In a separate recent post, Peter Farley described a frequently recommended process for dealing with a stuck bolt - drill it out with a left-handed drill and retap the hole with the appropriate threads. He also gave a pointer to a good place to get the bits:
I’ve never been able to pull this off successfully. Since it’s a very common recommendation, I’m guessing that it’s my fault. Part of my problem is that I’ve never been able to get a flat and level enough base on the broken bolt to be able to place a bit on it and keep the bit drilling in line with the bolt.
Would someone who’s good at this be willing to post a how-to tutorial on doing this right?
I’m sure (actually, for the sake of my ego, I hope) that I’m not the only one who’d benefit.
I’d benefit. Something new to learn is always welcome.
I’ve drilled out an awful lot of screws in my life, often successfully. And I’ve never used a left-handed drill. I have two large drawers full of hundreds of drill bits of every conceivable size, style, and material, but not a single left-handed one. All of my right-handed bits drill cylindrical holes and it’s hard to imagine that a left-handed bit would do any differently. The screws are usually stuck so hard that I cannot imagine the drill bit being able to grab on hard enough to back them out. Am I wrong about that? I am very sincerely asking for enlightenment.
Also, do left handed bits come in cobalt rather than HSS? I just drilled out eight 5/16" stainless steel screws in my mast heel plug (not to re-tap, just far enough to slide out the old heel plug and save the holes in the mast.) I did them all with cobalt bits - a really small one for a pilot/centering/guide hole and then the 5/16 bit - and both drills held up well. I started switching to cobalt whenever I bought new twist bits after doing a job in 2010 where I had to drill 60 holes in 1" thick mild steel. I bought a 1/4" cobalt bit for that project and I am still using it to this day, though it is slowing down a bit and it won’t quite drill stainless steel anymore.
BTW, if you are trying to drill out a broken screw yes, the bit will want to wander off-center. It’s worse with stainless. In either case, a carbide-tipped center punch is your friend. I have an ancient, government surplus one that works much better than my Harbor Freight ones. It hits harder and has a finer point. But even with a nice center punch, it is still helpful to pre-drill with a much smaller bit than your eventual size. And if your center punch isn’t dead-on, don’t be shy about tilting that tiny bit to get it centered before drilling it straight down. Just don’t put lateral stress on it. Tilt it and gradually straighten it out and it (usually) won’t break. If you are drilling #10 screws you are going to need a really small pilot bit - like 1/16 to 3/32. (Or maybe around #42 to #50.) You can get very small cobalt bits on Amazon, but you have to buy packs of 10. They aren’t that expensive, though, and the tiny ones do break, so it’s not as bad as it sounds.
This is helpful, Brian. I’d never thought of drilling a pilot hole.
I’m not sure if that’ll solve the centering and slipping problem for me. I’m wondering now if maybe it’s that I should be using some tool to grind the sheared-off bolt flatter first?
Bob, by all means grind the end of the bolt flat if you can. The next thing is to take a prick punch and prick a little prick as close to the center as you can get it and then take a spotting drill, sometimes called a Center drill and drill the diameter at the top of the angle larger than that the drill size that you’re using. That should help you stay on center it’s up to you the hold the drill straight.
Any Mistakes in spelling or grammar is due to spellcheck.
Best of luck, and I hope you get it done. Brian.
Once you have some purchase on the screw to be removed, I have had good success with a removal bit that has a reverse drill on one end and a reverse threaded tapered screw on the other.
