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Drilling out spar attach fittings

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  • Drilling out spar attach fittings

    Simple operation but critical -

    I'm getting ready to mount my spars into the framing jig and not sure if I should drill out the bolt attach holes with a drill press or by hand. Currently mine are #30 thru, and I'd like to drill them out to no more than #10 (3/16) for now.

    Drill press will need extra setup effort to ensure the spar is perpendicular to the spindle. Hand drilling would fully rely on the guiding of the pilot hole. Given this is half inch thick, I'm not sure which is less prone to error. Thoughts?

    Thanks!

    Capture.JPG

    Mark
    Scratch building Patrol #275
    Hood River, OR

  • #2
    My suggestion would be to go with the hand drilling using your drill with the bubble level. The pilot hole along with the bubble level should help guide it though straight. I have had some challenges getting the drill press precisely aligned when upsizing holes.
    Karl
    Bearhawk Bravo #1508B - Scratch Build (wings)
    Northern Idaho

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    • #3
      If your confident in your pilot hole then I’d say hand drilling would be fine. Step up slowly in size. Might consider straight flute bits or something that doesn’t wander like regular bits.
      Scratch Built 4-place Bearhawk. Continental IO-360, 88” C203 McCauley prop.

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      • #4
        An alternative is to take a block of aluminum at least 1" tall. A flat, level piece. Then through drill it with your drill press with a couple sizes you might need like 3/16 & 1/4. Then it can serve as a kind of drill guide to keep the drill bit straight. Mark

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        • #5
          Consider what rework options you have if the hand drilling option goes south. At a minimum you would have to remove and replace the root fittings. Then consider the possible damage done during that process and the rework options. At a minimum use a drill block, I would use a drill press. Consider the time to set up the drill press/spar interface to drill the hole against the time required to do the rework. The old saying" there's never enough time to do it right, but always enough time to do it over" applies. Bob recommends 1/4" on the main spar. Just my .02. Good luck. Let us know how it comes out.
          Gerry
          Patrol #30

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          • #6
            Thank you guys! The goal is to prevent a rework, and I'm not convinced a drill press would necessarily be without it's own risks. The drill block might be the way to go.

            I'll work with some scrap samples and see what works best.
            Mark
            Scratch building Patrol #275
            Hood River, OR

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            • #7
              I'm leaning toward drill press after all. Chucking a #30 drill rod should give pretty accurate alignment to the existing hole. But I do have a follow-on question, especially to those who have mounted their wings to the fuselage:

              Would you advise going all the way to reaming the full 3/8" hole, or slightly under, now while I have the ability to use a drill press? If I just go up to #10 now, I can't imagine getting a drill press in position on the completed wing. My thought is to attach the fittings to the wing first and then weld to the fuselage when the wing is in position. I do not plan to drill out the fittings until that time. I recall there are some threads on this subject, pros and cons.

              Thanks!
              Mark
              Scratch building Patrol #275
              Hood River, OR

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              • #8
                I welded and machined this jig and bushings that allowed me to get a very accurate alignment and hole. It took a lot of stress out of the drilling process. IMG_1460[1].JPG

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                • #9
                  How about some tool usage instructions for that jig.
                  Gerry
                  Patrol #30

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