I was going to say something about my previously listed bias… But apparently I forgot that in the first post and can’t edit it so…
Usual preface, I’m with PreciseBits so while I try to only post general information take everything I say with the understanding that I have a bias.
Said bias being listed there’s a couple things here in general I can address.
First is that coatings are not a total positive. When you are coating a tool you coat ALL of the tool including the leading edge. That has the effect of slightly dulling the edge in exchange for an increase abrasion resistance, surface hardness, and lubricity (depending on the coating). If it’s worth it, or “better” depends on the base tool, the material your cutting, and failure mode.
Noise is commonly caused by a few factors. Too little chipload, too much surface speed, deflection (bit, machine, or both), and poor hold down.
First, let’s assume that you don’t have deflection and you have good hold down. That leaves us with chipload and surface speed. Your 2 listed cuts are 20KRPM at 80IPM and 18KRPM at 100IPM. The 18KRPM at 100IPM works out to 0.0028" chipload, the 20KRPM at 80IPM works out to 0.0020" chipload. So if you want to see if the SFM is effecting the noise you need to run at either of those chiploads at the different RPMs to actually test it:
0.0028" chipload
- 18KRPM at 100IPM
- 20KRPM at 112IPM
0.0020" chipload
- 18KRPM at 72 IPM
- 20KRPM at 80IPM
Additionally, I would probably give a bigger delta as with a 1/4" cutter 18KRPM is 1178 SFM and 20KRPM is 1309 SFM. So only 131 SFM difference between them. Don’t know your RPM range but I’d try to get at least 300 SFM delta to test with.
The easiest way to test if deflection is causing it is to just chop the pass depth on a cut at the same feed and speed. That will give you less cubic material removed per flute, per rotation, while maintaining the chipload and surface speed. If you want to drill down on this further there’s a simple deflection test you can do that I previously posted: Nomad 3 tolerance in aluminum? - #43 by TDA.
Can’t really help much with hold down. There’s not really a good test for it that I’m aware of.
Depending on the results you can play around with things to get the best cut/performance.
Hope that helps.