So I need to re-drill the holes in the doors for the outer window felts. These outer felts screw into the door and the old ones were rusted so I had to use a cutting wheel to get them off.

So I’m trying to drill new holes and I broke 2 drill bits. They barely did anything.

Is there a special type / brand of drill bit that I should use to drill the new holes?

Thanks. Pics attached

 

So you are trying to drill thru the rusted in screws, or drill a hole beside them to mount the fuzzies? Best to use the original holes. I would soak the heck out of the screw studs left with a good penetrating oil , keep giving it a squirt for a day so it penetrates the threads. Since you already cut off the heads, they should be flat, center punch the stud and get a tiny hardened bit ..slowly drill into the steel stud, patience, and it will drill it. Chances are it will loosen the stud as you drill it and it will spin out of the hole. That’s what you are looking for. Use original screw holes, new screws. If drilling new holes get a hardened bit and some oil and drill slow, there is nothing hardened about that door metal.

 

Even if you can get those broken sheets metal screws out of the door skin you might have to oversize the holes in the window felts. Have you bought the window felts yet?

I could suggest a "hard metal" drill bit available on Amazon, but beware of Chinesium junk.

 

Pure carbide is best for tough metals, but they can also be brittle, esp. in small sizes. Cobalt, or hi-moly ones are more user friendly, and work well. I have a set of Viking ones I got 4 years ago, and love them.

 

Cobalt bits are a good choice for most applications on a car.

 

Ditto on cobalt, but they are very brittle. If you're trying to drill through the old screws then yes, that will be tough. It's probably better to drill new holes a few inches to one side or the other and make corresponding holes in the fuzzies.

 

I like carbide bits for a stationary drill press. I think cobalt is more forgiving in a hand-held drill. Both are somewhat brittle.

 

The door is mild steel. This isn't "tough metal" by any stretch. Get carbide drills, use lubricant and slow speed, and be sure you're pushing straight on the drill and not at an angle. There should be no need for anything exotic here. Just be sure you aren't trying to drill into a spot weld.

 

Yes - I am trying to drill thru the rusted in screws and use the original holes. I don’t want to drill new holes in the door and more holes in the replacement window felts.

I will try a small hardened bit and yes I will use new screws when I get the holes opened up again.

Thanks

 

Thanks Joe. The door isn’t tough but it seems the couple of screws that were rusted into the holes are... And no I’m not trying to drill into a spot weld, but rather the original holes with old oxidized screws (depth / length unknown…) in them

 

BOSCH Cobalt for me has been the best ever for me. I have an old 18-piece set. 5,700 ratings.

$27.78 for the set below on sale. Free delivery if you have Prime member or know someone who has.

 

To add some info to Joe P, there is nothing exotic in the steel or the screws.

When you used a cut off wheel, you "case hardened" the surface a few thousanths deep. "Conventional drills" (HSS or Cobalt) are not good at drilling through "hard" materials. Carbide is the thing to use with gentle pressure. You can also use a Dremel with an 1/8" carbide ball to break through the case hardening and centering the intended hole.

You can test this case hardening idea at home by drilling the end of a piece of rod. Then cut off the rod with a cut off wheel and try drilling again.

Any small drill bit is easily broken when you are pressing them sideways at an angle. .

 

Illegitimi non carborundum.

 

is that Latin for "spot weld"? 🤣