I'm still waiting for delievery of linear rails.

This is how I want to lock them if needed:

Milling machine - video-hgr-lock.png

C block with cut in one wall. This thin piece will bend slightly under pressure of bolt and will clamp around the rail. I think this is much safer for guide surface than using only bolt directly.

There will be two per axis:

Milling machine - video-hgr-lock-2.png

Bolts of levers will be shortened if needed.