Next, mark out a gradual curve or taper on the other long
edge of your tool. The ends should be half the width of
the tool at its midpoint – so a straightedge that is 2-1/4”
wide in the middle should be 1-1/8” at its ends. Cut this
long edge to shape with a bandsaw or frame saw. Remove
the sawblade marks with a plane. Drill a 1/4”-diameter
hole at one end to hang the tool when it’s not in use.
For comfort, you can chamfer the long edges of the tool
that are not used for layout.
4 - A straight taper is easier to saw and plane than a
gradual curve. If you cut a curve, clean it up with a
spokeshave and sandpaper.
Your straightedge is now essentially complete. Add a clear film
finish if you wish, though it will not protect the tool from
seasonal changes in humidity.
Testing and Truing Your Tool|
Immediately and again every few months, test the truth of your
straightedge. Lay it down on a piece of paper or plywood and
scribe a line along its length.
5 - To test your tool, scribe a pencil line along its straight
edge with care.
6 - Now turn your straightedge to the other side of your
line and show the edge to the line you just drew. If the
tool is not true, any error will be exaggerated twofold.
Next, spin the tool 180°, keeping the same face up, and show
the same edge to the line. Any error will be magnified twofold,
and you’ll see exactly where it needs to be corrected. Either
the edge will have a slight bellied shape or it will be concave
in the middle.
If the edge has a belly, use a long plane to remove a few shavings
in the middle of the edge followed by a few shavings all along
the edge. If the edge is concave, simply plane along the edge
until you bring the high ends down to the valley in the middle.
Test the edge and plane it again until the tool is true.
Editor, Popular Woodworking magazine