I am trying to modify ttsalo's fork of Marlin that is used for SCARA printers. The program begins by homing each axis like this:

G21 ; set units to millimeters
M107

G28
G92 X0 Y0 Z0
G1 Z5 F5000

G90 ; use absolute coordinates
G92 E0
M82 ; use absolute distances for extrusion
G1 F1800.000 E-1.00000
G92 E0
G1 Z0.300 F1800.000
G1 X79.507 Y77.641 F1800.000
G1 E1.00000 F1800.000

However once the homing is complete, the X axis rotates, then the extruder waits to heat up and then the print begins. My question is which part of Marlin governs this initial movement?

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[scara3dprinter.wordpress.com]

It's not marlin at all. Marlin just executes the G Code it's given.

For what you are looking for, I think you want to look at the start G Code that is inserted by your slicer.

Something else is going on because x and y home, then the x arm swings over, the z axis then drops 5 mm, this code has the hot end heating portion deleted but normal it would wait until the hot end heated up, then the z axis raises to 0.3 mm spacing from the hot end and the x arm swings the hot end to the center of the bed. Something else must be going on, some programed routine is causing this.

Its occurring right here:

G28
G92 X0 Y0 Z0

????????????

G1 Z5 F5000

Edited 1 time(s). Last edit at 03/29/2015 08:27PM by Evil Monkey.

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[scara3dprinter.wordpress.com]

Take a look at Marlin.cpp, that is where the G-code is interpreted.

Do you mean Marlin_main.cpp? I've been digging around in there but can't seem to find what is causing this.

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[scara3dprinter.wordpress.com]

I think it has something to do with the G92 command.

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[scara3dprinter.wordpress.com]