Today I had my first simultaneous “Eureka!” and “Duh!” moment. I’m trying to make a sort of adjustable bipod thing for my rifle, so I cut some steel tubing. It’s going to have a steel tube as the primary structural frame of the bipod but the adjustable part that slides in and out of the steel tube will be aluminum. I’m looking at the steel tubing and thinking to myself “man, it’s going to be such a pain finding a piece of aluminum tubing that has the EXACT same inner diameter as this steel tube. I wish I had a lathe….godammit.” and then it dawns on me. Duh, I have the ability to melt aluminum now, why not just plop the steel tube into some casting sand and pour some aluminum right into the tube? Eureka! That’s perfect! So that’s what I did and it worked out pretty well.
Click “Read More” for more pics
I forgot to take a pic, but I also made a tiny funnel thing out of some thin sheetmetal and vise-gripped them to the tubes and the aluminum poured right in with hardly any spillage.
After the aluminum hardened, I cooled them in a tub of water and tapped the aluminum rods out with a steel punch. They actually slid right out with hardly any pressure. After that, I clamped them in the vise with my rubber-jaw protectors and gave them a quick sand with a piece of 220 grit, shoeshine-style and did a test-fit. Perfect!
These parts cleaned up with only a few second’s work but after I give them a better sanding later, the surfaces with be completely smooth and even.
Ok that’s all for now. Back to the Dat-cave for me. More soon (same Dat time, same Dat….channel?).
-~D~-
June 12th, 2010 - 8:20 pm
This is probably a better solution than chucking some aluminum stock onto the lathe.
The steel tube stock is probably ever so slightly out-of-round, so the two pieces will fit the tube they were molded in best with the right orientation (you may want to check them carefully and then mark the tubes and aluminum rods appropriately). Looks great.
June 12th, 2010 - 8:43 pm
Thanks, Jeff! That’s a good point. This method also makes it possible to build a master steel mold of a custom shape (like say you wanted a piece of aluminum channel in an odd shape or wanted to make clips or brackets that could be sliced from a long piece of material) and cast a bunch of them with minimal defects and almost no setup time.
June 13th, 2010 - 10:19 pm
Nice job and good idea too. I’m glad you posted this I was just about to cast a round AL bar and lathe it down to size!
I think you’ll find complex shapes won’t come out as well though, the liquid aluminum contracts when it cools, so for a solid tube like this it will work great, and it doesn’t bond well with steel at all (I routinely pour excess into angle iron ingot molds and they fall right out after cooling)
I tried to make a steel mold for my ergoslope clamps, which were fancy C clamps, and the way the aluminum cooled and contracted made the mold never work. So for lessons learned, keep the cross sectional area of the aluminum pattern uniform, thin areas will cool faster and at the early stage of solidication the solid aluminum is extremely brittle, such that the rest of the cooling can pull that solid part apart, causing cracks. No sharp corners either, for the same reason. Keep corners to about 2 times the diameter of the cross section or so. If you need to change thickness of the part, make it a gradual change, 5 – 10 degrees I’d follow. Also the steel corrupts the purity of any aluminum liquid alloys that come in contact with it, but that probably won’t matter on the kinds of parts your doing.
I managed to get a tour of a local aluminum casting plant and was surprised by the preperation involved in the molds. They were doing wax molds, which they would dip in a special ceramic slurry about a hundred times, then melt the wax out. After that a special technician, more of an artist than anything, would grab small hand size chunks of cut fiberglass insulation, paint it with a generous coat of some muddy ceramic morter, then stick it to the critical areas of the mold which he thought needed to be insulated more to slow the cooling rate of that particular area. They then heated the mold to within a few hundred degrees of the melting temperature of the aluminum. Interesting stuff!
btw, where did you get your nice compact green sand from?
June 13th, 2010 - 10:50 pm
Thanks for the input, Matus. Yes that’s exactly what I was thinking…something in a complex shape like those clamps of yours. You could make a long channel in that shape, then just slice off a perfect 1/2″ piece for each clip. Oh well. Too bad it doesn’t work. Should’ve known that was too easy, hah. Yeah I’d love to make the jump into lost-wax casting but it’s a pretty significant financial investment by the time you add everything up (though I did find an “all-in-one” kit on Amazon for about $2400, pretty cheap, considering, but still hard to find that much just laying around).
I got my Petrobond sand from an actual foundry supply house (they’re around but are usually buried way back in an industrial park and they never advertise, so you kind of have to seek them out).
I actually tried making some more of these rods today and failed miserably. The aluminum would get really stuck inside the steel and didn’t want to come out. I must have had just the right amount of oil on the inside walls of the steel tubing the first time or something.
Oh, BTW I found a “castable foam” like we discussed a while back. Smooth-on makes it in a few different densities. The lower-density foams are really fluffy and mostly used to backfill molds so you don’t have to waste huge amounts of latex, but I bet the higher-density stuff would work well for your “lost foam” projects. I wonder if something like that might allow you to make complex clamp shapes because the aluminum would be cooling inside soft sand which would compress as the metal cooled.
Anywho, here’s the link:
http://www.smooth-on.com/Rigid-and-Flexible/c10_1121/index.html
-D