Made this one from a sheet of galvanised iron – 0.8mm. The Vac unit was originally a motor/centrifugal fan mounted on a trolley with a linen bag into which all the guff was dumped. Very inefficient and dusty, esp with wood work.
The fan unit just sits on top of the cone, with a door seal foam strip as seal. The large drum below collects all the stuff. Really only used for woodwork, as it is piped to all the wood machines, but I do cut a lot of aluminium sheet on the radial arm saw, so some 'metal' swarf goes in..
Very easy to make a small one from galv. sheet steel, more suited to metal work machinery.
There is a useful book:
Woodshop Dust Control, by Sandor Nagyszalanczy ( yes…) – the concepts are applicable to any cyclone type seperator, so ok for metal swarf too.
Folk have even made the cone section from one of those 'road works in progress' road marking plastic cones – maybe open you door as you drive past and loan one…(not really..)
The cone type separate using the change in velocity of particles from the top of the cyclone down to the bottom. A simpler separator, basically just a drum with the inlet of to the side ( the upper section in my photo) relies on centripetal force to push the particles to the outer part of the drum, where gravity does its job after a while.
Both types do really work well.
Joe
(edits just typo's..- Strange how reading the pre-posted text again and again shows no typo's, and when posted, a single re-read pops out the typo out right away! I suspect the Forum Web Host inserts typo's just for the hell of it..)

Edited By Joseph Noci 1 on 31/08/2018 09:41:03