Drill bits for hard steel

Nathan the Machinist said:
Yeah, that makes sense. A spade bit would be the ticket, and that is basically what in on the tip of a concrete bit. Might help to put a better edge on it on a green stone or something first.

I'll bet that works. Never tried though...
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They work well if you can sharpen the edge on a green or diamond stone plus they don`t break quite as easy .This is one trick I nearly always forget to try.
Richard
 
I have used the masonary bit on hardened steel with pretty good results. Only did it twice, but it worked each time. The bit wasn't worth much after, though:rolleyes:

Rick
 
eyeeatingfish said:
How does cobalt compare to carbide?
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I'm no metallurgist, but I'll try to tell you what I think I know.

Generally, drill bits are high speed steel. M2 is the most common HSS. M42 and others are harder variations containing a lot of cobalt, upwards of 10%. They get very hard, upwards of HRC 70. "Cobalt bits" are M42 or the like, they're still steel.

Carbide is not steel, and (I think) is not technically even metal, it is a ceramic, though most people think of it as metal. It is tungsten carbide dust cemented together with a cobalt binder.

All steel is the same stiffness, regardless of heat treat or alloy. The flex mod is about 30,000 KSI. Period. doesn't matter what alloy or how hard. All steel will deflect basically the same amount as any other steel (in a given section) within it's elastic limits.

Carbide is much stiffer than steel, thus it doesn't deflect as much during a cut. It is much harder. It is not at all ductile, it can not absorb much energy before breaking, it is very chip prone.

So, to sum up, cobalt bits are similar to regular high speed steel drill bits, but a little harder with better abrasion resistance and a little less tough. Used properly, they last longer. Carbide is much harder, more abrasion resistant and fragile. Because it deflects less, it tends to be more accurate and leave a better finish. Used properly, it lasts much longer. It is much more expensive.

Man, that got long didn't it...
 
eyeeatingfish said:
How does cobalt compare to carbide?
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Carbide is much harder than cobalt and will drill stuff cobalt won"t touch. It will also shatter much easier. No side loading and or sudden changes in torque.


Ah, the real expert beat me to the draw with a better answer.
 
ib2v4u said:
Carbide is much harder than cobalt and will drill stuff cobalt won"t touch. It will also shatter much easier. No side loading and or sudden changes in torque.


Ah, the real expert beat me to the draw with a better answer.
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Thanks, but I'm no expert. Seriously.

Re-reading what I posted, it gives the impression that carbide breaks if you look at it funny. It doesn't, it is very strong (5X stronger than titanium) But it is so much more expensive and somewhat less forgiving than HSS that I think of it as fragile.

On modern CNC controlled machinery, carbide is a no brainer.

Drilling a hard knife blank, in a bench vice with a hand drill, will ruin a carbide bit.
 
send it over to david at greatlakeswaterjet and see if he'll cut the hole out for you if possible! The waterjet machine will zip through it like butter.
 
ib2v4u said:
Carbide is much harder than cobalt and will drill stuff cobalt won"t touch. It will also shatter much easier. No side loading and or sudden changes in torque.


Ah, the real expert beat me to the draw with a better answer.
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At work when the airframe fitters break a drill,tap or ezy out we normaly get called over to fix their stuff up ,I usually end up grinding it out with a tungston burr or drill ,I like to put the bits in a high speed pencil grinder and barely touch the bit to be removed.I used one today at home to open up a hole in a tang because I forgot to use a clearance drill for the pin and hardened the blade.
Richard
 
Tinbasher said:
At work when the airframe fitters break a drill,tap or ezy out we normaly get called over to fix their stuff up ,I usually end up grinding it out with a tungston burr or drill ,I like to put the bits in a high speed pencil grinder and barely touch the bit to be removed.I used one today at home to open up a hole in a tang because I forgot to use a clearance drill for the pin and hardened the blade.
Richard
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In our situation as cutlers, if you break a drill bit off in a hole the easiest way I've found to get it out is to drop some ferric chloride in the hole and wait about an hour or two. It will easily come out after it has it's way with it and not mess up the hole.

This was a solution I saw on this forum some years ago. It works.

Craig
 
eyeeatingfish said:
I only have a hand drill.... suggestion?
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Yeah, get a rod - or even better a tube - of some kind (soft is better than hard) and some valve lapping compound from Napa etc and use your drill to abrade though it. I know this will work, but I'm not sure how long it will take.

If it were me, I'd take a piece of wood or something, drill a hole in it, then clamp it to your blade to act as a fixture to hold the rod in place for you, because it is going to take a little while.

Your profile doesn't say where you're at. If you're not too far from me, you could just bring it by and I'll mill it out.
 
I do have a few burs and I love them. Most of mine are a bit big for holes. I need to round up some more small ones. I love the grind thru with a rod method mentioned here. I may use that in the future at times. I would set it up with the block as Nathan suggested and then hang a weight on the press handle and check it every little bit.
 
Nathan the Machinist said:
Yeah, get a rod - or even better a tube - of some kind (soft is better than hard) and some valve lapping compound from Napa etc and use your drill to abrade though it. I know this will work, but I'm not sure how long it will take.

If it were me, I'd take a piece of wood or something, drill a hole in it, then clamp it to your blade to act as a fixture to hold the rod in place for you, because it is going to take a little while.

Your profile doesn't say where you're at. If you're not too far from me, you could just bring it by and I'll mill it out.
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I live in Hawaii, how would that work for you?
I know a guy in Hawaii who might be able to help, just gotta email him.
I will also try one of those spade tile/masonry bits made of carbide and see how that works.
I did take a stone dremel head and ground the hole which did get it started but from there the drill bit is making very very slow progress, like unreasonable to do with a hand drill. I guess I could just go buy a $100 drill press?
 
Wayne Goddard gets the credit here...

I needed to drill some holes in some S30V knives hardened by Paul Boz. I figured i could use cobalt bits. Chucked one up in the drill press and commenced to drill... what the?!?! Cobalt would barely even scratch the surface... even hanging my 200+ pounds on the press lever! I just started laughing and said; "Ooooo i'm in trrouble now!" Then i remembered Waynes idea like a light bulb going off in my head.

Got a few masonry bits... different brands. Figured one brand might be better than another. Took out a diamond file, (cuz the spade shaped carbide tips were anything but sharp as far as drilling metal was concerned)... filed the tip at an angle that was similar to what the cobalt bits had and then used a nice hard super fine stone to get the edges nice and clean and sharp. Chucked it up and went at it. (Oh, and i first centerpunched each spot with a centerpunch i made from an old broken tap... that was funny too cuz i had to sharpen the punch for each hole cuz each "punch" would crush the punch tip.) Those masonry bits drilled through that hardened S30V like warm buttah! BUT, notice i said "bits" not "bit". It took 2 bits to drill 3 - .250" holes. In other words, i got through one hole fine, but as i was drilling the next hole the carbide tip would start chipping, then cracking, and eventually fail. Next bit... would finish drilling the second hole, drill all the way through the 3rd, nice and clean, no problem, but the bit would be worthless to start with for a new hole.

Expensive holes. But, well worth it if the knife is worth it. I think i paid about 7 or 8 bucks for each drill bit. Obviously it's better to drill them before heat treat, but in my situation at the time i couldn't do it that way.

Conclusion: It works, and it works very well.
 
ib2v4u - You can't just apply a steady pressure with abrasive drilling. You have to constantly lift and lower the "Bit". It is the constant application of fresh grit to the spot that does the cutting.Lift the bit enough to allow the compound to fall in the hole every 15-30 seconds. Add a drop or two of cutting oil as needed to make the reservoir slightly liquid.
Stacy
 
Ok. I think I like the burr idea best and I have some carbide drills. I don't do well with the real slow going stuff. I can do it, just hate it. lol. The older I am getting the better I am at it though. I am 56 now and figure by 65 I may be ready for the grind thru hole with out bending the brass rod.
 
The masonry bits will drill the hole "at normal speed", in other words, just a few seconds per hole. Just like drilling warm butter! And the hole is nice and clean. Works perfect.
 
I just now saw this thread, but I'll confirm that masonary bits are the way to go. It was something my grandfather showed me years ago, and I've done it more than a few times since then. Some bits are better, the chrome plated looking ones will only last a hole or two. I found some black oxide coated bits that had a low helix (flutes look extra twisted, more like a wood screw than a standard drill bit). I don't remember the brand now, but they've held up for more than a dozen holes.

The masonary bits are pretty easy to sharpen, I use a diamond paddle and it only takes a few minutes. If you're drilling 1/4" or larger hole, it's easiest to drill a pilot using 1/8" first. This is also a great way to ream a hole slightly larger. I recently had a thong tube that mic'd out at .258", and I had .252" holes. The carbide inserts in masonary bits are slightly oversized. My 1/4" bit mics at .260". It only took a few seconds to ream the holes larger and the tube worked perfectly.

Good luck.
 
Masonry bits work, but the only bad thing is, they aren't exact. Generally they are +/- quite a bit from what you're wanting (I.E. 3/16 or 1/4...).

1/8' shank collared carbide bits will do it just fine. I use them all the time, and now I very rarely drill the steel before I heat treat it.

What size do you need? If it's under .220, I've got it. I have literally thousands of Carbide bits and I'll just send you a few, provided I've got the right size.

Or if all else fails, and you just aren't confident doing it, send it over, mark the spots and I'll drill it for you, no sweat.


Mark T.
 
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