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.

Dave


The logic is correct, but the math reasoning is wrong.

The calculated figure of 8 IPM for HSS is not based on half the surface
footage of carbide, as the spindle speed is 2000 RPM for BOTH, which
equates to the same SFM for the HSS as the carbide, therefore with the
same chipload, the feed will be the same.


2000 RPM = about 250 SFM







--
Steve Walker
(remove wallet to reply)