If you own a CNC mill without automatic end stops, you've probably had to restart a few jobs from the beginning because you over-ran where your end stops would've been, or you did something that set off your CNC mill's alarm. This optical alignment tool will help you get back on track from where you made your mistake rather than forcing you to start over by allowing you to manually re-zero your CNC using a cheap USB microscope you can mount to your CNC mill.

Parts Needed:

• A 12mm diameter USB microscope. I bought this one for another project a while ago. and share it between that other project and this. You may be able to adapt this part to fit other microscope designs, but although the above-linked product is no longer available, there are, at present, several other identical microscopes available on Amazon:
  • https://www.amazon.com/Koolertorn-Microscope-Adjustable-Collections-Inspection/dp/B01FZ0FNA6/ref=sr_1_21?s=electronics&ie=UTF8&qid=1504669228&sr=1-21&keywords=USB+microscope
  • https://www.amazon.com/Microscope-MixMart-Endoscope-Collections-Inspection/dp/B01L6L80Q2/ref=sr_1_35?s=electronics&ie=UTF8&qid=1504669280&sr=1-35&keywords=USB+microscope
  • https://www.amazon.com/Microscope-1600x1200HD-Endoscope-Collections-Inspection/dp/B06XHHJ1SS/ref=sr_1_39?s=electronics&ie=UTF8&qid=1504669280&sr=1-39&keywords=USB+microscope
  • https://www.amazon.com/Andonstar-10-300x-Microscope-ImagingOptical-resolution/dp/B071WK7QCC/ref=sr_1_63?s=electronics&ie=UTF8&qid=1504669298&sr=1-63&keywords=USB+microscope
• (Optional) 2x M5 Roll-in spring T-nuts. These are used for securing your target in a stable position. They are not strictly necessary -- the part might be snug enough in its design to not be too-easily moved, but if you do not use these, I recommend holding the target arm in place using a little bit of tape. If you do go the spring t-nut route, you probably don't need to screw them in using a bolt as you've seen me do in the above photos; the spring is probably more than enough tension to prevent anything from moving around.
• Software allowing you render crosshairs on your webcam's image. This is something that both bCNC and Chilipeppr can do with minimal effort.

After printing the target arm, you will want to either draw a target onto the top of the arm, or print, cut out and tape or glue on a gridded target like I've done.

Use Instructions:

1. Before beginning your print job, zero your CNC such that your camera's crosshairs are exactly aligned with the target image.
2. Machine your thing. If a problem occurs causing your CNC to become un-zero'd, move your CNC back to the zero position by moving to the point at which your camera's crosshairs line up with the target image as they did in step #1.