perimeter bits breaking

[BrintC]

Have mercy, I've only been operating our CNC for 3 years. And am mostly self taught on many problems that occur. This one's got me stumped. Yesterday I broke a perimeter bit, usually not an issue. It's happened a few times in the past 3 years, usually when I haven't slowed the travel speed or feed rate when cutting hardwoods. But this happened in plywood. O.K. maybe a flawed bit, it could happen. But then it happened again on the next program, again plywood. I went through 6 bits from 4pm yest to 9am today. I thought it was the holder so I swapped it, no good.So I tried the collet, which has been worn from other bits breaking again no go. I went back to the original holder and collet, fresh bit and it's been running all day. I'm clueless what I may have done right or wrong. Any suggestions?

[CH]

Check the shank diameter of the bits. We once had a batch of bad 3/8" bits that had some variation that caused a similar situation to what you described.

[BrintC]

Thanks for the tip CH.The old dull bits miked at .01 larger than the new broken bits.Was that about the difference in your situation?