The BLTouch is an attractive Z probe option because it works on any surface, is relatively cheap, and provides good accuracy and repeatability. However, it can be tricky to get working. This guide will provide some troubleshooting tips for the most commonly encountered problems.
- Avoid Clones. This guide assumes you are using a genuine BLTouch from Antclabs. There are clones available, but many users have encountered quality issues using them. The most current version of the BLTouch is the BLTouch-Smart V3.1 from Antclabs. Most clones are a knockoff of the older BLTouch Classic and may require a resistor to function properly with 3.3v logic boards. You must ask yourself, are you really saving any money on the clone if you end up having to buy 2 anyway just to get a working one?
- Mount the BLTouch Properly. The BLTouch must be mounted firmly and squarely to the print carriage. Any flex or tilt could make the results unreliable. Also, follow the BLTouch instructions carefully with regards to mounting height. The tip of the BLTouch pin, when not extended, must be 2.3mm to 4.3mm above the nozzle tip to trigger properly.
- Check the Pin. The BLTouch won't function reliably if the pin is dirty or damaged. The pin can be removed for cleaning or replacement. The set screw at the top of the BLTouch holds the pin inside the body, and also acts as the ferrous core for the electromagnet to draw up the pin. Try loosening or tightening the set screw slightly to adjust the trigger sensitivity.
- Double Check Your Wiring. Follow the installation guide carefully The BLTouch has 5 wires that must be properly connected to function. Check for a loose crimp connection, or a broken wire with a multimeter.
- Cut the Trace. Version2 BLTouch Smart probes have a trace on the PCB which can be cut to allow safe functionality with 3.3v logic board, such as that used by the Duet. Use a sharp xacto knife to cut the trace completely. Use a multimeter to verify that it is completely cut. The Duet should be able to handle it without cutting the trace, but there have been user reports of problems being resolved after making sure the trace is cut.
- Note that BLTouch V3+ no longer has a trace and is not needed to work with the Duet.
- Use the Resistor. Older BLTouch Classic probes and most clones required the use of an included 240 Ohm resistor to function with 3.3v logic boards. Again, this shouldn't be necessary with the Duet, but there have been reports that it has solved problems, especially with clones.
- Test the Probe First. It's a good idea to test the probe configuration before mounting it on the printer. You don't want the probe to fail during a home operation because you could damage your hotend or bed surface. See here for testing procedure.