The Making of Pocket-Safe Hammer Shrouds: Part 7

In Part 6 of my series on the making of Pocket-Safe hammer shrouds, I explained how I finally overcame my second major mistake and obtained a final design for thermoforming dies that is still in use. But also, how I lost access to the laser cutter I had been using to go from raw thermoformed sheet to finished shroud.

Losing Club Workshop wasn’t a blessing in disguise, but it was something-less-of-a-curse-than-you-might-think in disguise. I acquired a used Sherline CNC mini-mill and got it working with a $60 used computer controlling it. That thing has proven to be worth many times what I paid, and the convenience of machining in the basement rather than downtown is wonderful.

In addition, the break in product development that the closure forced let me to rectify my third big mistake: material selection (technically, this mistake preceded the “second” mistake, but it was rectified third). For reasons that I cannot explain, my prototype hammer shrouds were all formed from ABS. ABS is a fine thermoforming plastic, having good heat conduction and therefore forming nice even parts over the whole sheet. But it’s also subject to chemical attack, most notably by acetone, present in many degreasers used by gun owners for cleaning. I never liked that, but I lived with it because I didn’t know of a way around it. Of course, those of you who own holsters are wondering why I didn’t go with KYDEX ®. Great question! During the Club Workshop crisis I chucked ABS and ordered a bunch of sheets of the good stuff. It’s harder to form, has a narrower forming window, and is subject to hot and cold spots (putting the sheet outside the forming window in both directions at once!) if heating is in any way uneven. But it’s very sturdy and chemically resistant, and besides, everyone knows what it is.

Laser cutout is by far the best way to finish hammer shrouds. But reliable laser cutters cost thousands and thousands of dollars, and used ones of the appropriate size and power are actually pretty hard to find. I wasn’t interested in taking a chance on a cheap eBay laser cutter shipped from Tajikistan or wherever they come from, because I am not in the laser-cutter-repair business. I talked to a few people I knew from Club Workshop who owned laser cutters, but they turned me down because

Hot wire jig
Two versions of the hot wire cutting guide, with aluminum to guide the wires and a molded polyurethane to hold rough-cut shrouds in position.

KYDEX ® is known to release hydrochloric acid gas when burned, which is basically what laser cutting is. I don’t see the problem as long as your equipment is properly ventilated, but they did see a problem, so that was out. I also investigated serious commercial laser cutting shops who don’t mind burning plastic, but they said merely setting up would cost thousands of dollars, plus per-unit charges that would have required a doubling of price or more on finished shrouds. What now?

Hot wire original
A dimmer, on-off switch, and low-voltage supply (in box) to test out the idea of hot wire cutting.

My first idea was hot-wire cutting. I poured some semi-rigid plastic around a shroud and some nylon spacers, then used nylon bolts to attach aluminum sides cut to serve as guides for the hot wire. A shroud could be inserted and cut.

I rigged up a (probably dangerous) apparatus with a low-voltage lighting power supply and a switch from Home Depot .

I tried stainless wire for cutting, but it proved too brittle and usually broke after one shroud. Concept proved, however, so I got an inexpensive adjustable power supply with proper isolation and some plastic pliers to serve as a bow putting tension on the wire, and tried again . The stainless wire was too cold, however, when that power supply was maxed out. I ordered some nichrome wire and found it better, getting hotter on less power and breaking only after several shrouds.

Hot-wire cutting entails a compromise between heat, which cuts cleanly, and wire strength, which goes down as heat goes up. At fast-cutting temperatures, wires break easily. At lower temps, the wire cools quickly and requires a sawing motion to cut, which leaves a ridged pattern on the plastic. There may be a happy medium with a relatively thick wire heated relatively hot, but that required more power than I had available. Hot wire cutting ultimately failed.

Hot wire safer
A controllable power supply, nichrome wire, and a customized set of plastic pliers made hot wire cutting safer and more reliable. But not good enough.
Hot knife jig
The cast-solder hot knife cutting guide. The wavy lower edge resulted from the knife shaving bits of the guide off during cutting.

The next try was hot knife. You can buy what amounts to a hobby knife on top of a soldering iron for a few dollars at a craft store. It cuts plastic pretty well That in turn required a new cutting guide, since the external guide wasn’t very precise due to the gap between the aluminum guides and the flexible plastic. So I cast some plumbing solder in the silicone molds used to make the thermoforming dies, then milled and filed it down to the shape I wanted the plastic to have. That, like hot-wire cutting, sort of worked. It was difficult to get a smooth cut surface, though better than the wire. But plumbing solder is soft enough that it can be cut with a hobby knife—which, in fact, happened.


The whole time I was experimenting with cutting methods, I was also refining my cutting pattern to get the fit I wanted over the back of the revolver. That went well, even as I struggled to get clean cuts.

So by late summer I was getting very frustrated. I had a product fully designed and functional, but the price of actually putting it on the market was very high, entailing either buying a laser cutter or paying a hefty fraction of the price of one to a commercial laser house.

Previous | Next

Leave a Reply