Achieving exact thickness is really important when
making splines to reinforce box corners. The splines
have to fit perfectly in the saw kerfs—a few thousandths
of an inch one way or the other can make a
I cut my spline material on the tablesaw, making
it a bit thicker than needed, then plane it by hand to
exact thickness using this adjustable jig.
Here’s how the jig works. The plane rides on rabbets
cut into two rails. Both rails are tapered, like a
wedge. You adjust the height of each rail by sliding it
on a fi xed ramp attached to the jig’s body. To plane
a spline, place it on the body of the jig, snugged up
against the adjustable front stop, and start in. When
the plane stops making shavings, you’ve reached fi nal
My jig holds pieces up to 1-1/2" wide, 12" long
and 1/4" thick. It’s designed for a No. 3 plane, but it
would be easy to make a larger version to fi t a wider
plane. All of the parts are 3/4" thick hard maple; the
body is glued up from two pieces.
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