Drilling HT machine bolt-heads - 200mm stroke, 30mm Diameter

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Drilling HT machine bolt-heads - 200mm stroke, 30mm Diameter

Post by UniversityMachinery »

Hi,

I am looking to drill a couple of seized bolt heads clear on a large piece of University machinery. They are hi-tensile 5/8 hex machine bolts and secure a 3 tonne actuator to the underside of a large steel platform.

There is around a 25 mm diameter thread on these bolts with the cap head 33 mm diameter x 25 mm deep. I have clear access to the holes where these bolts are located, although the drill stroke is going to need to be around 200 mm and ideally around 30 mm diameter to ring the bolt head off as they are located at the bottom of a 175 mm x 36 mm hole. 2 of the 3 bolts have 5/8 hex tool hardened bits sheared off in them, one of the 5/8 hex turned a round in there, and another one sheared the bolt head off. (the other 15 cracked loose on a 5 x multiplier & bar).

This is ideally situated for mag drilling gear, with a large steel bed.

Please advise what products you supply might stand the best chance or advise if you can recommend an alternative. The ideal scenario is finding someone that deals with this stuff on a regular basis and just giving them to job. We are located close to Milton Keynes if this is viable.

Many thanks.

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Re: Drilling HT machine bolt-heads - 200mm stroke, 30mm Diam

Post by ultimatehandyman »

Firstly the actuator has no stored energy in it? I don’t want you removing all the bolts and it turning and killing someone if it weight 3 tonnes!

Cap head bolts are a pain in the backside to drill out because of their tensile strength, but it is possible using the correct drill bits.

Cobalt drill bits will drill a HT bolt but they soon go blunt.

Because of the broken off tool steel I would use Artu drill bits, these will drill through hardened steel as in this video-

The only problem is that (as far as I am aware) they do not make them any larger than 12mm diameter. If you could get the tool steel drilled out using the artu drill bits you might be able to use a rotabroach http://www.rotabroach.co.uk/cutters

Solid carbide drill bits will also drill hardened steel but they are extremely brittle and break very easily.
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Re: Drilling HT machine bolt-heads - 200mm stroke, 30mm Diam

Post by UniversityMachinery »

Thanks for the speeds response, It was this video that brought me here actually. And as I understand the 12 mm would require flats machining and extension bar to make full stroke. so not an entirely great option. Has no-one else scaled this type of drill up? Also someone mentioned taking a high quality masonry bit and getting it sharpened, then added it wouldn't be easy to find someone to sharpen one of those.. Having said that I have some great masonry bits, and they certainly run up to size? Thoughts?

RE the actuator, it is released and drained down thanks for the concern :), this unit is going off for a re-chrome and grind if we ever got these last bolts out.. Its that 36 mm by 175mm bore hole they sit at the bottom of that's going to be the trickiest part..
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Re: Drilling HT machine bolt-heads - 200mm stroke, 30mm Diam

Post by ultimatehandyman »

You could try a masonry bit, although I have never tried one on hard steel.

ARTU do sell a wheel for grinding their bits- http://bit.ly/1vs8TmO

But I'm guessing that you could do it using flap disc?

You can't get to it with a gas axe can you to heat it up and let it cool, it might normalise the metal?
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Re: Drilling HT machine bolt-heads - 200mm stroke, 30mm Diam

Post by Hitch »

Am I right in reading that they are counter-bored 175mm deep? Makes life very awkward....I gather you cant sacrifice anything to cut the bolts?

A rotabroach bit should drill the bolt easily enough, if you could get access to it, but the head with the hex bit sheared off may prove to be a problem....

A firm that specialises in line boring would probably make it look a piece of cake.

A picture is worth 1000 words sometimes!
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Re: Drilling HT machine bolt-heads - 200mm stroke, 30mm Diam

Post by UniversityMachinery »

It is indeed.. This is a 2.5MN Instron fatigue test machine. It's going off for a 10k actuator refurbishment.. I am considering just biting the bullet and bringing the mobile spark erosion unit in. Gonna rack up a £750 bill straight off the bat though..
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