Making and using casting frames.
The casting flasks are wooden boxes, topless and bottomless. They fit together tightly,
upper and lower. I have a nearly infinite supply of 2" x 2" lumber and
3/8" plywood. Therefore, I've made all my flasks so that each one is made of two
halves, each 4 1/2" high, and each composed of plywood walls with the lumber at
the corners to give it strength. Plywood tapered tongues on either side provide
positive capture and placement of the cope on the drag, retaining the alignment
of sand cores between top and bottom. By offsetting these tapered tongues, I can
ensure that the cope and drag will not inadvertently be rotated with respect to
each other. I also drilled a small hole near the bottom of the alignment tongue
on each side, through into the inner flask half, so that by putting pins through
these, the cope and drag are locked together. This was the result of an exciting
dance step I invented while casting a BIG casting in a small flask, which ended
up floating the drag on top of the molten aluminum, and the hot metal spilling
out the sides onto my toes. I'm a believer in these locking pins. I'm also a
believer in using drawer pulls on both the cope and drag, so that you have
something good and solid to hang onto, when you're trying to lift the cope off
prior to rapping the pattern loose. It also doesn't hurt to nail some lath strip
onto the insides of the flasks to give more positive retention to the sand, and
provide a step for cross-ribs and gaggers if you're concerned about the cope
dropping out while lifting it. I might mention that with my sand, I have to
punch the cope, QUITE hard, to get the sand to drop out, when I've finished with
a casting. I have never had a problem with a cope dropping out.
Riffles and sieves: Make your own riffles for sifting sand onto the patterns. Use metal mosquito netting for a fine sand riffle, and 1/4" hardware cloth for a coarse backing riffle. Use the fine one for initially covering the wooden form, until it has a good layer over the whole form, and press it onto the form gently. Do this a couple of times, before going to the coarse riffle. (Don't overtamp too much.)
It makes sense to me, since I'm building everything, to build my flasks and riffles in matching sets. Both my fine and my coarse riffle are 12 inches square. My flasks are 8" x 12", 12" x 18", and 12" x 24" for monster castings. The reason this works out so well is that the riffles sit firmly on the flask sides, giving them good support while you're smashing the sand through the riffle mesh. It's also really nice to have your riffles designed so that they have wood both above and below the mesh -- ie if you hammered together a frame out of 2x2" boards, nailed a mesh onto the bottom, then nailed another 2x2" frame onto the bottom of THAT, you'd have a sort of very flat H-shape. The reason this is so nice is that the container on the top holds the sand you're sifting so it doesn't slop out over the top, and the space on the bottom gives you extra clearance over the top of the mold, so the loose sand which you've sieved doesn't pack up to the bottom of the sieve as quickly.
This page written on 12/15/00, last modified 23 May 2023.
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