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With the
success last week of using the Incra Jig to make dovetails and box joints, I wanted to try
my hand at making a joint that really can only be made with this type of a system. Incra
calls it the Incra Cornerpost Eagletail—it's the one used in the jewelry chest in the
pic and I really like its look.
The project book from Incra is so clear in its instructions, that I decided
to make this chest to get familiar with making the joint. Now after having made 2 such
jewelry chests (3 if you count the one that I goofed up) , I can honestly say that
learning by making this chest makes total sense.
So in this site, my neighbor Bethany will go through the step-by-step with
minimal guidance from me.
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The project book is the "Incra Jig
Projects & Techniques" book written by Perry McDaniel. Just like the Incra
instructions, it is very well written and superbly illustrated. While it helps to be
familiar with the basic Incra Jig setup steps...as I discussed in the dovetail and box
joint section, one can use this book as the sole source. It covers techniques of Incra
joinery as well as it presents 13 projects. Anyone who has now or is considering getting
the Incra Jig should have this project book. That said, on on to the project...
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The first task with any joint is to
select the stock and router bit. The project book specifies the exact dovetail bit and
gives dimensions for each piece.
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Bethany sets the router depth from the
book's "approximate router depth" setting.
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She is using the Incra Measuring Gauge
that boasts accuracy to .004". It is ideal for setting bit height as here and a
number of other shop operations. Once the approximately height is set, she uses the depth
setting procedure detailed in the dovetail section.
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The following is from the dovetail
making instructions. This next step is kind of tricky. Its purpose is to set the
absolute correct depth of cut. You start by aligning the fence over the bit so that 1/2
the bit is exposed. At that point you slide the correct template so that an "A"
mark is under the line. You make the cut at this "0" position. Then you move the
fence to the next "A" point at make another cut. You make this cut on two boards
clamped together.
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Then you flip one board over and put the two
together. If they fit perfectly, your router depth is set exactly right.
Now back to Bethany and her project.
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Having cut an approximate center
position in one scrap board from both directions, she can now sight the bit to the exact
center. This procedure is basic to all Incra Jig operations and one that is quickly
mastered.
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She uses the micrometer adjustment to
visually center the trial cut to the bit. Once centered she can lock the center point.
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With the center point locked, she can
install the correct template and line the zero point to the cursor line. This centering
operation is essential for the rest of the milling operations. Both the router bit height
adjustment and the centering procedures are easy to do. Take your time and follow the
written instructions exactly.
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She is almost ready to start cutting the pieces. The first
task is to stack the ends and sides vertically in the right angle fixture. We used a wood
clamp when we did the original joints; this time we are using a quick release clamp.
Whatever you use, be sure that the pieces are secure in the fixture. Note also that a
backer board in included.
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There are three nylon screws on the
right angle fixture. The center one is used to lock the fixture. This is useful when
clamping the boards in the fixture. The outside two screws are for adjusting the amount of
lateral tension on the slide. It is important for the fixture to slide smoothly but not
wobble. There are lock nuts that should be tightened once the proper fit is determined.
The fixture must be adjusted properly to keep the cutting operation in tight tolerance.
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Now Bethany can start cutting. The book tells her
exactly what cuts should be made. She adjusts the fence so that the right position is
under the cursor; locks the clamp; and makes the cut.
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The cutting of both ends takes just a
minute.
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