Roy Underhill’s video shows the
spline blank placed in a grooved block. Then the blank is planed
to size with a block plane.
The problem is, this eventually
cuts some off the top surface of the grooved block causing the
splines to come out too small. Then the splines won’t do their
job well and look terrible.
My improved method has three secret weapons:
1. A Kerfing Plane to make the blanks
2. A modified Dado plane with skewed blade
3. A sizing block with a channel to guide the modified plane
Secret Weapon #1
Tom Fidgen, in his book “Unplugged Woodshop” describes a kerfing
plane. You can get parts to build one from Bad Axe Tool Works.
Tom's kerfing plane looks a lot like a stair saw with a fence,
you can see it
on his web site.
My version is made from a
vintage plow plane and a blade cut from an old rip saw. It’s
easy to cut a tempered saw blade. Just score it on both sides
with a Dremel grinder and cutoff wheel. Put the blade in a vise
and flex it, it will break along the score line.
problem is drilling holes in the hardened blade. It will wreck a
conventional twist bit, but I had good luck with carbide tipped
masonry bits. First, center punch the hole positions well, drill
a pilot hole with a 1/8″ masonry bit, then finish with another
masonry bit sized to fit your screws. Use plenty of oil while
This old plow plane has an inch or
so of the adjusting threads stripped so I added a spacer block
to the fence to skip over the bad spot. The next photo shows the
kerfing plane making 5/16 inch deep slots in the end grain of a
Walnut scrap. The modified plane is accurate enough that I can
easily slice four spline blanks from this 7/8″ thick bit of
Kerfing plane in use.
Now that three kerfs are cut, use a
backsaw to cut the four spline blanks free. I kerfed both ends
of the Walnut scrap while I was at it.
Cutting the spline blanks free.
The end result after a bit of block
planing to remove saw fuzz. Eight spline blanks ready to be
trimmed to size.
Batch of eight Walnut splines.