Yeah I used the SF1605 Ballnuts from Keling
Block and Rail in USA (scroll down the page) which are very similar in dimensions to the Linearmotion2008
3 ballscrew 1605-250/550/1050mm-C7 end machined | eBay and they are also larger than the Roton 5/8" Ballnuts
5/8 X .200 Right Hand Recirculating Lead Screws & Nuts for Power Transmission - Roton Products, Inc., so if you go with Roton you don't need to machine the Ballnuts themselves, and you go with LinearMotion2008 you will need to Machine off some part of the Ballnuts, and for both you need to make Ballnut mounts.
Also the mill bed slot where the Y axis screw is positioned is slightly off centre and I had to machine some side clearance off the Mill bed to compensate for the larger dimensioned SF1605 Ballnut, later I added a modification and extended the Y axis and for this I used a Roton 5/8" ballscrew and Ballnut and I was quite surprised at the smaller dimensions and had I gone with the Roton initially I would have saved myself a bit of maching....
and as Mystichrome said when you add the new X axis Ballscrew you will need to machine a small pocket clearance off the Y axis saddle to mount your new x axis Ballnut....
I hope I haven't confused you more and you can follow my explaination....
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