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fredfighter@spamcop.net wrote in news:1169587980.886995.205400
@s48g2000cws.googlegroups.com:
>
> Mustardbuilder wrote:
>> fredfighter@spamcop.net wrote in news:1169496475.404255.84720
>> @m58g2000cwm.googlegroups.com:
>>
>> > ...
>> >>
>> >> Dunno, that's what I was asking. I have laminated two pieces of ply
>> >> together before, just was wondering if it was practical or
advisable
>> to
>> >> do it curved.
>> >
>> > Laminating a curved piece is, if anything, better than laminating
>> > a flat piece, and also better than using a single piece.
>>
>> Yeah, that's what I reckoned.
>> >
>> > If you laminate it on the curve before the glue sets the
>> > laminated plywood will be pre-stressed to the desired curve.
>> >
>> > You do not need a mold, you can attach one piece, let it set,
>> > then glue the second piece over it.
>> >
>> > Regarding the veneers, the laminated piece should be symetrical.
>> > If the pieces have an A and a B face, they should be laminated
>> > ABBA or BAAB, not ABAB or BABA. The grain on the new front
>> > and back face should be parallel. I would put the A faces out, ABBA.
>>
>> Well, the do not really. This stuff is so fine it's beyond belief. For
>> instance the 1/4 birch IU have is 12 ply and is one direction on one
>> side and the other on the other side, so it doesn't much matter which
>> way you put it on.
>
> Aha, I bet that is exactly why they make it that way. Plywood with
> the grain on the front and back parallel is 15% stronger (or is it
> stiffer, I do not remember) vs bending across that grain. Made as
> you describe, it is more omnidirectional in stiffness.
>
> If I were to laminate it for the wing walk, I would do it with the
> outer face grain (outside and inside) parallel to the spar
> It should curve better that way and be a bit stiffer--like the
> way plywood is laid over joists.
OK, that makes sense. This stuff is pretty stiff as it is which is why
i'd prefer to make it out of two laminated pieces.
>
>> >
>> > But I think aircraft and marine plywood is supposed to have A-grade
>> > veneers front and back, right?
>> >
>>
>> This stuff has a grade all the way through..
>
> Over on rec.boats some people say they have found marine
> ply with voids in the interior plys.
>
Yeah, i think that's allowed in marine. This stuff is aircraft grade and
I have cut up quite a bit of it into small pieces. I have never found even
the tiniest spot in it. Bit of sworl on the outer faces from time to
time, but nothing even approaching what you'd call a knothole..
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Re: Wing walk ply question.
