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Lost wax casting?

6K views 55 replies 27 participants last post by  cymax666 
#1 ·
Has anyone here ever tried lost wax casting? I wonder how close to a completed ar15 lower you could get by doing it. I've often wondered if it could be done and only need minimal machining afterwords. What are your thoughts.
 
#4 ·
Don't know about heat treating. I knew about ruger and I remember seeing an article about their lost wax casting back in the late 80's or early 90's in guns and ammo I think. It seems like its feasable but I know nothing about casting other than bullets!I suppose you'd have to machine the threads and pin holes, but I think you'd be able to get the other openings pretty close and maybe even spot the pin holes. Hopefully some one here has actually done lost wax casting and can give some insight.
 
#8 ·
I was wondering about how much it would actually shrink and how strong it would be. I know the cast receivers in general are weaker than a forged or machined receiver, but didn't know how much weaker they would be and if they would be usable.
 
#10 · (Edited)
I used to work in a die cast shop (maintenance electrician) they age aluminum at 400 F for 4 hours to normalize it. I also worked in an exstrusion shop they did the same thing. I am not a metalurgist but it must be an important step..... hope this helps. You might try Lindsey publications. (Google will give you the site) they have books on eveything......
 
#11 ·
I did "Lost wax casting" in High School. It was for an Art elective, had to have one to graduate, I was the only one in the class who had come from the Metal Shop program. Basically my teacher outlined what the projects were and he let me run. Bronze was my metal of choice, silver and gold being too expensive when I was 17.
We had a Dentist's centrifuge. Basically you melted the metal in a pot and released the arm on the "fuge" and centifical force would inject the molten metal into the casting, after you had melted out the wax. I still have the bronze ring I maid. Very little cleanup, basically just the sprues had to be cut and filed and sanded to finish.
That's the major points I remember, unfortunately its been just a litttle over 20 years ago. Hope this helps you out.
 
#12 ·
Thanks blazerbender. I did some more looking at it last night. I even found an article by David Carodeine(?) the kung fu guy. He was making bronze castings of heads he had done in clay first. I guess I need to look at how much the ceramic material costs and how cheap you could make a forge and get a book on aluminum casting. The wife drinks enough pepsi to keep me in aluminum so thats not a problem. I even saw something on plaster casting that looks promising also.
 
#13 ·
Might want to take a look at this. Don't know if it would work.
LFMC

I thought that I had a link to lost wax casting. The big thing is heating the mold so that it doesn't break when casting.
 
#14 ·
Thanks Gunter, that looks like its a lot easier than the lost wax casting and it looks like you don't have to heat the mold either. They even had a forge design you can make out of an old 20lb propane tank which I have!
 
#15 ·
Just an Idea

I also did some hight school projects in aluminum. I have an old Charter arms survival rifle which is 2/3 plastic and aluminum. It has a steel barrel liner & everything else is basicly plastic & aluminum, if you found someone who fires clay pots you could try a trial balloon for cheap. Just an idea.
 
#16 ·
Thanks for the idea. I do happen to know someone that does pottery but they live about 6 hours away. I also have an uncle that does blacksmithing on a coal forge but he is also about 5 hours away. I have some fun money comming in from a side job and think I'll try to get a setup. It looks like you can even use charcoal with a blower which would be a pretty cheap setup. The only thing would be the smoke so I'm looking at propane for a heat source. I have a old 20lb propane tank to use as a shell and it looks like the refractory cement is about $50 shipped. I'll keep an eye out for an old gas grill to use the regulator and valve from (like I did for my parkerizing tank) and bust up the aluminum shell for some free aluminum. I think I'm going to give it a shot. If it doesn't work out I'll still be able cast other stuff.
 
#17 ·
Gunter , you will want to consider some alloy like pistonium instead of pop cans. Al alloys have many different working properties and straight al is fairly weak. As I recall the normal shrinkage is considered to be 10% off of the wax casting. Here is a couple of sites that may give you some more information. Lots of reading time , but looks like a fun time to me. If your going to use propane as a heat source , I would consider using a turkey fryer regulator as they are variable and not just the .5 psi... not considered hot enough to melt much.


metalcasting and general metalworking links


ABYMC :: Index
 
#19 ·
Yes , I spend hours reading on those two sites. I am enthralled by casting , whether Al or Cu or precious metals.
 
#20 ·
I did aluminum and bronze casting in college. Take any university fine art program, and they will have a sculpture class that teaches all you need to know about this technique.

One thing that will work great is to make a silicone mold of your part, let's say it's a receiver. Then you could do multiples instead of just one part at a time. Reuse the silicone mold, and cast the part in resin. Then check for defects, shrinkage etc. THen, if you like the output, cast the parts in wax. The next thing you know, you are casting several wax receivers. Not sure of the legal aspects of doing this, but it is an option. I wonder if this would work on say a glock frame? Hmmm.

Lost wax and lost foam are two simple techniques, lost wax being hundreds of years old technique. Super fine detail can be had with it. Not sure about metal hardness, or voids. etc.

Be safe what ever you do!
 
#21 ·
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.
 
#24 ·
The Reid Technique

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 :)
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.

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.
 
#25 ·
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 !!

Later,
VD
 
#26 ·
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".
 
#27 ·
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.
 
#28 ·
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)
 
#29 ·
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.
 
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