MadModder

Just a bit more progress: I've managed to extract the stub of that M12 Countersink headed screw by jamming a Torx bit up the hole that I'd drilled and using the Impact Gun:

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And I've identified the  bearing retainer nut that I need to unscrew from the shaft for the next step - It's a KM10 M50 x 1.5 mm pitch bearing lock nut - amazingly still an available standard. As this is deeply recessed it's hard to measure for making a suitable key, but fortunately it has KM10 stamped on it !

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Seems that I need a 100 mm length (minimum) of 50 mm bore x 70 mm o/d heavy walled pipe. My initial searches have drawn a blank here in the work shop.

(needs to be hollow to slip over the shaft and reach into the nut. The search continues. Theoretically I could turn it from solid bar but that a lot of drilling and boring !

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.

Yes- when you think that was just a splash cover the CSK screw was holding on, & the trouble it caused.

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 !

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.

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 !