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Barrel Chamfering

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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Do you think chamfering the inside of the barrel is more benefitial than chanfering the outside?

Poll ended at Sun Oct 14, 2007 11:53 pm

Yes
2
67%
No
1
33%
 
Total votes : 3
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Barrel Chamfering

Unread postAuthor: BigGrib » Thu Oct 04, 2007 11:53 pm

I've been looking around at all the different guns people have built and i have noticed one thing the have in common. Chamfering the muzzle of a barrel. Some people do some people dont maybe it's just a personal preference, but what i have noticed from the people that do is they chamfer the outside of the barrel making it look like a hypodermic needle. one thing me and my buddies figured out a long time ago is chamfer the inside of the barrel. it's a little harder to do, we found that a rasp file and some patience works fine. the reason we did this was you still have the spud cutter feature of chamfering it out but it makes the spud just a little bit bigger than the barrel so you get a nice tight squeeze againt the wall. and i'm not saying that i came up with it and that noone else does this but from what i have seen noone has, but then again maybe i havent looked back far enough. let me know what you think.

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Yea, that's definitely going to get you at least a tazer.

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Unread postAuthor: hi » Fri Oct 05, 2007 12:05 am

i do that with mine. I shapen it on the outside so that the potato isnt compressed while its in the barrel. i once did it on the inside and really regreted it because i could never get it down the barrel without putting a hole in the tater.
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Unread postAuthor: BigGrib » Fri Oct 05, 2007 12:09 am

One thing I did to circumvent that is to get a 2" hole saw and make a plug out of a 2x4 then srcew it to a 1" dowel of the correct length, i think once i even countersunk the plug so the dowel fit better then screwed it together. made a really nice ramrod
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Yea, that's definitely going to get you at least a tazer.

<a href="http://www.youtube.com/watch?v=AkMkGOpAF4s">DONT TAZE ME BRO.. DONT TAZE ME... AHHHH</a>
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Unread postAuthor: Killjoy » Fri Oct 05, 2007 2:33 am

I tried this once, cut the angle wrong and the spud was so tight the cannon couldn't fire it, the burning propane would just hiss out the back and burn me. Never tried it again, I just use those sponge ball pool toys, soak it and stuff it, makes great reasuable wadding.

But still this cutting the inside at an angle is a good idea.
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Unread postAuthor: MaxuS » Fri Oct 05, 2007 5:12 am

My tennis ball launcher has the outside chamfered for spuds, if i were to chamfer the inside, the spud will have to squeeze down too much. I like a tight fit, but not that tight.
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Unread postAuthor: williamfeldmann » Fri Oct 05, 2007 7:21 am

Unlike most of the others who have posted so far, Every one of my spud barrels have an inner chamfer.

I first sharpen the outside of the barrel like normal to shear the spud into shape. Then I put a tiny angle on the inside of the barrel. Only a couple of millimeter deep in both directions. This will make the spud shear off around 3-4 mm larger than the diameter of the barrel.

It is a bit tighter than normal but I have seen increased power (damage and energy, not speed) from the tighter seal.
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Unread postAuthor: silverdooty » Fri Oct 05, 2007 7:57 am

it doesn't take much of an inside chamfer. i'll use a piece of fine sand paper(220 wet sand) and give it a nice uniform chamfer by knocking the edge down. maybe a mm, not much more. then i'll give it a nice sharp exterior cutter.

tighter taters == bigger bang
bigger bang == more giggles
i've got 70 yr old friends who giggle as much as my 10 yr old granddaughters.
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Unread postAuthor: BigGrib » Fri Oct 05, 2007 11:41 am

silverdooty wrote:tighter taters == bigger bang
bigger bang == more giggles
i've got 70 yr old friends who giggle as much as my 10 yr old granddaughters.


You might be onto something there. When I chamfer the inside it is the whole inside from the very OD to ID and sometimes it is a huge pain getting a spud in but you do definatley get a bigger bang

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Unread postAuthor: jimmy101 » Fri Oct 05, 2007 5:20 pm

I would say that it is "generally accepted" that a small inner bevel will improve the perforamance of a combustion gun compared to no inner bevel.

The outer edge should be beveled first, 30 degrees is good if you can get it. 45 is pretty steep and the spud will tend to split instead of slicing. With a little effrot you can get an edge that is sharp enough to easily slice through a spud.

The inner bevel is only a small amount, and again 30 degrees would be a good angle.

The inner bevel significantly increases the static friction between the spud and the barrel. This is good. It delays the movement of the spud until more pressure has been built up in the chamber.

Too much inner bevel and you have a heck of a time jamming the spud down the barrel.
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Unread postAuthor: BigGrib » Sun Oct 07, 2007 3:07 am

Definatley right about heck of a time jamming the tater down the barrel, definatley gonna have to do a little work now that i have started making a breech loading system
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Yea, that's definitely going to get you at least a tazer.

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