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PostPosted: Sun Feb 10, 2019 4:48 pm 
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Location: Cypress, TX
I have been contacted by a cannon barrel foundry. They want a wood pattern for a Verbruggen barrel so they can cast them.
The pattern has to be in two halves.

So it has to be turned as one unit then split apart at the center laminating line.
For the moment, forget the trunnions.

How do I hold these two halves together while they are on the lathe?
The two halves will be about 43" long.
The rough stock will be 7.5" X 7.5" before it is round.
It will probably be pine.

I'm a little worried about the initial weight. My lathe is a big one. It will handle the length.

Here are some pictures of what I am going to attempt.
Forget the trunnions at the moment.

Here are two halves. I could make the yellow part a little longer and put a screw in there.
Could also do the same at the rear of the barrel.

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Each half will be drilled for removable pegs.

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Two halves put together.

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Setting a half into the casting sand.

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I have to figure out how to keep this thing from coming apart at 2250 RPM's

My lathe

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Zulu

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PostPosted: Sun Feb 10, 2019 5:41 pm 
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Some more pictures of the process. These are of several different types of cannons but you will get the idea.
Zulu

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Impression in the sand.

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The liner set in place.

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I have no idea what's going on here.

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PostPosted: Mon Feb 11, 2019 8:37 am 
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Said 2250 is a tad fast to turn IMHO in the roughing stage, granted OK once balanced out & in sanding stage. To mount halves together, make sure they match together with precision .... apply Titebond 111 to surfaces ...... insert newspaper between halves then clamp for 24 hrs. No need for any other fasteners but if you wish hose clamp either end & or move a single clamp away from tool area. Once finished it will split on newspaper joint, card scrapper, sand if desired.


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PostPosted: Mon Feb 11, 2019 10:32 am 
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Thanks,
I've done some internet searching. Some say use a single sheet of brown paper bag. Others say never use brown paper bag.
Some say use a single sheet of newspaper.
Others say use wax paper.

This is going to be big and time consuming. I sure don't want it flying off the lathe or getting messed up when I try to separate it.

Zulu

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PostPosted: Mon Feb 11, 2019 3:54 pm 
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Hey Zulu,

I second the suggestion to use the newspaper joint. I have used it many times myself. Only a single sheet of newspaper is needed.

Cheers,
Tom

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PostPosted: Tue Feb 12, 2019 8:32 am 
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I have spoken with the cannon foundry.

When the two halves go on to the lathe, the 1" wooden pegs must be in place. They will not be glued.
Note the peg holes in the picture.
They will use pegs to line up the halves when they put them in the casting sand.

They said the halves should not be glued but screwed or bolted instead.

In the past, they drilled and countersunk through both halves and bolted the two together with 1/4" all
thread. Of coarse, the countersinks were deep enough to miss the nuts when turning.

After turning, the holes are plugged with proper size dowels and sanded smooth.

This sounds like the way to go for me.
It could be pretty difficult to separate the two glued halves with the pegs in place.

Plus, there's no chance of the two halves separating while turning with the bolts in place.

Stay tuned, I'll post some pictures of the process.

Zulu

Image

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PostPosted: Sat Feb 16, 2019 8:34 am 
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Well,
I have started the attempt with the wood turning.
I countersunk 3" deck screws to hold the two pieces together and glued end caps on to help.
One end cap I made small enough to fit in a four jaw chuck.

It worked pretty well.

I started out at 350 RPM and it nearly beat me to death rounding it out but it worked.
I have no clue what I was thinking when I said I would start it out at 2250 RPM.

I might not have survived!!!

After rounding, I was able to increase the speed to 750 RPM's and later, after the thing started to take shape, increased to 1200 RPM's.

That is working well.
This is the biggest thing I have ever put on my lathe. It is 44 1/2" long and weighs 53 lbs. in it's unturned state.

I currently have it roughed out and it is ready for fine tuning.
I just hope when it is finished and I pull it apart, both halves remain flat.

Here are some pictures.
Zulu

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PostPosted: Sat Feb 16, 2019 9:14 am 
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Wow! This is sooooo cool. Glad you got it figured out. Thanks for posting this. :-D :-D

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PostPosted: Sat Feb 16, 2019 6:12 pm 
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More pics.

I got stage one finished. I'm happy.
It worked out and both halves are flat.

Now I have to figure out the trunnion issue. They will be 2 1/4" diameter, but they will be mounted below center line as opposed to centered in the barrel. I have to work that out.
They will be poured in the vertical position so they each have to have a 1 degree taper to allow the casting sand to release them without collapsing the sand.
That part is easy. The below center line boring of a 2 1/4" hole is harder.
I'm thinking on it.
Enjoy the pics.

Zulu


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PostPosted: Sat Feb 16, 2019 10:48 pm 
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Cut a block that's curved on one side to fit the curve of the barrel, and flat on the opposite side, such that it will act as a guide at the proper angle for the bit. That way you get a flat surface to start the hole and the drill will proceed into the barrel at the proper angle to the barrel curvature. Does that make sense to you? :)

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PostPosted: Sun Feb 17, 2019 10:44 am 
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That is one option Gene.
The trunnion pocket hole has to be 2 1/4" diameter. It only has to go in deep enough to accept glue.

I could probably use a Forstner bit. It would be like drilling straight down into a hillside.
One side would start to cut long before the downhill side started.

I'm thinking a Forstner bit might do it.

My other option is to take the halves to a friend's house. He has a CNC woodcarving machine and says he could cut the pockets.

I just don't want to mess up the barrel halves. :( They were too much work.
Zulu

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PostPosted: Sun Feb 17, 2019 2:52 pm 
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Zulu wrote:
That is one option Gene.
The trunnion pocket hole has to be 2 1/4" diameter. It only has to go in deep enough to accept glue.

I could probably use a Forstner bit. It would be like drilling straight down into a hillside.
One side would start to cut long before the downhill side started.

I'm thinking a Forstner bit might do it.

My other option is to take the halves to a friend's house. He has a CNC woodcarving machine and says he could cut the pockets.

I just don't want to mess up the barrel halves. :( They were too much work.
Zulu


I'd assumed you were thinking Forstner, which is where the guide block would come in, but the CNC might be a better option, since you could carve out the pockets starting at the shallow end rather that plunging straight down with a Forstner. The problem you face is getting the trunnions in the same identical plane - a 3 dimensional geometry problem. Good luck, and let us know how you solve it. :)

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