On Tuesday, 13 August 2019 00:17:02 UTC+1, Roger Hayter wrote:
Rob Morley wrote:

On Sun, 11 Aug 2019 14:49:03 +0100
brian wrote:

I need to drill 30 odd 4.5mm holes in a stainless steel pipe; I'm
drilling a small pilot hole ~ 1mm first . Usual type blunt too
quickly 4 holes ! Pipe wall thickness is only 1mm and I thought I'd
get away with it.

Carbide tipped and cobalt seem to be recommended .

Will tile drills do ?

Wrong geometry, a sharp masonry drill would do better (but still not
well).

Any experience or advice ?

If it's just a one-off job and the HSS bit is working OK until it
blunts, I'd probably just deal with sharpening it a few times. If that
was too tedious or otherwise unsuitable I'd order a couple of cobalt
bits. https://www.ukdrills.com/ used to be competitive and quick, I've
not used them recently.

The other thing if you have to sharpen them is to try different angles
from the ones classically set up for drilling thick steel. I don't know
the science or the names of the angles, but if you make the drill more
pointy, and shift the plane of the ground face into the flutes so there
is more clearance at the back of the cut then it may rip its way through
thin tubes quicker, perhaps at the cost of slight raggedness. Well
worth a try, especially if the holes are not going to be visible. Just
do it by hand, there is no point in using a jig if you are trying
arbitrary angles, at least for small drill. But don't let it get too
hot.

Twist drills are designed for steel as a compromise between jamming risk, breakage risk & cut speed. If you steepen the angles it will cut faster but be a lot keener to jam & break. Fine on wood, but trouble on SS.

A big impediment to drilling speed is the blunt zone in the centre. If you thin that down, a twist drill drills everything a good bit faster.


NT