Train control for etching

J

Joseph.Hollingworth84

Joined
May 11, 2024
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5
Hello!
After doing a search on this forum first, I have yet to come across anyone having a specific answer. I have an old train control that has both AC and DC outputs. The DC is 16v and the AC is 18v. I made my own handheld etching pad with a bolt and brass stuck in some wood. I checked voltage with a voltmeter and everything works/gets power as it's labeled. My problem is that I don't get a very deep etch, and the stencils that I had made keep loosing their outline. I'm using a homemade etching solution using iodized salt and cleaning vinegar. I've tried upping the salinity but have not had good results. Does anyone have any advice or info on what voltage a commercial etching machine output is? Thank you, Joe.
 
Hi Joe. I would think the voltage is maybe higher than what you would normally see. I think the AC/DC adapter that I used (I built my own machine like you) has 5V DC and something similar for the AC output. Even with this voltage I can feel the etching solution bubbling/boiling away when in operation - indicating that I am increasing the local temperature quite a bit. With higher voltage maybe the temperature is high enough to burn the stencil? I only apply pressure for a few seconds at a time, then pulling away. Rinse and repeat. With few repetitions I will get an etch that catches a finger nail, and that is good enough for me.
 
Interesting, thank you. I was able to get a somewhat deep etch on one knife that I made a long time ago, I haven't tried it on anything new yet. I think I might have to go another route because now my machine just gets hot and is barely bubbling when I tried it on another knife.
Red Beard Ops has a diy etching machine that I might look into, I was just trying to use what I had.
 
There are a couple key things to keep in mind to get a good etch with an electro-etcher.
1. Keep your contact time low. (Makes your stencil last longer, less heat).
2. Keep your voltage as low as possible. (Once again less heat, longer lasting stencils. If it's marking don't raise the volts)
3. Keep your marking pad as dry as possible. (You want it just barely damp, if there is liquid on the surface of your work, your mark will blur, and spread under the stencil)

Definitely more of an art than a science, and there are definitely differences between commercial etchants, each formulated for different metals.

Ac for marking, dc for etching.
 
Andy has the main advice. I will emphasize that the biggest issue with most etching is the pad is too wet. Moisten it with a few drops of electrolyte. Blot it on a folded paper towel a few times until it barely leaves a damp spot.
Big issue for many folks - Q-tips make a terrible pad!!! Either buy a commercial carbon block and felt pads, or make one. I recommend buying them.

Other things:
A simple solution to your issue will cost about $40. Plugging the train controller into a VariAC (variable voltage transformer) will make the unit complete variable voltage AC and DC. Search Ebay or Amazon for
"Variac Variable Transformer Model SC-3M, 300VA, 0-130V, 3A"

Make sure your stencil is firmly taped to te blade and there are no exposed edges that electrolyte can get under. Also, no exposed metal the pad can touch.

Etch at 9-12V for most etching tasks. Short etches work best. Play with it until you get good etches on some scrap steel before doing your good blades. Old junk kitchen knives from the thrift store or the back of the kitchen drawer are great for practice. Find some in both carbon steel and stainless. Dull te edged and grind the bevels to 400 grit and clean well. You can regrind the si]surface dozens of times while learning.

Make sure you have the leads right. Positive to the bade and negative to the pad.
 
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Voltage is the carrier and it doesn't have to be high. 2V is enough. Amps do the work. If the etch is insufficient, check the amps. Example, I use 3V and 100A for etching a blade with 40% coverage. For a makers mark at least 2A should be available. Higher, faster. Lower, way longer.
 
After consulting several threads and getting advice, I figured out what I was doing wrong. I was using way too much liquid and didn't have the proper amp output from the train control (it was less than one amp). My home made applicator had too much resistance and surface area as I was using a a 5/8" bolt and an unknown piece of brass from a bulldozer wear plate.

I ended up buying an Elenco xp 720 power source on EBay for $25 that has better control and a couple of different amp settings. I also bought a block of graphite on Amazon for $7 and a brass screw from the hardware store.
I used the 1 amp setting at 12v and did several 5 second etches, I then switched it to the AC output and did 6.3 amps with 14 volts to darken it.
I bought the etching solution from Pops and used an old children's ibuprofen syringe to place just a few drops onto the felt pad.

Thank you all for your help. It was a little frustrating to figure out everything, but way less expensive than the commercially made options.
 
Just a note for folks considering variable voltage stuff:
On Ebay lately I have seen some amazing deals on BIG autotransformers (VariAC). Ther was one that was 0-140VAC 7.5 amps for $80. Add a Bridge Rectifier and you have a powerful AC/DC setup that will add variable speed to 1/2HP DC drive conversion on a tabletop drill press, small lathe, or mini mill.
 
That's a good idea Stacy - do a search on ebay for item #166676508880 - it's a 15 amp for $55 shipped.
 
Just be aware of pitting above 2V. Best etch is under 2V. Current is the workhorse. If working above 2V the etch has to be fast.
Getting bellow 2V with a variac is almost impossible. Anyways, variacs are very useful. I have two.
 
I have had great results with the etchant from Pop's. I also recommend getting a bottle of the AMC cleaner/neutralizer.
 
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