Killer Drill Bit?
 

Who has a good drill bit to recommend for a tough steel drilling job? I have a broken starter bolt in my block that has been a thorn in my side. I finally came up with a way to center the whole for extraction and started drilling yesterday. Three different 1/8" bits and they all barely put a divit in the bolt. I hope I can just buy an individual bit for this first hole. I have left hand bits for going up in size

Re: Killer Drill Bit?
 

Not sure if these would work but they are for hardened steel. McMaster usually has it all.

https://www.mcmaster.com/products/dr...ardened-steel/

Re: Killer Drill Bit?
 

Yeah
Richard beat me to it.:lol:

One thing I will add is if you have drilled and the center is (Not) on center .
One of these (Uncoated Carbide Drill-Point Countersink
for Lathe Centers, Trade Size 3, for 7/64" Drill Bit
Part number
2925A13 ) from Mc Master Carr
Will get you back on center.

Re: Killer Drill Bit?
 

I'm no help on drill bits, unless you want to know how to break one off inside the stuck bolt. But here is what I do if I have a little room to work.

I try to do is get the face of the offending bolt cleaned up by: Flattening the surface with a demal bit, then with another very small round dremal bit I make a divot and start on a cone shaped cavity. I make is so the bit cannot wander. It's patient dental work, but I have success. I've even used small dremal bits to get a deep enough cavity to get an easy out in. Plus the cavity releases pressure.

Good luck, broken bolts are a bummer. :chevy:

j

Re: Killer Drill Bit?
 

I have not used these yet but want to buy a whole set. They are expensive but I like the step bit point as these always seem to get a good bite on metal no matter the hardness. I see you can get from ebay, walmart and others. I think snap-on or mac have their own version as well. Good luck
https://knkut.com/media/catalog/prod...1-16_3_1_1.jpg

Re: Killer Drill Bit?
 

Believe it or not for hardened steel I use masonry hammer drill bits. They will go thru a grade 8 much easier than normal bits.

Re: Killer Drill Bit?
 

Dang dude, that a GR 8 bolt? Took me forever to drill a GR 8 3/8" out of a head, heck my big ask son had to finish it. I like Irwin bits, but........

Good to know. With a hammer drill?

Lots of good ideas above.

Re: Killer Drill Bit?
 

This bolt is also recessed into the block, so no flattening. I'm hoping once I get an 1/8" pilot hole I can move up in size with left hand bits. Those are Harbor Freight, so hopefully can at least bite in enough to spin the bolt shank. I'll order up one of those bits from McMaster.

Those step-tip bits are interesting. I'll look at those, too

Re: Killer Drill Bit?
 

They also make left hand drill bits. The advantage to them, as you are drilling counter, clockwise it builds up heat, and sometimes the bolt will come out while drilling.

I believe McMaster Carr has them also.

Re: Killer Drill Bit?
 

No sir just in a normal drill at medium speed works pretty good. They will go dull but it takes a lot longer. Lefties work great too but getting them started in hardened steel can be a pain in the ass, definitely the best case is the lefty hooks and spins the whole thing out.

Re: Killer Drill Bit?
 

Milner Hauffen tool company. Their drill bits are not recommended for mild steel. Just hard materials. They don't actually the material but kind of file their way through. Not cheap but you can buy only one and they have a lifetime warranty.

I think they have left handed bits too.

https://millnertools.com/collections...dual-drill-bit

Re: Killer Drill Bit?
 

Cool, thank you

Re: Killer Drill Bit?
 

Thanks for more offerings to check out. Left hand bits are the greatest for drilling out a broken bolt shank. I bought a set to do this originally, because my old set was nowhere to be found. But they are poor quality I'm sure, came from Harbor Freight. I'm using a RH 1/8" bit for the pilot. I bought a hinge pin screw centering tool that fits, a bit loosely, into the hole the bolt is broken off in. I removed the 1/8" wood bit, ground a flat spot on a high speed steel bit, and inserted. But it's not cutting it. Tried a cobalt bit, no better. I have had great luck using LH bits on broken bolts. They have brought the shank out w/o need for an extractor. I don't think I've ever tried an extractor that didn't break off. This bolt wasn't ceased, so should thread right out once I get a purchase on the shank

Re: Killer Drill Bit?
 

A carbide burr on an air grinder at high rpm will work wonders compared to a drill. Drills will need to be harder than the bolt, and drills that hard will be more likely to chip since they're more brittle. One chip and they stop cutting.

If its not recessed that deeply then the best way to get a broken bolt out is to build up tack welds on the shank until its flush, then weld a washer to the tacks, then weld a nut to the washer and back the whole thing out with a wrench or socket.

Re: Killer Drill Bit?
 

A while ago I was rebuilding an old Kohler 10hp engine from a wheel horse garden tractor and one of the head bolts snapped off. It was one of two that straddled the exhaust port so they were subject to trillions of extreme heat cycles and thus were extremely hard. I chewed up several regular twist bit that just squealed and barely made a mark. I went go a local loss and got an 1/8" and 5/16" dewalt cobalt drill bits. They were pricy at $7 and $15 but destroyed my snapped off hardened bolt easily

Re: Killer Drill Bit?
 

The cobalt bits I have aren't cutting. I need a clean drilled hole, not eat the bolt up. This isn't a ceased bolt, just a broken bolt. Not rusted in. It should back right out once I get a grip on it. I figure a LH bit will turn it out. If not an extractor into the drilled hole.
I know about building up a weld in a hole using copper tube to line the hole. But I don't have a wire feed welder and this is a starter bolt hole in a 350 in the truck. Pretty tricky welding above on what you can only see from below. It would be nice with engine out and on a stand flipped upside down. I'm trying what I can with engine in truck

Re: Killer Drill Bit?
 

Whenever I have to drill out broken bolts, which are usually the exhaust manifold down pipe bolts, I buy a brand new set of bits from AutoZone. I start with the tiny one, it drills easier than the larger 1/8 bit. Don't push hard or you'll snap it right off. Once that is started use the next one up until you can fit your left handed bit.

Re: Killer Drill Bit?
 

Yes, I always use a really small pilot bit, then work up in size when drilling metals. I did try that starting with a 1/16" LH bit, and stepped it up twice before I realized the bit had crept way off center due to the uneven plane and flex in a tiny bit. This hinge screw centering tool uses an 1/8" bit, so kind of a big for a pilot hole and tougher on a bit. I am concerned about using these hard McCallister-Carr bits with a hand-held drill. All I can do is try. I use a thread cutting oil when drilling steel but not much help here with drilling 'up'

Re: Killer Drill Bit?
 

You probably don't have stuff laying around to make a Mist coolant system.

This would be a lot of trouble for one bolt.

I will just throw the Idea out there thou.:chevy:

Re: Killer Drill Bit?
 

That is a cool gizmo. what goes up comes down all over the drill and my hand...and hopefully not my eyes just off to the side of directly below.

I screwed around and haven't ordered a bit yet. Been too busy posting about this broken bolt situation I have :lol: