The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)

[awemawson]

Well another try:

I've managed to drill a 6mm  hole 20 mm deep into the back of the hex driving recess using an HSS carbide drill. Went in remarkably easily. Next size up that I have in HSS Carbide is 8mm - total rejection, just polishing the edge of the hole. Tried another brand new HSS carbide in 8 mm with the same result.

I can only assume that the core of the screw has been left relatively soft with the rest at 12.9 hardness.

It seems that 12.9 steel needs to be brought up to 400 Deg C to soften and I'm getting no ware near that with my propane torch. I do have a Mapp gas cylinder but that only burn a few degrees hotter so probably not the solution.

I've a pair of big old Oxy-Acetylene cylinders out side in the safety cage but I dread to think what the state of their hoses is - not been used in a few years. The logistics of getting them near the bench will be challenging.

. . . more cogitation 

[smiffy]

Is it possible they are left handed threads ? or some times tightening a bolt can loosen one that refuses to come undone when turned in the correct direction  Mike

[awemawson]

It did occur to me that it possibly could be a left hand thread, but there is no valid reason why it should be as the tool disk is rotated in both directions by the servo with the logic working out which way is quicker from 'current tool' to 'desired tool'

I did however try left handed vigorously with the big ugga-dugga !

[awemawson]

In a dark corner of my brain I had a vague recollection of having a few 'Cintride' brand solid carbide drills - just maybe they might work. Intended for slow speed drilling of hard steels in a machine tool able to exert significant pressure while rotating. Well I'm forced to use a hand drill so the 'significant pressure' is limited to what I can apply with my tummy 

OK I found the box, mainly empty cardboard boxes but I did have one 9.5 mm solid carbide genuine Cintride so lets see what happens:

I've managed to sink the hole now to 13 mm deep - there can't be much material left of the countersink - I'll have to do some maths -

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- go do the Maths Andrew !

[awemawson]

Another TWIT moment of course - the bolt shank is 12mm - assuming that the 9.5 mm hole is approximately concentric (it isn't quite) then there will be (12-9.5) / 2 wall thickness left or 1.25 mm which will have very considerably weakened it but it's very  tough steel. I'll have a go with a punch and see if it'll shear off.Very well supported of course as it's snugly sitting in the female countersink.

(a 12 mm Cintride bit is north of 50 UK pounds)

[Muzzerboy]

I think I'd have reached for the TIG myself if that had been mine. Between the added leverage of a large bolt welded to the head plus the effect of heat, I'd be surprised if it didn't budge. But there's no right or wrong method.

Csk machine screws with hex sockets are one of the least effective and most troublesome fasteners - hard to tighten adequately without damaging the head and a sod to remove when they get clagged up after the passage of time and corrosion.

[awemawson]

Sadly no Tig set up   

[awemawson]

Brute Force wins the day 

A large centre punch applied to the drilled counter sink head in three 120 degree spaced whacks sheared the head clean off:

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This exposed a ring of Allen headed bolts:

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Which held a cunning double taper arrangement

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Slowly it starts to come apart

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This allowed the bearing and half the rear curvic coupling to slide off the shaft.

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Now looking into the assembly I can see retaining nuts on the shaft  that will probably need special spanners to be made.

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But enough excitement, I need a lie down and a wet rag on my forehead !

[John Rudd]

Persistance wins the day! ..Enjoy your lie down..