Bill wrote:

I was hoping to use the 3/4" floor as a shelf, for stuff like drills
and what have you. Maybe in addition to the two2 2by4s shown, under
the floor, I could add 3 more going the other direction. The
simplest joinery would be to screw them to the floor from above, but
I'm not confident whether that will give satisfactory performance.

Bill

Another possibility I am willing to consider is using 2 layers of 3/4"
ply (Columbia "Purebond brand hardwood plywood, since it's
Formaldehyde-free--not Baltic Birch). Of course at +$40 a sheet,
that's a pricier alternative. I'll check with with local lumberyards and
see
whether they have started carrying the Purebond products (as LarryJ
keeps reminding me to do!) Maybe 2 layers is overkill for this
application...but maybe not--I know stacking layers of drywall is
"routine".


Hey Bill - here is a handy site you will probably find useful over time...

http://www.woodbin.com/calcs/sagulator.htm

You can select and/or plug in the values applicable to your project, and
immediately see the results. As you will see, 3/4" ply won't sag any
appreciable amount in your application. I quickly threw some numbers at it
and used 100 pounds per foot for the shelf load (not the load presented to
the wheels by the uprights), which is way more than you will ever put on
that shelf. The deflection is only .015".

Bookmark this site - it is very useful. It beats seat of the pants ideas by
a mile.

--

-Mike-