internal 6mm thread in 12mm hardened steel shaft

decbrad

Hi, can anyone help me with this? I'm trying to thread a 12mm hardened steel shaft with a 6mm tap. I am getting maybe 3mm deep and the tap breaks. I have heated the shaft up cherry red, allowed to cool, but it's still hard as nails. I even followed some youtube videos

Just to say, even the progressive tap sets are breaking.

Any advice would be great!

Thanks a million

Dec

T5180

it will be almost impossible to tap a hardened shaft without annealing it first . Google the annealing process for the grade of steel you have and stick to it. a slow rate of cooling is essential . Make sure the tap you have is sharp and preferably carbide and use plenty of proper cutting fluid, under no circumstances use lube oil .Go very slow , a broken tap can be tricky to remove.

Turbulent Bill

You could also try a thread insert (e.g., a Helicoil), which uses a larger-diameter tap. They're usually used where the female thread is likely to strip (or has stripped), but might be useful here purely because the tap is more robust.

JIdontknow

Not sure of the purpose of the thread but could you drill out a larger hole and weld an M6 nut to the end of the shaft so the threads can go deeper through the nut? Could cut back the end of the shaft the depth of the nut if it needed to be flush with the end? Some sort of pem insert / thread insert could be an option either.

decbrad

Hi folks and thanks for all the advice and suggestions. At this stage I think I will opt for a threaded insert. But just out of curiosity are there any small engineering firms around Dublin that one could approach to do this kinda thing? the threading part I mean, not the insert, I got that covered.

Thanks again

D