I have done primative Electro-etch engraving before with a car battery charger. I dunked a knife blade in candle wax, then scratched my initials in the candle wax. Attached one lead of the battery charger to the knife and put the other in a bath of salt water, then dunked the knife blade in the salt water for a couple of minutes. It works, but there are problems with this:
1. no good way to control how deep the etching goes, other than timing it, but....
2. the etching is uneven; deeper is some areas than others.
3. it's hard to get a thick layer of wax on pointed surfaces (like knife blade edges) which can cause etching where you don't want it.
4. dipping things in wax and then removing the wax is time consuming. If I wanted to etch all the tools in my tool box it would take a week, and my tools would feel waxy.

I have seen electro-etch machines for sale that use an electrolyte-wetted sponge electrode applied to a nylon stencil and I want to try to make one, but first I would like to know the principles behind it.

1. I noticed that the electro-etch machines (as well as welders, similar principle) usually use low voltage (12-24V); why is this? why would a higher voltage not be better? just for safety? I guess this means the Amps are more important than the volts...

2. what controls the depth of the etch? Time of exposure? amps? both?

3. would the voltage and/or amperage need to be adjustable?

3.a. would different metals require different amps/volts?

thanks


EDIT: Just to clarify, I'm talking about etching mostly steel; tools, machine parts, etc. Not PCBs

 

Different metals may require different metals for the other electrode, but I'm not certain about that. Probably not acctually, as long as you have a good power supply.
Amps are more important than the voltage in this case and time affects how deep it etches as much as the amperage.
Unevenness is often due to a buildup of gunk on the metal you're etching, it's a good idea to stay present for the whole etching process and use a stick or small brush or something to clean the plate intermittently.

I've used selotape as a resist before, however, even when over-lapped, it can leave lines where the separate peices of tape met unless you do two layers really neatly and fold it around the edge.

Additionally, metal is only etched from the side facing the negative electrode, the back of the peice of metal being etched may still be pitted though, but not as much as the front will be.

 

I know machinists who have etched their initials on things using wax as a resist and nitric acid.

I've had a Sears electric engraver for 40+ years and it lets me write anything I want on something. Just get one with a carbide tip and you can write on metals, plastics, etc. I also use metal letter stamps to put words/dates on things, but this is a lot slower.

 

use a normal mechanical engraver, or there was a prject i saw in a book once. you take a car batery, a hollow plastic handle, magnet wire, and a amall iron core (like from a solinoid) and some stiff wire. you run wire in to the hanle wind the mignet wire around somthing conect to the handle lead wire. the other end you conect to the plunger. the plunbger is the solinoid core, thick coper wire for the tip. connect the tool to the oposite terminal on the car battery and touch tothe tool the curent flows making a mark thn the plyunger drops because the magnetic field disipered. then it repeats as long as there is a conection between the pincel and the piece being marked.
that is all i remember from the book. you can try gooleing electric pensel there should be some directions on it somewhere. also check ot instructables.com thy may have somthing also

 

Can't help you on etching the sharp edge of a knife blade - never tried or wanted to do that.

However, for marking tools I find high current, low voltage thermal markers very handy and, I believe, much faster to use than electrochemical etchers. No wax, no masking, no chemicals, no mess. Results are not pretty, mainly due to arcing and stick-slip movement of the marking tip or perhaps inadequate manual dexterity on my part. The marking is, however, very effective, especially on hard metals that are otherwise difficult to mark.

Since the intense local heating actually changes the metallurgy a few mils deep I believe the marks would be difficult to erase by buffing or wire brushing. However, I've never tried to buff out a thermal mark.

Speed of use is comparable to the common carbide-tipped vibratory etchers but the thermal marking is deeper on hard metals.

The devices are simple. A low voltage, high current transformer, grounding conductor with high current clip to ground the object being marked, and a thermally insulated handpiece holding the etching tip that is connected to the transformer with a heavy, flexible cable with high temperature insulation. The handpiece has a ventilation channel through the handle, but still gets too hot to handle during long marking sessions. You can also ground the tool on a thick copper plate connected to the ground conductor.

I just conducted a quick search but couldn't find my marker in my vast collection of junk to allow me to give a brand name or better description. I also did a quick google search for "thermal tool marker" but didn't find anything. Might find something with a little more patience. I think Ideal made my marker long ago.

However, construction of a thermal tool marker is not rocket science. You'd want a transformer with low voltage secondary at 100 amps or more. Tapped windings allowing you to select voltages down around 2 to 5 volts OR a 5 or 6 volt 100 amp transformer controlled by a Variac would probably be fine. Use short (2 ft. or so) small, flexible welding cable to connect to the high current grounding clamp and to the handpiece. The handpiece is merely a ventilated handle with a clamp to hold the tungsten and connect it to the cable. The commercial markers use a tungsten tip imbedded in a 1/4" or so copper bar to conduct heat away from the tip. Good idea if you can rig it up. I'd start with a tungsten tip from a vibratory marker, since they are already about the right dimensions and tip shape.

You want low voltage to avoid arcing that makes an ugly mark, but you want high current to achieve the desired thermal effect on the metal. So you must have heavy conductors and use heavy pressure on the tip so you get a low resistance secondary loop and maximize current. gradually increase voltage until you get the desired effect.

awright