12 Gauge Blank Firing Cannon

[Powder keg]

Hello, I decided to start a new thread on this topic to cover the construction of this signal cannon. The finished cannon will be about 6" long and the wall thickness at the thinnest point will be about .375" thick. I got started on the pattern for my 12 gauge cannon. The breech end will be a one piece pattern, and the barrel will be a two piece pattern. I still have to add the tabs to the barrel where it will attach to the breech. Also I have to add fillets to the inside corners of the breech block. After I get the patterns finished I'll paint them with some glossy paint so they will come out of the sand nice and easy. I'll have my casting sand in a couple of weeks and I'll be able to continue then. In the mean time here is what I have so far. Later,

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[GGaskill]

What material?

[Cat Whisperer]

Good lookin' patterns.  I assume you have standard pieces for sprue and risers.  It would be very good if you could show a series of pictures of ramming up the patterns in prep for the cast!  Not many of us have done it personnally.  Will you use a core for the barrel (am I reading the end pieces right)?

[Powder keg]

Hello ,

The first run will be Aluminum. Mainly because I have some and my furnace will melt it. Later I hope to pore some brass :grin: I'm planing on posting pictures of the whole process. I still have some misulaneous tools to build (I can post pictures of these to?) before I can really get started. I am planing on poring with a core in the center. I know that cannons are pored upright, breach up, solid core, but for this aplication I think I will be Ok. The bore will be cast undersized then the barrel bored to size, once I figure out how to hold it :? Later,

[GGaskill]

What are you going to use for a crucible?  Iron contamination in aluminum leads to porosity which would be a bad thing in a black powder gun.  

Also, although you aren't intending this for use with regular 12 gauge smokeless shotshells, does the design have enough safety factor so it won't explode if someone fires such a shell in it?

[GGaskill]

Regarding holding the barrel for boring, besides the use of a spider for holding irregularly shaped objects, you could add three small flats on the top and sides of the barrel so you could hold it with a 4 jaw chuck, and then remove them when the bore was finished.

[Powder keg]

Hi,

I have A graphite crucible for poring aluminum. As for the saftey factor, I think it will be OK. The wall thickness at the thinnest part will be 3/8". Also the barrel is only 4" long. I've been thinking of shooting several live shootgun shells under controlled conditions just to see what happens. Any thoughts on this?

[GGaskill]

A graphite crucible sounds great.

I would measure several diameters along the OD of the chamber area before firing, fire one shell and remeasure.  If you find a difference, you have exceeded the elastic limit of the material which I would interpret as being not enough safety factor.  Repeat as many times as you like with measuring after each firing.  That is about all an ordinary guy can do without more sophisticated measuring equipment.

[Powder keg]

Thats along the line of what I had planned.  Thanks for the input,

[Cat Whisperer]

... I've been thinking of shooting several live shootgun shells under controlled conditions just to see what happens. Any thoughts on this?

Two issues.  It's probably do-able to put together a 'proof load' that would not conflict with the law (avoiding the Destructive Device issue).  Then the other issue is how much is enough vs. how much is too much.

If I had a set of identical tubes, I could test until one was damaged and back off by a good margin of safety.  One tube is problematic.

Metal will stretch and return to it's original size/shape unless you pass the point where it is no more elastic - then it deforms.  It is a short distance between going past the point of still being elastic and where it comes unglued.  THAT is the problem.

The pressure peak occurs early on in the timing of the shot.  The heavier the shot being propelled the more radical the peak.  That also is a problem - how do you sneak up on a good robust proof load without blowing it up?

So make some comparisons with other successful designs.

[Powder keg]

I usually tend to overbuild things. I've seen several of these little cannons and have come up with what I think is an over-built version. I'm making the barrel thicker than the ones I've seen and I'm using smaller ammo.(12 gauge instead of 10 or 8 gauge) On the matter of boring I think I'll use a angle plate on my mill and bore it to size there, mabey.

[Cat Whisperer]

I usually tend to overbuild things. I've seen several of these little cannons and have come up with what I think is an over-built version. I'm making the barrel thicker than the ones I've seen and I'm using smaller ammo.(12 gauge instead of 10 or 8 gauge) On the matter of boring I think I'll use a angle plate on my mill and bore it to size there, mabey.

Can't do much more than that!

[Powder keg]

Hello All ,

I've been busy gettin ready to pore some cannons :-)  I'm going to post pictures of the whole process. The first picture is some of the foundry stuff I've made. The big box will hold the sand and I'll screen it there also to break up any lumps that will show up in the finish. The two boxes on top are the screens. There is one with 1/8" squares and one with 3/8" squares.

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Here in the second picture you can see one of the pattern boxes I made. The tapered pins on the ends allow the box to be taken apart and re-assembled in exactly the same spot, like in the third picture.

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Yesterday I started melting some of the 50 pounds of Diamond plate aluminum that I aquired last week. This stuff melts nice! hardly any dross. (Dross is the crud that floats to the top of the melt) There are about 20 pounds of ingots in the picture.

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Hopefully I'll be able to start on the little 12 gauge signal cannon tomorrow. Later,

[Powder keg]

Hello, I almost didn't do this today because of the threat of rain. But, I couldn't wait any longer. There will be many pictures in this post. Please remember that working with molten metal can be dangerous. (Insert standard warnings here) Here in the first picture you can see the breech pattern sitting on a board with the drag upsidedown on it. The white powder is called parting powder. It keeps the sand from sticking where you don't want it to stick.
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In this picture I've screened some sand over the pattern. This finely screened sand is called facing sand. I've started ramming the sand. starting at the edges and working my way in.
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Here you can see the drag rammed and I'm striking the top off level.
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Here I've placed a board on top of the drag. this will aid in flipping the drag over.
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With the board removed you can see the bottom of the breach pattern.
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Here I'm placing a couple of wooden dowels in the cope section. these will be the sprue and a riser.
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This shows the pattern separated, gates cut, and cleaned up ready to be put back togather.
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Here is the barrel pattern at the same stage. Notice the long gates. this was a mistake. I think this caused my first barrel to have a bad shrink in the middle of the barrel.
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In this picture you can see the top of the assembly. before I pored they were taken apart and blew out, then re-assembled.
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The pore. Sorry about the bad angle. Please note that I do not have a long sleaved shirt on. This is bad do not do this!
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Here I'm calmly waiting for it to cool off. NOT!!
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Here is the barrel still in the sand.
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The first two parts were scraped they both had bad shrink defects in them due to bad sprue,  riser, and gating. That fixed the second pore was a sucess :grin:
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Here are a couple of the final castings.
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Overall I'm happy with the way things turned out. I was disappointed that the first attempt had shrink defects, but I'll just have to get over it. After all this only the third time I've made a sand casting. I still have lots to learn. before I start to machine the little cannon I want to cast another set of castings so I can have a couple of them to play with, err, Test :-)
If there are any questions please feel free to ask.

[Cat Whisperer]

Powder Keg -

Great job, great set of pix!

I really like the 'guide pins' aligning and holding the cope and the drag together.

Learning the ins and outs of casting (like the feeders being a bit long) is a valuable lesson to learn - and best done on smaller projects early on.  Thanks for sharing - now some of us THINK we know how.

Again, great set of pix - nicely done!

[jeeper1]

Very interesting. Very educational. Not something I'll ever do. Thank you.

[machinehead]

First off let me say this is just blowing my mind!  Yall need to quit doing this kind off stuff so i dont get anymore projects going in my head.  There is only so many projects that i can do at any given time.  Each one makes me get and build more stuff.  Everyone makes me spend more and more time on the computer learning how to do it.  Now i have to build a foundry and figure out how to use it.  Casting is something i have never thought about but with this post and the others about the howitzer in going to have to do it.  My wife gets madd at me with each one.  Not because im doing it but i never finish a project before starting something else.  

Ok here is my question.  I know nothing about sand casting so here it is.  What keeps teh sand together?  Is it like a concrete or is it just pounded in and it just stays there.  Im sure it is a special sand but what alows the molds to be moved and it not fall apart.  Forgive this rookie question but i have not searched anything yet because i cant do anything remotely close to casting yet.

[GGaskill]

Judging from the color, he is using Petrobond sand which is a mixture of sand, oil and some proprietary materials.  It is also possible to mould with "green" sand which is a mixture of sand, certain kinds of clay and a little water.  The oil (or clay and water) cause the sand to stick together.

There are other moulding techniques that cause the mixture to set hard, and yet others that use a liquid material that the pattern is dipped in and then coated with sand (you have to use a pattern that can be burned or melted out of the cavity in this process.)  All kinds of ways to cast stuff.

Regarding the shrinkage defects, the rule of thumb is to have the volume of the shrink feeder equal to the volume of the casting.  In your first pour, it appears that there was at least twice as much material in the sprue and riser as in the barrel.  You want the desired part of the casting to solidify first so it draws liquid metal from the sprue and risers.  If the casting solidifies last, the sprue and riser will draw metal from it instead.  Sometimes you have to include pieces called chills near the casting to absorb excess heat and force the casting to solidify first.

[Powder keg]

Hello Machinehead, Glad to spark your interest :twisted:  My wife took all the pictures today. We had fun spending the day togather. I have been interested in foundry work for a couple of years now. Mainly reading books. I had a chance to assist a guy giving demonstrations last September at the Gears model show in Portland, Oregon http://home.earthlink.net/~oregongears04/ It was a blast!!!

Here are a couple of pictures of the defective pieces I made. On the barrel you can see the shrinkage in the middle/top. I think it was caused by the long gates going to the sprue and riser. The metal froze in the narrow, long gates and there was no where for the barrel to draw molten metal from as it cooled. The result was a shrink cavity.

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In the breech section I had a simular problem. The gates were to narrow and froze before the breech had cooled. To solve this I placed a riser over the bottom of the breech. This way there was no gate to freeze, and there was a solid colum of aluminum to draw from.
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[Double D]

Since I know nothing about sand casting I'll be the one to ask the dumb question.

How do you get the wooden mould out?

[CU_Cannon]

I was amazed at how well the sand would hold together the first time I tried casting.  The only other experience I had was building sand castles as a kid.  I never thought that the sand would hold together so tight.  

My wife gets madd at me with each one. Not because im doing it but i never finish a project before starting something else.

Don't worry it happens to the best of us.  It is much safer just to unplug your computer.  Just when you think you have enough hobbies another one will come along.

[GGaskill]

"How do you get the wooden mould out?"

Since the mould is the cavity, I assume you are asking how to get the pattern out.  The pattern is shaped so it can be removed without damaging the cavity.  For an object with parallel sides, the sides on the pattern are made with a couple of degrees of slope (called draft angle) such that the pattern is wider at the parting surface.  To remove the pattern, you screw a handle into the back of it and lightly rap the handle is a couple of directions 90º apart and then carefully lift the pattern straight up.

[CU_Cannon]

Did you coat your pattern with anything (varnish, shellac)?  In the pictures it looks like they were just left plain.

[Powder keg]

Hi,
The sand is petrobond like GGaskill mentiond. I was to anxious to paint the pattern, so it is still bare wood.

GGaskill, I'm considedring making a matchplate for this barrel. How do you remove the cope without muking up the sand? Do you rap it like you do when you remove a pattern or what? Thanks,

[GGaskill]

What I did was allow a little slop on the locating pin holes in the matchplate so it could be tapped before lifting the cope.  It also made lifting the matchplate from the drag easier.
 
I noticed in the picture of you pouring the mould that you are holding the crucible with tongs.  This is not the best way to do this.  The proper method of holding the crucible is with a pouring shank (basically a ring [that fits the crucible] with a handle.)  Also the best way to lift the crucible from the furnace is with lifting tongs.  Both are visible in the following image.

(The image is no longer available.)

What you can't see on the lifting tongs is the handles bend to horizontal so the weight of the crucible causes the tongs to clamp closed.  The strange lever apparatus on the pouring shank (sticking out to the left) is a clamp the will retain the crucible in the shank even if it is turned over too far.  More expense I know but they are the safest way to handle the crucible and lower the probability of damaging it.

You can see a couple more images of the pouring shank in use at daedalus.csgeeks.org (this link is dead).  Here is another site: 5bears.com.

[Powder keg]

Thanks for the information GGaskill. I know I need to gather up some more stuff like a poring shank and lifting tongs. I'm going to build them in a day or two. Also going to set asside a spot for some sand to pore over, Like in your picture. Well better go get something done,

[Double D]

Powder keg how about some explanation of terminology.  

Matchplate.

Cope.

Petrobond, green sand, sand, screening sand, parting sand

Drag.

Gates.

Riser.


Oh, now I see it, the barrel pattern is 2 pieces.  Didn't notice that a first.  The Pattern is the positive mould to form the negative cavity in the sand.  The sand then becomes the negative pattern or mould in which the molten metal is poured into for the casting.  

In the case of the barrel you have two moulds top and bottom.  How do you align the two halves so they line-up.  How do you put the top and the bottom together?  Are they packed separately?
What makes this sand bind together?  How are the castings removed from the sand?

Kind of puzzling for one with no experience.

[Powder keg]

Hello, The Cope and Drag Are the top and bottom sections of the core boxes. (the boxes that hold the sand) A matchplate holds both halfs of the pattern, one on each side. It also has the gates and sprue/risers on it. It makes it faster/easer. The Sprue is where you pore the metal into the mold. A riser fills up with molten metal and feeds the pattern as it cools. And a Gate connects the sprue/riser to the cavity in the sand that you are casting. There are a couple different typs of sand. Both are called green sand. There is water bonded sand and oil bonded. Petrobond is a oil bonded sand. It is easer to work with than water bonded sand. When I start, I push the sand through a 3/8" screen (screening) to break up the lumps. There are two locating pins on the barrel halfs. I'll post a picture tomorrow. Oh, I messed with my furnace/burner a little and was able to melt about a pound of brass tonight, Yahoo! Brass barrels :grin:  If anyone can add or amend my descriptions please jump in. I'm still new at this. Later,

[GGaskill]

DD and others,
   I am not trying to insult anyone here but we need to be correct with the terminology.

The cope and drag are the upper and lower frames that hold the sand that is made into the mould (collectively, they are called the flask.)  The mould is really the cavity or the object that contains the cavity.  A core box is a secondary device that is used to make cores.  Had Powder Keg cast the barrel hollow, the piece filling the bore area would have been a core.  Cores need to be strong enough to maintain their shape when handled and when the mould is poured, but they also need to be able to collapse when the metal is solidifying so they don't cause tears in the casting.  They are usually made from somewhat different material than the casting sand.

There are many kinds of "green" sand, but basically the sand is not made into a hardened mass before pouring the mould.  Other sand casting processes involve hardening the sand prior to pouring.

Sand is screened (the actual term is riddled, and the screening device is called a riddle) to reduce the particle size to give a smoother surface to the mould, and hence, the casting.  Parting compound is a material that is dusted over the pattern and moulding board or matchplate to prevent the moulding sand from sticking to it.  

Screening sand is not a term I am familiar with.  Facing sand is a finer grit sand that is used first to cover the face of the pattern and give a smoother finish to the casting.  Coarser sand is used to back the facing sand; this is both cheaper and makes the backing sand more porous which lets any gasses formed when the mould is poured escape through the mould instead of being forced into the metal making it porous.

How do you put the top and the bottom together?
>> The sand will stay in the flask when it has been rammed (the term for packing the sand in the mould around the pattern.)  The drag is placed on a moulding board (a flat board to guarantee the sand will stay in the drag) cavity up.  The cope is turned cavity down and put onto the drag with the alignment pins causing the cavity halves to register properly.

Are they packed separately?
>> More or less.  When using a matchplate, they are held together but still filled and rammed one side at a time.

What makes this sand bind together?
>> The oil or water and clay are the binder that makes the sand clump.

How are the castings removed from the sand?
>> After the casting has cooled, the mould in placed over the sand bin and the sand is pushed out of the flask.  Eventually the casting (and sprue and gates and risers) comes out and the burned sand sticking to it is removed.

[Powder keg]

Thanks GGaskill. That was a much better discription than I provided. Like I said I'm really new at this and theres lots to learn. Thanks again,