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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.
 
#32 ·
the common thing i see at work with some of the castings at work is shrinkage
some of it isnt too bad still usable-we usualy fill with weld and another one is gas porosity sorta like swiss cheese which renders it useless
we do quite a number of recievers and we xray them all due to the pressures they will recieve penetrant dye and magnetic particle testing-magnaflux basicly-wont catch some of the internal imperfections that can render it non usable
for the most part we dont have a lot of failures but on occasions we have a few
once you have the process down its usualy consistant
id say out of a 300 we might have one or 2 criticals
 
#36 ·
I lucked out (I hope) and found a ceramic kiln that was local and cheap. Its a 110/220 volt paragon kiln thats rated to 2300 degrees. I need to get a plug for it as they were running it off of a 110 line and I'm gonna run it off of 220. I went ahead and bought it even though I've welded up a body for a propane fired one and just need to weld in a tube for the burner, cut a vent hole in the top, and put in the refractory. I figured the electric one would be easier to control for heat treating steel especially with an electronic controller, and I'd have something to do the lost wax molds in.
 
#37 ·
This is a great site, with tons of details and pics on lost foam casting of aluminum. The parts he made are nearly as complex as your basic 80% AR receiver. I think you could do something similar if you have the patience and skills to make the foam blank with a cnc hot wire cutter(less expensive than a real CNC mill by far).

The first link just shows the final/perfected process and results:
LFMC

The below link has more pages and details of his previous attempts and failures, which are very informative:

Home-brewed linear bearings
 
#38 ·
Thanks for the links, I've seen them before. I got the idea for using the propane tank from the bearings one, and the idea of using a pressure tool from the foam one to reduce shrinkage. Even if I'm unable to cast a good ar lower I figure I'll have fun making other things.
 
#39 ·
So why doesn't somebody go into the wax model selling business?

If you made good molds and then molded an 80% or less lower in wax, you could sell them cheap and ship to folks who want to try and make their own metal ones.

In wax you wouldn't need anykind of approval to sell them and if you had good molds I think you sell a ton of them.

Then folks could engrave and drill the wax models prior to encasing them and melting out the wax.

You might have to make wooden magwell plugs to both cast and ship them but you could offer discounts on follow up orders for the folks who returned good wagwell plugs.
 
#41 ·
Lost wax casting of AR uppers and lowers requires some pressure to insure the proper resolution. A knowledge or sprues, risers, and runners is also vital. I recall that Ruger pours their AR alloy from a 10 foot drop for the needed pressure. Yes, Ruger casts or has cast AR uppers and lowers for other manufacturers. One of the big challenges of the process is dealing with warpage. Some parts can be straightened others are tossed back into the melt.

Casting wax is harder and has a higher melt temp than say candle wax. A friend makes his own wax shapes and ships them to California to be cast in nimonic alloy (small turbine parts).

Other than as a fun casting project I would suggest using the forged AR blanks and machining them at home, much less grief.

Have fun !!!
VD
 
#42 ·
Viper Dude, as usual you've hit the nail on the head. It's mostly going to be a fun winter project. If I get a useable lower out of it great. If not I'll still have a better means of heat treating steel and the ability to cast some truly crappy parts to machine.
 
#43 ·
Great thread, I've been interested in this for a long time(big ruger fan). I was thinkin that the finished project wouldnt need to look EXACTLY like the original. It could have extra "meat" where needed for the areas where cast might not be up to snuff. Then all you got to worry about is shrinkage. Good luck and keep us posted.
 
#44 ·
I got the 220 plug for my electric kiln and fired it up...... sort of. Only the lower half heated up. I traced it down to a couple $5 parts which are on their way from the manufacturer. I'm still working on the burner tube for the propane fired one.
Mtdew, I also was thinking that some parts could be beefed up slightly to make them easier to cast and stronger. I've thought about inlarging a basic model using tape or clay to make a first mold to cast a wax model from, then detail the wax model and make a new mold from the wax model. As far a shrinkage goes I think I'll have a steep learning curve for figuring out how to make the leads/runners. On the plus side all my mistakes can be melted down and recast. Kinda like casting bullets. You get a few bad ones when you first start casting, you throw them back in the pot and go on.
 
#45 · (Edited)
I got my repair parts for my electric kiln in earlier in the week and installed them. It looks to me whatever moron originally wired it for 110 decided the easiest way to do it was only use 1 of the 2 heating elements. My guess is that they didn't have a big enough circut breaker to run both. I still need to get a new longer cord for it but the kiln now heats up a lot faster with both elements working. I got the casing done for the propane fired forge and hope to get it cleaned out and filled with refractory this weekend. The lid is on a simple hinge made from two pieces of pipe cut at an angle and a section of 3/4" rod. when you start to swing the lid out of the way the hinge lifts up the lid so that its not dragging accross the lower half. Heres a pic with the lid installed upside down.

Edit: I mixed up the refractory and packed it in the forge with a 2x2 and 2x4. I ended up having to make a second batch because there wasn't enough to finish the lid. I'll let it sit for a day or two before I pull out the forms
 

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#46 ·
After a day and a half of drying I pulled the forms out of the forge. I let it sit a couple more days then I stuck a 90watt lightbulb inside the forge and left it until today. The lightbulb kept the forge slightly warm to the touch to help it dry faster.
For a burner I took a 1.5" to 3/4" reducer, a 10" section of 3/4" black pipe and a 3/4" to 1" reducer. To mount the HF brush torch to the pipe I unscrewed the torch burner tube and set it aside. I then drilled out a 1.5" pipe plug for the tip of the torch head to go inside and cut away the sides to allow air to enter. A 1/4" (or possibly an 1/8") brass compression fitting out of the junk drawer fit the threads on the brush torch head, so I used it as a nut on the inside of the 1.5" plug. I need to open up the air ports a little as the flame isn't perfect, but it worked well enough for a test run. I fired up the forge and let it run for about 2-3 minutes, then after a few hours I ran it for about 5 minutes. It didn't come through in the picture very well, but the bottem of the forge was starting to turn reddish orange.
 

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#49 ·
Thanks alpine44. I have seen the ray-vin site before, but forgot what it was called. The Zoeller site looks great also. Santa has been nice and is letting me read a stocking stuffer book called "lost wax or investment casting" by James Sopcak. "Lost wax investment casting" by C.W. Ammen which was recomended by jrenyard is also on the way.
 
#51 ·
:redface: Funny cause I was just thinking I started this about a year ago last night and had better get my butt into gear. I have a 17hmr ar15 upper, sgn-9, and suomi build "on going" as well.
 
#53 ·
mole, my 17hmr upper is canceled. after A LOT of research the 17hmr is prone to OOB problems.....you may want to reconsider
I actually debated it for quite a while before deciding to go ahead with it. I've shot a remington 597 17hmr and was pretty impressed with it (when it would cycle, the mags suck). I was trying to find an easy to make a delayed blow back design for it, but couldn't find anything. If anyone knows a simple delayed blowback design I'm all ears! The reported injuries I could find were for leftys which would make sence because their head and body would face the ejection port. I'll try it out and if all seems well, I'll keep it as a 17hmr, if not I'll rebarrel to 22 mag. What are you doing with your 3/4 scale one? It'd be a shame not to use it, perhaps a 22 mag or lr?
 
#54 ·
Hello moleman,
A simple delayed blowback can be an op rod and piston attached to the bolt pulling forward with some gas pressure from the barrel (behind the piston). The WW-II German VG-1 and the later H&K P-7 Squeezecocker pistol did this biased gas pressure thing.

The gas piston can also be a shoulder on the barrel and the cylinder surrounding the barrel blows forward pulling on an op rod or slide. This is much like the VG-1 carbine.

A set screw valve on a gas block or valve gas vent on a sleeve will allow variation of the delay pressure so you can tune it to your favorite station !!!

Combined with a fluted chamber this system will operate with most any size ammo. I don't believe that the .22 HRM would need a fluted chamber.

VD
 
#55 ·
I finally got around to melting some aluminum in the propane forge. I had a few hours so I fabbed up a small crucible and fired up the burner. I used a set of 3' bolt cutters to break up the head from a briggs & stratton lawn mower into several pieces that would fit in the crucible. After a half hour the crucible was red and the aluminum was melted. I poured it into a large steel ring that was laying on a steel plate to make a round button about 3.5" in diameter x 1" thick. I plan on using the aluminum button to help test out a fly cutter I plan on using to repair the two broken gears on my sheldon lathe I'm restoring. I still need to make a mold and try casting some simple parts. Here's the button made from a b&s head next to a tecumseh head.
 

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