ETCH CNC

ETCH CNC displaying a globe

I am using a retrofit machine that fit within my budget. It's a 2-axis machine with approximately 170x130mm travel.

The circuit board is my own design, using a ULN2803 per motor to supply approx. 0.3 amps per winding. The power supply is a standard AT hard-drive power connector, with the +12V used to power the motors. It's a simple constant-voltage L/R drive. I made the circuit board using EAGLE, and milled it on Chris's real CNC milling machine (which is powered by EMC and AXIS, of course).

The copper side of the board

The populated board

The motors are 7.5 degree steppers in halfstepping configuration. One step is approximately 0.4mm travel. They probably have tens of oz-in of torque.

It's fairly fast. The globe in the image above takes just under 1 minute to draw. Because the scale in emc is set wrong, I don't know the exact ipm figure. Since the globe is about 4" "tall" and there are 12 verticals, I'd have to guess it's over 60ipm.

The coupling between the stepper shafts and the etch knob shafts needs to be improved, and EMC needs to be tweaked. But the machine is nearing "usefulness".

I should note that others have done this before. http://instruct1.cit.cornell.edu/courses/ee476/FinalProjects/s2004/jml66/EAS_final.htm and http://neil.fraser.name/hardware/etch/ are the ones I am aware of. However, I believe this is the first one which can be programmed with industry-standard g-code, or indeed run by my own AXIS software.

Sierpinski Gasket Fractal

Spiral

Update, 2005/1/2

Globe

I had a pile of trouble configuring emc. The etch is capable of >2inches/second, even without acceleration. But I get nothing but weird results trying to use emc.

The etch also runs just fine without dealing with acceleration, so I used rs274py to provide a g-code parser, and wrote my own simple stepper controller in C. It also features backlash compensation. Here are some designs made with my software:

The etch-a-sketch screen sure is starting to show some wear. The magic dust is escaping at an ever-increasing rate, too, from around the shafts.

Update, 2005/1/16

I finally got around to taking a movie of this thing. I recompressed it using mencoder and the "mpeg4" codec. Plays just fine with mplayer, I don't know (and barely care) about other players. Total time to draw the globe: approx. 40 seconds. There is no sound in the file. Download/view the movie (approx. 1.4 megabytes)

Schematic of the driver circuit

Layout of the driver board

Update, 2005/2/12

Added a screenshot of the Eagle schematic and board layout. The trace layout is a little different than the one that was actually milled.

Update, 2005/10/09

Welcome to everyone from http://www.hackaday.com. I hope my DSL lives through the attention!

Update, 2006/04/06

I'm working on the closed-loop upgrade for etch cnc. For more details, see my blog entry.
-- jepler