After looking at a few well done jigs in here, I threw this one together.
Consists of two pieces of wet wall liner glued together with the smooth sides out.
Routed a 10 mm slot nearly on the centre line, then changed the bit for a 22mm bit set to the thickness of the locking plate and went over the same line.
Then cut a piece of mild steel to the width of the wide cut and filed till it fitted in the slot and slid easily.
Drilled and tapped a 10mm hole in the flat, cut the head of a 10mm bolt and screwed into the plate till it stopped.
Used a knob off a computer chair to lock the sliding bit to the wet board.
Drilled holes in the end of the lower board to fit my router and away I went.
Designed to make Lazy Susans so I just drill a 10mm in the centre of the timber where the pivot goes.
Another pin would have to be made up for cutting on large sheets unless you need a hole in the centre.