thanks for the replies guys.

With regards to the HGH20CA blocks ive found some at a great price but the spec is HGH20CAZOC Very light preload. Or should i go for Z1?
Ive had a look around and this thread said z0 (http://www.mycncuk.com/threads/3711-Hiwin-linear-blocks-HGW-20-CC-what-preload-to-spec)

Thanks again.

Trev