Thread: W.I.P. Making a pattern for a cannon.

I hope so. I always wanted to build a car with working gunports down the side.

Originally Posted by artful bodger

The original cannon is not a working one.
It is set up for display purposes only and is owned by a reputable tourist attraction here in the south island. It will go BANG and emit a big cloud of smoke. That's all. It is a very rough casting and out of round.
If I thought anything about the job would compromise my clean "criminal history" record then I would have backed away.
I hope this is the end of the legal debate.
It was meant to be an interesting thread on an avenue of wood working that is seldom in the spotlight these days.

It goes bang and smoke comes out but thats all Your Honour. Good luck with that one.
We now are burdened with gun laws, wether we like it or not. As a keen shooter and gunsmith
I take the time to offer you information which could be useful to you and others. Sorry if that offends.

Can we now get this thread back on topic please, I think the legalities have been well and truly covered.

Originally Posted by ian

out of interest.
Is a rod to support the sleeve while in the mold "normal" pattern making practice?
and how do you go about supporting the open end of the sleeve ?

and lastly, for what is basically a cylindrical object, should it be cast vertically or horizontally? and is this something a pattern maker would advise on,
or something the foundry would dictate with the pattern maker required to adjust the pattern to suit?

Good questions Ian.
Regarding the rod to support the sleeve being normal patternmaking practice. I would have to say it is not normal. I have not seen this done before however my last full time job as a pattern maker was in the 80's so I am not exactly at the cutting edge of the game. Also I have never had a particular job where a steel insert is cast into the molten metal. It (the rod) is obviously a method that has worked before so credit to the client for researching it. Of course in the final casting that rod, which will be a different metal to the cast iron will still be there and will need to be cut off and ground to the shape of the ball type projection on the end of the cannon.
The open end of the sleeve is supported by what in the trade is called a "print". A print is another shape or imprint that is added to the pattern to support a core. Cores are usually made from sand to cast a hollow and the cores are usually made in a corebox. In this case the core IS the steel insert. So back to the pattern, where the open end of the cannon is, instead of a hole there, there will be a length of timber turned to the diameter of the steel insert projecting out from where the hole will end up being.You can actually see this impression on the end of the sand mould in the first picture. It's what the steel pipe is supported by.
Here is a picture of a basic split pattern and corebox for a straight length of pipe. You can see the prints on either end of the pattern that the core will sit in in the sand mold. The prints therefore do not end up on the final casting.
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As for casting horizontally or vertically, it looks like the one in my previous posted picture shows it was cast vertically. However the particular foundry that is going to cast this one may well have other ideas so I will visit them to find out how they want to go about it before the pattern is made. It is important to work out the most suitable way to go about a job first so that all parties are on the same page. Ultimately it is the foundry that dictates how the thing will be cast and the pattern is made to suit.

Well here we are 8 months later and there is finally movement at the station.
The main holdup has been waiting for the steel insert to arrive. It is here now and the client has had a 16mm metal rod welded to the plugged up end.
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DSCF6738.jpg A view from the business end.
DSCF6741.jpgThe pattern will be a split turning to make molding easy. There are 3 x 16mm dowells that are pre drilled and fit so that the 2 halves locate accurately once turned.
The timber is Tas oak which would probably make most patternmakers wince however it is relatively easy to get here compared to say Jelutong.
I only have one half round section router cutter from a previous job and as luck would have it, it is a 16mm one. What a bonus!.
Using my lucky router cutter I have routed 2 half round channels down the centre of one end of each pattern half.
Into the channel will go a length of 16mm steel which will essentially be the "print" for the closed end of the cannon. See pic below.
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The 2 halves of the pattern are screwed together using 4 tech screws.
"He says with a little trepidation"
You could glue both halves together with newspaper sandwiched in between...but it makes a bit of a mess to clean up afterwards.
16mm seems to be the double lucky number today!, It is exactly the size of the spigot end of the screw in a Vicmarc chuck and that is what I hope to hold onto the metal rod in the pattern while it is turned.
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The tailstock end will be held with this bracketty thingy that is held on with 4 tech screws and 2 nails.
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Only other job that has been done is to drill a couple of 38mm holes in the centres of where the cannon spigots will end up. The reasoning here is that it will make it easier once the pattern is turned to actually fit the spigots which are larger than 38mm.
DSCF6749.jpgDSCF6748.jpg
Will probably knock the sharp corners of the blank before turning tomorrow too.
Happy to see a bit of action on this job, it has been getting in my way for too long.

Please keep the photos coming. It's not often you get to watch a job like this from start to finish. (A video at the foundry would be awesome as well )

Was thinking about this job last night and thought there was a couple of aspects that needed further attention before turning started.
First concern was that although the Vicmarc chuck should hold the 16mm rod ok, there is however no real driving part for the actual turning...only a clamping action of the 2 halves of timber onto the rod, which is a big ask for such a heavy workpiece. More'n likely the rod will just rotate inside the workpiece.
So this morning, undid the 4 tech screws, took off the bracketty thingy thing , a bit of rough grinding and drilling plus a couple of 2 inch nails and Bingo!.
A makeshift low tech driver

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Second concern was there is going to be a length of metal rod exposed between the chuck and the timber, and the force of the tailstock pushing inwards might be more than the chucks jaws can handle causing the job to move inwards on the lathe... causing the end of the turning coming out of the tailstock WHILE turning.....with a certain unhappy ending.
Made up an m.d.f spacer to fill the gap and hopefully thwart the above scenario. Pictured below between the work piece and the chuck, the steel rod is of course inside it.
So now ready for turning, the corners have been taken off with 6 hungry swipes per corner with the electric planer.
DSCF6755.jpg DSCF6754.jpg



Rouged down to a cylinder first. Started at the tailstock end and taped up the very end when it was a cylindrical. Its only about a 50mm tech screw that end because of the eventual diameter and a bit of a safety net cant hurt.
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Using the original pattern layout/mark up etc, I have projected the important diameters using the edge of the layout like a pencil gauge so the diameters locations can be marked onto the job.
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Showing the fatter end of the cannon.
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And the thinner (business) end.
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This end is the start of turning. So its now just a matter of chisels and callipers and a hoping the screws hold tight and you don't end up getting clonked on the noggin.
This Tas oak is pretty heavy and I donned an open face motorcycle helmet for most of the next part. Nothing worse than a brain injury before lunch.
Just a bit concerned about the holding power of 4 tech screws. They use to teach you at tech/tafe to glue the two halves together with a sheet of newspaper between the glue as well. But that was in the days before cordless drills and tech screws and bog filler. Plus that was using lightweight jelutong.

Nibbling cautiously away. It's nice that the more you turn the weight reduces.
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The other end in progress.
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The other end done. You can see that I've turned right down to the metal rod and also taped up the m.d.f. spacer because it looked and felt like it might let go. Probably no big issue but you never know.
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Will try and post a picture of the end result. Picture is on my new fandangled mobile telephone/televison and I can't work the thing out right now......


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Next job is to make the split turnings for the cannons spiggots, fit them, set up a 1200 x1200 x18 mm board of mdf to sit one half of the pattern on (an "oddside"if we must be technical) for the foundry, spray the whole shebang with automotive lacquer and it will be just about job over.
At last.
Client still has 2 other cannons eagerly waiting for patterns, I am wondering if the bill may temper the urgency of the next ones.

no no

deleted

what went wrong?

posting error or did the work piece fail?

rust you are OK

Originally Posted by ian

what went wrong?

posting error or did the work piece fail?

rust you are OK

Hi Ian
Could not get a picture off my new phone last night. It was driving me batty so gave up.
Nothing went wrong with the job. Couldn't be happier with it.
Have put a picture up of the finished turning in the original post now.
Thank you for your concern.
Cheers
AB

I have run this past the firearms registry- By way of a request to manufacture. I have been advised by them, "Without the necessary licencing the manufacture of any form of operative firearm is illegal. All firearms must be serial numbered and registered unless they meet registry requirements for exemption ie antique or de activated." An out of round bore does not come under the deactivation schedule. It would still be perfectly capable of firing shrapnel. What you guys are doing is highly illegal and the Court doesnt except ignorance as an excuse. Just so you know.

Originally Posted by rustynail

...... What you guys are doing is highly illegal and the Court doesnt except ignorance as an excuse......

Interesting view, RN, but I don't think the Artful One is breaching any law. There is simply no law that says you cannot make or possess a pattern.

The situation could be quite different for the guys who do the casting or the later machining and final assembly and possession. Possibly the caster is OK as the raw cannon casting could not be fired. Somewhere along the production line the situation will change, and a cannon capable of being fired is certainly illegal.

Perhaps the machiner should engrave or emboss serial number: 1, on the cannon barrel.


Cheers

Graeme

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