Hi Ross. Try Chester tools,they sell add on quick change tool holders in different sizes. Dont know what size mine is, pretty sure its their piston T1, has dovetail slots, but its big and fitted to a 11 inch lathe and never had any trouble. Be prepared to bore them out / make a bush to fit you cross slide post. Most after market posts will need some tinkering to fit. You wont look back if you get one they are wonderful, life IS too short! Re machining ball screws, some are ground out of very hard stuff! Cheaper ones are case hardened and light hand grinding will remove this easily. The simple route is to cut em off and make a collar to attach to a custom turned end. If you mean to turn the actual screw ... v diff to get the linearity you need. Many people refer to a ball screw but mean an acme screw with an anti backlash nut (apologies if you mean a ball screw!) The are plenty of suppliers of acme screws, Chester sell spare lead screws for their lathes and they are relatively inexpensive (compared to say a replacement myford lead screw) and you can buy acme taps. You can cut a long acme thread but unless you have spent a lot of money on a very accurate lathe.... it wont run well and the backlash nut will bind in certain places. TC indexable are good but go off quick, horses for courses, TC isnt always the best. That all sounds rather negative, its not meant to be so sorry! Shame you dont live next door mate, we could stare at the problem for a bit over a few beers and I'm sure all would fall into place!