I'm trying to drill through 1/4" hard steel. the thicker bit went through relatively easily one time, but on the second go just spins. the thinner bit did not go far .. i think both need to be sharpened or are low grade bits. I'm doing this by hand. Wondering if they are Cobalt, Titanium, HSS, M35, M42? likely none of these.

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Basically i'm trying to drill through the flat side of a T-post. The steel is harder than a mother. Any suggestions?

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  • `The small bit appears to have a titanium nitride coating (gold color) but that says nothing about the content of its character. If you can't find identifying information on the bit, it's practically impossible to say what it was unless you have the package from when you bought it. You could try torching the spots you intend to drill before you drill them, but that might not help much depending on what the T-post metallurgy is. You can get drill bits for drilling very hard steel, but they have to be used in a very rigid setup (drill press or milling machine) as they are very brittle. – Ecnerwal May 24 at 16:11
  • It's usually better to use things that clamp/mount to the T-post rather than try to drill them. Such things are pretty commonly available from a T-post dealer. – Ecnerwal May 24 at 16:15
  • Do you have a drill press? The extra pressure from a drill press is very helpful. I once had about a hundred similar sized holes to drill in various shaped 1/4" thick pieces of steel. The pieces that I could get into the drill press were a lot easier. Use new bits and don't overheat them. – Mattman944 May 24 at 16:58

Yeah, newbies + metal drilling is usually a recipe for disaster.

Usually I'm a fan of having newbies use hand tools for a good while until they get the tactile feel of the tool and the material. That's hard to do in drills, though, as proper, usable hand drills are practically unobtanium these days. So I'd prefer newbs start with a drill press where parameters are easier to control. So let's talk about that.

To drill a metal, you start with what material it is, then you go off to a chart of feeds and speeds for what engineering and experience has shown is correct for that material. I work a lot with mild steel and I prefer to start with 1/8" drills because they're dirt cheap and they break about when they get dull.

So feeds and speeds chart tells me that for tool steel speed wise I should be at about 60 surface feet per minute, or 720 inches per minute. A 1/8" drill is about 0.4 inches circumference. So 720/0.4 gives me 1800 revolutions per minute.

Since we're not milling or lathing, and I don't have a drill press with an autofeeder, feeds must be dialed in "by feel". "Feed" coarsely maps to "pressure" when in a drill press or a hand drill.

When you have feeds and speeds correct,

  • Cutting is efficient and makes good progress.
  • Chips are long - they are not chips but slivers/tendrils, and they are so long and consistent that they threaten to wrap themselves around the drill bit! So you back off for a second which has the effect of breaking the tendril.
  • The drill bit does not get hot.

So if the above isn't happening, newbies tend to go "oh, that's normal" and continue with bad technique. STOP. Don't have any tolerance for bad drilling into metal, because that only work-hardens the surface, making it even harder to get restarted.

First, make sure your drills are sharp.

Then, recheck your speeds and make sure they're at least in the ballpark. Like I said into hard steel you need 1800 RPM on a 1/8" drill. (more like 3000 RPM into mild steel). That can be a problem. Everybody these days has one of those studly drill-drivers which is mainly for driving drywall screws, and it maxes out at 400ish RPM. That would be about right for a 1/2" drill bit into tool steel, but the tool doesn't have the torque for that.

A Dremel moto-tool (whose arbor is 1/8") only develops significant power around 7000 RPM. Then there are the cheapie corded drill-NOT-drivers, which like to spin around 1500 RPM. They're not a bad fit actually.

For Feeds, you have to dial that in with pressure. And the usual mistake is to not use enough pressure and again, work-harden the material. IME enough pressure requires pushing hard enough. And - this takes skill - you have to push straight down the drill bit, not partly to the side, otherwise you'll break the bit! Note that the handle is not in line with the bit.

You know when you have pressure right, because you start getting lovely, stringey chips and cutting proceeds at good pace. Learn to do that again.

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  • disaster is a bit dramatic... The thinner bit snapped and i took a grinder to it with much more aggressive angle and was able to drill 4 holes at a nice and steady speed! There definitely is a feeling when it's cutting you can't understand when your a noob like I was 30 minutes ago.. ha.. BTW, what's it like calling somebody a noob? I've never done it especially in person. :) – Hell.Bent May 24 at 17:49
  • @Hell.Bent I didn't say noob. That's a different word with a very different and very unkind meaning. It does not apply here. Even if it did apply, I wouldn't say it about someone here lol. "Newbie" is just a new person. "Noob" is sophomoric: both incurably ignorant AND arrogant. – Harper - Reinstate Monica May 24 at 17:58
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    i wish I was new person, but I'm an old person. ie (unlike in noob-ie) somebody who's been around. no worries. – Hell.Bent May 24 at 18:05

The pics aren't clear enough for me to comment on the specific bits, but a couple of general hints:

  • start with a small hole and increase drill bit size until you get to your desired size. It's particularly hard for a large-ish bit to make the central dent that gets the rest of the bit cutting

  • slow is better than fast, as you have less risk of overheating and de-tempering the drill bit. (Once you de-temper, the bit is basically trash.)

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  • you saying after de-tempering you can't even sharpen? These are small bits. Only need like 1/8" hole or so. I updated one of the pics if that helps. – Hell.Bent May 24 at 16:00
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    You can sharpen, but it won't stay sharp, especially in a hard substance, as in "de-tempering" you have softened the drill bit. While it is possible to reharden and retemper, it's not easy, and with a drill bit you are likely to warp it into uselessness while attempting that. i.e. basically trash is correct. – Ecnerwal May 24 at 16:06
  • Thank you for the speed overheating comment. heard and seen before but a reminder and it really does make a difference and helped . – Hell.Bent May 24 at 17:38

They are finished, buy new bits. It would be very unusual for a home craftsman to properly sharpen a bit. I suggest buying three bits of graduated sizes, drilling small ,medium , and final size holes. That little straight section in the center of the bit point is called the chisel, it does not cut but pushes metal aside. So by using a small drill first( with a very small chisel) you cut out the metal that would otherwise be pushed away by the chisel of the larger bit.Alloy makes no difference to the home craftsman as long as it is HSS ; A gold color means it has a very thin layer of Titanium carbide , worn away with use. The particular HSS steel makes a difference when you drill 50 holes in steel , properly resharpen and repeat several times. Larger bits should turn slower with high pressure. They must be cutting, when a bit spins in the hole it work hardens the the steel , then you really do have strong steel . More difficult for even a sharp drill to cut. Cutting oil helps, the old high sulfur oil was best ,but it is now politically incorrect and not available. Overheating is an "after-the-fact" problem for HSSteels. The damaging heat can only occur after the drill is dull and spinning in the hole. HSS are tempered at 1050 to 1100F + and they actually get harder at those temperatures.. So they would need to be heated well above 1100 F to be hurt; dull red heat in a dark room. Carbon steels can be hurt at 300 F depending on how hard they are.

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