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Drill out the nds cup to the largest size you can without cutting in to the frame, this should allow you to knock the cartridge out, they normally only sit in the drive side cup it’s not usually one piece.
This will then leave you with the two cups still in the frame.
Use a hacksaw to gently cut through the nds cup at around the point where the chain stay meets the BB shell, as that will have the least amount of threads that could be damaged.
When getting close to the threads, you should be able to chisel the cups inwards, break what remains of the threads and fold the cup in on itself. It should then come undone relatively easily.
On the DS cup you could do the same or do big bolt thing to get it out, since it’s a left handed thread.
Dogtemple-
I attempted this. It took two or three evenings and maybe four charge cycles of the Makita. And it killed like five drill bits. The spindle is now out, as is the NDS cartridge bearing, but most of the BB has stayed put.
NDS situation:
DS situation:
I could maybe nibble away at the remains of the NDS cup some more, though I've already troubled the frame's BB shell threads in one small area. It might give me a chance to knock out some more BB parts (hammering from DS side). But without a spindle I would just be drifting that 2mm black surface showing behind the shredded alu teeth.
I'm quite tempted to just dissolve the whole lot out with caustic soda but I would then need to repaint (which is a shame as the paint is quite cool). Does anyone know of a way to protect paintwork in a caustic bath? Like can I coat the whole area in silicone bathroom sealant or maybe heavy grease / vaseline? Peanut butter?
Ndeipi
Hole saw is exactly the kind of evil genius tip I've been looking for.
Should I hole saw the DS or NDS cup? I think body and spindle of the BB are connected to the DS cup btw.