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Thread: Fit of steel elevator bushings in bronze bearings

  1. #1
    FoxTrotter's Avatar
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    Default Fit of steel elevator bushings in bronze bearings

    I've recently started a 7SS build and am about to assemble the 11060 bushing into the 93021 bearings (which are already installed). The manual says that if the 11060s don't fit into the 93021s (and they don't begin to fit), sand them down. My question: what kind of fit am I striving for? Should the 11060s fit tightly in the 93021s, or sufficiently loosely that they can easily be rotated after insertion?


    Thanks!


    Michael

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    Senior Member aviator79's Avatar
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    Default Re: Fit of steel elevator bushings in bronze bearings

    The ideal is frictionless rotation with no noticable diametral play. It took me a lot of work chucking up the steel bushings in my drill press to get them all to work.

    Also, press the bronze bearings into the elevator before sanding the bushings. When the bearings are pressed in, the ID will compress some, so if you had the steel fit perfectly before pressing, it will be too tight after, and you'll be back to sanding.
    --Brian
    Flying - S7SS

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    FoxTrotter's Avatar
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    Default Re: Fit of steel elevator bushings in bronze bearings

    I've spent some while using 180 (followed by 220 and 400) grit sandpaper on the steel bushings, with no noticeable progress. Bronze is a lot easier to work. Is reaming the bronze bearing a viable option?


    Thanks


    Michael

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    Senior Member aviator79's Avatar
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    Default Re: Fit of steel elevator bushings in bronze bearings

    How are you sanding them? Chucking up in a drill press? It did take me some time and many, many iterations. Change your sandpaper frequently, With patience you will get there. I think reaming the bronze accurately would be more difficult. You definitely don't want them too loose or off-center.
    --Brian
    Flying - S7SS

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    Default Re: Fit of steel elevator bushings in bronze bearings

    Yes, chucked up in a drill press.

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    Default Re: Fit of steel elevator bushings in bronze bearings

    For me, this was a frustrating part of the build so far. Not sure if you have ever flown a plane with worn out control surface "bearings" but the controls chatter and feel super loose, so don't sand to much. Like others have said, spend a lot of time sanding these until they move freely, but have no play. Took me a couple full days doing this until they are right. I am sure it will pay off down the road so you don't have stiff controls.

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    FoxTrotter's Avatar
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    Default Re: Fit of steel elevator bushings in bronze bearings

    Thanks, that helps me to calibrate.


    Michael

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    Default Re: Fit of steel elevator bushings in bronze bearings

    I used my cordless drill and 220 sandpaper. I would sand one half and then the other half. Fingers got hot from holding sandpaper, so I would switch to next bushing until it cooled down. After a few passes, one end finally fit into the bearing, so I knew that I was actually making progress. Once it fit in tightly, I relaxed the pressure on the sandpaper so I didn’t over do it. When it started to slide in with a little resistance, I switched to 400 grit to polish it up. All in all, it took about an hour to get all 7 done. If you double up the sandpaper, it allows you to hold on longer before the finger tips get unbearably hot (that’s when I would move to the next one). When I finished, they looked real nice. Too bad you can’t see them when they are installed.

    There is probably a smarter way to do it, but I like to do things the hard way and find out the easy way later, once the work is done.

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    FoxTrotter's Avatar
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    Default Re: Fit of steel elevator bushings in bronze bearings

    Thanks, Flyboy66, that's basically what I've been doing but progress has been virtually undetectable.

    I don't know if it's this batch of bushings or if it's always like this, but the OD seems way over!


    Michael

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    Senior Member aviator79's Avatar
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    Default Re: Fit of steel elevator bushings in bronze bearings

    Mine were pretty far out too, and FlyBoy66's experience is exactly the same as mine. Can you measure the OD of the bushing and the ID of the bearing? I suspect you just need to put on some loud music and be patient, but I don't want to tell you to just keep at it if you genuinely have a problem with your parts.
    --Brian
    Flying - S7SS

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