Thanks thats a good idea about the college class. I saw a tv program where they made a silicone mold like you said. Thats the route I'll go because If I'm going trough all the trouble I might as well make a bunch. As far as the strength I doubt I'll get one as strong as a factory one. But one of the great things about the ar is that the lower really just holds the parts in alignment and doesn't get much stress. I'm sure for limited use you could even make one out of a can of the automotive fiberglass bondo.
Originally Posted by moleman
Aluminum shrinks .006 per. in. from 1200deg. (molten) to room temp.
I did some lost wax casting in high school, in bronze.
It is not hard to do, I would start with a mold made from an AR-15 lower made from rubber or latex so it will stretch just a little for shrinkage. Then use it to make a wax form, attach round wax called sprews to it, then mix & pour casting plaster (it looks like plaster of Paris) over it to form your mold let it dry, set it in a kiln or oven to melt out the wax & heat and temper the mold.
Get your aluminum molten you could just pour the molten aluminum into the mold, but if you want to make sure it fills the mold with no gaps I would look into buying or building a centrifugal caster. The one I used in high school had a spring that you wound up & when you were ready to cast you pulled it back the stop pin dropped out of the way, then you let it go to start it spinning. And the centrifugal force of the molten metal will press into your mold & fill all the gaps. When it stops spinning the mold will still be hot, but your metal will be set. You take the mold then dunk it in a bucket of water, & the casting plaster will crack and fall off. The hard part is digging out the plaster from the inside of the casting, a pressure washer helps here.
Last edited by AKarl_12; 09-29-2009 at 01:51 AM.
Here's an oddball article I found awhile back on using a microwave oven as a foundry.
Microwave melting of metals
If you wind up with some good 80% receivers, add me to your list of buyers
The Reid Technique
That idea of melting metals in a microwave oven is just incredible! I am going to have to try that. I have many times needed small parts that could have been easily cast from aluminum or brass if I had only had a way.
Originally Posted by vbrtrmn
It just so happens that I have an old 800W microwave oven sitting on the kitchen floor waiting to be disposed of and it works just fine. It is just ugly as sin and the glass plate inside is gone.
Hello AR Casters,
A little over 20 years ago I considered doing this same sort of aluminum casting but for AR-10 lowers. Having previously studied casting technique as a grad student I thought I had a handle on the process. Not quite.
Contacting the casting engineers at Ruger Corp. in Prescott, AZ I discovered that they design their parts to be cast rather than the other way around. They pour from approximately 10 ft to pressurise the lost wax ceramic molds. Many cast parts still come out warped and are either mechanically straightened or remelted. They also cast AR-15 receivers (lowers and uppers) which were designed originally to be made from a 7075 aluminum forging for max strength. These AR parts are for other companies not in-house use.
The cast auminum AR receivers do work but are not mil-spec and can crack (about the rear take-down hole) from sustained fire. The castings are sufficient for semi-auto plinking.
Cast aluminum as already mentioned generally shrinks a bit while cooling from its' liquidus temp. However it can expand when cooling too when excess dissolved gas comes out of solution. This creates adverse pourousity and weakness. Chlorine bubbles are one method used to clear out the gases.
To minimise shrinkage, hot tearing etc one must design proper risers and runners to feed the cooling parts from a liquid resevoir or molten (and pressurised) source. Centrifuging is used for small stuff such as jewelery. Some hobbiest have used steam pressure to force-feed the melt.
We experimented with sand cast AR-15 0% receiver shapes and experienced nasty shrinkage. Not the trick set-up.
My suggestion for those with zero casting experience is to take the course(s) and learn alloy casting skills. For those who just want an 80% receiver casting make your waxes from silicone rubber molds pulled from a sample receiver. Take those waxes to a small mom & pop casting shop and have them poured.
Making the precision waxes is a skill in itself as the silicone rubber mold sections must be keyed and lashed together or boxed to preclude distortion. Then they are filled with casting wax.
There are numerous casting techniques. Cast firearms parts are typically cast via lost wax. There are other companies that do this firearms work besides Ruger Corp. Oh by the way Ruger wanted to serialise the 80% cast receivers regardless and do strictly a manufacture to manufacture transfer. In approximately one year of dickering with partners the AR-10 parts kits went ballistic in cost.
Have fun !!
I haven't given up on casting yet. I've been considering different heat sources and think I'll go with propane and a torch kit from harbor freight.
Harbor Freight Tools - Quality Tools at the Lowest Prices
With a little bit of modification I think it'll work great as a burner and should get plenty hot enough. I'm still debating on what to use as the foundry case. I have an old 20lb lp gas tank with the old style valve that I could use and also a larger 14 gal portable air tank that has gone past its service date. I'm leaning towards the air tank as getting the lp valve off is a real pain in the butt. I'd take the valve off and fill it with water to make sure there was no propane left in it before making any cuts on it. I don't want to make any headlines as "man blows himself up".
Gunco Addicted for life
many older lowers made for the public market were made form a cast alloy. as i recall they were not as strong and the later forgings and they had a pretty rough overall look when finished. EA and Olympic are two that i can recall making cast lowers but there could be others as well. the olympic "plinker" might still have a cast lower???
i have seen some very nice stainless lowers that were cast along with some other exotic alloys. you can make a very fine lower by investment casting.
i considered trying it myself with either silicon-bronze or maybe some nodular cast iron!
seems like some of the 80% lowers were cast alm alloy as well.
i think i will just machine out a 0% forging and silicon lap it--then hard coat.
Hi I am desperately trying to find the URL of a website that describes the whole investment (lost wax) casting process from A to Z with pictures and all. The guy even build his own smelter and now produces model cannon wheels and other parts for sale. Bear with me.
However, you cannot use and original receiver as the initial model for the wax piece because of the shrinkage of the molten aluminum. This shrinkage must be built into the model by making it x percent larger. I used to work in a model making shop and we had measuring tools that would give you bigger dimensions than they would read. There were different sets for different alloys.
Since you have to machine the initial model from scratch why not just machine the receiver you desire. Investment casting is great for larger batches or artist's stuff that does not require tight tolerances. I carved my wife's engagement ring out of wax and had it cast in gold by a jeweler. Came out beautifully but it does not have to match her finger to within .001".
If you had access to stereolithography equipment and a solid model (3D computer file) of the receiver a one-of cast may be the way to go. Otherwise you would be faster to hog the receiver out of a billet or 0% forging. (There is a great site for this as well. If I just could find it in my URL junk yard)
I finally used up the last of the propane in the old style tank. I removed the valve and purged the tank with water. If I have time I'll get it cut in half this week and start on the stand for it. I think this is the oldest project I have going.
at the job i work at now thats there gig Investment Castings, Lamothermic Corp. Brewster NY
they make numorous recievers without any trouble
m1 carbine m1a a few revolvers and a few bolt actions
i would imagine an ar shouldnt be all that hard
i wouldnt know about the cost effectiveness though
making the dyes for the wax and stuff