Finger Lap Joints with the Table Saw
finger joint (or box joint) is one of the strongest joints used
in woodworking. Featuring a series of pins or fingers that are cut
to slip into mating slots or notches in an opposing workpiece, it
offers incredible strength, thanks to the generous amount of gluing
surface provided by the interlocking finger surfaces.
the finger joint is used for projects such as jewelry boxes, utility
chests, drawers, cabinet carcasses and more. Although they can be
used on projects where the joints are hidden, more often, they're
used in situations where they're fully exposed...and frequently
on projects where the mating components are of contrasting woods.
the widths of the fingers are about equal to the thickness of the
stock being used. If you're making a project with 1/2" thick stock,
each finger should be about 1/2" wide. There are exceptions. For
example, if you're building a shallow box or similar project with
1/2" or thicker material, such heavy fingers may not be visually
appealing. In this case, you may choose to use 1/4" wide fingers.
Some woodworkers prefer smaller fingers on virtually al of their
projects. It's a matter of personal preference.
Another important consideration in choosing your finger size is
the overall dimensions of the pieces that are to be joined. It's
best to make equal width fingers that are a multiple of the boards
to be joined. This will help you avoid the creation of partial fingers,
which many consider to be unsightly. It's usually best to design
your projects so the width of the mating components are multiples
of 1/4", 3/8", 1/2" or 3/4".
1 Construction details of a MARK V-mounted finger joint fixture
Finger Joint Fixture
at first glance, finger joints appear to be difficult to make, they're
really not. A simple miter gauge-mounted fixture such as the one
shown in Fig. 1 makes easy work of cutting precise, tight-fitting
finger joints every time. Note that this drawing covers a fixture
designed for use with the Shopsmith MARK V, and since miter gauges
may differ, dimensions will vary if you're making a fixture for
another brand of saw.
make the 3" x 12" fixture blank as shown. Drill the mounting holes
for attaching the blank to your miter gauge with 1/4"-20 bolts.
Do not attach it, yet. Note that the example shown in Fig. 1 is
for making 3/8" wide fingers. If you're planning to make fingers
of a different width, you may wish to consider the special Adjustable
Finger version of the fixture shown in Fig. 2.
2 Construction details of a MARK V-mounted finger joint fixture
designed to cut fingers of varying widths
our example, start by using your miter gauge without the fixture
mounted to make a cut that's EXACTLY 3/8" wide on a piece of scrap
stock. Set your depth-of cut to be about 1/32" deeper than the width
of your intended fingers. This way, you'll be able to sand the fingers
off flush once assembled. It is extremely important that your dado
cut be of a precise width.
your dado blade is set, bolt the fixture blank to your miter gauge.
Place your gauge in the left-hand miter gauge slot on your MARK
V and cut the first fixture slot. Remove the attaching bolts from
the fixture blank and slide it EXACTLY 3/4" (double the width of
your fingers) to the left. Use a C-clamp or handscrew to clamp it
to your miter gauge face while you make the second notch cut, as
shown in Fig. 1. Once you've made this cut, you'll have an EXACT
3/8" cut, followed by an EXACT 3/8" spacer pin, followed by another
EXACT 3/8" cut.
make a 2-1/4" long guide pin that's EXACTLY 3/8" wide, as shown
in Fig. 1. Mount this guide pin into the right-hand slot with a
countersunk, flathead wood screw. Drill a 1/4" hole up through the
bottom of the spacer pin on your fixture and glue a 1/4" reinforcing
dowel into position to keep the spacer pin from breaking off.
3 The finger joint fixture in use on the Shopsmith MARK V
The Finger Joint Fixture
a spacer stick that's EXACTLY the width of your fingers (in our
example, 3/8"). Place the spacer stick in position against the guide
pin, as shown in Fig 4-A. Position your workpiece against the spacer
stick, clamp it firmly to the fixture and make your first cut. CAUTION:
The upper saw guard is removed when using this fixture. Work with
first cut will leave an "L-shaped" notch on the end of your workpiece
that's exactly the width of your fingers (in our example, 3/8").
For your second cut, loosen the clamp, remove the spacer and move
your first workpiece to the right until your "L-shaped" notch rests
over the guide pin. Place your second (mating) workpiece in front
of the piece you just cut with its edge resting against the left
side of the guide pin, as shown in Fig 4-B. Clamp your two workpieces
to the fixture and make your second cut.
For each subsequent finger, move both workpieces one notch to your
right, clamp them in position and make your cut.
4 Make your first cut with a spacer stick between the workpiece
and guide pin (A). Make subsequent cuts as shown (B).
type of fixture will also work quite well with router tables. Dimensions
and actual construction may have to vary somewhat to suit your router