Marlin end code - relative distance

[kd7eir]

I am trying to set my end GCODE to raise the Z axis 25mm above the top of the print.

Right now I am using G1 Z25 F5000 ; lift nozzle but if my print is higher than 25 the
head crashes into the print.

Will this fix that -

G91 ; set relative positioning
G1 Z25 F5000 ; lift nozzle

[dustmann]

Which slicing software are you using? slic3r sets a G90 command at the beginning of a print to use absolute coordinates. Your G91 command set at the end of the G-code can remedy this as you have noted.

edit:

I have noticed that after completing a print and homing X/Y, it appears that when a new print begins without resetting the printer, the motors try to home even further (from the home position) resulting in a lot of skipped steps or mechanical crashes. Therefore as Mjolinor mentions below this is definitely not the recommended solution.

[Mjolinor]

It will work but the potential problem is that with relative distances and only a Z switch you may not have room to raise 25mm.

These are the sort of problem that are caused by using only a subset of proper Gcode. In real Gcode you can do conditional things and make more complex decisions.

[kd7eir]

I pay attention to the height of the printed object and if that would put me too high to raise 25mm I just set it to raise 2-3mm. Most of my prints are not that high, so I am good...for now.

[dustmann]

It will work but the potential problem is that with relative distances and only a Z switch you may not have room to raise 25mm.

These are the sort of problem that are caused by using only a subset of proper Gcode. In real Gcode you can do conditional things and make more complex decisions.

Does this break the parameters of the limits set in firmware? When I add a G91 followed by a G1 Z25 on a 10mm test cube, the LCD is reporting 35.0mm as the final Z position before homing. A G92 command without parameters would set all axes to 0, which could cause mechanical issues (loss of current position relative to endstops)

[dustmann]

I have had quite a few mechanical crashes after adding this end code, it works fine for the first print, but causes crashes at the beginning of a new print. See my original post above.

[kd7eir]

I'm using Simplify3D. It issues a G90 at the beginning as well.
I have not seen any change in my homing and auto bed leveling behavior since implementing this.