Get Every Deck Board End Dead Flush With a Router and a Straightedge

The Problem

Deck boards don't come out of the bundle at identical lengths — the creator's stock varied by up to a quarter inch — and cutting each one exact before laying it means measuring every board against a frame that may itself not be perfect. Against a picture-frame border, every length error shows as a gap.

The Technique

1. Lay the decking with the field boards running long — no length cuts yet.
2. Fasten a straight piece of scrap (OSB works) across the boards as a straightedge, set so the trim line lands where the field meets the picture-frame border.
3. Chuck a flush-trim bit with a top bearing in the router. The bearing rides the OSB straightedge while the cutter takes off the overhanging lips below, one pass down the line.
4. Finish the spots the router can't reach with an oscillating tool: the last few inches at the border corner — crowding the router there risks nicking the picture-frame board — and the run against the house. Both land where they won't be seen.