Molding a plastic part with hand moldable plastic

One of our most exciting materials is hand moldable plastic. It is so exciting because customers use it to build prototypes and make parts quickly. In addition to speed, our customers do not need expensive tooling to make plastic parts.

We are starting to see quite a few interesting projects and different techniques for hand moldable plastic. We plan to share the techniques and have plans to carry some of the tools and components that make it easier to work with.

Today we interviewed Ryan Pinto from Toronto about how he designed and built the swivel joint pictured below for a baby gate.

It took Ryan 3 attempts to get the part just right. He used his hands to form the part and the first two times ended up melting the part down and starting over.

We asked Ryan to explain his process and he sent over this explanation:

1) I quickly get the hand moldable plastic into a simple 3D shape that best approximates the final model, in my case it was a cylinder.

2) While the block is still very soft, I got it roughly into the shape I wanted, in my case I had to slightly pinch one half ( lengthwise ) and elongate the other half. Also I did this on a metallic surface, so the wall facing surface of the pivot would be perfectly flat. I found that cold metal does not stick to the hot plastic mass easily. This made it a great surface for shaping.

3) I pressed the plastic spoke of the baby gate into mold to create a good fitting joint. At this point the plastic is still quite warm and transparent. Since it is transparent it makes it possible to see the spoke and adjust how far down you want the impression to go. It's important to remember that the parts of the end product that will take the load/stress, need to be sufficiently thick. In my case the plastic around the pivot impression needed to be at least 4 mm thick. I removed the spoke and checked the hole for any deformities. I reinserted and reshaped it a few times.

caution: The spoke of the baby gate was made of plastic, so I had to cover that spoke in wax paper (baking paper) before I used it to make the impression. This is very important because the hot hand moldable plastic bonds very strongly with other plastic surfaces and it's nearly impossible to fix the resulting mess. I used a common latex based glue to attach the wax paper to the plastic spoke.

4) I used a thin metal screw driver to impress suitable holes into where the wall screws should go. Again the cold metal makes good dents and holes while the hand moldable plastic is hot. The region around the screw holes had to be at least 1 cm thick to withstand the pressure of a tight screw fitting.

5) With my fingers I gave it the finishing touches as the plastic cooled. I carefully watched to make sure I did not deform the spoke impression. Remember you can always reinsert the spoke to correct it if needed. The cooling period is the best for finishing touches. At the temperature comes down the material becomes more rigid, so major features cannot be added, but a little extra pressure here and there will certainly smooth out the uneven sections.

I let it cool to room temperature - it took about 10 minutes, I could have done it faster by immersing in cold water, but I didn't bother. When cool the unit felt very solid and strong. It's been nearly two weeks now and it's working perfectly - a very solid joint.


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