Matching Mortise Size
Whenever I teach a class, at least one student will say to me
"you really don’t like measuring, do you?" I don’t dislike mea-
suring, but I try to avoid it whenever I can. When I’m trying
to get one part to fi t another, the numbers become irrelevant
and measuring often becomes an opportunity to make an
error. As a perfectionist I recognize that I’m not perfect, but
there are some things that I, and most humans do pretty well.
One of these things is dividing a space in half visually, and I
stumbled across a way to take advantage of that while work-
ing on my Morris Chair. The goal here is to cut a tenon on the
end of this board that will fi t nicely into this mortise.
I held one face of the board against the edge of the mortise,
and made a pencil mark on the other edge. This defi nes the
size of the fi nished tenon. Because I’m marking directly, I have
precision without involving numbers, but I’m in the wrong
place; the tenon should be centered in the board. I could
measure, in fact I did with a pair of calipers. The mortise is
(^5) ⁄ 8 " wide, and the board is (^7) ⁄ 8 " thick. Logic tells me I should
just mark in^1 ⁄ 8 " from each edge and start cutting. Experience
tells me I would need to perfectly measure and perfectly mark
four times to get it right, and if my reading or marking is off a
little, I’ll need to make one or more corrections. I can do that,
but it will take a while.
I decided instead to take my marking gauge and set it by eye
halfway in between my pencil mark and the edge of the board
that gets the tenon. I’m not sure if it’s because of our physical
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