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Speed and feed confusion

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

Reply to
Dave, I can't do that
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"Dave, I can't do that" wrote in news:7de866b9- snipped-for-privacy@q12g2000yqj.googlegroups.com:

You started out with .002" per flute for both carbide and HSS. You calculated IPM based on two diferent RPM's

Then you made the RPMS the same by multiplying by DIFFERENT ratios. That's where the percieved magic comes in. Nothing special is going on since you started with the same cut per tooth for both HSS and carbide. When you made the RPM the same for both (2000) the cut per tooth is still the same (.002") so the IPM is the same (8).

Reply to
Charles U Farley

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
Reply to
Steve Walker

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.

Reply to
DoN. Nichols

Thanks Don, Steve and Charles,

OK, I got it. Definitely a senior moment there. Once I became fixated on the expectation to see a difference, logic left the building.

Dave

Reply to
Dave, I can't do that

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