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  1. #1
    Join Date
    Dec 2014
    Location
    Tasmania
    Posts
    102

    Default Water rocket nozzle

    Just completed this tricky little project.

    A friend approached me recently asking for a tap fitting but with soft drink bottle threads inside. He builds water bottle rockets with his son and they use the tap fitting as both a nozzle and a means of launch control, once the pressure is right they pull a lever which disconnects the hose fitting and the rocket flies. But their system to interface the tap fitting to the bottle with glue was not lasting very long and prone to failure so he asked if I could turn this up from aluminium on the lathe. Easier said than done! It turns out that soft drink bottle threads are their own unique standard of 27.43mm x 3.18mm and so you cant actually precisely cut that thread pitch (at least on my old Hercus model A lathe). But I thought well lets see which thread is the closest, and its damn close to 8 tpi so I went with that. I also had to grind a custom profile single point threading bit from HSS to match the bottle threads. Internal threading for me is hard enough and not to mention that even with the back gears engaged 8tpi is quite an aggressive thread, especially turning into a blind hole with very little room for over shooting! I ruined it on my first and second attempts but 3rd time was the charm. And the bottle screws in very nice and snug indeed. I found that threading inwards, stopping the lathe and reversing the boring bar back out was the way to go.

    The part has not been tested on a rocket yet with high pressure but it clicks snugly onto my garden hose and is water tight at mains pressure with thread tape so I think it should be fine.

    20220427_121519.jpg

    20220502_140824.jpg

    20220502_140924.jpg

  2. #2
    Join Date
    Aug 2011
    Location
    Melbourne
    Posts
    4,779

    Default

    Thats ace!

    I've got to see the end results. You gotta post it on YouTube.

    Simon

    Sent from a galaxy far far away
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

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