I’ve been wanting to make a mold of something, anything, for quite some time now but haven’t had any good actual practical use cases.
Finally I had one. I’ve been doing a lot with RC Planes lately. I have a Bixler that I’m learning to fly, and I mean mostly crashing, and in another post I managed to strap my GoPro on to it (which made it very heavy and crash faster). What I wanted to do, and never completed was to make a mold of the cockpit “glass” out of some sort of plastic then carve out a “window”/housing for the GoPro so it could sit easily inside the cockpit without the funky wood mount that I came up. (Spoiler alert: Ultimately the plastic I used in the mold was way to heavy to make it “flyable”, I might as well have made it out of brick). Since, I didn’t want to ruin the stryofoam cockpit cover carving out a hosing so here was a great opportunity to make a mold. Here’s what I started with:
I went to the local Dick Blick store and after a couple of choices for molds I settled on this:
It’s kind of like Jell-O where it comes from algea/seaweed and makes a rubber like substance without being actual rubber. You pour it and it slowly hardens. So first I needed something to pour it into so I made a plexiglass case (I’m sure there is a more accurate term than “case”). I just used pieces of plexiglass, a dremel to cut them, and a hot glue gun to keep them together:
First casing was too big, requiring more mold material, so I broke it apart and made it a more snug fit.
I learned a trick somewhere in my research to use clay to take up space so you use less mold material and also to prevent leakage at the edges. This time I used some on the outside edges because I was worried the mold would be too thin. I did ultimately but some in the areas I had a lot of space to fill and I wasn’t sure what would happen with the material and if I’d end up with some kind of algae and clay Frankenstein mess.
I placed it on some wax paper in case it did leak:
I then mixed x parts mold mix, y parts water and stirred. The stirring is the tricky part and I later learned I did a real bad job, so some parts were too firm and “airy” (meaning too much mix to water) and other parts were not firm enough (too much water to mix).
From this I learned that next time I will take an egg beater or wire wisk, cut it and insert it into a dremel or drill (probably drill) and use that to thoroughly mix the agent and water a lot better than by hand.
I poured it in and watched it dry, some parts got very bubbly when drying, I think too much mix not enough water there, or it was lumpy:
Now to make the sides come off. I bent and pryed till the glue let go but I probably could have used a heat gun to remelt the joints:
Now to get this bad-boy out:
The mold mix I got had about a 8 min set time, I think I gave it about 25 mins, and then it would also “keep” for around 24hrs before it started to break down.
You can see that once I removed the plexiglass housing, the mold was uneven and could support it’s own weight in some places but not in others, not a good sign:
The middle was very gooey, you can see it got on my fingers as well, so I ended up with a failure. There is not enough rigidity throughout the thing, the “inside” edge would fall right in to the “outside” edge leaving a paper thin “windscreen”. Plus the inside didn’t even fill right, I had pockets of air and liquid:
In the end I think that my lack of good mixing technique was my downfall and I didn’t even try making a part, it all went right in the trash. Lessons to keep in mind for next time:
- Mixing is important – maybe mix some and add it in, then do some more, small batches of mold rather than all in one shot and not properly mixed.
- Mixing by hand is hard work, use a whisk or even a small paint brush in a hand drill to use as a mixed to more evenly mix the mold and eliminate the air pockets as well as the uneven distribution.
- “breaking the mold” can be tough, heat gun without burning the mold or melting the plastic rather than the glue is going to be tricky.
After this I did make a rubber mold of the same part by painting on layer after layer of a rubber/latex mold agent and allowing it to dry, which was a much much much slower process (20 or so coats) and I did end up with a fairly firm mold that allowed me to make a nice copy of the windscreen, the mold also had a much longer shelf life since it was rubber/latex but as I mentioned above the plastic resin was way too heavily compared to the Styrofoam and wasn’t going to fly.