[MrForbes]

The bending load on the shaft is going to depend on how far apart the load is, from the support bearing. If the two are close together, then you don't need a very large shaft. But if they are far apart (because you're using thick arm materials such as wood, instead of steel, for example) then you might need a larger diameter shaft.

There are no dimensions or mention of the weight or anything, so it's pretty hard for us to be able to evaluate the design....