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Thread: Double acting Double cylinder Oscillator

  1. #61
    Join Date
    Dec 2015
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    Chilliwack, BC, Canada
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    WOO HOOO! ! ! Another fine looking engine. I'm already looking forward to the video.

    You're an inspiration to me Brian. When I stop and consider all the bits and pieces that have come out of my machine shop I realize that they have mostly been tools for the shop or bits for this or that. The actual "projects" that can stand alone have all been things for others or the clubs I'm in. So this fall and winter with the "dark days" I'm going to do my first engine. Not sure if it'll be a steam/air engine or a flame licker. But an engine for sure. And somewhere down the road I want to do a glow ignition engine that can be put into a model airplane and flown. Or perhaps go back to the early model aviation days and do a compressed air motor.

  2. #62
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    Mar 2008
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    Barrie, Ontario, Canada
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    Once I get this all buttoned up you will never get to see this. So--This is the compression spring and nylock nut that pull the flat base on the cylinder tight up against the side of the angle frame to minimize any air leaks. I don't have a lot of room between the angles when fully assembled, but there should be about 0.030" clearance between the two nylock nuts.
    Brian Rupnow

  3. #63
    Join Date
    Jan 2010
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    Kansas City area
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    I like this engine the best of all. I'm wondering if Bellville washers might be a good choice to hold the cylinders in place? You could probably have a shorter stack and more clamping force both at once. I'm sure it will work fine as is, too. Thanks for all the pics!

  4. #64
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    Mar 2008
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    Barrie, Ontario, Canada
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    Everything is back together. It is stiff, but I expected it to be. My butt is kicked for today, but tomorrow I hope to make the manifold and maybe get some air on it. A 1" diameter cylinder at 50 psi will give a force of 40 pounds, and this has two cylinders, so I expect any stiffness will give up fairly quickly with a total of 80 pounds of force acting on the crank arms.
    Brian Rupnow

  5. #65
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    Dec 2015
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    I think the coils will do just fine. Plus they are made and there's room for them even if things are a touch on the tight side.

    Another possibly compact size solution for this sort of requirement would be curved spring washers. Short "travel" but you only need to provide force with no movement. Or a stack of flat and curved spring washers would increase the range of compression. For this size I'm not even sure that they make Bellville washers small enough for this sort of use. But I know that curved spring washers are somewhat more common in the really small sizes and you'd only need one to provide the pressure needed for something like this.

    I only mention it as an option for some future time since you're done, it's done and you allowed for this option to work.

  6. #66
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    Mar 2008
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    Barrie, Ontario, Canada
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    BCRider--Probably Belleville washers would work fine. I never even thought of anything but "compression spring". There is a rather delicate balance here, of having the springs exert enough force that all the air doesn't escape between the cylinder and the frame, and yet not so much force that the engine is too stiff to run. Since it is a brand new engine, I don't know if the stiffness in it comes as a result of spring compression too tight, or just accumulated tolerances on everything. Once I get it up and running, I will decide if I have to take a coil or two off the springs.---Brian
    Brian Rupnow

  7. #67
    Join Date
    Jun 2001
    Location
    North Central Texas
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    Great looking build Brian!
    Taking coils off a spring increases the rate. If you mean removing them for another reason, disregard!

  8. #68
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    Mar 2008
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    Joel--You are correct. Taking coils off a spring does increase the rate.--But--When you compress a compression spring by a given amount, it will give a value for total reactive force. (The pressure a compression spring creates by wanting to "uncompress" itself.) If you want that total reactive force to be less, you cut a couple of coils off the spring. Then when you compress it to the same amount as before, it creates less "reactive" force. Why would I want to lessen that "reactive" force?---To lessen the amount of drag created by the cylinders pivoting on the frame.--As I said before, it's a bit of a balancing act. You want the cylinders pressed against the frame tight enough to not have steam or air escaping at the interface, but not so tight that it creates too much friction for the engine to overcome.
    Brian Rupnow

  9. #69
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    Mar 2008
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    Barrie, Ontario, Canada
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    I have a couple of small single cylinder "wobblers" from early days ten years ago when I started machining. Brass 1/2" bore cylinders and aluminum frames. Never had a problem with them and was tickled pink when they actually ran. Fast forward ten years, and I have built what is a monster double wobbler compared to those early engines. If I have trouble with "galling" of the aluminum under the 1" bore cylinders, I may have to mill away 1/8" of aluminum and J.B. Weld a piece of cast iron or 660 bronze in the area where the cylinders pivot. Someone had suggested that earlier, but I decided to wait and see whether I would need to do it.---Brian
    Brian Rupnow

  10. #70
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    Mar 2008
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    Barrie, Ontario, Canada
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    So folks, here we have it. It runs just as well as I had hoped it would, and will self start with the crank throws at 90 degrees to each other. It runs on about 10 psi of air. This engine has the fewest parts of any engine I have ever built. If anyone would like to build this engine, I sell a complete set of plans for $25 Canadian funds. You can contact me at brupnow@rogers.com
    https://www.youtube.com/watch?v=AllNZnfLpZc
    Last edited by brian Rupnow; 06-13-2018 at 11:02 AM.
    Brian Rupnow

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