Casting aluminum parts

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270 totheend

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GunNutz
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I have been watching some youtube videos on how to cast aluminum and was wondering if anyone has tried making replacement gun parts that way. I am thinking that you make a silicone negative mould of whatever you want to make, then a wax positive for lost wax casting. I have seen the silicone for making moulds for sale at Industrial Paint and plastics, I could make a kiln for the melt and I can get some aircraft grade scrap aluminum, this is do-able.
The items I would want to start with would be replacement trigger guards (old Mossberg plastics, Savage 24 also plastic, and a replacement for my brother's Rem 660). Once started the wish list of things to make is endless, cast parts for a rifle bench rest, aluminum chassis for precision bolt gun etc......any thoughts?

270 totheend
 
With the proper sand and layout, there's no reason that you shouldn't be able to make whatever you want. Trimming and polishing are a big part so having a big enough machine with sufficient power is real handy. Sounds like a blast, have some fun!:cheers:
 
I would think this would be great for small or light duty parts like heat shields, grips, fore ends, sights, etc... but anything that takes a beating would need some sort of hardening, no?

Also (and I am just spit-balling here), I would think that a closely controlled commercial process using specific aluminium stock (for your purposes , like 7075 etc) would be needed for consistency and confidence in a frame casting or similar item...and them some tempering, surface anodizing and finish..

I want to do a cast of my airgun stock using an old POS aluminium ladder section... then drill/mill it out creatively for weight adjustment. I think it would be a good cast project :)
 
Grizzly Adams said:
Molten aluminum oxidizes like crazy, would that present a problem ?

Grizz
Click to expand...

No, not really. A proper mould allows all the air to vent and the mould to fill completely, no air no oxidation. Sand cast parts are usually machined or polished anyway which would remove any surface oxidation.
 
I've done a little casting with lost wax and foam molds, foam molds are a similar process to lost wax casting without the removale of the positive. Lost wax gives a great finish provided the wax had a smooth finish to begin with. I made a silicone negative, then made a wax positive, then coated the wax with plaster, melted out the wax and put the plaster mold into a pail of magic sand, pourded the melt and let it cool down on it's own.
Foam casting is much rougher but also a much faster process. Carve your positive from foam, coat it with plaster, burry it in sand and then pour your melt right on top of the foam. The molten aluminum melts and displaces the foam. The finish is a little porous but it works surprsingly well. I didn't make anything of value or of use with this method (Aluminum knuckle duster lol), it was more just to satisfy curioity. With this method make sure your sprue is long and wide like a large funnel at the top, this allows the melt into the mold quicker and sufficient extra melt on top for weight and shrink back = better fill out.
 
I helped out as a kid when my father ran a small aluminium foundry for a few years along with a business partner. One of the things I picked up on is the need to allow for shrinkage as the metal solidifies and cools. So your pattern will want to be some percentage larger in all dimensions than the stock part.

For single parts or small runs on simpler shapes like a trigger guard the lost wax method is needlessly complex. It's a part that can be easily done with a plate and pattern in sand molds then be smoothed and polished.

Because of the need for the parts to be significantly larger to allow for shrinking you'll need to bet pretty good at woodworking to make the patterns. Other than some small items you cannot use the original as the pattern due to this shrinking. In particular something as long as a trigger guard will simply not work if the original part is used as the pattern. If you try it the fit into the cutouts of the stock will be a very poor fit both in terms of the "feet" being smaller than the hole as well as somewhat closer together than on the original.
 
I would think machining something out of a solid billet would be much more cost effective. I am toolmaker at an aluminum die cast plant. We melt and cast about 25 tons of 380 and 383 aluminum alloy a day. Rough casting aliminum would be a lot of work and buy the time you polished and finished the end product it would just be easier to machine it out of solid stock.
 
Save the ladders and extrusion type materials for stuff that will not be machined, as when cast, it machines about the same as sun-warmed chewing gum or alternatively, add a large portion of copper (4 or more percent) to it to allow it to age harden.

Pistons are about the easiest feedstock source, but other cast aluminum auto parts are also usually pretty decent stuff. It won't machine like clean bar stock, though.

Keep you heat as low as you can, to get a melt, and only for as long as it takes to get the metal melted, and gas absorption is minimized. De-gassing is a common step though.

Green sand works pretty well and most of the home foundry guys I know use it mainly, but oil sand is pretty nice stuff!

Keep a couple cat food or tuna tins around your foundry area. Place them over the sprue hole (where you pour the metal in) while you are fiddling with your melt, to keep the spiders and other things out. No joke, there is nothing funny about having a couple pounds of melted aluminum go airborne all of a sudden from a steam explosion from a spider in the mold!

Wear safety equipment! No nylon or other synthetics fabrics. Heavy leather boots, face protection. Better even, to invest in proper spats and heat protective gear. my understanding, is that molten metal burns really suck a lot more than most.

Lots of good reading out there. Dig around the web, etc.

Cheers
Trev
 
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badboybeeson said:
For somthing like a trigger guard I'd just have it 3d printed out of carbon fiber
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Half a million dollar solution, to a 15 dollar problem.

The 3D printers that the unwashed can afford to play with, are NOT in any way equal to what is out there as state of the art, and even the best, are nowhere near the 'replicator' that each of said unwashed seems to think they are headed towards with their reprap or similar toys. Those are limited to thermplastics. Which ain't carbon fiber.

Cheers
Trev
 
One of the things brought up here is the amount of shrinkage for aluminum from molten to solid. I found this on the net:

Metal Pattern Oversize Factor Finish Allowance for machining
Aluminum 1.08 – 1.12 0.5 to 1.0%

Copper Alloys 1.05 - 1.06 0.5 to 1.0%

Gray Cast Iron 1.10 0.4 to 1.6%

Nickel Alloys 1.05 0.5 to 1.0%

Steel 1.05 –1.10 0.5 to 2%

It looks like if I cast a trigger guard of 3 inches the hole spacing will be about 10% short or about 1/4 inch short. I would have to create % bigger.
Does anyone have a suggestion as to how to make this easier?
As to metal I have already scrounged some very good aluminum alloy metal from the scrap metal bin at work :redface:(read aircraft quality alloy).

270 totheend
 
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270 totheend said:
One of the things brought up here is the amount of shrinkage for aluminum from molten to solid. I found this on the net:

Metal Pattern Oversize Factor Finish Allowance for machining
Aluminum 1.08 – 1.12 0.5 to 1.0%

Copper Alloys 1.05 - 1.06 0.5 to 1.0%

Gray Cast Iron 1.10 0.4 to 1.6%

Nickel Alloys 1.05 0.5 to 1.0%

Steel 1.05 –1.10 0.5 to 2%

It looks like if I cast a trigger guard of 3 inches the hole spacing will be about 10% short or about 1/4 inch short. I would have to create % bigger.
Does anyone have a suggestion as to how to make this easier?
As to metal I have already scrounged some very good aluminum alloy metal from the scrap metal bin at work :redface:(read aircraft quality alloy).

270 totheend
Click to expand...

Shrinkage rates matter a GREAT deal when you are making a pattern that will be used to make a product that will be as near to perfect as possible, straight out of the sand, but if you are making one, you can afford to spend the money on the extra metal that goes in to making it oversize and filing or milling it down to fit.

You are not going to generally, cast the holes locations, or otherwise try to produce exact dimensions, at least, not until you are well into the addiction!

The general system used, is to make it oversize and cut it down to fit.

When you make wooden patterns, you lay it all out with a shrink rule, for the material you plan to cast. Shrink rules alow you to measure directly in inches or whatever, and have the casting come out the proper size, as they have made the rule to allow for the shrinkage.

Aircraft quality alloy means sqat bugger all. Come up with the actual alloy numbers, or it's pretty much useless, or worse than. It can be worse than useless, if it not only ruins the pour, but makes a right bloody mess in your shop, as some zinc and Magnesium alloys can.
Pure Al. (1100) is good, as is 2024 (a copper alloy), but 7075 is crap to melt (zinc as the primary alloy).


Cheers
Trev
 
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He'd probably be better off trying to melt down some old pistons, or something of such made of a decent cast aluminium alloy, might be a bit high in silicon but eh.

No such thing as aircraft grade when you start melting it..

But... a piece of flat bar, a drill and a file would get you what you want quicker and be better than a casting attempt.
 
SND said:
He'd probably be better off trying to melt down some old pistons, or something of such made of a decent cast aluminium alloy, might be a bit high in silicon but eh.

No such thing as aircraft grade when you start melting it..

But... a piece of flat bar, a drill and a file would get you what you want quicker and be better than a casting attempt.
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Pistons were the preferred scrounge when my friends were hunting for casting stock. Larger items like heads and manifolds, need to be broken up or sawed into pieces to be able to fit into the crucible.

Yeah, hogging it outta bar stock is like to be faster, but then, what do you learn about castings from that? :)

Cheers
Trev
 
Neighbourhood kid runs an aluminium foundry out of a cut up fire extinguisher, charcoal, a hair dryer and a plaster of paris lined garbage can. I think it's the $20 solution from googling "diy aluminium foundry"
He makes all kinds of stuff out of pop cans.
So if a preteen with no training and experience can do it...
 
safehunter said:
Neighbourhood kid runs an aluminium foundry out of a cut up fire extinguisher, charcoal, a hair dryer and a plaster of paris lined garbage can. I think it's the $20 solution from googling "diy aluminium foundry"
He makes all kinds of stuff out of pop cans.
So if a preteen with no training and experience can do it...
Click to expand...

There is no doubt at all that the kid is learning a lot about casting. If he's doing anything more than making ugly lumps of stuff that he machines down he is already learning much or all of what we've been telling the OP in this thread. The kid might be using the most crude basics available to melt the metal but it doesn't change the realities of what he needs or needed to learn to make castings that are of any sort of final shape.

OP, the 10% total thing was both for shrinkage allowance AND to have enough stock to remove for a machined surface finish. At least that's how I read that information you gave. In actual use the shrinkage by itself is a bit less than that.

The problem is that you can't really use the old trigger guard as a pattern at all. Oh sure, you can use modeling clay or something to extend the length and thickness. But the trigger loop opening will be reduced in size too. So really you need to make a whole new pattern in wood or other material to allow for the shrinkage.

So if you're keen on learning casting I'm afraid it's either all in or fold and walk away. You'll need to get into pattern making and from there mold making to produce the proper size copies of these parts. It's a lot of work for only one to maybe half a dozen such parts. It would certainly be a labour of love. Carving what you want from some aluminium plate stock with basic tools would be way easier for one to three such parts vs all the effort needed for casting.
 
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