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Making great dovetails in plywood takes more work...but not that much more. In fact, if
you follow the same steps in all woods, perfection will be more assured.
The wood I am using here is birch ply from a home center — admittedly
not as good quality as from a cabinet lumber supplier. Where the poorer quality shows up
most is in the layers in between the faces and in the gluing. Delamination is very
probable when routing this ply. The following are steps that I used to get the
perfect joint, shown here.
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The first step in
dovetailing is to rabbet the insides of the tail boards. This is where the most tearout
can occur. It is easy to eliminate, or at least, minimize tearout. All you have to do is
score the inside where the top of the bit will cut. Since I have the router bit height set
at 1/2" exactly, I score at that height.
In the photo, on the left, I am using a tenon marker/cutter to score the mark
— all it takes is one or two passes. At the right, I have simply measured the
1/2" and am using a utility knife to make the score. Both methods work well.
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The rabbet cuts are
as clean as can be. So, on to the next step.
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Here, I have clamped a
piece of 1/2" MDF in front and behind the two rabbeted tail pieces. MDF machines very
well and will keep the plywood from chipping. Other stock could be used.
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The sandwich is clamped
securely, and I can make the tail cuts. I purposely make the cuts very slowly. I do not
want to rush the cutters. By the way, when you flip to do the other end or place other
pieces in the sandwich, you can use the same MDF pieces. Carefully keep the same
alignment, and these pieces do not need re-cutting.
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Here are the elements
of the sandwich after cutting. You can see how clean each of the tails are in both the MDF
and the ply.
Routing the pins in the end pieces is done exactly as before. If you take the
cuts slowly, there should be minimum tearout.
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This is the
final results. Both the outside and the inside of the corner show a tight and crisp
dovetail that will glue up well — and look great.
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Routing MDF and plywood
calls for extra sharp and clean router bits. This was a new bit when I started these
drawers. Now it looks "burned." It isn't. The MDF and glue of the plywood leaves
residue that needs to be removed.
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A quick scrub with
bit/blade cleaner and a 3M scotch brite pad brings the orange bit back to "like
new" condition.
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I use a fine diamond file
to gently remove any burnt residue from the carbide edges. I try not to touch the actual
cutting edge. The bit should look as good as new before returning to its storage place.
Next week, I will finish this cabinet and start the first real project —
a Stickley style writing desk that I will adapt to hold a laptop.
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