the dust Tardis

[yetloh]

I could be wrong, but I think the entire thing needs to be cylindrical all the way through.

If my Oneida is anything to go by I don't think that is right. On that there is a big fan at the top above a big cylindrical tobe about as high as it is wide, underneath which there is a cone the narrow end of which connects to the dust drum. I seems to me that all the cyclonic work is done in the cylinder and cone and the waste just drops into the waste by gravity. When the drum is fullish surface of the waste is biased towards one side but there it is not conical. In an ideal world a cylindrical drum may be preferable but I doubt that it is critical. For the diy constructor it is probably eaasier to contrive a good seal with a circular drum but that's a different problem.

Jim