I’m trying to remember exactly how I em-biggened some d’oh-(forehead
slap)-too-small holes on one of the past builds...
Against policy to discuss, I know, but it involved clamping a (ssssh)
tailed router mounted on a ¼” plywood base and plunging the ¾” bit  to the
maximum depth, with the typical horrific noise levels and clouds of
pulverized wood dust in the atmosphere,  (2 ½ “ deep, or maybe a bit more,
can’t remember).  That gave me a nice clean hole that allowed me to
continue through the rest of the thickness of the top with some other bit I
had.  It worked, but admittedly it’s not a ‘hand tool only’ solution (half
by hand, does that count?).
  As mentioned already, it’s difficult to enlarge a hole on center without
special tooling.  If you have a tool bit grinder you can roll your own by
grinding your own custom counterbore tool, but then you wouldn’t be asking
here, right?  I did see a flea market spade bit that was crudely ground
down to counterbore on a regular bench grinder, but it was a small
one-5/16” CB, probably for plane counterbores (for the brass nut to fix the
tote, the narrow part fit into the 5/16 hole, and enlarged it to the
diameter of the fixing nut).  I can’t imagine that would work well for the
larger sizes, but I don’t know.  You would need some Popeye sized arm
muscles to rotate a large diameter by hand.
  Maybe you might have a bevel geared barn boring machine drill (the kind
you clamp down, and sit on, then crank on both sides)?  Or, if you’re
really into the ancient stuff, look up “beam drills” that use a wimble or
brace and the lever principle with a 8” to 10” diameter log to give you the
downward pressure you need.
Claudio

On Sat, Jan 20, 2018 at 12:26 AM Michael Suwczinsky 
wrote: