Do cobalt and carbide bits actually last longer?

Chiro75

Chiro75

Joined
Feb 4, 1999
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I know cobalt and carbide bits can drill through harder materials than HSS, but does that mean they'll last longer, too? I finally started using cobalt bits instead of HSS yesterday and was pleased to get two whole 1/8" holes from one bit! And I made a 1/4" hole without burning that bit, either! But, I've had nothing but terrible luck with drilling and even after two 1/8" holes the bit started it's squealing routine, so I'd be surprised to get another hole out of it. At $1.25 per hole or so that's kind of expensive.

Here's what I do for 1/8" 1084: run my drill press at slowest speed. Center punch hole, clamp work to drill table. I use a cutting fluid that works for drilling and tapping on most metals. Use "chip" method... light pressure, get a couple chips on the metal, turn the press off, wipe the chips away, wipe the bit, do it all over again. Someone suggested that my 1084 may have a hard center, which isn't uncommon with that steel, but I'm wondering if I invested in a carbide 1/8" and 1/4" bit, would they last a lot longer than burning out bits every 1-3 holes? I've used this method on 1084 and burned out 2-3 bits on a single hole before. Confused....
 
The carbide bits will last longer. You have to do some research before buying however. Twist type carbide drills do ok but are weak and chip easy. I prefer the straight flute style. They make them for several types of materials. Get the ones they make for materials over 50rc hardness and you should do great.
 
I can't imagine why your going through drill bits that fast unless the steel is really hard.
Cobalt bits should last longer, for the very same reasons that you can drill harder materials with them. I don't have much experience with carbide bits. The solid ones have a habit of shattering from what I've read, and the ones with tips brazed on can lose the tip if your overheat them. But under good conditios they should stay sharp longer than the others.

I'd suggest either getting some different steel. Or learning to sharpen drill bits. Its not very difficult to sharpen a 118deg twist drill. I've been using the same set of porter cable HSS drill bits for several years now.
I'd suggest using HSS bits if you decide to try sharpening them as well. The cobalt bits I've tried have a thicker cross section and require 2 different bevels at the tip to get the chisel point right. They also grind away a lot faster.
All you need is a bench grinder with a good wheel on it. I've got one that runs at 1725 rpm with a 120 grit wheel on it. Does a real nice job. the faster ones will work, you just have to remember they remove material alot faster. You've got to keep the wheel dressed so that its nice and square too.
 
I've got a 1/8" carbide bit that I've probably drilled 20 holes with ...thru 10xx steel ranging from 3/16" to 1/4" thick. Then I used it to drill out a busted tap ...it squealed and smoked as I dumped 3-in-1 oil on it as a cutting fluid. Thinking I smoked the bit, I was ready to relegate that poor 1/8" bit to the 'thrasher' bit bin, but before I got a chance to, I needed to drill a few holes to facilitate cutting out a blade blank, and I gave it another go. To my surprise, the bit drilled thru the 3/16" 1095 like it was butter.

(I go slow and use plenty of 3-in-1 oil as a cutting lubricant, trying not to let the bit ever smoke. i.e. If it's smoking, you're going too fast.)

Carbide bits are my best friend. (Yeah I don't get out much)
 
You need to learn to sharpen drill bits, I have been using the same set of HHS bits for 15 years and never bought a replacement. The spade type carbide bits I use 1/8, 3/16, 1/4 and work great on hardened 5160, 1-80 & 90 some times I use oil and sometimes I forget and thy still work. One thing about drilling steel is you need a enough pressure to keep the drill working or you may work harden the steel, that is why the drills get dull so quick. Drilling is one of the easiest machining procedures there is. Gib
 
All I use are colbalt bits. I had a similar problem and found that dropping the speed down as slow as it will go on your drill press will reduce bit and steel heat up. Try dipping the blade to cool it while you're drilling. Drill part way and before it gets to hot, dip the area being drilled in water to keep it cool. Slow down with drilling, because if it gets to hot it will work harden and get even harder to drill.
Scott
 
I have used one cobalt bit to drill all of my 1/4 in holes so far but i think it is starting to dull... definatly way better that the chepo type bits
 
On a tangent, I've been using a Drill Doctor for a couple years and it has more than paid for itself. I always enjoy using a nice sharp bit just like a nice sharp belt. Even the cheapest bits will drill more than what you are getting from yours. My guess is the steel is not fully soft.
 
I use the same HSS bits for 4 years. I was sharpening them with a bench grinder but for a couple of moths I sharpen them on my belt sander. But if you sharpen one side differently only one side of the bit will work thus it will dull and heat faster.

Here is my rule: Faster drill speed as the material gets softer, slower speed for harder material. I drill the steel at the lowest speed with max pressure, brass - copper - hardwood etc. at medium speed & pressure and soft wood and corian at maximum speed minimum pressure. Works well.

Best wishes
EMRE
 
Chiro,

What condition is the material in when you start ie: cold rolled, hot rolled ect.
I've found that stuff straight from the mill routinely has hard spots even though it is suposed to be annealed.

I normally anneal everything that comes through my shop so I know for sure its dead soft.
 
I'm using hot rolled 1084 from Koval's, purchased 4-5 years ago. Once I get through that, I'll switch to the same, but 1095. Maybe my next purchase will be a Drill Doctor.
 
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