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Re: [taigtools] Drill Chuck Arbor

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  • Tom Benedict
    ... Hey, altogether too happy to get other people into this hobby. ;) This is going to be a little long, so if you re not interested in water rockets, feel
    Message 1 of 4 , Sep 1, 2000
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      > You just HAVE to tell us about 2-stage water rockets!!!! I want one
      > already. MJ

      Hey, altogether too happy to get other people into this hobby. ;)

      This is going to be a little long, so if you're not interested in water
      rockets, feel free to skip it.

      My first introduction to water rockets was one of those little water
      rocket toys with the red and white rocket and a hand pump. You fill it
      about half way with water, pump it up 'till it won't pump any more, and
      release. Whee! Up it goes.

      A friend of mine bought about five of them, and we lost them all the same
      night. Gosh, that was fun. A week later I'd forgotten all about it.

      Not so my friend. He wanted to see if he could build some out of 2-liter
      soda bottles, and went looking around on the web. Turns out there are
      people building these things all over the world, and not just out of
      2-liter bottles. He started building them, and never quite managed to
      stop. About two or three months after we'd played with the rocket toys,
      he invited me out to see a launch. He had a long skinny rocket made out
      of some kind of plastic tube sitting on a launcher made out of PVC pipe.
      He pumped the rocket up with a tire pump, pulled the release string, and
      BANG! It just about disappeared from view.

      I was hooked...

      There seem to be two camps of people who do water rockets. One is the
      school-sponsored event people. Here in the United States the official
      organization is the Science Olympiad, who publishes the rules and regs
      under which they're built. For the most part the rules are to promote
      good sportsmanship and safety (like not having anything metal in contact
      with the pressure vessel.) Science Olympiad events tend to focus
      primarily on hang time, that being something that's relatively easy to
      measure. As a result people focus on parachutes, parachute deployment
      systems, etc. They're limited to 60psi launch pressures, so building high
      pressure vessels isn't their thing.

      The other camp is the unlimited group. No rules, no regs, just don't kill
      yourself or get hurt. Until recently there was really only one event
      here: max altitude. One of the masters in the craft is a guy named Bruce
      Berggren. He holds the current record of 1060 feet above ground level. He
      did it with a two-stage rocket. The bottom stage was made out of 3 liter
      bottles that had been spliced together to form a pressure vessel with
      about a 7 liter capacity. The top stage was made out of a 4 foot long
      fluorescent light tube cover (the kind that are used on shop lights to
      contain broken glass in case the tube gets hit).

      Bruce subsequently tried to break his own record with an even larger
      rocket that had four booster motors, each with a 7 liter capacity, and an
      8 foot tall fluorescent tube cover sustainer rocket as a second stage.
      Problems on the launch pad pretty much shredded the rocket, and he vowed
      never to build one that complicated again.

      Here's where it gets fun...

      Of the people I've talked to who are making water rockets, only two have
      any kind of background in machining. They both own lathes, and have used
      them extensively in their rocket designs. In an odd sort of way, there's
      almost an attitude of, "If you have to apply that much technology to it,
      you're doing something wrong." I don't believe it for a second.

      After explaining that the lathe I'm using costs only a couple hundred
      dollars, people at least relaxed a little. But I haven't seen anyone else
      go out and get one yet. I'm giving them some time.

      With a lathe, though, I've been able to make some stuff that no one else
      has tried yet:

      Custom nozzles - Water likes to have as straight a nozzle as possible.
      Air, on the other hand, wants one shaped more like what you expect a
      rocket nozzle to look like: a double cone. Let's just say I'm glad I got
      a compound slide when I bought my Taig. I haven't been able to
      successfully test the custom nozzles I cut (I wound up blowing the back
      off my test rocket), but if this gives me more altitude, my compound slide
      will be getting a serious workout.

      Hose fittings - There's some advantage to be had from having multiple
      "motors" on the booster stage of a two-stage rocket. The problem is, the
      staging coupler relies on knowing when the pressure in the booster stage
      drops to atmospheric pressure. The only way we've been able to get around
      that is to have the booster "motors" share pressure. Voila, hose
      fittings. (Bruce's record-setting rocket only had a single booster
      motor, so no pressure sharing was involved. That rocket's successor
      relied on having each booster motor let go of the sustainer independently,
      so no pressure sharing was required.)

      Staging couplers - Bruce Berggren came up with a design for a staging
      coupler that's tough to beat. He also designed it in such a way that you
      don't need any special tools other than a drill. Even so, I tweaked the
      design on my lathe and managed to shave off some weight. You don't
      strictly need a lathe for this, but it helps.

      Launcher parts - Most launchers are made from PVC. It's cheap, it's
      locally available, and the tools for working it are easy to use. But
      bring a lathe into the equation, and you have one other advantage on your
      side: PVC is almost trivial to machine. Cutting big chunks of aluminum
      or steel on my lathe makes me worry about chatter. Cutting big chunks of
      PVC is a snap. I have yet to get any chatter, even on sizable chunks.
      The one catch with PVC is that it's very very flexible and will jump out
      of the chuck jaws. Jigs and fixtures that might be optional on an equally
      sized metal part are a requirement with PVC.

      I think the most exciting thing about making water rockets on small shop
      tools is that so few people are doing it, there is almost endless
      unexplored territory to go after.

      Which is where the second (potential) event comes from. A couple of
      people have made water rocket powered cars, but most of these have been
      pretty clumsy looking affairs. (The one exception is a guy in Japan who
      has made some FANTASTIC water rocket cars. But no one remembers his
      e-mail address, so we can't find out how well they work!)

      I started making one. It's not done yet, but it's getting there. Using a
      slightly tweaked water rocket simulator, its got a projected top speed of
      180MPH. I don't believe that for a moment, so I figure 120-150 is a safer
      bet. But I want to make one that will top 200.

      If other people get interested in land speed record attempts for water
      rocket powered cars, the unlimited camp has two events to compete in.

      Gotta love it.

      In case you're interested in getting into water rockets, here are the two
      links I use the most:

      Bruce Berggren's Water Rocket Garage -

      http://www.geocities.com/CapeCanaveral/Lab/5402

      Clifford Heath's Water Rocket Page -

      http://www.osa.com.au/~cjh/rockets

      Bruce has some of the best drawings online, including a full set for the
      rocket he used to set the altitude record. He's also got one of the most
      complete simulators available for download.

      Clifford has an online simulator that uses the same math as Bruce's
      explicit single-stage simulation, as well as the most complete set of
      water rocket links I've seen. He's also the guy who maintains the water
      rocket mailing list.

      Hope you get interested in building these things. They're addictive!

      Tom
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