I'd be inclined to remove the chuck from the back plate and then heat the back plate a bit.
You dont want to damage any gearing in the head.
It'll probably be some surface rust on the thread or someone has jammed something being held into a cutter, either way it needs to be loosened.
It should be even tidier by Saturday, you are more than welcome to search the workshop, sheds and alleyway.
I might even try to tap your knowledge regarding my intermittent leaky flat roof....☹.
Is tea and cakes in the back garden ok, socially distancing of course....
About time I updated this thread, lots of things have happened in the past year.
My Father pasted away last year in September so yet another round of stuff to sort out.
The garage/workshop was put on hold again, I now have 3 phase but had to change utility provider as SSE wouldnt play...
Bernard snub nose holder,,,expensive but worth it, imo.
I've used them for best part of 40 years now, one lasted for roughly 33 years. I now have another 2 Bernard holders one each for my large and small dinse plugs for my 2 welders..
Theres 2 standards for all makes of decent drill bits, the expensive ones are ground from a solid piece of hss bar, the cheaper ones are drawn out/ formed from heated bar and then ground to size to save material costs.