One of my half scale mountain howitzers

[Cat Whisperer]

So does the matchplate protrude on both sides? Or just one side? This is where my confusion is I think.

The use of a matchplate can be done either way.  

I've seeen matchplates used for a 'tree' of parts that were cast again and again - the paterns being permanently attached to the match plate.  But in that case the parts were only on one side of the board (match plate).

[Double D]

I was looking through CANNONS An Introduction to Civil War Artillery by Dean S. Thomas for something and came across the chapter on Manufacture of Cannon.  the chapter discusses making the  flask and features put in the model for casting and machining.  Things like a large dead head or sprue for metal for shrinkage a pressure for better density or  making the cascable  as a square projection as aid in machining.

For a none foundry guy, I found it pretty interesting reading.  The cannons was cast solid and then the bore was machined out.  George is that how you did yours?

[GGaskill]

Yes, mine are cast solid and machined and drilled.  Essentially, there will be no as-cast surface left on the barrels when I am finished machining. 



The casting solidifies from the outside inward, leaving the shrinkage along the bore centerline.  Drilling the bore removes the metal from the area of maximum shrinkage, leaving the sounder, first solidified material as the tube.  The class instructor was continually trying to get me to cast with a core as art pieces are cast hollow to conserve expensive metal and make the casting of more uniform thickness which produces less shrinkage problems.  But I refrained since accurately positioning a core supported from only one end is very difficult.
 
If you look at the match plate, the end of the barrel is only about a half inch into the upper bulge.  All the rest of that space is for shrink feeder.
 
The sprue is actually the channel through which the molten metal is introduced into the mould.  You want the metal in the sprue to solidify so it doesn't suck metal out of the casting.  The gating system does a progressive fill of the mould so that hot metal is introduced into the shrink feeder as the last step.  This allows it to remain liquid and flow down into the main part of the casting as that area solidifies, preventing shrinkage voids.  The top of the shrink feeder is squeezed down to minimize the area exposed to the atmosphere to prevent heat loss.  The ogee curve is to make the edge of the cavity strong enough to prevent collapse of the sand.

[Powder keg]

Here are a couple of shots of my 3/4 scale Mtn Howitzer. I kind of messed it up though :?  I bored it out to 2.5", if I had went to 2.625" I could shoot pop cans. Now I'll have to make a ball mold. It is going to get a copper vent liner when I find that piece of copper I had here somewhere.

Thanks for the pictures GGaskill. I've got some good ideas now on how to cast some more barrles/parts using a matchplate.

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[GGaskill]

Nice barrel, especially the cascable.  But chuck it back into the lathe and bore that sucker out.  Might have to make a spider to protect the muzzle band from the steady rest, or could just take a skim cut afterwards.

And you're right, brass plating would look even better.

[GGaskill]

All the original images in this thread were lost when the C drive on my web server crashed.  So I reshot all the pix and re-posted them on my web server so anyone interested in a half scale mountain howitzer can see the whole thread again.

[Victor3]

Hi GG,

I just read through this thread. Impressive work indeed.

I'm wondering about something - I've worked quite a bit with White Tombasil castings. Most large castings similar to yours that I've worked on have areas of porosity that go undetected until machined. Do you find this to be true with the castings you've done?

[GGaskill]

It has been several years since I machined that casting so I don't really remember a lot of details of doing the work.  (But I have three more to finish so I will experience the process again.)  I did find some surface flaws, apparently from loose inclusions, on the outside, but I don't remember any in the bore.  As you can see from the image of the sawed off shrink feeder (deadhead), there is some porosity in the center, at least at that point, but that will all be removed while drilling the bore.  The vertical casting orientation causes substantial pressure on the bottom of the casting, and combined with the progressive fill, should make the bottom end of the casting (the breech area) sound.

[CU_Cannon]

Thanks for reshooting the pictures.  I would still like to cast my own barrel but my projects have turned in a different direction right now, maybe in a couple more years.  I found itÂ’s much easer to machine from solid.  For one or two barrels casting is hardly worth the effort.  There is still something about it tough.

[Kuntrykouple]

just a pic of my 1/2 scale golf ball  howitzer, wellthe length is just a' tad under 1/2 scale.

[Cat Whisperer]

Kk -

How's that do on Par 3 golf?  I would think putting would be a challange.

[claypipe]

This is one of my half scale bronze mountain howitzers.  I cast it in silicon bronze.....

First, let me praise your workmanship, GGaskill. But, I don't know about this. You should have at least use 660 / 932 CDA bronze. Silicone is crystaline in nature and may facture like tempered glass upon firing.

Gun Metal bronze is an alloy, 88 parts copper, 8 parts tin and 4 parts zinc, rated at 65,000 pounds per square inch.

Please use a good length of fuse and have a protective wall or trench.

[GGaskill]

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