Alright, I finally have time to sit down and post this up. I will try my best not to miss anything, if i do, just post the question and i can go back and edit or just answer it for you. Any way, here it goes.
This technique that i use involves routering the edges or the sides with a rabbiting bit, and routering a groove in the top, bottom, front and back pieces with a straight cutting bit. This will allow you to have a very small groove to tuck your carpet into when the time comes. Not only that, but i believe it makes the actual assembly easier. Here is a pic of a rabbiting bit that i use.
You will need to set this router to a depth of a hair over 3/8" if using 3/4" MDF. Your straight cutting bit should be set at a depth of about a 1/4". By doing this, the rabbited edge will sit in the groove and still leave about a 1/8" seam around the whole side. So after you get your design, you will need to add 1/4" to EVERY edge that will get the rabbited treatment. For example: If you box is outside dimensions of 12" Wide x 12" Tall x 12" Deep, then your panels will consist of 12 x 12 for the top and bottom and 10.5 x 12 for the front and back, and typically your sides would be 10.5 x 10.5 if you were to inset them. So you need to add 1/2 inch to the length and width bringing your sides to 11 x 11. I hope this all makes sense, if it doesnt now, it should as the tutorial goes on.
So after all your pieces are cut, you need to router them accordingly. The sides go the the rabbiting router table and the back, bottom, front, and top go the the straight cutting router table. You can set the straight cutting router table to cut in however far in you want your sides to sit from the edge. I go in about an inch, making a 1/4 inset lip when it is all said and done. Here is what the rabbiting pieces should look like when the are finished:
Here is what the straight cut routered pieces should resemble:
When they are assembled together, here is how they will look:
Notice there is a small groove all the way around the sides. This is where the carpet will be tucked to achieve a seamless finish on the sides.
You will need to repeat this for the other side and all the panels. Then glue it up and screw it together. Be careful not to screw too close to the ends in order to prevent splits in your wood. Now the build up will be complete. I will continue on to the carpeting section in my next post. Keep reading.