Z Endstops - 3018 CNC Mill

Z Endstops - 3018 CNC Mill

This installs a pair of Z-axis endstops for a 3018 CNC table top mill.

Most of the cheap 3018 CNC mills out there seem to be very similar.  I expect that this will work for many/most of them.  There are probably simpler, easier ways to do this but it works.

An earlier attempt by a different method was a complete failure, vibration being the main villain.  To quote a co-worker from long ago about a different but similar situation, "It hummed like a 6-penny finishing nail hit with the round end of a greasy ball peen."  This project captures the lessons learned from the earlier one and was completely successful.  As my Son-in-Law observes, if it looks stupid but it works, it's not stupid.

This project does not require any drilling to any part of the mill and only light drilling to clean out and properly size the printed holes in the two Switch Actuators.

The images above should communicate the concept pretty clearly.  An M5 threaded rod anchored to the Z carriage/spindle motor carries the switch actuator discs.  A structure attached to the top of the stationary Z motor mounts the two switches.  The lower switch is the up limit and vice versa.

EDIT 8/15/25: I should note here that part of my design criteria was to not restrict the X-axis range of the mill.  This accounts for everything being stacked up over the spindle and Z-axis motors.  If not for that restriction, this could probably have been a little less complicated. END EDIT

Installation:

Print all parts. Note two Switch Actuators are required.  

Install brass threaded inserts in the Z Motor Cap (6 M3 inserts) and the Z Motor Cap Bonnet (7 inserts; three M3 inserts and four M2.5 inserts). NOTE: All the 3D printed holes for brass inserts are shouldered.  Be sure to install from the correct end.  Heat setting should not be needed; pull them in cold with a screw until they're shouldered.

Press or glue an M5 hex nut in the pocket in the Actuator Mount. Install a ~ 175 mm M5 threaded rod flush with the pocketed nut. Secure with an M5 flat washer and nut on the top of the Actuator Mount.

Drill out and tap the center hole in the two Switch Actuators - 4.2 mm and M5.  As-printed, the hole will probably be a little undersized.

Remove the four existing Z motor screws and install the Z Motor Cap on top of the motor using four M3 X 35 mm Allen head cap screws and M3 flat washers. The screw pockets in the part are sized to accept the washers. The side without holes faces the front of the machine.

Install the Z Motor Cap Bonnet on the Z Motor Cap using six M3 X 18 mm Allen head cap screws with M3 flat washers. (20 mm screws OK here).

NOTE: I found it easier to perform the step below after the Z Motor Cap Bonnet was secured to the machine but if you prefer, the step above and the step below this note can be reversed

Install the two switches, with wires already attached, inside the Z Motor Cap Bonnet through the large slot at the back. The smaller slot on the side provides access for an Allen wrench. Secure the switches to the Z Motor Cap Bonnet using four M2.5 X 14 mm Allen head cap screws; flat washers are optional - the plastic of the switch bodies is hard enough that the washers aren't really needed (15 or 16 mm screws OK here).

If necessary, bend the actuator arms of the limit switches so that the roller protrudes at least 2 mm from the face of the Z Motor Cap Bonnet; a few mm more is OK.

Disconnect the front motor lead spade connector from the spindle motor (red wire on mine).

Push the Actuator Mount over the spindle motor, all the way down until bottomed.

Reconnect the front motor lead spade connector to the spindle motor.

Install the two Switch Actuators on to the M5 threaded rod, with an M5 hex nut and flat washer above and below each.  When adjusted and set these are triple-nutted with the two hex nuts and the threaded Switch Actuator jammed together.

Install the Actuator Support to the top of the Z Motor Cap Bonnet with three M3 X 14 mm Allen head cap screws and flat washers. (15 or 16 mm screws OK here).

Set the Switch actuators as desired on the M5 threaded rod and lock them with the hex nuts.

BILL OF MATERIALS

Printed Parts:

- Actuator Mount
- Actuator Support
- Switch Actuator (2 req'd)
- Z Motor Cap
- Z Motor Cap Bonnet

Purchased or Parts Box Parts

- M5 threaded rod, ~ 175 mm long
- M5 hex nut (6 req'd)
- M5 Flat washer (5 req'd)
- M3 X 35 mm Allen head cap screw (4 req'd)
- M3 X 18 mm Allen head cap screw (6 req'd)
- M3 X 14 mm Allen head cap screw (3 req'd)
- M2.5 X 14 mm Allen head cap screw (4 req'd)
- M3 flat washer (13 req'd)
- M3 X 5 mm diameter X 3 mm long brass threaded insert (9 req'd)
- M2.5 X 3.5 mm diameter X 4 mm long brass threaded insert (4 req'd)
- Micro Limit Switch SPDT 1NO 1NC with Roller Lever Arm (2 req'd)

Printing Notes:
[None of these are carved in stone; do what works for you.]

- PLA
- 0.4 nozzle
- 0.15 or 0.2 mm layer height as desired
- Supports: Z Motor Cap Bonnet (for slots); Actuator Support (for bushing)
- Shells: 0.8 mm
- Infill: 16%