Bending 1/4 " marine ply
M. Ernst
Can 1/4" marine ply be bent on very tight turns just by soaking in water or
does it need to be covered in boiling water or steamed?
Thanks for the input.
Martin
Foster Price
> Can 1/4" marine ply be bent on very tight turns just by soaking in water
or
> does it need to be covered in boiling water or steamed?
Heating the ply with a heat gun (paint-stripper) can work just as well as
"wet" heat, you just need to be careful not to burn it. The biggest factor
in bending ply is to check the "balance" of the plies, e.g. a 6mm ply
composed of 3x2mm layers will be unbalanced, and very difficult to bend in
compound curves. A 6mm ply of 3x1.5mm layers and 2x0.75 mm faces will be
"balanced" and much easier to work with. We have found this to be
especially important in heavier plywoods e.g. 9mm and 12mm
Good Luck - Foster Price
Classic Boatworks of Maine
Plywood does not make too tight of a turn due to the cross grains in the
plys. How tight of a turn were you hoping to make?
M. Ernst <mer...@istar.ca> wrote in article
<y%081.30$Am4.4...@NewsRead.Toronto.iSTAR.net>...
> Can 1/4" marine ply be bent on very tight turns just by soaking in water
or
> does it need to be covered in boiling water or steamed?
>
Bateau2
In article <y%081.30$Am4.4...@NewsRead.Toronto.iSTAR.net>, "M. Ernst"
<mer...@istar.ca> writes:
>Can 1/4" marine ply be bent on very tight turns just by soaking in water or
>does it need to be covered in boiling water or steamed?
>
>
If you plan to use resin, epoxy or fiberglass, at any point during the
building, do not get your plywood wet. Here are some figures that we use:
max. bending radius along the length of the panel: 150 cm or 5'
across the panel: 60 cm or 2'.
Now, this is for fir 3 marine 3 plies.
- 5 plies is stiffer,
- Okume bends easier
Lauan bends very easily . . .
If it still does not work, for epoxy-plywood boats that will be fiberglassed,
to kerf is the way to go. This means that you cut some "grooves" in the ply, on
the outside of the tight radius.
All this is about bending, not compounding. If the boat has not been properly
deisgned, you can push and pull all you want . . .
Jacques Mertens - Boat Plans OnLine
http://bateau.com
Bill Kreamer
Kerfs on the INSIDE, yes?
Bateau2 wrote:
> (edit)
> - 5 plies is stiffer,
> - Okume bends easier
> Lauan bends very easily . . .
> If it still does not work, for epoxy-plywood boats that will be fiberglassed,
> to kerf is the way to go. This means that you cut some "grooves" in the ply, on
> the outside of the tight radius.
> All this is about bending, not compounding. If the boat has not been properly
> deisgned, you can push and pull all you want . . .
>
> Jacques Mertens - Boat Plans OnLine
> http://bateau.com
--
Bill Kreamer
129 Miller St. phone: 207.338.9513
Belfast, ME 04915 email: kre...@mint.net
Bateau2
In article <35621B25...@mint.net>, Bill Kreamer <kre...@mint.net>
writes:
>Kerfs on the INSIDE, yes?
No, on the outside of the panels. For some other parts, like inwales, we
sometimes kerf on the inside.
Glenn Ashmore
> Maybe this works for you but common sense says: outside layer is
> under tension, inside layer under compression. Wood is much better
> under tension so by cutting your kerf outside you are cutting away
> the stronger part of the bend.
Kerf bending 1/4" is hard to control because the width of the kerf is so large
compaired to the thickness of the wood.
For thicker material, the procedure is:
1. Cut a kerf on the back side of the panel about 3/4 of the thickness at the
beginning point of the curve.
2. Flip the panel over on a flat surface and bend it until the edges of the
kerf touch.
3. Measure out the radius of the curve along the edge and mark. Then
transfer the mark to the front side.
4. Measure up from the flat surface to the front side of the panel at the
mark. This is the distance necessary between the kerfs to produce a curve
with the desired radius.
Knowing how deep you can safely make the kerf is an aquired skill. It depends
on the type of plywood and the orientation and thickness of the outer
structural ply. You need at least one ply with the grain running across the
curve.
Glenn
Bateau2
In article <35638F...@cc.curtin.edu.au>, Klaus Sussenbach
<isus...@cc.curtin.edu.au> writes:
>> No, on the outside of the panels. For some other parts, like inwales, we
>> sometimes kerf on the inside.
>
>Maybe this works for you but common sense says: outside layer is
>under tension, inside layer under compression. Wood is much better
>under tension so by cutting your kerf outside you are cutting away
>the stronger part of the bend.
Technically correct but how do you get a circular saw inside the bow of a small
boat? Even if you can reach, you will not be able to get your saw flat against
the panel.
You could kerf before planking but what a job!
Anyway, good designs do not require kerfing.
I used that method sometimes to build plugs. I did not worry about
developability and anyway covered the whole thing with many layers of glass:
the strength of the wood was not an issue.
Hans Valk
Bateau2 wrote:
>
> In article <35638F...@cc.curtin.edu.au>, Klaus Sussenbach
> <isus...@cc.curtin.edu.au> writes:
>
> >> No, on the outside of the panels. For some other parts, like inwales, we
> >> sometimes kerf on the inside.
> >
> >Maybe this works for you but common sense says: outside layer is
> >under tension, inside layer under compression. Wood is much better
> >under tension so by cutting your kerf outside you are cutting away
> >the stronger part of the bend.
>
> Technically correct but how do you get a circular saw inside the bow of a small
> boat?
Wood much better (= stronger ?) under tension than under compression ?
I've always thought it was the other way around..... (measuring in the
direction of the grain, that is).
Greetings,
Hans Valk (a.j....@bk.tudelft.nl)
Klaus Sussenbach
Hans Valk wrote:
>
> Wood much better (= stronger ?) under tension than under compression ?
> I've always thought it was the other way around..... (measuring in the
> direction of the grain, that is).
>
> Greetings,
> Hans Valk (a.j....@bk.tudelft.nl)
Nah, you're wrong Hans, just ask any tree :-)
Klaus