Practical Backyard Foundrywork - Part 4: Moulding Boxes

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Moulding boxes are generally made from metal, but this is not essential. Wood is perfectly adequate, especially for smaller boxes. Sand is a great insulator, and wooden boxes won’t singe even with molten metal separated from the side by only an inch of sand.

I have a few metal boxes for larger work, they are easy to knock up if you have a welder, or you may be able to get them second and from a commercial foundry. A lot of foundries have converted, or are converting to “flaskless casting” which uses a special type of strong, chemically bonded sand which doesn’t require boxes. These foundries are likely to have a few surplus boxes lying around.

The drawing should be pretty self-explanatory. I built two sizes of boxes: 3” x 6” x 4½” and 4” x 8” x 6½” inside measurements. Remember that boxes come in pairs – or strictly speaking, two “half boxes”, known as the cope (top) and the drag (bottom).

The two halves of the box need to line up when the box is closed (if you need to aks why, you shouldn’t be reading this, Fred). To achieve this we use locating-pins, which I haven’t shown on the drawing. For the size of the box shown, basically all that is required are nails and holes.

I used 4mm diameter x 10cm nails. Grind off the head, cut the nail in equal halves and sharpen one blunt end of the top half. You will now have two sharp 5cm nails without heads.

Round off the two remaining blunt ends (to make it easier for them to slip into the locating holes). Hammer at X and X or Y and Y (See drawing) (does not matter which) to approximately 2.5cm depth. Naturally, you should drill holes for the nails first to prevent the wood from splitting.

You should now have a half box with approximately 2.5cm of nail, with a rounded top, protruding at X and X or Y and Y.

Line up with the other half box and drill holes of slightly larger diameter (eg 5mm) to match, slightly deeper than 2.5cm. That’s all there is to it. And with the proviso that you don’t want to get the locating holes jammed up with sand when you’re moulding, it doesn’t matter at all which half box you use for the cope and which for the drag.

I’ve grooved the inside of the boxes along the “long” side. If you have a router, so much the better. I don’t so I used a small wood grinding bit. The result was not exactly even, but the grooves don’t have to look flash. The ideas is to simply to give the sand something to hold onto so it doesn’t fall out of the box.

In fact grooves are not really essential. My metal boxes are smooth sided and hold the sand perfectly well, even though they take a greater weight of sand than the wooden boxes. I just have to be more careful lifting them.

A few explanatory notes about the drawing. The 2” blocks on the corners are there to strengthen the boxes. I have found that 1 ½ mm x 3 cm nails hold the thing together without any problems. I would also recommend glue – not water based, as moulding boxes get damp – at the joints. Construction doesn’t have to be super accurate as long as the boxes are rigid and reasonably flush where the two halves meet.

Just as a guide for each small box (ie two halves) you will need approximately five and a half feet of 3” x ¾ “ timber – pine is fine – 48 x 3cm nails and 2 x 10cm nails. The larger boxes require the same number of nails and approximately six and three quarter feet of 4” x ¾ “ timber.

With care boxes like this should last for years. They don’t rust and are easy to patch with plastic wood or similar if they get a bit charred from minor metal spills.


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