My next project involves cutting a number of mortises with my trusty little router. I've been playing with templates recently, and looking online there's a number of ways to cut mortises and this appears to be the simplest...
...but the instructions stressed how important it is to line up the pin holes and the cutter perfectly, otherwise the mortise won't be centred. However, the base of my router has four screws holding the base-plate in place, two of which are already centred to the cutter... one pack of 150 m4 machine screws from the pound shop and two of these strap buttons that i had knocking about...
...which just happen to have 4mm holes, and I've got my self centering router guide without the need for any cutting, measuring, drilling or head scratching, for less than tuppence.