drills for stainless steel

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 ?
Any experience or advice ?
Brian
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Brian Howie

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On 11/08/2019 14:49, brian wrote:

I wouldn't try them.

I does slightly depend upon the grade of stainless steel. However, what is usually important is that the drill is not allowed to dwell during the feed. That quickly causes local hardening of the steel, which blunts your drill.
Ideally, use a powered feed, having first looked up the speed and feed speed in one of the many available charts. If you have that option, use solid carbide drills and flood the work with lubricant.
Failing that, use a pillar drill, use a good lubricant and keep a steady pressure on from start until break through. Trying to drill most stainless steels with a hand held drill is simply asking for problems.
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Colin Bignell

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Yes, what are the holes used for? If its just breaching the material, then you could cut slots. Brian
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On 11/08/2019 19:51, Brian Gaff wrote:

Hi Brian,
It's a boom for a ham radio antenna. I need holes. The holes are on both sides to support the insulated elements. I need the pilot holes on one side to make sure everything is in line before using the pillar drill. I'm using a small hobbyist power drill to do the pilot holes ;it struggles a bit.
The material is 15mm BS4127 Stainless Steel Permatube. I've a few surplus 3m lengths. Normally I'd use aluminium, but I thought I'd try this as it's a bit stronger for the wall thickness.
Brian
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On 11/08/2019 15:08, nightjar wrote:

Nor me

Agreed

Both overkill?

Agreed, pillar drill is a far better bet. I've always been impressed with the new cobalt drills. For 4.5 mm, fairly low speed and firm pressure. 3-in-1 should work, or Toolstation do an aerosol cutting and tapping fluid.
eBay item 183034379363 is £2-75 for 4.5mm. I'd buy two or three to be on the safe side (although I reckon you should get 30 holes out of one).
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On 11/08/2019 22:39, newshound wrote:

...

Not IMO if it is 316 stainless steel. Probably not essential with 304 or one of the 400 series steels, but I did say 'ideally'.
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On 11/08/2019 14:49, brian wrote:

Stainless steel will work harden so you need to keep the pressure on the drill as you feed it in.
The idea is to be cutting the next bit before the previous bit has had a chance to work harden.
DO NOT PAUSE in the drilling, keep going !!!!!
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On Sun, 11 Aug 2019 14:49:03 +0100

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

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.
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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.
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Roger Hayter

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That's ambiguous, I meant back into the flute behind the cut, so there is more clearance behind the cutting edge.
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Roger Hayter

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On Tue, 13 Aug 2019 00:16:59 +0100 snipped-for-privacy@hayter.org (Roger Hayter) wrote:

I get different angles every time I sharpen a drill bit. :-)
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On Tuesday, 13 August 2019 00:17:02 UTC+1, Roger Hayter wrote:

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
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On 13/08/2019 10:23, snipped-for-privacy@gmail.com wrote:

This is one of the "points" about high speed steel (as well as cobalt and solid tungsten carbide). These materials retain their hardness at red heat, at which temperature most steels have the mechanical properties of lead. So you get frictional heating in the centre which softens the target material here while allowing the cutting edges to do their thing just away from the soft zone with much less local heating.
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Or, as the OP has done, drill a pilot hole first.
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Roger Hayter

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