Z Axis Limit Switch Instructions

The Z axis limit switch mount allows you to have your Thing-O-Matic self-teach the Z axis HBP Heated Build Platform position. I rarely tweak the Z offsets on my builds with this update.

Parts: Limit switch block (Plotted), 2 M2 x 25mm screws, 2 M2 x 12mm screws, 4 M2 Nuts, 1 Makerbot Limit switch assembly (Available from the Makerbot Store).

Assembly:

(Note, the build platform needs to be leveled before proceeding)

Plot the limit switch block. Lay it on its largest flat side (4 hole surface down)

Place the limit switch assembly on the thin flange with the limit switch trigger leaf extending below the edge nearest the 2 mounting screw holes.

Fasten the limit switch assembly to the thin flange of the block via the 2 M2 x 12mm screws and nuts.

Mounting the Limit Switch Block:

The limit switch block mounts with the switch down in-line with the plotting nozzle as you look across the HBP surface. I found just touching the corner of the build platform at the X-Y home position works well.

Lower the Z axis assembly to just clearing the HBP then Home the HBP (push it by hand). Place the limit switch block on the side of the Z axis assembly in between the nozzle interface PCBA and Z axis guide shafts (edge of the limit switch block ~25mm from the rear edge of the Z axis assembly, such that it triggers when slid vertically down to contact the corner f the HBP. Scribe/mark 2 holes in the center of the slots in the limit switch block.

Drill two 2 mm dia holes and mount the block to the Z axis assembly with the remaining 2mm screws and nuts. Adjust the limit switch vertically to trigger before the nozzle contacts the HBP surface.

Connect the new Z axis limit switch cable to the limit switch assembly and route down to connect to the Z axis home location on the mother board.

Code Changes:

Locate the Start Code in the ReplicatorGxxmachinesThingomatic directory. Add the lines to the code described between the comment lines (HBP Z Limit Switch Start) and (HBP Z Limit Switch End) below:

(**** beginning of start.gcode ****)
(This file is for a MakerBot Thing-O-Matic)
(**** begin initialization commands ****)
(… initialization code is here…)

(**** end initialization commands ****)
(**** begin homing ****)
G162 Z F4000 (home Z axis maximum)
(G92 Z10 (set Z to 0)
(G1 Z0 (move z down 10)
(G162 Z F150 (home Z axis maximum)
G161 X Y F2500 (home X & Y axis minimum)
M132 X Y Z A B (Recall stored home offsets for XYZAB axis)

(HBP Z Limit Switch Start)
G1 Z10 (Move Z down to 10)
G161 Z F250 (Move Z down until switch contacts platform)
G92 Z0 (Set Z to 0)
(Edit the following line to “fine tune” the height of the nozzle after the limit switch is set close)
G1 Z0.4 (Move Z to tweak offset due to sensor location)
G92 Z0 (Reset Zero after the tweak)
G1 Z10 F1500 (Move Z up 10)
(*** Z is Ready ***)
(HBP Z Limit Switch End)

(**** end homing ****)
(**** begin pre-wipe commands ****)

(… more start code continues here…)

(**** end of start.gcode ****)

Set-Up And Calibration:

Run a small test part such as a 20mm x 20mm x 3mm thick plate.

Adjust the line in G-Code “G1 Z0.4” above to set the correct offset of the nozzle to the platform.

Note: You will get a warning message from the Replicator software that you are homing in the wrong direction (just answer “Proceed Anyway”), and the build will start.