Drill bit advice

[TA^Guy]

I have a hardened bolt I'm trying to drill out. I have drill bits that say they are for metal but they aren't doing much good and dull quickly. What type of drill bit should I be looking for so I can get through this bolt?

 

[spartan1]

i would use a carbide bit.

 

[treasureseeker]

I have had good results using Craftsman Cobalt drill bits to drill out harden bolts, but after one job they are pretty dull.

 

[alex71]

i would use a carbide bit.

Presumably the OP is using a hand drill. That would make a carbide drill bit unusable.

a sharp HSS drill at the right speed with a little bit of lube should be able to drill out a grade 8 bolt with no problem. Done it plenty of times.

Nothing fancier is needed.

 

[BQuicksilver]

As mentioned here before, slow speed drilling is most important.

 

[TA^Guy]

Presumably the OP is using a hand drill. That would make a carbide drill bit unusable.

a sharp HSS drill at the right speed with a little bit of lube should be able to drill out a grade 8 bolt with no problem. Done it plenty of times.

Nothing fancier is needed.

Yes I am doing it with a hand drill, why would a carbide bit be useless in a hand held drill? The bits I have no say High Speed Steel but don't seem to be doing the job.

 

[tube_guy]

Carbide is very brittle, so even a little bit of bending will break the drill bit. It would be pretty tough not to bend the bit using a hand drill.

 

[ptschram]

Presumably the OP is using a hand drill. That would make a carbide drill bit unusable.

a sharp HSS drill at the right speed with a little bit of lube should be able to drill out a grade 8 bolt with no problem. Done it plenty of times.

Nothing fancier is needed.

I've got a hub with a drive flange bolt broken off you're more than welcome to come down here and take a shot at.

It's eaten a bunch of bits.

If it's hard to begin with, chances are poking at it with drill bits has made it hot and harder yet. Might be time to get it hot, try to anneal it and then drill it out.

I ran into another one last week, a hub with broken drive flange bolt. It didn't make anybody happy, not the broken bolt, not the broken extractor, not the drill bit I tried to use, and certainly not me.

When I get really, really stuck, I find direct heat from oxy/ac torch sometimes helps to weaken the broken bolt, but it's easy for it to go awry.

 

[Weps]

what brand of bits do you have now and how many rpm are you using? too fast and you can still dull and smoke them. high speed steel doesn't mean you can spin them faster, if means they cut faster.

 

[bart1]

When I did the suspension on one of my cars, we ended up spending 6 hours or so trying to get one bolt. It involved cutting a shock in half, replacing a brakeline... The answer ended up being to go and guy a cobalt bit.

 

[amolaver]

best luck i've had is with cobalt bits. got a set off the mac truck for $70 or thereabouts as i recall. i needed it, he had it, and i just happened to see him stopped at a shop. as others have said, patience is required. a little lube and slow drill speed is necessary. if you're going to try and use one of the fluted extractors, you have to make sure the hole is dead center. any offset makes it likely the extractor will break.

as was also suggested, heat helps if you can shield things so nothing catches on fire. i'd rather try a propane/mapp torch before an oxy/acetylene - a lot less likely to cause collateral damage IMO.

ahm

 

[gj67stang]

Heat is your enemy as it will cause the edge of the bit to dull quicker. I'd suggest a cobalt bit (Craftsman makes a couple sets that aren't too pricey) and slow down the drill speed. Also, either use a decent Drill Doctor or sharpen the bit by hand every-so-often while drilling to maintain a nice cutting edge.

Another option is using carbide burrs in a die grinder to slowly chew away the broken bolt.

 

[TA^Guy]

Thanks for the suggestions everyone. I've been using oil to keep it lubricated. I think I'll go this weekend to buy new bits.

I've got a hub with a drive flange bolt broken off you're more than welcome to come down here and take a shot at.

It's eaten a bunch of bits.

If it's hard to begin with, chances are poking at it with drill bits has made it hot and harder yet. Might be time to get it hot, try to anneal it and then drill it out.

I ran into another one last week, a hub with broken drive flange bolt. It didn't make anybody happy, not the broken bolt, not the broken extractor, not the drill bit I tried to use, and certainly not me.

When I get really, really stuck, I find direct heat from oxy/ac torch sometimes helps to weaken the broken bolt, but it's easy for it to go awry.

Yeah I'm trying to stay away from getting it too hot. If the carpet and seats weren't still in there I'd heat it up more.

what brand of bits do you have now and how many rpm are you using? too fast and you can still dull and smoke them. high speed steel doesn't mean you can spin them faster, if means they cut faster.

I'm not sure the brand I've been using. I've had the set for many years. As for the drill I've been using a inexpensive single speed black and decker corded drill so I didn't burn up my DeWalt cordless.