Could anybody tell me the formula for calculating drill speeds, (
specifically mild steel ).
I normally just go by eye or from experience, but I need an accurate answer
for a college
assignement.
I have found a couple of items on the net, but they seem to result (in my
opinion), in
totally unrealistic RPM figures.
John

For mild steel about 100 ft / min should be O.K, for a 1/4" drill that is
about 1500 rpm
What speeds have you worked out ?
--
Jonathan
Barnes's theorem; for every foolproof device
there is a fool greater than the proof.
To reply remove AT

I was looking to find the speeds for 3.3mm and 4.1mm drills, I was coming up
with speeds of around
2500 RPM for a 4mm drill. Your 100ft a minute also brings up a similar
figure.
Is this the sort of speed you would use? I have been a toolmaker for 20
years and have always done
things by sight (and sound) and would only use about 850-900rpm for a
4.1dia, and about 1000rpm
for the 3.3mm.
John

Far be it for me to argue with twenty years experience, but I was quoting
from the students shop reference handbook.
I generally find that with a machine ground ( new ) drill what they
recommend works, but if I have resharpened a drill by hand I generally want
to run a little slower.
Normally I'm to lazy to change from the pillar drills bottom speed of 500
which is defiantly as fast as I want to run a 1/2" drill in 316 stainless
steel :-( ...... I'm looking for a drill that will run a lot slower, as I
have to use the mill to work with hole saws at present.
Jonathan
Barnes's theorem; for every foolproof device
there is a fool greater than the proof.
To reply remove AT

Your figures are right - 2366 rpm at 11.8ipm feed for 4.1mm
- 2940 14.7ipm for 3.3mm
Triple those for Carbide drills.
Those figures are from Cimco's tables. They are for coolant and
maximum speed, not taking into account tool wear.
There's a good article and tables here

formatting link

They make the point about most economical speeds/tool wear/cost etc.
--
Steve Blackmore

Thanks everyone, thats all I wanted to know.
I did ask others at work before posting here, but nobody knew the correct
speeds,
the cnc guys tended to run at a higher rpm, but generally on the manual
machines
people run similar speeds to me.
I can't remember being taught to run anything at specific speeds, but
personally
find that higher rpm = more drill wear and more squeeling.
John

Hi
Formular you need for imperial measurements is 12 x cutting speed of
material, divided by PI x dia of work or cutter, divide answer by number of
teeth on cutter.
Hope this helps,
Cheers
Keith

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.