Wayne.B wrote in message . ..
On Tue, 7 Sep 2004 00:01:52 +1000, "David Flew"
wrote:
Original construction looks like 15 mm ply ( probably marine back then - it
wasn't gold plated .. ) with fibreglass on top, and many many layers of
paint.

=============================================

I know from experience that 1/2 inch (12 mm) plywood is fairly bendy
and would not be a problem over the large radius you describe. Since
15 mm is only slightly thicker it would probably be OK also. If you
do a test and decide that too much force is required, you could make
shallow kerf cuts in the bottom of the panel with a table saw, and
then fill them later with thickened epoxy.

Hi All,

I tried the kerfing approach on some 0.5" plywood.
It wasn't a marine job, just a caravan (aka Travel Trailer in North
America?)
Similar though, wooden frame, glass cloth etc.
Didn't come out all that fair - seemed to me I could still see the
kerf cuts through onto the top surface - the surface seemed a bit flat
between the cuts.
I probably should have used more cuts, and cut them less deep...

Anyway, in the end, I took it off and tried again.

I put the old panel back into place - it was easy to see where it had
been from old paint lines etc. I drilled through it into the wooden
frame in three places, and glued a dowel into each hole, being careful
to glue them only into the frame, not into the panel I was removing.
I then removed the panel and used it as a template on the new panel.
Drilling through the same holes into the new panel meant I could use
the dowels for alignment of the new panel when fitting it back onto
the frame. I left the panel way oversize (as much as I could given
the size of the sheet I was working from), except where it was to butt
up to the next panel (which I wasn't replacing).

When fitting, use the extra length on each edge gave me more leverage
when bending the panel to fit the curve. It took no more than
fingertip pressure to pull it into shape and hold it there. The
dowels made sure eveything was aligned as before.

Although I did epoxy coat the new sheet of plywood before fitting, and
re-did the edges after trimming to size, I didn't epoxy the panel onto
the frame, just sikaflex (which doesn't set hard) and plenty of
screws. If it rotted before, it could (will?) rot again, despite my
best efforts...
The screws were staggered across the width of each frame batten to
minimise the chances of splitting.

I then cut it back roughly to the line marked from the template. I put
the original panel back over the new, again using the dowels to align,
and trimmed the new panel back to meet the old with a bearing-guided
straight router bit. The router was used upside down and overhead -
pretty unpleasant, but managable.


Hope this helps.

Regards,

bookieb.