First of all Jerry there are at least three sizes of lock mitre bits covering; 12-16mm,
14-19mm and 19-28mm wood thicknesses. I sit the wood at the side of the bit, where it would be placed to commence routing, I then "squint" along the table so that I can set the height of the bit and the position of the fence. These settings are of course approximate and it then takes several test cuts on scrap wood in order to achieve a perfect result. After completing a perfect project I then make a test piece for quick set-up next time that I use the same thickness wood and with a thickness planer it is easy to duplicate the thickness. Even using the test piece very slight adjustments may still be necessary.
Like most things, practice makes perfect so, after your first perfect box, make several more and the process will no longer be a worry.
Nothing but heaven itself is better than a friend who is really a friend. - Plautus
Last edited by harrysin; 04-10-2014 at 08:25 AM.