Introduction: Steel Etching and Marking From a DC Adapter

Picture of Steel Etching and Marking From a DC Adapter

As a knifemaker, I like to etch my logo into my knives. I have a pretty fancy machine to do this, however others have asked about etching and marking so I came up with a fairly straight-forward device that one can make for around $20.

But first a little background. A lot of folks etch with DC power supplies and batteries. The current flows in a circuit through an electrolyte such as salt water. The etching process removes metal from the surface of the knife and makes valley where ever the Direct Current (DC) is allowed to flow. If we apply a little Alternating Current (AC) after we etch, we blacken the etched area. This is called marking.

So the secret to an etching and marking power supply is to have both DC (etching) and AC (marking) capabilities.

Before we proceed:

A little know-how is required to complete this project. You will needs some basic tools and a soldering iron.

Please be advised that the information provided is for educational purposes only. I will not be liable for use or misuse, damages, injuries or death resulting from this information. You must also be aware that the modifications shown here will render any product approvals e.g. UL/CSA invalid.

I originally published a long form of this build on my knifemaking blog: D.Comeau Custom Knives

Best wishes,


Step 1: What You Need

With the legal stuff out of the way, lets take a look at what we need to get started.


  • Hacksaw
  • Wire stripper
  • Crimper
  • Adjustable wrench
  • Screwdriver
  • Scissors
  • Multimeter
  • Soldering iron


  • "Old style" 5 to 12 VDC adapter
  • DPDT toggle switch
  • Scrap wire
  • Alligator clip
  • Crimp type ring terminals(3)
  • Epoxy
  • Piece of plastic or polycarbonate
  • 8-32 machine screws (2)
  • 8-32 hex nut (4)
  • Small piece of stainless steel
  • Flat-head stainless steel machine screw
  • Hex nut for the stainless steel machine screw
  • Small block of wood

Step 2: The Old Style $2 Adapter

Picture of The Old Style $2 Adapter

This is the kind of adapter you want to use. Do not use the rectangular one's from modern computers as these are "switch mode power supplies" and will not have the AC available inside. We want the old kind that feels like it's got some weight to it. Try for at least 5 Volts DC and 1 Amp or more. My local 2nd hand store has a bin full of these puppies for $2 each.

Step 3: Opening the Adapater and IDing the Parts

Picture of Opening the Adapater and IDing the Parts

Let the fun begin! I opened this adapter up with a hacksaw. Carefully cutting around the seam. Do not go all the way through as you may cut some components. Rather, you want to get really close and then make the final cut with a utility knife.

Once inside you should see something like a little circuit board and heavy iron thing called the transformer.

The schematic and component ID image is for your enjoyment. Let's take a look closer at the schematic.

The transformer is powered from the 120 VAC mains, or possibly 240 VAC depending on where you live. It steps down this voltage to say 5 to 15 volts AC. Typically four diodes (called a bridge rectifier) convert the AC to DC and the filter capacitor smooths the DC before it goes to the output jack.

Step 4: Tagging the Secondary Winding

Picture of Tagging the Secondary Winding

The etching/marking power supply schematic looks like this new one shown. You can see we need to tap into the output of the transformer and install a Double Pole Double Throw (DPDT) toggle switch. This will let us switch between DC "ETCH" and AC "MARK".

In this transformer the output can be identified as two heavier copper wires coming out of the transformer into the circuit board.

Once you spot the output leads, follow them to the back side of the circuit board. Note where they come through. You should be able to trace these and make sure they go to the diodes. Now strip two 15 cm (6") pieces of 20 or 18 AWG hookup wire and solder them to where the transformer leads come through. Apply some solder to make a nice clean connection. Be sure not to blob any solder and create a bridge across some traces on the circuit board. We're trying to only connect to the pads that have the transformer leads on them.

NEVER CONNECT TO THE PRIMARY SIDE OF THE TRANSFORMER WHICH CONNECTS TO THE MAINS (120 V or 240 V). This should be obvious, but it's worth clarifying.

Carve a half circle in the cap right next to where the DC power lead comes out. Carefully route the two new wires along side the DC lead and temporarily tape the adapter back together.

Step 5: Wiring the Switch and Testing

Picture of Wiring the Switch and Testing

Now that we have both the DC and AC leads coming out of the adapter case, lets wire the switch.

The switch must be a Double Pole Double Throw type and will always have 6 pins. The part I had handy was a few bucks from Digi-Key, P/N EG2398-ND which is good for 5 Amperes and 120 Volts.

The blue wires shown are AC and we don't care which way they go. In other words, swapping the blue for the other blue has not effect on the operation. Strip about 1/8 of an inch of insulation and press the wire into the hole. Apply heat from the soldering iron and then flow some solder into joint to make a good connection.

Cut about 15 cm (6") of red and black 20 or 18 AWG hookup wire. Strip and solder these to the center pins of the switch as shown.

Now we have to get the DC polarity right...

The black and red wires in my diagram are DC. Your wires may be also black and black with a stripe. The solid black will normally be DC- and the black with stripe is normally DC +, but the manufacturer may or may not follow any convention.

Here the wires from the adapter are marked with --- (positive). We need to know the polarity of the DC supply so we know what wire will go to the pad and what wire will go to the clip.

Once I wired the switch, I connected my multimeter's red and black test leads to the red and black wires coming from the switch. Set the meter to read DC volts and plug in the adapter. With the switch in the DC (etch) position, see photo of switch, the meter will read some DC voltage. Mine is reading 16.32. Check that there is no - or minus sign in front of the number. If there is, make a note of this as we'll have to flip the wires going to the pad and clip.

Now switch your multimeter to read AC volts. Flip the toggle switch and you should be reading some AC voltage. Mine reads 12.44. This is good. We may unplug the adapter and proceed with wiring the terminals.

Step 6: Making a Switch Plate

Picture of Making a Switch Plate

For a switch plate I had some 3mm (1/8") polycarbonate handy. Any non-conductive material such as plastic or what-have-you will work.

Drill a hole for the switch, 1/4" for my little toggle switch and the electrical connection holes to 3/16" or to suite whatever machine screws you have. 8-32 x 1/2" machine screws will be fine.

Assemble the switch plate by mounting the switch.

Strip and crimp two ring lugs on the ends of the red and black wires coming from the switch.

Now that we know the circuit is going to work, it's time to epoxy the adapter case back together. Mix enough 5 minute epoxy to reassemble the adapter case and a few ml more to attach the switch plate to the adapter case. Once the switch plate is glued in place with 5 minute epoxy, wait for the epoxy to set.

You may take this time to make some labels for your machine. I made the following:


and "Poor Man's Etcher" 12 VDC 1.2A


Step 7: The Etching Pad

Picture of The Etching Pad

Although an alligator clip and Q-tip or cotton ball will work to etch, I found that a proper felt covered pad works best.

I started with a small piece of stainless steel, say 12mm x 50mm (1/2" x 2") and drilled a hole about right in the middle of it to accept an 8-32 machine screw. I then countersunk the hole so that the screw head didn't stick out so much.

I found a small block of wood and drilled a hole for the screw in that as well. Attaching a nut and filing the screw head flush to the surface will give you something like shown alongside the ruler.

Step 8: The Leads

Picture of The Leads

For the leads I had a piece of lamp cord.

Start by crimping two ring lugs on one end of the cord.

At the other end, crimp one ring lug and strip back about 3 mm (1/8") and solder to the alligator clip.

Remember to slip the alligator clip's insulator before soldering.

The last step is to attach the single ring to the screw on the pad. A single hex nut is fine here.

Step 9: Felt for the Pad

Picture of Felt for the Pad

For the pad I cut some dollar store felt into a rectangle and folded it up. Here we can attach it to the block with some rubber bands or in my case I used an small cable tie.

Electrolyte goes on the pad. You probably won't have a purpose-made electrolyte solution which is not a problem. Many use a simple brine made of water and salt. Add a teaspoon of salt to a 1/2 cup of water and stir.

Wet the pad, but not to the point of dripping. Tamp the pad on some paper towel if you over wet it.

Step 10: Test Etch and Mark

Picture of Test Etch and Mark

For your first etch and mark, you'll need something steel to make your mark on. I chose an adjustable wrench.

Apply a thin coat of nail polish. This will be the mask. Make the mask much larger that the area you plan to etch.

When the nail polish is hard, scratch your name in with a pin or scribe.

Connect the alligator clip to the steel you are etching.

Plug in the etcher and set the switch to "ETCH".

Press and hold the pad for 15 seconds and lift. Wait 5 seconds and then apply the pad for 15 more seconds. The etching goes deeper as you hold the pad down. Lifting allows the surface and the pad to cool. Cooling becomes more important when you use a stencil. In my example I went with three 15 second etches.

Now set the Etch/Mark switch to "MARK" and repeat at least 2 times for 15 seconds. Unplug the etcher.

Wash the steel with water and wipe to remove any brine. With some fine grit sandpaper or Scotch-brite pad remove the nail polish mask. Acetone works really well here for removing the nail polish too. (You probably already know that nail polish remover is primarily acetone. )

If you want a really cool etching like my logo, look into getting a stencil made. Shown is my stencil and the resulting etch/mark on an old scrapped knife project.

I hope that you have found this informative. As always, I have tons of stuff on my blog for knifemakers.

D.Comeau Custom Knives - D.I.Y. Knifemaker Info Centre




ColinS64 (author)2017-07-03

HI! I was thinking about using something like this...

It is a 3-12 Volt/2.5 Amp Adapter - I know you have said that around 10 volts is recommended but what about amps? What role does amps have in the etching/marking process? Also have you ever heard of plating (etching but the leads are backwards)? Thank you in advance for your input!

TrojanRiG made it! (author)2016-05-04

I made it too, thanxx to your instructables, but the blackening appears to be dark greyish.i used 9v 2amp.Tea mark in10 sec and coffee in 5 sec, n coffee i got ome patches Please suggest how to achieve perfect ink black mark and minimise duration.any change in electrolyte or technique?sendin you the snap.
Thanks again

dc-labs (author)TrojanRiG2016-05-04

I use an electrolyte solution intended for stainless steel. Also, the preparation of the surface is important, clean of any grease, fingerprints, scale etc. My timing on stainless steel is 15 seconds on ETCH, wait a few seconds, then 10 seconds on MARK.

robcoon (author)dc-labs2017-01-31

Where did you get the Electroyte solution?

dc-labs (author)robcoon2017-01-31

I got my electrolyte solution from a knifemaker supply store.

Amit g (author)dc-labs2016-05-15

Hi i used salt solution along with 1.5% nitric acid,doing great ,now i got a sample of solution from outsource it taste like same but results very good means ink black on my 12v ac adaptor,it smells like a little touch of own solution gives thick darkest brown touch not jet black.if i remove nitric acid its patchy n rough.but with same current outsorce solution doing much better.pls tell me what should i add to salt solution
To get fine jet black patchless results.Thanks

tzny made it! (author)2017-01-18

Thank you for great instructions! The mark turned out very well for me using the AC/DC switch.

tzny made it! (author)tzny2017-01-18

Sorry forgot to include in previous post - the mark turned out nice and dark.

agguilar (author)2016-08-26

My adapter is not plug in and is reading cd or ac voltage :( I'm lost right now ?

dbunting (author)agguilar2016-12-23

Ive seen that on some meters. This is usually because the manufacturer left the reference connection floating (not tied to + or - or ground)
If you touch your meters probes together your reading should drop to Zero

dc-labs (author)agguilar2016-08-27

Wow, I have never seen that before. I'd check the batteries in the meter.


agguilar (author)dc-labs2016-08-28

In ac I'm reading Dc and in ac I'm getting DC why ?

dbunting (author)agguilar2016-12-23

You may have the poles on your switch wired backwards. Just flip your labels and you should be fine

agguilar made it! (author)2016-08-11

hi can i use this type of adapter ???

dbunting (author)agguilar2016-12-23


dc-labs (author)agguilar2016-08-11

That looks like the right kind.

agguilar (author)dc-labs2016-08-12

is this the right place (showing by the pencil)??? because i solder the wires to the big dots of soldering ( on the back of the transformer )

agguilar (author)dc-labs2016-08-12


agguilar (author)dc-labs2016-08-11

Thanks! I will try and make it

agguilar (author)2016-08-11

I was using this adaptor in this part that I just engrave I will make another one so that the image be black

Nixxen (author)agguilar2016-09-17

How'd you make the stencil for that one? Was it too a DIY project or did you have one made for you?

agguilar (author)Nixxen2016-10-02

i have a vinyl cutter,thanks !

Nixxen made it! (author)2016-09-24

Fun little project.

Used a 7.5v DC charger with 0.7A. For some reason when I measured it turned up as 11.3vDC and 9.8vAC.

It worked though.
Would recommend getting something with a bit higher voltages.
Etched horisontal liter measurements and numbers next to them on a steel pot I use for homebrewing.
Took the better part of 5 minutes for etching and marking every piece.
Luckily the pad I used was so wide that it could cover two stencils at the same time, so I saved some time there.

It turned out ok. Some spillage where the water somehow managed to get under the tape I used to lock the stencils in place.
The marking was a different story though.
I did 4x 10seconds, with 5 seconds pauses. Barely made a mark.
Then I did 2x 30 seconds on top of that with a 5 seconds pause (only for the numbers though).
Most of the numbers turned out ok, but some were uneven.
Some of the horisontal lines lost all the markings after rinsing them.
Not entirely sure what happened there. They were all given the same treatment.

For stencils I used black electrical tape for the lines.

For the numbers I bought a pack of cardboard stencils at a hobby store, then transfered those to a map/book plastic coating (the kind you pull off a back paper and stick the transparent plastic to your book as extra protection), then cut out the letters using a very sharp fruit knife (Yes, fruit :P - it was sharper than my carpenters knife ><)

Great project though. Was fun to dabble with :)

ch5 made it! (author)2016-09-24

Thanks for this easy and useful tool idea!

Mine wasn't as fancy as some people's here, but it sure got the job done.

It works a bit slower in brass, but I got etches deep enough in steel to add solder inlays.

agguilar (author)2016-09-01


agguilar (author)2016-08-28

This is the reading I'm getting

dc-labs (author)agguilar2016-08-29

That looks great!

agguilar (author)dc-labs2016-08-29

Thank you !

dc-labs (author)agguilar2016-08-29

It should be noted that with a toggle switch, the internal contacts are opposite the lever. So when the lever is down the center and top contacts are closed. This isn't a problem as you can either label the switch based on the output (AC or DC) or you can simply rotate the switch in the hole 180° to match your labelling.

Good luck!

agguilar (author)2016-08-29

reading ac dc

agguilar (author)2016-08-28

Ok I notice some errors in you diagram the ac Is the (blue wires ) and the black ( dc) but in your picture of the multimeter when you are testing the blue wires you have the switch up and is reading (AC)? In the second picture you have the switch down to the black wires and is reading (DC ) ? Can you please help me I'm trying to make one but I'm lost rigth now

Dauschdog (author)2016-08-22

Great stuff thanks!

FrancoL3 made it! (author)2016-05-28

done with 3d printed box and laser cut/engraved panel :)

12V, 1.2A, DC/AC switch using a relay, 3.6mm round pad

FrancoL3 (author)FrancoL32016-05-28

ops, i mean 36mm, not 3.6

FrancoL3 (author)FrancoL32016-05-30

Amit g (author)2016-05-16

Thanks for your instructables,i made that too i used salt solution,working good ,now i got a sample of solution from outsource it taste like same but results very good means ink black on my 12v ac adaptor,it smells like a little touch of own solution gives thick darkest brown touch not jet black.if i remove nitric acid its patchy n rough.but with same current outsorce solution doing much better.pls tell me what should i add to salt solution to get fine jet black patchless results.Thanks again pls reply

dreiduke made it! (author)2016-02-18

I need to build a pad to complete the device....
will try it this weekend

dreiduke made it! (author)dreiduke2016-04-20

works fine

DanielM242 (author)2015-12-22

I apologize if this has already been covered (I didn't see it if it was), but what's more important here, voltage or amperage? I have a battery charger that is 120v AC in 2.4v DC out(I think) and 1.4 amps. Will it work?

dc-labs (author)DanielM2422015-12-23

My guess is that 2.4 volts is the bottom end of the useful voltage scale. It should etch but it will take longer than say 8 or 12 volts with a given electrolyte. You will want to experiment with the concentration of your electrolyte, for example adding more salt. If the electrolyte offers higher resistance (too little salt) it will required more voltage to etch properly. Also saturate your pad and tamp off the excess. The 1.4 amperes is the capacity of the charger. The current will be limited by your electrolyte. Less is cooler. Too much heat will destroy your mask or stencil.

DanielM242 (author)dc-labs2015-12-28

So it sounds like voltage is more important, I'll just find an adapter that is better suited for the job, thank you.

Lochtar made it! (author)2015-12-15


Thankh you for the instructable, here is mine version.

As you can see I placed the switch a litle different. And it works great!

As you can see I placed the switch a litlit

dc-labs (author)Lochtar2015-12-15

He's that's a good idea. Now you have the switch in your hand instead of back at the transformer. Smart.

Lochtar (author)dc-labs2015-12-17

Thanks, and I think it was easyer in a way.

Impoinc (author)2015-12-07

Just tried this out. Worked great! Awesome instructable!

dc-labs (author)Impoinc2015-12-08

Thanks mate!

Bdagraca (author)2015-10-25

I made one as well. I also labeled the switch wrong. Issue I'm having is in AC mode I get huge sparks, small flame, and the stencil blows apart.. Any ideas or suggestions would be appreciated! Btw, DC, you rock man.. Love the blog

dc-labs (author)Bdagraca2015-10-25

That is not good. It is possible you have your mains (primary of transformer) going to the switch and not the secondary lower AC voltage. Be sure to check the output in both modes with a voltmeter before touching anything to anything. Including your body. There should be no sparking at all.

Bdagraca (author)dc-labs2015-10-26

Is that image of your logo done by this machine, or by the fancy one you mentioned earlier in your post? If it's made by your other machine, how can I get info on it?

dc-labs (author)Bdagraca2015-10-26

Yes, my logo etched in the photos above is made by this etcher as built in this Instructable.

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