Lowering Z-Axis for cover

Hi, I just setup my mini last week. I purchased an acrylic case because I print in a cool basement. The acrylic top is supposed to sit flush with the top of the case. With my printer when I finish a print the printer head is going to the top of the case and knocking off the acrylic top.

I placed a 5mm shim above the Z-Axis limit switch which keeps the print head just under the case, but now when I start a print the extruder is digging an extra 5mm into the cleaning pad. I tried dropping the max print height 5mm in Cura as Lulzbot support recommended but it did not make a difference. Is there a G-Code command to modify the firmware? Thanks.

My Mini.
Normal_Top.jpg
Normal Plate Install.

I believe you want to change the Z in these lines of code found in the start of your gcode files:

G1 Z0 F1200 ; CRITICAL: set Z to height of top of scraper
G1 X45 Y174 Z-.5 F4000 ; wiping ; plunge into wipe pad
G1 X55 Y172 Z-.5 F4000 ; wiping
G1 X45 Y174 Z0 F4000 ; wiping
G1 X55 Y172 F4000 ; wiping
G1 X45 Y174 F4000 ; wiping
G1 X55 Y172 F4000 ; wiping
G1 X45 Y174 F4000 ; wiping
G1 X55 Y172 F4000 ; wiping
G1 X60 Y174 F4000 ; wiping
G1 X80 Y172 F4000 ; wiping
G1 X60 Y174 F4000 ; wiping
G1 X80 Y172 F4000 ; wiping
G1 X60 Y174 F4000 ; wiping
G1 X90 Y172 F4000 ; wiping
G1 X80 Y174 F4000 ; wiping
G1 X100 Y172 F4000 ; wiping
G1 X80 Y174 F4000 ; wiping
G1 X100 Y172 F4000 ; wiping
G1 X80 Y174 F4000 ; wiping
G1 X100 Y172 F4000 ; wiping
G1 X110 Y174 F4000 ; wiping
G1 X100 Y172 F4000 ; wiping
G1 X110 Y174 F4000 ; wiping
G1 X100 Y172 F4000 ; wiping
G1 X110 Y174 F4000 ; wiping
G1 X115 Y172 Z-0.5 F1000 ; wipe slower and bury noz in cleanish area
G1 Z10 ; raise z

Probably want to set the first Z to 5 and the following Z’s to 4.5.

In simplify3D you can easily change this part of the Gcode in their program. However, I don’t see this gcode in cura’s start.gcode. So i have to assume that their wipe routine is hard coded into their version of cura.

To test your theory, create a gcode file, then go in with a txt editor and modify the wipe routine to see if it fixes it.

Jim

Thank you. I do not want to edit my G-Code each time so I am going to ditch this top. I guess the design is not perfect, and for me it is not worth the hassle.

Put the 5mm shim in place to stop upward travel before it hits the acrylic top.

Then do ONE of the following:

  1. Get firmware source, edit configuration.h file, change Z_MAX_POS from 159 to 154, rebuild firmware and reflash. This will tell the firmware that it is at 154 instead of 159 when hitting the endstop, and that will allow the existing clean/wipe scripts to function correctly.
    OR
  2. Send the printer the commands “M206 Z-5” followed by “M500”. The first command offsets Z coordinates, which will effectively make the end-stop position 154. The second command saves the change to memory (otherwise it would be lost at next reboot). The next time you “home” the printer and it hits the endstop, the Z position will effectively be 154 instead of 159. Existing clean/wipe scripts will function correctly.

Either of those will compensate for the lower effective endstop position caused by the shim. All existing scripts will work – unless they command the printer to go higher than 154. Trying to go >154 would hit the endstop and be ignored.

If you choose #1… You’ll need to do it again if you want to flash a newer firmware from Lulzbot. Other than that, the change will “stick” permanently.

If you choose #2… You’ll want to check the offset if/when you ever flash a new firmware. The setting may survive a new firmware flash, or it may not (depends on firmware layout). If it doesn’t survive, you just need to send the “M206 Z-5” and “M500” again. Other than that, the change will “stick” permanently.