david lang wrote:

It's really an assembly thing, difficult to glue up without screws in my
somewhat cramped workshop.

I thought -all the way through this thread, that you were talking about
putting screws near the end of the face of the MDF.

(You need to pilot drill and countersink screwing through the face of
that stuff. And you need to keep as far from the edge as possible. 3
inches is getting close.)

MDF is a medium density fibre. That means laminations that are not even
tightly bonded. An example of well bonded fibre board is Formica.

OK that is a different medium entirely. I doubt though that you would
get screws into the end "grain" of higher density fibe board.

What you need to do is put some architrave or 2x1 on the uprights where
the shelves are going to sit. Remember when measuring out for them that
you need to keep them the thickness of the shelf down.

You want a 10 inch space from the top of the bottom shelf to the bottom
of the next shelf up for books that are 8 inches high. So with a 3/4
inch board as the shelf the batton needs to be 10 3/4 inches from the
top of the batton for the next shelf up.

(Another point to note is that shelves over 2 feet long need either
extra thickness board or some other sort of extra support. A nice
edging strip will act as a feature and help keep dust out of the shelf
below.)