Mechanical Etching of PC Boards

This page started out as a contribution to a discussion being had on the Yahoo! CAD_CAM_EDM_DRO group, but as I typed it got longer and longer so I decided instead to set up a web page on the subject. First a little background. I don't even have so much as a mill or even a stepper motor connected to a computer for that matter, but this is something that I really want to get going, and I think I'll be able to finish something up shortly after Christmas. I have tonnes of parts laying around including steppers, drivers, sensors and various bearings and other mechanical bits, and have just purchased a 7x12 mini-lathe from Grizzly, so compared to some I have a reasonably well placed starting point. I went to college for Electronics, so the manufacturing of printed circuit boards is something I've had to do from time to time, but really yearned for a better solution. The most inexpensive I'd found so far was a laser printer, overhead transparencies and a household iron. Like everyone else, I want cheaper (after initial setup) and more reliable. I've had Eagle 4.01 for a bit and have been playing aroud with it, but want to take things from the screen and use them in the real world... since this is what it's all about. After reading Ian Eagland's informative post in CAD_CAM_EDM_DRO, I went out and grabbed outlines_gcode.ulp and started to play with a board I've been working on.
NOTE: The above link seems to have stopped working so here's some local copies including some that have been modified by Manoel to also output to Excel.
outlines_gcode_excel_mirrored.ulp
outlines_gcode_excel.ulp outlines_gcode.ulp

All you have to do is select Files->Run->outlines_gcode.ulp and it pops up a window asking for Device (Select gcode), Width (of cut), Layer (for a single sided board use 16), and Output file. At first I just pulled a width out of the air (well from Ian's post) so I typed in "0.1" and after some flashes on the screen got a lovely file containing wonderous gcode!!! The flashes were actually the script figuring out how to do things, but my machine just chews the work up and spits it out. This is near magic to me...I love it! At the moment however, the code doesn't mirror the image for bottom traces, so it's not 100% usable out of the box. I'll just have to change the rotation of my X drive to suit, or bite the bullet and make the code changes myself as time permits (right now building something seems like more fun).
Ok, so now I have Gcode, but I'm away from home and my EMC machine. How do I have a look at what the code is actually doing? Using a combination of UltraEdit32 and Excel I converted the gcode to a spreadsheet so I could plot the results. The final data plot looked like this.
So I tried the same thing again this time with the width set to 0.025".
Better, but many traces are still attached. So I set out to figure out what the actual cutting diameter might be. Looking at the G-code resulting from the outline_gcode.ulp, they mentioned "Think&Tinker Mechanical Etching Bit with 60-degree tip angle" and a cutting depth of 0.007". Ok so we're dealing with a 60 degree isocelese triangle. That means (if my trigonometry holds), we're dealing with approximately 0.008" cutting diameter.
So I tried outline_gcode.ulp again with a width of 0.008, and the resulting tool path looked much more promising. I don't pretend that this is the proper value, as I have nothing on which to run the code, but with my Excel model at least all the traces were isolated and clean.

Niiiiiice!!! I can't wait to get home and feed this stuff into EMC and watch it draw everything for me... Even more I'm itching to actually build a machine capable of cutting traces. I hope to make this an ongoing project, and in the tradition of the Yahoo! groups documenting as much as my time allows while actually continuing to build something useful. If you have any questions or would like more information on anything you see here, please don't hesitate to email me.

Mechanically Etched PC Boards