Endmill turned black

So, today I did a bunch of post-holiday gifts, and at some point, my “go to” endmill had its tip turned black… and it ended up cutting like a drill bit from the on. (in the “every drill is an endmill if you push it hard enough” vince sense).

So clearly I’m doing something wrong in my F&S (although I’ve been using this type of endmill with these F&S for like 2 years)… just looking for advice on what that wrong is

The bit in question is https://www.amazon.com/HOZLY-3-175X2X12mm-Downcut-Efficiency-Aluminum/dp/B073TXC45Z/ which is a single flute, 2mm diameter downcut endmill.

I was cutting hardwood at 30 to 35 ipm, 0.045" DOC with 45% or so stepover (carbide create has bugs if you do exactly 50% so I always reduce it a tiny bit) at 22k RPM (with PWM spindle control so that’s pretty accurate). Some slotting (for a 0.25" deep cutout) was involved as well

At $4 a pop did you just get a poorly made one by chance?

perhaps… it worked ok for an hour or two prior, but sure, it’s only $4 (normally they last longer… and if they snap, it’s just $4)

Carbide turns black just like hss when it is overheated. Carbide can lose its temper just like hss. That is why your bit is dull now. Hard to say why but sometime maybe you sit some extra hard wood, knot or just because it was time to wear out. Who knows how these things happen. For me it has happened when I had a malfunction and #201 buried itself into the spoil board and then tried to plow forward. At the point of the blackness it is done and replace it. It is possible it is dirty but you could soak it with oven cleaner or other types of commercial bit and blade cleaner but I think you would be wasting time.


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