This bike is built from British fittings and lugs quite likely BSA but was not I think built in the UK - it looks very American in style to me. Date wise I would guess late 30s/40s. That means the tubing is likely to be Reynolds 531 or Accles and Pollocks... As I mentioned in replying to the original posting this was a frame that was updated at a later date - I would guess the late 50s early 60s. The pedals are one of the patterns of Lyotard Faucheaux, the stem is a Cinelli steel track and it looks as if the wheels were re-rimmed at the same time with more modern Mavic aluminium sprint rims; the originals were likely to have been wood. The Campy seatpost would have been one of the upgrades, if steel that dates that upgrade and probably the others to the late 50s, if aluminium to the early 60s. Its probably 27.0 or 27.2mm - that would indicate quality butted tubing as suggested above.

This is one really rather nice older track bike - if as the poster originally suggested it was made in Milawaukee local public libraries there might be able to check to see if there was a framebuilder named Keller - though I think it more likely that this was the rider's name - but it might also be possible to check to see if anything is known about a track rider of that name...