Silicone Mold making and tube-in casting pen blanks

Silicone molds! One of the coolest materials to work with. I have always been interested in the idea of making molds for casting. But it was after I got into pen turning, and discovered these pen blank molds that I really got inspired. Let me tell you, these molds are very nice. I bought one, and it worked great. But I was mainly interested in tube-in casting, and I found it very inconvenient to match pen tube sizes to a mold. Not only that, but it is rather cost prohibitive to buy a mold for each type of pen kit you plan to make. So I opted to design a more flexible mold for a variety of pen tube sizes. 

Additionally, I wanted to do some investment casting for metal. I got about 3/4 of the way there, which I'll detail in this post. 

Silicone is sold as a two part mix (Similar to epoxy). You mix the two in the specified proportions, and then cast it into the shape you want. For my pen mold, I 3D printed two positives, stuck them side by side on poster board, and then made 4 walls out of the poster board, which I then hot glued  down around the positives. At that point it was easy to pour the silicone into my make shift mold. 

Here you can see what the silicone mold looks like after it was removed from the poster board mold
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At this point I had a perfectly fine pen blank mold. Once you cast your resin, you could then use it like any other pen blank, drill it out, glue in the tubes, and turn down to size. But I wanted to skip the step of having to drill out the hole for the tubes. That's where tube-in casting comes in. For tube In, you cast the brass pen tube right into the resin. This requires that the pen tube is both suspended in the center of the mold cavity, and plugged on both ends (So that resin doesn't fill the tube). I designed these special plugs, that plug the tube and fit into the mold to hold the tube exactly where you want it. Mold with the tubes and plugs in place pictured here.

And then filled with Alumilite resin that has been colored using mica powder. Notice how the plugs actually created a liquid tight seal and dam up the mold so that there isn't too much waste when doing shorter pen tubes

 The pen pictured here is not the same as the one I was casting above. But the process was  identical. Here is the end result!

One advantage of tube in casting is the ability to glue things directly to the pen tube before casting in resin. This makes it possible to print images, patterns, stamps, flags, etc. and make a pen with those details. I had some mother of pearl lying around, so I glued it to the pen tube, and cast it in undyed resin. After a couple of tries, this is what I ended up with. I'm actually very proud with how it turned out!

 There is one  last detail about casting clear resins. It is very very important that you degass and/or pressure cast it. When you mix the two parts together (And even left over from the manufacturer) there are many many tiny bubbles that are trapped in the resin. If you don't remove them, they will cause your final piece to look cloudy, and worst case, cause pitting when you turn down to the bubbles. I only own a degassing chamber, and it works adequately. But it is recommended for perfectly clear casts, with no bubbles, that you degass in a vacuum chamber to remove as many bubbles, and then allow it to cure in a pressure chamber to crush any last bubbles to microscopic. Here are some pictures of my vacuum chamber in action

 

Part two I will go over my attempt at investment casting, and my success in casting pewter directly in a silicone mold