"Rumpty" writes:
IF you want to use the two 1/2" plys, rout out matching 1/8" wide groves
1/4" deep in each ply sheet, epoxy in a 1/8' X 1/2" steel strip into the
groves and glue up. This won't sag.


I think I will go with this idea since it seems to meet my criteria
best though it does entail additional work (but at least I get to play
with my new DEWALT DW618B3 router

My plan is to do the following.
1. Use two strips 1/8" x 1/2" with each strip aligned with the depth
of the shelf pin

I assume that "two is better than one" and that aligning with the
plane of the shelf pins should help transfer the weight directly
from the shelf pins to the steel supported part of the shelf (Is
this correct?)

Also, I assume that two strips spread out that way is better than
one larger central strip of the same total mass.

2. I plan to build a template for routing the groove out of a similar
4ft x 12" piece of plywood with slots routed out. Then I will use
a 1/8" straight cutting bit (is this right? I am new to the world
of routers)

3. One other thought I had. Would I be better off adding an additional
3rd row of shelf pins down the center.
i.e. even thought they are 1/4" and have glued-in sleeves is the
support itself marginal?

Please let me know whether I am barking up the right tree now.
Thanks