Best drill bit for hardened steel?

I recently asked this question and received a few different answers.The recommendations were.Tungsten,diamond tip and titanium.Are all these answers correct and if so which is the best one? Thanks all!

Answer:
*If you are going to use it for mass production , then go for diamond tip with proper emulsion / coolant advised by the manufacturer.
*You can go for unconventional methode like wire cut for larger diameter holes.
*Carbide Tipped Cutting Tools:

The cutting edge of these machine tools are carbide tips brazed onto hardened tool steel bodies. Carbide tipped tools in general have a longer tool life than high speed steel tools and are more resistant to wear making them effective in long production runs. C-2 Micrograin carbide tips are used for cutting most non-ferrous and cast iron materials, while C-5 carbide tips are used for cutting most steel materials. The carbide tipped reamers are available in 3 grades of carbide tips for specific applications.
*Diamond drills are used on glass, stained glass, ceramics, ceramic tile, porcelain, porcelain tile, limestone, marble, granite, slate, stone and fiberglass. Drills used on wood or metal have a sharp metal tip or teeth, that cut into the material. These types of drills do not work on glass, marble, etc. as the tips do not "bite" into the extremely hard material, and cause heat build-up that burn up the bit and cause "heat fractures" in the material. Carbide tipped Spear Point drills are sometimes used on the "softer" types of hard materials - like untempered glass, sandstone and marble and some of the less hard ceramic and porcelain tiles.
*Water or coolant must always be used to cool and lubricate the tip. The lubrication reduces heat build-up, prolonging drill bit life and helps avoid heat fractures in the material. Water is most often used as the lubricant, since it works very well and has no cost. Oil based lubricants do not work well on diamond drill bits.

Good lubrication is critical. Minimal lubrication will keep the bit from burning up, but very good lubrication techniques will extend bit life by a factor of 5 or even 10.
diamond tip ,
Bosch do A Special one on sale at B&Q
A diamond tip can not be beaten for cutting through steel but is expensive. I have used Cobalt steel drills for hardened metals with no problems
you can use them all but it all depends on how much they cost.Tungston is my partners choice they seem to last longer and are a reasonable price
Carbide or Diamond.
Diamond will cut longer but is a lot more expensive.
Carbide can overheat and weld itself to the steel. Be sure to have lube or coolant constantly running on the piece.
Tungston will do it, just keep the revs slow and use coolant if possible.
Tungsten carbide bits are excellent for drilling through hardened steel. However, a bit more information is required to give a GOOD answer.
How hard is the steel (if you know)
How deep is the hole, and will it be a through-hole, or a blind hole?
What diameter will the hole be when completed?
What tolerance is permitted on the final diameter?

There are other methods of making holes through hardened steel which may be more appropriate than drilling.
Tungsten carbide drills. Do what the two guys above me says. Run it slow with coolant.
Carbide is your best bet, and like the other answers, use a coolant, molyD or other extreme pressure cutting fluid is best. be sure to keep constant pressure on the slow turning bit, if you ease up, you may work harden the already hard steel.
First, diamond is WRONG! None of the PCD (polycrystalline diamond) grinding wheel or cutting tool bit manufacturers would recommend it, as it won’t work, and the reason is simple. Steel has a chemical affinity for carbon- a diamond tipped cutting tool will merely dissolve into the workpiece. Diamond is great for aluminum, and is used for high speed machining of those alloys: but for steel and titanium, NO WAY.

Cemented carbide, the generic name for a class of materials for which tungsten carbide is a part, is a good bet.

While titanium or titanium alloys would also be an improper recommendation (all titanium alloys are softer than hardened steel, so they won’t cut it), I suspect your responder was referring to a coated grade. You’ll see a lot of gold colored drill bits these days in the various hardware stores, and they get that color from a 2 micron thick layer of physical vapor deposited titanium nitride. The coating gives lubricity and decreases the wear on the tool. Merely coating a tool steel bit will help a lot, but coating the carbide will make it work much better.

So if you have to use a drill bit to cut a hole in hardened steel, I’d recommend a coated carbide grade. But if I had to put a hole in hardened steel, I’d take it to the EDM department of the plant and let them cut it with a graphite electrode.
Tungsten carbide. I've never seen a diamond tipped drill for hardened steel. Get the correct drill speed and drill tip profile before you drill. Youll also make it easier if you drill a pilot hole first.
Carbide acue drill Ti coated it's best for most steels. If you get to higher Rockwell's, you could always small hole E.D.M the hole . Depending on how close tol. you need it ram edm is great for shallow or blind holes, for the most accurate tol's I have wire edm'ed with the best result.
I've drilled holes in power saw blades using an ordinary masonry drill, slow speed, enough pressure to keep it cutting ,lubricant, and when the point shows through turn the job over and drill from the other side and when you are nearly through go very carefully and gently, with practise it is quite easy.

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