|
|||||||
|
|
|
|||||
|
|
|||||||
Here are some things
that I have learned about building pneumatic air cannons.
This page will be added to as regularly as I can.
Threaded conections:
I have tried many times to get an airtight seal with teflon tape
on a 4" threaded conection. Out of a dozen tryed only once
did it work and it was so tight that I was worried that the pvc
would crack. Later I tried useing silicone on the threads,not
intending to ever unscrew it again.... well as things go I
desided to open the gun. so I clamped the handle in a vise and
got ready to twist really hard on the cleanout cap to open
it..... It came right off!
It should be noted here that the silicone acts as lubricant on
the threads before it cures, so care should be used so as not to
over tighten the fittings and crack them.
Glued Connections
Hey, I have a question about glueing the Barrel to the Bell
Reducer. Since I'm making kind of a "Miniature Version"
(1 1/4 Outer Chamber, 3/4 Barrel). I had to use a Bushing and a
Coupler to act as the Bell Reducer. Now, I filed off the ridge of
the Bushing so the 3/4 Barrel can now go through it. But, I was
kind of puzzled on how to glue the barrel into the
Bushing/Imitation Bell Reducer. I was thinking to just pull the
barrel out 3 inches (The 3 inches being the part of the barrel
that actually goes into the Bushing. And applying glue there and
just pushing it in. But, if there is a better way, please
enlighten me. Thanks a lot!
Another good question.
First, some things should be done to get as good as possible
glued joint
from this "modified" part <the bushing>.
1. You should remove only the ridge in the bushing
and not any of the
inner wall that is to be glued to the pipe. The fit should be as
tight as
possible. If it is not tight , it will leak or blow off. I marked
my pipe
and used a pipe larger than my barrel to slid down and
"hammer" the bell
adapter down into place. When you apply the glue , the glue will
act as a
lubricant to help the bushing slide down the pipe... so be
careful not to go
to far down .... it might stick before you can put it into it's
proper
place.
2 I would add a small bevel to the leading edge of the
bushing where the
barrel will go in. This will help to get the glue into the joint
and not be
scraped off by a sharp edge .
3. It won't hurt to prime a little more of the barrel
than will go into
the joint.
4 Mark you pipe so you know where to stop.
4.b When you know just where you want the barrel to stop when you
slide it
into the bushing , temporaraly put a hose clamp on the barrel so
that when you
apply the glue and bush the barrel into place it will stop when
the hose clamp
hit the bushing. Now the pipe will be glued injust the right
spot.
5. Slid the barrel into the bushing, but stop about 2
" before it is in all
the way. What you want to do is put the glue on the pipe so
that when you
slide the pipe into place it is going into the joint the
direction it would
go if you had not cut the ridge out and you where sticking
the end of the
pipe into a regular bushing. As you probably know the bushing has
a tapered
hole to get tighter as the pipe goes in. So it is very important
which way
the glued part go together.
6. If you can, before the pipe gets stuck, give it a 1/4
turn to help
spread the glue.
7 It is recommended by the pro.'s that you assemble
glued joints while the
primer and glue are still both wet.... you have to work
fast. I prime all
part first. Then I place the glue and primer and the two parts to
be glued
in place on my work table within easy reach... when I am
ready to glue, I
apply more primer to both parts < a lot so it stays wet>
then I apply glue
to both parts and quickly assemble them and hold till they will
not slip
apart < about 15-20 sec.>
Keep all this in mind an you should have no problems...
Oh yea, keep a rag or two handy to wipe off excess glue and your
hands.
Barrel Extensions, the correct way.
As some of you may have noticed, that when
using threaded adapters that the ID of the adapter is actually
smaller than the ID of the pipe.
So here is how I think a barrel extinction could be made.
Let's assume that you want to add to the length of you gun that
has a 2" barrel.And take it off again maybe for storage or
transport.
1. Build an assembly like this.
2" x 3" adapter bushing,3"
coupler,3" threaded female adapter,3" male threaded
adapter, 3" coupler,2" X3" adapter bushing.
You will need a 2" REPAIR coupler not a regular coupler. A
repair coupler will slide over a pipe with almost no resistance.
This is important. Remove
the "stop" in each of the 2" x 3" adapters so
they can be slid down the 2" barrel several inches by
whatever means you have available to you. Put the first have of the assemble with the female
thread on the barrel open end out. slide down till flush with the
end of the barrel. put
the other half on the barrel extension open end toward the gun. glue the 2" repair coupler
on barrel extension inside the 3" assemble. but place the
coupler so that only half of it is on the barrel extension, the
other half will slid over the barrel on the gun ,BUT NOT BE GLUED
ON, it is for alignment only. When the glue is dry on the 2" coupler sled the
3" assembly toward the coupler as far as it will go. Thread the 3" adapters
together. push the
barrel extension down till it hits the 2" barrel and the
coupler is over both 2" pipes. Mark the 2" pipes where the 2"x 3" adapts
are<at each end of the assembly> Temporarily place a 2" hose clamp on the 2"
pipes as close to the assembly as you can. these will help to
keep the assembly from sliding to far on the pipe when you glue
it into place. Unscrew
the assembly and verify that the 2" coupler is sliding over
the barrel attached to the gun, if not adjust as necessary. Slide assembles down pipe
prime pipe with primer for gluing. NOTE:prime the ID of the 2"
x 3" adapter before sliding onto on the pipes. Add glue to pipes<on at a
time> and slide assembles back up against hose clamps.remove
clamp and wipe off excess glue. Let glue dry,enjoy. Note: If there is a small ridge of glue inside the
2" coupler , grind an angle or bevel on the OD of the barrel
to clear this so that the ends of the two 2" pipes will meat
flush. the 2"
pipes must be flat and square. I am thinking that a regular 2"coupler could be
used IF you sanded down the OD of the barrel so that the fit is
not so tight that it binds. It you want to make a permanent connection. Use a regular coupler. A pressure
coupler is longer that a non pressure coupler... either should
work, but use the pressure coupler if you can get it. You need to bevel the OD of both
pipes a small amount to clear the stop ridge in the center of the
coupler so that the pipes do not have a small gap between them
that can hang on projectile. or just use a repair coupler...Just be sure not to use
so much glue that it squeezes out into the ID of the pipe and
hardens there<not good> putting a bevel on the OD of the
pipe also gives the excess glue a place to go so it does not end
up on the ID of your pipe. I have not actually built this<yet> and there may
be some unknown problems with it.Just check everything before
gluing and use some common sense and fore thought...... a
little for thought goes a long way to preventing unnecessary
misery. This
is all open to corrections and opinions
Patrick Parsons.