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
Carbide tipped and cobalt seem to be recommended . Will tile drills do ?
Any experience or advice ?
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
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.
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.
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
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).
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 !!!!!
Wrong geometry, a sharp masonry drill would do better (but still not
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
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.
On 13/08/2019 10:23, firstname.lastname@example.org 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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