Just to add a few things about the ballscrews, most if not all of the low cost C7 ballscrews are actually made in Taiwan by the larger better known ballscrew manufactures, it is just the low cost ballnuts that are made in China.
Fitting a spring between the nuts while eliminating the backlash is not done commercially because it causes early wear.
There are a few ways to eliminate backlash and the best way is to have two nuts with a spacer between the nuts and the thickness of the spacer accurately place the balls on opposite sides of the thread.
As long as you look after the ballnut and screw by lubricating it, it will last for years even if you push it hard.
The argument of the spring takes up the slack when the nut beds in or wears is a bit daft because if you look after the nut, it shouldnt wear, especially on a hobby machine.
I have known 20 year old machines that are worked hard and still maintain good repeatable accuracy with a good ballscrew.


The low cost chinese ballnuts are ok for hobby use but i would not even consider them for a production machine.