Going to try building a CNC via lost foam castings for body, need advice

[OneAndy]

Namely, what sort of alloy would be best for my purposes?

Right now, I'm using a decent home-built gantry style MDF cnc machine. Second generation, and I took pains to make it stable, rigid, and accurate... but it's still MDF. There are parts of it's travel where it will nevertheless flex on me.

So I'd like to use my current machine to cut out wax or foam parts for a smaller, more rigid aluminum version.

So what alloy can I find in plentiful amounts that won't cost me an arm and a leg, but be hard/inflexible enough for my purposes? And what would be the most likely places to find these?

Or for that matter, would it be possible to take plain old beverage can aluminum and alloy it with something else as easily obtained... say zinc from pennies or copper from house construction scrap bins? Or even cartridge brass from fired .22lr shells?

I've never cast anything but lead before now, but I built a dave-gingery type of foundry from an old air bottle. Just waiting on a welder buddy of mine to make my crucible before I get started.

Any help ya'll could throw my way would be MOST appreciated.

-Andy

[ViperTX]

Take a look at buildyouridea.com and backyardmetalcasting.com

Paul

[Geof]

Using pop cans is not likely to be very successful. First you will need an awful lot because they are very thin and light, second when you melt them a large percentage is burned away as oxide.

One place you could try for aluminum scrap is car wreckers for rims. You should try finding some books about casting aluminum. It is fairly easy to make the patterns and actually cast but then working with what you have cast by drilling holes and tapping threads may be very difficult. Most aluminum alloys whether cast or extruded or heat treated for greater strength and better machinability. Not to say you cannot build something but you might encounter less frustration by getting some background information first.

[OneAndy]

Thanks for the replies, fellows.

I'd seen buildyouridea, but had totally forgotten about backyardmetalcasting. Gracias!


As far as post casting machining goes, I hope to minimize machining steps and alignment issues by combining as many parts into single castings as possible.

For example, rather than cast a spindle holder, a z-axis body, rails, etc and worry about drilling holes and tapping them to fit everything together, I'm going to try to cast that all as one distinct piece.

[multiplex]

sounds cool, but sounds like a big project. Don't forget to account for shrinkage, etc.

I don't think you will be able to get the accuracy you need with just casted holes. bearing alignment,etc?

[OneAndy]

sounds cool, but sounds like a big project. Don't forget to account for shrinkage, etc.

I don't think you will be able to get the accuracy you need with just casted holes. bearing alignment,etc?

I figured I'd try casting the bearing plates with just a pilot hole and use that to cut the relief for the bearing on a drill press with a forstner bit. That way I get a properly positioned and sized bearing holder even if I don't figure shrinkage correctly.

[mcphill]

I figured I'd try casting the bearing plates with just a pilot hole and use that to cut the relief for the bearing on a drill press with a forstner bit. That way I get a properly positioned and sized bearing holder even if I don't figure shrinkage correctly.

You are going to drill aluminum, with a Forstner bit, to make a press fit for a bearing?! Good luck, would love to see pix!

[stevespo]

I've drilled some decent sized holes in aluminum (7/8", 30mm) using carbide forstner bits and my crappy drill press. Clamp securely, go slowly, use cutting fluid, and you can actually drill a hole this way.

Now getting it sized accurately enough to press fit a bearing - not so sure about that. They seem to come out a bit oversized even in wood. I guess that's runout on my drill press. In aluminum the holes are a bit ragged with my setup.

You would probably be better off using a hand router and a circle cutter and sneak up on the size you need. Maybe start with the forstner to waste out the bulk of the pocket.

Steve

[mikey_d]

Making a press fit hole with a drill press and frostner bit sounds like bad idea. The idea comes even more worse when you are planning to machine a cast piece where a mistake would likely to mean that you have to cast it again.

When it comes to casting machine tool parts you are on the correct tracks as all real CNC-machining centres have at least cast foundations, mostly all critical frame parts are cast and then aged.

Desing it, show it here and then correct the design mistakes. After that you can cast it and take it to a capable machinist to bore bearing housing etc.

As for source of a aluminium I would recommend old aluminium automotive engines.

[Roy Omnigopilus]

Lindsay Publications has some good books on aluminum casting.

[Fastest1]

Buy a center cutting end mill and you will get a much better result, even in your drill press.

[RiseUp]

Andy,
I'm right there with you man. I was looking at my MDF machine and it suddenly donned on me that I have a furnace and could easily cast most of the parts from AL. I've got about 350 soda cans, some scrap AL bars,rods,angle,etc, and could easily obtain more. It takes roughly 30 cans to make 1lb of AL,melted down. I have a supply of 3/4 foam, and plenty of time, so I'll probably be trying this out soon to see how it goes. Yes, 'soda can' isn't the BEST alloy, but it would be a major improvement over the current MDF. If nothing else, cast parts to replace the MDF parts of the machine.