Electrolytic Etching, For What A Dremel Can't Do 242
Dustin writes "A lot of people modify computer cases, often requiring them to cut intricate custom designs in
sheet metal. For most, there is the Dremel tool. But
sometimes, that just isn't good enough. Possibly due to an insanely complex design, or
unsteady hands, a Dremel just might not cut it (pun honestly wasn't intended). JimBob, a member at OverhauledPC.com, has a much better way. Using
readily available salt water and electricity, his technique is much easier than trying
to cut patterns with a rotary tool."
Dremel Casemod (Score:2, Interesting)
Re:slashdotted already. (Score:5, Interesting)
Re:"much easier", where's the fun in that? (Score:3, Interesting)
Re:Can also be done in a much simpler... (Score:4, Interesting)
I don't see why this wouldn't work on cases. You use an iron to transfer the toner from the paper to the surface to be etched. Extremely narrow traces can be obtained ("MUCH less than 0.01 inches") with this method, so I'm sure it would give good results for case mods.
This website has the detailed instructions:
http://www.fullnet.com/u/tomg/gooteepc.htm [fullnet.com]
Dan East
Are you sure it's not electrodynamic machining? (Score:4, Interesting)
Items used every day may have under gone this process, turbine fan blades, air bag explosive chambers, hard drive motors (meow), test sabot rounds for tanks.
Are you sure those are all built by electrochemical machining? I suspect some of them are built by its close relative: electrodynamic machining.
Electrochemical machining is reverse electroplating. It pulls metal atoms out, not just from the cut, but from the surrounding metal that is intended to remain, changing its properites.
Electrodynamic machining is a spark to the workpiece through a dilectric solution (typically water or oil). It can cut through anything that can be made to conduct. (You do diamonds by flashing a bit of metal over them for the initial contact. As you're removing diamond, the surface that's left has a microscopic layer that is converted to graphite to keep you going.)
Three sorts of tools:
- Use the end of a wire as a drill. (Feed the wire as the end erodes.)
- Use the side of a wire as a bandsaw. (Feed the wire in the inches-per-minute range so the cutting edge is always smooth and of a known size.)
- Make a graphite electrode in the shape of the hole you want and burn your way in. (Graphite doesn't erode much at all. Replace as needed.)
Cutting action: The spark vaporizes a path through the dilectric and melts a tiny pit in the workpiece. (Polarity is chosen so most of the melting is on the workpiece.) When the spark stops the channel collapses and the shockwave blasts the molten material out of the pit before it can re-harden. Repeat at a rate in the kilohertz range. Spark generally forms at the shortest space, which is where you want to remove the most metal, giving you a mirror finish.
(This effect was originally discovered in Russia about WW II when an engineer tried increasing the life of ignition "points" by putting them in an oil bath to cool them. They disintegrated within hours. It's also why you always use a brush to run current around a lubricated ball- or roller-bearing instead of passing it through the bearing: The effect would destroy the bearing surfaces in a similarly short time.)
The cut-away material ends up as a contaminant in the dilectric. So you pump that through a filter to clean it out.
Motion control is paramount: You sense the spark voltage to tell how far you are from the workpiece and use it for feedback, advancing or backing up to keep your spark path at the correct length.
Contaminants (especially chips) sometimes short the gap, so you back out until you clear it and can spark again. Sometimes you end up machining away the chip. Sometimes you may have to back far - even completely - out of a cut to clear the contaminant from your gap. This may mean retracing your path around several turns. (In the shaped-carbon-rod drill-in mode you also run the rod in little circles and/or back-and-forth it now and then to pump the dirty dilectric out and clean stuff in.)
You're CONSTANTLY backing-and forthing. MOST of your tool motion is back-and-forth, a small fraction is motion into the workpiece as the cut advances. So you MUST use an integer motion-control algorithm that retraces its steps exactly (or within an LSB or so) and doesn't accumulate roundoff err. Any accumulated roundoff, even a TINY bit, quickly walks you out of your path and into the workpiece, shutting you down.
The device is essentially a big power supply, a resistor, a switch, a voltage measurement peripheral, a computer, a motion table, and a dilectric pump/filter. Most of the energy ends up in the resistor. You do it that way as the easy way to control the spark's waveshape. The switch might be a bunch of paralleled FETs on a big heatsink. The resistor might be a bunch of foot-long power resistors, with a fan blowing on them so you can run them far beyond their normal ratings, carefully wired to minimize parasitic inductance.
That's the bulk of the specialized knowlege you'd need to build one, as they were about 15-20 years ago (when I did software for one).
Electrolytic deplating is for pussies. (Score:3, Interesting)
Re:Wait a minute. (Score:3, Interesting)