End Milling Strategies

To All:

There is an interesting article in Modern Machine Shop titled "Steering
Clear Of Corner Concerns" (at least *I* thought it was interesting).
Here are a few excerpts from the article.

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http://www.mmsonline.com/articles/020604.html

Typical tool paths often drive cutting tools into corners where the
machining load increases, requiring NC programmers to use reduced
machining parameters. This means lowering spindle speeds, feed rates or
depths-of-cut, reducing stepovers or some combination of these in order
to preserve the cutting tool.

When a cutting tool enters a corner, more of the tool becomes
surrounded by, or engaged with, the workpiece material. This engaged
portion of the tool can be measured and expressed as an angle, the tool
engagement angle (TEA).

?So, for all its history, basing toolpath strategies on maintaining a
constant stepover between cuts doesn't appear to follow the best logic,?
Mr. Coleman concludes.

Although a TEA cannot be held strictly constant, the company contends
that it can be controlled to great advantage.

?Designing a toolpath strategy to accomplish this was not trivial, and
implementing the solution was even more difficult, but it has been
done,? Mr. Coleman says.

Mr. Coleman offers other examples of successful applications. One site
in the Midwest machined 4140 steel with a ½-inch diameter, solid
carbide, four-flute end mill, at a 12,000 rpm spindle speed and a 1,000
ipm programmed feed rate. This was not accomplished by using light cuts.
The axial depth of cut was ½ inch and the TEA was 64 degrees, which
equates to a programmed stepover of 0.140 inch.
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Back to real-time here. I think that's pretty darn impressive. We cut
a lot of materials but I've NEVER come close to being able to cut 4140,
or 4130, with a .500" end mill at 12,000 RPM and 1,000 IPM with an axial
DOC of .500" and radial DOC of .140".
Forget the high speed control needed to pocket at 1,000 IPM, AND the
special toolpathing to keep a low TEA, has anybody come close to these
numbers EVEN on the the OUTSIDE of a part and had the end mill last more
than a few minutes? Now I'm sure rigidity of the machine and setup are
of paramount importance, but still, those seem like some significant
SFPM (1,500+) and chip load (.020+) numbers for 4140.
Has anyone else come close to matching these numbers in a real world
situation?

--
BottleBob
http://home.earthlink.net/~bottlbob
.