Re: [CAD_CAM_EDM_DRO] Re: chipload

Hi Keongsan:
You have hit on an important point about calculated chipload as an
estimate of feedrate for real world applications.
There is a lot more to put into the mix to get a result that will actually
work.
The strain that the machine, the cutter and the job experience will depend
on all kinds of factors that calculation of chipload alone does not address.

Someone mentioned that a cutter with more flutes can be fed faster because
the chipload per tooth is smaller...this seems intuitively reasonable but in
fact does not often work out because of the power limitations of the
machine.
An easy way to see this is to put a large, fine toothed cutter (say a 1" six
flute carbide endmill) 0.200" into a block of aluminum and feed sideways on
a manual mill with a full width pass.
Now substitute a 2 flute +ve rake insert carbide cutter, and see how much
more freely it cuts, and how much easier it is to turn the handle.
Despite the far fewer flutes to cut with, the 2 flute can remove equivalent
amounts of material per unit time, while consuming far less power even
though the chipload per tooth is far higher for the two flute cutter.
A six flute cutter will use up a lot more ponies to do the same work, and as
the cutter gets smaller, the machine gets flimsier, or the job gets more
delicate, this factor rapidly becomes overwhelmingly important.
It's the gullet depth and the number of flutes in the job that determine the
force needed to advance the cutter.
Try, as another experiment, using a 2 flute 1/4" endmill vs a 1/4" diameter
bur with say 20 flutes.
You,ll likely clog and snap off the bur, and you won't remove much metal at
all.

Depth of cut is similarly important, which, of course, is what you alluded
to when you spoke of saws of different thicknesses.
That is why slavish devotion to chipload calculation alone = busted cutter
and screwed up job.

Chipload calculation is used by the wise as only one of a number of factors
that is considered befort cutter meets steel.

Cheers

Marcus

----- Original Message -----
From: "keongsan" <keongsan@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Saturday, September 21, 2002 11:00 PM
Subject: [CAD_CAM_EDM_DRO] Re: chipload


> --- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
> > Chip load is generally the thickness of the chip, and is
> approximated in practice
> > by the "feed per tooth". So, if a 4-tooth cutter is turning at
> 1500 RPM, and
> > the feed is 15 IPM, then you have a feed per rev of .01", and a
> feed per tooth
> > of .0025". Small end mills may use a feed per tooth of .0007", a
> 1/2" end mill
> > might use .005" feed per tooth on aluminum, for instance.
> >
>
> Does not the width of the tooth (saw) plays a part too? Or the depth
> of cut of the milling cutter?
>
> For example, if we have a case of a cutter with a specific chipload
> of say, 0.0025" at a particular feed. Now we use a cutter with double
> the width (or double the depth of the milling cutter) if chipload is
> express as a linear dimension, there will be no change in chipload
> although my feeble mind tell me that the power requirement (or
> something else) will change. So if we calculate the feed rate based
> on a specific chipload (linear dimension) that feed rate will be
> independent of cutter thickness/depth, which doesn't sound reasonable?
>
> Keongsan
>
>
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