Snapped drill bit

[squirrelciv]

I've inherited a snapped drill bit 10mm into the cylinder head of my XT! Seems the previous owner sheered off an exhaust stud, tried to drill it out to tap a new thread and broke the drill off.

Any ideas;

A) how to get it out?
B) if I can't get it out, how to fix a new stud in the head with only 10mm depth of hole (unthreaded)

Do they make a drill that will cut HSS or would a dremil be able to grind it out?

[guest146]

You have  a major problem. When this work is done it needs great care and quality drill bit and taps to avoid this. My best guess would be to cut it out or drill round the bit with lots of small holes so it breaks away and make a hole. This could easliy be alloy welded up and then ground flat and re drilled.  Saying that I am sure there are L/H stud removers that are like a drill bit but when the bit you drilling turns it unscrews.

Ken

[Steve H]

Spark Erosion is supposed to sort stuff like this. Not used it myself, and I doubt it is cheap, but my guess is you will end up messing the head up if you are not careful.
This is the sort of service but they are rather a long way a way. http://www.sparkeroding.co.uk/

Another option might be to use springs to hold the headers on. But that would need holes drilled in the cooling fins and some loops welded on you nice new shiny headers.

[steveD]

Pat, if you look closely at a drill bit you will see that the front cutting part is like a spiral or a twisted piece of metal or a bar with flutes in it. With a small, hard, sharp punch you should be able to chip away at the edges or alternatively loosen the broken end. Tapping to rotate the bit anti-clockwise is also an option. Years ago when I was Toolmaking there was also a small product that had two prongs that would fit into the flutes on each side and you could wiggle the part out. We did have spark eroding at our disposal in those days!

Hope some of these ideas might help.

[guest27]

Must have been well jammed to snap a 10mm bit.  You may be able to shock it back with a drift / punch, or the two pronged thingys can be good and can be made fro scrap - may not be as robust as the real thing mind.

Spark erosion is the preferred way.  I would not try drilling it etc as even if it is a cheapo bit and not that hard it is a darn sight harder than the ally head.

R

[guest1017]

HI
Is there enough of the drill bit showing to weld say an 8mm bolt to it , then you could jiggle it out , it may take a few attemps to get it to stick to a drill bit but the heat will free it up aswell .
Ian

[squirrelciv]

Don't think I've explained this correctly. the snapped off brill bit has sheered off 10mm into the cylinder head. Think of a 6mm hole 10mm deep with a 6mm drill bit at the bottom of it. The broken edge of the drill bit is flush with the bottom of the hole so pretty well not accessable with any type of gripping tool. As for passing something down the flutes... this is a no go as the flutes are full of waste material from the drilling.

What do we think to the dremell grinding option?? You can use those things for sharpening HSS drill bits so surely it can grind away the snapped off piece eventually.

I really don't want to take the head off if I can possibly avoid it as that means the bike will have to come off the road which is a MAJOR grief.

Come on guys, get inventive.

[themoudie]

Aye Pat,

My thoughts went to a cobalt drill, but even so I think you are being ever the optimist to carry out the op without head removal. You need stability of the head and drill along with depth control of the bit. That isn't going to happen with a bike on a wobbly stand and the drill bit in your Black & Decker!  Also, cobalt drills are potentialy more brittle due to their hardness than HSS drill bits! One tweak and you've filled the hole with only one option. Spark erosion. Alternatively, scrap the head and start again or install slip-on spigots in the exhaust ports!

All this lot adds up to angst, time and money when you've got a kitchen to build! Either bite the bullet strip the head and get it spark eroded then helicoiled and rebuilt. Or put it in the back of the shed until after the kitchen extension, then fiddle with it on the kitchen table in the warm! 

Try this url for some background: Cobalt drill comparisons by punters!

My regards, Bill.

[Dave#22]

Hi Pat, Another solution I have seen used and also done myself is to build up a pillar of weld onto the broken tap/easiout, using 680 stainless rods, slip a nut over the pillar and weld, giving a solid drive to the tap. Is it definately a tap...... because if it's easiout, it will have to be turned clockwise to remove and a tap anticlockwise.
  Good luck
    Dave

[guest146]

You will be hard pushed to make a weld stick onto hard tool steel unless its not very tight. the one thing that will remove hard steel is a grinding stone like the dremmel you spoke of.If you are very carefull and paitent you may do it with one of these.

Ken

[themoudie]

Aye Ken,

Agreed, but he's 10mm down a 6mm hole already and hoping to go deeper! A stone in a hand held drill is going to kick and move about until it cleans the working face up. With the cylinder head 'off', solidly mounted on a bed or in a vice beneath a pillar drill or milling machine you stand a chance of keeping the hole true and controlling the depth.

If Pat wants a proper bodge, then 6mm threaded MS rod Araldited or 'Monkey' metalled into the head could be the way to go  A wee inscribed plate beside it would read " Good enough for colliery work"  A bit posher would use galvanised or SS rod and for the 'dogs testicles', stick a short helicoil into the hole you have and then Araldite or 'Monkey' metal the lot!  but would make an engineer

Cheery cheery, Bill. 

[Furry John]

Don't think I've explained this correctly. the snapped off brill bit has sheered off 10mm into the cylinder head. Think of a 6mm hole 10mm deep with a 6mm drill bit at the bottom of it. The broken edge of the drill bit is flush with the bottom of the hole so pretty well not accessable with any type of gripping tool. As for passing something down the flutes... this is a no go as the flutes are full of waste material from the drilling.

What do we think to the dremell grinding option?? You can use those things for sharpening HSS drill bits so surely it can grind away the snapped off piece eventually.

I really don't want to take the head off if I can possibly avoid it as that means the bike will have to come off the road which is a MAJOR grief.

Come on guys, get inventive.

Pat, I have been stuck with an almost identical problem on a Velo, I used a diamond tipped burr to grind away the web of the drill, the core if you like, and once this was cut away enough the bit lands will come out leaving the old stud threads, these can be pulled into the hole and withdrawn leaving the hole ready to take another stud. If you want to call round I still have the box of diamond tipped tools, which fit a standard Dremel chuck, you are welcome to borrow them and have a go yourself, it does need a good light to see what you are doing and some patience but you can do it.

John

[themoudie]

Nice John, 

Pat as an orthodontist!!!!  There's a national shortage! Let us know how you get on Pat!

Toodle pip, Bill.

[squirrelciv]

Cheers guys.

Bill, the problem with taking the head off [and in doing taking the bike off the road] is this is my only form of transport to and from work [and anywhere else come to think of it!]

Furry, thanks for the offer matey, I will take you up on that if I can. Might be a day or two till I pop down though. I'll ring to to sort out best time to call and receive some guidance.

I'll keep the forum updated on progress.

Cheers,

[mini-thumper]

I think there's a Channel 4 documentary in this somewhere. Any chance of a live video feed from you shed Pat? Charge pay-to-view and all your costs are covered............

Boyd