[quote author=Aquila  link=1103322332/15#15 date=1103471536]Trend do an Offset Trenching Base that goes on the bottom of the router. It is pentagon shaped and the distance from the shortest edge to the center is 100mm, when you turn it each side is 1mm wider so it will cut up to 5mm larger than the cutter without moving the straightedge. Part No TEMP/OTB/A
hope this helps [/quote]
The trouble with this guide is that you are likely to make the first cut and then turn the router base to make the next cut further away from the straight edge. This means you climb cut which is difficult to hold the router against the straight edge.
The best way is to make the first cut with the 5mm gap so that the next cut is closer to the straight edge.
You can only make each subsequent cut at 1, 2, 3, 4 or 5mm different so you cant get the width perfect.

Thanks John, i did not go for it coz it is a tad long for me (may only use it once every 2 months and i have no idea where about you live, i am still trying to recover from my trip to JerryD's for the pipe freezer)