# Marking Parts By Electro-Etching



## randyc (Feb 11, 2015)

I'm not sure if this is a good place to post this but the idea might be useful for marking tooling -

My youngest sister makes a living as a custom jewelry designer/maker. She visited recently and asked me to make a personalized jewelry chasing hammer for her birthday. These are weird-shaped little hammers weighing only a few ounces that are used for delicate work.

She provided dimensions suitable for her hand, the desired weight of the head and directed me to a number of web sites where the shapes of the handles are depicted. (The handle is not a part of this post, just mentioned in passing.)

A specific request was that the head be marked with my name and the date. I’ve searched the forum and the internet and have yet to come up with an answer suitable for my capabilities. The workpiece is shown below. It is pre-hardened 4140 and fairly small – the body is 0.700 square and the head is about 1 inch diameter, the ball at the end is 0.400 diameter. The socket for the handle is semi-elliptical and THAT part was done on a rotary table and definitely not much fun. (A vinegar patina was added at my sister's request.)





A promising idea seemed to be electro-etching the head in a salt solution using a high current DC power supply. I’ve tried this on several samples of low carbon steel and the etching part works fine. The problem is producing the lettering mask !   Note that this is not suitable for non-ferrous materials.

The process requires that areas that are not to be etched be protected, incidentally.  There are a few (overpriced ?) simple etching tools available from internet suppliers. They seem to require some special masking material that can be processed on a laser printer, which I don’t have, with some graphics software, which I don't have. (I’d likely never use this thing again if I bought one.)  Also they do not produce raised letters, the letters are etched rather than the background metal.

It’s my desire to mark this part with resources/materials commonly available in the shop. I have no confidence in my ability to do a good job using small steel stamps by hand (tried it). At a suggestion, I ordered and received a sheet of various size dry transfer letters from Chart Pak (pricey stuff). This is a greatly enlarged photo of the first trial of the process on a piece of carbon steel scrap. The scrap piece is approximately the same size as the hammer head that will eventually be marked. I learned several things from this short experiment.





First, the process is very simple. Clean and dry the steel part thoroughly (don't touch the clean surface) then rub on the transfer letters. Mask off anything that shouldn't be etched (I used shellac because it's fairly easy to remove after etching with denatured alcohol from the paint store).

Attach the part to the POSITIVE side of a power supply with modest current capability (a five volt supply from a computer would be more than adequate). Connect a sacrificial piece of steel to the NEGATIVE terminal of the power supply.

Mix the electrolyte, in this case 1 cup water, 1 teaspoon kosher salt and one capful of white vinegar. I used a "pyrex" measuring cup for the "etchant tank" and mixed everything well (obviously the container cannot be electrically conductive).

Place the work and the sacrificial piece in the container with the side to be etched directly facing the sacrificial item and an inch or two away. While monitoring the current, I adjusted the voltage on my lab power supply to achieve 1 amp current flow (arbitrarily) and noted the time.

Pulled the part out after fifteen minutes and washed with clean water. The raised letters were clearly visible but the background had been etched away only lightly. Put the part back in the pyrex container and etched for another fifteen minutes, producing the results shown above, about 3 - 5 mils high. On my laptop screen, the image is scaled up about ten times so the etched result looks considerably "rougher" than the actual part.

Nevertheless, it is still apparent from inspecting the real part that a good surface finish is required ! This part was only lapped on a sheet of 220 grit wet/dry. I think that taking it down to 600-800 grit and then lightly buffing will do the trick.

The remaining challenge - and a big one - is getting the transfer letters located and aligned on the hammer head with my shaky motor movements.

  Tried this again because I wondered how etching time affected the quality of the result. First, here’s a photo of my primitive etching setup. I have to say that I'm liking the results so far.





The variable power supply at upper right in the photo is adjusted for about one amp current as measured by the analog VOM (lying down on the lab bench). As noted in the last post, this was an arbitrary setting. The applied voltage for one ampere of current was around five volts (in THIS setup with THIS solution) but this doesn’t seem to be very critical. Taking the part out and rinsing it periodically will give a good idea of etch time - this isn't rocket science at all.

This is the result, magnified about seven times. In actual size, the marking is not so pronounced, incidentally, it is more subdued.





The test piece is the same low carbon steel scrap used before. Variables were more/less the same except for the etching time – from 30 minutes I changed it to 45 minutes. I think that it looks pretty good although the depth of the background etch seemed to be only a few mils more. The copper coloring may be a result of the lighting under which I photographed this part.

This simple process seems tolerant of solution ingredients. I’ve not tried currents over one amp but if the power supply is not variable like the one used here then I suspect that the etch time could be varied to compensate. I like the results.  The residue left in the etching container can be safely discarded down the sink without environmental harm.

This is more arty/crafty than shop-practical, masking is required, takes a while and small parts are most suitable BUT for my particular marking problem it seems appropriate.  This is what the dry transfer letters from “Chartpak” look like:


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## John Hasler (Feb 11, 2015)

randyc said:


> I'm not sure if this is a good place to post this but the idea might be useful for marking tooling -
> 
> My youngest sister makes a living as a custom jewelry designer/maker. She visited recently and asked me to make a personalized jewelry chasing hammer for her birthday. These are weird-shaped little hammers weighing only a few ounces that are used for delicate work.
> 
> ...



I suggest that you try sodium nitrate as an electrolyte.  It tends to leave a smoother finish.


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## randyc (Feb 11, 2015)

John Hasler said:


> I suggest that you try sodium nitrate as an electrolyte.  It tends to leave a smoother finish.



I failed chemistry - is it safe to use, safe to dispose, easy to find, what is the process ?

Thanks


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## John Hasler (Feb 11, 2015)

randyc said:


> I failed chemistry - is it safe to use, safe to dispose, easy to find, what is the process ?
> 
> Thanks



Sodium nitrate is completely safe to use and dispose of.  You just use it instead of salt (don't add vinegar or anything else).  I bought mine from some vendor out there on the Web.  I'll try to figure out who.  I use it for ECM (electro-chemical machining).


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## randyc (Feb 11, 2015)

John Hasler said:


> Sodium nitrate is completely safe to use and dispose of.  You just use it instead of salt (don't add vinegar or anything else).  I bought mine from some vendor out there on the Web.  I'll try to figure out who.  I use it for ECM (electro-chemical machining).



Very much appreciated !  I'd like to get an idea of the mixing proportion and the voltage/current profile, too.


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## Bishop (Feb 11, 2015)

I used the salt and vinegar solution and 12v car battery charger, seemed to work well. Didnt measure anything just added salt till the vinegar wouldn't disolve it anymore. 

Shawn


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## randyc (Feb 11, 2015)

Bishop said:


> I used the salt and vinegar solution and 12v car battery charger, seemed to work well. Didnt measure anything just added salt till the vinegar wouldn't disolve it anymore.
> 
> Shawn



It's a very forgiving process, obviously, since I used only 1 teaspoon of each and a cup of water   Thanks for the information.


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## Rbeckett (Feb 14, 2015)

That is about as slick as glass!!!  I have a need to etch a few items and that would work perfectly for what II need done.  Right on time with a great idea!!

Bob


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## Pontiac Freak (Feb 14, 2015)

so do you cut around each letter exactly and apply it?  got any pics of the how the letters look when you are putting them on?


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## Tony Wells (Feb 14, 2015)

I have a commercial ECM unit, and I believe a chart showing the proper electrolyte and current (some ac and some dc IIRC). I'll drag it out and see if I can post the charts.


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## randyc (Feb 14, 2015)

Rbeckett said:


> That is about as slick as glass!!!  I have a need to etch a few items and that would work perfectly for what II need done.  Right on time with a great idea!!
> 
> Bob



No, the large sheet of letters is transparent so the entire sheet is positioned so the desired letter is in the desired location.  The letter is then rubbed with a ball point pen, dull pencil or whatever (I used a nut-pick) to transfer it to the work.  You have to be a little careful holding the transparency to prevent undesired letters from sticking to the work in odd places.

After all letters are applied, another sheet of coated paper (comes with the letter set) is placed over the letters and they are burnished to assist in adhering.  Follow the instructions in the original post above and Bob's yer uncle !


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## randyc (Feb 14, 2015)

Oops, I replied to the wrong person.  I was answering the following:

_"so do you cut around each letter exactly and apply it? got any pics of the how the letters look when you are putting them on?_"


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## davidh (Feb 15, 2015)

i thought i asked. . . with the letters rubbed onto the metal, and after applying shellac to the whole surface and letting it dry, did you carefully remove just the rub on letters, prior to putting the hammer in the solution so the letters would be raw steel for the etch to attach   or am i missing something completely here ?  
on a side note, we used those letters to pretty up our mechanical drawings back in the 60's


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## randyc (Feb 15, 2015)

davidh said:


> i thought i asked. . . with the letters rubbed onto the metal, and after applying shellac to the whole surface and letting it dry, did you carefully remove just the rub on letters, prior to putting the hammer in the solution so the letters would be raw steel for the etch to attach   or am i missing something completely here ?
> on a side note, we used those letters to pretty up our mechanical drawings back in the 60's



Yes, you're missing something 

What you suggest would work if one desired etched _undercut_ letters but I wanted _raised_ letters so the background material is not masked - only the letters.  Shellac is applied to the rest of the part but not to the immediate background area where the letters are positioned.

I used the transfer letters back in the sixties too but a Leroy set was faster for most work.


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## Cb750r (Feb 16, 2015)

Wow I remember those letters from my youth, my Grandad was an architect and must have brought some of those sheets for me to play with! Cool project you have on your hands!


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## davidh (Feb 16, 2015)

randyc said:


> Yes, you're missing something
> 
> What you suggest would work if one desired etched _undercut_ letters but I wanted _raised_ letters so the background material is not masked - only the letters.  Shellac is applied to the rest of the part but not to the immediate background area where the letters are positioned.
> 
> I used the transfer letters back in the sixties too but a Leroy set was faster for most work.


your age is also showing. . .   ok, makes sense what your saying.  my thought was you were adding a material to the steel similar to brass and chrome plating. . . . thanks for the clarity.  my age is showing too. . .


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## randyc (Feb 17, 2015)

davidh said:


> your age is also showing. . . ....my age is showing too. . .



We're old warriors and don't need to be stripped, sanded and repainted.  The external wear marks are badges of honor, right ?

randyc
2nd Battalion, 8th Cavalry Regiment, First Cavalry Division
B Troop, 10th Cavalry Regiment, 4th Infantry Division


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