Vibration cleaner bowl centre

[CompoSimmonite]

I've got the vibration motor and have found a suitable bowl for a diy project build.
Simple question - does the bowl require a central column ?

 

[cardiffrob]

I've a feeling that the cone-shaped bit in the middle helps to get the material to flow in a suitable pattern.

 

[CompoSimmonite]

After finding a suitable, stainless, bowl lying around in the garden now the search is on for a funnel shaped "thing" !