Thread: casting aluminium

It is hard to work out what size model you are referring to in your post. If it is just a few inches long then you can use lead and something simple like cuttle fish as a mould. I am suggesting lead because it has a similar finish and a lower melting point than aluminium.

Warning make sure there is absoluelty no moisture in your mould or steam gets trapped and the molten metal will explode over you. Casting is a dangerous passtime so make sure you have goggles and leather coverings for safety.

Casting aluminium will require more specialised equipment and for one small job it may not be worth the trouble.
If you are keen then here is an Australian link that shows how it is done in the backyard.
http://members.optushome.com.au/terrybrown/

A much safer way would be to shape a prop out of balsa or other wood and try to match the colour with paint or if you are real keen shape the prop from a chunk of aluminum with a dremil.

There are specialised epoxy glues for aluminum but for a model Araldite should go the trick.

When you are finished make a glass case to store it in so little
hands (and big ones too) aren't tempted to play with it.

If possible, look for other ways to get what you want, like Rod there suggested.


It is possible to cast the ally to what you want, but regular means do not lend themself well to precise work nor artistic stuff.

If you are heck bent on casting it, let me know, I'll bash in some info that will get you there without too much trouble.

(Yes, I can and do cast ally and bronze occasionally.)

Thanks Rod and Sctoo for the info. Here's a couple of pics so you get a sense of the size. It's a sweet little thing isn't it. It simply must be cast out of aluminium (even a rough cast that I can refine with a dremel) to preserve the "spirit" of the piece. So if you could send some info Sctoo, thet would be appreciated.
I understand it can be a hazardous endeavour, but I am a (non practising) research chemist in organic chemistry and am used to dealing with quite dangerous substances!
Cheers
Michael

I reckon you could make the prop from a piece of heavy aluminium sheet easier. Roughly cut it to shape with a hacksaw and tidy it up with a file and dremel. Sounds a lot easier than mucking about with moulds and hot metal. It's still in the spirit as it's solid aluminium, once you have smoothed it off there is no way of telling how it was actually made.
For the stand can you drill and tap a hole in the broken piece and put a machine screw up from under the base? Alternatively it could be welded by someone with a suitably hi-tech welder and then the weld lines filed back smooth.

Good luck whatever you decide to do

Ian

Ok, if you insist.

(I think you will find less trouble, like 1/100 of it, from cutting the prop from an existing chunk of ally sheet.)

I would get some plaster of paris as your mold material. Either make a pattern from wax or carve the rough prop into some set plaster. The better you make the mold, the better the casting will be. I think that carving would be simpler and better, so try it that way. Take a block of set plaster, sand one side flat and carve the prop shape into it.

When you have a prop cut into your plaster take a pin and drag a groove into the surface of the plaster away from each prop tip. Grab another chunk of plaster, sand one side flat and put a hole through it to the hub of the prop. The grooves are to allow gas to escape, the hole is for the ally to come into the mold.

Make sure the hole is at least 1/4" diameter.

Even better would be to make the hole (sprue) as long as possible, with a large well on the top. Kinda like a wine glass really. A big resevoir up top, the sprue is the stem, the prop pattern forms the base of the glass. Add some kind of reference so the sprue and pattern match up. Up to you, but pins are most common.

Once your pattern is ready, you will need to make sure it is very dry. For that, stick it in a cool oven (over 100C) for a while. You have to get all the moisture out. Very important. Once it's dry, tie it all together with some wire and put it aside for now.

Melt some ally in a steel pot of some kind. You could use some charcoal in the barbie with a hairdryer to add some air, a decent gas torch or oxy, etc, etc. Whatever way, you will need to melt the ally. Some guys use an old tin can, and don't have too much trouble. I don't like the idea much myself, but for a one off, it should be ok.

While the ally is melting, heat up the pattern. The hotter the better. Make sure it lies undisturbed while it's heating, because too much action might kill the pattern.

The ally is ready when you stir it with a steel rod and the ally does not stick to it too much. It will always stick, but provided it doesn't clump up, it should be fine. Pour the ally into the hot mold very carefully, and any excess into something that can handle the heat (about 700*c, lots of stored energy too). A hole in some sand might just be ok.

Let everything cool down, and break open the mold. You should have a serviceable prop that just needs to be cleaned up.

The base could be done in the same way, but the mold would be more fiddly.

That's the guts of the whole thing, and what is described is basically investment casting, without the wax investment pattern.

But you have to burn (calcine) the mold or expect things to get pretty exciting.

Mic-d,

Sorry, may have missed it, but where do you live?

I have my own furnace, and will be pouring this week (assuming no changes in plan), and next week also.

The really tme consuming part of metal casting (and the really tricky part) is the actual mould making. If you would like to do the mould, or make a pattern, would be more than happy to pour it for You.

Shane

Originally Posted by Beerbotboffin

Mic-d,

Sorry, may have missed it, but where do you live?

I have my own furnace, and will be pouring this week (assuming no changes in plan), and next week also.

The really tme consuming part of metal casting (and the really tricky part) is the actual mould making. If you would like to do the mould, or make a pattern, would be more than happy to pour it for You.

Shane

That is a top offer thanks. Was not top priority, but can make it so!
Will pm you...

Cheers
Michael

Michael, you are one lucky fella.

Jump on it with both feet, and go see Shane there before you even make the mold. I am sure he can show you things you need to consider before you make the mold.

Shane, nice offer. Have a greenie.