I recently bought some flat pack DVD/CD cabinets. While they were easy to put together and generally sturdy enough to hold the collection, they're spaced to hold 1116 CD's (which they do nicely). However if you use the cabinet for purely DVD's you end up with a huge unusable gap at the top and bottom (about 80mm). Sharing out with CD's doesn't work either as you still end up with the same problem.
The solution is quite simple however, so read on.
Step 1: The Solution
By drilling a half way hole between two shelves, you can fit two rows of CDs in nicely without changing any of the other holes. You can utilise every bit of the cabinet storage by having a mixture of DVD's and CDs.
Start by making a hole drilling template out of a bit of scrap. The spacing and hole size will be dependent on the cabinet you have. For this particular cabinet the holes are spaced 32mm apart and 24.5mm in from the face and 5mm peg holes. So I've drilled a series of 5mm holes, 32mm apart - except for the end one which is spaced 16mm. You can use the template in any directly you like.
Use a 5mm drill bit through one of the end holes to space the template with the existing holes, then drill through the 16mm spaced hole. One row from the top of the centre of the cabinet and again from the bottom centre of the cabinet (I wanted all the CD's to be in the centre of the cabinet).
As you can see in the second photo I've added a 1/2 way hole (I tried to eye ball the holes and they ended up being inconsistent, hence the template approach). A bit of plastic wood filed those botches up and you don't see it anyway with the shelves.
Note: Even though you'll be drilling in from both sides and the holes will generally align, it's still good practice to have a depth marked on your drill bit. Whether that be a piece of tape or in my case I drilled through the length of 15mm square piece with the drill press and cut it to the length I needed and slipped it over the drill bit.
Job was done in about 10 minutes then I just had the cleanup.
Notes: I went flat pack as the price for materials wasn't that much cheaper. And the hassle of cutting everything up. This was a nice afternoon sort of project to pop the unit together and a 10min mod.