How best to drill through bolt in Stihl hedgecutter head?

[Cordata]

I have a bolt which sheared off in my long reach Stihl hedgecutter head attachment.

 

I have a bolt extractor to remove the sheared off bolt, but when I tried drilling through, a cobalt drill bit has done almost nothing to the bolt..

 

Any advice on  which type of drill bit to get, and what material these Stihl bolts are made of?

 

Thanks

[Haironyourchest]

The sheared surface is probably slightly angled, so that bit it just gonna skate around on it. Are you drilling by hand? I'd make sure that head was clamped tightly to the table of a piller drill and get that cobalt drill precisely centered, and go real slow and easy. Cobalt should cut anything, but maybe it's taken damage to the bit and needs a new one?

[Haironyourchest]

If the bolt goes all the way through, I'd start the drilling on the other side, against the factory bolt end. Drill it right through.

[spudulike]

I would drill it from the other side as that surface will be flat.

Those screws are nothing special, relatively soft. Has your drill been used a few times before? Is it a decent brand...Dormer or Heller? Probably a blunt drill rather than the screw being overly hard.

You could use a diamond dremel cut off bit to grind a flat on the other side part of the screw but a decent quality drill should go straight through it.

[woody paul]

Never had much luck with stud extractors were you drill a hole. Tack weld a washer then weld nut to washer then just undo it. 

[Cordata]

It might be a dud cobalt drill bit, not sharpened at the end properly perhaps? I got it for a couple quid at the shop.

 

I don't have a pillar drill unfortunately, just a steady hold on a cordless drill..

 

Borrowed a carbide bit from someone which google says is far harder than high speed steel or cobalt, so it should be able to do the job!

[Cordata]

16 hours ago, woody paul said:

Never had much luck with stud extractors were you drill a hole. Tack weld a washer then weld nut to washer then just undo it. 

 

I do like this idea.. I guess I'd have to use a washer with a super small hole in the middle so I only tack the bolt and don't damage anything surrounding it.

 

Been and got the bolt extractor already so I'll try this for now

[openspaceman]

51 minutes ago, Cordata said:

 

 

I don't have a pillar drill unfortunately, just a steady hold on a cordless drill..

 

Borrowed a carbide bit from someone which google says is far harder than high speed steel or cobalt, so it should be able to do the job!

carbide bits are very brittle and fragile. If possible support it with a sleeve which fits in the bolt hole. Once you start a hole with it you could try an ordinary HSS left hand drill, with the drill in reverse and it may snag and wind the remaining thread out.

[Haironyourchest]

Carbide drills are more for ploughing through rough stuff like timber with metal in or masonry+ timber. I thought. Not sure a carbide is capable of precision cutting?

 

[spudulike]

I reckon that once the drill bites, the screw remains will unscrew as you drill as the screw remains will be under no tension.

2.5 - 3mm drill up it with an easy out in reserve. Relatively easy job.

You can sharpen drills very effectively if you have a bench grinder and know the basic angles of a drill head.