Subject: Re: [baidarka] laminating [was: Holsclaw bender]
From: Peter Chopelas (pac@premier1.net)
Date: Tue Oct 14 2003 - 21:52:40 EDT
Paul wrote:
>
> Do I remember from a past post that you make ribs up of laminations,
rather
> than steam bending? If so, can you explain your process?
sure, I have steam bent too, but it is difficult to get good quality wood
from salvage sources, so I find laminating more productive.
I find that I can get the exact shape I want this way too, I use it make
both ribs and real light deck beams. I have also considered using for the
bow piece, just to save weight.
I take 3/4 inch plywood or particle board, scraps of course, and cut the
shape I want to get, minus the rib thickness (you can also make a "female"
jig, which means the shape should be exactly what you want the outside of
the rib or deck beam to be). With a number of large holes drilled around
the edge so I can get clamps in them. I rip fairly clear strips of wood
from my stock into about 1/8 or 1/10 in think strips (you need thinner
strips for small radius bends, and you can get by with thinker ones for less
severe curves). Perfect grain is not as critical since you will try and
overlap any defects into the build-up, effectively canceling any weakening
caused by grain defects. Though it is most important that the outermost
layers be as near perfect as possible, so save the longer and clear tight
grained veneers for the outer layers.
I then just clamp them up with polyurethane glue (keep it out from between
the part and the jig, or you will glue the rib to the jig!). I mostly use
the spring clamps because it is faster, though sometimes on the tighter
bends I need screw clamps to keep the stack-up tight. No need to hurry, you
just keep adjusting the clamps and stack-up until everything lines up the
way you want and you get all of the gaps out from between the layers. You
can even wrap the assembly with bungy cord, or simply weights, if it is
difficult to get a clamp in the right place.
After it dries overnight, it comes out of the jig, almost perfectly shaped
with no spring back. It just takes a bit of light sanding to get the excess
glue off and round the edges. Other less expensive glues will work too
since the glue loads are actually quite small.
I use Doug fir, because it is very strong and easy to get, though I have
thought it would save some weight without loss of strength to only use the
DF on the outer layers, and use something real light for the inner layers,
like low density Western Red Cedar.
On the deck beams I laminate in between the layers wood wedges at each end
to thicken it to give me enough width to attach dowels through the gunwales.
I leave the ends a bit long, and them trim them to the exact compound angle
of the gunwales using a simple angle tool and my table saw.
They come out really clean and "high-tech" looking, yet retain the natural
look of wood. And without all the trial and error fitting of "grown
lumber". Including the jig making, I think it saves time overall. Once you
have developed hull shapes you like, building the next one becomes much
faster. And since you can use almost any size and type of scrape wood, you
save a lot of money too.
You can also alter the shapes of the jigs some by placing shims or spacers
in the right places to get the new shape you want. I also find that putting
a thin layer of foam or thick fabric padding between the jig and the
laminating layers makes the clamp-up stay in place better and smoothes out
any bumps in the jig or caused by varying stiffness in the laminates.
You have a much better opportunity to get the hull shape the way you want it
since it all comes down to how you lay-out the shape on the scrap wood you
will make the jigs from. You simply take your time and keep adjust it until
it you get the shape you want. Of course it is important you cut each one
out symmetrical, so a bit of sanding to adjust it is to be expected. I
trace the shape on paper and flip the jig to check symmetry.
It is not that complicated nor exotic. I really like building hulls this
way, and I am considering building a small sail boat using laminated frames
and deck beams, and perhaps even the keel. And to save all the planking and
caulking, doing a skin on frame hull with the heaviest polyester fabric I
can find.
Good luck.
Peter
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