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A water rocket is a type of model rocket using water as its reaction mass. The pressure vessel (the engine of the rocket) is constructed from thin plastic or other non metallic materials (usually a used plastic soft drink bottle) weighing 1,500 grams or less. The water is forced out by compressed air. It is an example of Newton's third law of motion.

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Widening an out-of-spec soda bottle nozzle

Discussions about rockets, construction materials, adhesives, nozzles, nosecones and fin design.
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Widening an out-of-spec soda bottle nozzle

Post by anachronist » Fri Jun 09, 2017 1:22 am

So, I was in this Japanese grocery store near to where I live, and I found this bottle of Calpico soda (called Calpis soda in Asia). I bought it because of the nice aerodynamic shape, but the soda turned out to be pretty tasty too, even though it looks like carbonated milk. I've tried the uncarbonated Calpis and found it vile, but the carbonated stuff is pretty good.

The bottle is 1.5 liters, but it's as tall as a 2-liter bottle, and narrower, with a nice taper toward the neck. It's similar in shape to the rocket that currently holds the WRA Class D record; that's also a 1.5 liter rocket.

The bottle, however, is strangely made of two pieces rather than a single piece of plastic. The neck looks like it's made of HDPE, bonded onto the PET bottle body. That seems needlessly complicated when one-piece bottles are easy to make, but whatever.
The outer profile of the bottle neck meets the international specs (see https://www.bevtech.org/assets/Committe ... 253-19.pdf for the details), the inside of the neck does not. It may be hard to tell from the picture, but the wall of the neck is thicker than a normal bottle neck, by nearly a millimeter it seems.

The inside of a bottle neck should be 21.74 mm (which we round up to 22 mm). This bottle clearly has a smaller inside diameter.

Needless to say, a 1/2" PVC launch tube won't fit.

Does anyone have any ideas how I might get a launch tube in there? I can't seem to find any reamer tools the right size, and the ones that are close are quite expensive. Reaming the hole would probably be easier than trying to sand down a PVC pipe to fit.
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