Whilst I did make the rotating ballnut housing with CNC, that didn't really gain anything except aesthetics. If you just don't bother with the rounded corners and change the pockets for the pulley/motor to rectangular instead of having rounded ends then the design is much easier to make manually (since it doesn't require a rotary table) and none of those things will affect its performance.


The difficult bit is boring the 70mm hole for the 7207 bearing since the lathe needs a lot of swing to accommodate the plate and also a large chuck or faceplate to hold it. However it seems your MF42B machine has 420mm swing, which is plenty. To avoid buying those you could machine somthing in the extisting chuck to hold them using the pattern of holes already present.You will of course have to run it slowly. The other option is to use a boring head in the milling machine. You could also make the bearing housing and motor mount separate parts. If you clamp the two halves together whilst boring them this will ensure the bearings are concentric when it is assembled.
I made the shaft for the first one on the manual lathe out of two pieces, which was a mistake as it's harder to fasten them together reliably and ensure the face upon which the ballnut mounts is normal to the axis of revolution. Instead make it from some 3" aluminium bar and take it slowly. When you get close to 35mm diameter for the bearing use very small cuts and keep test fitting the bearing as it needs to be very accurate. Also thread-cutting the shaft and using a locknut to pre-load the bearings turned out to be a much better solution.

Quote Originally Posted by kingcreaky View Post
To be clear forget about 3 meters. the bed im planning to make will be at best 1700mm by around 1100mm
So just to be clear, am I right in thinking you want 1700mm*1100mm working area, but the available space for the machine is 3*3m? If so then that's very close to my machine - 1700mm*740mm and you would be best just using rotating ballnuts on the 1700mm axis as the ballscrews will be about 2m long. It's possible to do it without, but you'll have to spend a lot more money on the motors and drivers to get similar performance. With two bearings at both ends of the ballscrew the critical speed of a 25mm ballscrew will be about 760rpm, so you could get 7.6m/min with an RM2510 ballscrew which is an acceptable feedrate but it is rather close to the limit so may not be very 'stable' compared to the rotating ballnut which allows at least twice that feedrate. The other option is to use RM2525 ballscrews, but again these are much more expensive.