I need to turn some 4" stock and currently don't have the means to drill a proper center hole(rebuilding G0704) to enable chucking the 4" stock to turn between centers in my 3" vise. So I decided it's time to upgrade. I want to max out capacity since I have upgraded my cross slide to extend out another 0.75-1" which I may increase later if I can remove a little more material from the carriage and or cross screw nut. I know the 4 jaw chucks have more capacity than the 3 jaw and mini-lathe.com lists that the 4" 4 jaw outside jaws have a max capacity of 5". I have also found some running a 5" 3 jaw chuck and the best information I can find is that the 5" 3 jaw with inside jaws has about 1/4" clearance with the bed which concerns me if you were to use the outside jaws on a 5" 3 jaw much less 5" 4 jaw.
Pretty confusing to try and type this with all of the 3,4 and 5" chuck size, 3 and 4 jaw plus inside and outside jaws but hopefully clear enough. I'm basically wondering would a 5" 4 jaw limit clearance vs a 4" 4 jaw assuming both were extended out fully utilizing outside jaws?
I am also including some pictures of my cross slide extension mod. It was done without buying a thing(rare for any upgrade/mod) using a piece of scrap 6061 and some bolts I had laying around from my 3D Printer build a few years ago. I have just enough lead screw to reach the center of a part for facing, boring and drilling plus almost an inch of extra travel which this lathe sorely needs. I know there is an upgrade that includes a new lead screw and carriage top but it's $75 and offers very little.
Also, don't cringe at my ways I know they look terrible. Probably worse since I started working them and stopped half way through. Still a work in progress.