I was trying to put a 1.125" hole through a piece of steel that's 1.5"
x 2.5" x 1". I was using a mill and the only 1 1/8" cutter that the
shop I was in had. It made a really lousy rough cut that's also about
..012" oversized. This piece needs to be split to clamp down tight on a
1 1/8" post.

Anyone have a suggestion for how to fix it up?

I've never used JB Weld... would it work to line the hole with that
and then bore it to 1 1/8"? I've made a jig so I could put the piece
on the faceplate of the lathe to bore it there; I may not have access
to a mill for quite a while now, so a lathe approach is best.

I was also thinking about a sleeve, but I'm not sure if there is
enough room to bore it out to fit a sleeve in there. If I did, what
size OD on the sleeve would work out? Or should I say, how thin could
the sleeve wall be?

Last resort is to smooth the hole out as well as possible and then
slit it much wider than I had planned, but that's not the best way.

Thanks.
-Bruno