Hey Randy!

I've got a Spiers infill coffin-body smoother that probably fits the
description of "gaping mouth". The mouth itself is .313". I don't know
about Norris planes, but I was told I had to use 5/32nds 01 tool steel
for the replacement blade. The blades aren't tapered, either. In any
case, not sure what the clearance is when the blade's in place, but it
takes an extremely light cut. I think there was a thread once about guys
keeping more than one blade for these, and using an 1/8" blade when they
really want to cut stuff down. Seems to be one possible reason why these
turn up with obviously wrong blades in them.

I made my own blade and it works great. I do have a milling attachment
for my machinist lathe, and that made life a whole lot easier. The only
thing I might try differently if I were doing it again would be to try
A2 Air hardening tool steel, (think that's the designation) which is a
whole lot more expensive but also another level better. I've done a bit
on the forge using old car springs, and the difference is amazing. In
any case, 01 puts most factory blades to shame, and I regularly replace
the original blades with it, even on the fillister bed of my '41.

Hope that helps.

Regards,

Matt Turner (known to have cut a few dadoes in his time...) Turner
Racing Shells Ltd "Manufacturers of Only the Finest Quality Red Ink..."