How to Diagnose Home Switches.  

Homing is the process the CNC uses to drive each axis to a known location, generally the location of X, Y, and Z home switches so that the firmware can accurately calculate the travel limits of the three axes. 

Every time you turn your CNC you will home the machine. First, the Z axis will travel upward, bump the Z Home Switch descend 5 mm and then slowly rise to trigger the home switch for a final time.  Next, the Y Axis will travel until it triggers the Y Home Switch while simultaneously the X Axis will travel back until it triggers the X home switch.

But what if your machine will not home?  The following are the recommended steps to diagnose the problem.

STEP ONE: Verify Home Switch connections to the controller (Self Squaring Gantry)

STEP TWO: Using UGS to Confirm Home Switch Function.

  1. Connect the computer to the CNC with the USB cable (verify the cable is connected to the controller). You do not have plug in the power supply. Open UGS and verify the comport, the firmware must be set to GRBL and the Baud Rate set to 115200. Click the connect button.
  2. With the UGS screen open manually trigger the Z Home Switch. Note that ALARM: X Z appears at the bottom of the DRO. This indicates that the Z Home Switch is operating normally.  (NOTE: the X axis is also shown as triggered because the self-squaring gantry feature uses one pin on the controller to designate two separate axes.  Once the Z axis has been homed it is shut off and the X axis is used).  Machines without a self-squaring gantry will show ALARM: Z in the DRO (shown below).

When the Y Home switch is triggered the ALARM: Y is displayed.

When the X1 Home swith is triggered the ALARM: X is displayed unlike the X2 Home switch which shares its pin location with the Z home switch .

If a switch does not trigger, make sure the switches are mounted correctly and that that the switch housing isn’t bolted too tightly which can keep the switch mechanism from functioning properly.

Make sure the X1 and X2 Switches are positioned and wired correctly, see below. The location of the switches is shown from the back of the machine.

June 23, 2020 — Keith Havens