Introduction: Steel Etching and Marking From a DC Adapter

By D.Comeau Custom Knives

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