Once the sides were cut, and before any of the battons are screwed into place you should route the slots for the t-molding. This is a very easy thing to do but you have to have the right tools for the job. Using a slot cutting bit I was able to route the slots around both cabinet sides in about a 1/2 hour. It was easy!
The most important thing to do for this task is to make a few practice cuts on scrap MDF and fit a t-molding sample to make sure the depth of the cutter is set properly. You only get one chance to get it right on your actual sides and you don't want to have to start over now!
Here are some shots of the router with the slot cutting bit installed. There is a ball bearing that will ride along the edge of the cabinet side and a blade will do all of the cutting. The idea is to get the blade on dead center of the edge so the slot will be cetered and as a result the t-molding will be centered too. This is why it's a good idea to practice on scrap MDF.
The above picture should give you an idea on how this is supposed to work. Note that the router is upsidedown - you will be holding the router on top of the MDF as you route the slots.
This is what the edges of the cabinet sides should look like with t-molding slots routed.
1. Double and triple check the router depth to make sure it is exactly centered.
2. Test your cut on a scrap piece of wood.
3. How to tell your slot is perfectly centered: Place your router upside down on the work table (off, of course). Put the test piece on the router base and slide it onto the blade. Next, turn the test piece upside down and do the same thing. If the piece slides onto the blade then you know it is centered. If not, make an adjustment and try again. It also helps to fit a piece of t-molding in the slot you just cut to see how it looks.
Thanks for looking!!