Quote Originally Posted by Smiler View Post
What speed were you drilling? Rule for stainless is low speed high feed.
I know what went wrong, I pushed too hard at break through and the metal extruded in to a collar on the inside of the tube. This collar instantly hardened undersize and started deforming to match the bit as it went round. Less than a second later the bit was red hot and deforming to match the collar

I got my 4 holes drilled this morning nil problemo. Should have binned the rest of the bar but didn't :D