Homebrew PCBs

>
>Which diameter would a delrin shaft need to be if we say the tube is 50mm
>dia and 20cm long? the shaft is supportint the tube via the two endplates.
>How would i make the bearing with a delrin shaft? Does it run well in ptfe?

You may be aware of this, but some plastics, like nylon, absorb water 
nicely, and swell.