I am looking at some good quality linear stuff but the rails are only 346mm long. This is 35mm rail, overkill but the stuff is good quality, so keen to try and use it.

The carriages are 105mm long, 95mm ish if the grease nipples are removed. Assuming some spacing between them, I cant see myself getting more than around 130mm of travel on the Z. Is my maths correct, surely it doesnt matter if the rails or the carriages move .... 346mm - 200mm - some spacing = not much left ...

I could possibly source longer rail and use the carriages there - just trying to understand reasonably for around 200-250mm Z range, realistically what length of rail is needed - 450mm?