I've created this writeup on my current Cricut PCB process, and posted to the hackerspace Wiki.
I make PCBs on the Cricut by the following process:
1. Design a one-sided board in Eagle. Export the trace and pad layers only to a monochrome PNG file. 150 dpi seems to work well so far.
2. Using GIMP, add a fine outline around all traces.
- select the entire background color (black) with the "Select by Color Tool". - Do a "Select->Shrink" and shrink the selection by 1 pixel. - Fill the entire selection with the trace color (white) using the Bucket Fill tool. Make sure you have "Fill whole selection" set. - "Select->Shrink" by 1 pixel again. - Fill the entire selection with the background color (black). - Finally, save out your image as a PNG file.
3. Import the GIMP image into whatever software you are using to drive the Cricut (such as Make-the-Cut). In Make-the-Cut, I use the following settings for the highest accuracy tracing: Threshold 180, Resample x5, Smoothing 0, Optimize 0. If you use a PNG image it should import to the correct size. I have had trouble with other image formats becoming larger or smaller when importing.
4. I highly recommend using a fine-point pen tool to draw a preview test of your design on paper to check for sizing and other issues before potentially ruining expensive copper.
5. Prepare your PCB material. I am currently using super thin 0.015 single sided FR4, but the machine should be able to handle thicker materials, as long as your tool holder and tool can still clear the work piece. For an etch resist, I put on a single thick coating of spray paint as my etch resist, but plan to try Future floor wax next.
Information about using Future floor wax as etch resist.
5. Load some kind of "scratching" tool in the Cricut. My current preference is a deck screw or a sharpened nail. (The scribing tool is a bit too fine and can result in bridging). You can use a custom tool holder or just masking or packing or other "hard" tape. Pay careful attention and set the installed height of the tool high enough to make sure it won't drag across your work piece while "up".
6. Finally, use the Cricut to scratch your design into the prepared PCB, and etch. I have been experimenting with different settings for pressure and multicut, but currently I like "high" pressure, multicut x2.