Recommended drill bits for hardened steel?

[wyatt1963]

Need to get some drill bits for around the farm. Thinking cobalt?

Drill-Bits for drilling metal/iron/steel, buy only COBALT, preferrably M42 or better, this refers to the amount of COBALT alloy, M42 being 8%. The COBALT bits can be sharpend since they are COBALT alloy thru and thru, (not coated). Bosch makes one that withstands temps up to 1,100 degrees. For best results and life of bits, take your time use oil for cooling of bit and if necessary stop drilling and allow bit to cool down. M42 super high speed steel is a premium cobalt high speed steel with a chemical composition designed for high hardness and superior hot hardness. These properties make the steel an excellent choice for machining high-strength and pre-hardened steels, high-hardness alloys, and the difficult-to-machine, nonferrous super alloys used in the aerospace, oil, and power generation industries. M42 exhibits excellent wear resistance by virtue of high heat-treated hardness (68 to 70 HRC), and the high cobalt content imparts the hot hardness. As such, the cutting edges on tools made from M42 super high speed steel stay sharp and hard in heavy-duty and high-production cutting applications.

 

[Falco de Negro]

The best bits I've used on the worst material are split tip carbide. They will go through nearly anything, providing you know how to regulate your speed and feed. It's a fine dance to get it right, especially with a handheld. It's a little easier with a drill press. Stay far away from HSS, High Speed Steel. They plaster it all over packaging as if it's something special. In reality, it's the worst crap you could make any cutting tool out of. Carbide costs more, but it's your best friend in the cutting/drilling business. And that includes woodworking as well.

 

[rtv9001]

The best bits I've used on the worst material are split tip carbide. They will go through nearly anything, providing you know how to regulate your speed and feed. It's a fine dance to get it right, especially with a handheld. It's a little easier with a drill press. Stay far away from HSS, High Speed Steel. They plaster it all over packaging as if it's something special. In reality, it's the worst crap you could make any cutting tool out of. Carbide costs more, but it's your best friend in the cutting/drilling business. And that includes woodworking as well.

yeah but if he's holding a drill by hand a carbide bit will break in about 4 seconds. HSS is not crap for normal materials. Tons of endmills and drills are HSS which is perfectly fine most of the time and costs a fraction of carbide and is WAY more forgiving to a non rigid setup like a hand held drill or even a cheap drill press.
If it was truly hardened tool steel materials nothing will drill it. It could be milled or turned hard, but not drilled.

 

[Anakist]

Good info on sharpening by hand there. He has a follow up video showing when a drill doctor works and when it doesn't.

Practicing sharpening by hand and having sharp drills will trump most other things (as long as they're reasonable quality).

 

[5030]

He also talks about the Vevor drill sharpener using ER collets and how it does an excellent job, which it does but it ain't cheap. If I were to ever get one (probably won't), I'd get the complete unit with a full selection of ER collets. I believe it's around 400 bucks.

One nice thing about the Vevor is it comes with a Cubic Boron Nitride wheel as well so you can sharpen Tungsten Carbide bits as well. If I wasn't adept at offhand sharpening, I'd consider one.

Even though I am, I still toss bits under 1/8" and buy new ones. Under 1/8" is just too hard to see.

 

[5030]

On an entirely different subject, I sharpen saw chains with an Oregon (Tecomec) chain sharpener and for kicks and grins (and I needed a second grinder just for setting (grinding rakers), I bought the 100 buck Vevor chain grinder and in many ways it's better than the Oregon / Tecomec chain grinder. Much improved dept control and easier wheel changes, not that I change wheels anyway because I use CBN wheels that never need dressing or forming. I was amazed because it's Chinese and I was expecting for 100 bucks, something sub standard and it's not at all.

 

[the old grind]

I wish anyone luck sharpening carbide with CBN. It was never made for that. Expect poor stock removal and heat cracks possible when you find out, but hard to beat for HSS. (diamond wheels are cheaper these days)

That said there are resin bonded diamond wheels for carbide only and some with a different (more open) concentration for CBD tip inserts in HSS tools to work with either/both mat'ls.

JMHO after 12 yrs in cutter grind with Toolmaker's card. (#6940 GM/UAW local 599)

 

[oldtimer 66]

I have mentioned this before. 4 X SFM/ Dia = RPM. M4 high speed steel/ a bright drill/ can run at 100 SFM starting point. So here is the RPM for a .50 dia. HS drill. 4 x 100/ .50 = 200 RPM starting point. But that is generally ideal conditions, rigid set up, plenty of HP. Now this is for drilling mild steel.

Use 80 SFM and you get 160 RPM. That will work. If you are going to drill some tough material like 4140 HT aka 28/ 32 Rc you will probably want to drop down to 60 SFM with the M4. Now you are at 120 RPM.

Lets say you can use a carbide drill, you have the HP and the the rigid set up. The carbide rule of thumb is 300 SFM. So do the calculation and you come up with 600 RPM for the .50 dia drill. Note you have gone from 200 RPM to 600 RPM as an example. What that has done is tripled your HP requirement though. I say that because you would want to keep the same chip load.

Maybe I am to old but nobody talks about subland drills or core drills. The subland drills had a second margin drawn into the drill. That way you could drill and chamfer and or counter bore in one operation for a tapped hole or bolt hole.
Core drills were used to open up cored holes in a casting. A core drill needs a hole to start, it does not center cut. They were either 3 flute and or 4 flute, generally. They were loosely used a a reamer on some operations. They were rigid and made round holes.

Jobbers length drills are generally used /discarded after 1/3 of the margin is consumed. The reason being is the web gets to thick to cut effectively, and it takes more HP to drill with. The PTD salesman told me that.

In 1969 the shop was machining a diffuser for a test/ development turbo. They were tapered holes in aluminum approx. .88 dia down to .44 dia and about 8.0 " deep. around 30 holes per diffuser. The finish reamer would load up with chips/ some welded on, and gaul up the hole finish. That problem was solved using kerosene as a coolant. The holes were like glass then.

Just a little "Bit" (pun) of history.