Casting your own parts in resin

[Beekster]

I've mentioned flawed castings and mold failures several times here. The vast majority of the time this is my fault, especially with the mold breakage and such. But there is something to be done about the casting problems, which I will address the next time I order up chemicals. The RC-3 resin which comes in the kit used here is really fast setting, for a quick cast-and-demold sequence. It only has an open life of two minutes, which means that's all the time you have to get it poured once it's mixed. For what I'm doing, that is sometimes a problem in that the stuff will begin to thicken before I have all the material poured into molds. Alumilite also has an RC-7 resin, just a little more expensive, with a seven minute open time. It also takes significantly longer to cure, on the order of one to three hours. That's fine for me; I can let molds sit for hours while resin cures. If I have a longer open time to work with, I can take more time working air bubbles out and will be able to effectively use more of the mixed resin before it begins to go off. I've used about 3/4 of the resin that came with the kit, so when that's about gone I will order version with the longer pot life. If this thread inspires you to do this yourself, get the following materials:

Alumilite RC-7 resin and Quickset RTV
3ml pipettes and 30ml mixing cups from Amazon
Popsickle sticks for mixing and clay (I use Van Aken brnd; lasts decades) for mold bases at Michael's or the like
Various sizes of Lego bricks to make mold boxes

Buying the chemicals in bulk, such as a pound of RTV and quart (2 pint bottles) of resin is more cost-efficient than buying the starter kit, and so is ordering mass quantities of mixing cups and pipettes. You'll be able to remove cured resin or RTV to re-use the cups for a while, but pipettes are only good for a couple of uses before they have to be discarded.

[JCON]

Thanks for sharing your knowledge on this process with us!!!

[Beekster]

First casts from the new batch of two-piece molds:






This is better. I just pulled these from the molds, and most of the flash came away as I did so. The transmission shift linkage is fully cast, and no mold damage...yay! The shift forks and transmission actuator arms are good too; just a couple of bubbles to fill on one of the actuators. Same goes for the half-round end of the transmission; easy to fix as I have done before. And the driver's track levers are fully cast too, though it may be a chore to clean those up and they are bound to be fragile so we'll see how that goes. But I now have repeatable molds for all the major driver's compartment elements which are common to Sherman-family vehicles so I'm good for all these eventual M10 projects. I've got a couple more molds to make for M10-specific parts, but I ought to have enough RTV left to do that.

One potential benefit of two-piece molds is that you can sometimes de-mold the parts sooner than with a single-piece mold. The reason is that the resin continues to cure after it has gone solid, and in the earlier stages of this proces it will hold the detail but remain pliable. That isn't what you want, and parts pulled too early from a single-piece mold can be warped. Sometimes you can straighten them out, sometimes not. With a two-piece mold, you can pull it apart for inspection without necessarily removing the piece, so it's sometimes possible to see if the casting is complete before you pull the part. You can then leave it to set up harder for a while before pulling it out and cleaning it up.

[Steve Ski]

What a trip, you make it look so easy, love it!

[JED]

Great result

[Beekster]

The new two-piece molds are working well. Shown below are the molds for the transmission and a storage rack with box that sits atop it, and the first two castings from those molds. Both casts are excellent, with only a couple of small bubbles to fill on the rack & box part. Very easy to fix and a perfectly usable part. Also in the image are castings for the transmission end and the shift forks, and both of those came from another two-piece mold. I have enough good molds for repeatable castings to do full driver's compartments for all four of my Tamiya M10/Achilles kits. I'll only do one other interior as detailed as the one in my Desert Rat Achilles thread, and I will modify the other castings to fit in the Tamiya hull without the surgery necessary to fit a full-dimension transmission assembly. The other two models, whatever the subjects will eventually be, will have closed driver's hatches so I'll only put in what can be seen through the turret opening.


So that about does it for this tutorial. I've shown the full process, warts and all, and would encourage you to give this method a try when you need to make a few copies of something for a project. I do still have some RTV left from the one-pound tub I bought. Where are those bits for tow bars & other tank recovery stuff? I know I have them here somewhere...

[JCON]

Very nice!!!

[dogfish7 (R.I.P.)]

This is awesome Beek!

[Beekster]

Glad you fellows have enjoyed the thread and found it useful. I've been rummaging through the spares box and came across an old master for British pattern rucksacks, and found half a dozen British canteens in an infantry figure set. I will probably do a new mold to cast some of those up for stowage on the Desert Rat Achilles. I've got a question out on ML about the canteens. We stowed them in a row of five on the inside hull wall on the right side, below the turret ring. I hope to find out if the British used the same location for theirs. Makes sense that they would, but you never know.

[dogfish7 (R.I.P.)]

They probably had the Tea and crumpets there instead.