Drilling stainless steel.

[macd]

You're mixing up symptoms with causes. Heat doesnt harden austenitic stainless steel and neither does pausing. Indeed heat softens it but heat in that case is about 1050C - thats the temperature at which we annealed stainless wire after drawing it. What work hardens it is work, so if you put work into it without achieving cutting or just limited cutting then it gets harder and ever more difficult to cut. To put it another way, you need sharp drills, decent steady pressure and a lubricant to avoid the flukes of the drills getting to tempering temperature and softening. At all costs avoid anything remotely like rubbing or skidding across the surface that would come from a blunt drill.[/QUOTE]

Thanks for the technical heads-up. I think you'll find that your practical advice (italicized) is substantially as mine in post #3.

 

[simonfraser]

+1 to above, recently drilled 5mm diameter through 4mm SS battery powered, slow speed with a new drill bit, water cooled the tip, no problem.

 

[Boathook]

Did you have to resharpen any of them

Not yet, but I purchased them for a project and when last used seemed ok on s/s.

 

[KellysEye]

I found HSS drills don't work on SS but Cobalt ones do use machine oil to lubricate.

 

[SteveGorst]

+1 for Cobalt, it just makes it a whole lot easier.

 

[Gunfleet]

I love this board. I’m just considering drilling some stainless tube and along comes a thread telling me how to. ��

 

[Brent Swain]

Around here we us a cutting fluid called " Rapid Tap." Works well.
I once built a 36 for a guy who had his drill press outside. He would set a 5 gallon pail of water with a 1mm hole in the side near the bottom, along side the drill, and point the 1mm stream of water at the point of his drill bit, while drilling. He never burned a drill bit. Keeping your drill bit cool is critical, as is keeping a steady pressure on it. I have used a 2x4 with a lashing holding down one end ,the drill part way along , and put pressure on the opposite end , for a primitive, use anywhere, drill press. You can usually rig something like this, in many awkward positions, where a drill press would never fit. A bit of innovation goes a long way.
If your bit starts to squeal , take it out and resharpen it. Pushing on a squealing bit, just heats it, takes the temper out ,and hardens the stainless. It should just continue cutting cleanly. Anything else, is time for re- sharpening.
When you sharpen it, avoid overheating the bit. Make sure your cutting edge is higher than the back of that surface, or it will just ride on the back shoulder, not letting the cutting edge reach the stainless.
I once had some holes to drill in stainless, with a high speed drill. I just bumped the trigger, to avoid the high speed, cutting thru in short bursts. Not as good as a variable speed drill run slowly, but got the job done, without burning the bit .The last bit, which tended to grab, I reved her up, and when it was racing, just bumped it thru, in short bumps.

 

[guyd]

If you have burnt the hole, as we all have, then re sharpen the drill to a significantly different angle to the usual 112 degree - ie very flat or very pointy, this often is able to cut through the hardend bits.

 

[DownWest]

I don't bother with cobalt, just use good HSS and sharpen them as soon as there is a hint of a problem. Cutting fluid everytime and a pillar drill. If not possible to use a pillar drill, then a slow hand drill. Likely a decent battery drill can do a better job of controlling the speed than mains one.
A while back, away from resources, I had to drill a bunch of 12mm holes in 12mm SS bar. Used a 600 rpm hand drill..but it was a bit 'character building'.

 

[KellysEye]

One thing I forgot to mentions is I only found out about cobalt drill bits when I asked a marine work shop what they used to drill SS.

 

[lw395]

If you have burnt the hole, as we all have, then re sharpen the drill to a significantly different angle to the usual 112 degree - ie very flat or very pointy, this often is able to cut through the hardend bits.

I was modifying something which had previously been drilled, it was a piece of 4mm(?) ss plate which I'd 'recycled' from a scrap bin many years ago,
I first tried a brand new HSS drill, proper oil/water cutting fluid, drill stand, slow power drill which went in about 1/2mm then blunted.
I didn't have a cobalt drill of the right size, 5mm iirc.
So I took it to a mate, who has a pretty serious workshop.
He ground a carbide tile bit to size on a diamond wheel. Went through the stainless with no fuss at all.

Very variable stuff 'stainless'. Particularly when you don't know where it came from, where it's been or how it's been abused.
Things like the bent bits of a pulpit can be stupidly tough.

Lots of people relating stories of how they've had no problems using an HSS bit is not much help when you get a bit of stainless that some previous sod has work hardened already.
I have a mini lathe. Bit of a toy really, I keep wanting to push its limits. I've turned stainless in that. I use carbide tools which I sharpen before use using a 'green' stone in a dremel.
So, my experience is that nice new stainless, you should be OK with HSS and a pillar drill.
Stainless with 'history', at the first sign of trouble carbide is a good answer.
Cobalt alloy drills are somewhere in between.

Whatever bit I use, water or water based coolant is good IMHO.

 

[Brent Swain]

If you have burnt the hole, as we all have, then re sharpen the drill to a significantly different angle to the usual 112 degree - ie very flat or very pointy, this often is able to cut through the hardend bits.

Good one ! Thanks! If one is drilling a lot of holes in stainless, of a certain size, one can have on hand a couple of bits with different angles,so it becomes simply a matter of changing bits.