Tapping holes while material is still clamped to my mill table?

[Kn8]

Hi The square end on my M4 taps is 3.10mm the hex drive for most standard srewdriver bits is 1/4". I could if it would help spark a 3.1mm square hole in the end of an old driver bit if it would solve your problem.
Regards
Ivan.

[HankMcSpank]

Hi The square end on my M4 taps is 3.10mm the hex drive for most standard srewdriver bits is 1/4". I could if it would help spark a 3.1mm square hole in the end of an old driver bit if it would solve your problem.
Regards
Ivan.

Ivan,

That's a very kind offer. I've got home & measured mine - it's 3.8mm. I've being a little bit slow here - ie taps have different sized ends!

Rather than put you out I think I'll go with that little hex shaft chuck I linked to ...I reckon It'll get some use around my workshop anyway. (that said, I'd love to know how you 'spark' a square hole in the end of a bit though!).

Many thanks.