Drilling and tapping stainless

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.

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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.

Reply to
Andy Burns
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No, I wasn't allowed to because I was GCE material so metalwork would have been 'wasting my time'.

so I'm lacking in the basics,

Are you sure that's right?

hopefully an 18V cordless drill/driver isn't going to struggle? Take it very steady.

Oh God, hand tap! It will be a total f*ck-up otherwise. It's a bit of an art. Practice first. Buy the tap that only makes a shallow thread, use that first, then the normal one.

No use the crossbar type. You have to put quite a lot of force into it. But you also have to have a precise and careful touch.

Don't do it!

Bill

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Reply to
Bill Wright

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:

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

Good luck

Reply to
Bob H

Round our way, Grammar school did woodwork, secondary modern did metalwork.

No, but it's *an* answer I found, happy to be told different.

Yes, I suspect my short offcut will look rather bullet-ridden before I try the real holes.

Do they have proper names?

OK

That is an option if I f*ck up all my test holes, metal bashing is my neighbour's original trade.

Reply to
Andy Burns

Good enough?

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Thanks, that confirms the 4.2mm drill for M5x0.8

:-)

Reply to
Andy Burns

I've just remembered somewhere with a substantial pillar drill I can probably talk my way into using ...

Reply to
Andy Burns

Yes that will do just fine. Give the drill bit plenty of it when its cutting.

Reply to
Bob H

Ah. You had that one as well. :((

Reply to
Ericp

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

Reply to
Jim Hawkins

Whilst true for a blind hole there is no need to run anything but a taper for 2mm material with plenty of clearance behind.

I'd be a lot more worried about using cheese type HSS taps in stainless for a bottom hole but I would certainly have a go with one on thin material. For this I would view excess force as a warning of impending breakage and an invitation to back off (breaking the swarf) before resuming.

With cobalt drills being so reasonably priced these days I would buy 2 or 3 for the job, just in case, they will make it sooo much easier, they really are a joy to use but more brittle. No need for a pilot at that diameter but an automatic (or manual) centre punch will make centring easier.

Reply to
fred

Thanks, makes sense

I find it odd that they only specify suitability for "some" stainless steel, without saying which

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I presume 304 is less hard than 316?

Yes, I always bargain on a having couple of spares for small diameters, had already put some cobalt ones in the basket.

Reply to
Andy Burns

A 2mm wall thickness ain't going to give much of a thread for M5 bolts. The usual way would be to weld in bosses to increase the thickness. As a rule of thumb, you want about the same thread length as the diameter as a minumum.

Reply to
Dave Plowman (News)

The Grammar school I went to did both, but only until the 3rd year, then if you wanted to continue with metalwork you had to do Technical Drawing which I disliked somewhat :) Ok, disliked a lot, I ended up doing maths/chem/phys/bio instead :)

Reply to
Lee

It's what's specified by the manufacturer of the tube and brackets, nonetheless.

The balluster posts are available pre-cut/drilled to take the glass clamps, so I've purchased those, which are M8 tapped, I don't think they use thread inserts for them.

Reply to
Andy Burns

Would threaded pop rivets be suitable? e.g.

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Reply to
Tony Bryer

If you thought Apple were the masters of the "some sequences shortened" video, try this

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Contrary to my earier reply, they do seem to use an insert on the M8 bolts, I'll check when they arrive, if they use them in the pre-made posts, then rivnuts may be the way to go for the M5 holes.

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Reply to
Andy Burns

Yes, just started considering that, the tool is as cheap as buying tap & holder, and sounds an easier process.

Reply to
Andy Burns

contrary to common opinion ordinary Stainless is not hard per se but it is tough, it is softer than a lot of steels.

Reply to
F Murtz

Taptite screws would be better IMO. They are shaped to roll a thread into thin sheets as you screw them in. they don't cut the metal like self tapers do.

Reply to
dennis

It's not practical to tap metal only 2mm thick for an M5 screw. SS is a bugger to anything with, esp.tapping threads.

Welding job really by someone who is good at it.

You might be able to drill a clearance hole and fish a bolt down the pipe and out of the hole.

Reply to
harryagain

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