Picture of A Coaxial Golfball Cannon
This is a instructable for my coaxial golfball gun, or any coaxial spudgun. If you're wondering, a coaxial is where the barrel is inside the chamber, much like a piece of coax cable for your TV.
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Step 1: Safety

Picture of Safety
All spudguns and launchers are dangerous, and should be used in a safe manner in accordance with your local laws and regulations. Using them in a unsafe manner may lead to injuries or even fatalites you have been warned.

Step 2: The operating principles

Picture of The operating principles
A coaxial spud gun consists of a barrel with the pressure chamber surrounding it. Like a piece of coaxial television cable, The valve for a coaxial is either a diaphragm or piston(this project uses a piston)The piston seals up against the edge of the barrel that is contained in the chamber section when air is compressed is behind it. Channels or holes in the edge of the valve allow the air to pressurize the section of the chamber infront of the valve. When fired the air pressure behind the valve is vented through another valve, the piston is then forced back by the greater air pressure infront as the air pressure to the rear decreases, unsealing the barrel allowing the air to flow down the barrel firing the payload.

Step 3: The parts

Picture of The parts
You can get all the parts for just about $45-50usd
All fitting and pipe are schedule 40 unless stated.

2x4" adapter 4.50
4" cleanout and cap 4.00
4'feet 4" pipe hardwall pipe 6.75 (foamcore this is NOT pressure rated)

4' section 2inch schedule 80 pipe donated (est $15)
4' section 1 1/2 inch SRD-21(class 200 pipe) donated (est $2.50)
(you can't get is pipe at home depot/lowes, try a plumbing supply store Near pittsburgh try PipeCo in leetstale,PA)

2x pipe test caps 0.50 each
a section of scrap 3" pvc
a mouse pad

Filling valve:
(already had all parts below)
Shrader(tire) valve 1/4NPT (est $3.50)
Pressure gauge 1/4NPT (est $4.00)
Ball valve 1/4NPT (est $4.00)
Four way coupler 1/4NPT (est $3.75)
1/4NPT thread tap (est $5.00)

PVC Primer (est $3.00)
PVC Cement (est $4.00)
15minute epoxy (est $5.00

Ianhtaylor5 years ago
Wait the holes are drilled at the edge of the piston the part that goes over the center 3 inch pvc rite?
Mmm... don't know spudguns at all, but military technology definition- "coaxial" is most definitely a term for secondary weaponry or multiple systems or barrels linked in aiming along the same 'axis' of fire. Traditional tank layout, turret MGs being 'coaxial' are aimed by the entire turret momvement, often in the exact same mounting as the main cannon; they cannot be aimed seperately from the the '-axial' it shares with whatever weapon is the 'co-.' Mebe DeathBlade is just better at making sick improvised weapons and instructables than goofy descriptions that are irrelevant anyway.
uhhh... they're the same, in a coaxial airgun, the barrel is on the same axis as the air tank. for military equipment it's the same, just the barrel isn't inside, it's next to it...
MrCrowley7 years ago
Why the hell are you using DWV in a 4" piston valved pneumatic?
Derin MrCrowley6 years ago
yea dwgv is full crap
unless it's LIEK A BOMB, W00 W00!!!!!!!!!!
The best part is the dangerous DWV that could explode at any time and kill you! isn't that great!
...with a laser pinter to increase accuracy..........from 5 feet away.....
finnster7 years ago
re dots don't increase accuracy they just make it easier to aim
Cadaoryn7 years ago
Your mouse pad has an air tight seal? Dang that is very clever and way easier to get than neoprene disks!
good details, i made one of these but on a much MUCH larger scale. the diaphragm doesnt work well when its large and under high pressure though.
the diaphragm should work exactly the same no matter the diameter or how high of a pressure it is under, it's your diaphragm that is bad, doesn't mean that because it doesn't work, physics wont allow it to work.
mrpages7 years ago
I've never heard that definition of "coaxial" before, and I can't find anything to back it up. Can you link to something? A coaxial weapon is one that is alongside the main gun of a vehicle, like a machine mounted beside the main gun of a tank. It fires in the same direction that the main gun is aimed (along the same axis) hence, coaxial machine gun.
DeathBlade (author)  mrpages7 years ago
It could be 'coaxial' in the way that is similar to coaxial cable, a conductor(barrel)is surrounded by the shielding and insulation(chamber)

In a coaxial configuration, the barrel is placed in the center of the chamber, and the breech end is near the chamber endcap. The design makes a very compact and rather nice looking launcher, since part of the barrel is enclosed in the chamber.
DeathBlade (author)  DeathBlade7 years ago
A coaxials chamber and barrel are also in the same axis to that is also a workable definition.
Those have parallel axes while these pipes actually share the same axis.
Yes, I understand why the term May be co-opted to apply in this case, but he is using it in a way that I have never seen before and can't find any other use of. His definition "in case you are wondering, a coaxial is where the barrel is inside the chamber" implies that this is a known term, but I can't find it anywhere. It seems he just made it up. I'm not necessarily arguing with is definition, I've just never heard it before and wanted some backup.
You mean you've never heard coaxial in terms of a spudgun-style shooter? He didn't make it up, there are lots of coaxial shooters out there.

spudfiles definition
Awesome, thank you. I never thought that it might only apply to spudguns, so I didn't specify that as I googled. Thanks again!
I think I should upload instructions for my propane potato cannon. That thing left a dent in a tree and when I fired from 10 feet away. Too bad the launch it competition's over. Nice work. I may try making a silencer using your coaxial technique.
Coolbreaze7 years ago
Nice gun. BTW that is no MICROMETRE that is a Vernier Caliper....big difference lol =)
Exactly what I was going to say, but it is clear what is meant.
DeathBlade (author)  willofgod7 years ago
I know I always mix those up, kind of how I sometimes call my garage a refrigerator.
how does the air get passed the piston to fill the gun?
DeathBlade (author)  WesDoesStuff7 years ago
By drilling one or two small holes in the edge of the piston, or if the piston is loose enough right around it.