Cool.  What's with the hook up front?

on lost wax - bingo!





keep in mind, you cast anything from Zink (pennies ... Canadien not to deface currency) to Aluminum to Bronze. There are fairly cheap formulas for investment casting.


The thing is, polymers are similar to steel in that they have inherent flex to them. I've used Smoothcast 300, which is not rock hard. It's spec-ed to be Shore 70D:



So when you hit it with hammer, it bounces back. ABS tends to be harder, but more brittle. Some composite lowers are claimed to be lighter and tougher. Good example is the MEAN AR-15. They use Ali reinforcement piece in the area which problem:



I am trying similar, but cheaper alternative:



We'll see how it works.

Also to keep in mind, I made a mold from a receiver that was meant to be aluminum. Most plastic lowers have thicker sections in strategic place. You can replicate that by adding clay onto the receiver.


The mold is about Shore A hardness, so it's flexible so that I can extract hard piece from it. But is firm enough that it small parts like rods that fill holes stand erect unassisted. It can manage stretching when you pull out finished receiver. I like to use mold release on the mag part because it lubes it up and pulling the mold out is easy. But I cast plastic dry without problems. I just have mold release handy and I start to like lubrication. Casting wax into mold is no problem, it self lubricates.

Have to ask War Fairy.

Interesting.

I briefly started a similar project but abandoned after researching cost for the mold and epoxies, it wasn't a lot, but more than I wanted to spend at the time.

Mine would have been a two part mold using Smooth-on two part epoxy, I thought about using a microfiber fiber glass additive.  Also got hung up on what
it would take to build a vacuum chamber to de-bubble the mixture.

OP has done an awesome job using a low tech approach!!!  Legos!  Awesome as are the inserts.

For clarification, I was going to incorporate the buffer tube into the receiver for a dedicated .22 build.

Best. Post. Evar.

If there's an easy way to adapt this to a high strength material it could be revolutionary.

amazing.  I'm going to have to do this for my now impossible to purchase AXTS lower for a dedicated .22 build

that's a big mold. You may be better off doing a brush-on silicone with either pop (plaster of paris) or fiberglass backing. That way the silicone layer is not very thick and not a lot of it needed.

Tin cured silicone rubbers are cheaper, but not that much. Many platinum cured silicones do not require degassing. Moldstart 30 (which is what I used here) is very thin, it doesn't trap bubbles like tin cured silicones.

Great job as always Boris.

 
A couple of stupid questions for you...




1.  Is there any reason you couldn't use a slightly less viscus material with a Shore D of 80 or does it need to be around the 50 cps to flow into all the crevasses properly




2.  Do you think applying a vacuum would help any to make it stronger or is it not really necessary?




3.  How would you go about putting one of those inserts into the buffer tube area?




4.  Have you sand cast one out of metal yet?  How's the finished metal come out?  I'm assuming you'd have to re-tap all the holes.  How would you go about compensating for the shrinkage as the metal cools?


 

Saw this yesterday and went back to look at it again. I'm impressed. People's skills and ingenuity never cease to amaze me.

Easily produced and disposable receivers. I am in love with this build.

From the above website:
"Wood's metal is toxic because it contains lead and cadmium, and therefore contact with the bare skin is thought to be harmful, especially in the molten state. Vapour from cadmium-containing alloys is also known to pose a danger to humans. Cadmium poisoning carries the risk of cancer, anosmia (loss of sense of smell), and damage to the liver, kidneys, nerves, bones, and respiratory system. Field's metal is a non-toxic alternative."

Think I would pass on using Wood's Metal

Yes, but also saddens me a bit.

It's a silicone mold.  Years ago my dad showed me a "toy" from his childhood: a huge kit that did vacuum forming, let you mold lead (!) toys, lost wax casting, all sorts of things that today seems like arcane black magic.

This is a cool thread and Boris' site links to a bunch of great articles he has written.  The lower is cool but the first thing I'm inspired to to is grab my boys and duplicate some of their Skylanders figures so the can paint & play with them.

Where do you buy your rubber and plastic from?

A couple of stupid questions for you...

00> Nothing is stupid, I am glad to help if things not clear.

1. Is there any reason you couldn't use a slightly less viscus material with a Shore D of 80 or does it need to be around the 50 cps to flow into all the crevasses properly

MoldStar 30 when mixed is extremely thin, like runny snots. You can see on mold that it flows into every crevice and orifice when mixed. It does not trap bubbles by itself. Some cheaper castable resins are fairly thicker and that's the reason they put them into vaccuum chamber before casting to let bubbles expand and flow to the top easier.

Shore D 30 is when it hardens. Different castable rubbers harden to different hardness. But it does not indicate their viscosity when they are just mixed ("pot life" - is the term)

2. Do you think applying a vacuum would help any to make it stronger or is it not really necessary?

I don't see vacuum doing anything here. Like I said, vaccum chamber is used to degass some castable rubbers which are thick when just mixed. Because of vacuum, bubbles become bigger and have easier time to flow to the surface.

3. How would you go about putting one of those inserts into the buffer tube area?

Simply put it into the mold. That clear receiver with steel wire in it. I just wound the wire and put it onto the rubber pegs of the mold (which represent voids (holes)

4. Have you sand cast one out of metal yet? How's the finished metal come out? I'm assuming you'd have to re-tap all the holes. How would you go about compensating for the shrinkage as the metal cools?

Not yet. Lost wax is different technique than "sand cast". Sand castings is making a mold out of foundry sand, typically petro-bond for aluminum or green sand for cast iron. Making a mold for sand casting would be incredibly difficult, but doable. Apprentice graduation exam of old times included making and casting a sand mold of a tea cup on a saucer ... with a tea spoon in it. It is very difficult.

Lost wax has been done for thousands of years to cast bronze. It is still done today to do jewelry, dental work. Is easy but takes a lot of time to dry molds properly and uses some expensive investment plaster or ceramic shell suspension. I'll try to do it on cheap.

Where do you buy your rubber and plastic from?

I've used Smooth-on brand because they have a local distributor in Boston area and prices are the same as on web. I've used them for over decade, pretty happy with them and too lazy to switch. There are alternatives, but price wise it does not make sense for me to switch and start figure out different product lines. Smooth-on customer support is great on phone and at local distributor. You can ask them questions like what would be the best product, or I want plastic that's this and UV resistant and this hardness, and they will point in right direction. Also my local distributor has samples and exmaples of everything they carry, so if I am not sure if I want different hardness, I can touch and bend samples with my hands.

To your question: MoldStar-30 as castable rubber, Smoothcast-300 for most receivers. I don't remember the names for some other clear ones.

In terms of casting low temp metals. There are some alloys that melt at 140-150 C and MoldStar30 suppose to hold up to 230C. Some of these alloys are $20/# and contain no lead or cadmium.

I ordered of this shit and I have a sacrificial rubber mold that I can use to check it out. I'll post that once I get and do the deed.

To measure the amount of cool in this thread is unpossible!

Thanks for the info. I'm curious to try it out. Too bad we haven't had a buy back program around here in a while.

I am totally going to restart my past attempts at this.  Thanks for the great info.

Please post about any metal casting attempts

right click save as > webpage complete... done. +1 awesome thread

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If it were a situation where one needed to produce a bunch of lowers of reasonable durability quickly,
1) Skin toxicity might not be high on one's priority list.
2) Breaks?  Just remelt and recast.
3) Need it "single use?"  When done drop it in a pot of boiling water.  Or a fire.

Low temp melting point alloys + Deer Gun design=Hmmmmmm......

a brass upper/lower would be awesome



 

Awesome.

From a guy who does a lot of casting and mould making.  A vacuum will up the quality of the build.

please elaborate im curious about this,thanks



 

I want a brass AR w/ wood furniture.  

Brass really sucks for casting, it's possible but really difficult. Brass is copper and zink and zink tends to burn out and it does not flow like bronze (copper/tin)

very impressed!

Bronze would work too.   Either one would make a cool/unusual looking AR.

Awesome.

Are you the same Boris than made the shovel ak? If so, you are my hero.

if you look at his website, you will see the answer is "yes"

And the Iron Glock.  

Love it!

Sorry I was away from the computer for a couple of days.

De-gassing RTV with a vacuum makes the mould stronger and removes any bubbles that will cause surface defects on the casting.  Also the 2 part plastic should be de-gassed to make it stronger, especially when reinforcements are added.  The vacuum can be modified to aid in the casting as well to draw the compound into the mould for a more consistent fill.

Are we talking a modified Hoover here, or something more sophisticated & less redneck?

Harbor Freight AC vacuum pump?

This is true with all school and most RTVs now, but I used MoldStar 30, which does not require degassing. I've been using this stuph for a long time, it's the best thing that happened to castable rubbers. Again, no degassing for it.

For plastics, smoothcast 300 has really short pot life, like a minute or two. There is no time to degass it and it has viscosity of water. Some bubbles get trapped, but there is little choice. Plastics with longer pot life are probably better candidates.

Ok, let me introduce you to alloy 281: 58% Bismuth and 42% Tin. a.k.a. Roto281 or cerro-whatever. It's a pretty common alloy available from various sources, priced 19$/# and up.

In terms of toxicity, it does not contain lead or cadmium. Tin is only toxis if you are having sex with tin soldiers and Bismuth is the main ingridient in Pepto-Bismol. Also Bismuth is used in making meds to make your shit ... smell less. Now this is some magical f-ing metal! You just lick your Bismuth-Tin receiver and go grab some beans!

The melting temperature of 281 ... wait for it ... 281F! The MoldStar30 rubber can be used up to 450F. This alloy can be melted on a stove top no problem.



and cast into your rubber mold:












How strong is it? In thicker sections it's pretty strong. It's brittle though ... and it weights 1.5 pounds.




On the plus side, if you break it ...



I'll be back!

Now THAT'S what I'm talking about!  (see above post)

I'll be expecting my royalty checks shortly.

Would gentle agitation -- say taping the mold to a brass tumbler, or maybe an "electric toothbrush" -- get bubbles out or just make a bigger mess?

Go through your wife's underwear drawer looking for a (wink, wink) massager.   Yes it works, though not as good as a vacuum, something like this is what I use.

http://www.amazon.com/DENTALNY-Denture-Vibrator-Medium/dp/B00CB1ZV4Q/ref=sr_1_1?ie=UTF8&qid=1435088078&sr=8-1&keywords=dental+vibration+table&pebp=1435088104582&perid=1F0V9QDHPVB67YFSWSF6
 

Think you need about $50 & a box of Legos.

Something like a small concrete vibrator?  I think Hitachi makes one.

I ain't spending $130 on no vibrator that doesn't have his 'n her ends

wait, wut?

How much shrinkage does the Moldstar 30 give you?  I'll have to defer to your expertise in plastic casting, I do mostly metals.  I bet the low temp metal you are using now is too malleable and will shoot loose pretty quickly.

For the guys asking about vacuums.  For larger stuff like this you need an air tight chamber to hold the piece/liquid, and a pump that will pull 25-30 inch Hg.

http://www.amazon.com/Gallon-Aluminum-Shatter-Vac-Kit/dp/B00JTNTPA0/ref=sr_1_3?s=industrial&ie=UTF8&qid=1435088668&sr=1-3&keywords=vacuum+pump&pebp=1435088682215&perid=040Y6C9AKACE31FCVS8D