On 2010-06-06, Dave, I can't do that wrote:
Hi All,

Must be a senior moment but I am stumped.

1/2" dia. two flute carbide cutting SFM 850, cut per flute 0.002" it
calculates out to around 6500rpm at 26-IPM

1/2" dia. two flute HSS cutting SFM 425, cut per flute 0.002" it
calculates out to around 3250rpm at 13-IPM

No surprises there. However, I don't like running the the spindle at
top speed (3000rpm) so I tried to figure the IPM for say 2000rpm. My
thinking for carbide...

6500 / 2000 = 3.25
26 / 3.25 = 8 IPM at 2000rpm

OK, still so far so good, but using that same thinking with HSS

3250 / 2000 = 1.625
13 / 1.625 = 8 IPM at 2000rpm HUH???????????????????

Where am I going wrong here? The HSS should be half the carbide IPM.

You are using the same feed per tooth, the same RPM and the same
number of teeth, so the feed comes out the same for both. The carbide
could handle a lot more RPM, and under those conditions, it would have a
higher feed -- but as long as you are sticking to the same RPM, the same
number of teeth, and the same feed per tooth, you are stuck at the same
feed.

Enjoy,
DoN.

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