Even though it *is* what is recommended by the manufacturer (they only use rivnuts or flowdrilling for M6 and M8 holes and the brackets require M5) I've taken on-board the difficulties of tapping, and have ordered some A2 M5 rivnuts and a setting tool - plenty to practice with.
2mm is not very thick for a thread, but stainless is quite soft ... drill with lubricant, white spirit will do if you don't have proper cutting fluid.
Use a taper tap first, keep it 100% vertical ... don't waggle it about, moderate pressure, screw it in gently ... it will start to bite .. then
1/2 turn fwd, followed by 1/4 turn back, and keep going until through.Then put through the 2nd tap (or plug) depends which you have.
Well then that would work, no tapping required. Be sure to make a good indent with a centre punch in the pipe before you start to drill. The drill tends to wander on SS, esp. on a convex surface. I don't think you will need practice, pretty straightforward. Just lots of coolant. I find WD40 OK for this.
Yes you *definitely* need a pillar drill, and a good centre punch mark to start. And clamp the pipe securely, ideally in a proper machine vice. Wrap with cardboard to prevent marking.
Low speed, but IME quite high pressure. And a sharp drill.
See if you can find someone with a tin of trefolex cutting compound, ideally for the drilling but especially for the tapping. And definitely tap by hand, with frequent reversals (each time it starts to tighten significantly) to clear swarf.
Good point. Rivnuts are another good option.
Thanks all for the education ...
The parts should arrive this week, I'll have to cut the (5 metre) tube into the banister and balustrade lengths, mark it, then take it for a quick trip up the motorway to use the pillar drill.
I've got one of those kits and it's very useful. Not tried it in tube, though. They're really designed for a flat surface.
I've bought some with countersunk heads
and some flat head ones
Hoping the countersunk ones will work best, the internal deformed portion will be what resists pulling-out, the reduced head will be less good at resisting push-in, but that will be sandwiched between the surrounding tube and the saddle-bracket, so should not be much of an issue.
I saw a suggestion that the flat ones could be peened over if necessary, there are some inbetween small flat head ones too, but I didn't buy any of those.
I'm sure it will provide an adequate fixing. Just how good it will look - if you can see it - will be the issue.
It would be worth buying a centre drill for starting the holes...
I'm not sure how much use those are in a pillar drill - they're more designed for use in a lathe. And tend to be made out of rather softer steel than ordinary twist drills - so go blunt more quickly.
A decent centre punch should do the job - perhaps with a support down the tube inside to avoid damage.
IME they are ok as long as the quill is not too sloppy. Even then, if you adjust the table so you don't need to use the drill at full depth they usually give a marked improvement on the smaller twist drills.
I remember dad having a set of them, but those were rusted to hell 30 odd years ago.
They don't seem to come in metric sizes (or at least not a full range), so e.g. a 1/4" centre drill would only be useful as a pilot hole for a
7mm hole for the rivnut.
You only use a centre drill to make a "countersink", not to make a through hole! I agree with John, they are fine in any reasonable pillar drill.
Oh OK, see I told you we didn't get taught it at school!
Split point drills will do a significantly better job and will only require one operation.
The size is not that important - its just to get a hole started in the right place. You don't have to drill that deep with them.
I was trying to remember what they were called.
I think the main danger with thin SS is the drill gabbing and breaking as it breaks through the metal. You need not to be pressing too hard when you are almost through.
Oddly, mine did both, in the interests of providing an all-round education.
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