This is a rhetorical question about an observation that I do not understand.
Why is it that when using either a ball mill or a radius end mill, good
finishes can only be achieved by climb milling? This is an observation I
have made over many years and many machines. This phenomena is true with
perfect setups and new cutters taking large or small cuts, high or low
speeds and feeds.
Steve

Why is it that when using either a ball mill or a radius end mill, good
finishes can only be achieved by climb milling?

At a guess, it's because conventional milling requires cutting into
stock from the thin side of the removed material, making it more
likely that the cutter will deflect, smear, or skip before it has
enough tooth load to dig in and cut, but a round endmill exagerates
this even further because you're cutting an even thinner chip down on
the radius, and that switching to climb milling loads the teeth enough
to put the cutter back into a reasonable cutting depth.

--Glenn Lyford

wrote in message
...
Why is it that when using either a ball mill or a radius end mill, good
finishes can only be achieved by climb milling?

At a guess, it's because conventional milling requires cutting into
stock from the thin side of the removed material, making it more
likely that the cutter will deflect, smear, or skip before it has
enough tooth load to dig in and cut, but a round endmill exagerates
this even further because you're cutting an even thinner chip down on
the radius, and that switching to climb milling loads the teeth enough
to put the cutter back into a reasonable cutting depth.

--Glenn Lyford

Good guess. Also implied in what you're saying is that the cutting speed
near the centerline of the cutter is 'way too low, which makes the problem
worse.

With climb milling you'll get a more adequate chip load near the center,
because all of the deflection is working in your favor.

--
Ed Huntress

Glen & Ed,
I have thought about that as well, but if cutting speed were the key, I
would have noticed a finish difference across the width of the cut, but I do
not. In aluminum, it actually galls. I think it has something to do with
chip clearance, but I don't understand it.
Steve

"Steve Lusardi" wrote in message
...
This is a rhetorical question about an observation that I do not
understand. Why is it that when using either a ball mill or a radius end
mill, good finishes can only be achieved by climb milling? This is an
observation I have made over many years and many machines. This phenomena
is true with perfect setups and new cutters taking large or small cuts,
high or low speeds and feeds.
Steve

On Mon, 17 Nov 2008 16:05:57 +0100, "Steve Lusardi"
wrote:

This is a rhetorical question about an observation that I do not understand.
Why is it that when using either a ball mill or a radius end mill, good
finishes can only be achieved by climb milling? This is an observation I
have made over many years and many machines. This phenomena is true with
perfect setups and new cutters taking large or small cuts, high or low
speeds and feeds.
Steve



What's special about ball and radius endmills? The same (to some extent)
applies to all endmills doesn't it?

"Steve Lusardi" wrote in message
...
Glen & Ed,
I have thought about that as well, but if cutting speed were the key, I
would have noticed a finish difference across the width of the cut, but I
do not. In aluminum, it actually galls. I think it has something to do
with chip clearance, but I don't understand it.
Steve

Chip geometry and clearance are not easy to imagine in a case like this, but
it's true that the periphery of the cutter sweeps across the area cut by the
center of a radiused endmill, wiping out some surface roughness that may
appear at the centerline of the cut. However, that's not the case with a
ball-nose endmill. Surface finish issues are common with ball-nose cutters
but the problem usually disappears in practice because most applications
involve multiple passes to flatten the cusps left after rough milling.

In any case, a ball-nose cutter cutting at feeds and speeds that are
appropriate for the outer diameter of the cutter is turning way too slow for
cutting at the center. And conventional milling makes it worse. If a machine
has the ridigity for climb milling, that will solve some of the problem.

--
Ed Huntress

On Mon, 17 Nov 2008 18:46:39 +0000, Mark Rand wrote:

What's special about ball and radius endmills? The same (to some extent)
applies to all endmills doesn't it?

Only when plunge cutting. With side milling (climb or conventional) the center
of flat bottom endmill does virtually nothing. With a ball end the center is
still cutting *some* material.
--
William

On Nov 17, 10:05*am, "Steve Lusardi" wrote:
This is a rhetorical question about an observation that I do not understand.
Why is it that when using either a ball mill or a radius end mill, good
finishes can only be achieved by climb milling? This is an observation I
have made over many years and many machines. This phenomena is true with
perfect setups and new cutters taking large or small cuts, high or low
speeds and feeds.
Steve

I assume there's some good reason a ball end mill doesn't just have a
single flute at the very bottom?
Take a regular ball end mill, grind back all but one flute close to
the center/bottom.

Seems like that would let the slower (surface feed rate) part take a
bigger bite, but the rest of the mill would have appropriate rates.

I Imagine one drawback would be you'd have to go slower on the plunge
parts.


Dave

On Tue, 18 Nov 2008 05:57:57 -0800 (PST), wrote:

On Nov 17, 10:05=A0am, "Steve Lusardi" wrote:
This is a rhetorical question about an observation that I do not understa=
nd.
Why is it that when using either a ball mill or a radius end mill, good
finishes can only be achieved by climb milling? This is an observation I
have made over many years and many machines. This phenomena is true with
perfect setups and new cutters taking large or small cuts, high or low
speeds and feeds.
Steve

I assume there's some good reason a ball end mill doesn't just have a
single flute at the very bottom?
Take a regular ball end mill, grind back all but one flute close to
the center/bottom.

Seems like that would let the slower (surface feed rate) part take a
bigger bite, but the rest of the mill would have appropriate rates.

I Imagine one drawback would be you'd have to go slower on the plunge
parts.


Dave
Greetings Dave,
Some router cutters are made this way except they remove completely
one flute. I have used these on aluminum. But grinding away one flute
does make the cutter less rigid. So use on steel might be precluded
due to excessive deflection.
ERS

wrote:
Why is it that when using either a ball mill or a radius end mill, good
finishes can only be achieved by climb milling?

At a guess, it's because conventional milling requires cutting into
stock from the thin side of the removed material, making it more
likely that the cutter will deflect, smear, or skip before it has
enough tooth load to dig in and cut, but a round endmill exagerates
this even further because you're cutting an even thinner chip down on
the radius, and that switching to climb milling loads the teeth enough
to put the cutter back into a reasonable cutting depth.

--Glenn Lyford

Exactly right, thin to thick and thick to thin, milling cutters (all)
like thick to thin but the lash in the machine after a certain point
does not. Cutters (all) last longer if you climb cut.

Matt