Step 3: MDF Edging and Filling
Because of minor inconsistencies in cutting the shelves, your best bet is to measure each shelf, and cut the molding pieces for them individually. I used 1/2" white oak, and cut them on a miter saw set at 45 degrees. See Fig. 1.
Cut slow! If you don't, you will have bad miter cuts, and fitting the edges will be a little harder. You still might have to adjust the corners with a bit of sandpaper to get the best fit. See Fig. 2
Make sure you lay out your shelves so 3 work in one direction, and 2 in the other (or 3 in the other if you want a 6 shelf rack).
Install the molding with 1.5" finishing nails.
When you install, line up the molding as best as possible with the top edge of the shelf. See Fig. 3.
The shelf will stick out a bit on the bottom of the molding. This is normal, and since it's on the bottom of the shelf, you can't tell it actually sticks out.
Make sure you miss the shelf mounting holes where the rods will go. 3 or 4 nails will be fine for each piece of molding.
Since the molding isn't exactly straight, you can put 1 or 2 nails in and align the molding to the MDF as you go. Use wood glue where the molding will join the shelves, and also on the corners. Use your nail set to hide the nail heads into the molding (only a bit is necessary).
Ok, by now you've got your shelves ready, but you've noticed that there might be gaps, the molding might not be even with the shelf itself, or the corners might be a bit off. This is where wood filler is your friend.
With wood putty and a plastic putty knife, fill any gaps, inconsistencies, etc. where the MDF meets the molding. Also remember to fill the holes to hide the nail heads you sunk into the molding. See Fig. 4
Let the wood filler dry well. You don't want to sand semi-wet wood filler, you'll just clog up your sandpaper.
Start with 120 grit sandpaper on a sanding block. I like the rubber ones, and you will get 4 pieces per sandpaper sheet using them.
Sand the wood filler to get the surface, edges, corners, etc. as even as possible. You can see in Fig. 5 where I had to fill a LOT in order to get the molding and MDF even.
Fig. 6 shows what you really want to aim for when installing the molding. This corner only needed minimal filling and sanding.