20100816

Electro Etch is GO



This article describes my homebuilt AC/DC electro etching device. It's built from plans I got online -- I got the original plans from http://www.knives.mlogiudice.com/knifeshop/etcher/index.shtml . During the design phase, this site was the most helpful for the hardware building. I now know I can go ahead and use any basic power supply design pretty easily, so the next one will surely be a circuit of my own design.

The etcher is mounted in an aluminum case salvaged from a parallel printer sharing switch from the 1980s.

This is the second build of this circuit that I have done. This one has a much better case and a larger capacity transformer than the first, but the components are all salvaged from the first build except for the case and transformer. Total cost was <$30 -- it's only that high because I bought almost everything new the first time around. Just about any power supply will do -- I have used a wall wart transformer with the plug cut off and a couple of alligator clips soldered on to do etching and plating. Stick to lower voltages like 6-24v for sharper results, since the image tends to bloom with higher voltage for longer time. Make sure you get the biggest current rated tramsformer you can, since this circuit can easily put out over 1000 mA of current through your workpiece and a smaller transformer will definitely overheat or short out in an exciting manner. I would recommend looking for at least 1 amp output to avoid overheating.

BUILD IT:
The plans at http://www.knives.mlogiudice.com/knifeshop/etcher/index.shtml are abundant with parts list, schematic, etc.

Here's a link direct to the schematic: http://www.knives.mlogiudice.com/knifeshop/etcher/electro-etcher_circuit.pdf

FIRST POWERUP:

Safety glasses on! The first time you start the circuit you risk finding accidental short circuits and bad solder joints, defective components, etc. Please protect your precious eyes so you can keep having fun.

Use your hand (or go to Harbor Freight for a $10 IR thermometer, for safety) to check how warm your components are when you power up for the first time. Check every few minutes on the heat level of the transformer, bridge rectifier, and other heat-generating power components. After it's running stable, you can thus be confident that your circuit runs in a known manner.

STENCILS:

For stencils I have used all different things like electrical tape and contact paper; anything electrically insulative will work. Draw your design with a Sharpie or paint pen (or a graphite pencil) and cut ewith a utility or craft knife. You can also cut with stencils or punches; I used a tiny round punch to make dot matrix letters and it worked fine.
You can even paint on the surface or use asphaltum, wax, or almost anything resistive. See a printmaking book for further suggestions.

Currently I have stencil paper that starts out completely insulative, but turns conductive where it's written, typed, or stamped. It's a fine plastic mesh ribbon with blue waxy emulsion which you push out when you impress the ribbon. Thanks to a friend with contacts in the marking industry, I got this for free because they ordered the wrong material.

You can get (or better, make) steel stamps made of your logo or words, for stamping straight onto the stencil paper. The mint box was done this way, using a CNC milled 23b Shop logo as the stamp. (I actually burnished it with the flat of a Sharpie; I didn't stamp it because it is a large and thin milling.)

The stamp doesn't need to be hardened like a metal-marking stamp does, since you are just stamping the paper on a soft wood or plastic surface -- you can use wood or plastic for this kind of stamp, or a piece of softer metal like copper. You could even electro-etch a plate and burnish it into the stencil paper.

Note that a greater exposed surface area of your stencil will mean a slower etch. Same with a larger probe.

ELECTROLYTE:
Storebought electrolyte solution is probably more effective, but I have table salt and baking soda to work with at the moment, and they both provide good results.

Starting with oil-free metal is a must. Otherwise the oil will insulate parts of your design and ruin the line quality. This means scrub with #0000 steel wool and a bit of dish soap, or use another degreaser of your choice. You can sandblast it as well -- this removes the oil plus a bit of metal, leaving a satiny finish to contrast the smooth melty appearance of electroetching.

Salt water electrolyte rusts metal very quickly, so rinse and brush finished work well and dry thoroughly with forced air, a warm sunny spot, or a heat gun or hair dryer. Apply oil or WD-40 right away.

MAKING PROBES:

You can probably use any fabric to protect the probe surface from direct contact. I've used t-shirt fabric and synthetic felt to good effect.

I have made several probes
with stainless welding rod for the conductor and brazing or welding a banana clip lead on, then sliding into a plastic hollow rod for a handle and taping, wedging, or gluing it in place. Favorite shape so far is a hockey stick with about a 3 inch exposed conductor, bent at 60 degrees or so, 1 inch down from the plastic handle. This allows wiping across a roughly 2" swath, or leaving it in place to etch a small design.

I also made a probe from a circle of heavy stainless screen, a few layers of t-shirt material, and a 4" PVC pipe cap. It's used for longer duration etches, flat plates, and larger designs. Wired it all together with a bit of stainless wire and clipped a banana jack into the inside. I can set the probe on a workpiece with the pad downward, and pour electrolyte into the cup shape. This trickles through and collects in a plastic dripcatcher pan, so the electrolyte stays really fresh and the current stays high. It can then be recycled until the current drops too low. This design is win.


A spot probe with a stainless mesh and a felt pad, all on the end of a 3/4" or 1" plastic dowel, will come next.


HOOKING UP THE PROBES:

The workpiece is attached to the positive terminal with a spring clip or wire hook. Stainless steel or titanium are best if the piece is to be immersed in electrolyte. No copper should be exposed to the electrolyte anywhere, or else you risk polluting your solution and plating your workpiece or probe.

The probe is at a negative voltage to the workpiece during DC operation -- so clip the probe on the negative or ground of your output terminals, and the workpiece to the +12 or +5 side. The metal from the workpiece migrates toward the negative terminal, is my understanding.

Avoid touching the probe's metal to the workpiece directly; this maximizes current and minimizes electro-etching action, heating your circuit and possibly shorting components.


You can clean the probe off when it gets gunked up by reversing the voltage and DC-etching the probe; the cruft will collect on your sacrificial workpiece. This is also the basis of a larger electrical de-ruster; plans and pics of our 35 gallon de-rusting device to follow.

FUTURE PLANS FOR THIS PROJECT:
I am going to be adding a voltmeter / milliammeter to avoid having DMMs clipped in all over the place, but it runs stable and cool at 10.5VDC out sending about 500mA through the circuit.

Also making more smaller spot probes would be nice, for doing a small touchmark or logo on a tool or knife handle.

I'll be soldering the whole thing permanently together and removing most or all of the spade connectors.

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