Saturday, October 6, 2012

First Pull

A day of discoveries.  More or less the concept for molding these things proofed.  More or less.

Not bad for a first-ever pull.  I think the last casting I made was fifteen years ago, in some-one else's mold (it was an overnight repair of a show-critical prop, and fortunately the master mold was right there in the shop where I could find it.)

Not great, either, but actually I only need the one.  The client has only ordered one box...the only real reason to cast is to be able to model in any material but deliver in sturdy resin.

The master survived de-molding, too, with just a few dings.  So I could in theory make up a better mold from it.

That was not something I could actually hope for.  All my reading suggested that masters rarely survived coming out of a silicone mold, and this is a particularly fragile master, being mostly from lightweight floral-type foam, balsa, and wallboard spackle.

So here's lessons:

1) I'm sensitive to tin-cure silicone.  The first mold I did made me rather nauseated -- enough to skip dinner that night.  The second one, I worked right under a window and made sure not to hold the measuring or mixing cups too close.  I still got a slight upset stomach, but not enough to make me skip lunch.

2) A small apartment is no place to be casting.  I need to take this sort of thing to a shop space -- where there is good ventilation, where a spill doesn't mean I risk my cleaning deposit, and where I don't have to sleep next door to chemicals and dust.

But enough of enumeration.  Back to essay style.

The first mold is actually a two-piece.  Since the Shapeways print already had the desired thickness, it was pretty much cast one face, flip it over, slather the silicone with petroleum jelly as a mold release, cast the inside face.  That worked pretty well, but....

a) The first pour was shy a few CC's and didn't end up with a level surface.  This meant only mold stiffness held it flat when I cast.

b) The mold was a bit small for a box mold (I'm really, really broke and can't afford much silicone), and had no registration keys.  When I did the first pull, one wall ended up being quite thin as a result.  I should be able to firm it up with a little Bondo, tho.

c) Locating a thick pour spout on the inside wasn't the best idea.  It was a pain to carve away once it was cast.

The second mold was a one-piece open-top box mold for a slush cast.  What did I learn on this one?

a) I fixed the model to a slab of wood, and built a basswood box around it.  But by "fixed," I mean with clay.  And the master is so light, when all that silicone got into the box with it, the master floated right up!  As a result I wasted a bunch of mold material under it, I had to cut a big nasty hole to release the master, AND the master ended up at an angle to the box thus some of the mold walls were very thin.

b) It takes more than you think.  It took the entire starter kit of Oomoo to do these two molds.  And it was still a little short.  Fortunately I had some plaster I could square off the end with; that was the base after I flipped it over.

c) Yes, you can clamp wood together for the box, but it would be worth it to spend longer in carpentry and have a solid box that could be dissembled and re-assembled in exactly the same position.  At least it didn't come apart on my mid-cast and spill resin all over the kitchen!

d) Smooth-cast 30 is not optimal for slush-casting.

 This is what the inside looks like.  More slush than cast!  Also quite heavy; I used up over half of the resin in the starter kit as well.

Fortunately all that has to go in here are the electronics, but I'd be way out of luck if I tried to make a battery door now.  Well...I'd have to take a Dremel to it to chew a decent hole.  And that would be messy.  Very messy.

As I said, all I need is one, and even the electronics is a stretch goal.  But given my budget, time, and the lack of funds to get yet more casting supplies, I may just back-burner casting the MEDKIT for a few weeks.  Oh, and I really wouldn't mind taking a break from the chemicals for a while, too!  I really, really, should not be messing with MEK (and spray paints, and superglue, and Bondo, and so on) in a small not-that-well-ventilated apartment!

Heck...once the next show is up and running, I might just drag my casting supplies over there and work on that during the day before a performance.  Seeing as they got that robot from me labor-cost free (and the debris from that project is STILL kicking around here), I think they might owe me that much.

I could always wave the master for the MEDKIT around, anyhow.  Now that it has finally gotten shiny enough where I'm willing to call an end to the days of spackling and sanding.

That might even give me time to order some vinyl lettering for the controls.  Although I kind of like the spooky effect of unlabeled controls.

 And delaying the MEDKIT also gives me the time -- and the funds -- to give Shapeways a little more love.  Like the funky shape here in shiny stainless steel.  This is the "treatment comes out here" part for the MEDKIT.  Not to scale with the box models you see behind it; the largest dimension is barely 3 centimeters.

Shapeways could also knock out some new knobs in study metal, that I could tap so they would fit firmly on the shafts of the rotary switches.

Such useful services aside, I'm still horribly attracted by the idea of doing an electro-etch of custom graphics, then rubbing color into the metal.  Because that's all I need now; to be electrolyzing metal and creating hydrogen in my apartment!

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