Drilling stainless steel

[Seascaper]

I am having terrible trouble drilling through 3mm stainless steel. I have newly sharpened the drills for the job, I need a 10 or 12mm hole. I can’t get the drill to cut, quite the opposite, red hot and burning metal. Someone I have spoken to recommends cobalt drill and a cutting paste instead of 3 in one oil. I have drilled stainless steel tube before and not had this problem. Any ideas welcomed....

 

[sploo]

Low rpm, and use a cutting compound such as CT90. Cobalt drills are a good idea, and you could also start with a small bit (e.g. 3mm) before moving up in sizes.

 

[Seascaper]

Low rpm, and use a cutting compound such as CT90. Cobalt drills are a good idea, and you could also start with a small bit (e.g. 3mm) before moving up in sizes.

Thanks, will give it a go,
Regards

 

[D_W]

it depends on the stainless. You could have an austenitic stainless that will create heat and then air harden almost instantly, or you could have a type that's work hardening.

or you could have one with a mill finish or polish that's creating surface hardness that won't go through the thickness, but is still hard to get through.

Cobalt and low speed - even water is better than nothing- and will warn you of heat.

I've drilled a fair amount of stainless just with good HSS bits and water as the coolant/indicator. It's not "the right way", but I learned about how easily it will air harden the hard way. Agree with the comment about step drilling - 12mm can be a big ask with any bit dullness at all.

 

[Seascaper]

Hello,
It would seem to harden where it heated up
Regards

 

[Simon89]

A step drill could be your friend

 

[Spectric]

It would seem to harden where it heated up

what type of stainless? You need a pilot hole and then drill slowly without trying to push the drill through, just let it cut .

 

[D_W]

Hello,
It would seem to harden where it heated up
Regards

It'll be very hard to anneal if that's the case. I'm sure there are work arounds. Going slow and dripping water into the divot you drill will give instant feedback about heat since it steams off so easily.

one of the two that I drill air hardens almost instantly. to avoid becoming an expert in the right way, I drill the hole part of the way, drip water into it and stop each time it steams off. Works a charm.

I sharpen my own bits so if I only get two dozen holes, it's not a big deal - I also do use one single norseman (very high quality HSS) bit for the task about the width you're going with. The result is a neat hole and no heat for follow up work (so no hardened stuff around the drilled hole).

 

[Sideways]

As an old engineering mate of mine says about stainless, "get in, do the job and get out !"
Stainless will harden if you let the drill rub.
Slow speed, plenty of pressure and don't hesitate even for a moment, keep the tool cutting.
Imagine that it has a hard skin and you must get the cutting edge under that and keep it under or you're sunk.

I've made 22mm holes in 3mm SS plate using a tungsten carbide tipped holesaw and it can be a devil to cut.
I'd say cobalt drill bits are essential.

 

[--Tom--]

You’ll want to work up through the sizes to 12mm. If you’ve got it hot and hard you’ll not be having much fun as it will have dulled your 12mm bit too

 

[sawtooth-9]

Sideways is totally correct.
I have drilled lots of stainless steel.
Start with a drill about 4 mm at a speed of around 400 rpm - plenty of EVEN pressure.
I find that going 6 mm, 10 mm then 12 mm will work fine. Reduce speed as you increase drill diameter. Probably around 200 rpm for 12 mm drill.
I drill and machine ( lathe and mill ) stainless steel without lubricant but drills ( tools ) need to be sharp. Never had to use cobalt drills for stainless.
If you do not apply quite firm drill pressure, you will just generate heat and blunt the tool.
Drilling stainless is quite easy when you treat it right - tapping blind holes in stainless is another ball game !

 

[Seascaper]

Thanks for all the advice will get back on to it with this knowledge.

 

[Spectric]

If you think stainless is hard going try inconel !

 

[whereistheceilidh]

Agree mostly with Sideways & Sawtooth but if it is marine/A4 stainless then cobalt for me would be essential...especially if someone else is paying.
BTW this is much more interesting than the Royalty thread...........

 

[Fergie 307]

Cobalt will certainly be easier, just depends whether you think the extra cost is justified. If you only do this occasionally then good sharp HSS drills will be fine. Whatever you use the method is as described, moderate continuous pressure all the way through and some lubricant.

 

[Fergie 307]

Sideways is totally correct.
I have drilled lots of stainless steel.
Start with a drill about 4 mm at a speed of around 400 rpm - plenty of EVEN pressure.
I find that going 6 mm, 10 mm then 12 mm will work fine. Reduce speed as you increase drill diameter. Probably around 200 rpm for 12 mm drill.
I drill and machine ( lathe and mill ) stainless steel without lubricant but drills ( tools ) need to be sharp. Never had to use cobalt drills for stainless.
If you do not apply quite firm drill pressure, you will just generate heat and blunt the tool.
Drilling stainless is quite easy when you treat it right - tapping blind holes in stainless is another ball game !

I always try and use spiral machine taps for SS, so much easier.

 

[sawtooth-9]

I am having terrible trouble drilling through 3mm stainless steel. I have newly sharpened the drills for the job, I need a 10 or 12mm hole. I can’t get the drill to cut, quite the opposite, red hot and burning metal. Someone I have spoken to recommends cobalt drill and a cutting paste instead of 3 in one oil. I have drilled stainless steel tube before and not had this problem. Any ideas welcomed....

I should have asked earlier, are you using a drill press or trying to do this with a hand held drilling machine ?
If the latter, I doubt you will have much luck.
Drilling stainless requires relatively slow constant speed with quite a degree of constant force.
If you do it right, you will get a lovely spiral swarf from the flutes of the drill.
I have NEVER used any lubricant / coolant ( except when tapping threads ) - if you need that your drill is going too fast.
With such a thin material, I doubt you will need to retract the drill to clear the swarf.
I have never needed cobalt drills, just standard drills - sharp
Most of my work is with stainless, and just the other day I drilled an 18 mm hole - 35 mm deep with a standard drill and had no problems. I usually go up in steps of 4 mm

 

[clogs]

I was tought go in slow n hard.....no coolant.....on S/Steel

Cobalt drills are really not that expensive anymore...perhaps 50% ......
I dont buy HSS anymore......
I have to drill hundreds of holes in angle iron and other carp steels, often up a ladder and overhead......
Sorry for the PUN but unless u have super branded HSS ^they just dont cut it).....
I've bought thousands of HSS drill bits over the years and even quality bits can often do with a lick on the grinder before use....
PS, as my holesaws wear out they are also replaced with cobal now....
come to think of it, my smaller HSS metal lathe tools have cobalt in em....most of the standard stuff I've given away.....

Sawtooth, have u tried the metal lathe cutting steel from Eccentric Eng, also of ur Parish, OZZ....
I'm quite impressed with it on my smaller lathe.....

 

[imageel]

I've drilled and tapped a fair bit of stainless and I found it can be tricky to judge how much pressure one needs to put into the drill bit to ensure it bites and doesn't skid on the surface, since if the latter happens then stainless will work harden very quickly.
If the latter has happened -as indicated in the original post then the only solution in my experience is to lower the revs, flood with lubricant - WD-40 works well, and increase the pressure to remove the hardened skin on the service and then as soon as the drill bites, back off the pressure to cut at a lower feed rate.
Really this can only be done when the workpiece is firmly clamped and where one can easily control the pressure - as in with a drill press or similar

 

[John Hall]

Have you tried a split point 4 facet bit, preferably cobalt? Much better than standard ground bits on stainless