Date: Fri, 19 Nov 2004 12:52:10 -0500

Author: John Cockman

Subject: Re: vacuum bazooka

Post:

>Have you tried taping the center
> seam with packing tape of duck tape?

I meant *instead* of duck tape.

At one time, I had a leaky valve that caused the demo to be unreliable.
There would be a loud bang, but the ball would barely roll out the end. If
you are getting a "phhhttt", then you have a really big leak.

I use a thin packing tape. It never fails. The noise is loud, and the ball
strikes the opposite wall of the lecture room hard enough to crack and dent
the ball.

My current arrangement (around 180 mph) will crush an empty soda can and
destroy the ball, and I am hoping that the 40mm balls will be fast / hard
enough to go through.

John



----- Original Message -----
From: "Roger Boyce"
To:
Sent: Friday, November 19, 2004 9:57 AM
Subject: Re: vacuum bazooka


> Thanks everyone. I am looking for better than 99.5% success. I give the
> big buildup put on the ear protection, poke the hole and instead of the
big
> bang and the can getting ripped to shreds, it goes phhhttt. Makes me look
> bad.
>
> I have tried all of the different seal materials. While testing a heavy
> packing material and testing for leaks, the material failed while my hand
> was in front of the muzzle. The ball hitting my hand was like hitting it
> with a hammer. The ball split apart scratching and bruising my hand in
> several places and smashing a finger nail.
>
> If the pump is sufficient to work 80%, it should work 100% so I am ruling
> out the pump. Since I often must reload for a second show I have a
concern
> about bits of tape being carried down the pipe. To make that less of a
> problem, I have been placing a small piece of paper towel on the sticky
> part of the tape so there is less chance of tape sticking inside the
> pipe. When I am through for the day, I swab the inside of the pipe with
> alcohol and spray WD 40 in the pipe and swab it out again with a clean
> swab. I'll try a single 5 foot length but I want lots of noise and
> destruction, two elements of a successful road demo.
>
> At 08:32 AM 11/19/2004 -0500, you wrote:
> >Hi Roger,
> >
> >My success rate using thin packing tape is 100%. No vacuum grease, no
> >machined ends, and no external fittings. Have you tried taping the
center
> >seam with packing tape of duck tape? Or better yet, just use a four-foot
> >vacuum cannon while on the road.
> >
> >The projectile velocity of my five-foot cannon is less than 200 mph --
not
> >fast enough to break a can. However, I haven't tried it yet with the
40mm,
> >harder-shelled balls.
> >
> >John Cockman
> >
> >
> > > Roger Boyce wrote:
> > >
> > > > What is the success rate people are having with their bazookas? I
have
> > > > suspended taking mine on the road because it only works about 80% of
> > > > the time. My hearing is not good enough to hear leaks is a big
> > > > problem, I'm sure.
> > > >
> > > > I use the packing tape and I have machined end fittings to allow
more
> > > > surface area for the tape to stick to. To allow it to be portable,
it
> > > > is in two, four-foot pieces. One length has a coupler cemented in
> > > > place. When I connect the two pieces, I use vacuum grease and wrap
> > > > duct tape around the connection that is not cemented. It is an
awesome
> > > > road show demo but a demo that is inconsistent in that environment
is
> > > > practically useless.
> > > >
>
>
From rogerk@csufresno.edu Fri Nov 19 13:03:20 2004

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