing is disabled in firmware).

If you want to use buttons for speed add 10mm to height, then z=10 will be theoretical z bed level but you can still go deeper. And once it is calibrated you subtract height considering the 10mm extra value.