FLowen wrote:

Newbie has some dumb (for anyone who knows about boring) questions. I
am using an off-set boring head (APT) with "spoon type" cutters on a
vertical mill to drill a number of odd size holes (eg .342", .543",
etc), all between .3" and .75"; some shallow, some 1.3" deep, in
carbon steel FS 1141 (heat treatment: normalize @1200F air cooled,
hardened @ 1525F, oil quenched & drawn @ 700F) w/ Rockwell hardness @
A60-70.
1) Do these boring cutters plunge into the steel like a
center-cutter?..., or do they need a pilot hole to enlarge?...would it
be good practice to run a slightly smaller endmill down through the
center anyways?

Start with a twist drill or center-cutting end mill, and take it fairly
close
to the final diameter, if possible. You might want to leave .020" on the
wall of the deep holes, in case the drill wanders.

2) Would you suggest boring these holes out in one pass?...or more
than one pass with increasing diameters? If so, what is a good
incremental increase per pass?

I usually can handle .010" per pass in a Bridgeport, a lighter machine
might need a shallower cut.

3) The surface where the hole will go is irregular, ie. not flat:
within the hole I want to bore the surface probably has up to three
different levels, and I have parallel holes partly within the target
hole. Does this present a problem for these standard boring cutters I
am using?

Probably not.

4) Does anyone have any suggestions rpm and quill feed rates
for what I'm describing? Without knowing any better, I would tend to
use 300-400 rpm and feed by feel.

Figure the surface speed in FPM for the diameter and materials. Then,
calculate
RPM from that. HSS on steel would be 60 - 100 SFPM, carbide could be
150 - 600 SFPM. For .3", 100 SFPM comes out to 1300 RPM, for .75" it
is 510 RPM.

5) My mill (Bridgeport Series 1) has an auto quill feed which I
have not used nor know much about. Should I be using that mechanism
either automatically or manually?...or is the standard quill feed
lever handle just as good?


The power feed gives a consistant feed per rev, and you should use it to
get the smoothest holes. You don't really have to use the auto cutoff if
you are going to be watching it.

Jon