Bugsy
At least the solution to your problem was "clear cut"!
For several weeks (on & off), I have been making some pulleys for mounting below deck.
Having just completed them, I realised the ones with a mounting bracket were u/s because the bracket was going to foul the thread on it's way round the sheave. Thought "Oh bother" (or something very similarilar).
One would have thought that the guy in the drawing office would have spotted that - but his "senior moments" seem to be coalescing these days.
Solution: Make new mounting brackets using thinner brass and reduce the thread on the blocks from 4BA to 6BA. So...
Mounted one of the blocks in the lathe to skim off the threaded section...but not enough material in the chuck for good grip, so tool tears it out and chews it up. Thought "Oh bother" (or something very similar).
Plan B: Start afresh with new rod. On cutting 6BA thread, find it's chewed up. Thought "Oh bother" (or something very similar). Turn down a bit more rod and try again - with the same result. Thought "Oh bother" (or something very similar). Close inspection of the die (c. 50 yrs old), reveals the reason - needs binning. Success with fresh die.
First attempt at milling the slot results in the work coming loose and the cutter destroying it. Thought "Oh bother" (or something very similar).
(I don't have a milling machine, so it's a bit hit and miss with the pillar drill.)
Make yet another block - O.K. this time round.
On making the new mounting brackets, I had to destroy the first one to retrieve the tap as the solder had caused it to jam. Thought "Oh bother" (or something very similar).
Eventually, however:
Just goes to show what can happen when a biochemist tries his hand at engineering!
Mike