If you have to make irregular shaped things one way to do it is to scribe the curve on to your board. There are specialized tools that look like a compass that will do it but I made a quick tool to get this little job done.
The basic idea is this. You look at the lumpy post as just a curvy line and you just need to copy that line but make the copy move over to your piece you are going to cut.
The little blocks hold the piece strait and the pencil and the wire have to be adjusted so that the distance between the end of the wire and the pencil lead is the same as the width of the blocks. I twisted the wire more or less around the pencil to adjust that length. To use the scriber just use the pencil on the block to be cut and point the copper wire perpendicular to the block and towards the post. The trick here is to keep the wire parpendicular and move the pencil down the board while the wire bumps along the post. The direction it moves is not important going forward and backwards is not a problem, messing up and drawing a second line is no big deal just figure out which line is right. I used a jig saw to cut the piece and nail it up.
One small idea for the mental tool box. Perhaps it will inspire other soultions in the future. As always leave a comment.