From: wcscses2@alfred.carleton.ca (Geoff Hamer)
Subject: Oxy-acetylene bombs & cannons
Summary: Explosive devices I made as a kid.
Keywords: acetylene,bomb,cannon
Organization: Carleton University
Date: Wed, 11 Nov 1992 19:47:36 GMT

Just started reading this group and I thought I post some of the
explosive experiments I use to do as a kid. Please note that I was
probably lucky that I didn't blow my face off a couple of times but
what the hell. Every 13 year old knows he's immortal.

A buddy of mine and I use to have a past time of blowing up mail boxes
in the neighborhood we lived in. (Aren't you glad you never lived near
me eh?). We use to do this by constructing what we called
oxy-acetylene bombs. We would fill plastic bags up with varying
mixture of oxygen and acetylene from the old man's torch. We use to
experiment and see what ratios would make the loudest bang. Counting
off second while holding the torch tip in the bag would usually
suffice. I dont remember the final mixture we would use but something
like 1 second of acetylene and 5 seconds of oxygen would probably be
close.

We use to test our bombs in my Dad's garage by inserting a piece of
speaker wire into the bag with only one strand from each lead twisted
together (an old igniter trick from model rockets). We would then run
the other end to the pos&neg terminal of a battery charger. After
attaching a _long_ extention cord to the battery charge we would set
the bomb off by simply plugging it in. The two wires glow red hot and
break apart with an arc... BANG!!!!

Of course we couldn't carry a battery charger around with us in the
middle of the night, so in order to blow up mail boxes (usually ones
owned by gruppy old people that told us to bugger off during
Halloween) so we needed a fuse. Well, my friends Dad use to pack his
own shotgun shells so this gave us access to gun powder (which,
incedentally we use to make rocket with by pouring it into folded up
pieces of paper.) We made fuses by putting kite string in white glue
and shaking it in a bag of gun powder then hanging it up to dry. It
always amazed me how little acetylene would be required to blow even
the best made sheet metal and wooden mailboxes into pieces. Of course
we did have some morals and I wouldn't blow up boxes with mail in them
but we were finally caught when my (less intelligent) buddy blew up a
guys pension cheque on his own and told his parents who showed him who
to make these things.

With the threat of police involvement we decided that it was time to
move on from bag bombs. It was time for a new game... CANNONS. These
were constructed from ABS tubing (the rigid stuff). The biggest trick
was to find a way of plugging up one end. No amount of tightly fitted
plugs would do. What I eventually came up with was a plastic
connecter ment to join two pieces of tubing together filled with
hot-melt glue and held in place with several screws. What we needed
now was a way of igniting the acetylene without using a fuse or a
battery charger. I ended up stripping apart one of those hand-held
bar-b-q starters that use a piezoelectric crystal to generate a spark
(an old camera that uses flash cubes would probably work too) and
attaching 10 ft of speaker wire to them. I put two screws in the side
of the cannon so that they nearly intersected inside the barrel to
which these wires would attach. 

A suitable projectile (usually a golf ball) would be selected and
stuffed in the end. There were two small holes in side. One for
putting oxy-acetylene in, one for atmospheric air to escape. Once
these holes were covered the cannon could be fired. Our first couple
of shots were disappointing since the golf balls would be shot so fast
we couldn't see them go. We fixed this by aiming it at things (no,
nothing destructive anymore) like barn walls and pieces of ply wood.
Before we quit playing with the thing we were able to shoot suitably
shaped projectiles clear through a piece of 3/4" plywood at a distance
of 10-15 feet.

I think I stopped playing with it after almost blowing my face off
with it. The electrodes in the barrel had a habit of carbon-fouling
since we had to use a rather 'rich' mixture of acetylene in order to
insure ignition. After a mis-fire I blew all the oxy-acetylene out of
the cannon (or so I thought), took the projectile out and stared down
the barrel while clicking the igniter.... BANG!!!! The thing goes off
and everyone who was standing around (I was probably showing it off)
jumped about 10ft in the air. All I ended up getting was a case of
ringing ears for a few hours but I was lucky... any dirty in there
could easily have blinded me.

I'm sure Fire-Marshal Bill would have loved it!

              _
          Mr. Geoff
          Carleton University
          Ottawa, Canada