BobMCT wrote:
I'm in the process of replacing 1/2 my decking boards with new 5/4 x 6
boards. It works out to half the width of the deck measured side to
side. Where the old and the new meet I'll be intermingling the old
and new boards with a 32" intersection (kind of like putting ones
fingers together). The old decking used concealed fasteners (which I
hated). My question is: any ideas how I can cut the old decking
board midway across a joist without destroying the adjacent two?

A sabre saw needs space below the board; a circular saw won't cut to
the edge; an ocillating tool doesnt really make a straight line; etc.

An oscillating tool will cut very straight if run against a straight board edge.
used one to shorten a kitchen cabinet and the joint formewd by the cut edge and
the wood end of the cabinet looked as good as new.