Bumped his topic as I had to make more improvements to it's condition. Plus I need to excercise the hands caused by R/Arthritis, so glad to get back into the workshop.
The spindle/chuck mounting bodge of a cut off piece of bolt shown in earlier pics was just not good enough.
I made a new complete spindle from 3/4" (19.05mm) dia silver steel. Set up in the lathe and acurate to within 2 ten thousandths of an inch (0.00508mm) over it's length.
Pic below is after machining the chuck thread on the end-
Comparision of the old and newly machined spindle ends-
After measuring, I found I could reduce the length of the 3/16" (4.75mm) wide cut slot for the new one, which produces a better bearing surface. the chuck thread for the English made Jacobs chuck is 1/2" x 20 tpi UNF, and the smaller diameter top end threaded 3/8" Whitworth. Both were screwcut on the lathe (my 1st attempt at power feed screwcutting)-
Did a check with a 5/16" (7.95mm) diameter long Dowel Pin fitted in the chuck while still on the lathe and it had only 0.0015" (0.038mm) runout at 1.5 inches (38mm) from the chuck jaws!, so pretty good allowing for the age of the chuck.
Did the same after fitting back into the drill and adjusting lower bearing clearance, I got 0.003" deflection while applying a side load, so I am more than happy now with it's condition.
Regards