For those who don't want to search through the above link, I am reposting what I said
in that thread
.........................................................
Simple Shop Vac System with silent operation
I made one from a grease drum
My Vacuum system is outside to keep noise down, but my drum keeps almost all the dirt and chips inside for cleaning every 6 months.
I soft soldered a 2 inch copper pipe tangent to the drum.
I took the cover, with the center suction (PVC) and mounted a coffee can deflector, so the chips spin around, but lighter air and a bit of dust will go down and then up inside, while the heavier chips and dirt follow the wall to the bottom.
The drum is not conical, like most collectors, but does not need to be. I added a heavy weighted air flow restrainer at the bottom . When the air hits it, it slows down and drops the chips. The retrainer looks like a flag, and I leave it with about one inch space from the inside wall, just to add drag.
The photo shows it at a angle, but I generally have it at right angles to flow.
This unit comes apart very easy using the original barrel ring clamp,and because the suction pipe is in the lid with push fit PVC ( No Glue !) I can pick up the drum to dump it.
I have to remember to retrieve the restrainer however, even if it is only scrap.
My Vacuum outside is a cheapo Sears shopVac, ( 3/4 HP ?)
The inside chip/dust collector takes out the vast majority of stuff, so the shopvac outside maintains a high level of suction for a long time
It has one of those corrigated filters ( 200 sq ft area ?),not a bag !
Rich