Steel Etching and Marking From a DC Adapter

215,479

1,722

130

Introduction: 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,

DC

Step 1: What You Need

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


Tools:

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

Materials:

  • "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

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

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

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

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

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:

PAD
CLIP
ETCH
MARK

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

...

Step 7: 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

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

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

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

Regards,

DC

17 People Made This Project!

Recommendations

  • Pocket-Sized Speed Challenge

    Pocket-Sized Speed Challenge
  • Metalworking Contest

    Metalworking Contest
  • Maps Challenge

    Maps Challenge

130 Discussions

0
DanielR184
DanielR184

6 months ago

Hey DC-Labs,
Thanks for your instructable, very good idea. I am making this project. One question, can replace the stainless steel for a piece of aluminum for the pad. More easy to find...
Thanks

0
dc-labs
dc-labs

Reply 6 months ago

Aluminum will work from a conductor perspective, but I would imagine it will become very corroded. If you keep it clean by refinishing the face with sandpaper it should be ok. I find the stainless gets pretty corroded after a dozen etchings or so and I clean this with 100 grit sandpaper to keep it working smoothly.

0
DanielR184
DanielR184

Reply 6 months ago

Thanks for your answer

0
_Pim_
_Pim_

7 months ago

Hey there DC-Labs,

I've watched your setup a while ago, and used your diagram to make my own. Based it off a doorbell-transformer. The bell transfomers tends to get a little warm after running a while, so I will add a fan still.

I made a similar style etching pad with felt, but the metal underneath turns black very quickly. It seems like this stops the etching/marking as good as it does. Did/Do you run into this as well?

I have been using it for etching and afterwards marking, so DC and AC are working fine. I have included pictures below.

Cheers!

photo6021481558889836580.jpgphoto6021481558889836578.jpg
0
dc-labs
dc-labs

Reply 7 months ago

Hey your build looks great.

Yes, the cathode does corrode. The electrolyte can be pretty nasty. Some folks use salt water, others use some form of salt and vinegar. I use a commercial electrolyte for stainless that smells like sulfur. These are not friendly to metals, even "stainless steel."

I shine it up the cathode steel with some 120 grit sand paper whenever I change the pad. Maybe three times a year. I have found that most cases of poor etching is result of not enough electrolyte on the pad.I have recently been pieces cut from felt insoles from the shoe department which is thicker than craft felt.

Thanks for your comments and photos.

DC

0
_Pim_
_Pim_

Reply 7 months ago

Thank you for your reply and confirmation. I expected it was a normal thing to see, since AC wave works on both pieces (removing and putting back carbon). I just didn't expect so much so soon, but that could be due to the workpiece as well.

Made my first proper example piece as included, etched with DC first to gain some depth, then with AC to mark. Proudly mounted on our mailbox.

Thank you for your tutorial, I've now gained a new skill after finishing this build.

EtchExample.png
0
c_hayes111
c_hayes111

1 year ago

Hello. Thanks for this post, I've got a similar set up were I use a 16VAC power supply and a bridge rectifier to transform it to DC. I'm getting great results with the DC etching, but my problem is with the AC marking. I can easily scrub the black off with a green scrub pad. Is there anything I'm missing?

0
dc-labs
dc-labs

Reply 1 year ago

That's a great idea. In its simplest form an AC adapter and a diode would work good too. The green "Scotch-brite" type pads can be very aggressive. I use the blue and grey pads which are much less abrasive. A little buff with 0000 steel wool works too.

0
ColinS64
ColinS64

3 years ago

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!

02731122_00.jpg
0
agguilar
agguilar

3 years ago

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

image.jpgimage.jpg
0
dbunting
dbunting

Reply 3 years ago

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

0
dc-labs
dc-labs

Reply 3 years ago

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

Dan

0
agguilar
agguilar

Reply 3 years ago

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

0
dbunting
dbunting

Reply 3 years ago

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

0
agguilar
agguilar

3 years ago

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

image.jpgimage.jpg
0
Nixxen
Nixxen

Reply 3 years ago

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

0
agguilar
agguilar

Reply 3 years ago

i have a vinyl cutter,thanks !

0
agguilar
agguilar

3 years ago

This is the reading I'm getting

image.jpgimage.jpg
0
dc-labs
dc-labs

Reply 3 years ago

That looks great!