One thing missing from our CNC routers is an automatic axis home circuit. This is something that signals the control software that the gantry is in a known position (usually at the origin). A lot of CNC hobbyists like to use the end mill as part of the homing circuit – this is OK, but does not take into account different sizes of bit diameter. A better solution is to have the X/Y home switches attached to the linear axis. Then the home position will be the same regardless of bit diameter.
Initially I wanted to use Hall Effect sensors, but the detectors themselves proved difficult to get. I’ve had some QRD1114 reflection sensors for some time, so I thought it was about time I put them to good use.
Initially I used a PNP transistor to amplify the switching signal from the sensor, but this proved to be way too analog. The resulting signals were not very clean. So instead I used an LM324 opamp configured as a comparator, with a simple potentiometer providing the reference voltage. A 1M resistor is used for feedback, providing some hysteresis around the switching point. Eliminating any potential chatter that can occur.
Once we have the system fitted and working – I’ll be publishing a howto guide.
This switch will be used to home the X and Y axes, the Z axis will be using a touch plate.