Breaking router bits

[sm38240]

All,

I am cutting Cumaru which is a hard exotic almost as hard as Ipe. Cutting on a CNC at a feed rate of 60 IPM with a cut depth of 0.1”. Using an Amana 1/4” down cut spiral bit with the spektra coating. Here is my problem: they break. I have about a 50% failure rate. In contrast, I cut use a standard Bosch 1/4” down cut spiral bit all day long on the same tool path without breakage. It just gets dull quicker. I have about come to the conclusion to use the cheaper bits and change them out more often. What am I missing here? Amana tech support says to go slower. Does not make sense when I can run the Bosch at the same feed rate and cut depth. Granted, the Cumaru is hard, but the 60 IPM seems conservative? Work piece is secure and bit is tight in the spindle collet. 18,000 RPM in both cases.

insight welcomed

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[awerby]

What kind of CNC machine are you using to do this? The feedrate seems slow, if anything, and the depth of cut seems conservative enough. I'd suspect the machine is not rigid enough, but you say another type of bit works okay. Is the Amana tool solid carbide while the Bosch is High Speed Steel? The former is more brittle, but it still shouldn't be breaking that much. Have you tried an up-cut bit? Usually down-cut bits are used when cutting plywood, so as not to disrupt the top veneer, but it sounds like you're cutting solid wood. I don't think the coating's really necessary either.