I'm trying to drill out a bolt and have burned up three drill bits (appx. 1/8" +/-) without making nearly a scratch.

Can anyone recommend a type/brand of bit for this project? The bolt isn't hardened...

 

Theres your problem


Seriously though, get some cutting oil...

~Nate

 

No, the bits are regular "Made In USA" stuff...and I used some AeroKroil while drilling. Just wondering if there's a particular type of bit that works better than the run-of-the-mill offerings from Sears or the local Big Box.

 

Danny, it sure sounds like it is hardned. But unless it is major hard, it can still be drilled. If normal bits don't do it, and if you don't have the drill set on reverse. (Don't laugh, it can happen especally with the smaller bits where you don't see the rotation well and have little torque feedback) Then you are going to have to go with some of the more expensive stuff. Cobalt bits are the more heat resistant, but here you need more toughness. For the money right now, that means Titanium Nitride coated.
You see them listed as TiN coated. They are gold colored. Sears should sell them.
They used to be really expensive, but mass production has brought them down to the point that I don't even bother with the cheap ones any more.
Get a few of them, double check your rotation, center punch the bolt with a sharp punch to get a good dimple for the bit to get a bite into, keep it flooded with oil, use firm pressure and slow the drill down some and you should be able to drill it.
If the TiN bit does not make a mark, then the bolt is good and hard.
If so, then you probably will have to do something more creative. Either drawing the temper of the bolt, or get the whole assembly off and take it somewhere that has a plunge EDM machine.
Let us know how it turns out.

J.

 

Thanks for the info. I'll try a cobalt bit or the Ti bit...

My attempts at drilling so far have left a nice centerpoint, but that's about it.

I'm only trying to remove a broken mirror mount bolt. I have the towing mirrors on my F350 and one of the three bolts that hold the top frame of the mirror into the door is snapped off. It's not a critical part, but every time I get into the truck I have to look at it...drive's me nutz...

 

It may also be that your bits were not sharp when you started. Learn to sharpen them yourself. It's pretty easy, and just take a few seconds once you get the hang of it. The other thing you want to do is to run the bit at slow speed. You should see little chips pulling out right away. If not, sharpen the bit, apply cutting oil (or honing oil,) apply moderate pressure only, and don't turn it too fast.

Examine the bits with a magnifier under a light. If the leading edge of the cutting flute shows bright, it's dull. It should be a clean angle. Lack of oil, excessive drill speed or too much pressure will take that edge away quickly.

 

I agree, the slower the better! I just use Vermont American bits...nothing special, just run them slow with lube and they seem to last forever.

Kenny

 

I use the titanium coated bla, bla, bla, cheap chinese knock off that I got from Tractor supply company. It's like a 50 some piece set for $20.00 I have drilled a lot of tempered steel with the same bit's never sharpening them. The key to it is to go slow( like around 120-400 rpm) and use dark cutting oil. Keeps the bit cool and sharp. Start with a small pilot hole, like 1/8th" and go progressivly larger till you are at your final size. I.e. 1/8 -> 3/8th -> 1/2". Usually I just start with 1/8 and go to final size. But was always told to do progressive so.....
Slow and cutting oil are manditory. There hasn't been any kind of steel I haven't been able to drill that way. Oh yeah, I use a 1/2" Bosch Hammer/Drill set to Drill at low speed. (around 400) I use the secondary "T" handle to help control it. However, only push with the back handle as you don't want to put any stress on the bit other than forward. if you use the side handle to push you are "bending" the bit which will cause it to break.

 

Is this a Stainless steel bolt? Stainless is very hard to drill.

 

Those usually are stainless. I use the Hitachi bits from Lowes, I can't remember exactly what they are, but it's a black bit in a green plastic sleeve, pretty pricey especially when you get into the larger sizes, but they cut through metal like it was pine.

 

Drilling bed frames (which are very hard) I found the bits from Dewalt sold at Home Depot are the best that are generally available without doing mail order.

 

For bits 1/2" and smaller, I use dewalt ti coated pilot points. I generally use them dry, with ridiculously low RPMs. I have an old hand drill that at full throttle, maybe hits 100 RPM. Perfect for drilling harder metals. They drill into anything other than tool steel.

 

Yes, I really like the pilot points for accurate start too.

 

Yep, the pilot points are great for that, especially with hand drills.

On a drill press this is less important of course, especially if you have an XY table. Generally one doesn't put their F-series frame on their drill press though

And they are a PAIN to sharpen should you ever need to. Took me a while to figure out how to do it. The 5/16" bit needed to be resharpened after 1500 holes in mild steel. Not a bad survival rate.

 

Do you guys sharpen bits by 'hand' or use a machine?