On Tue, 18 Apr 2017 13:10:04 -0700, "Bob La Londe"
wrote:

I do a lot of spiral milling instead of drilling on my little high speed
(RPM) mills. There are a couple reasons. One is it allows for fewer tool
changes. I can point vent, dump vent, rough cavities and make the holes for
pins and clamping screws all with the same little 1/8 SE end mill. The
other is those little high speed spindles just aren't suitable for drilling.
I've worked out a few operations I can drill with them, but they just aren't
suited for it. It takes a lot of figuring and testing to find something
that gets the speed, feed, and HP curve to all line up so it drills without
smearing the drilling in the collet, wearing out the drill prematurely,
breaking the mill, or causing lost steps. I am sure somebody has it all
worked out, but that is not what I am asking.

Here is what I am asking. When I am spiral milling to drill holes I noticed
at more than about 0.40 inches it starts making some noise that annoys my
primordial hind brain. Since I work with a lot of 1/2" bar stock that
leaves me finishing on the drill press among my other secondary operations.
What causes that eerie noise, and what can I do about it? I am already
blasting the area with water soluble flood coolant. If I could spiral mill
all the way through it would save a fair amount of time in secondary
operations. Often I have several molds to do the hand finish stuff on at
once. Each half will have atleast two alignment pin holes, and anywhere
from 2 to 20 clamping screw holes to be finished.

Greetings Bob,
Are you using carbide endmills? It sounds like you have a rigidity
problem. .400 depth of cut for a 1/8 endmill is pretty long.
Especially for HSS. I think what is happening is chatter. You can
make things stiffer, slow the cutter, and increase the feed to help.
Sometimes these options are not viable. But there are also cutter
options. Carbide cutters are made in 1/8 diameter with 3 flutes that
are not evenly spaced. This helps with resonant vibrations which I
think is what you are experiencing. What size are the holes you are
making? When spiral milling are you cutting a .125 slot? Is the hole
diameter smaller than .25 so that the chips have somewhere to go? You
may be having problems with chip evacuation which leads to chip
recutting.
Eric