Bob H wrote:
On 21/09/2013 19:51, Andy Burns wrote:
At some point in the next week or two, I'll want to drill and tap a
dozen holes into stainless steel tube, this is 2mm wall thickness,
42mm diameter handrail, I'll have a 100-200mm offcut to practice on.

Now, we didn't do metalworking at school, so I'm lacking in the
basics, but a bit of searching seems to suggest ...

For M5 bolts, use a 4.2mm drill, assuming it's 0.8mm course pitch
(need to check) hopefully an 18V cordless drill/driver isn't going
to struggle? Drill slowly to avoid work-hardening

Lubricate (use WD40 at a push)

As I'm tapping through, rather than into, the steel use a spiral
point, rather than spiral flute, tap.

What flavour of HSS (cobalt, vanadium, extra vanadium, nitride/oxide
coating etc) does the tap need to be to cope with 304 stainless?

I see 1/4" hex shank taps are available, e.g.
http://uk.rs-online.com/web/p/threading-taps/6699384

Will these work OK in the drill/driver? Or should I hand tap?

Given I'm unlikely to ever want/need a full tap/die set, can you buy
screwdriver or T-handle style single taps?

Any other tips appreciated.


To drill stainless steel, use a slow speed drill, and don't put too
much pressure on the drill. Also, I strongly recommend you use proper
metal cutting fluid or paste.

You said you were going to tap the drilled holes, so make sure you use
the correct sized drill bit for the tap size.You can do a search for
that. Well I've done it for you:
http://www.engineershandbook.com/Tab...ictapdrill.htm

I have only had about 30 odd years experience in the engineering
trade, so I know nothing, lol.

Good luck

Taps come in setrs of three - taper, second cut and final cut.
use them in that order in a hand tap wrench, and do it very slowly,
in a series of small cuts - one or two turns cutting followed by a few
turns in reverse to clear the swarf from the flutes of the tap.
Lubricate with white spirit.

Jim Hawkins