"RogerN" wrote in message
m...

I'm getting close to start cutting metal on the AR-15 receiver
forging. The first holes will be for the pins that join the upper
and lower receivers. I have the .251 reamer, I'm considering
spotting with a 1/4" end mill, center drill, drill 5/32, drill with
3/16 end mill, drill 15/64, then ream to .251". I'm thinking that
drilling with the 3/16 end mill will position the hole in line with
the spindle, if a single point tool would be better, I could grind a
3/16 end mill to a single point boring bar. Would this process get
the hole positioned about as a good as possible without jig boring
or grinding? Would spot drilling, drilling, and reaming be just as
good? Any better ideas?

Thanks!

RogerN

Here is an old way to position holes as accurately as you can measure,
requiring only a lathe with good spindle bearings and a trued and
tested faceplate.
http://www.neme-s.org/Model_Engineer...%20Buttons.pdf

My milling machine won't bore a straight cylindrical hole because the
quill play increases as it extends. I can bore to more constant
diameter by raising the knee, or using the lathe. I didn't notice the
tiny effect until I rebuilt a hydraulic pump to closer than my usual
hobbyist tolerances.
jsw