Pam Niedermayer
Wow, I'm flattered; but I also just realized that the full story requires photos or video . I'm thinking of making a tiny boxwood coffin smoother for that plane build off over on Neanderthal Haven, but I'd just as soon build it and document it here instead. I also still owe Ellis a Japanese smoother. So let me think it through a bit.

In brief, for the mouth you have to have laid out where it will start and end on both top and bottom, highly dependent on the blade size. (If you do a Japanese blade, be sure and mark an approximation of the ura as the back boundary, leaving it more forward than you think you'll need. But, you say, the ura's on the opposite side of the blade from the bevel; to which I reply, there's a small ura on the bevel side, too, but you wouldn't notice it until you tried to fit the blade to a flat bed.)

Then with a drill (press), start from the bottom, on the line, and drill straight up, it helps to drill through to the top. (This could also be done with a mortising chisel, probably very narrow, but it's easier and less messy to use a drill.) Then chop out the full mortise following the lines, the chisel will typically be a wide mortiser/chutaki. The holes you drilled will help guide you.

Then saw the edges of the abutments with a small saw and clean them out using a 3mm (1/8") paring/bench chisel, adjusting the depth by fitting the blade. I try to use it bevel down where possible. Also, making a 3mm single tooth float/scraper helps to make them level, but you really don't have to use this since pencil on the blade edges will mark the high spots.

I use a large ultra thin paring chisel to fit the bed, again using a pencil on the blade to mark high spots.

Tom, what did I miss?

Pam