The Saga Continues

Hi All.

After breaking an exhaust bolt in the head, I managed to drill right through the bolt so I could use a stud extractor. The extractor broke. I ordered some Cobalt drill bits from www.toolstation.co.uk which arrived today. All I can say is these are fab. They cut through the stud extractor with ease.

Sadly I then broke another stud extractor trying to get the bolt out. I used heat, WD40, heat WD40 etc. etc. etc and it still would not budge.

But then drilling out the second extractor the Cobalt bit snapped! So I now have a really hard 2mm drill stuck in there that I can't drill out.

My next option is to use a 4mm Diamond Core drill bit. Does anybody know if these will drill through fairly hard steel? This way it will miss the really hard Cobalt as it will pass up the middle of the Diamond Core.

Please help, I am running out of options.

Also does anbody have an M8 Helicoil kit I could borrow if I do get this mess sorted out?

Thanks again
Tim.

By the way, I mean't to mention that the Diamond Core drills are meant for drilling through Glass and Ceramics using a constant flow of water.

Tim

Take a look at the following drill bits:

C1150 (next up from Cobalt)
D200 (next again)
Solid Carbide (and again).

Be careful if you get a Solid Carbide bit, because they fracture easy if pressure is applied in the wrong direction.

You might also want to consider a spot weld cutter. Basically, a drill bit that's like a hole saw, only with a smaller hole in the middle. I'm not sure if these would cut Cobalt, but in the right size might just be the trick.

[NedSVS]

I'm not optomistic the diamond drill will work. It's some years since I did my technical engineering training, but diamond tools were mainly use for machining non ferrous materials (ie no steel content), because if they get too hot they lose their edge. That is why you need a constant supply of coolant when cutting glass or ceramic. Spark erosion is probably the way to do it but as you'll have to remove the head, you may as well fit a secondhand head anyway as it may well cost less than the engineering repairs! A bit late now but stud extractors are generally a waste of time, as they are tapered and only expand the stud so it is even tighter to remove.

Originally Posted by Baph

Take a look at the following drill bits:

C1150 (next up from Cobalt)
D200 (next again)
Solid Carbide (and again).

I looked for these, but nobody seems to advertise them. Do you know of anywhere?

www.cetdirect.com do a few carbide bits in different styles. That's the only place I've used for high density/strength bits though.

[northwind]

If you know of a good, well equipped engineering firm, then spark abrasion could do the trick...

There's always The Last Resort, replace the whole barrel.

Could you try and use the stuck cobalt drill bit as an extractor? You'd need to grind the end so you can grip it - and then try and turn it anticlockwise with a spanner or very good plumbers wrench. If you grind the end off square that should help.