O.K. So I messed up. Normally one uses the same setup to cut all items that need that particular cut. But this time, I goofed up and had to break down a setup and then go back to where I left off. The culprit was a precise dado in a side and back panel. So how to reset the setup to be super perfect. Here is an approach that worked super fast and super accurate.
The dado is meant to recieve a slab of 3/4 in baltic birch which is some form of metric thickness. Forget about buying a router bit for this stuff! Instead, I took my trusty porter cable 690 equiped with a MICRO FENCE and installed a 3/8 in two flute spiral cutting bit. The exact dado is something on the order of 0.710 in and is located 4.750 in on the bottom side up from the edge. In other words, the edge location is 4.750 + 0.710/2 or 5.105 in up from the reference edge to the aproximate centerline of the dado.
So begin by locating the micrometer leadscrew on the Micro Fence to midpoint. Eyballing is fine. I like to eyeball and then set the dial to zero. Lock it down. Then undo the rapid movement and set the router to cut apromimately the midline of the dado. Accuracy here is eyeball close enough. Lock down the rapid movement screws. Set the router depth to the dado depth. Complete your first cut.
Now using a caliper, measure the upper and lower cheeks of the first cut and write these numbers down. The lower cut is position dependent on being at 4.750 in so take the lower cheek cut number and subtract the 4.750 number from it. Dialing the micrometer clockwise pulls the router to you and dialing the micrometer counter clockwise pushes the router away from you. Dial in the amount you just calculated minus say 5 or 10 thou clockwise and take a tiny cut. Take a measure and verify your where you need to be. Use the 5 to 10 thou wiggle room to adjust as needed. Compete your lower cut. Then dial the micrometer counter-clockwise the exact thickness of your material and and complete the upper cheek cut.
This sounds like a lot of work but really isnt. You just need to familarize yourself with the concepts and then you see that its easy. This approach will cut spot on router cuts accurate to within a hair's thickness. What makes this approach so darn simple is the excellent design and workmanship of the micro fence. I have two micro fences setup for porter cable routers and given a choice between a brand new festool router and my porter cable with a micro fence, you couldnt give the festool! I think there are now adapters available but they seem clumsy to me. The micro fence, configuration A, is the original design and it simply fits the base of the porter cable router. No clunky adapter hardware or base modifications needed etc. Once you have used the micro fence with a router, you will be so spoiled you wondered how you lived without one. Now in order to really adapt a festool 1400 to a festool guide rail, you really need to get the micro fence circle cutting jig. In this jig are adapters and the famous micro fence micrometer that allow you to interface the festool 1400 to the guide rail with that famous micro fence accuracy eand ease.
So I am one really happy Micro Fence customer! Its great to see such a simple and accurate and well made tool being made these days!