Machine Shop Soaps Are Good, Clean Learning Fun

At first glance, it’s easy to dismiss the creation of custom bath soaps as far outside the usual Hackaday subject matter, and we fully expect a torrent of “not a hack” derision in the comments. But to be able to build something from nothing, a hacker needs to be able to learn something from nothing, and there is plenty to learn from this hack.

On the face of it, [Gord] is just making kitschy custom bath soaps for branding and promotion. Cool soaps, to be sure, and the drop or two of motor oil and cutting fluid added to each batch give them a little machine shop flair. [Gord] experimented with different dyes and additives over multiple batches to come up with a soap that looked like machined aluminum; it turns out, though, that adding actual aluminum to a mixture containing lye is not a good idea. Inadvertent chemical reactions excepted, [Gord]’s soaps and custom wrappers came out great.

So where’s the hack? In stepping way outside his comfort zone of machining and metalwork, [Gord] exposed himself to new materials, new techniques, and new failure modes. He taught himself the basics of mold making and casting, how to deal with ultra-soft materials, the chemistry of the soap-making process, working out packaging and labeling issues, and how to deal with the problems that come from scaling up from prototype to production. It may have been “just soap”, but hacks favor the prepared mind.

35 thoughts on “Machine Shop Soaps Are Good, Clean Learning Fun

  1. Just … wow.
    He’s actually adding oil and cutting fluid to the soap. I don’t know where people get these ideas from, but introducing motor oil and cutting fluid into the wastewater stream by way of soap is quite the achievement. I wouldn’t want to use this soap for pretty much anything. Also, why is he calling it unscented when it does contain cutting fluid and motor oil to provide the scent? I don’t quite get it.

    1. I hope that you bottle up the effluent of your shower and take it to a hazardous waste collection facility like I do, since the average human makes an incredible amount of oil and other organic ooze which collects on our skin and hair and is washed off while we shower. Wouldn’t want that getting into the ocean!

    2. A whole one drop of oil. This is obviously going to lead to a catastrophe. UN is already declaring the state of emergency.

      What I would consider though is allergies and skin compatibility in general. While washing your hands after working with much the same substances isn’t going to make anything worse, I’m sure someone’s going to get the bright idea to shower with this for a year or something.

      As a compromise I suggest adding a glycol or polyglycol. Those are used as cutting fluids, machine lubricants, and *surpise* cosmetic fillers. Silicone-based lubricants should also be highly biocompatible but I would be wary of additives in the ones sold for industrial applications. Might interfere with the mold too.

    3. The motor oil, as a long chain hydrocarbon, will broken down by the saponification just like any other fat (not sure about the fully synthetic stuff, mind), and the cutting fluid is essentially fine sand in a light petroleum distillate, which will evaporate.
      Here in the UK we have teams that go into the sewers after Christmas to tackle the “fatbergs”, created by people pouring the fat from their roast dinners down the sink.
      Think they’d probably welcome the non-problem of watching a little foam from novelty soap flow away.

          1. T-Cut? You mean the automotive scratch remover / polishing compound? Why would anyone use that for drilling / cutting / tapping? It would wear your cutting surfaces horribly.

          2. “Cutting fluid”, when referring to machine work, is a broad term meaning some kind of fluid meant to aid in cutting operations. That includes coolants/lubricants for milling, tapping, grinding, etc. Pretty much always just some kind of oil, water, and a surfactant to make them play nice, though some are straight oils and, technically, plain water qualifies, too.

            Waterjets don’t have any kind of special mix. They use plain old water, and feed abrasive grit into the stream shortly before it exits the nozzle. Barring the rare operation on very soft material that just uses straight water, of course.

          3. Waterjets almost exclusively use water as the carrier medium, though in theory any reasonably inexpensive fluid could work. Most are open loop though, so using roughly a gallon of oil per minute of cutting could get fairly expensive (waterjetting is already a fairly expensive process) and filtering oil down to a few absolute microns for reuse is harder to do than the same process with water. Plus, every part would be literally covered in oil and you would have to fill the catch tank with probably a thousand gallons of oil. Let’s not even get into the splashing of oil everywhere. I also don’t think the author was talking about waterjetting with oil. The fine particles are generally garnet and they are added to the stream of water right before the cutting process occurs.

      1. Fats are triglycerides (chemical formula C3H5-3(CnH2nCOOH) ), and saponification removes the glycerine backbone to allow the fatty acids (CnH2nCOOH) to form salts. The chemical reaction is 3NaOH + C3H5-3(CnH2nCOOH) => C3H5-3(OH) + 3NaCnH2nCOO + 3H2O.

        Long chain hydrocarbons like motor oil lack the carbolyl group (COOH) on the end, and thus can’t form fatty acid salts. So it won’t be broken down by the saponification

        1. True, motor oils can’t be saponified, but that’s not how soaps clean.They clean by micellization of hydrophobic materials – the greasy tails of the surfactant (soap) are attracted to the oils, sequestering them in a micelle that’s water soluble.

  2. It’s obvious a lot of commentators today don’t play with their cars much. There’s way more than a drop of oil on my skin to mix with soap when I come in from the shed.

    I could see a great marketing campaign around motor oil scented soap for those really manly types :o

    1. There’s “Gun Oil” brand personal lubricant. But that seems to mostly play off people’s sense of masculinity and / or fears and / or inferred corollary between their genitals and a personal firearm as the lubricant actually doesn’t appear to be that particularly good.

      Also, people used to play with asbestos snow for their holiday tree decorations. Not quite the same immediate risk factor but that still didn’t make it a good idea either. I work on my cars too, but I wear gloves and long sleeved shirts too, to both keep cleanup easier but also to prevent getting a whole host of somewhat skin unfriendly items all over my skin. Doesn’t take that much extra work (saves time cleaning up so it might actually net out) and it feels worth it to me. Your mileage may vary.

  3. I normally get enough grease, oil, whatever on me when i’m working on my vehicles or machines that even after I do shower I still have a light scent of grease or cutting oil. Not sure I would really want to add more, but hey to each their own

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