[mactec54]

Re tensioning screws: I don't know the force required. Never seen it done on a DIY machine.

I do it that way for all ballscrews over 12" / 300mm I install on my builds, ( if you use a rotating nut then you don't need any added tension to the screw ), it works and is worth the extra, very little force is needed from 4lbs to 9lbs ( or around 1Kg to 4Kg ) is the max needed I use a bellevue washer to create the load this way the screw can still expand if it has to