On Wed, 17 Jun 2015 14:26:14 -0500, Ignoramus7394
wrote:

I am eyeing a job that would involve pulling large gears off their
shafts. Gears are 3ft in diameter and some may be even 4ft.

This being the United States of America, I am sure that commercial
solutions have been developed for that kind of thing. I wonder what
sort of places should I call to rent some big gear pullers?

i
Years ago I had to pull some large diameter flat belt pulleys off of
their shafts and at first it was not obvious what was holding the
pulleys on. It turned out that they were held in place with tapered
keys. I don't remember if it was the keyseats in the shafts or the
pulleys were tapered to match the key. Anyway, the keys weren't just
a straight taper, at the big end there was a step. After the key was
installed you could pound on or pry against this step to remove the
key as it was taller than the rest of the key. I think this type of
key is called a "Gib Head" key. So if the big gears you are going to
pull don't have any obvious clamping feature it may be they have the
tapered keys.
Eric