Fail of the Week: Cutting Steel with Baking Soda

[NightHawkInLight] wants what may be the impossible – a dirt cheap replacement for a laser cutter or a water jet. He’s got this crazy idea about using electrolysis to etch sheet steel parts, but he just can’t get the process to work. Sounds like a job for the Hackaday community.

In theory, electrolytic cutting of metal  is pretty simple to understand. Anyone who lives in the northeast of the USA knows all about how road salt can cut holes in steel given enough time – say, one winter into payments on that new car. Adding a few electrons to the mix can accelerate the process of removing metal, but doing so in a controlled manner seems to be the crux of [NightHawkInLight]’s problem.

In his research into the method, he found a 2010 video by [InterestingProducts] of etching reed valves for DIY pulse jet engines from spring steel that makes it look easy. [NightHawkInLight] deviated from the reed valve process by substituting baking soda for salt to avoid the production of chlorine gas and changed up the masking technique by using different coatings. We applaud the empirical approach and hope he achieves his goal, but we tend to agree with frequent-Hackaday-tipline-project notable [AvE]’s assessment in the YouTube comments – the steel is just too darn thick. Once the etching starts, a third dimension is created at 90° to the surface and is then available to electrolyze, causing the corrosion to extend under the masking.

What does the Hackaday hive mind think? Is there any way to fix this process for thicker steel stock? Narrower traces, perhaps? Somehow modulating the current in the tank? Perhaps using the Hackaday logo would have helped? Chime in down below in the comments, and maybe we can all throw out our laser cutters.

47 thoughts on “Fail of the Week: Cutting Steel with Baking Soda

    1. Meaning basically the corrosion rate is no longer a function of the etch current, it eats it all… unless you use a reasonable grade of stainless that is attacked really slowly by lye…. or a better mask, since half the story is that it’s creeping under it… but then you’d still probably have to etch, get it out quick and rinse thoroughly or you’d still maybe get over etching… raggedy edges and pitting on the good piece if a cutout for example.

          1. I wonder if the difference is, that NaCL is an acid salt and inhibits action of sodium hydroxide while in solution with it, while sodium bicarb is a buffer and also basic and enhances it.

      1. Hmmmyyyynnno… very weak solutions I think just let the water ionise so you’re electrolysing water into O2 and H2, stronger solutions and higher voltages than the bare minimum of a couple of volts, start ripping up the bicarb.

        1. You get this… 2NaHCO3 (aq) + 2 H2O (l) → 2 NaOH (aq) + 2 CO2 (g) + O2 (g) + 2 H2(g)
          I think that starts to happen when you go past “gentle bubble forming” at the O2 side and O2 starts dissolving back into the water, because rate of production high….. though we might get some water pressure/depth in play here, and might get more O2 solubility if your electrodes are deep, and it’s got a ways to go to the surface. vs when you keep it super shallow and it’s close to surface.

          1. Electrochemistry is a lot more complicated than this. Baking soda doesn’t breakdown because the water splits apart at a lower potential. All the water has to be turned into hydrogen and oxygen before the baking soda breaks apart, and at that point you don’t have an electrolyte anymore.

            I have used baking soda for electrolysis several times and I can assure you the electrolyte doesn’t become caustic.

      2. Based on my not very technical experimentation, you just want something to reduce the water’s resistance. Could be baking soda, or lemon juice, or salt, or whatever. You want more amps per unit time, is all.

    2. I’ve been doing electrolytic rust removal using washing soda (sodium carbonate) rather than baking soda (bicarb). I wondered why the carbonate is recommended–and I suspect the creation of lye with the bicarb is the problem.

      I’m struck by the presence of rust on the workpiece–exactly the opposite of what happens with the rust removal process.

      Could agitation or pumping, to keep fresh electrolyte at the cutting site, help with this?

      1. bicarb is transformed into carbonate by heating it in a 200 F oven for 30-60 minutes.

        It gives off CO2 with heat which is the whole point why sodium bicarb is used in cooking – it makes cookies rise.

  1. 3D print or make a silicone cap or series of progressively deeper caps lightly lined with grease or some other non reactive agent that could slow/retard the erosion along the sides. obviously this would require meticulous work and defeats the point of a one shot etch…just thinking out loud…

    1. Same thought. What about 3D printed EDM tools? As in the laser sintering type — IIRC they are sacrificial metal.

      A wire type might be pretty easy to do and can use the 3D controllers for 3D printers. Hmmmm.

  2. I once read a Grey Matter on this. You need to keep the electrode very close to the workpiece as the etching goes on. It won’t work well unless the electrode is gradually moved in to keep the current and spacing constant.

  3. If one could do an energy calculation you could see if it’s possible.
    2200W CNC router head vs EDM machine vs Water Jet vs chemical etch.
    I suspect you would soon realize chemical etch is just not enough energy to do the work of cutting metal.

  4. I’ve done this successfully: pulse jet reeds cut with baking soda in water. (Based on instructions from that crazy pulse jet guy in New Zealand.) What I found: you need thin steel (I used spring steel about 0.010″/0.25mm thick) with a very durable resist (because otherwise you get pinholes everywhere and it strips off the edges of your scribed lines during the cutting process) and you need the resist to be very thin. I used something that claims to be epoxy spraypaint. There’s also a limitation that I, at least, can’t successfully etch deeper than the width of the scribe line, including the thickness of the resist, hence the need for a thin resist. What worked for me was using a double-sided scribe line, which I did using a cnc mill set up for pcb milling and set to cut just through the resist, and a saturated baking soda solution (which as mentioned above I feel is purely there to reduce the water’s resistance and increase the current) with the anode and cathode just far away enough from each other that bubbles forming didn’t get trapped between them, and a peristaltic-type pump keeping the water moving fast enough to blow away the bubbles (and, quite often, start eroding the edges of the resist.) Run for five minutes, pull out the workpiece, touch up the edges with a Sharpie, put it back in, and about fifteen minutes in, it was done enough that I could pull the reed valve loose with my hands, with a bit of flexing to break reluctant bits.
    At a previous job, my boss wrote a number of papers on photoelectrochemical etching (like this https://www.google.com/patents/US5486264) where he used a laser in an etchant to do quite selective high aspect ratio photolithography, but that requires a lot of stuff that most of us don’t have.

  5. Obviously having a vacuum where the water and electrolyte is, and having a high enough electrical potential will etch things very nicely, you can even use a few electromagnets and charge plates to save having to mask the work piece.

    But if electron beam lithography is a bit fiddly for you perhaps just electroplating the iron first with another metal? The idea being to expose the iron to an environment that attacks it but not the metal plating. So you need to pick your metal and etching solution combinations carefully.

  6. Although I never got 100% perfect results, I have done this, but NOT with baking soda. A nitrate, NaCl, or a mixture of both would be better. For etching brass it must be pure nitrate.

  7. As [Nighthawk] noted, the undercut will kill you. If you over-etch a PCB too long, your traces will come undone from beneath, and that’s with (whatever thickness of copper-plating) which is two-dimensional compared to what he wants to do.

    The problem is that you want straight walls, but there’s no way to make chemistry move in straight lines.

    (Where by “no way”, I mean “here’s an incredibly difficult challenge”.)

      1. They use acids that eat into the silicon crystal’s matrix by different amounts along different axes. You need a single, homogeneous crystal cut along a certain shear plane, and masks oriented to the other planes to make it work. Bulk steel isn’t that tidy.

  8. An EDM by hacker goddess Jeri Elsworth: https://www.youtube.com/watch?v=uUN4_-xp1Wc simple, cheap and easy to mount on an x-y table. Probably slow, but cheap and reliable. Another route would be to cut your anode out of Aluminium foil or some such and back it with a nonconductive material; then you could coat your target metal and reveal the metal to be etched in the normal way. You then want to hold the anode and the work piece close together and flow the electrolyte between them. As the metal erodes you slowly advance the anode so that the nonconductive material protects the edges of the cut. The problem is to keep fresh electrolyte flowing through the gap after the anode sinks below the metal’s surface. A porous anode might be necessary.

  9. Hypothetically, if you coat the metal (bar the part you want to etch) in a carefully considered acid resistant compound, which is also non conductive, then fill the tank with a compound which eats away at the designated metal, basically a conductive liquid etchant, which doesn’t erode away at the acid resistant compound, this would work.

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