help with screw joint in cosmosmotion

[posix]

hmmm now I don't know how to forumlate my question

ok I'll try

a screw and nut combination. the nut is fixed. the screw rotates and at the same time translates along the axis of rotation. with me?

where do I place the joint and where is it's direction? (in the property manager for screw joint)?

for example, do I place it at the egde of a top of the screw and it's direction is the cylinder that forms the screw? or do I place it at the top face of the nut and the direction is cylinder that forms the nut? or a combination?

tutorials and online docs are frighteningly brief on screw joints!!!

[posix]

basically the problem is that whatever I do at some point (a few miliseconds after the simulation starts) the nut starts to rotate slowly in the same direction with the screw. and I don't want that!