Stainless steel - Work hardening

[PaulJ]

I have been trying to drill a 6mm hole through 5mm stainless, so far without success. I drilled a smaller hole first, a 3.5mm drill seemed to go through easily enough but when I tried to enlarge it to 6mm, it simply squealed and wrecked the drill bit. A second (new) drill bit also failed. I am using a pillar drill and both bits were of good quality and sharp, to start with!...... What can I do to overcome work hardening? Is it possible to soften stainless by heating it?

Paul

 

[sailorman]

what spd are you using
you need the slowest spd possible

this was a hh battery drill with an 8mm hss bit, 25mm deep

 

[sarabande]

Cutting fluid needed; also when enlarging the hole make sure the work piece is really well clamped as the bit will grab it as it breaks though, so not only slow rpm but slow feed especially at the end.

 

[rogerthebodger]

I have been trying to drill a 6mm hole through 5mm stainless, so far without success. I drilled a smaller hole first, a 3.5mm drill seemed to go through easily enough but when I tried to enlarge it to 6mm, it simply squealed and wrecked the drill bit. A second (new) drill bit also failed. I am using a pillar drill and both bits were of good quality and sharp, to start with!...... What can I do to overcome work hardening? Is it possible to soften stainless by heating it?

Paul

For a 6mm dia hole you do not need a pilot hold. In fact drilling a pilot hole for 6mm will cause the cutting edge to dig in and damage the drill bit.

I often drill holes up to 8 to 10 mm without a pilot hole using a pillar drilling machine.

As Sailorman says you need to drill at a slow speed and endure there is enough pressure to make the drill bit cut and not run.

 

[macd]

With a pillar drill, it should be straightforward. No need for a pilot hole (which, as you've found, risks work-hardening) unless the size is large. Sharp bit (HSS is fine), slowest speed, plenty of pressure, lubricant (as much to cool as lubricate, so nothing special required). The bit needs to keep cutting: if it just spins, it's doing bad things.

 

[lw395]

Much smaller pilot hole would be good.
But now you are where you are, a carbide tile bit might work.
Or a carbide masonary bit, you'll need to get it really sharp using a green grinding wheel though.
Plenty of water for cooling.

 

[Topcat47]

Slow speed, lots of cutting oil (3 in 1 will do at a pinch) and cobalt steel drills. Carbide tile drills won't have a good cutting angle when new and you'll spend too long trying to re-grind one to the correct angle, even with a green wheel.

 

[Ian_Edwards]

I started a thread on this a short while ago:

http://www.ybw.com/forums/showthread.php?474518-Drilling-Stainless-Steel&highlight=

I found drilling SS a bit like Jekyll and Hyde, sometimes it was very easy, other times I made no progress at all.

The best combination I found for drilling 8mm holes was:

Go with the lowest RPM you can, really slow.
Use the maximum axial pressure you can, to the point of almost stalling the drill.
Use a Cobalt drill with at least 6% cobalt and ensure it's very sharp.
I started with 3 in 1 oil, but found that cutting paste was better.
I found that drilling a pilot hole didn't make much difference.
If you work harden the SS with a blunt drill or drilling too fast, it's really hard work to make any progress, even with a new cobalt drill. I was simply bloody minded and persistent!
I manage to drill 28 @ 8mm clearance holes through 5mm 316L SS plate and 28 @ tapping size for an 8mm tap through 5mm 316L SS flat bar.
It took much longer than I'd expected it to do.

Good luck

 

[lw395]

Slow speed, lots of cutting oil (3 in 1 will do at a pinch) and cobalt steel drills. Carbide tile drills won't have a good cutting angle when new and you'll spend too long trying to re-grind one to the correct angle, even with a green wheel.

I've found tile drills to work, I've got a supply of ss sheet offcuts which is hard as any stainless I've ever encountered.
Well, it was free!

For thicker work, carbide drills are not silly money:
http://www.ebay.co.uk/itm/Tungsten-...hash=item1c810f4327:m:m_CiEEaRYgtWwsChkuueTsg

 

[bigwow]

I take my jobs, that need holes, to my local engineering place, they punch them out on a press thingy.

 

[PaulJ]

Thanks to all for your quick replies, I am now happy to report...... SUCCESS! I was already using the slowest speed on my pillar drill and had been using oil to cool it. I had one remaining HSS drill bit so I decided to have one last go. This time I used water for cooling and LOTS of pressure and thankfully it worked.

Thanks again to all for your advice.......... There's a lot of knowledge and experience out there!

Paul

 

[d4dunmor]

Surprised at how often this comes up
There are a few simple things to do when cutting stainless
First make sure your bit is correct and sharpened correctly
6mm no need for a pilot
Spot /centre drill for a start for your drill
Coolant a cutting fluid that will cool and lubricate
Low speed
Rigid set up clamp work pillar drill will give better results than a hand drill
I would not use a solid carbide drill these are more used for production drilling and automatic feeds
Use a plastercine mould around the drilled hold to hold the cutting fluid

 

[William_H]

I use just ordinary machine oil. (sump oil) This as the advantage tht it smokes something terrible if you get the SS or drill too hot. So stop let it cool and add more oil. Glad OP got past the work hardening and succeeded. olewill

 

[reeac]

The one thing that I was once told is to make sure that swarf is always being produced whilst drilling. . If it isn't then the drill bit will skate over the surface and work harden it.