I guess, if possible, I would prefer to avoid a back column of holes
since it will be visible (even though pretty perhaps with the
sleeves). The holes on the sides will be less visible due to a
combination of the angle and the fact that the face frame will overlap
the sides by about 1/2" or so.
I'm thinking that I will build without a middle back column of pins
and only add later if sag seems to be a developing problem.
Sleeves will definitely add tear out prevention strength to your shelves and
are pretty cheap. I'd buy a small package of sleeves and use several to make
a mock up side to see if they're visually appealing enough to you.
When it comes to installing them, instead of hammering them in place, I've
found that you can make a neater installation by using a sleeve setting
punch and a clamp to press them into place.
Tight fit only. In over 20 years of using sleeves in plywood, softwood and
hardwood, I've never had a sleeve come out or even noticed one start to come
out. The pressure is sufficient to hold them. Also too, if I'm going to
paint or stain or finish in any way, I do all that first with the sleeves
being one of the last parts of the construction process. Even with slight
splinters caused by drilling the holes for the sleeves, the outer, wider
edge of a sleeve finishes off a hole very nicely if it is pressed hard
enough into the hole to make it flush with the surface.
Some points haven't been covered by other replies; first, in terms of
double 3/4" plywood has the same stiffness as double 1/4" plywood with
space (glued lightweight ribs or hardwood at the pin-stress points) of
about 1.25 inch.
Overall height of the sandwich is then 1.75 i nch... but there's a
lot less shelf
weight and cost.
Also, the pins are stressed downward at the face of the upright, BUT
they tilt slightly
and the pins actually press upward at their deepest point, so your load
is carried on the
surface area of (roughly) the width of the pin times half its depth in
the upright. That is
why a pressed-in collar is such a good idea (the area of the collar is
larger, and if the
tilt of the pin doesn't deform the collar, the useful area is doubled
For heavy timbers, where stresses are near the material limits, pins
instead one makes a circular cut and presses a ring (like a pipe
section) into it. The shelf
depth would tolerate 3/4" pipe sections instead of little pins, and
with suitable (hardwood)
trim at the composite plywood endcaps, Forstner drill/routing a recess
to hide the pin
would be easy enough.
I've always hated high-stress points, like metal pins in wood, because
and changes in moisture can crush the wood so easily. Even if it
doesn't fail soon
enough to catch in a test, it WILL fail.
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