close up look at the printhead

Preface#

When tuning settings on my printer I do a lot of test prints. For best adhesion and dimensional accuracy you want to probe a bed mesh which stays valid as long as you don’t move the bed.

I happen to be very impatient so I take the build plate off of the print bed to have my print ten precious minutes earlier. Now, it so happens that probing the bed with the original probe — slowly; point, by, point — takes about five minutes which can be a significant slice of the printing time on short test prints. One day, while watching YouTube, the existence of eddy current probes was brought to my attention. When I saw the ability to scan the bed in mere seconds I was already sold.

However the price, inability to have downtime 1 and the need to modify my firmware kept me from them for a few months. As soon as I had a few days free I switched over my printer to mainline klipper by following this guide.

My buddy Eddy#

BTT Eddy probe seen from the front
Exploded view of BTT Eddy probe

I landed on the eddy coil from big tree tech because it was well supported and cheap. The schematic for the print head board seemed to indicate that I could get access to all the pins I needed.

I bought a spool of ASA filament which was recommended for parts that need to be close to the hotend to print the probe holder. A quite uneventful — if smelly — part of the process. 2

BTT eddy probe taken out of plastic shell and mounted to printhead with the probe holder mentioned earlier

Unfortunately after a few hours of fruitless attempts to get the probe to talk to the printhead’s µc with loose wires — pictured above — the unthinkable happened: I shorted the probe’s 3.3V input to the print head’s 24V rail through a floating wire! 😱

Though quite bummed I was relieved I wouldn’t have to figure out how to make the i2c version work. I bought the USB version — slightly more expensive — to make sure I would have a working system in the end and painstakingly fed the wire through the existing cable path.

Same as before but this time with a cleaner cable that goes to the cable bundle instead of the printhead PCB

After following the a guide I finally was able to calibrate the probe and get scanning:

Since then my prints have been slightly more reliable and short prints have been made even shorter. (plus it’s fun to watch)

  1. I was — tragically — working on the Eurobot cup ↩︎

  2. Please ventilate well when printing ASA it’s not good for you! ↩︎