Myford lathe chuck issue

[TonyB]

That thread shows evidence of abuse, probably from putting the chuck on without thoroughly cleaning the internal thread. It's easy to clean the spindle but the chuck is often forgotten. Although you say you've cleaned it let me suggest grinding up a threading tool and using it to scrape the thread by hand. A boring bar would make a great handle. I've revived many threads this way. I've also used a smaller tap with the same thread count as a scraper, if available. It takes some time but it's effective.

[berger]

allways put a chuck down jaws facing downwards it stops swarf dropping into the threads, and i know nowt about lathe turning but i am very good at drinking the old black&tans. today i am out out out and then home to bring in the lump of smokeless fuel at midnight, i can't get coal the green police have banned it. thankyou for listening and a HAPPY NEW YEAR to everyone on /off this bestest forum int world ,

[Jules]

thanks Tony, thats basically whats happening "soon", an old toolmaker said he will chase the thread for me :)...
Happy New Year Berger, its 11:30 here in Melbourne and our kids have just gone home - no stamina these days lol!! we still follow our old english/Yorkshire traditions and have a "first footing" process with salt and coal at midnight - we have a scottish bagpiper carved from coal that we use, cheers!!

[Jules]

I got the chuck back today from a retired toolmaker who lightly chased the thread in the chuck, and when fitted it went on further, but still jammed where the broken out piece of thread is  . I tried a small file cleaning up around that local area, which made only a smidgeon of improvement in engagement, so then used Rex's idea of lapping paste - worked like a charm!
I had to rotate it a few times around the thread before it rotated freely with the lapping paste, then cleaned it all out, applied a bit of vaseline and viola, seated home with just hand screwing  ...
thanks for all your thoughts, I'm back functional again....