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Thread: Plywood differences

  1. #1
    Registered User rheuschele's Avatar
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    Plywood differences

    It's time to order plywood, can anyone tell me the difference between basswood and birch?

  2. #2
    Registered User snaildrake's Avatar
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    Re: Plywood differences

    Quote Originally Posted by rheuschele View Post
    It's time to order plywood, can anyone tell me the difference between basswood and birch?
    Without going to the Forest Products manual for exact numbers, here is a start:

    Basswood: low density, moderate shear strength (at best), high workability with machine and hand tools, virtually grainless, relatively porous - takes finishes evenly

    Birch: high density (> rock maple, >>mahogany), very strong (> mahogany), close-grained, color varies from tan to dark gray/brown, not said to absorb epoxy like mahogany.

    What do you need the plywood to do? -Dan

  3. #3
    Registered User Lucrum's Avatar
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    Re: Plywood differences

    ANC 18 lists Birch as a medium density plywood.

    Other than a general description of Basswood I don't see it in the tables.

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    Registered User 57Marty's Avatar
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    Re: Plywood differences

    Basswood is a very traditional carving wood because the grain doesn't tear or catch when carving. Basswood is very soft, Birch is very hard. Typically basswood is a plywood core a and birch is an outer layer veneer. Other common core in aircraft ply is poplar. Poplar is a more yellow/green in appearance. Overall, poplar is the most dimensionally stable wood out there. Most high end furniture that has plywood in it will use poplar core. Mahogany is the other surface veneer used in aircraft. Mahogany is softer than birch, more red in color. Don't confuse mahogany with lauan ply; they look alike but lauan is Home Depot quality, good for door skins but no good for structural aircraft use. Lots of experience here, 30 years teaching Industrial Arts.
    Marty57

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    Re: Plywood differences

    Mil P 6070B lists Birch (Sweet and Yellow with min Specific Gravity of .58) as a Group I High density plywood. Birch (Alaska and Paper with min Specific Gravity of .53) as a Group II Medium density plwood and Basswood (min Specific Gravity .36) as Group III Low density plywood....

    So it depends on what you are using the plywood for...

    And that's as a plywood by itself (not like 57Marty is mentioning where the Basswood is the core and the Birch the outer plies)

    Hope that helps a little.

    M

  6. #6
    Registered User Dan Thomas's Avatar
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    Re: Plywood differences

    Birch aircraft plywood is immensely strong. I once did some tensile tests on 1/16" three-ply Baltic birch aircraft ply to test my scarf joints, and found that a one-inch-wide strip took 1500 pounds of straight pull to break. I don't think poplar or bass would come anywhere near that. Probably not mahogany, either.

    Dan

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    Registered User 57Marty's Avatar
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    Re: Plywood differences

    Dan,
    Your right about the strength of the plywood;just check out the British Mosquito. That's why the little 1/16" gussets on a rib are plenty strong enough. A friend has a wood wing from a very early Aeronca and some of the gussets are made from cardboard! I think I would replace that with plywood. I guess weight was everything early on. big thing about aircraft ply vs regular ply is there are no voids in the individual plys. That is not true of most ply from the big box stores. Marty57

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    Re: Plywood differences

    Birch wins over basswood in every category except weight.

    Interesting story about a builder deciding to go cheap...he was building a Flybaby and decided to use Luan/doorskin plywood to skin the fuselage. The ply on the fuselage bubbled and warped and warped shortly after applying it and much work was involved in removing the cheap stuff and preparing the surface for aircraft grade ply. There are places to save money on an airplane, but the basic structure isn't one of them.

  9. #9
    Registered User rheuschele's Avatar
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    Re: Plywood differences

    Well, I'm using it for the sides of my fuselage. The plans call
    for 3mm birch. After much discussion with other builders of my
    plane, it seems very rare that any two planes have been built the
    same. Instead of 3mm, I'm considering 2mm at a weight savings of
    approx 5lbs. The basswood would save another 2lbs. One builder has even not included any plywood on the sides. I don't know how that is possible but it seems to work. With all my woodworking experience, I realized that I have never used basswood. I don't even know what it is. I see the birch/basswood is the same weight, but the birch/poplar is 50% heavier. I think I'll be going with birch/basswood.

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    Registered User WonderousMountain's Avatar
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    Re: Plywood differences

    Basswood is the substitute for inconsistent and expensive balsa. I doubt the tree feels this way, but being a plane may not have been it's retirement plan anyway. Basswood is usually used as a core material with birch or something else on the outside.

    I've not heard any problems with using basswood. Fuselages don't need plywood, but who wants to accept a life of bare necessity.

    Wonderous Mountain

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