here’s a useful tweak from michael for the billy book case cd insert to reinforce the shelf and close unsightly gaps.
“the billy book case CD insert is a good idea in principle but has at least 3 drawbacks:
the standard fixing method is not very solid,
it puts the front face of the insert in line with the front of the bookcase, which looks bad,
and to add to the bad looks it leaves a small but noticable gap between the top of the insert and the shelf above.
these can all be cured using the leftover packing pieces from two tall wide billy book cases and four small brackets, as follows:
make two “L” shaped inserts from the packing pieces and two brackets. any small brackets will do, i used surplus billy wall anchors. these will be used to space the insert from the back of the book case.
using the “L” shapes as a depth guide, screw the assembled insert to the bottom of a shelf with two more brackets. you may have to bend the brackets out a bit so that the shelf fits snug against the insert.
replace the inserts and slide the shelf / insert combo in in front of them. voila!