2 flute vs 4 flute Question

[Michael Burnside]

David, you’re not terribly far off at 0.005” moving at 175, so you don’t really fall into the dust category. Those are at least chips. I don’t know a lot about your machine or your depth of cut used on hardwoods but it’s possible you’re still spinning a tad fast or you could increase IPM a little.

[David Falkner]

David, you’re not terribly far off at 0.005” moving at 175, so you don’t really fall into the dust category. Those are at least chips. I don’t know a lot about your machine or your depth of cut used on hardwoods but it’s possible you’re still spinning a tad fast or you could increase IPM a little.

Depth of cut on hardwoods is sufficient to cover the bottom of the compression bit which is 0.25" on the bit I use, so my DOC is usually around 0.300" on 3/4" thick stock. If it's a piece that I've planed or resawn down to around 1/2" then I cut it in one pass, same spindle speed and feed rate. I've cut the same pieces at 250 ipm but unless it's a production run 175 ipm works out fine for me, especially for one-off pieces.


I'm not understanding where the 0.005" came from, though (chip load, maybe?). Can you enlighten me, please sir?

[Michael Burnside]

Depth of cut on hardwoods is sufficient to cover the bottom of the compression bit which is 0.25" on the bit I use, so my DOC is usually around 0.300" on 3/4" thick stock. If it's a piece that I've planed or resawn down to around 1/2" then I cut it in one pass, same spindle speed and feed rate. I've cut the same pieces at 250 ipm but unless it's a production run 175 ipm works out fine for me, especially for one-off pieces.


I'm not understanding where the 0.005" came from, though (chip load, maybe?). Can you enlighten me, please sir?

Yes the 0.005" is the rough estimate of chip-load given you are running at 18K RPM, moving at 175 IPM with a 1/4" 2-flute endmill. Ironically given the 18K RPM as a fixed target, I'd have started with 225-250 if my machine could handle it, but again, I don't think you are too far off. I'd say you're in the -20% to -30% category, unlike many that are >100% off The only thing that saves poor chip-loads is taking shallow bites, but it won't stop dulling bits or burning wood and honestly their jobs are just taking longer than necessary.

[David Falkner]

Got it, thank you! I have cut at 600 ipm but it was due to a typo in my setup. However, the bit, machine, and piece of wood handled it without any issues. I was a mess watching it cut that fast but the machine just grinned and rode it out. But that also tells me I could be cutting much faster than 175 ipm.

[John TenEyck]

Forgot, slotting with a 4 flute puts a flute on centerline, which is trying to deflect ... 'things' ... while the trailing flute is generating one of the walls.

A climb cut might need a finish pass to get the dimension and finish you want, depending on material, thickness ... and the rigidity of the machine.

A 2 flute ramps its way in and out of the cut, with less deflection... usually.

Tools last longer as well, on finish passes ... the flute gets a good bite into the material, instead of 'rubbing itself to death' from the progressive entrance with a conventional cut.

Disclaimer: I'm mainly a 'metal dude'.

I mostly use 2 flute end mills. On my machine a climb cut always results in a tapered sidewall, so I use a conventional cut when I need a true 90 deg angle. I haven't tried a finishing pass with a climb cut, however, so that may solve the problem. I'll have to give it try sometime.

Overall, I'm not worried about bit life. I'm more concerned about part quality. 80 ipm with a 0.25" 2-flute bit and 0.175" doc gives me parts with a nice smooth finish. The chipload is only 0.004 but bits still last a long time.

John