I'm sure this idea is not new but here goes. I needed to drill several pieces of dowel and need to find the centre point to drill from. This is the little jig I came up with. A scrap of wood cut in an L shape at exactly 90 deg. with another piece set across it at exactly 45 deg. Place the dowel in the corner and mark A line across it, then turn the dowel about 90 deg and mark another line and there you have it a cross exactly in the centre of the dowel.
Malc