Richard Ferguson wrote:

I was going through my Machinery Handbook, and trying to figure out the
optimum drilling RPM. I ended up having to look at one table to get
recommended FPM for the material, and then another table to convert FPM
to RPM. The RPMs seem high to me, so I wanted to run them by you guys
as a sanity check.

For HSS drills in low carbon steel, I read 100 FPM, and maybe half that
for harder steel.

Converting that to RPM, I will list a range of RPMs for a given drill
diameter.

1/4 inch - 1500 to 750 RPM
1/2 inch - 750 to 400 RPM
1 inch - 400 to 200 RPM

Is this anywhere near right? If so, I need to change the pulleys on my
drill press, as I drill a lot of holes in the range of 1/4 inch to 1/2
inch, maybe set it to 750 RPM or so. It is a pain to change, so I want
to pick a compromise value.

The other question relates to pilot drills. I did not find anything in
my Machinery handbook on pilot drills. Does it make any sense to use a
pilot drill for finished hole sizes of 1/4 inch or less? If so, what is
the rule of thumb for pilot drill sizes? Do I need to change RPM
between the pilot hole and the final drill size?

Assume that most of my drilling is in low carbon steel of 1/4 inch to
5/8 inch thickness.

You're in the right ballpark. Running HSS a bit slower won't hurt much.
Remember MH is written for guys for whom time is money, and big $$ at that.
Use some cutting oil and take it easy on feed.

For HSS on mild steel, remember "300 divided by your drill bit size."

For example, 300 / ¼ = 1200 rpm, or 300 / ½ = 600 rpm.

And if you ever see blue chips coming off a HSS drill bit, STOP and slow
it down. Running really small drill bits often leads to breakage. If your
drill press table is really rigid (unlikely) then drill 1/8" right through
and then drill your final hole in one go. Else take it in a few steps. - GWE