Saturday, November 16, 2013

SciFi Saturday – Cruiser Construction, Pt. 2

Last week I showed off the mold-making I did to duplicate the cruiser miniatures for the Star Frontiers: Knight Hawks game (the largest molds I've made to date). This week I'm taking them into kitchen for the actual metal casts.

As I take this photo, I've got the biggest chunk of metal I could fit in my ladle melted and hot on the stove. The mold for the UPF cruiser figure has been cleaned, prepped, dusted with talcum powered, and joined together with cardboard and all the big rubber bands I could find.

Usually the first few casts are playing around with how big the pour-hole connector needs to be. Small means the metal won't pour in properly, large means the sprue is hard to clean up and may snap part of the model off when you try to clean it. Since you can open it up with a knife but can't close it down once rubber is removed, I start pretty small and open it up a tiny bit with each pour. The very first pour just clogs up in the pour-hole and doesn't get any in the figure at all. Here on the second pour (shown below), most of the model filled up, but the pour-hole clogged before it was complete.

By the third pour we have metal in the whole figure but a minimal sprue (and so easy to clean up in the nose area). However, a new difficulty raises its head: the rubber bands don't get this mold very tight, and there's a rather large amount of leakage and "flash" around the seam of the entire figure. I try putting on more rubber bands, or placing them in key areas more carefully, but that doesn't change anything. That's going to be a big cleaning job with needle-nosed pliers & file.

Next problem: The cleaning job is so big, in particular the internal space between the engines, that the fairly delicate engines tend to snap off with the flashing as I try to remove it. Here are two casts that have been wrecked at the end of the cleaning because of that, and will have to get re-melted down. (Also shown are the extra engines I'm making to add to each figure.)

Another day, and I decide to bring in some more serious equipment. My partner Isabelle goes to her sculpture studio and brings back a big 3-foot-long clamp for molds such as this. I put the mold between blocks of wood (not just cardboard) and ratchet the clamp into place carefully.

Well, this almost works but not quite. The mold is now tight enough that there's no leakage or flash around the edge -- but the downside is that it's so tight the cast has actually lost some of the detail around the tops of the engines. I try using the clamp a few more times with very gentle pressure, but this issue can't be fixed. After musing about my options, I decide to go with the rubber band technique, get all of the sculpt filled in, and just commit to carefully cleaning the flashing I get around each figure. I'm only planning on making a few of these, anyway.

Another problem: My standard cool-down time is insufficient for these much larger molds. For example, here's the Sathar light cruiser after about 5 minutes of cooling down on the kitchen table. What happened here is that the pour-hole (the biggest volume in the mold) formed a solid shell around its exterior, but was still molten metal inside. Not knowing that, when I went to separate the mold, the pour-hole cracked open and spilled liquid metal over the table and almost myself. (Wouldn't be crippling but probably pretty unpleasant.) Note to self, etc.

Of course, the spindly extended engine-struts on the Sathar ships (which I've always thought the most attractive part of the design) don't always get the metal flowing all the way into them. That's actually not so bad, because I'm intending to snap some good legs apart anyway for additions, and throw the rest of the figure back in the ladle for re-use.

At some point, waiting for a mold to cool down, I realize that the handle on my ladle is actually sliding apart sideways as I watch it! I've had it going so long and hot in the kitchen this weekend that the plastic in the handle has started to melt and slip off the arm. I quickly shut off the burner at this point and rescue the ladle handle, eek.

So: There comes a point where I finally have the duplicate casts I was looking for (a pair each of UPF and Sathar cruisers), with miniature bases, stands, and extra engines, and I get some time in my workroom to assemble them. The official cruiser miniatures only come with 2 engines apiece, which doesn't match the Campaign Book rules, and generally doesn't make much more of an impression than the 2-engine frigates (although having more engines connected would make the mold prohibitively difficult). So below you can see me bracing up the Sathar cruisers, and adding the extra engine struts I cast, for 4 engines total per ship (equally around the radius of each). This involves placing & filing the struts for a smooth connection, drilling the ship & engines with a pin vice, snipping off some paper-clip wire for an internal anchor, and super-gluing the whole thing carefully together.

Nearing the end of the process, I've primed the miniatures with gray spray-paint and set up to paint them. My painting process is exceptionally simple for these ships.

First step is a flat base coat. I make the UPF ships navy blue, and the Sathar a greenish-black mix. On my initial tests Isabelle said the Sathar color wasn't any good, because "it looks like something diseased". At which point I said that was exactly what I was aiming for, because in fact many of the Sathar ships are famously named after diseases. So, a happy little accidental compliment.

Then for the finish I use dry-brushed metallic paint: silver for the UPF ships and gold (kind of suggesting brassy/bronze archaic armament) for the Sathar. These look really good! The UPF ships in particular have all kinds of nice details to them, and the dry-brushing really brings them out. On these large ships I'm happy to have more of the dark base color peeking through, representing some amount of age and battle-damage, and this brings out more contrast and detail to everything (whereas the smaller ships need to look sleeker and faster, and so a bit flat). All I have to do now is put them on their stands and they're ready for use in-game. A success! But not without a lot of trial-and-error, and learning that this is probably the upper bound of what my rubber mold-making technology can handle.


  1. Nice work! I don't have the technical knowhow (or the patience) to undertake a project like this. I look forward to seeing some battle reports with your new forces.

    1. Thank you! There will be a battle report coming next week. :-)

  2. Suggestion: To improve flow to the extremities, make a thin venting sprue. This allows air to escape, and the metal to move past the model, filling all the voids. You can probably carve this into one side of your mold. Have them come up to the end that you are pouring into. They also serve as an indicator of when you have put enough metal in.

    1. That's an interesting idea. Currently I go kind of partway in that direction -- if the extremities don't work the first time, I take an exacto knife and start cutting little filaments up in that direction as vents (maybe 1" long or so, not visible in photos). I guess I'm being conservative to start and not wanting to deal with positioning more wires (or whatever) during the mold-making process. I was in fact wondering if anyone made vents all the way through the mold. Interesting to use it as a "popup" gauge the way you mean, cool!