This one:

http://www.amazon.com/Narex-NAR81341.../dp/B0049MXKZM

I will be making through mortises in oak, or possibly some other
hardwood. Some of the stock will be 1.5" thick. I was worried that
squaring the corners of the routed mortises was going to be a
debilitating chore, but I am encouraged by my first couple of tests with
this chisel.

At its "just-from-the-package" sharpness, it makes a nice clean corner.
Any imprecision will thus be attributable to my lack of skill rather
than the tool. I intend to practice up some.

Next, it's not terribly difficult to plow through the oak. OK, I'm only
gouging out a 1/4 x 1/4 corner in a 1/2" mortise, but it sure is easier
with this purpose-built tool. My test runs have been on 3/4" scraps, so
half the thickness I'll need, but it is very quick. My attempts with
standard bevel-edge chisels were much more cumbersome. I think that the
bevel on this chisel may be at a steeper angle, besides the corner
configuration.

Now I need to learn how to keep it sharp. People recommended diamond
hones, but I see at least 5 "colors" (grits). Any tips as to which
one(s) I need?

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