I own one of the original Leigh FMTs and an aspect of it has always confused me. Assuming a 5/16" thick tenon is appropriate for 3/4" stock the max depth of the mortise is around 1". This accounts for bit length and accuracy/deflection of the bit at extended distances. Regarding what mortise depth is appropriate, I have read anywhere from 40% to 60% of the width of the mortise stock. Using 50%, a 1" deep mortise would be appropriate for 2" wide stock.
When making a door frame, rails could easily be wider than 2" so is a 1" deep mortise inadequate? This seems to be a limitation of all router created mortises. To get a deeper mortise you would have to use a larger bit. For instance a 1/2" bit could do 2" deep mortises but the resulting tenon would be inappropriate for the tenon width (in 3/4" stock).
Using 3/4" stock, would a 1" deep mortise be satisfactory or is this a slight of hand with router mortising jigs that you never think about until after purchasing?
Any help with this confusing router mortise topic would be greatly appreciated.
Thanks,
Bill