Thanks, Bob. When I take a step back I think of the history of the parts we've made in the past I think it HAS to be the taps. I look at them and the rake and relief seem okay to me but I'm probably giving my eyes too much credit...I imagine a degree here or there can make the difference. I've got some coming in from Widia so we'll see!
Judging the tap geometry by eye is not easy task. One tap looks OK but binds like hell and another one is visibly worn but works still ok.
(I'm the leading expert of chinese qc reject taps sold for pennies on ebay)
Tapping couple of holes by hand (or cordless drill or whatever lets you sense the torque) might tell you more than 20 broken taps on cnc.
Like is the needed torque reasonable, is there something binding or is it making cracking noises as cutting edge is chipping away. And if the tap breaks way too easily.