BB Cups - Teeth + cups completely ruined. What to do?

More bottom bracket mayhem. After my mirth with seized cups, I've acquired a retro early-mid 90's GT Avalanche. Great little project, however, both BB cups have seriously decayed. This was confirmed when pressure was applied to the BB tool and almost all of the teeth, then the actual cups themselves, started to peel apart. Looks like some cheap ass plastic/faux/metal materials going on.

So this is my predicament, is there a way to get these out via a bit of DIY? I'd imagine cutting a groove into them to tap them out or some jazz. Thanks in advance.

if the cups are the shitty shimano plastic ones I'm thinking of then just cutting them out should do the trick or if the paintwork isn't that great wrap some baking foil around the bb shell and completely melt the cups with a blowtorch.
In advance when working on BBs, a bit of heated up penetrating oil dripped around the edges to seep into the threads should at least give you a fighting chance of normal removal.
THUN plastic BB cups were of a similar ilk but with a Campagnolo half moon shape on the edge of the cups, shame because the bearings in them were SKS & crazy smooth.
GL

I know white spirit degrades plastic tubs... I wonder if this could be any use to destroy the plastic cups?

have you got just one cup stuck or both?

If you have shredded both, then probably time to get creative with a dremel/drill/chisel/ blowtorch.

Old BB's are the suck.I remember working in a shop and a sweet Cannondale black lightening came in with a mashed BB, in order to save the wicked paint we stuck to chemicals and brute force, 3 guys and a huge bench vice. 1 guy to just bold the frame down into the BB tool/vice, the other two bracing off walls tweaking it....

result = BB stayed attached to BB shell, rest of the frame rotated around the shell = twisted mess of expensive tubes.

Thanks for the suggestions, haven't had time to try anything yet. It's both cups that are mashed, real messy. The teeth are almost none existent anymore so I think your suggestion of dremmel/drill is the best shout.

Am I right in guessing the threads would still be ok/useable with a thin, straight groove cut across them (worst case scenario)? I'm just going by steerer threads having those notches cut down them for tabbed washers etc

~Maybe if you remove most of the cup material, you can push out the bb axle & cartridge?

Seems plausible with what I've got, the problem could end up being the solution by way of the cups corroding every time I even look at them. They fall to bits with the tap of a screwdriver...

If you can place the frame on black of wood so it lies flat with a block of wood under the BB shell but with a BB sized hole in it. Then hit the axle with a lump hammer. It should be forced out eventually. so long as the frame is properly support the frame won't be harmed.

A straight cut across the BB threads would be fine, I had this done by LBS on a Principia RS6 that some turkey had left an eroded Octalink in. Took them ages to get it out though.