On Nov 1, 5:06*pm, Ignoramus31297 ignoramus31...@NOSPAM.
31297.invalid wrote:
...
The problem is almost certainly one of machine rigidity. Yesterday I
milled several 1/2" holes through 1/4" HRS (3" sq tube) with a three
flute center cutting end mill with no pre-drilling and no issues at all
on my Bridgeport. The holes milled smooth as butter with a few drops of
cutting oil, and finished with the usual thin disk of metal hanging by a
thread that knocked off with no effort.

That's how it worked with my manual Bridgeport too.
i-

My ~700 Lb Clausing is marginal for boring steel cleanly with an
endmill. It's OK at 1/2" diameter but not much larger. It has some
trouble fishmouthing 3/4" and 1" pipe with large taper-shank endmills,
not that chatter marks hurt a stick welded joint.

I think it's a little less rigid than a mill-drill. I didn't cut much
steel on the RF-31 and have bored only plastic and sheet aluminum on a
Bridgeport.

jsw