I intend to make 3 curved rafters for a garden application. Each rafter
needs to be 7ft(L) x4inch(H) x 1-1/2inch(W) finished. The radius of the
curve will be 10ft.
Material will be 1/4 inch external grade ply laminated to make up the width,
glued and screwed over a former. How much "spring back" should I allow for?
I had Resourcinol in my head but a previous post suggests this is OTT for
this sort of application (probably mega expensive too), suggestions
I can probably buy these, but then thats just another learning opportunity
If I didn't miss by a mile, I get that the total drop (assuming the 7'
is the chord length, not the arc) is just under 8". If so, why not
simply scribe the rafter on tuba-12 stock and cut them to shape? You
may be just under 4" depth, but not by much or you could cheat just a
little on the radius if the depth is absolutely critical.
The rest of the frame is conventional timber section which is "tanalised" -
pressure treated with preservative. I was planning to coat these rafters
with preservative spring & fall like I do with the garden shed, furniture
nope. marine ply has glue that will be up to the task, but the
transverse plies still present end grain to the weather, from top and
bottom. water will soak these plies. expansion and contraction will
tear the beam apart after a short while.
Marine ply is not made from rot-rsistant wood though the glue is
_supposed_ to have a mildew retardant additive.
Even if you can find Mahogany-faced marine plywood chances are good
that the inner veneers are poplar.
The most popular marine plywoods are Okoume, Sapele, and Doug Fir.
The latter is probably more rot-restant than the other two.
Unless these are exposed to the weather, resorcinol should not be required.
Understand the new TiteBond III is pretty good for wet, not underwater,
applications, but no personal experience.
Personally, I would use 1/4" solid material such as quarter sawn white
oak rather than plywood for laminating stock.
Don't have a clue about spring back, but close spacing of clamps will
help minimize it.
OP is in UK, I think...although I know they have some "super stores", in
my limited times over the pond I never had the opportunity to
investigate what would be their Borg--although by now, maybe they've
been exported there as well??? It's been some time since I was last
I've posted it before, but my favorite related wreck-related experience
was visiting a chap in his shop--what attracted me was the sign "Joinery
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