I was at Sears last night to try to get a replacement (or supplement) to my trusty 5/32 Cobalt drill bit for AK work and they were all out...  (Too many AK builders I guess )  

The guy in the hardware area asked why I needed Cobalt and I told him I was drilling through some hardened alloy Steel and I thought cobalt was the best there was....

Well, he indicated that the Zirconium drill bits were better as they remain cooler....  I was about to buy one and give it a try when the next words out of his mouth was ... it's the yellow color that keeps them cool

So, I didn't waste my money and I am going to go to another sears tonight to get me an extra COBALT drill bit....  I just didn't trust the opinion of some idiot that thought the color had anything to do with the performace of a drill bit...

Anybody use the Zirconium or Titanium coated drill bits?  I am going to a build part on Saturday and I don't want to experiment on a limited timeline but I have never really tried these so perhaps they would work...  

I use titanium coated drill bits and I do seem to remember that those will stay cooler longer than ordinary drill bits.  Probably harder too.

I've used all three types and the cobalt bits hold their edges longer IMO.

The real trick to drilling hardened steel, is, use cutting oil and the slowest RPM you drill will deliver. Go slow, don't lean on it and let the bit do the cutting.

You can get Cobalt bits that are coated with Titanium Nitride...... Cobalt bits usually have the stepped end on the chuck side

This is the REAL inside scoup on drill bits.  Go down to you local dollar general store, on the very back aisle, right side, all the back into the cornor and laying on the bottom shelf are the bits to buy.... Super ultra KRIPTONITE lamated bits.  Cuts through anything - even supermans cape.   $1.99 for 5.

Quoted: This is the REAL inside scoup on drill bits.  Go down to you local dollar general store, on the very back aisle, right side, all the back into the cornor and laying on the bottom shelf are the bits to buy.... Super ultra KRIPTONITE lamated bits.  Cuts through anything - even supermans cape.   $1.99 for 5.

But they are not yellow are they...  It's The Yellow color that keeps them cool....  the Guy at Sears said so

Just in case this thread takes a serious turn -

http://www.diydata.com/tool/drillbits/drillbits.htm

(quotes from the site)
Twist bits are also available coated with Titanium nitride (TiN), these are easily identified by the gold like colour. This coating increases the hardness of the bit and adds a self-lubricating property. The coating is only really effective when metal is being drilled, it has little effect when working with other materials.

Titanium nitride bits cannot be sharpened without destroying the coating (although if the drill needs sharpening, the coating will probably have already been destroyed). Forming the correct angle at the tip is important for efficient cutting.

I have had great luck with cobalt bits, especially for small sizes.

Quoted: The real trick to drilling hardened steel, is, use cutting oil and the slowest RPM you drill will deliver. Go slow, don't lean on it and let the bit do the cutting.

My brother the metalergical engineer tells me to use the slowest speed on my drill press and to use water, not oil, to cool the bit. Its worked for me.

Quoted: I've used all three types and the cobalt bits hold their edges longer IMO.

+1

..and polypam there is no such thing as a "metalergical engineer".

As someone with a degree in metalurgy, who works doing tool and die work...

( I should laugh at that Sears guy... but I also know retail sales... anything to make the sale )

Water is not a proper coolant/lube for drilling. - On hand operated equipment variations in tool pressure and feed rate can cause thermal shock of the cutting edges and cause the tool to wear much faster.

A water soluable oil at about a 4% mix is a good coolant for Aluminum. For steels including free machining stainless I would up the mix to about 10%.  I prefer Rustlick WS5050. I work with NuCut daily ( management taking the cheaper short term way out...)

For the home workshop user - tapping fluid or black oil ( can be bought at plumbing supply to cut pipe threads with a die ratchet.)  is the best choice.

And those drills with a Gold coating are Titainium Nitride - it was the hot ticket almost 20 years ago. Today I run some tools with a Black Diamond film.  Cuts like a red hot branding iron thru a block of lard... { without the smoke... }