I am cutting 1/8" 6061-T6 on an Avid Pro CNC using a .25" 2-flute upright Zirconium Nitride (ZrN) coated aluminum bit.
Settings were:
SFM 800 -> RPM = (12/pi) * SFM / Dia = 12,000
I chose a chip load (CL) of 0.002in -> Feedrate = RPM * flutes * CL = 48 ipm.
Multiple passes, DOC (depth of cut) was 0.01".
On first try, I used an older bit and got horrible heat.
Then I put in an identical, but brand new bit, and increased the CL to 0.0025 -> Feed rate became 60 ipm. Heat was much better but still present and I think this is not a sustainable way to work in terms of tool life and finish even with such a simple and short contour.
Any advice on how to reduce heat if I want more complex patterns? Should I increase the CL to 0.003 (feed 72ipm)?
It seems like in the RPM formula, the only variable is SFM; the others are fixed. In the second the CL is the only variable, so these are my degrees of freedom. Should I reduce the SFM and thus reduce the rpm? Should I increase the CL further? Or should I do both?
Any advice is gratefully appreciated.
First try on left
The spoilboard shows the heat.
Less heat on spoilboard on second try.
Finish is poor.