Sondre Eknes -- the parts have to be constrained specifically as Pin Joints. When you are defining your constraints for whatever part you are assembling, you have to make sure you select Pin Joint from the drop down menu. If it says "User Defined" it will not suffice.

Thanks so much i have been looking for this for sometimes now , can you please create a worm gear mechanism, thanks.

Hey, mechanism is fine. But how can i model a rack and the corresponding mating gear in Creo. Kindly provide some information on this.

Also provide some information on how to provide a slider constraint on for rack. I have changed user defined for rack to slider, now after that pls guide me through steps. I am a beginner.. Thanks is advance.

Creo doesnt let me select the motion axis or pinion, any ideas?

what type of assembly is this pin or rigid.

Too bad you didn't get it correct. The basic rack do not have curved teeth, they are straight sided.