Molding Rubber For A Pre-production Prototype Using A 3D Printed Model


When you’re getting close to a production run the prototypes really need to hit the mark before pulling the trigger. [Bob’s] still hard at work getting his scoreboard off the ground and his most recent endeavor was to find a way to prototype the rubber gasket without blowing his shoestring budget. His solution was to harness the power of 3D printing to generate a model from which he could create the mold from which he cast the rubber part.

To make things a bit more difficult, the band isn’t just decorative, it doubles as the tactile part of the scoreboard buttons. You can see all six of them (before being painted to make them stand out) in the inset image above. Just above that image is a picture of the mold making process. The toothpicks are suspending the 3D printed model of the rubber band while the lower half of the silicone mold sets up. Once that had happened [Bob] sprayed release agent to ensure the top half of the mold wouldn’t stick while it cured.

The results turned out just great. Sure, this isn’t the way to go if you’re making a lot of these things. But we’re impressed at the quality he achieve for a one-off item.

If the finished product on the left looks familiar it’s because we looked in on the project last June. [Bob] continues with improvements and plans to launch a crowd funding campaign this week.

16 thoughts on “Molding Rubber For A Pre-production Prototype Using A 3D Printed Model

  1. Did anyone else read this part and say…uhh?

    “The next step was to mix up the mold material. It comes in two parts, and requires a mix ratio by volume, so I used a small scale to pour the exact amount required.”

  2. This is one of the best use cases I’ve seen for 3D printing technology. It’s definitely where the DIY printers shine. I think with 3D printing technology people are forgetting how to use simple metalworking tools to make parts. A hacksaw, drill, and set of files can take you a *long* way and you can make much better parts than you could print… but for something like this, 3D printers are perfect.

    1. You have said something that I’ve felt for a long time. I see a lot of 3d printing projects for parts that can be easily made with common metalworking tools, often times much faster than by designing them to be made on a 3d printer. Plus, as you said, making a metal part in the traditional way generally results in a stronger part.

  3. The rubber mold is cool.

    The product is ridiculous at that price point and ultimately unnecessary. $30, you might get some sales. There it’d compete with plastic flip numbers. But $200? You are out of your mind.

        1. Well, first I wondered why you spent three months in China when you could have learned most of the same information from the comfort of your computer chair. Then I wondered why you would work full time on it, without having a successful product first – usually it’s the other way around; someone has a product, works on it in their spare time, and once it gets some real traction you leave your job and focus on it / grow it.

          I think the digits are hard to read and are ugly, not to mention the waste in having such a huge PCB. There are certainly other ways to go about it.. Take a look at those big segmented leds that they produce in china for cheap. If nothing else, at least put some diffusion panels in front.

          And finally, the price. Maybe it really will need to be this price for you to make a profit, but if that is the case, you are going to be hard pressed to find buyers – your target market consists of mostly students who are poor.

          Don’t take my comments the wrong way, I admire your work ethic and ambition, but I think you are wasting them on the wrong product.

          1. Those are all valid points, and good questions that I’ve been asked before. I appreciate that you took the time to mention them. I’ll address each one, and I apologize for the long post:

            China: I was accepted into a hardware startup accelerator called HAXLR8R. Besides being in China, we got a small amount of capital so our expenses were mostly paid for, we were given access to mentors, toured factories, and sourced components. A computer chair is great, but there’s something to be said for watching someone pull the label off a reel of Panasonic components and put it on a reel of knockoffs to really understand how things work in China. Ultimately it gave me the experience necessary to save a lot of money and prevent myself from getting swindled, but also to see first hand that manufacturing in China has a lot of costs that aren’t part of most people’s spreadsheets.

            Full time: The first prototype dates back to 2008 and was done in my spare time. I was working on it part time during all of 2011 while I did contracting on the side, but I realized that I wasn’t progressing fast enough on it and wasn’t making enough money doing the contracting; I was just treading water. The feedback from the prototypes I had built was positive, and I saw the potential for the scoreboard. I was also accepted into the accelerator around then, which demanded I work on it full time while I participated. After that it made sense to keep working on it full time.

            Digits: The digits have gone through a few revisions to get to where they are now. I know it’s a bit of a cop-out to say, but the scoreboard is hard to photograph because it’s always on the far side of the field and the action is taking place in front of it, and the effects of lenses haven’t been flattering. I promise you that our beta testers and the people we talk to when we take this places do not have those comments.

            As for the PCB, assembly cost was a huge consideration. LED strips require wiring harnesses, which are expensive, and labor, which is even more expensive, and an enclosure to hold them, which is very challenging. In large quantities, labor costs don’t scale cheaper, so automating everything is the key to cost reduction. The LEDs that are used in strips are cheap because they aren’t as efficient or bright, and battery life is important for this product. With a single PCB with black solder mask, I don’t need a special cover over the strips, I don’t have ANY assembly by hand, there’s no risk of mechanical failure in an impact (no cables to get knocked loose), and the LEDs are exactly what I’m looking for.

            We’ve experimented with diffusion on the front. Indoors it’s fine, but outdoors in sunlight we need every photon getting out of the scoreboard, and even a 10% reduction hurts. I posted about a month ago how we test every aspect of the design. We experimented with color films to see if that would increase contrast and reduce washing out, but besides getting mediocre results, we found that manufacturing tinted polycarbonate, or applying a color film, was prohibitively expensive.

            Our target market isn’t poor students at all; it’s institutions like schools, gyms, leagues, and camps, all of which have yearly equipment budgets and a clear need for this product as opposed to a casual desire for the product. There is competition in this space, but at 2-4x the price of our unit, and they are too bulky and expensive and difficult to use. The problem we’re having now is that many of these institutions have antiquated buying processes that require spending at specific times of year, from specific catalogs, and approved by a higher up, and the organizations we’ve talked to have all said “this is a great product and we’d love to buy/sell it. Let us know when you’ve gone to production.” So we have a chicken/egg problem. We’re seeking investors as well, but we are doing this campaign in parallel so that we can try to raise the funds we need without giving up equity. Our hope with this campaign is to attract adults who play recreational sports or who have children that do, like soccer moms, and teams who could each pitch in a 20 each for a scoreboard that they could use for years. We’ve been pretty popular among ultimate frisbee, flag football, roller derby, hockey, volleyball, and some other sports that have sought out our product.

            I hope that sheds some light on our process. Please let me know if you have ideas to do it better or if our reasoning doesn’t make sense.

  4. Mold making

    Casting silicone into a silicone mold can be tricky. You must completely coat the mold with release or the casting will bond to the mold. A better mold material for casting silicone is urethane rubber. Alternatively, casting urethane rubber in a silicone mold.

    Silicone and urethane won’t stick to each other without special preparation and a bonding agent.

    To make the buttons in a permanent color that will not rub off, get some silicone pigments like Smooth-On’s Silc Pig. Mix up a small amount of one part of the silicone with the pigment so you have it ready to mix with the other part.

    Mix up a small amount then use a toothpick to apply it into the button recess and let it cure to a firm but still tacky state. Then assemble the mold and cast the black silicone.

    You could also apply some of their Psycho Paint to the mold before casting the part. A problem with that can be breaking the release layer and getting the paint bonded to the mold.

    1. Brilliant! Thanks Galane. Your trick for the colored buttons is a great idea. I borrowed my girlfriend’s nail polish for the photo shoot, but it doesn’t last long on the silicone and isn’t a viable solution for production. Your method definitely sounds like it would work.

      It seems I got lucky casting my silicone in silicone. Everybody at Sector67 was watching the progress as it unfolded over the few days and thought it was a complex mold that would not be likely to succeed. We were all surprised and relieved when it popped apart so well.

  5. A nice creation. Silicon / Nitrile / Neoprene Rubber/ EPDM / Viton Neoprene Rubber, Natural Rubber Sheet, Nitrile Rubber Sheet, Neoprene Rubber Sheet, EPDM Rubber Sheet, Silicon Rubber Sheet, Electrical Insulation Rubber Sheet, etc Applications of Neoprene Rubber, Rubber Products: Belts, Conveyer Belts, Side Wall Coverings, Ceilings/Roofs, Insulators, Floor Mats, Etc. Rubber Products

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