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Posted by Joe788 on September 3, 2009, 4:28 pm
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e:
> >> =A0There's machines that lower the feed as needed to hold a location w=
ithin a
> >> tolerance. But....that sux.
> >> =A0The reason is the rpm stays the same.
>
> >> I think the reason the rpm doesn't change is mechanics, getting a spin=
dle to
> >> ramp up or down takes a lot of energy. But has anybody heard of one th=
at
> >> changes the rpm when it slows the feed proportionitely?
>
> >> =A0Sounds like it doesn't matter, but these things don't just race to =
a corner
> >> and slow down, they variably slow down on the way to the corner. And i=
n some
> >> reall jagged toolpath they might be feeding half the feedrate of the o=
pen
> >> areas.
>
> >> =A0If you were milling 1000 parts out of graphite, and your rpm wasn't
> >> relative to the feedrate, as in now it's feeding half as fast but spin=
ning
> >> full speed you will get cutter wear. Anyone who doesnt think so can cu=
t a
> >> few pockets in graphite using a HSS cobb mill. If you get the rpm and
> >> feedrate at the right point that cutter will last years. You spin too =
fast
> >> and feed too slow that cutter won't make it thru more than 1 or two po=
ckets
> >> before it wears the edges off.
>
> >> Doesn't sound like a big deal, but in production milling...could mean =
a ton
> >> of money in cutters.
>
> >The key is to use a toolpath that doesn't make sharp corners, so the
> >machine doesn't *have* to slow down. I would tell you to just use the
> >Dynamic Mill toolpath, but NX doesn't have it, or anything
> >comparable.....
>
> =A0 How do you know this?
A little birdie told me.
> =A0 Why call the functionality "Dynamic Mill toolpath"?
Same reason Surfcam calls it "TrueMill", Celeretive calls it
"Volumill", and Cimco calls it "Adaptive Clearing." It sounds cool.
> =A0 And why not just radius all sharp corners in the first place
> if that's what you want?
Because that's not what I want.
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> tolerance. But....that sux.
> The reason is the rpm stays the same.
>
> I think the reason the rpm doesn't change is mechanics, getting a spindle to
> ramp up or down takes a lot of energy. But has anybody heard of one that
> changes the rpm when it slows the feed proportionitely?
>
> Sounds like it doesn't matter, but these things don't just race to a corner
> and slow down, they variably slow down on the way to the corner. And in some
> reall jagged toolpath they might be feeding half the feedrate of the open
> areas.
>
> If you were milling 1000 parts out of graphite, and your rpm wasn't
> relative to the feedrate, as in now it's feeding half as fast but spinning
> full speed you will get cutter wear. Anyone who doesnt think so can cut a
> few pockets in graphite using a HSS cobb mill. If you get the rpm and
> feedrate at the right point that cutter will last years. You spin too fast
> and feed too slow that cutter won't make it thru more than 1 or two pockets
> before it wears the edges off.
>
> Doesn't sound like a big deal, but in production milling...could mean a ton
> of money in cutters.