No pictures of the old jig I'm afraid, today I
use a Makita compound miter saw with tilt and angle. Probably the most-used
tool in the shop.
But here's how I made it: Dimensions are all
"whatever you have".
Take an almost one foot wide plank about 3 to 4
feet long and screw two 2x4s of the same length onto it. Put one
along each side with their outer edge matching the outer edge of the plank.
This makes a U-shaped tray with open ends and having 1 1/2" high
sides. This tray what you clamp the stringer into, so the inner faces
of the 2x4s should be straight.
Next take two pieces of your 3/8x3/4
material also the same 4 feet long and screw them flat down to the top of
the 2x4s so that they are at a shallow angle to the long dimension of
the tray. The actual angle doesn't matter because the scarfs you make on
your own jig have to match each other. Somewhere around 10 to 15 degrees is
good. I shot for 12 degrees. Space these stringers from each other far
enough so that the foot of the circular saw can just fit between them and rest
on the 2x4s. You may have to adjust the width of the 2x4s to accommodate your
saw. My saw has a big foot, so all these spacings worked for it.
You now have an angled "runway" for the saw on
top of the 2x4s.
The jig is almost ready.
Wax the runway and set the saw for 1 1/2"
depth of cut and run it down the runway. Yes, it will cut most or all of the way
through the 2x4s, so you may have to put some more wood on the bottom of the
plank to keep the jig stiff enough.
Now you can clamp a stringer into the tray
against one of the 2x4s and run the saw down the runway to cut a
If the C clamps you use to clamp the stringer
are so big that they interfere with path of the saw, use a hole saw or jig
saw to cut some holes in the bottom of the plank and clamp the stringer by
positioning the clamps from beneath. In that case, the jig won't sit flat
on the workbench anymore, so it is laid across two saw horses. In
fact, that is the only reason why the jig needs to be 4 feet long......so
it can span the horses. Otherwise it could be shorter.
That's all there is too it. This jig will
cut the same length of scarfs on your stringers regardless of which way that you
are doing the scarf. You either clamp to the 2x4s or to the floor of the
tray. I've done it both ways. Normally one wants to cut a scarf with the
largest possible glue area because that way it is stronger and will bend
more naturally. That means that to get nice limber scarfs they have to
be cut the "hard" way...remembering that it really depends on which
way you want to bend the stringer. On yours with this jig you would clamp the
longer side of the scarfs against the side walls of the jig. When assembled and
glued, you would see a vertical line running from edge to edge at right angle to
the larger flat side of the stringer. Looking down at the 3/8" edge on the
assembled stringer you would see the angle of the scarf running from side to
side. Remember to use a couple of finish nails so that you can clamp the
scarf well for gluing without it trying to slide. I also dampen the
joint before gluing.
If scarfing the hard way is too difficult, try
making some the other way. Really, once you make a few of them for practice and
get the gluing down you'll probably find that for slight bends it doesn't matter
which way it is scarfed.
How do you know if the joint is good? Well, just
go ahead and break a few of them. A good scarf joint will be the strongest place
on the stringer. The wood should break before the glue joint does. That's will
make you trust them.
I knew a guy in California (Terminal Island,
Ca., early 1970s) that re-built a fairly large vintage wooden
fishing using short pieces of lumber - most of which he
scavenged. That guy was a true scarfing master. BTW, the best glue
clamps I know of are strips of inner tube half an inch wide and a few feet long.
Hold one end with your thumb and wrap the first couple of wraps over it to hold
it down and then just wrap the whole joint under rubber band tension.
Tuck the final wrap under a previous one. This clamp will maintain pressure as
the joint cures, and it removes easily.
----- Original Message -----
Sent: Sunday, January 13, 2013 9:09
Subject: Re: [Airolite_Boats] Re: Boat
length Measurement question
On 1/13/13 10:55 AM, Roger L wrote:
Thanks for the tips there, Roger. Do you happen
to have a picture of your scarfing jig that you could post? I've come to
the conclusion that I will have to scarf all of the lengthwise pieces due to
the length of the Arrow that I am going to build. For the gunwales,
inwales and rub rails, the pieces are about 3/8" thick x 1" wide, on which
dimension did you do the scarf joint? If using 8:1 ratio one way
requires a joint that is 8" long and the other way only requires 3" for the
I used to be afraid of scarfing. What I did
to fix that was to build a simple jig out of scrap wood so that I could
clamp a stringer in the jig and run the circular saw against one side
of the jig. Not knowing what was best, I made it for a 7:1 scarf. The
result was a perfect scarf angle every time. No sanding required - just
enough to break the glaze left by the saw - and the joint would always
fit exactly. Then to test if it worked, I clamped and glued half a
dozen scarfs up to make a single long stringer about 20 feet
( Be sure to lock the scarfs prior
to gluing with a couple of finish nails or the joint will
Figured I'd use the long stringer as
a batten for drawing long smooth curves. Flexing it to draw curves
would give a chance to see how it stood up to stress and whether the
glue joints took the same bend as the were the same. To my surprise, it
performed as though it was one piece of wood. It's still fine and been
over 20 years now....and there are far better glues today. This one
is stored across the rafters of my workshop.