Looking for help with cutting balsa fins at an angle

Discussion in 'Techniques' started by Bill S, Jan 29, 2020.

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  1. Jan 29, 2020 #1

    Bill S

    Bill S

    Bill S

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    I'm getting ready to start on my scratchbuilt UNN torpedo, and I have a problem. I have fins that have a central crosspiece, with two pieces attached at the ends at an angle. I have no idea how I am going to join the pieces. I really doubt I will be able to use a sanding block to get all the angles correct. Is there a better way to cut the pieces at the proper angles so they align correctly? See rear view picture. fin config.png
     
  2. Jan 29, 2020 #2

    David Schwantz

    David Schwantz

    David Schwantz

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    Make aaaa jig to sand them. Long snding block held at correct aaangle and the part laying flat on table. Can sand them all to same angle. You only need to sand either the central parttt or the ends, not both.
     
  3. Feb 13, 2020 #3

    jqavins

    jqavins

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    Joseph Avins TRF Supporter

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    If you don't sand them both then the thicknesses won't match and you'll want to do something else for a nice finished look. Splitting the angle and sanding all faces seems simpler to me, but you can go either way.

    If you're open to it, there is a third way. Do you actually want the angles, or are you approximating a circular arc? Would you be happy with a circular arc? If so, you could bend the pieces around a mandrel of some sort; there's likely either a body tube or pipe size that would work nicely. Bending balsa is surprisingly easy, I hear from others.
     
  4. Feb 14, 2020 #4

    Bill S

    Bill S

    Bill S

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    I actually need the angles to better match the original source material.

    I haven't made any headway on this project, other than to order some of the parts, but I'll get to it eventually. :)
     
  5. Feb 14, 2020 #5

    neil_w

    neil_w

    neil_w

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    I'll also go with a jig and sand, and I would only bevel one piece on each joint. The extra thickness that Joe mention would be on the inside, hardly visible.

    I have not had good luck trying to cut a bevel onto balsa pieces, but it is possible that you could do that with a jig as well (and then do some clean-up sanding).

    In such cases, what I *always* do is start making test pieces until I'm happy with the process, and then build for realsies.
     
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  6. Feb 15, 2020 at 4:41 AM #6

    caveduck

    caveduck

    caveduck

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    That's pretty much exactly the same thing as putting dihedral in glider wings, and it's pretty easy (with a little practice) to just use an angle fixture and flat sanding block to do it. Personally I'd sand both sides because I find it easier to make them match when I do it that way. I haven't looked recently but a long time ago you used to be able to find wing dihedral fixtures in the model airplane world that had adjustable angle and would clamp the pieces in place for sanding. Most of them were too large though - for this you'd need one designed more for handlaunch gliders.
     
    Last edited: Feb 15, 2020 at 4:47 AM
  7. Feb 15, 2020 at 11:35 AM #7

    Bill S

    Bill S

    Bill S

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    Caveduck, thanks for the idea. I'll look into that.
     

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