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Best drill bit for drilling metal?


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10 replies to this topic

#1 grossgary

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Posted 17 April 2009 - 08:12 AM

I did some plugging around on the internet and other than places selling stuff I can't really find out what the best drill bit is for hardened steel.

Cobalt, Carbide, seem to be thrown around a lot. Can someone decipher this for me? I'd like to order a nice set of drill bits for all my sheared/rusted bolt madness needs!

Seems like Cobalt is the way to go? I think that's what my current set is.

Edited by grossgary, 17 April 2009 - 08:15 AM.


#2 lostinthe202

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Posted 17 April 2009 - 09:45 AM

I would suggest getting some cutting oil. It amazing how much better the cut will be and how much longer your tool will last. Get something with sulfur in it. smells kinda nasty, but it offers better heat resistance for harder steels and stainless steels and the like.

I don't have much experience with the carbide sets. I've used the cobalt ones before but never really noticed them as being superior. I would imagine the carbide sets to be prohibitively expensive. Also I think carbide is kind of brittle and prone to chipping if not run at the proper speed and feed (at least in a milling cutter). We used high speed steel at the shop (like what most bits are made of) 'cause I can sharpen them on the grinder.

Let us know how you make out if you go with one of those.

#3 grossgary

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Posted 17 April 2009 - 10:45 AM

woah, nice call will. and to think i was going to PM you about this thread, but you saw it anyway! correct in that the carbide bits are brittle and prone to chipping. they are expensive, but $15 a pop is more than doable if they're that good. since i don't have the time or patience to take care of a drill bit though i'll pass!

i'll try the cobalt ones again and maybe pick up some cutting oil if i can find it.

seems like the oil would just keep burning/running off anyway, so i never use it. i can't continuously feed it for 30 minutes like the CNC machines automatically do that I've used before.

#4 The Dude Abides

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Posted 17 April 2009 - 10:51 AM

Where i work we have some very harden metals we work with. I have always had problems with carbide drill bits. Even with oil they dont match up. I use cobalt drill bits with cutting oil. Slick and quick, i learned long ago to use that and only that. And i used this stuff daily.

#5 lostinthe202

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Posted 17 April 2009 - 11:35 AM

seems like the oil would just keep burning/running off anyway, so i never use it. i can't continuously feed it for 30 minutes like the CNC machines automatically do that I've used before.


Yeah, machine drilling and hand drilling are way different animals huh?

Any decent hardware store should have some tapping fluid like tap magic or one of those. That would do ya. I get this stuff. At $15 a gallon it's a good deal and works well and a gallon would be a lifetime supply for home use!

#6 grossgary

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Posted 17 April 2009 - 11:58 AM

hmmm, now that you say it i bought this stuff before for my tap set, might still have it. thanks folks!

#7 subiemech85

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Posted 17 April 2009 - 02:06 PM

have had good results with TiN bits when hand drilling with the bosch bulldog 11225vsr http://en.wikipedia....itanium_nitride

also use re-li-on for aluminum and exotic metals, titanium, etc.

#8 shadetreemech

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Posted 17 April 2009 - 06:12 PM

in my humble opinion: for mild steel (which is not all that hard), High Speed Steel, or HSS is just fine. HSS with the gold-colored Titanium Nitride coating is a little bit better. By the way, the Titanium Nitride modification was developed by the USSR a couple of decades ago.

For real hardened steel, the tough stuff, you need first class cobalt steel bits. Stainless is also hard to drill, and cobalt is the best for stainless. Cobalt is the real thing.

Carbide is used as a welded tip on percussion bits for hammer drills. This is for drilling in concrete, not steel.

#9 coldfusion21

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Posted 18 April 2009 - 02:32 PM

Cobalt would be your best bet. Carbide would be ideal but without good feed and speed control its not really feasible. I would buy a nice set from a reputable machine tool retailer. ENCO is a popular one, they are connected to MSC and generally have a good monthly sale flyer with some kind of drill sets.

The suggestion for tapping fluid or some kind of cutting oil is a good one, especially on hardened steel. Heat is your enemy.

#10 lostinthe202

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Posted 18 April 2009 - 05:31 PM

[quote name='shadetreemech']By the way, the Titanium Nitride modification was developed by the USSR a couple of decades ago.[/quote]

I love learning little factoids like that, thanks for sharing!

[quote name='shadetreemech'] Stainless is also hard to drill, and cobalt is the best for stainless. Cobalt is the real thing.[/quote]

Yeah, stainless is funny stuff. The desired feed is surprisingly fast and the speed slow due to the tendency of stainless to work-harden while being machined so it's hard to get that right when you're drilling by hand. [/QUOTE]

[quote name='coldfusion21'] I would buy a nice set from a reputable machine tool retailer. ENCO is a popular one, they are connected to MSC and generally have a good monthly sale flyer with some kind of drill sets.[/QUOTE]

+1 MSC generally carries a mixed bag but, in my opinion, what sets them apart from Mcmaster is that they list in their catalog if the item is USA made or an import and in most cases will give you the brand name of what you're buying. MSC also has a much superior knowledge base about their products. they will even contact the manufacturer on conference call if they can't answer your question. McMaster generally caries quality stuff, but you don't really know until you get it. And as coldfusion21 mentioned, MSC has awesome sales regularly.

#11 grossgary

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Posted 18 April 2009 - 10:46 PM

i had dropped this hub off two weeks ago and was just going to pick it up and do it myself since they hadn't finished it yet. when I got there they had broke the drill bit off inside the bolt...nice. i'll pass on that :rolleyes:

but i'm still interested in keeping a handy stock of good drills bits around.




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