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Safe to drill through Reducer?

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Safe to drill through Reducer?

Unread postAuthor: Imkindofabigdeal » Sat Dec 18, 2010 1:22 am

Hey everyone,
If you read what i wrote before, scratch that idea. I came up with a new one, but it really is impossible to word. Jut one question though. Is it safe for me to drill a 1/8" hole through my reducer to put a bolt through it. I will be using a thermoplastic and PVC glue around the area the bolt enters and exits the reducer, but will the holes weaken the material? I just dont want my gun to explode on me because of a little mistake like that...

Thank you all very much,
Ben
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Unread postAuthor: POLAND_SPUD » Sat Dec 18, 2010 2:18 am

will the holes weaken the material?
Yes
Is it safe for me to drill a 1/8" hole through my reducer to put a bolt through it
I'd say that the answer is yes. If you're using a rated reducer (not a bell reducer or whatever you call them) it can be considered safe
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Unread postAuthor: Imkindofabigdeal » Sat Dec 18, 2010 3:00 am

Ok. Thanks for the info... I will be starting this glorious 9ft gun after christmas.

Some specs:
3 ft chamber
6ft barrel
Metered propane fuel
stun gun ignition
120mm 12V fan
breech loading
red dot sight/scope
professional paint job (my girlfriend's father owns an autobody shop and said he'd paint it for me, might be a bit expensive though, so i dont know haha)

plus more, stay tuned. Will upload right when complete.

Can't wait,
Ben
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Unread postAuthor: omniscient » Mon Dec 20, 2010 11:57 am

I wouldn't suggest drilling a hole through your reducer bushing, as most "bell" reducers have a shallow socket depth and a thin wall. Your chamber (if it is SCH40) will weigh approx. 10lbs and the barrel (if SCH40) will weigh about 8 lbs.

I went back and read some of your prior posts and saw that your chamber was to be 6" pipe and the barrel to be made of 3" pipe... That's going to give you an approximate 2:1 C:B ratio. - Why so high?

Making your C:B ratio smaller, somewhere around 0.8:1 or even as low as 0.7:1 will make your launcher easier to handle and more efficient.

If you really want something almost 10 feet long though, make the entire cannon out of a 10 foot length of 3" SCH40 pipe. With 50" of it for the chamber portion and 70" of it for the barrel portion, you'd have a 0.71:1 C:B ratio.
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Unread postAuthor: Technician1002 » Mon Dec 20, 2010 12:02 pm

On a quick note on chamber shape, a short fat chamber has a faster burn rate than a long skinny one and more of the chamber volume is farther away from the nearest cool surface so less heat is lost to the chamber wall.

A short fat chamber is better than a long skinny chamber of the same volume.
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Unread postAuthor: omniscient » Mon Dec 20, 2010 10:12 pm

Technician1002 wrote:On a quick note on chamber shape, a short fat chamber has a faster burn rate than a long skinny one and more of the chamber volume is farther away from the nearest cool surface so less heat is lost to the chamber wall.

A short fat chamber is better than a long skinny chamber of the same volume.


I've also often wondered if a combustion cannon benefits by having the burning gases accelerate through the choked transition between the chamber and the barrel?

I've built combustion cannons before though, with a single length of pipe and seemed to have no problems with performance. These have included a 3", 4", 6" and 10".

a 6" to 3" does have the benefit of not having to "trim-a-fan-to-fit" in the 3" pipe. I was merely thinking of terms of less money on less fittings, as well as the more readily available 3" cleanouts and plugs, as opposed to the 6" fittings. I've paid as much as $8, just for the male cleanout plug on the 6"

It'd be a good test to pit the two designs against one another. :wink:
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Unread postAuthor: saefroch » Tue Dec 21, 2010 3:57 pm

omniscient wrote:I've also often wondered if a combustion cannon benefits by having the burning gases accelerate through the choked transition between the chamber and the barrel?
Probably about nothing, unless you can make it work like a DeLaval nozzle, which pretty much requires that your barrel be far greater in diameter than the flow restriction, and that your projectile be almost massless. Theoretical benefits, yes. Practical... probably not.

I would be very interested in the results of a short fat chamber versus a longer, skinny chamber, provided of course that the chamber diameter is no smaller than the barrel diameter. The results could be very interesting, but are probably beyond most of our ability to measure.
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Unread postAuthor: Technician1002 » Tue Dec 21, 2010 4:57 pm

The dimensions on a nozzle is highly dependant on pressure. A nozzle for a 100 psi pneumatic or 1x combustion will closely resemble a bell reducer because there will be little pressure drop and resulting expansion from the nozzle into the barrel.

The nozzle throat and barrel ID will be almost the same. Pressure drop and resulting expansion will be longitudinally in the barrel with little diameter expansion.
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