An Impressive Modular Mold Box

Prolific maker and product designer [Eric Strebel] has years of experience making reusable mold boxes for silicone and resin casting. He’s always used 3/4″ plywood before, but it comes with some problems such as inaccuracy, screws that eventually slip out, and no room at all for expansion. Now [Eric] has decided to devise a modular mold box system that’s so awesome, it’s even stack-able. Check out the design and build process in the video after the break.

[Eric] took advantage of additive manufacturing and made fancy trapezoidal walls with recessed bits that allow for the magic that this modular system hinges on — a handful of M6 socket cap screws and matching nuts for tensioning. Once the prints were ready, [Eric] pounded the nuts captive into the walls and marked fill lines every 10mm. As usual, [Eric]’s video comes with bonus nuggets of knowledge, like his use of a simple card scraper to clean up prints, smooth the sides, and chamfer all the edges.

If you want to mold stuff like concrete and plaster, you may be better off using flexible filament.

26 thoughts on “An Impressive Modular Mold Box

  1. I’d say it looks like a good first iteration. I’d go with some sort of a lip and groove joint, coupled with fewer bolts and maybe a way to grow the box sideways instead of only up. The angled sides work well for corners, not so much for extending a wall.

    1. You may have missed his whole explanation of what he meant by “modular”. He can print sides that are any odd number of cm in length, with the example he shows being 5cm x 7cm. If he wants a 7 x 13 box, he already has the 7cm sides, so he just has to print the 13cm sides, and a 7×13 base. It’s kind of like the modular picture frame systems.

    1. I’ve used melamine coated MDF which releases better for me, I’d probably be using acrylic / plexiglass if I was doing anything for profit…Still reinforcing the boxes with tow-strap, sufficient keying, and plenty of edge space (that’s where I see the biggest advantage over my personal method, using less mold mix) I haven’t felt like it’s the materials and not my technique that’s fouled an effort.

      1. I just use what ever scrap material is handy at the moment I decide to make a mold. I don’t really consider a ‘pretty’ mold form, or even if the outside of the mold is ‘pretty’ either. The molds themselves, usually out-last my need, when I made them.

        What would be nice, would be a program, that takes a 3d model, and does all the work, so you just print a form, that only requires you to pour silicone in both halves, let cure, remove the finished mold and use. Figuring out the best orientation of the part, undercuts, gates, vents, and all those little details that can go wrong. I know I don’t have the math or programming skills, but seems like it could be done.

        1. If I follow you correctly, and you want two ‘masters’ one for the left half and one for the right, with all the features for pouring in your resin/metal/wax so you can just fill, combine and use I think you would be rather disappointed in the results… Unless you are using SLA printers.

          Depending on what is important on the part dimensions and surface finish wise it could be done and get a useable result from FDM, but the very distinct layer lines and less than perfect wall smoothness just won’t let the two halves join that well – so you will get awful flashing, and almost certainly some geometries will be out.

          Also to do those details for casting you need to know what you are casting – if its a super low viscosity long set epoxy you can get away with a great deal more restriction in the feed and air paths than thicker/faster stuff. The undercuts depend on the silicone choice and desired lifespan of the mold – if it only has to do 5 parts you can get away with much deeper overhangs than if you want it to do 100+ without tearing, and some mould rubbers are tougher than others anyway..

          With so many variables I don’t see a program like that really being useful, except as a rough guide for making your mould – perhaps picking the orientations of the separate parts to minimise overhangs and pointing out airtraps.. But in the end it really is an art not a science as every mould has such varied requirements, based on object, and materials oh and casting method – if you are using a pressure pot you really want a nice large resivour at exposed to the high pressure so you have more resin to push in and fill the crushed air bubble caused voids for example.

          1. I do decorative/ornamental pieces, nothing has to be perfect in every way. There is clean up, cast or printed. I cast in lead/pewter, and my modeling, mold making isn’t great, but good enough to get by.

    2. Soooh?

      This site is for hacker and makers. Not much of what we do makes economic or time efficiency sense.

      We all know (should know) that. You could just buy a mold box, right?

      I bet whatever anyone would make with the mold box, could likely be bought somewhere cheap also.

      Some have an idea, and go with it. I like seeing what they did, and how and why they did it.

      As far a wasting time, they don’t spend a lot of time leaving unhelpful comments on every HD post.

      ( I feel a little bad leaving this under BrightBlueJim’s comment, since I usually agree with him. And, ‘yes’ , of course he’s right. It’s more geared toward all the other negative poster, who are sure to chime in. I just felt a little triggered. Can’t wait for a new President … )

      1. ” Not much of what we do makes economic…”

        Actually, I think a_lot of what we do makes economic sense.
        a. Repairing equipment/software abandoned by the manufacturer support.
        b. Improving the functionality of equipment (e.g. Rigol oscope enhancements).
        c. The current HackADay Prize with a focus on helping 3rd World problems (although a number of critics point out the possibilities of 3rd World locations not having the infrastructure to sustain some of the entries)
        d. Re-purposing equipment/software for wider usage (I look at the “mold box” as useful as a strong project case.)

        1. I know what your saying, but lets be honest.

          We all have stellar salvages we are proud of, where we maybe even saved a chunk of money. And projects, where we beat the crap out of some p.o.s., and made it finally submit to our will. Exactly the way we want. Can’t even buy one like it.

          However, common project timeline:
          research online every last webpage on the main subject: 20 hours, buy parts, read up on related subjects: 10 hours, build, trash, re-research, re-buy more expensive parts that don’t suck as much, build, “project burnout”: set-aside, buy better tooling, try-again, use, too frustrating, let dust collect, build another project that is supposed to improve first project, abandon both (supposedly just for now), find a solution two years later for $28.00 incl shipping on banggood, and buy it. Add all the costs: time, materials, equipment, beer*, across all projects. What is your time worth? If you are making money on one-offs and repairs, more power to you. Most here don’t, needing to have a “real” job.

          That pure monetary $500 you saved on one repair is easily wiped out by one or two other projects. If you take the thrill of challenge, desire of added knowledge, or just plain joy out of it, I’d be surprised if most here would claim, that they would do what we do.

          The hackaday prize is actually a good example. I’m sure most adult entrants are not competing for fortune.

          * Not an endorsement, just my personal choice, frustration-dampening lubricant.
          Never use hacking as an excuse to drink.

      2. I get it — I’m not usually the guy who says “what’s the point of this”, but Eric Strebel is a product designer. This is what he does for a living. So I think that “what’s the most efficient way to do this thing I do all the time?” is a valid question.

        1. I know, like I said ….

          I just feel that sometimes we are too hard on HD and content providers. There just aren’t that many valid, documented projects that equate to “How to Make an Electron Microscope out of a Dollar Store Laser Pointer, Grandma’s glasses, an Arduino, a 555 timer, and a Coat Hanger” …

          Critics are always welcome to improve the pool …

  2. Plain old Lego bricks are a very popular choice for reusable mold boxes among model makers. This system here is very neatly looking and a beautiful construction – but does it offer any advantages over the simple way?

    1. Having used Lego for larger moulds I can say it doesn’t handle the bigger stuff very well (at least not in one pour). The Lego I used also leaks round the bricks pretty bad – not enough to escape fully but enough that many blocks need unsticking from each other with the silicone that has leaked inside.. But as I can’t bring myself to use good Lego bricks they are all the castoffs from the second hand piles that have been painted, glued in places that might be largely from that…

  3. Corrugated cardboard. Clear packing tape. Hot glue gun + glue sticks. Knife. Scissors. Those are all the supplies required to make a leak proof mold form of any size or shape, *precisely* the size and shape you need.

    Cover the cardboard with the tape on the side that will face in. Cut a piece for the base. Cut strips for the walls. Setup the master on the base so it’s held to it. Glue the wall strips around it, to the base and to each other.

    After the first half of the mold is made the base and wall parts can have the glue removed and be re-used for making the second half of the mold.

    The cardboard can easily be obtained for free, glue sticks and packing tape can be bought at Harbor-Freight or a dollar store.

    When I started doing resin casting 20+ years ago I made some sets of L boards to clamp together and glue and clamp down to various smooth and rigid things for the base. But despite using a vacuum pump on the silicone I kept getting bubbles in tight inside corners and subsurface bubbles along vertical surfaces. Those bubbles would cause little spikes and balls on the surface of the casting when the molds were put in a pressure tank.

    Then I found that the silicone wouldn’t stick to shiny surfaced cardboard. I started making one-off mold forms from it, hot glued together. Then came a time I needed to make a mold and had no shiny cardboard, couldn’t find any.

    So I took clear packing tape, covered plain cardboard with it and it worked even better than the shiny cardboard. That’s what I’ve used ever since.

    So don’t bother wasting time with fancy mold forms that don’t work very well and can’t fit into a pressure tank. Same for vacuuming the silicone. Make the mold forms fit into a tank and pressure cast the mold. Faster, less mess, *less cost*.

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.