Jig for Through Mortise
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A jig is, by defi nition, a problem-solving device. As such, it
shouldn’t take more time to make the jig than it would to
perform the operation without it. If the purpose of the jig is to
replace an operation that requires a lot of skill, how can you
make the jig if you lack the skills? There is no shortage of pub-
lished jigs that fail miserably on the above points. I think there
may be woodworkers out there whose hobby is limited to
building jigs, but for the rest of us, here is a simple method for
making a jig to cut a square hole. In this case, I’m making the
through-mortises in the case sides of a Stickley music cabinet.
I cut a piece of^1 ⁄ 2 "-thick plywood to the width of the case
side, and long enough to include the through-mortises at
the top and bottom, as well as the shape of a cutout at the
bottom (the pencil lines at the left) and a rounded drop at the
front of the cabinet (the pencil lines at the right). I also cut
some strips a couple inches wide to support the router, and
some^1 ⁄ 2 " wide, which is the width of the fi nished mortise.
You can see my layout lines for the mortises on the right side.
I’ve taken some double-sides tape, and covered the layout
lines so I can stick the small plywood pieces to the large piece.
The quality of double-sides tape can vary, I like to use Speed
Tape which is strong enough to be a permanent adhesive. I
place the plywood strips around the layout lines for the mor-
tises. This is easy to do and it saves me from cutting a square
hole in the plywood.
When I’m fi nished, I take a dead-blow hammer and tap on the
strips to set the adhesive on the tape. Now I’m ready to take a
router with a fl ush-trimming bit and make the cut outs for the
mortises, after I drill a^3 ⁄ 8 "-diameter hole in the middle of each
opening that allows the router bit to pass through.
I put some blocks on top of my bench, fl ip the plywood over
and proceed to rout the openings. The bearing on the bit
follows the little pieces of plywood and makes the cut right
on my layout lines. The bit leaves the corners rounded, but
I’ve accomplished my goal; I have nice straight edges that are
square to each other and the exact size I want.
I don’t need the strips anymore, so I pop them off. There are
circumstances where I might want to have the jig a full 1"
thick. In that case I would hold the strips down with yellow
glue and leave them on permanently. The extra thickness can
help guide a chisel for squaring the corners. I don’t care for
that method, even though it makes a good chiseling jig. The
downside is you can’t see inside on a narrow mortise and you
have to chisel the corners of the plywood square.
I just leave the corners of the jig round. I lay out the mortise
locations on the solid-wood case side, and mark them with
a knife. The knife cuts will guide my chisel when I trim, and
prevent the router bit from tearing out around the line. This jig
was quick to make, I didn’t have to do a lot of fussy cutting to
make it, and it allowed me to make eight through-mortises in
a short period of time. Here is the end result:
2 28-29_JigThroughMortise.indd 28 8 - 29 _JigThroughMortise.indd 28 3/25/13 9:55 AM 3 / 25 / 13 9 : 55 AM