Toughest drill bits?
Thread Starter
Melting Slicks
Joined: Aug 2005
Posts: 2,606
Likes: 4
Toughest drill bits?
I'm trying to drill out a bolt and have burned up three drill bits (appx. 1/8" +/-) without making nearly a scratch.
Can anyone recommend a type/brand of drill bit for this project? The bolt isn't hardened...
Can anyone recommend a type/brand of drill bit for this project? The bolt isn't hardened...
Melting Slicks
Joined: May 2003
Posts: 2,387
Likes: 2
From: Meriden CT
Originally Posted by majic1984
Dewalt cobalt bits... haven't broken one yet.
those are good bits... generally, the more $$$ you spend on a bit, the stronger it'll be. Try going up a size or two if you've got the room... smaller bits always break easy.
Drifting
Joined: May 2003
Posts: 1,634
Likes: 2
From: Melbourne, Victoria, Australia, the World
By now the broken bolt is "heat treated" by the drilling. It will be hard to get started even with a good bit 
Perseverence will get through the tough section to the "softer" material.
Perseverence will get through the tough section to the "softer" material.
Instructor
Joined: Mar 2005
Posts: 141
Likes: 0
From: Brampton, Ontario
Cobalt bits should do the trick, but because you have hardened the area already, you may want to try carbide. Carbide WILL drill through anything, but be careful it is very brittle (because the drill is so hard). Keep a steady hand and constant pressure. DO NOT re-grind carbide without a proper mask, carbide dust is entremely dangerous!.
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Melting Slicks
Joined: Apr 2000
Posts: 3,341
Likes: 6
Trust me on this one gentlemen, I know of what I speak...
When you are in a situation where a high speed steel drill bit -assuming is is not dull- cannot get the job done, go to your friendly local hardware store and buy a masonary drill bit.
They retain the toughness needed for pistol drill use via the steel shank, yet have the extreme hardness needed to cut the hard workpiece because of the carbide brazed onto the end.
When you are in a situation where a high speed steel drill bit -assuming is is not dull- cannot get the job done, go to your friendly local hardware store and buy a masonary drill bit.
They retain the toughness needed for pistol drill use via the steel shank, yet have the extreme hardness needed to cut the hard workpiece because of the carbide brazed onto the end.
Drifting
Joined: Apr 2004
Posts: 1,651
Likes: 11
From: Seattle WA
Originally Posted by 45ACP
Trust me on this one gentlemen, I know of what I speak...
When you are in a situation where a high speed steel drill bit -assuming is is not dull- cannot get the job done, go to your friendly local hardware store and buy a masonary drill bit.
They retain the toughness needed for pistol drill use via the steel shank, yet have the extreme hardness needed to cut the hard workpiece because of the carbide brazed onto the end.
When you are in a situation where a high speed steel drill bit -assuming is is not dull- cannot get the job done, go to your friendly local hardware store and buy a masonary drill bit.
They retain the toughness needed for pistol drill use via the steel shank, yet have the extreme hardness needed to cut the hard workpiece because of the carbide brazed onto the end.
First choice carbide, second choice cobalt. I would suggest you find an industrial distributor locally that has a walkup counter (WW Grainger if available). They will most likely have what you need. Here's an example: http://www.grainger.com/Grainger/wwg...736796&ccitem=
Also get a split point drill as they will not "walk" as much. Use an oil lube (30 wt motor oil works) and above all be patient.
Le Mans Master
Joined: Jun 2002
Posts: 8,339
Likes: 24
From: I can walk to MA
If possible ... torch it up cherry red and let it cool slowly.
This will de-temper the steel and make it softer.
Twisting off the head of a bolt will harden the area where it broke.
This is known as "work hardening" - the same thing that lets you
bend a coat hanger back and forth to break it ... the hardening
of the steel in the area where bent (worked) makes it more
brittle and allows it to crack. Hey, that materials science class
from college days finally paid off.
So, even a non-hardened bolt that twists the head off can
become hard - and not from rapid thermal or chemical treatments.
Drilling from the opposite end may work better, too.
If drilling ends up not working, you could try a diamond point on
a dremel, but that will be slow going. Something like the 7105 shown here:
http://www.mytoolstore.com/dremel/dmdbits.html
Good luck
This will de-temper the steel and make it softer.
Twisting off the head of a bolt will harden the area where it broke.
This is known as "work hardening" - the same thing that lets you
bend a coat hanger back and forth to break it ... the hardening
of the steel in the area where bent (worked) makes it more
brittle and allows it to crack. Hey, that materials science class
from college days finally paid off.
So, even a non-hardened bolt that twists the head off can
become hard - and not from rapid thermal or chemical treatments.
Drilling from the opposite end may work better, too.
If drilling ends up not working, you could try a diamond point on
a dremel, but that will be slow going. Something like the 7105 shown here:
http://www.mytoolstore.com/dremel/dmdbits.html
Good luck
Instructor
Joined: Mar 2005
Posts: 141
Likes: 0
From: Brampton, Ontario
Originally Posted by toolking
Also get a split point drill as they will not "walk" as much. Use an oil lube (30 wt motor oil works) and above all be patient.
Just for future reference. To keep from burning up drills, instead of going high RPM and slowly pushing the drill (which will burn-up the edge), try a slower RPM and a more constant push on the drill. This is especially true for carbide. Carbide likes to be pushed, but always use your own judgment. Never exceed stability of the drill for a faster feed on the bit.
Last edited by jester4; Mar 30, 2006 at 03:36 PM.
Drifting
Joined: Apr 2004
Posts: 1,651
Likes: 11
From: Seattle WA
Originally Posted by toolking
I agree to a point (no pun intended) .... for this application because they are 2 flute drills most likeley will be too coarse to easily do a good job.
First choice carbide, second choice cobalt. I would suggest you find an industrial distributor locally that has a walkup counter (WW Grainger if available). They will most likely have what you need. Here's an example: http://www.grainger.com/Grainger/wwg...736796&ccitem=
Also get a split point drill as they will not "walk" as much. Use an oil lube (30 wt motor oil works) and above all be patient.
First choice carbide, second choice cobalt. I would suggest you find an industrial distributor locally that has a walkup counter (WW Grainger if available). They will most likely have what you need. Here's an example: http://www.grainger.com/Grainger/wwg...736796&ccitem=
Also get a split point drill as they will not "walk" as much. Use an oil lube (30 wt motor oil works) and above all be patient.
Team Owner
Joined: Jul 2004
Posts: 40,330
Likes: 786
From: Redondo Beach, California
Originally Posted by fast idle
the dremmel diamond wheel is NOT for metal.and will not work.
Thread Starter
Melting Slicks
Joined: Aug 2005
Posts: 2,606
Likes: 4
Thanks for the tips, all.
I guess my problem was drilling at high speed. I'll start over with a good bit on "slow".
Can't use a masonry bit as the bolt I'm drilling is only about 1/4" or so. Can't use a torch as this bolt is broken off in my door (mirror mount)...don't wanna melt the paint. Can't get it from the other side...cause the other side is inside the door.
I guess my problem was drilling at high speed. I'll start over with a good bit on "slow".
Can't use a masonry bit as the bolt I'm drilling is only about 1/4" or so. Can't use a torch as this bolt is broken off in my door (mirror mount)...don't wanna melt the paint. Can't get it from the other side...cause the other side is inside the door.
Safety Car
Joined: Jun 2002
Posts: 4,135
Likes: 1
i got masonary bits small as 3/16 come in the kit for tap cons(concrete anchors) as far as bits she bought me a drill doctor to sharper my old bits,,,works great,i go,slower for steel ,,,faster for alumn i believe alum is 1600rpm on a press,,,but dont qoute me its been years since shop class
Le Mans Master
Joined: Oct 2004
Posts: 5,269
Likes: 54
From: Orlando Florida
St. Jude Donor '05
Slow speed and cooling will work better (if the bolt is not hardened already from drilling at high speed).
try a small masonry drill - as funny as it may sound - these do work if the steel drill doesn't cut ....
You could also try a drill that is made for counterclockwise rotation, swith the drill to 'counterclockwise' and see if it turns the bolt. It may work.... good luck
try a small masonry drill - as funny as it may sound - these do work if the steel drill doesn't cut ....
You could also try a drill that is made for counterclockwise rotation, swith the drill to 'counterclockwise' and see if it turns the bolt. It may work.... good luck
Melting Slicks
Joined: Nov 2000
Posts: 2,507
Likes: 114
From: St. Louis Mo
Originally Posted by TonySinclair
Thanks for the tips, all.
I guess my problem was drilling at high speed. I'll start over with a good bit on "slow".
Can't use a masonry bit as the bolt I'm drilling is only about 1/4" or so. Can't use a torch as this bolt is broken off in my door (mirror mount)...don't wanna melt the paint. Can't get it from the other side...cause the other side is inside the door.
I guess my problem was drilling at high speed. I'll start over with a good bit on "slow".
Can't use a masonry bit as the bolt I'm drilling is only about 1/4" or so. Can't use a torch as this bolt is broken off in my door (mirror mount)...don't wanna melt the paint. Can't get it from the other side...cause the other side is inside the door.
Drifting
Joined: Oct 2003
Posts: 1,426
Likes: 1
From: VetteMOD
St. Jude Donor '05-'07
If you know someone that does production machine work, they may have a supply of carbide, 2-flute, stub ball end mills that need to be sharpened. The cost to sharpen these is usually more than the replacement cost so they are disposed of. I have used these in the past as drills and they make quick work of drilling just about anything.