[jeffshaw]

I am designing a carriage assembly that guides a cable through a set of rollers. The carriage is driven by an acme leadscrew and is supported by two round rods. The carriage has a set of flanged plastic bearings for each rod. I am having a hard time with the free body diagram of the carriage. I am trying to determine both the axial load on the acme nut (so I can determine the amount of torque required to move the carriage) and the loads on the bearings so I can estimate the frictional forces I must overcome and ensure I have a suitable bearing material and bearing size. I don’t need too detailed of an analysis, just something quick and dirty to ensure I’m in the right ballpark. I would like to simplify the diagram by assuming point loads at each of the bearings. However, I’m not too sure where I should place the point loads or where contact should be assumed to be made or not to be made. I would like to assume the worst case and design for that. I have attached a sketch of what I am working on. Any suggestions would be greatly appreciated.