[JoergS5]

I searched a while no with no result, so I try to ask here:

when I install a linear guide with two carriages, is it an advantage for precision to connect them with higher spacing? (Let's exaggerate: if I have a 2 km guide and move 10 cm, the height will be changed very little at the 10 cm distance).

The connection will bend however. So there may be an optimum. And if it plays a role, is preload important?

I know that there is a waste of movement space, but if it gains precision, this may be worth it. One could even build a portal with flexible carriage spacing.

[awerby]

You want to install linear guides on something that will flex as little as possible. That being said, more spacing between the carriages will translate into more stability. However, that will also have to be balanced against the amount of travel being lost. If you've really got 2km of rail, that's not a big concern, but for most machines there's a trade-off.

[JoergS5]

Thanks, after thinking about your arguments, I understand dynamic aspects like stability may be more important. Maybe I try different solutions and measure the results.

[frunple]

Not to hijack this but I think my question fits here...
Is one rail on each side of a slaved Y axis enough?
I'm thinking of 20mm Hiwin with 2 blocks on each rail but I've never used them before and I'm not sure if one rail would cause movement "side to side" if that makes sense. Would the gantry 'rack' at all if only one rail?

[JoergS5]

It depens on your requirements which configuration is best. You should consider how and where you move the blocks. There is a 2:1 rule which is a rule how to avoid stucking of the blocks. It has to do with the distance between mover (ball bearing e.g.) and the block:

https://www.machinedesign.com/motion...lip-phenomenon

If you use two blocks on one rail, this 2:1 rule is easier to reach.

Another aspect is which forces you have on your spindle/Z Axis: if you plan to route steel e.g. you have huge forces and want to avoid rotation, so a second block would help.