The Making of Pocket-Safe Hammer Shrouds: Part 3

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In Part 2 of my series on the development of the Pocket-Safe Hammer shroud, I showed you my thermoformer, meant to produce the shroud more cheaply and easily than injection mold tooling. It turns out the thermoformer also had another advantage: the ability to produce prototypes and test runs for pennies. You can’t do that with an injection mold! Considering how many times I tried before getting it right, I am very glad I went that direction.

I also mentioned last time that I had an engineer working on the proper design for the thermoformed shroud and dies to produce it. Here’s his first draft of the new die next to the shroud it made:

First thermoformed version
The first draft of a thermoforming die, and the corresponding first draft of a hammer shroud. It looks an awful lot like the nylon prints, doesn’t it?
Mold
A silicone mode made from a RapidMade 3D printed die. The “X” indicates it is an outdated version–most of those get thrown away to avoid confusion.

RapidMade used their 3D printer to make that die, out of relatively fragile ceramic particles bonded with cyanoacrylate, or “super glue.” If you form hot plastic around that and then try to pry it out, you’re going to break it. Besides, those things are expensive, so I didn’t want to buy 100 of them to stick under the hot plastic even if they were durable enough for the job.

To reproduce dies in quantity, I made a mold by pouring 2-part liquid silicone around the printed masters from Rapid made, producing something that looked a lot like the one at right (I don’t have those originals because I diligently discard molds that don’t work, lest I confuse things that all look alike until you break out calipers and make actual measurements).

I used Alumalite ® liquid plastic to make the dies by pouring it into the molds. Alumalite is relatively expensive (compared to other liquid plastic products) and results in porous, fragile parts. But it cures in just minutes and the parts, while not nearly as strong as they could be, are plenty strong enough to be pried out of formed plastic sheets multiple times. Or at least, they were once the design was refined to remove sharp cusps on the dies. Those cusps tended to break off after a couple of uses, but with their elimination, the limit of reuse is still far off after at 10 cycles.  With a multi-caviity mold, thanks the rapid curing time, a whole sheet’s worth of dies can be made in a couple hours.

I once I had disposable dies, I formed a handful of shrouds into a 6”x9” piece of 1/16” thick ABS and cut them out with heavy-duty scissors.  As you can see above, the first thermoformed shrouds worked. They really worked! I was very excited. And as I sat and looked at my nifty creation, I thought two things: 1) I need to make this conform to the back of the revolver so that it looks nice, and 2) As long as I’m doing that, I should make it come down a little bit over the sides so it won’t twist off easily if the back gets bumped. So…redesign began again.

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