drilling out broken off bolt

I have 5/8 bolt broke of a couple treads in the hole I always have trouble finding center and keepping drill bit straight well drilling out hole anybody have any ideas they do when they do this that they want to share Thanks John

i have had better luck welding a nut on a broken bolt and backing it out -- the heat seems to do the trick --- gregger

Don't know if there is a magic way of doing it. After a person does a couple dozen or more of them he starts geting the touch. I just guess punch it with a center punch, then I start drilling with a small bit, maybe 3/16 or 1/4. Drill a little dimple and look to see if it's centered. If it's off center slant the drill, if you can, to one side so the bit will drill it's way toward center. It takes a little patience. Once a small hole is drilled on center, follow up with a bigger left handed bit. That's one way of doing it. You're going to get a lot of other good suggestions too. Jim

If you actually have a hole a couple of threads deep a centering punch works fine. I got a cheapo set at HF and they have been great for drilling out bolts and lining up holes in stuff I fabricate.

With a little room into the hole, in this case a 5/8, I usually use a 5/8 bit to drill just enough to find the center of the bolt. Then I drill maybe a 1/4 inch diameter hole with a split point bit. Then keep over sizing until I get it drilled out.

Left handed drill bits help sometimes

welder is the best way by far. weld won't stick to cast and it also heats the bolt. save yourself the headache/heartache and either weld yourself or find a local shop. the threads will be in much better shape.

I assume your "centering punch" is equivalent to a transfer punch. If so, I agree it should be an aid.

All good advice.
I usually tap lightly on the center punch, then look very carefully to see if centered. If so, then center punch again with a harder hit. That way, you can adjust your punch mark if not centered. Then, as said, start with small bit, like 1/16, and work your way up. Take time and patience. Its not an easy thing, so don't get mad. Try to hold drill as straight as possible. If muscles begin to fatigue, take a break, then go back at it. Hopefully its not a grade 8 bolt--very hard. Even if you wind up off center a bit, you can drill until you get close to the threads, then use center punch to knock it loose, or try to turn it out with center punch an hammer. Drill as large as you can, before you get into the threads, possibly use an easy out. I've drilled large as I could, accidentally off center, then knocked the remainder of the bolt around and sort of chip it out, then back it out in direction of threads.
And yes, if you have access to a welder, weld a bolt or anything to it, then work it back an forth as you turn it out.
Douse it with penetrant as well.
Just work with it as you go, and if off center, play with it till you get it out. Takes alot of practice. I've only hit dead center a few times, and was very proud when I did. Of course, clean the female threads up with a tap when done--oil it alot, and go slow and easy. You don't want to break your tap off. If you do, they are brittle due to hardness, and you can chip it out with a center punch as well. If you wind up getting into the threads, not the end of the world, just go to auto shop or wherever and get a heli-coil kit for that size thread, and install. Directions with heli-coil kit. Inserts are also available, if to wallered out to install a heli-coil.
Patience, take breaks, and do your best. Tis a difficult task, no easy way.
Again, if you are unsure and it is a critical bolt, take it to a machine shop--let them enjoy the headache.
Probably more good advice comin' from others...good luck.
Dan

On Edit--easy does it when drilling, breaking a bit off only complicates things...

I think I'm almost an expert at this now. I spent 2 weeks drilling out broken bolts on a 950 ford just a while back.

on the bolts that sheared weird so they are hard to center punch for the drill, I would take a small abrasive stone for sharpening a chain saw blade and use it to manually make a flat or domed pilot spot that I could then punch.

for a bolt as big as a 5/8 I wouldn't bother withleft handed bits... on smaller bolts i start with a small bit then drill up and when I get up to at least half the bolt diameter I'd switch to a lefty to see if it would pull it out. pas tthat keep drilling up till you can get a big extractor into it then pray. if that don't work, don't get brutal and break off the extractor.. insteadkeep drilling up till you get to where you can chase the threads and pick the thin stuff out. I like to use carbide bits for drilling out if not using lefty's..

use plenty of cutting coolant so your bits last and stay sharp.

soudnguy

Welding a nut or washer first then a nut works really good but the weld could stick to the cast or melt the threads if the weld was to go on the cast. As long as you can get the weld in the middle of the broken bolt and not the cast part it's the easiest way(as long as you have a welder)to go.

All good tips below. Another thing I have done is use a centering guide before center punching. More than likely, the part to be attached has more than one bolt. Put it back on with two or three bolts. Using the proper size bit, in your case 5/8, drill just enough to get a center dimple started. Then remove the part, center punch & start working with small bit.
If clearance problems on attached part, make a guide from 3/8 or 1/2 in scrap bar stock, clamp or bolt it on, start through there to get center dimple.
Willie

I measure and center punch a sharp dint. I then measure again. Most of the time I will be slightly off center. I take a hand drill with an 1/8" drill bit and angle the drill and walk the dint back on center. I then hold the drill straight and drill with the 1/8" drill. I check with a small square or a square block as I drill using a different 1/8" drill bit for the check before I am in real deep. With a 5/8" bolt I would then drill a 1/4" hole in the straight 1/8" hole followed with the tap drill for 5/8. Sometimes after the tap drill size is drilled thru I can pick out the threads with a small sharp pick. Most of the time I chip out the threads with the tap. I make sure I back the tap up after a 1/4 turn to make sure the threads are broken off in chips.
This propbly takes less time than typing how to do it. The secret is to drill a small pilot hole straight and on center. also find center on flat enough surface that you can measure and walk or draw the center punch to the center.

So the broken part is flush with the surface then how do you weld a nut.

drill a hole down center of bolt and as large as posable. Then get a good easyout tool and it should come.

Gene,
Hold the nut with a pair of vice grips so it can't
move, use 3/32 6011 or 7014 centering your electrode in the nut so that the arc starts in
the center of the bolt, building the puddle in
the center of the nut until its 1/2 full, then
circle the electrode just a little to get good penetration on the nut in the top 1/2. I have never tried to weld a nut on a sheared bolt less than 3/8 diameter, but have had 100% success on 3/8" and larger sizes. On smaller sized nuts, they will be be so hot by the time
you get the first 1/2 filled you probably won't have to circle the hole any to assure good penetration on the nut. The vice grips also help
heat sink so that the nut edge doesn't melt on the
top 1/2.
Let the nut cool until its not showing color, then
use your least favorite wrench or socket to first
wiggle, move back and forth, and then turn out the
broken off bolt by hand, stopping on any resistance and working it back and forth if needed.

Weld a heavy flat washer on first . then the nut.

Welding a flat washer and nut works for me...

7018 or a stainless rod would be much better than 6011 or 7014 for a really tight bolt.

mig welder makes it easy