Science Technology Workshop
Choosing a silicone for casting soft buttons

MAKE pal Steve Cooley, who manufactures the Beatseqr hardware performance controller, has posted the lab notes from his recent experiments with various silicone products for casting monolithic soft button arrays. I love it when people do this–the steps and missteps that happen along the way are often as interesting, and as helpful, as the finished product.


4 thoughts on “Choosing a silicone for casting soft buttons

  1. One of his issues was degassing. Another option is to degas the mold instead of the mixing container. The only roblem there is losing volume.

    FWIW, if you are going to just do a one-off instead of production runs, hardware store silicone in the tube can be thinned to a pourable consistency with xylene.

    1. So true about degassing. The problem is that the physical amount of silicone is so very small and my mold cavaties are also so very small that the surface tension was too much to overcome on the home made degassing chamber and cheap vacuum pump that I own. I did some test pours using shore hardness 50 silicone, and had all kinds of problems whereas the degassing chamber only enlarged the bubbles rather than raise them to the surface to pop. This was the case in the mixing container, where the highest physical volume of silicone was pooled at once. Degassing with the silicone inside the mold was also tried, and the results were, for me, worse, due to the much much higher surface area that the silicone was touching. So if you’re going to degas thicker silicones, you’re probably going to have better success if your pour is larger than mine. ~1 ounce of mixed silicone was too hard to degas. The shore hardness 30 silicone I tried afterwards worked much better, and I may be able to achieve a crystal clear state with degassing… I just haven’t needed to do this since I wrote the article.

  2. Slightly off topic, but I have used epoxy glue and sand to save money when casting or potting electrical parts, mix the epoxy, then add sand, perhaps 2 parts sand to one part glue, then handle like mortar and fill your project. if you have a temporary shell then spray that with WD-40 or use a waxed cup. When done pouring and you have surface bubbles, spraying WD40 before the glue sets helps to break up the bubbles.

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I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I am a long-time contributor to MAKE magazine and My work has also appeared in ReadyMade, c't – Magazin für Computertechnik, and The Wall Street Journal.

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