[Greenworks]

Hello all,
Tried searching SFM, but I guess I'm inept at search, because it kept saying no results found.
Anyway, I understand the concept of SFM, but I have a question about it's realistic application. My lathe has a maximum RPM of 4000. I have a 35° profiling insert that recommends 1800 SFM. My finish pass is at 0.94". At that dimension and SFM the RPM should technically be 7314, well above my lathe's maximum RPM. How do you compensate for this? The only variable I could see to change would be feed rate. Do I reduce it to keep the ratio of rpm to feed, or is it inversely proportionate where I would increase feed to compensate for lack of surface feet travelled. Or am I thinking about it all wrong because IPR is IPR, and no matter the RPM it will slow or increase proportionally because it's per revolution? Or am I just thinking too hard??lol The relationships wouldn't be so confusing if there wasn't the caveat of the realistic limitations of my lathe's RPM.
Thanks

[rcs60]

the only thing that changes is the sfm
it would decrease to 984 sfm from the 1800 sfm as the max rpm is 4000
feed rate is determined by the insert (what it was designed to turn for a feed rate)
the feed rate would remain the same through out the cut (ipr is ipr)
the only thing you would see is a decrease/increase in ipm depending on the rpm's
ex-- 7000rpm at .005ipr = 35ipm
4000rmp at .005ipr = 20 ipm

[Greenworks]

So keep my G96 set to 1800, G99 to .004, and G50 at 3600 (where I like the cap on my little aluminum parts) and the only thing that changes or suffers is my cycle times. Good to put that quandary to bed. Next logical question would be why some metals have a different SFM than others if feed is feed and a revolution is a revolution. It's gonna shove that tip in just the same if it's going 10 or 1000 RPM. My guess is heat or horsepower? Heat being the biggest. Slow down the cut, slow down the heat, slow town fatigue on the insert.

[rcs60]

The sfm is based on the tool composition (substrate, coatings/ no coating) and the material being machined
this example is from the machinist hand book
free machining steel uncoated tool sfm = 600 -----coated =1350
aluminum un coated =1800 sfm
the feed rate is based on the inserts construction (chip breaker / edge prep ect.) and the manufacturer will have it listed on the package or literature
chip breakers come in different designations a general statement would be finish/medium/rough styles