9 X 20 Lathe Z travel Ball Screw

[Me2]

Hello all,
I've purchased a Chinese 9 X 20 lathe recently to convert to CNC. I've noticed all the lathes on this site have placed their Ballscrew in place of the lead screw. Has anybody placed the screw down the middle of the bed under the cross slide. In my case this would reduce the moment load on the cross slide particulary as I will be utilizing the back end of the saddle for tooling. I'm also looking at machining the Vee ways off the cross slide saddle and fitting linear slides to increase the avalible travel. Extensions will have to be fitted to the saddle casting on both the front and rear to allow the extra travel. The other advantage of this is that I can fit a ball screw under the cross slide table rather than on the side under the chuck or tail stock. Obviously some machining of the Cross slide casting will be nesessary but I can't see this being a major problem. A new cross slide table will need to be made to fit on the linear slides and fit the ball screw nut. My plan is to have tool stations mounted across the table rather than use a traditional tool post holder. With the additional stroke I can fit 5 tool stations. My CAD layouts show that I won't lose the clearance between the chuck and new cross slide table.
On another note, I must admitt that whilst stripping this thing down the quality of the build is very poor. The cavity in the headstock still had core sand inside as will as some 2" nails cast in. The core sand was bound in place with orange paint. Some had come loose and made its way into the bearings. I sand blasted the thing and repainted it. Bearings have been replaced with SKF units.
Anyway be interested to see if any of you guys who have done a conversion and have a comment on my idea's.

Cam

[LeeWay]

Personally, if you want to go the route you are talking about with centered screws, I would start completely from scratch.
It would be much easier than trying to rework and rebuild the existing lathe.
You could use the spindle assembly off this lathe when your build is otherwise complete. Then you would also have use of this lathe to help build the second.

I did a non intrusive conversion on a 7/12. While it did the job I wanted it to do, it was lacking in many ways. Mainly power and structural rigidity. Backlash also wasn't pretty, but could work around that with some hand coding.

Built a totally new lathe from just 80/20 extrusion as a base. Much like you plan on doing yours, sans the lathe bed.
The two lathes are so different in comparison. No more backlash. Plenty of power. Plenty of travels. Acts like a real machine.

Just something for you to consider. Lots of nice lathe builds on the Zone to see. Check them out if you haven't already.