Removing a broken drill bit?

[wespete66]

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?

 

[butchjth]

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.

 

[goldstar31]

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.

 

[Brian Rupnow]

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.

 

[Theclockworks]

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

 

[wespete66]

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?

 

[goldstar31]

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

 

[goldstar31]

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

 

[DJP]

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.

 

[goldstar31]

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.

 

[kiwi2]

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

 

[goldstar31]

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

 

[ShopShoe]

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

 

[goldstar31]

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

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

'Amateurs Lathe'

 

[ShopShoe]

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

 

[mcostello]

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

 

[MachineTom]

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.

 

[SmithDoor]

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

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?

 

[B-Bee]

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.

 

[dalem9]

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 .