Ah,
I to have run into this situation before on bar stock turnered out to be the material was a little difrent in the mid of the bar stock than on the ends go fiquire like to drove me nutttsssss!!! It could be a chemical dif or mechanical like its ben work hardend. I would try a slighty higher feed rate and or more depth of cut to keep the tool loaded. Also what type of tool (insert) are you using (I.E. CNMG 431, CCGX 430 exc.) pluss lead angle of. Oh and material condition.
Oh ahh is this a first op or 2nd and or 3rd? just asking cause I have seen parts change by diffrent ops, you know one guy may be more agressive than the other and or vis/versa just a thought.
John |