A question for the drillbitists

[8ob]

I need to drill out quite a large number of 8mm HT steel bolts that have become well and truly part of what they are screwed into, access isn't good and they will need centre drilling before drilling. What would be the best drill and centre drill for this job, don't mind expensive but it would need to do the job, also cant afford for these to be china hard/brittle and snap off in the hole. Any suggestions?

Bob

 

[123hotchef]

how HT are the bolts?

 

[8ob]

how HT are the bolts?

I would have thought 12.9 ish.

Bob

 

[gaz1]

if in flat steel or box section best way dont, use a mag drill with a 9mm or 10mm

 

[zzr1200]

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[8ob]

Its the bolts that hold the discs onto the hub on my truck, I can get it under the drill ok so thats not the issue. Just need a centre drill and drill bit capable of drilling them out.

 

[Agroshield]

if in flat steel or box section best way dont, use a mag drill with a 9mm or 10mm

I am not sure if you are suggesting the mag drill just a a means of turning the bit or suggesting he use a rotabroach-type cutter. If the latter, that is not a good suggestion. I am not sure you can get rotabroach bits that small. Any you can get will have a severely limited depth of cut. The two sizes you suggest would cut both the bolt material and the surrounding material.

 

[Johnnybravo]

I’ve drilled loads of those bolts out for a customer of mine. Normally set them up on the 2 axis Cnc mill..Is that a DAF by any chance? Get hold of drill services in Horley. Forget about carbide. Get their 8% cobalt drills,they work a charm .

 

[Agroshield]

Its the bolts that hold the discs onto the hub on my truck, I can get it under the drill ok so thats not the issue. Just need a centre drill and drill bit capable of drilling them out.

Are they the ones at the top of the photo with projecting stubs? If so, make a sleeve to go over them with the top half drilled the diameter of a 3/4/5mm pilot drill. That will get them centred very well and very easily, keep the hole square and will help if you want to re-tap the holes. Once you have the small hole established, you can change to a long series drill of the same diameter and go right through. Then follow up with the final size. Dormer A002 are good drills.

 

[nickk]

What about those ragged/ rounded ends,I’d make some pre sized bushes that slip over said ragged ends,tack onto stud ends,make 1 set to suit centre drill shank,1 set drill bit shank,as for bits,dormer,guhring.

 

[Johnnybravo]

Cut the protruding shanks off will a dremel or ,if on the mill, bash them off with a milling cutter. Long ,wafty , thin shanks of broken bolts are not your friend….And be prepared to Helicoil all twelve bolts because ,I can tell you right now,the corrosion doesn’t stop where the bolts enter the hub….

 

[Shiny Steve]

They look to be slightly high of the surounding material, could you cut em of square ish with a splitting disk to give a decent surface to center drill, then just a good carbide pilot, and final size?

 

[brightspark]

Cut the protruding shanks off will a dremel or ,if on the mill, bash them off with a milling cutter. Long ,wafty , thin shanks of broken bolts are not your friend….

thats what id do then center punch them pilot drill then drill to fiinshed size . a standard dormer hss jobber drill will do that no probs using cutting compound

 

[Johnnybravo]

Are they the ones at the top of the photo with projecting stubs? If so, make a sleeve to go over them with the top half drilled the diameter of a 3/4/5mm pilot drill. That will get them centred very well and very easily, keep the hole square and will help if you want to re-tap the holes. Once you have the small hole established, you can change to a long series drill of the same diameter and go right through. Then follow up with the final size. Dormer A002 are good drills.

The bolts corrode so badly,you will never find the centre of all of them with a bit of tube.If you measure them,I guarentee out of the twelve bolts,you will have at least four different diameters, if you want to call that shape a diameter

 

[Melvyn Best]

Whatever drill bits you use a guide sleeve would be a good idea, something like a Ridgid tools stud extractor kit perhaps?

 

[Johnnybravo]

Whatever drill bits you use a guide sleeve would be a good idea, something like a Ridgid tools stud extractor kit perhaps?

Good luck with that idea….

 

[hotponyshoes]

I have got some of these in 8.1mm if you want one?

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I would expect them do do it in a single operation if you can get them set to center.
Would be worth squaring up the broken ends first and probably taking them as low as you can to save a bit of drilling time

 

[Johnnybravo]

I have got some of these in 8.1mm if you want one?

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I would expect them do do it in a single operation if you can get them set to center.
Would be worth squaring up the broken ends first and probably taking them as low as you can to save a bit of drilling time

If it is indeed a DAF, those are M8 bolts

 

[gaz1]

I am not sure if you are suggesting the mag drill just a a means of turning the bit or suggesting he use a rotabroach-type cutter. If the latter, that is not a good suggestion. I am not sure you can get rotabroach bits that small. Any you can get will have a severely limited depth of cut. The two sizes you suggest would cut both the bolt material and the surrounding material.

rotabroach type i was on about if the bolt is stuck in as the bolt snapped on the threads part

with an adaptor

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[stuvy]

I am not sure if you are suggesting the mag drill just a a means of turning the bit or suggesting he use a rotabroach-type cutter. If the latter, that is not a good suggestion. I am not sure you can get rotabroach bits that small. Any you can get will have a severely limited depth of cut. The two sizes you suggest would cut both the bolt material and the surrounding material.

I have an 8mm and 10mm rotabroach but it’s a solid drill bit not cutter. Still goes in the mag

If it was me I’d make a sliding clamp to hold a grinder, slitting disc and take the main of the head off then drill less out and a flatter surface to drill