Bois,
When you clamp or screw the jig to a bench, the front of it overhangs enough so that the sides of the drawers can be loaded and clamped into the jig vertically. The fronts and backs of the drawers load horizontally, and butt the sides. You have to insure that the end grain of the sides sticks up to be is exactly flush with the inside face of the front or back.
The front (or back) is offset from the side by half a pin width, and you rout through both at the same time, following the fingers on the jig. So you are cutting completely through the sides (vertical) but leaving a rounded edge on what will become the inside of the side.
You are at the same time creating basically a "stopped" french dovetail with a rounded end (corresponding to the angle of the router bit) going part way through the thickness of the fronts and backs of the drawer, and stopped by the jig at exactly the point necessary so that when the sides are pounded into the fronts and backs, the outsides of all are flush.
Pbaker,
I agree with you that a PC jig bigger than 12" is a waste of money, and more of a pain than it's worth, unless you are using a Leigh to simulate hand dovetails. For the type of cabinets joasis is building, 12" is plenty.
And as far as making money goes - the only time it pays to make your own finger dovetailed drawer boxes is if you do not have time to buy them already dovetailed and prefinished, and are only doing a few.
Joasis,
I think you will get real tired of your jig in a very short time. Dovetailing drawers makes the most obnoxious screeching tools we own - routers- schreech about twenty times worse than they do on any other job. The racket is immune to the influence of ear muffs, and having an apprentice do it is even worse unless you send him to a different county.
Hand cutting dovetails will begin to look more and more appealing the more time you spend in front of that jig.
By the way, I will be selling surplus Russian astronaut helmets soon that would be a bargain at half the price. Just something to keep in mind.
Have fun.
jimc