How do I remove this keyed Jacobs drill chuck?
Final update - I managed to machine something close to a MT0 taper into the old arbour.  I also cleaned up the surface rust from the outside.



This lathe has a head stock that can rotate for tapers, which was a little sketchy given how much stick-out there was.



This shows the rotated headstock, so the taper is very approximately straight.  I didn't have a good solution for calculating the 1.49 degree rotation - will have to do better.  Perhaps a really big protractor?



And here's the newly finished drill chuck in use, drilling a hole in the top of a schrader valve cap... for reasons.

Only downsides - 1) its not stunningly accurate, but has already proven way better than "aim and pray" with a hand drill.   2) the tail is quite long, I did not want to remove the center hole on the end, so it only gives 20mm of travel on the tailstock.