drill bits

P

pike3e

Joined
Sep 28, 2008
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I am trying to drill 1/4 inch holes in 1/8 D2 and it is eating up the bits. One bit was good for about 10 holes and the rest have not even finished one. I am using a drill press and drilling at the reccomended speed in the manual for steel. Any tips or bits to try would be great.

Thanks
John
 
You need to feed hard enough that you're not work hardening the steel. lean into it harder

I'd guess a 1/4" cobalt HSS bit should turn around 800 RPM in D2. You will benefit from some kind of flood coolant to keep the bit cool, and it shouldn't be intermittent.

I recently used a clapped out, off hand ground resharpened bit to drill 3/8" clearance holes in 50 D2 knife blanks at 1,500 RPM and feeding in at 5 inches per minute. That RPM is a bit high, but my reason for that is another story. But the moral to the story is that junk bit wasn't much junkier after 50 holes in D2. In fact, I don't think I had sharpened it from the last batch of D2.

My guess is you just need to lean into it harder to get better bit life. I know that sounds counterintuitive, but this is one thing that I know what I'm talking about.
 
Oh, but you do need to let off some as the bit exits or you will over feed during exit and screw up your bit that way.
 
And don't drill unhardened steel with masonry bits, you'll get a crappy hole.:rolleyes:


No offence fivefold.
 
I always work on D2, I use the regular HSS bits. I drill small hole first then enlarge them. It really ease the work. Also I run my drill at the slowest speed (I dont know thr RPM though) and with very steady pressure. If you change the pressure while drilling the drill bit stops cutting and probably work harden that area... Using WD 40 does also help....

Emre
 
I just tried going a little faster and fried the bit and made it about 1/3 through the steel. I tried a variety of bits from home depot about two to five bucks each and keep having similar results. I think that the speed is around 1100 but i will check. Do I just spray some wd40 before?? I tried rem oil.
 
Well, just to be a nerd about it (just for kicks) I punched the numbers... That Nathan character is damned good! :)

Uddelholm's suggested cutting speed for annealed D2 is 50 sfpm.

So... RPM = 3.82 X CS / diameter

RPM = 3.82 (50) / 0.25

RPM = 764
 
I have use a carbide end mill to put a hole into hardened steel. I does work but the material and cutter need to be very rigid or you will break the end mill. Carbide drill bits are pretty fragile and I would not recommend trying it with a drill press. A mill would be the best way.
 
I checked with all the tool guys at work (for what its worth) Mac Tools Guarentee's their drill bits. They are pricey but its the last set I'll have to buy. I use straight flute solid carbide bits on hardened steel. I'm bad about forgetting to drill a hole,now and then.
 
Just had the need to drill three holes in hardened D2 at 61RC. Used carbide bits with great success. One 1/4" hole and ran the bit at 2000 RPM. Two 5/32" holes and ran the bit at 3000 RPM. Used tapmatic cutting fluid as lube. Used a mill as a drill press would not be rigid enough. Need a firm setup for carbide bits.
 
Straight flute bits work pretty well. They are stronger than a regular twist style. Nathan did a great tutorial on drilling through a hardened steel a while back.
 
Most carbide drill bits are designed to drill abrasive materials such as circuit boards, fiberglass and in production drilling of filled plastic and aluminum (which can be surprisingly abrasive, think aluminum oxide sand paper). The geometry of most of these bits are aggressive for soft materials and are too weak to work well in steel or hardened steel.

Then there are carbide tip masonry bits, which are quite blunt because any cutting edge would be lost quickly, but steel would be abraded away to nothing quickly in concrete. They make ugly holes because they aren't designed to cut a chip. Your hole will not be round and your burr will be nasty, it isn't the right tool but it will work.

There are carbide drill bits designed for hardened steel, but they are not common. They are thick with straight flutes. They are expensive, they don't last particularly long or cut particularly well, but they are necessary when drilling hardened steel.

There is no good reason to resort to carbide for unhardened steel, and they are not forgiving in use. I have never heard of D2 coming from anywhere that wasn't spheroid annealed (soft). I'm pretty sure you're work hardening it. If you're getting any chatter, the hammering will do it in a hurry. The way to prevent both is to feed harder. You have to lean into a 1/4" bit when drilling something like D2 or stainless.
 
I drill annealed D2 quite a bit. I use regular drill bits. I put quite a bit of weight on the drill press down feed and turn fairly slow just like Nathan says. But, I also center punch then line up my drill to my piece mounted in my cross feed vise that is mounted to my drill press bed. Then I put a good sized drop of Moly D cutting oil on the steel and go 1/2 way pull out refill the hole with Moly D and then finish. Probably could skip the second oil step if I was doing 1/8" thick or less. Moly D is some good stuff for drilling and tapping. A piece of scrap aluminum under the piece will help the exit, which I can feel and back off the pressure a bit
 
I have been drilling 1/2" holes in a 5/16 piece of D2, used rapid tap. Plain HSS bits, no problems. I believe the lowest setting on my press is 720 or 740 rpm. That Rapid tap makes a huge difference. The smell if you make the stuff smoke is pretty nasty. But that was my fault for not maintaining the constant flood.
 
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