I do a lot of countersinking in carbon fiber, and I have found that it dulls ordinary high speed steel countersink bits very quickly. Each set of my CElipse wingtips requires 96 #12 holes to be countersunk, and a brand new bit is basically done for by the time I get to the last one. I have tried sharpening the bits, but it is finicky and I don't really trust them.
I have just ordered a solid carbide countersink and a less-expensive carbide-tipped countersink from Pan American Tool. Once I make sure they work well in the material, I will see how well they hold up.
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https://www.panamericantool.com/countersinks.html)