[Shop-talk] hole sawed 1/4" thick steel post undersized

[Steven Trovato]

When I have this problem with wood, I just nail a piece of plywood 
over the hole and use the hole saw through the plywood.  This 
provides a pilot and then a guide bore for the saw.  If I try to 
extrapolate to your problem, why don't you just tack weld a piece of 
steel over the hole and then use a larger hole saw?

-Steve Trovato
strovato at optonline.net