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Drilling out a broken bolt

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Old 11-14-2004, 12:12:59 PM
Chris Kirk Chris Kirk is offline
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Default Drilling out a broken bolt

I've heard that when a bolt is broken off flush with the hole and badly stuck, drilling it out is often the best way to remove it (Yes, using a milling machine would usually be the best way to go about it, and I realize that you can use other methods, i.e. weld on a washer, but let's stick to the drilling for this thread).

My question is this - When you're drilling out a broken off bolt, how do you start and keep the drill centered on the bolt so that you don't destroy the threads by being off center, and how do you make sure that that drill bit goes in and stays straight as you drill the hole out, other than eyeballing it?

I know that it's a good idea to use a punch to make a starting point for the bit so that it doesn't "walk" when you start drilling, but you'd have to make the punch perfectly centered so that the drill will be centered as well.

Thanks in advance for everyone's advice.

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Old 11-14-2004, 03:28:10 PM
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Eric Schultz Eric Schultz is offline
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Default Broken bolt

Chris, when I drill out broken bolts, I start with a small drill, and work my way up untill I just touch the threads. If you are off center a little bit it wont really matter. When you get to this point, take a small chisel, and try collapse the remaining bolt into the hole you drilled. If you are pretty close to center, you can drill upto the tap drill size and just go in with a tap, but be careful. sometimes the pieces from the broken bolt can jam the tap. Also, a set of left-handed drills can be used. I know they may cost a bit, but they are just the ticket for this kind of thing. nine times out of ten the drill will grab and screw the stud right out! Stay away from eazy-outs!!!! they cause nothing but problems. Also be careful not to drill too deep if you are going into a blind hole.
Good Luck!
Old 11-14-2004, 07:30:56 PM
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Craig A Craig A is offline
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Originally Posted by Chris Kirk
My question is this - When you're drilling out a broken off bolt, how do you start and keep the drill centered on the bolt so that you don't destroy the threads by being off center Chris
Well, we've in business a LONG time and seen a LOT of broken bolts and studs AND customers who thought they were going to save some money and try getting them out themselves. Long story short: There is about 1/2 percent of the population who get it drilled in the center....and THAT is good for US!
Old 11-14-2004, 11:39:51 PM
hit-n-miss166922 hit-n-miss166922 is offline
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Default drilling broken bolt or stud


Try using a "centerdrill" to start, they do not walk the way a drill does. Then drill a small hole thru the stud or bolt, and sharpen an old tap to a taper that will go into the hole, try to get it square, four sides, and drive it carefully, when it gets tight try turning ether way, hopefully it will come out. "Its the olde square peg in a round hole trick." If you can heat the bolt or stud, it can't hurt>>>>> Good luck
Old 11-15-2004, 12:36:47 AM
BobRR BobRR is offline
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Once you have drilled a pilot hole all the way through(I/2 the diameter) between the heat created and vibration some times you get lucky and they come out easily with a easy out!(of coarse thats on a good day) Thats also where the left hand bits come in handy ! Good Luck! Take your time and you will get it if all else fails use more heat and penitrating oil! BobRR
Old 11-15-2004, 10:20:48 AM
Orrin Orrin is offline
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Default Re: Drilling out a broken bolt

Here's the method I use and it has rarely let me down.

Carefully "eyeball" the center of the bolt and dimple that spot with a center punch.

Starting with a small drill bit, drill a hole the length of the bolt. Then, enlarge the hole with bigger and bigger drill bits. Stop the very instant you see that you are getting into the threads.

Mount a small stone, carbide burr, or diamond burr in a Dremel-type rotary tool. (I like to use a flex shaft for this next step.)

Ever so slowly, grind out the rest of the bolt to the point where you see the threads start to show all the way around the periphery of the hole.

Now, one has two choices. Use a tap to clean out the hole; or, dig the threads out with a scribe or some other sharp-pointed tool.

That's it.

Note1 : If you have to start the hole with a portable drill motor, make a drilling guide to keep the hole square. To make one, I square off a piece of round stock (it can be any shape) and, using the drill press or a lathe, drill a perfectly perpendicular hole down through it. Use a bit that is the same diameter as your starting hole will be when you tackle the broken stud.

When you drill the initial hole in the stud, simply hold your drilling guide flat against the part that has the broken stud.

Note 2: If the stud is broken off in a cast-iron part, there's an easier way to do the job. It relies on the principle that cast-iron is not readily "cut" with an oxy-acetylene cutting torch. Here's how.

Drill a hole down through the broken off stud.

Take your oxy-acetylene cutting torch and heat the stud red hot. Then, give it a big blast of oxygen. Work fast, because if you're pokey about doing it, the cast-iron can get hot enough to melt the tips of the threads. If you do melt the threads a bit, no problem. Just clean them up with a tap and they'll still have most of their holding strength.

If you burn out the stud, the starting hole isn't really necessary, but it makes the job a whole lot easier and you don't get anywhere near the slag blowback into your face.

I have even used a cutting torch to burn steel threads out of a steel part. The threads were very large and the main part was even much larger. I was able to do it because the part was so large it never got hot enough to burn. I worked very fast in order to make sure it didn't.

My 2˘

Old 11-15-2004, 09:09:38 PM
Smoke Smoke is offline
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Default Re: Drilling out a broken bolt

Boy did this thread come just in time. I had a bolt broken off in the frame rail of a loader tractor that I am working on. After reading the threads, I used a center drill to center the hole, then I used a small drill and worked my way up to a large "easy-out" size. The heat by drilling did loosen it up and it turned right out. Good Thread
Old 11-16-2004, 12:22:27 AM
Dick Welty Dick Welty is offline
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Default Re: Drilling out a broken bolt

If you ever fail to get a broken bolt or stud out of a hole in cast iron without screwing up the threads here is a trick you can use as an alternative to using a Helicoil repair kit. In this case lets say the stripped threads are 1/2". Drill the stripped 1/2" hole out to 3/4" or 1" then use a pipe tap to tap the hole for a cast iron pipe plug. Use the old solid type iron pipe plugs not the newer ones that have a partial hollow center. Make sure that the hole was tapped deep enough that the plug will go in far enough for maximun strength. Clean the threads with starter fluid or solvent and then put JB Weld or epoxy liberally on the threads in the hole and on the plug threads and run the plug in extra tight. After the JB Weld set grind and finished off the plug flush with the surronding surface. Then drill and tap a new hole to replace the original. Even before painting the repair will be practically invisible and probably as strong as the original.
Old 11-16-2004, 05:46:46 AM
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Paul Spence Paul Spence is offline
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Default Re: Drilling out a broken bolt

I love those "LEFT" handed drill bits. Works 90% of the time for me. Usually as you are trying to accurately drill out the broken bolt, the heat loosens it and zip, it turns right out. If it's to big, like pipe, I hack saw with a blade down to the threads in several places. Then with my small, really sharp punch, I collapse the pipe and then it comes right out-SOMETIMES . Paul
Did you make a new friend today, and a lot. Paul - "OLDIHC"
Old 11-16-2004, 01:40:22 PM
Chuck Rich
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Default Re: Drilling out a broken bolt

Chris if you can, use a drill guide. If your not familiar with this item go to NAPA or other automotive parts house and ask. They will be happy to explane Im quite sure.

Chuck in Central Oregon
Old 11-16-2004, 11:16:08 PM
GarysToys GarysToys is offline
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Default Re: Drilling out a broken bolt

Don't forget if you get to see the threads when you do drill into the stud, add lotrs of penetrating oil. I tried this without and had difficulty, a little oil and away it went.
Old 11-17-2004, 04:18:44 PM
DesertExplorer DesertExplorer is offline
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Default Re: Drilling out a broken bolt

I've had no luck in using easyouts to remove broken studs especially if the stud has been rusted in . The easyout wants to force its way into the stud causing it to expand to the inside of the hole making it more difficult to remove. The more force you use on the stud by turning out, the more it expands into the threaded hole making it more difficult to remove.
I use a couple of different methods to remove broken studs. One is to heat the stud to red then let it cool, this swells the stud and when it cools it shrinks to a slightly smaller size and comes out fairly easy. The other method is to set a nut on top of the stud and weld the inside of the nut to the stud. This can be done with either a wire feed or a stick welder and almost always works .

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