Cobalt Drill Bits

Hello All,
I had the occassion to drill through some very hard fasteners.
Standard HSS bits were becoming dull in a very short timespan, so I
opted for cobalt bits to continue.
Armed with a set of Craftsman bits, I went back to work. Not much
difference. Altering speeds, using light oil, nothing really worked.
Ended up using a Dremel tool with a cut-off disc to remove the
fastener heads (which presents other problems).
What gives?
Regards,
Ernst
Reply to
Ernst
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--Next time you might try lubricating with Moly Dee. Also I've found cobalt drills are best on things with surface hardness like stainless stampings, as opposed to right-thru hardness like what you're up against. For those situations maybe you're better off with carbide drills?
Reply to
steamer
------------- There are cobalt bits and there are cobalt bits. From personal experience and the many postings in these news groups it is apparent that "Craftsman" quality has slipped in the past few years. You may want to try some name brand cobalt drills from a mill supply.
Another consideration is that the cobalt bits are not necessarily "harder" than HSS (although they are more brittle) but the cobalt provides higher heat resistance allowing higher RPM and faster drilling, which may be important in a production environment.
If you have a very rigid setup [good fixturing, good spindle, and a steady hand] carbide drills may be "better" as these are definitely harder than HSS. These are also much more expensive, difficult to resharpen, and are *VERY* brittle and prone to breakage at the slightest provocation. for example
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?PMAKA=619-0846&PMPXNO=16718590&PARTPG=INLMK32There are special "die" drills for very hard workpieces.
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Unless speed of production is an important consideration, the total tooling cost may well be lower with good quality HSS drills, slow(er) speeds, and lots of HD cutting oil.
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?PMAKA=825-8100&PMPXNO=942746&PARTPG=INLMK32
There are many other good brands/suppliers available, I used Enco just as an example.
Let the group know what you settle on.
Unka' George [George McDuffee] ------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?
Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).
Reply to
F. George McDuffee
Since I'm in a cranky mood, this may be a good time to clarify something for the newbies, who we may be confusing with some terminology.
What you're saying about these materials is correct, but "cobalt" is misleading. There are many middle grades of HSS that contain some cobalt, maybe 4% - 5%, such as M4 and M30. These are often called "cobalt high-speed steel." And then there are the "high-cobalt" grades, often called "super high-speed steel," or "cobalt super high-speed steel," or just "high-cobalt high-speed steel." An example of a grade you'll find in quality tools is M42. There also are more exotic grades used in industry.
But even M42 contains only around 8% cobalt. These are ALL just high-speed steels, with more or less cobalt. There is no such thing as an all-cobalt cutting tool, or even one with a lot of cobalt in it. There used to be some very high-cobalt superalloy grades used in cutting, but they've long since been replaced by carbides.
If you're buying from a clueless supplier, or one who thinks we're clueless (like Sears), their "cobalt" tools might be M4 or something like it (if you're lucky). If you buy good brand-name tools from a mill supply, they're probably talking about M42. There's a big difference.
There. I feel better now. d8-)
-- Ed Huntress
Reply to
Ed Huntress
ews: snipped-for-privacy@4ax.com...
Mmmm, I suspect that even with a super-duper cobalt HSS drill bit the original poster is running it too fast for drilling a "hard bolt".
Supposing the bolt material is grade 8 or a socket head cap screw, the bit should be running 40 t0 50 FPM cutting speed.
Or he is using just plain crappy drills which wouldn't do the job at any speed.
Wolfgang
Reply to
wfhabicher
Or he's using the wrong machine to drive them. If it's a drill press, you need some technique to drill hard steels. If it's a hand-held drill motor, good luck. I'll watch.
-- Ed Huntress
Reply to
Ed Huntress
That the best you can do for a cranky mood? You need to try harder.
FWIW, I just made a wrong turn heading for my favorite shrimp shack and went down the causeway to KCB. your old home town.
Karl
Reply to
Karl Townsend
Thanks for the response(s). I suspected that cobalt bits came in different flavors. Three things to help clarify the situation:
1. I'm basing comparative performance on experience in a manufacturing environment. Once had to remove a fastener made of very hard material (set screw as I recall). Went through several HSS bits and barely made a divet. One of the other techs provided me with a cobalt bit that went through the piece like butter.
2. I am using a hand held drill motor, variable speed, and have tried several rates from slow to max.
3. These fasteners are used to hold storm shutters onto window frames, have been in place for a while, and are apparently made of nuclear-grade steel. I can't imagine why such a hard fastener was used in the 1st place; I've had less trouble removing a broken head bolt from a 302 with the engine in the car......
Lopping off the heads with a Dremel leaves the remainder of the screw in place (obviously) which pins the screen frame to the window frame. Trades one problem for another.
I have nine shutters to go.
Ernst
Reply to
Ernst
Most likely some sort of self-threading/tapping screw.
A useful trick that sometimes works is to get an old heavy plumber's soldering iron, the type that you heat with a blow torch, get it really hot, apply to the center of the screw head, get the screw really hot, [tends to break the corrosion seal between the aluminum frame and steel screw as the aluminum expands more than the steel does] and unscrew ASAP. You can also try penetrating oil, but I have never had much luck with this. Anyone have a "secret formula" or brand for aluminum/steel corrosion?
Unka' George [George McDuffee] ------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?
Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).
Reply to
F. George McDuffee
Those hard and tough fasteners are very hard to drill through. It seems as though the drill gets much hotter drilling through that, than through regular steel. (not surprising, since higher tenslie strength means higher energy required to tear off those chips from parent metal).
For anything very tough, I use carbide center cutting endmills or carbide (solid or tipped) drills, my mill.
There is also a whole another level of drill bits called "harbor freight $9.99 set". Those, not only fail drilling through mild steel, but they also manage to leave some hard layer on it after they fail.
Do not forget lubrication.
Reply to
Ignoramus14229
Colbalt are tougher, and stay sharper longer, and while a SIGNIFICANT improvement over high speed steel IN THE PROPER APPLICATION....
they arent miracle workers.
Carbide, on the other hand.....those do work miracles if used properly. If not, they become nightmares ........
"very hard" indicates to me...carbide.drills are required.
Gunner
"Upon Roosevelt's death in 1945, H. L. Mencken predicted in his diary that Roosevelt would be remembered as a great president, "maybe even alongside Washington and Lincoln," opining that Roosevelt "had every quality that morons esteem in their heroes.""
Reply to
Gunner Asch
Also, I've come across some plain ol' not-very-good HSS bits that were gold-colored to resemble cobalt bits.
Reply to
Joe Pfeiffer
You are right, sir.
Just the sight of the screws begged for saturation with Aero Kroil (which happened). Wonder if application of a 100W Weller soldering gun would work vice the plumber's iron?
Ernst
Reply to
Ernst
I've had good luck using cheap masonry drills for drilling out hardened steel fasteners. Flood cooling does seem to help. I've always used a drill press or mill, but I suppose freehand could work on smaller fasteners.
Joe Gwinn
Reply to
Joseph Gwinn
What would be the best approach when using carbide bits with a hand drill motor? One other thing: Ever used a diamond-coated bit? A long, long time ago when I was a Navy jet mech, we had to drill out some super-hard fasteners on an N1 case. If memory serves, someone went to dental and got some "diamond dental bits". Whatever they were, they worked pretty well.
Ernst
Reply to
Ernst
Ernst,
What you describe is a horse of a different colour. Self-drilling & tapping sheet metal screws are case hardened with the case hardness approaching Rc70!
Tungsten carbide drill bits applied carefully are required to deal with these. Unfortunately in a hand-held drill these drill bits often break due to side-ways bending. With care though it should work, and the higher speeds available would be a benefit.
Small T-G drills and endmills are available in Canada at Princess Auto at very reasonable prices. They have a website catalogue but may not list irregular surplus tools and equipment.
Wolfgang
Reply to
wfhabicher
FWIW: I have used diamond coated bits in my Dremel to drill stones. I had bits from two sources: One from Calgary which were awful and one from Hong Kong which were fine. I built a baffle of plasticine around the prospective hole and poured water in it and drilled the hole underwater with some success.
I tried the same thing only once with steel: Removal of a broken 6-32 tap. Success was limited...
Reply to
Michael Koblic
Since diamond would vaporize or dissolve into the metal it would be best to use another super hard stone that wasn't pure carbon.
MSCdirect sells carbide drills. I used one to drill a hole into a High speed steel 1/4" square metal turning steel. Normally one would grind a shape and then cut steel with it. I drilled a hole and ground off the front - now a U and a form tool.
It was red hot and cut through nicely.
Martin
Michael Koblic wrote:
Reply to
Martin H. Eastburn
Craftsman? Are you *sure* that they were real Cobalt steel? Go for Cleveland or one of the other serious US drill bit makers, not Craftsman, which could be imports from anywhere -- pseudo cobalt steel. Judge Craftsman by the difference between Sears advertised horsepower on a shop-vac or an air compressor, and the *real* horsepower determined by objective measurements.
Second -- can you measure the hardness of what you were trying to drill? Fastener heads -- *good* ones are quite hard, especially the black-oxide finished ones, and probably would burn out most bits other than perhaps solid carbide in a rigid enough machine. (Don't even *try* solid carbide in a hand-held drill motor. :-)
Good Luck, DoN.
Reply to
DoN. Nichols
I have also read about but not seen Stellite drill bits - apparently these can operate red hot - maybe even orange hot, and so you just push hard and let them melt their way through the hardened whatever you are trying to drill.
for the particular application, left hand bits might be helpful because there is a small chance they can start to loosen the fasteners.
note also, anti-seize may help reduce the problem the next time
Reply to
Bill Noble

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