Recommended drill bits for hardened steel?

[jyoutz]

Cobalt is not the best you can buy...heck, carbide is a lot tougher than cobalt! Diamond tips are even better, but now your talking serious money. However, carbide requires a steady pressure and even feed. It is very brittle and will chip or crack at the blink of an eye! A slow drill press or a milling machine with the correct feeds and speeds work better with it.
One of the things I tend to shy away from is drilling stainless steel with a hand drill! Even with a drill press it can be a challenge! Work hardens in an instance! If you really want something that is even more fun to drill, grab a piece of titanium and try to drill it without the exact speeds and feeds for it! Work hardens faster than stainless, and becomes a nightmare once you let off the feed or speed!
Good luck, and study up on speeds and feeds for different grades of metals and your drilling will improve faster than you would think!
David from jax

I had a brain fart last night when I posted. I meant to say carbide.

 

[CliffordK]

Project Farm did a piece on drill bits. I believe that he attempted to drill various metals including some rather hard metal.

If you are drilling hard steel, then expect to either resharpen or replace bits frequently.

 

[ArlyA]

Project Farm did a piece on drill bits. I believe that he attempted to drill various metals including some rather hard metal.

If you are drilling hard steel, then expect to either resharpen or replace bits frequently.

I love his practical testing.

 

[LouNY]

I have purchased drill bits from here;
Drill Hog®
several times, seems to be decent prices and the bits a decent quality.

 

[Williy]

IMHO you should use some cutting oil when drilling metal

willy

 

[shock]

That was a great video and helped me tremendously. I've narrowed it down to a few sets. Thank you folks!

 

[etpm]

My Bona Fides: I am a retired machinist with about 50 years total experience with about 30 years experience owning my own shop. I would say that cobalt HSS drills are the best choice for what you want to do. Buying high quality drills will pay off in the end. Precision Twist Drill is a good brand. But any brand that MSC sells will be good. Don't be fooled by TiN coated drills. Even though the TiN coating is very good at resisting wear and is also quite slick it needs to be of sufficient thickness to work well. The problem is that there are a lot of cheap drills and other cheap cutting tools that have a coating that is way too thin to have any positive effect. So don't be fooled just because the drill has TiN coating, the drill must also be a high quality to begin with.
If you don't need a long drill then don't use a long drill. The best short drills are going to be Screw Machine Length, AKA Stub Length. The best point is a Split Point. These are the most common point for stub or screw machine length. They center better and require less pressure to penetrate the work.
You must use cutting oil for good tool life and least effort. Don't use motor oil, it is a bad cutting oil and will shorten tool life considerably. Any decent hardware store sells thread cutting oil is small containers. It has sulfur in it which is good for the high pressures encountered when drilling hard metals. There are better cutting oils but the stuff sold in the hardware store is commonly available almost everywhere. If you buy drills from MSC you can also buy some cutting oil from them.
When drilling tough steels to get the best results the drill must be spun at low RPM and the pressure must be kept high. There must always be a chip formed while drilling. It is best to keep the chips from being blue. If the drill stops cutting then either increase the pressure or stop drilling. There are lots of charts online that have the proper RPM for material and drill diameter. Use these for a guideline but try to keep the RPM a little lower. Remember, for your situation, it is better keep the drill spinning slower. This is because with a hand drill it is easy to get the drill spinning too fast. Also, when the drill starts to break through the work back off on the pressure. This will help prevent chipping the drill point.
So, to sum things up, use cobalt split point stub length drills, low RPM, high pressure, and cutting oil. And back off the pressure as the drill breaks through.
Eric

 

[kozal01]

A lot of good info here. As a former tool and die maker and CNC machinist myself my one last piece of advice is to use a quality cutting/ tapping fluid, tap magic is a reputable brand that you can usually find locally. It makes a big difference especially in hard to machine materials. Dont use engine oil, or WD40, or grease, or soap or anything else besides cutting oil. You would be shocked to see some of the nonsense some people use for cutting oil. I'm an apps engineer for a cutting tool company now days and it never ceases to amaze me when I see a customer take a high end drill or tap and try to use crisco, or bacon grease or some other crap that some dude 40 years ago told them to use.

 

[Sawyer Rob]

Tap Magic is some good stuff, I much prefer it.

SR

 

[shock]

My Bona Fides: I am a retired machinist with about 50 years total experience with about 30 years experience owning my own shop. I would say that cobalt HSS drills are the best choice for what you want to do. Buying high quality drills will pay off in the end. Precision Twist Drill is a good brand. But any brand that MSC sells will be good. Don't be fooled by TiN coated drills. Even though the TiN coating is very good at resisting wear and is also quite slick it needs to be of sufficient thickness to work well. The problem is that there are a lot of cheap drills and other cheap cutting tools that have a coating that is way too thin to have any positive effect. So don't be fooled just because the drill has TiN coating, the drill must also be a high quality to begin with.
If you don't need a long drill then don't use a long drill. The best short drills are going to be Screw Machine Length, AKA Stub Length. The best point is a Split Point. These are the most common point for stub or screw machine length. They center better and require less pressure to penetrate the work.
You must use cutting oil for good tool life and least effort. Don't use motor oil, it is a bad cutting oil and will shorten tool life considerably. Any decent hardware store sells thread cutting oil is small containers. It has sulfur in it which is good for the high pressures encountered when drilling hard metals. There are better cutting oils but the stuff sold in the hardware store is commonly available almost everywhere. If you buy drills from MSC you can also buy some cutting oil from them.
When drilling tough steels to get the best results the drill must be spun at low RPM and the pressure must be kept high. There must always be a chip formed while drilling. It is best to keep the chips from being blue. If the drill stops cutting then either increase the pressure or stop drilling. There are lots of charts online that have the proper RPM for material and drill diameter. Use these for a guideline but try to keep the RPM a little lower. Remember, for your situation, it is better keep the drill spinning slower. This is because with a hand drill it is easy to get the drill spinning too fast. Also, when the drill starts to break through the work back off on the pressure. This will help prevent chipping the drill point.
So, to sum things up, use cobalt split point stub length drills, low RPM, high pressure, and cutting oil. And back off the pressure as the drill breaks through.
Eric

This is excellent! Thank you for taking the time to educate me, and probably, others on here!!! A+++

 

[Skeletor]

Boron steel bits work pretty good and are easy to get. I use them when drilling hardened steel at work. As stated go slow. If your an animal you’ll work harden it and your done.

 

[rScotty]

This is excellent! Thank you for taking the time to educate me, and probably, others on here!!! A+++

Eric wrote: "So, to sum things up, use cobalt split point stub length drills, low RPM, high pressure, and cutting oil. And back off the pressure as the drill breaks through."

To that excellent advice I would add to start with a center punch, drill a pilot hole, and step up in reasonable increments.

And don't forget that the drill chuck is important too. There is a lot of variation in the quality of drill chucks, and the mounting system is fairly standard. Chances are good that an upgraded chucks is available in a taper and thread to fit your drill.
Now that you are getting some good drill bits, might as well put some thought into holding them so they don't slip....much.....
rScotty

 

[sandman2234]

my one last piece of advice is to use a quality cutting/ tapping fluid, tap magic is a reputable brand that you can usually find locally. It makes a big difference especially in hard to machine materials. Dont use engine oil, or WD40, or grease, or soap or anything else besides cutting oil.

I just wanted to mention that WD-40 makes a very good lube when machining aluminum! It keeps the aluminum from sticking and leaves a pretty good finish on a part if you are milling a piece. Otherwise, I never use WD-40...
David from jax

 

[jaxs]

You've received good information but imo no one made strong enough case for using a drill press. I'm able to drill far more holes with a press between sharpening and through material I can't drill with hand held drill. If you've never owned a press even a $40 used bench model will make a world of difference. I'm no good at sharpening bits freehand so I have an electric sharpener with jig. I have some expensive bits I rarely need,99% of holes are with HSS bits that have been sharpened and re-sharpened. Even HSS in large sizes are really expensive so I watch for boxes of misc bits at estate sales and auction. What you save buying a box of used bits for $3 will go a long way in buying a sharpening machine.

I have simple holders with double rows by size. If I dull a bit before finishing I put dull bit in a rack with others to be sharpened then take it's twin from sharp bit holder.

Experts will probably frown on this but I've done it several times without regret. To put a hole through hardened steel without a special bit I torch heat the spot past cherry until it gos to orange/yellow. For a small piece I bury it in a bucket of sand which I had buried a piece of hot metal earlier. For a large piece I clamp Kaowool or ceramic blanket on front and back then throw a welding blanket over it. Allow part to cool until it can be handled with bare hands. Needless to say,material surounding hole will no longer be hard as before unless going through hardening process before puting part to use. I usually opt for the expensive bit if hardness near hole is critical.

Easier but uglier than above. Torch cut oversize hole then weld mild steel patch(es) with drilled hole or washer over torched hole. Did I mention how sloppy my torch cuts are?

 

[Sawyer Rob]

For aluminum, I usually use Pam (the cooking spray) it works very good.

SR

 

[shock]

To follow-up, I ordered some Cobalt m42 drills, a Drill doctor sharpener, and 2 cans of cutting oil.

I appreciate all the input provided - very very much!

Oh, and I already have a drill press !

Any thoughts on use of step drill bits? Obviously not what I'd consider precision holes, at least not in my hands, but can make larger sized holes when needed and large drill bits are expensive when you don't use them 1x a year.... Thoughts?

 

[ArlyA]

Eric wrote: "So, to sum things up, use cobalt split point stub length drills, low RPM, high pressure, and cutting oil. And back off the pressure as the drill breaks through."

To that excellent advice I would add to start with a center punch, drill a pilot hole, and step up in reasonable increments.

And don't forget that the drill chuck is important too. There is a lot of variation in the quality of drill chucks, and the mounting system is fairly standard. Chances are good that an upgraded chucks is available in a taper and thread to fit your drill.
Now that you are getting some good drill bits, might as well put some thought into holding them so they don't slip....much.....
rScotty

Any hole over 3/8 that's I'm drilling, I pre-drill a small pilot hole. I thought everyone did? All with cutting oil.

 

[the old grind]

Any thoughts on use of step drill bits?

Stepped bits are for sheet metal to make round vs oddly shaped holes. One can fake it for slightly thicker metal than the distance between steps. As with any drill bit they have a cylindrical margin and wobbling will do more to dull the tool than to improve the hole in any way.

btw, glad to see other toolmakers check in. Oh, and with a trickle going on plain water is a vastly underrated coolant when out in the yard. IMO so is ATF in moderation elsewhere. Carbide is better left to use in mills than DPs and will typically crumble if used in a hand drill. This has all been covered above and was a good read till I showed up.

 

[kozal01]

Stepped bits are for sheet metal to make round vs oddly shaped holes. One can fake it for slightly thicker metal than the distance between steps. As with any drill bit they have a cylindrical margin and wobbling will do more to dull the tool than to improve the hole in any way.

btw, glad to see other toolmakers check in. Oh, and with a trickle going on plain water is a vastly underrated coolant when out in the yard. IMO so is ATF in moderation elsewhere. Carbide is better left to use in mills than DPs and will typically crumble if used in a hand drill. This has all been covered above and was a good read till I showed up.

Water soluble coolant like used in CNC machining centers works great from a spray bottle on drills in the press or hand drill and I prefer it over oil, its just harder to come by for most people.

 

[Rustyiron]

I don't know you or exactly what you're drilling, so don't take this as an insult or attack. I worked construction and fabrication and know lots of people who needed some coaching when using drills. Number one issue was mashing the trigger all the way. Others were not enough pressure and no lube. Some could go through 10 X as many bits as others.

There are all sorts of bits with regard to the material they're made of, grinds, etc. More information would help someone more knowledgeable than I give you some great input.

Very "gently" put!