I have an assembly I’m making and one of the parts are these small studs of stainless steel. They have an M8 through the center, three M6 blind holes from the back and an M5 from the side.

It’s 303 I think and I’ve not had too much trouble on the lathe. The mill was tricky but I got it down in the end but tapping it is another story.

Feels to me like its binding or something, after a few turns it tightens up quickly, then makes a loud creaking, then breaks the tap.

The force it takes to twist the M8 tap, to cut a few degrees of thread is just under how much force it takes to break the tap so I got an M8 done with lots of oil gong very very slowly.

The M6’s I’m not having so much luck with, broke three taps already and scraped one part. After a certain point the force it takes to cut the thread is just more than the tap can take no matter how slow I go.

I’ve tried everything I could think of today, someone once advised me to mix some anti-seiz and tapping oil for lubrication with stainless so I’ll try that tomorrow. I have a pot of the nickel stuff knocking about somewhere but I think I’ve already tried machining with that concoction and as I recall I didn't notice much difference.

I could really do with some advice.