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Barrel 'Droopage'

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Barrel 'Droopage'

Unread postAuthor: MountainousDew » Thu Apr 16, 2009 10:05 pm

Howdy Everybody,
My name is Joey, I enjoy long walks on the beach and drinking Mountain Dew.
But the real reason I started this topic is because I am in midst of building a pneumatic piston cannon, and I need your help to stop my barrel from drooping so much... Please help me!

First off, here are some specs: (I don't know if it's necessary...)
-Barrel Diameter= 3/4 inch
Barrel Length= Maybe 5 or 6 feet?
-Chamber Diameter= 2 inch
Chamber Length= Possibly 2 feet?
-Piston Housing= 1 1/4 inch tee
Piston Porting= 3/4 inch

Note: I haven't build the cannon yet, so opinions are welcome!
And yes, I have tried Viagra...
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Unread postAuthor: Carlman » Thu Apr 16, 2009 10:16 pm

In the past for a 1/2" barrel i have secured it to a broom handle (that was straight) to eliminate the bend.
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Unread postAuthor: jook13 » Thu Apr 16, 2009 10:22 pm

Try sleeving the barrel inside of a larger pipe, possible even some form of metal. You may even think about switching out that barrel with a copper one, I got a ten foot section of 3/4 copper pipe for around 15 bucks.

If you have an over-under setup, do you have a barrel support going from your chamber to the barrel?

A picture of the cannon may help us to help you.
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Unread postAuthor: MountainousDew » Thu Apr 16, 2009 10:37 pm

jook13 wrote:A picture of the cannon may help us to help you.

Well, thats going to be a problem, I haven't built it yet...
And I only bought a ten foot section of 3/4 inch pipe and a 1 1/4 inch tee, for testing.

What I'm trying to figure out is how to keep it from drooping.
But I'll probably try the metal sheathe idea...

Edit: @Carlman Its not that its bent, it just droops.
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Unread postAuthor: grock » Thu Apr 16, 2009 11:04 pm

you could try taking a block of something and cut out 2 half circles and put it between your barrel and your chamber, and if that is secured correctly, it also turns the back half of your barrel into a carry handle. best used with a chamber closer to the length of your barrel though
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Unread postAuthor: MrCrowley » Fri Apr 17, 2009 12:10 am

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http://www.spudfiles.com/forums/viewtop ... tml#186844


That's one idea and doubles as a nice breech loading support :)
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Unread postAuthor: jackssmirkingrevenge » Fri Apr 17, 2009 12:16 am

Easy ;)

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Unread postAuthor: Gippeto » Fri Apr 17, 2009 12:24 am

You could rib the barrel.(doesn't have to be vented, but, it looks cool. :) )

http://www.midwayusa.com/midwayusa/stat ... 155347.jpg

Adding the rib and (shear) web, will stiffen the barrel without adding too much weight.

Use wood (1/4"x1/2" is plenty) with the grain running along the barrel for the top of the rib, the web could be wood as well (vertical grain). Join it together with epoxy and glass cloth where needed.
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Unread postAuthor: jook13 » Fri Apr 17, 2009 1:36 am

HAHA! I had to laugh out loud at JSR's suggestion. Woke up my 2 year old baby girl.
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Unread postAuthor: jackssmirkingrevenge » Fri Apr 17, 2009 1:44 am

Apologies to your daughter ;)

Shame the residents of Paris weren't similarly amused :roll:
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Unread postAuthor: jook13 » Fri Apr 17, 2009 1:49 am

Its kinda funny because it reminds me of another members cannon from this forum
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Unread postAuthor: Carlman » Fri Apr 17, 2009 3:58 am

I secured mine to a broom handle so it wouldnt bend, not to fix its bend
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Unread postAuthor: psycix » Fri Apr 17, 2009 5:22 am

Ah the BBS! (Bendy barrel syndrome)
Well to sum it up this are your options:
-Use sturdier pipe.
-Sleeve the pipe.
-Reinforce with something else.
-Shorten the pipe.
-Have a long chamber and add barrel supports.
-Aim upwards in order to fire horizontal and watch your barrel explode.
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Unread postAuthor: mark.f » Fri Apr 17, 2009 11:14 am

I think MrCrowley's suggestion is the best. Lengthen the chamber to 3-4', and then use two or more barrel braces to keep the barrel aligned. Like he said, you could make the braces loose enough for the barrel to slide through when breech loading.

I've used 3/4" SCH-40 as a barrel up to 5' in length before, and don't recall having the same problems in the extent you are talking about. My friend has too. But the methods above should work.

EDIT: forgot to mention, but my friend uses a 10' golfball barrel on his cannon, which we debated using an actual cable support system like the Paris gun JSR posted. Just saying, it's an option if you're not concerned with looks.
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Unread postAuthor: elitesniper » Fri Apr 17, 2009 11:21 am

Yup go with MrC suggestion I use the same type on my gun and it works great! :)
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