Steel Etcher Circuit

This is a circuit for etching shapes and logos into steel.

My brother makes custom knives for a hobby. Last week he and I were talking, and he told me he was just using an old RC car battery and some jumper cables to etch his logo into the blades. He asked if I knew a more sophisticated way to do it, so I told him I'm build him something.

Make It from Metal - Stupid Easy Etching in Stainless Steel!

To build this etcher circuit, you'll need some perf board, LEDs, switches and other common electrical components, an LM317 voltage regulator, and a 120VAC to 16VDC adapter and plug. See the attached PDF files for a complete list of needed parts and supplies.

Designate a 16 volt rail and a ground rail. I used hot glue to attach a male barrel socket with screw terminal to the board, then wired the negative side of the screw terminal to the ground rail.

Wire the positive side of the barrel jack to your on/off switch. Wire the other side of your on/off switch to the positive rail, so the switch determines whether the circuit is powered or not. I actually used 120VAC switch. That's probably overkill, and it took some fooling around with the multimeter to figure out how to connect with DC, but it works. Given the low power draw, a 12VDC switch would probably work just fine.

Wire the center terminal of your three-leg 2-position switch to the positive rail.

For power, I used a switch that lights up when in the "on" position, so I didn't add a power LED. You can however, use a yellow LED in place of the red one in the 16-volt circuit, then use red as a power LED. Just run it from positive to LED to resistor to ground. Assuming a 16-volt source, most diffused LEDs will run well with a 680 ohm resistor. If you choose to use blue, I recommend a 3.2K ohm resistor.

I used two 3mm machine screws with nuts and washers as my alligator clip terminals. Drill holes in the perf board far enough apart to accommodate the alligator clips without shorting. Then use semi-permanent Loc-Tite to secure the nuts in place.

Now decide which terminal of the two-position switch will activate the 16-volt circuit. Run an RL207 diode (D1) from the switch to the positive alligator terminal. These diodes are black with a gray (grey) ring, so remember: gray goes to ground. In this case, we're actually connecting the diode in series to the positive alligator terminal, which will, in turn, be connected to ground by way of the material to be etched. Connect the positive terminal of the red LED (D4) to the junction between the switch and the diode. Now connect the negative terminal of D4 to a 680 ohm resistor. Connect the resistor to ground.

Connect the other terminal of your two-position switch to C1. Connect C1 both to ground and to the Vin pin of the LM317. Make sure the polarity of C1 is correct (electrolytic).

Connect a 1K resistor (R1 in the schematic) from the adjust pin to the output pin of the LM317.

Now, from the junction between the adjust pin and R1, connect R2 and P1 in series. Remember to connect the potentiometer (P1) in the rheostat configuration. In other words, connect one end of R2 to R1, the other end of R2 to one side of the pot. Tie the wiper of the pot to ground. This should be done in such a way that turning the knob of the pot clockwise increases its resistance.

From the junction between R1 and the output pin of the LM317, connect to C2. Connect C2 to ground, making sure the polarity is correct. Connect C2 to another RL207 diode (D2) with gray pointing away from the LM317. Now connect the gray end of the diode to the positive alligator terminal. Connect the positive leg of the green LED (D3) to the junction between C2 and the diode (D2). Connect a 680 ohm resistor to the other side of the green LED and then to ground.

Make sure to do continuity checks and short checks before connecting the 16-volt power supply to the jack! You assume all responsibility for basic familiarity with the risks of experimenting with electricity and for your safety while building and using this circuit. Be on the lookout: sparks will fly if you short the alligator leads!

Put a splash of water into a small dish - say, 3/4 inch deep (1 1/2 - 2 cm). Stir in common table salt until no more will dissolve.

Prepare the steel. Clean it if needed. My brother uses vinyl sticker paper with his logo printed on it, but you can use electrical tape or duct tape too. Cut out the design with a razor knife and apply it to the surface.

Connect an alligator lead to the negative terminal of the circuit. Connect the other end of the negative lead to your piece of steel.

Soak a Q-tip in the solution. Connect your positive lead to the positive terminal of the circuit and then attach the alligator clip on the other end to the wet end of the Q-tip.

Brush the steel with the wet end of the Q-tip to begin the etching process. The wet solution should "fizz" noticeably and cause the Q-tip to turn dark brown and black.

For my test, I used a cheap stainless steel butter knife from the kitchen utensil drawer. (Please, nobody tell my wife! Tee-hee!!) My brother says the carbon steel he uses causes a much faster reaction. For that, consider switching to variable voltage mode. Set up your multimeter to measure amps and connect it in series between one terminal of the circuit and your etching project. Turn the knob to determine how fast a reaction you want.

DIY Metal Etching - Instructable

During my field test, I found the circuit draws about 0.6 amps at 16VDC. Assuming my weekend-warrior math is correct...

16V / 25 ohms = 0.6 amps

In other words, the saltwater solution is creating approximately 25 ohms of resistance or load.

0.6A * 16V = 9.6 watts

So it uses at most about 1/6th the power of an old-fashioned incandescent light bulb.

Using the actual tested values of my components, math for the LM317 circuit was as follows:

1.25(1+(9420+996)/996) = 14.32 V

1.25(1+(0+996)/996)= 2.5 V

Sorry, in this format, the LM317 formula is just about as clear as mud! You lose just under half a volt through the diodes, so in my case, tested values came out to between 2.05 and 13.90V.

How It Works - chemistry article on exploratorium.edu

Alternatively, you can use a digital potentiometer controlled by an Arduino to set your variable voltage input. You can set up a touchscreen with buttons and a neat little interface to put voltage adjustment at your fingertips.

There are simple ways of using an Arduino to measure amps and volts, so you can display that on your screen as well. Obviously, you can have the Arduino calculate power consumption in watts and display that in real-time too! If you're a chemistry math whiz, you could get really crazy and figure out how much ferric hydrochloride you're generating, or how much steel you're removing per second.

In a few weeks, I'll be going to visit my brother to deliver this thing. He and I will spend the day learning to use his new 3D printer to build a housing for it. With any luck, I'll be able to get some video of him putting it to good use. More as it develops...!!

Upstate Ramblings - Etching your Stainless Steel Drink Cup