[smdubovsky]

I know this has been discussed before (drills/taps) but I couldn't find the thread. Anyway, I needed to tap some 4-40 holes in some thin steel. Drilled the pilot holes and went to look for my taps. Crap, don't have a 'good' one in the box so had to settle for my made in ??? HSS kit. Im reluctant to say china as they're typ quite well made. Even HSS vs carbon steel. No Greenfield (USA) but decent. Except the 4-40 it turns out...

So, I start tapping the hole and hear light 'crunching'. I figure its just the chips and keep turning it back a partial turn to break them. After about the right depth I pull (!??!?) the tap out. Something doesn't look right. They undercut the root of the threads so thin the teeth just break off FWIW, The thread form doesn't look very good either.

NOW, I have to order a real tap and hope I can clean the HSS bits out of the existing hole so I don't ruin that one.