The proof of concept starts by taking piece of cherry for the body out of my “save-for-later” box and milling it to just under ¾” square and about a foot long. A piece of maple from the same box is milled to the same thickness as the planned total thickness of the three-layer stack.
The first step is to set a jig up on the table saw to
make the 40-degree cut through the body.
To set the angle an adjustable triangle from my drafting days and a
Sliding T-Bevel are used. The photos
show how the triangle is set and held against the table saw rip fence to set
the Sliding T-Bevel to 40-degrees.
Using the Sliding T-Bevel the fence on the jig is set to
the 40-degree angle making sure the T-Bevel’s edge is tight to the blade
without touching any teeth and the handle is up tight to the jig’s fence. 
Next the jig’s stop block is set so about 2” of the
blank’s body will get cut off. It’s
important that this setup is not changed from here on out so all the pieces
that make up the knot are properly aligned.
A sliding clamp is used to hold the blank securely in place while the
cut is being made.
To use glue is applied to the cherry pieces then the
maple piece is set between them hanging over on the far and near faces of the
cherry. The two horizontal orange clamps
pull the cherry tight to the backstop and the blue clamp pulls the three pieces
tight together. The notch in the
backstop lets the maple piece extend beyond the face of the cherry without
interfering with the cherry faces alignment. 
After letting the glue cure overnight, the clamps are removed
and here are two views of what the piece looks like. Note that the maple piece that was down
during glue-up (side 3) is flush with the cherry while the other three sides of
the maple piece are proud of the cherry.
You can also see numbers on the cherry faces. Each of the four faces are numbers one
through four and I will explain what they are for in just a bit.
Before moving on to the next step all the edges of the
maple have to be brought down flush with the cherry. That’s done with a no-set pull saw followed
by some light sanding using a sanding block with 120 grit paper.
Making the cut for the second piece of maple is
next. Here is where the numbers come
in. The blank is put back in the jig
butted up against the stop with the number two up. The first piece was cut with the number one
up, this time the cut is made with the number two up. The same process will be used later for faces
three and four. 
Once cut the glue-up process is the same as with face
one.
After the glue cures the blank gets unclamped and the
maple edges are trimmed flush with the cherry body using the no-set pull saw
followed by some light sanding. The top
photo shows faces one and two with the meeting corners (red arrows) of the
maple and cherry all lining up as expected.
However, in the middle photo one of the joints did not line up as
expected. The vertical maple piece on
face 4 identified by the top red arrow should be over to the right so it meets
the vertical piece identified by the bottom red arrow. Now that’s a problem which when the cut was
made for face three really showed up since the vertical maple pieces on the cut
face (circled in red) should line up and they clearly don’t. At first, I was at a loss for why since the
3D drawing did not show this as a problem.
After a thinking about it for a while I think I know what happened. Because I wanted the individual lines of the
knot to be thin the thickness of the maple piece is .085” thick but the saw
kerf is listed on the blade as .125”.
This means that each time I make a cut and glue the maple piece in there
is a net loss of .068”. I know the
difference between .125” and .085” is only .04” but due to the angled cuts the
actual loss is .068”. This matches up
with the photo in that the offset is slightly less than the .085” thickness of
the maple piece. By the time I make
fourth and last cut I think the difference will be a lot more and any
possibility of getting a Celtic knot out this test piece is gone. However, I am going
to go ahead and finish it up then turn it round to see what the results look
like.
Here the top two photos are after the third piece of
maple has been glued in place and brought down flush with the cherry. The bottom photo shows after the cut has been
made so the fourth maple piece can be inserted.
As you can see the alignment of the maple pieces is getting more and
more out of whack. It will be
interesting to see just how bad the pieces will be misaligned after the fourth
piece is glued in place.
While the glue was curing, I made a cut on the table saw
in a scrap piece using the same blade as I use when making the four angled cuts
above. Now the blade says it makes a
.125” kerf but having been burned once when the maple inlay didn’t match the
blade kerf, I wanted to make darn sure it matched this time. The top photo below shows what thickness
piece of maple fit in place with no slop and it’s not .125” but is a little
thicker at .1305”. The bottom photo
shows the piece milled to fit in the saw kerf.
Now I know the difference is only about five thousandths of an inch but
as there are four cuts the total difference is .020” and that’s about the
thickness of my fingernail.
Nevertheless, because the finished Celtic knot is going to be less than
a half inch in diameter, I am concerned that the misalignment would stand out
if I used a .125” piece.
Next Up – Turning 1st & 2nd Test, Gluing Inlay Blank
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