Removing a broken drill bit?

[goldstar31]

Already said Alum and styptic pencil earlier.

Regards

Norman

 

[wespete66]

Well I've made progress. I got the .375 drill a bit deeper, and in trying to bust up the last of the broken bit I knocked the end of the bolt right off. This left the drilled part that is engaged thread behind. Good deal, right? Well it still won't turn with a screw extractor & big wrench on it! So it's soaking with PBBlaster to try it another night.....

 

[t.l.a.r. eng]

You didn't say what material the stud is broken off into. Is it a large casting?
Try drilling a hole next to the .093 broken drill piece so you can create a channel or a place for the broken bit to be driven sideways in to.
If you can get a .375 drill into the stud piece it must be rather large part or casting you are working with?
An old trick that works well with iron castings is to use a torch to heat up the broken stud end cherry red and blow it out using an oxy/acetylene torch. The piece holding the stud won't reach red hot as fast as the stud so the parent part wont get hurt.
Truck engines were good for breaking exhaust manifold bolts off flush with the head, and after removing the manifold you could heat the stud cherry red and blow it out of the cylinder head and not even damage the threads!
In fact the new bolts usually screwed into the head without any thread repair needed.

Sometimes you can drill out the broken piece by using a small drill bit to find center then progressively using larger bits in steps until you reach the threads. Then it is a matter of using a chisel to tip the pieces in onto themselves until the threads are visible.

 

[DJP]

In the event that you damage the original threads in the process you can always retap the hole in a metric size (slightly bigger) or go for a helicoil insert. You have options should this not go as neatly as described in some posts.

In my case, when there is no progress the tools get bigger and the forces go up. Thats when it's good to have options to deal with damage.

 

[kiwi2]

Hi,
I don't think it's necessary to be exactly on centre when drilling out a broken stud. If you drill a pilot hole all the way through which is roughly on centre, then keep increasing the drill size by 1/64" until the tips of the female thread show up down one side, the worst that can happen is you will take 1/128" off the thread. Once the thread appears, you can then use a fine, sharp centre punch to push the remains of the stud in towards the centre. It is then usually loose enough to unscrew with a pair of fine nosed pliers.
Regards,
Alan C.

 

[RichD]

Several years ago I had the same problem. After exhausting all the usual remedies, I finally had to call my Father. I brought the cylinder head over to him. He tried a dremel (he was beyond 80 years old then) to no avail. Finally he broke out the oxy-acetylene torch with a small burning tip.

It was amazing to watch. He was shaking some from the bent over sideways stance he had,but slowly like gas welding he brought the center to the point where it was on the verge of sparkling into a puddle. One quick shot of oxygen, and in under a second it blew through into the water jacket. You'll know because smoke will shoot out of the adjoining water jacket openings plus the distinctive noise it makes when it pops through.

That left us with a molten hollow (the remains of the bolt). That part came right out using a small extractor. The threads were untouched. I drive that old truck still a1960 Dodge D300.

I miss my Dad. There's no one I can call now, but at least he showed me plenty of tricks.

Rich

 

[Toolguy]

I usually drill taps out with a solid carbide spade drill smaller than the tap drill size. If the tap is broken off at an angle, a 4 flute carbide end mill will flatten it out for the spade drill. By going under tap drill size you can usually save the thread because the flutes of the tap make the center skinnier than the minor thread diam. Spade drill are cheap, very strong and come in many sizes. I recently drilled out a #8-32 tap with a 3/32 carbide spade drill. At the end the threads looked the same as all the other threaded holes.

For drilling broken bolts I use a left hand twist drill. Often the drill will catch the bolt and unscrew it. If not, there is still the hole which can be enlarged to tap drill size, then the threads picked out.

 

[Blogwitch]

You have one last chance to do it mechanically, after that you are in the hands of the gods when you start to use extractors and welding.
You say you can get to the good end of the stud down the hole.
Then get some penetrating oil down into it (WD40 or diesel oil) and leave overnight.
Then get the largest drill you can without taking out the threads and drill from that good side. The drill should bite in, then if you are in luck, it will screw the broken stud and drills out of the hole the same direction as they went in, but if not, then the drill should at least dislodge the drills that you have broken down there, allowing you to carry on drilling the stud out.

John

 

[goldstar31]

Several years ago I had the same problem. After exhausting all the usual remedies, I finally had to call my Father. I brought the cylinder head over to him. He tried a dremel (he was beyond 80 years old then) to no avail. I miss my Dad. There's no one I can call now, but at least he showed me plenty of tricks.

Rich

I'm over 84 now. I have to still muddle on as best I can.Perhaps our poster will actually take a bit of the very valued time which many people have given freely. It would be interesting to hear something positive out of what is an every day minor problem. I'm sure that others will echo my thoughts.Norman

 

[wespete66]

Thank you to all for the wealth of suggestions! I hope I can remember all of them for future use.
I guess I didn't explain what this project was on. It is an industrial air compressor, Fairbanks-Morse, vintage ~1935. So chances are these studs have never moved in all this time, and are very much stuck! I find that the stud material is kinda brittle & the exposed edge breaks off before bending towards the drilled out center. Right now I'm letting it soak with PBBlaster till l get back to it. I sure don't want a broken easy-out in the hole!
I've heard you can easily remove a stuck bearing race by laying a weld bead along its inside, shrinking it. Suppose I could do that with a spot of brazing (don't have welder)?

 

[goldstar31]

If things are- nearly as old as me- beware! Several points do come up. The first is that cast iron is 'hot short' which is old fashioned words for - well, the easiest way to break cast iron is to get it red and hit it with a hammer! Not been mentioned but that was a little lad learning over the anvil- in 1935!Me, I would tend to ignore some of the advice given. There is nothing really wrong but I would turn a guide to fit the hole as a steady for a drill. made out of copper- or use a diamond dentists drill. I'd use oil and coarse grit from an knackered old abrasive wheel. It would take a long time to get through the drill but once it has gone, as Swifty says- peck with a drill . Yeas, messy and tedious but that is how glass plate is drilled by some.Good luckNorman