Optical Tramming Gauge Mount for accurate build plate leveling

Update 2-15-13:
I've been having trouble getting consistent results using the first iteration. I'm uploading another version that will allow me to use the leveling process included in the firmware. There's an arm on the side that depresses the limit switch, tricking the bot. This puts the sensor exactly where the extruder will be when it is time to print.

Hopefully this will solve the consistency issues.

I used a Keyence fiber-optic DIN rail amplifier (FS-V31C) and sensor head. I like the optical solution because it doesn't touch the build plate while you're working. I used some post-it notes on each corner so that I would get uniform reflectivity for the sensor head. I also put a single note at rear center just above the thumb screw.

First, jog the printer head to slightly left of the the rear center and use a thin strip of paper between the extruder and acrylic to set the initial height. Don't use a business card, it is too thick. Ensure that your optical sensor is pointing directly at the post-it, and take a reading. Take readings and adjust at each corner post-it until all 4 readings are close to the same as the initial reading.

It may be possible to mount the sensor head next to the nozzle using a FU-35tz.