Disappointed with carbide drill bit performance

I recently discovered carbide drill bits. Wow, heavy, big, gold(TiN), and expensive.(Cheap on the bay). So, I drilled an 1/8th i hole through a 3/8 tap. What a thrill, but it took 2000 rpm on a drill press to do it. I think it spot annealed, then drilled a bit, then spot annealed etc. So I ran out and got a 5/16 carbide tipped die drill from ptd and a

5/15 hiroc drill. Also a 1/8" tile bit too. Put it in my Rigid 18v and tried to drill through a 6" mill bastard file. No chance. Used the carbide tipped die drill on a piece of 1/4" plate. Yeah, it'll drill, it just doesn't want to. Cobalt works fine on this. If it cant even drill through a file what good is it? Why cant you use soild carbide jobber bits with steel? One place claims their M-7 bits will "drill through" my new CTD cobalt drills. BS? How can m7 drill through m42? Is there a carbide drill that will "drill through anything this side of roswell", quicky, smoothly, acting just like a jobber drill in steel? Anybody heard of
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the way, they look good, but will their drills be as good as cleveland twist?
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Basically two types of carbide drills. One for hard materials like hardend die steel. One for abrasive materials, like glass filled epoxy, green ceramics. Not really interchangable.

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Way too fast! Try about 100 rpm with lots of pressure and oil with a pristinely sharp bit.

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Tom Gardner

Because the file is hard it will take lots of pressure to drill through unless you are using abrasive, So no carbide drill is going to go through a file like it was mild steel. Your observation that the metal seemed to anneal is sort of on target. Used properly, one advantage of carbide is the relative hardness compared to the material being cut. With the proper pressure the metal being cut deforms and heats up because of this deformation. This in turn softens the material so the relative hardness of the carbide becomes even greater. I.E. the red hardness of carbide is much higher than the red hardness of the file you are drilling. Since carbide is so brittle it cannot be ground the same as, say, a cobalt HSS drill. This means that it will take more pressure to drill a soft material because the cutting edge is ground to have enough strength to support it and this grind does not penetrate as well. Another thing to consider is that it is hard to get a drill press to keep the constant pressure needed to make carbide drills perform best. Using a hand drill would be really hard to do with carbide. ERS

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Eric R Snow

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