[koenbro]

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.

[koenbro]

Progress report: I increased the speed to 66ipm (CL 0.0027), and increased the DOC to 0.02", keeping the same RPM. Also used a brand new 2 flute 1/4" bit. Edges are much cleaner, there is no burning of the MDF spoilboard, and the chips look good. The third try was good, and is shown.

Could probably increase to 72 IPM (CL 0.003) and the DOC to 0.04".

[koenbro]