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Old 06-25-2010, 06:27 PM  
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Default Need Help Removing a Broken Bolt

Ok, I have gotten a bolt stuck in an annoying place and the head of it straight ripped off in my socket wrench (I put too much torque on it). Anyways, so I got a bolt stuck without a head to it. I resorted to drilling it out completely but I have run into problems.

I heard that cobalt drill bits work best, but that titanium works too. So I bought some titanium drill bits, and I am still struggling to make any progress drilling into the broken bolt.

I need some suggestions on what to do. Will a cobalt drill bit actually work (because titanium is not even making a dent in the bolt)? Or if that isn't working, should I go straight to using a dremel to grind in new marks in the bolt to exctract it with a screwdriver or something? I don't want to buy a welder and weld on a new nut to the broken bolt, so that's out of the question.

So, if titanium drill bits won't make a dent in my bolt, does that mean cobalt won't either? Should I just dremel it out? Thanks so much, I really need some help on this one. Take care

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Old 06-25-2010, 09:21 PM  
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You need to know that there is an important difference between standard high speed steel drill bits, cobalt drill bits and titanium nitride coated drill bits.

High Speed Steel is a kind of steel that has a high "red" hardness, meaning that it retains it's hardness better than other steels when it's red hot. That property allowed for faster machining because the tool wouldn't dull as quickly when it got hot, and so this kind of steel is called "high speed" steel. Typically, a high speed steel drill bit will have a Rockwell C hardess in the mid-50's to low 60's.

Cobalt steel drill bits are made from a harder kind of steel. Consequently, cobalt bits will last longer than HSS drill bits. And, when a cobalt bit dulls, you can have it sharpened and you essentially have a new cobalt bit. Cobalt drill bits have a Rockwell C hardness from the mid-to-high 60's.

The "gold" titanium nitride coated drill bits are high speed steel drill bits coated with a VERY hard titanium nitride coating. The titanium nitride coating on a titanium bit has a Rockwell C hardness of about 82, and so it keeps it's sharp edge longer than any other drill bit. However, once the sharp edge on that titanium coating is worn down, then sharpening the bit will grind off the super hard coating, and you're left with an ordinary HSS drill bit. Titanium nitride has a low coefficient of friction, so the coating actually helps the bit clear cuttings as well.

So, I think what happened is that you simply dulled the titanium bit or wore off the coating completely, and the bolt is probably harder than the high speed steel bit, so you're not making much progress. It's going to cost you more than the price of one drill bit to drill a hole in this bolt. I'd either buy some more titanium bits and just go through them on this bolt until you get a deep hole, or buy a cobalt bit and keep having it sharpened. There's no steel in the world that's got a Rockwell C hardness of 80, so titanium bits will eventually put a hole in it. You might want to try one cobalt bit just to sell how long it lasts.

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Last edited by Nestor_Kelebay; 06-25-2010 at 09:26 PM.
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Old 06-26-2010, 12:02 PM  
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You may need to use a smaller drill to start with. Larger bits don't have much cutting power to start holes unless they have special flutes. Centerpunch the bolt first and use a small drill to start -- like 1/8" and move up from there.
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