# Removing a broken drill bit?



## wespete66 (Nov 3, 2014)

Not a scale model at all, but a general machining question please? A large threaded stud I was removing snapped off in its hole. I then began to drill it out, thinking a small pre-drill would be best. But of course the .093 drill broke off in the hole. I then drilled .375 dia down to the broken bit. But it is wedged in tight and I cannot get it to come out. What can I do to get that broken bit out of the hole?


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## butchjth (Nov 3, 2014)

Hi,

 Sorry to hear of your bad luck.  I have broken several drill bits over the years.  My best success has been using a diamond tipped bit in a high speed die grinder to grind enough away to break it out of the hole.  I hope this helps.


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## goldstar31 (Nov 3, 2014)

Surprisingly a twist drill is soft and  can be drilled and a left hand extractor can be used.  Failing that, you might be able to crack it with a cow mouth  chisel.
 Failing that is the time for a Plasticene/modelling clay dam and time for assorted things like nitric acid or sulphuric acid.

 Maybe you have a steady hand and can burn it out with a carbon arc from an electric welder or MIG/MAG a bolt onto what is left. 

 There will be lots more suggestions.


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## Brian Rupnow (Nov 3, 2014)

Twist drills are not soft. Try cutting one with a hacksaw if you doubt me. They are softer than a carbide end-mill, and if you can get the part up onto a mill table, it may be possible to machine the drill and the bolt away with a carbide end mill.  Some people have had success by mig or tig welding a nut onto the broken bit of bolt and then unscrewing it, but if you have a piece of broken drill bit in there, that method may not work.  If all else fails, a machine shop equipped with an EDM (Electric Discharge Machining)machine can remove it without doing any damage, but it isn't cheap.


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## Theclockworks (Nov 3, 2014)

wespete66 said:


> Not a scale model at all, but a general machining question please? A large threaded stud I was removing snapped off in its hole. I then began to drill it out, thinking a small pre-drill would be best. But of course the .093 drill broke off in the hole. I then drilled .375 dia down to the broken bit. But it is wedged in tight and I cannot get it to come out. What can I do to get that broken bit out of the hole?



Just a thought how about spark erosion


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## wespete66 (Nov 3, 2014)

I don't have access to EDM or spark erosion, but I do have an oxy-acet torch. This stud is threaded thru a cast iron wall (not a blind hole) & I can poke my finger in and touch the back side of it. Could the oxy-acet torch blast through the remaining stud?


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## goldstar31 (Nov 3, 2014)

I'm not clear whether you made a 3/8th hole or have gone down that distance but the average car body guy should be able to create a weld pool  to the  broken drill  or even weld on the afore mentioned bolt. 

 I would do a dummy run on another bit of thick cast iron which had a similar hole drilled in it and a steel peg inserted. 

 If you think about it, most welders actually work the weld pool in a circle as they progress, filling it with filler rod as they go along. 

 Nice task.

 Norman


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## goldstar31 (Nov 4, 2014)

Having mislaid my chart for Model Engineer 32 and 40TPI taps, I was Googling for a reprint. 

Oddly I came across that 'Tubal Cain'- Tom Walshaw, Ian Bradley of MAP's Drilling Machine book, Sparey of the Amateurs Lathe all agreed with me about drilling drills. I've got a drawer full from my Northumbrian Small Pipe days but no help on doing a silly little tool from the Model Engineers Workshop Manual.

I still was without my chart and I ploughed my way into the suppliers and still nothing but a note about removing broken taps, drills and reamers.
I'd forgotten- I use an electric razor now and don't need one of these styptic sticks to stop the bleeding. Of course these things are ALUM which will dissolve steel.

So on with the search- for what I was doing.

 ---------------------------------------------------------------------------------------------------------------

 Eureka.
                 Not the tool to relieve gears- but a whole heap of tables in sealed A4 things

 And a heap of stuff on drill grinding

 Cheers

 N


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## DJP (Nov 4, 2014)

Page 40 of my KBC catalogue shows a square solid carbide die drill which is capable of drilling through hard steel up to 70 Rc. If removing this broken drill bit is critical to the project I might try one of these square drills or grind your own version from a carbide milling cutter.

The challenge will be to keep the drill straight in line with the broken drill as the tendency will be to follow the softer metal around the broken drill. 

If this was my project I would probably make a mess of it, create an insert and rebore the hole. Usually I get this kind of surprise when working on the exhaust manifold of an old car when a stud breaks off.


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## goldstar31 (Nov 4, 2014)

OK, I have a Sykes/Pickavant screw extractor in my tool box as a left over from when I used to re-build my cars and rework cylinder heads and all that jazz. I confess to taking a cylinder head off a Reliant Rebel  with a garden spade but I have never snapped a cylinder head stud.  A snapped a few on corroded exhaust manifolds but this is the time when you keep an oxy/acetylene torch to 'jump' the corrosion which is what usually jams the stud. I always cooled the red hot part with a shot of oil. Stinks a bit, but it does save what could  happen. You should mill a flat or grind a flat to centre pop and then put a Slocomb/centre drill in. followed by a drill just smaller than the  thinnest tapping drill. If you don't flatten before centre popping, the drill wanders off centre- and - well, trouble. When all is said and done, the thread should be retapped to clean out the rust/corrosion.

 There is a quicker way but it might not work.


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## kiwi2 (Nov 5, 2014)

If the .375" wedged drill is still intact you should be able to get it out by unwinding it using a pipe wrench. This should then expose the end of the small drill. I have had success (not 100%) in the past at removing broken drills by sharpening a centre punch to a fine point and belting the hell out of the end and down the sides of the broken drill. If you're lucky, it will break up and you can get the bits out separately. 
It's not an elegant solution, but if all else fails .....

Regards,
Alan


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## goldstar31 (Nov 5, 2014)

I did say earlier 'a cowmouthed chisel' which is actually more robust than a centre punch.  It's old fashioned blacksmithing- long forgotten but my father, grandfather and great grandfather made and used them. I still use them - you can cobble one up from a blunt cross point screwdriver that is ready for the scrap. 

 Cheers

 Norman


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## ShopShoe (Nov 5, 2014)

goldstar31,

I may know your "cowmouthed chisel" under a different name. This also seems like a useful tool. Do you have a picture that illustrates the tool you are talking about?

Thank you,

--ShopShoe


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## goldstar31 (Nov 5, 2014)

All that it is a round taper punch with a flat made on part of it. It varies with jobs but will go into a space or cut a semi-circular gouge in metal.

Grand tool for when you haven't got the right C Spanner!

I've got one which Dad made out of half inch high tensile bolt- before the war. Took it to Spain where I can't keep many tools. 

Took a bolster chisel which was made at the same time. 

Ys?


Norman

 ----------------------------------------------------------------------------------------------------

 Mr Ian Bradley who wrote under Duplex  called it a round nosed chisel. There is also a diamond one.

 'Amateurs Lathe'


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## ShopShoe (Nov 6, 2014)

Thank you goldstar31.

I have done something similar to get rid of a broken tap, but I was so upset breaking the tap in the first place that I didn't think of it as a very elaborate solution at the time.

--ShopShoe


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## mcostello (Nov 6, 2014)

If it's not elaborate We won't tell. It just has to work.


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## MachineTom (Nov 6, 2014)

You said that your could touch the far end of the broken bolt, Correct? If you can get a drill in there drill until the new hole hits the broken bit then get the largest bit that will fit in the hole and again drill until you hit the broken bit. With a straight punch the same or slightly smaller diameter than the broke bit, and a good size hammer, drive the broken bit out.

If you cannot drill from the bottom get a 3/8 carbide 4 flute end mill center cutting, and the most powerful drill motor and that mill cut that drill bit out. You need lots of pressure to do this by hand, be careful not to cock the drill motor, carbide will break.

Don't bother with a carbide drill then can only be used in a rigid setup DP or Mill. If the work can be put oor a Mag drill used, then a spade carbide drill will cut that bit out in quick time.


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## SmithDoor (Nov 6, 2014)

I have a nut on top with mig welder and welded to the broken drill bit to the nut. I say I had a lot practice removing broken taps and drills. 
 If this just I time event take to a auto shop with a edm call around for best price.

 Dave



wespete66 said:


> Not a scale model at all, but a general machining question please? A large threaded stud I was removing snapped off in its hole. I then began to drill it out, thinking a small pre-drill would be best. But of course the .093 drill broke off in the hole. I then drilled .375 dia down to the broken bit. But it is wedged in tight and I cannot get it to come out. What can I do to get that broken bit out of the hole?


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## B-Bee (Nov 10, 2014)

Carbide spot drill, I've always got an old one  I use for broken taps/drills
,got to be careful because you dont want carbide stuck in the hole.
Other thought is if you could drill from  other side until you reached the broken bit you could hammer it out, had success with this method but only if you can access the back of it.


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## dalem9 (Nov 10, 2014)

Try some Alum it will eat metal .It will eat the drill bit and the bolt .so keep an eye on it .You may have to keep changing the alum ,but it will work .


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## goldstar31 (Nov 10, 2014)

Already said Alum and styptic pencil earlier.

Regards

Norman


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## wespete66 (Nov 10, 2014)

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.....


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## t.l.a.r. eng (Nov 11, 2014)

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.


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## DJP (Nov 11, 2014)

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.


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## kiwi2 (Nov 12, 2014)

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.


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## RichD (Nov 12, 2014)

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


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## Toolguy (Nov 12, 2014)

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.


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## Blogwitch (Nov 13, 2014)

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


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## goldstar31 (Nov 13, 2014)

RichD said:


> 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


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## wespete66 (Nov 14, 2014)

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)?


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## goldstar31 (Nov 14, 2014)

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


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