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I'm trying to drill pilot holes through my exterior door frame in order to install a weather seal.

I purchased a few new cobalt drill bits labeled for hardened steel.

However, each new bit was only able to drill one pilot hole before losing its ability to drill holes.

After two bits, I tried applying some oil to a third new bit to keep it from overheating, and while that worked in keeping the bit cool, it still was only able to successfully drill one pilot hole. After the initial hole, the bits stopped working and could no long drill through the steel.

Any thoughts?

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    To me it sounds like cheap bits or two high speed. I have used standard high speed steel many times to work on steel security doors. – Ed Beal Jun 29 '18 at 22:18
  • I'm using Irwin 5/32" cobalt bit for hardened steel with a spit point to start drilling on contact... I don't see any indication of the bit being high speed though – Steve Jun 29 '18 at 22:24
  • High speed steel is the cheapest of bits. Cobalt and titanium nitrite. Bits cost more and are usually better carbide can even last longer but tend to shatter because they are so hard. – Ed Beal Jun 29 '18 at 22:41
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Use a masonry bit! Don't believe me just try it. You may need to sharpen end a bit into a pointy arrow type shape, med speed, grease the drill site, reasonable push as you drill

  • I admit I've never tried this, but I'm skeptical. I feel like the manufacturers would sell bits like this if it really was an improvement. – Rob Elliott Jul 23 '18 at 14:10
  • Oddly enough, the masonry bits worked. They are brittle, and I ended up breaking a couple of them throughout but in the end it was these that worked. – Steve Jul 23 '18 at 19:53
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If it is possible that you used the drill bit with the electric drill set to the wrong rotation direction, without realizing it, the freshly ground new drill bit will likely be able to drill a hole through the thin steel but at the same time will dull and round off sharp edges so much that a second reverse operation would never start to cut into the metal.

The electric drill has to be setup to rotate the drill bit in the direction shown in this picture:

enter image description here

  • Another maybe: do you have the drill set to 'hammer' or 'percussion' mode? – User95050 Jul 1 '18 at 12:36
  • I'm using a Bosch 12V, 2 amp cordless drill. I put in a fully charged battery and made sure that I was drilling in the right direction. There's no hammer or percussion mode that I know of on the drill. – Steve Jul 1 '18 at 16:38
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A Steel Step Drill Bit.

This is what I have used to drill through steel beams. Mind you this is much cheaper than what I use for commercial use but still works very well and can be found on Amazon or most hardware stores.

$10 Amazon.com link

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You don't mention the specifics of the technique you tried, so I'll offer general metal drilling advice:

  • Drill slow. Assuming you have appropriate drill bits, the thing that is dulling them is too much heat. As a test, if the bit is too hot to touch, you're going too fast.

  • Use Oil. This reduces friction (heat) and helps dissipate heat. Any type of lubricating oil will do in a pinch, but cutting fluid is designed for this.

  • Use a Step Bit for larger holes. These function essentially as progressively larger pilot holes, so you're not cutting so much metal at once. Not necessarily applicable to your scenario.

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You do not have hardened steel doors . Your bits are almost certainly dull from turning too fast with-out enough pressure. Get new sharp bits, you don't need high speed steel but most of them claim to be that. Turn the bit slowly with a variable speed drill , with high pressure and oil. You should see metal shavings quickly. Drilling in a spot where you spun the bit previously will be more difficult because that steel will be cold worked. Cold working can easily triple the hardness of the steel ; maybe you do have hardened steel doors ( in small spots). It will be easier to start with a small bit then a larger bit. The oil is mostly to lubricate; real high speed steel will cut at 1000 F so cooling is not so important. The gold color on bits is a very thin layer of titanium nitride ; nitriding is also done on steel but is just black. Carbide point mason bits have poor geometry to cut steel.

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