Digital Kiln

A kiln or foundry is too often seen as a piece of equipment which is only available if a hackspace is lucky enough to have one or individuals are dedicated enough to drop the cash for one of their own. [The Thought Emporium] thought that way until he sourced materials to make his own kiln which can also be seen after the break. It costs half the price of a commercial model not including a failed—and exploded—paint can version.

As described in the video, these furnaces are tools capable of more than just pottery and soft metal baubles. Sure, a clay chess set would be cool but what about carbon fiber, graphene, aerogel, and glass? Some pretty hot science happens at high temperatures.

We get a nice walk-through of each part of the furnace starting with the container, an eleven-gallon metal tub which should set the bar for the level of kiln being built. Some of the hardware arrangements could be tweaked for safety and we insist that any current-carrying screw is safely mounted inside an enclosure which can’t be opened without tools. There’s good advice about grounding the container if metal is used. The explanation of PID loops can be ignored.

What else can you do with a kiln? How about jewelry, heat treating metal, or recycle your beer cans into an engine.

31 thoughts on “Digital Kiln

  1. It costs half the price of a commercial model not including a failed—and exploded—paint can version but also importantly, also not including any of the maker’s time to research, experiment or actually build anything either. These costs should not be completely glossed over if you want to be accurate about the total cost involved to build something. This kiln was not a thirty minute build from start to finish.

    It’s not really fair to say that somebody built a plane from a kit and saved a bundle over buying a plane when it took hundreds of hours alone just to put it together.

    Neat build though it still seems a bit rough around the edges at present.

      1. ahhh… and there we have it again. One of those people who works 24 hours a day and has not hobbies at all.
        Seriously, how do you spend your SPARE time, by doing something you like (at least that’s the way it should be).
        If you like to build a kiln… in your spare time… then time is free.

        Stop shouting that nonsense that “building something yourself isn’t free, you should calculate your time working on it as consider that cost”. Nonsense, time is free, unless somebody else builds your projects and charges you for it!

        1. It’s silly not to take the time spent into consideration. If I can save a little money, but have to spend 100 or 200 hours of my time on making it work, it’s much more likely that I’ll just buy a solution than if I just have to spend 2 hours. Even if you don’t get paid for your hours, they’re worth something. 20 hours spent on a furnace to save a buck is 20 hours not spent with the lads or the kids. Unless you enjoy building a furnace for the sake of it, it’d be stupid not to take the time spent into account.

          We’re not even taking the limited nature of your free hours into account. If you spend 40 hours building a kiln, that means 40 hours less for other projects. Time has a value, whether your boss pays you for it or not. Time is never free. It’s the one thing we can’t make more of, which means it has intrinsic value.

          1. Well, to this guy, working 20 hours to build a furnace for 180$ must have been worth it. You know…he might have learned something about kilns in that process which may have been the point of it all.

            You know, anything done voluntarily in ones free time is, IMO, not work. Hence why i personally do not take time spent doing it into account. If i’d started taking time into account, i could aswell go and buy an off the shelf product, so why friggin bother building it myself?

          2. It comes down to “how long will it take to complete this project with the information provided” factoring in one’s knowledge and skill as well as resources. The maker has done all of the hard work. Their time isn’t our time for that reason.

      2. Eh, but the other aspect of it is some people like doing this. I like working with electronics and woodworking… To me its relaxing and since some people pay for the same relaxation… wouldn’t that also start to affect the price too? If I were to go on vacation somewhere… and pay to do… etc.. So its not so much of what you value your free time, its what value you place on things you do. If it has a net benefit (relaxing, educational, etc) then the calculation would get much more complicated. Do you start adding the comparative prices of tech schools or universities? Would you also start associating the costs of other time off/relaxation things? Which should I choose, a massage to compare it to or movie tickets? Oh and the physical labor. Does that count as exercise? Does the individual value exercise? so then do we add the cost of gym membership?

        Bottom line: yeah it would be cheaper, if I included my labor rate, to buy a bookshelf instead of building one. But If I like building things (and I want to have fun with tricky puzzle mechanisms) then its worth more than that labor rate anyways.

    1. Well whose gonna pay us for our time? No one that’s who unless we’re fat cat contractors with a paying gig. Most people here are hobbyists who enjoy learning and making things. So his cost was $180.00 for his home brew kiln.

      1. Yeah, I expect most people here are like me – researching, designing and building things is a major part of the fun. Working at my standard consulting rate is not at all substitutable for working on any of my hobby projects. I agree that there comes a point where it’s no longer worth my time, but time spent working on my own tinkering fills a different need.

        1. It does. All I am saying is that one should not assume the total cost is truly only the parts and nothing else when summing up the entire project’s total monetary and non-monetary costs. That’s all.

          1. And as always.. Your comment is worth every penny we paid for it.

            Time spent learning something is time well spent.

            Working out billable hours for a fun hobby project is however, an utter waste of time. Almost as bad use of a finite resource as time spent whining at faceless strangers on the internet.

    2. What if I told you some people enjoy putting hours into something just for the sake of the craft? I feel bad for people who take the “if I don’t make a cash profit, my time is worthless” paradigm even into their social lives. Enjoy your curiosity and creativity!

      That said, if you’re planning to use the kiln in some professional capacity, probably best to get a nice commercial model. But I doubt many of us are.

  2. And Enameling metals, Slump molded, pate de verre glass, doping silicon(+vacuum), and a bizillion other things!

    The refractory recipe I have concerns about. He mentioned Paster of Paris but under that umbrella you have Gypsum based, Cement based or Lime based. There is a heat resistant plaster used to line chimney flues but in my opinion any hydro set compound is going to deteriorate in a high heat setting.
    Also with any new kiln or a kiln you haven’t used in a while you should slowly ramp up the temperature to 600 F and allow the kiln to “soak” at that temperature before going higher. You need that time to dehydrate the materials used in your kiln.
    Best of luck!

  3. Interesting how people are commenting on how all the time he spent on the build should be factored in, but nobody mentioned all the time it took to shoot, edit, narrate and produce the video, which was for our benefit :-)

      1. Is it a monetized Youtube video? It gives back to the community either way but if so, would also return some (a small fraction) of the ad revenue that Youtube makes off of it back to the person who put the time into produce the video.

        Which is not unlike what many companies out there do professionally. Not being critical of the work put in, just trying to be realistic about how it all works. It is hard work to make, edit and produce a video. This isn’t necessarily all simply to give back to the community is all I am trying to say and I am also not arguing they should not be able to profit something for the time they put in either.

  4. For those commenting about value of time vs buying a product. You can buy a fish at the store for less than your time in effort of going fishing. But millions of fishermen would remind you, they they still enjoy fishing all the same. It’s the basis of nearly all hobbies. It’s just something you want to do and have a feeling of accomplishment.

  5. And really on the time/work tradeoff thing: it’s just that, a tradeoff.

    If he wasn’t going to spend his time that he spends on the kiln working, but instead by going to the movies which costs around $5/hour, then his building the kiln actually saves him money. Or maybe he would be going downhill skiing instead, then he saved hundreds of dollars by DIYing the kiln.

    You don’t know his marginal value of a “free” hour. Neither do I. We can make educated guesses by how he spends his time (“weak axiom of revealed preference”), but that won’t ever support the argument that he’s spending his time wrong, because it starts from the assumption that he knows better than you do.

    Oh, and this is Hackaday. Not armchair-economist-a-day.

    1. Uhh.

      *scratches head at this fallacy*

      Just to clarify. Your point is that going to make a kiln for free instead of spending $5 per hour on a movie actually saves him money? I don’t think it works quite like how you are suggesting as a fair argument.

      I am not saying he was spending his time “wrong” either. All I am asking is that people try to consider being a bit more reasonable about factoring time spent into the equation when they try to boast about how much money they saved by doing something themselves.

      I also want to point out that I very much appreciate the intrinsic value of education and learning that goes into projects that is not monetary. Sometimes it is easier to buy something, sometimes you want to enjoy the process or simply try, fail and try again. Those are not right or wrong.

      But my point is that one should capture the time element of the project to be able to truly account for the total effort and resources necessary to complete the project. That’s all.

  6. I sent Elliot a link to our experiments with a 3+KW induction fired metal melting furnace that was based on an inexpensive imported induction range. We were able to melt roughly 50 pounds of aluminum in 2 hours with it. Here is a link to a video of me dropping a piece of an old aluminum street lamp housing into the crucible. The piece weighed just over 2 pounds and was 28″ long. It was wicked cool watching it just sink in and disappear. http://neon-john.com/Induction/furnace/50_lb_furnace/feeding_street_light_parts.avi

  7. Neat video. Thanks for sharing.

    I’m designing a kiln/furnace/forge with magnets in the perimeter to shape the magnetic field of what I fire/treat so I’ve been researching what can insulate the best with cost effective off the shelf materials.

    I also designed the system to be more versatile so can have multiple uses in a stack-able fashion (bottom sphere inner mold a beach ball (yoga ball for larger scale if implemented), ring sections with design to elongate if want larger chamber so thought is to maybe have vertical pieces though will most likely use a more trough like bin for that design and stick with horizontal slice sections, and the top sphere or like I noted using the radius of the beach ball for corners basically in an elongated shape with the exit hole damp-able for oxidation/reduction firing and to also be able to set a tray to do blacksmithing if wanted. .

    I haven’t fabricated yet as I was almost thinking to make a larger seal for the beach ball to add sand or more likely foam into to support as I am not sure how solid yet at a higher packing pressure the ball will be to maintain the spherical sections shape. I’ve thought maybe using fiberglass to make a mold from also.

    For my design, I thought something similar at first though was more clay and refractory cement and sand with perlite.

    I am changing the refractory mix to be mostly silicate and perlite based.

    I found Walmart has Silica Gel kitty litter and a cheaper version for less than $5 US a bag. At the Ace Hardware you can find the pure 100% Sodium Hydroxide drain cleaner. Plaster of Paris is also suitable and/or Baby Powder that is Pure Talc.

    Like the cheap silica gel from kitty liter, the magnesium silicate baby powder contain fragrance. This can be heated off in an oven or on a hotplate I am thinking if wanting to purify more. I haven’t verified the fragrance and boiling point yet or if the manufacture will give the ingredient on an MSDS or disclosure.

    Perlite can be found as well as different grades at a variety of locations in pure form. Distilled water or no iron water is also required.

    I also was thinking to add aluminum oxide and found harbor freight didn’t have the white material, so I found on eBay sand blasting media that is white aluminum oxide from the “theabrasivearmory”.and bought 10lbs for prototype starters

    I like “clkindred” on Youtube as the best formula and example for the refractory I was thinking about using and plan on making now I have the materials. His “How to make a coffee can forge” is the best example I’ve found on Youtube or online.

    If I remember, I’ll try to film what I am doing also… though have to see on time as I hardly have the time for most of my projects. :-)

    1. I can note that I wanted the best insulation to make sure the magnets are not brought up to or past the Curie Point so they don’t lose their magnetic properties since I am most likely going to use permanent magnets unless I need a special electromagnetic field shape or more timing specific control and mechanical positioning is more a pain to deal with using permanent magnets. I want to make some scientific ceramic and glass materials as well as ferrite, metglas, nanocrystaline and 99.5% Iron under hydrogen. Kind of scope creep way science fun more advanced complex domesticated than the simple ferrite’s I’ve found online.

      1. We found it helpful to use refractory cement in places where you need things fixed in place and don’t want them moving, and than lots and lots of vermiculite for the bulk of the insulation. Vermiculite is very inexpensive and does a great job.

        BTW, watch your baby powder. A lot of that has corn starch in it.

        1. Will do on the baby powder. I made sure before I forgot to grammar check before I hit the “POST COMMENT” to have “Pure” noted and some comment regarding fragrance as I’ve not found anyone performing purification to remove the fragrance that I assume will leave carbon and most likely on the nano scale once fired.

          There was a period where I was planning on making with high carbon content clay as when making carbon pottery/cermic crucibles versus carbon fiber or EDM material versions that would be way more expensive though maybe a better inner liner..

          I’ve read about silica based aerogel on HaD, though nothing DIY relating to the silica/carbon or carbon aerogel yet since I want to say off the top of my head those were invented around 2013 or later. For a period I was thinking about lining with… then realized they are way more costly complexity manufacturing processes with no off the shelf materials really… unless you’re really into synthetic chemistry at home. Not for me… at least on this income level.

          Interesting using vermiculite. I’ve used before farming… though don’t recall in either foundries I’ve worked in. I was reading vermiculite is used up to 1150 degrees C and perlite up to 850 to 900 degrees C though the perlite data is based on manufacture and I’m not sure how either performs with a silica coating over time. The vermiculite melting point is 1350+C and perlite 1200C so does seem better other than perlite has a little better R insulation value of 2.7 per inch loose fill versus vermiculite R value being 2.08 per inch loose fill.

          If not for having a bunch of perlite on hand already… I’m thinking I would modify to use vermiculite for a higher temp kiln though need to do more research.

          I do have dense and lighter inner liner refractory brick also for the final large scale project. The inner liner plan is like in the video using only the silica glass, plaster of paris (not sure if required), magnesium silicate and aluminum oxide, I do have some carbon fiber also and am wonder how like with the silica glass performance on perlite and vermiculite… the performance is on carbon fiber or even graphite added.

          Thanks for sharing as I never thought about using vermiculite. I wonder how long term performance is?

  8. I forgot about titanium dioxide as I was looking at forms for the bottom to focus the heat to where the feed, using a ball half sphere or cone maybe, is on a rocket stove for the heat source and in other uses for the rockets stove and remembered I didn’t comment about titanium dioxide in my qualitative formulas where aluminum oxide is demonstrated above… I’ve not seen a demonstration video or website for titanium dioxide where I’d prefer a larger particle size to insulated better using air gaps… though as a surface white wash coat smaller is better.

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