Monday, May 4, 2015

Distressingly Analog

Another TechShop member (who was in the middle of a 3d print), asked me how I liked the vacuum-forming machine. I told him "Distressingly analog." I think he got what I meant.

For all that the high-tech fabrication methods are replete with numbers; for all that they come (often) out of computer models, go through digital positioning; and for all that the knob-setting is replete with numerics and other quantization, the final results still depend too much on the less quantifiable.

Even at the laser cutter; although the beam position may be as accurate as 10 micrometers, and the beam around .001 inches wide, the width of the kerf will depend on not just the laser settings but how good the focus is, how flat the table is that day, even the color of the plastic.

I've been lasering out holocron pieces with an aim to get a good snap fit. But the necessary precision for this is roughly the same as the variation in thickness between different sheets of material from the same manufacturer, and variances in how wide the laser kerf is. I can adjust the latter a little to take up errors in the former, but that still means trial and error. As digital as the process seems, it needs that analog touch, that craftperson's touch, to get the desired results.

This was my first start-to-finish use of the vacuum former as part of the build of a prop. This is the oxygen mask for the pulp "space" helmet. And as usual, half the techniques were chosen because I wanted to learn more about those techniques. And half the remaining decisions were forced by time and availability of materials (I'm trying not to spend much on this particular prop!)

First step was a duct-tape dummy. This is a well-known budget technique for getting a rough body cast. As it happens, not the best technique for a partial cast like this, or a chest plate; the mold tends to flatten out considerably once off the body.

I reinforced the first try with plaster bandages, and when they started to dry out and come apart, paper towels dipped in white glue. It was heavy and didn't look right and I abandoned it half way through the modeling process.

The next one, I poured plaster in and carefully propped it up to keep it from flattening out too much. This was closer, but what was more useful, is I was able to pry the plaster out and thus work on the actual inner surface instead of the less accurate top surface of the duct tape.

There's a lot of discussion about what materials are strong and temperature stable enough to make a vacuum former "buck." Consensus is that there is little competition for MDF for the small props builder. Hydrocal rates a good second -- in the form of a positive mold taken off a garbage mold of the original cast.

The selection of air-hardening clay at my favorite store was poor, so I tried Sculpey for this project. It will never replace FIMO in my heart.

Unlike other clays, Sculpey seems resistant to smoothing. So I baked it then used sanding paper and spot putty to get the final surface.

Which was an adventure on its own. I used a toaster oven rescued off the street. Those things do not have precise temperature control, and my first cook was a little cold. My second cook burned the material, and because the additions expanded slightly, it cracked the surface. A little Bondo repaired that, but that made sanding an even more onerous task. I'll use clay next time!

Before finishing off the sculpt I roughed in what the other pieces were going to look like. The side plates will be laser-cut acrylic, but are simulated here with sheet styrene.

Oh, yes -- and after taking this shot, I re-thought how the inlet should work, and built up a different shape on the finished sculpt.

And here is the last of the three pulls I got in .040" PETG. I mentioned above there were concerns about certain materials holding up to forming? Well, I'd managed to forget since taking the SBU for the machine that the heater hood was not controlled from the front panel. I left the heater running, bubbled the PETG and cooked the buck hot enough to soften the Sculpey.

But I was able to repair the buck with sandpaper and some quick spot putty, and it held up for the pull to the left without collapsing. So it was a good mistake; now I know more about the limits of the material.

And I like the extra dents. Of course, if I had sculpted them, they would look even better, but oh well. This is rough-trimmed, primed with Krylon Fusion for Plastic, and I'm testing the rubber edging that will go on after it is glued and painted.

Today I picked up webbing and d-rings. Not quite right; I'd like some nice hardware and leather straps, but the only place for those seems to be Tandy, and I'm eager to get this thing out the door. And keep the expenses down on it, too.

In the meanwhile I made a plaster mold from the bits of carved foam and apoxie sculpt I carefully pressed into the eye slits. The mold looks horrible and I'll be lucky to have one good pull from it. I'll be pouring clear acrylic into it tonight.

I have several different approached to the insignia on the painting table. The only other major bit for this prop, then, is to create substitutes for the vintage oxygen canisters (which are chemical oxygen generators that we almost certainly do not want to open up). I've been measuring soup and oatmeal cans but it looks like I'll have to fabricate these from scratch as well. There might even be a little vacuum forming for the distinctive top (or I might do as I did for the insignia; heat it up with hot air gun and press it over a form with my fingers).

I need this project to complete and clear the decks. My holocron just got a mention at Adafruit, there's interest at the RPF and the Jedi Master is getting closer to purchasing a half dozen or more for his students. And the "Tiki" raygun needs to start machining before the end of the month!

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