Just a caution. Having made quite a few successful scarfs of 4' wide sheets
of plywood, I managed to screw up the last set badly. My sin was to mix too
much wood flour in the epoxy. The result wasn't fluid enough and I ended up
with voids at the edges of the scarf joint. For scarfing, the mix should be
a fluid, not a paste since there is limited clamping force available, even
with my scheme of driving drywall screws thru the joint into a backup 2x6.
You do want lots of epoxy squeezing out all the edges (and a drop cloth to
protect the stuff underneath your work area.) (I'm working with 3/8"
marine ply sliced into strakes for a lapstrake hull so the voids can't hide
easily.)

I'm fixing the bad areas by playing dentist; cutting the voided area back to
solid wood and epoxy with my 4" grinder and then filling the cavity with
epoxy thickened with milled glass fibers. A layer of fiberglass on the
outside finishes the job with what I think is "good enough." I can lift a
20' long strake at one end and wave it around without it breaking. When the
strake bends, the curve is smooth and uniform thru the scarfed and unscarfed
areas.

8.1 degrees is a 7:1 scarf, while 8:1 is the roughest I've seen
recommended, 7.125 degrees. On the other hand, some people use butt joints
with fiberglass on each side, so ????

Roger

http://home.earthlink.net/~derbyrm

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Started working on my Tolman Skiff. I began by cutting the bottom
pieces from 1/2 marine ply but these have to be scarfed together to
make longer pieces. The specified angle is 8.1 degrees and the
directions describe a scarfing jig to be made with a circular saw but
they require a larger saw than mine. However, I did buy a "Sawzall" to
deal with some rot on my house. I tried various ways to do this with
little success. Finally, I simply cut inclined cuts about 2" apart all
along the scarf area angled at the 8 degrees. Then I used the Sawzall
to cut the scarf cutting each of these out. This gave a reasonable
first and second attempt. Then, I used the sander to make it nicer and
make sure the layers of ply formed parallel bands. I think my first
two scarfs are ok.