Z Axis Preload

Hello everybody,

I have been looking around at all kinds of 3D printer designs and have noticed that the new Prusa i3 lacks the preloaded nuts for the Z axis. Can anyone explain why this has changed? I understand that gravity will pull on the X axis, thus ensuring that the nut always sits on one side of the threads of the rod, but wouldn't quick Z lifts rattle and be imprecise?

Also, when I also want to use my printer as a light mill (will base my own build on a heavily beefed up i3), shouldn't preload be mandatory for good results?

You can't do quick Z lifts with threaded rod, so no it doesn't rattle without the second nuts. An advantage is it can't drive the nozzle into the bed with more than the force of gravity because the nuts pop out.

You might want them for milling.

Not sure why the option is not there on the I3. I retained them on Mendel90 but I don't fit them or provide the parts in my kits.

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Thank you, nophead.

I would like to fit my printer with TR10x2 rods, though. Not that the lead is much steeper on those.
Wonder how the head will survive if it crashes down on my current rigid fixed nut layout (still have to build it).

I had the same conceptual pb with the preloaded nuts for the Z axes

so for my printer I designed the system as on the picture

the nut support the z carriage and the spring keep it in place

but in case of collission the nut just pop out the hexagonal hole and nothing wrong happens

one the bright side there is only one nut which decrease the friction (even with brass nut less friction is better)