Author Topic: Cobalt drill bits?  (Read 1260 times)

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Offline mattmass

  • Posts: 42
Cobalt drill bits?
« on: October 14, 2017, 08:36 AM »
My dad is doing some work in his garage, and had to drill through a steel beam. After struggling for a while, he picked up some cobalt bits. Said they worked like magic. I'd never heard of that material used for drill bits before, and it got me interested. Does anyone here have any experience with them? I basically only ever drill into wood, but curious to hear what you all think.

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Offline antss

  • Posts: 1453
Re: Cobalt drill bits?
« Reply #1 on: October 14, 2017, 08:51 AM »
They're the only thing to use in stainless steel.

They seem more brittle to me , especially in the smaller diameters.  I don't have any data to support that though.

Offline Cheese

  • Posts: 4825
Re: Cobalt drill bits?
« Reply #2 on: October 14, 2017, 09:55 AM »
As antss noted, they are required if you're working with stainless. Cobalt is more abrasion resistant and will withstand higher heat levels than standard HSS drills. Stainless work hardens, which means if you're drilling holes in it, you need to attack it with speed and force. A brand new HSS drill will drill stainless, however you'll only get a couple of holes before it dulls. A dull HSS drill just rotating against the stainless surface will generate heat and thus, will work harden the surface. Good luck getting through that hardened layer of metal.

Over the years I've slowly replaced almost all my HSS drill bits with cobalt versions. I use them for all metal drilling including aluminum.  If purchasing some, look for M42 which will be stamped on the shank.

As far as brittleness goes, I've never noticed a difference between HSS and cobalt. As a matter of fact, just this week I was drilling some ASTM structural steel and I chipped the tip on one of the last HSS bits that I own. 

Offline rst

  • Posts: 1946
Re: Cobalt drill bits?
« Reply #3 on: October 14, 2017, 11:25 AM »
I've been supplying plastics and making fixtures for a stainless fabricator for 30+ years.  The guy running the place showed me how to drive stainless quickly and reliably.  This was before cobalt was readily available.  Extreme pressure and jogging the trigger.  The pressure insures that you are cutting and not skimming...jogging the trigger allows the heat to dissipate thru the material and drill bit.  It's worked for be for 30 years.

Offline Peter_C

  • Posts: 656
Re: Cobalt drill bits?
« Reply #4 on: October 14, 2017, 01:40 PM »
Coming from the automotive industry, all we used is cobalt drill bits. When fabricating steel or stainless it is all I ever use. I have two sets of cobalt drill bits and sharpen them fairly often. I have broken my fair share of bits though. A drill press is the easiest way to drill metal if possibly. Oiling definitely makes them last longer. I keep an oil can hanging off my drill press. Step drills work surprisingly well for enlarging holes.

Offline Cheese

  • Posts: 4825
Re: Cobalt drill bits?
« Reply #5 on: October 14, 2017, 02:00 PM »
The guy running the place showed me how to drive stainless quickly and reliably.  This was before cobalt was readily available.  Extreme pressure and jogging the trigger.  The pressure insures that you are cutting and not skimming...jogging the trigger allows the heat to dissipate thru the material and drill bit.

I like the tip...it makes sense. I’m going to try it out the next time.

Even using cobalt on stainless doesn’t guarantee 100% success. Ease up on the pressure a little bit or dwell just a little too long and it becomes case hardened.

Offline Laminator

  • Posts: 319
Re: Cobalt drill bits?
« Reply #6 on: October 15, 2017, 04:40 PM »
In my experience cobalt bits are far superior.  I first used one when I had to mount hinges to stainless. They worked great compared to HSS. 
On another job,  I had to drill 1400 holes in heavy steel door jambs and the cobalt drilled faster with less effort and at the end of the job still cut better than the cheap hss bits did brand new.  Cobalt bits all the way for me now.

Offline Bob D.

  • Posts: 807
Re: Cobalt drill bits?
« Reply #7 on: October 15, 2017, 05:00 PM »
Rapid Tap or Tap Magic will make a difference, especially when drilling stainless.
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It's a table saw, do you know where your fingers are?

Offline Michael Kellough

  • Posts: 3469
Re: Cobalt drill bits?
« Reply #8 on: October 15, 2017, 05:01 PM »
I barely managed to drill one hole in 1/2" stainless with a HSS bit.
I had a lot of holes to drill so googled and then when out to buy a cobalt bit.
The cobalt bit drilled only 2 holes so while I was at lunch I bought several more cobalt bits.

The next cobalt bit made it through more than a dozen pieces of 1/2" ss so that first one must have been defective.

Tap Magic was used for all holes.