TLDR: We aren’t using a bag or dust separator on the aluminum only vacuum any more.
The dust separator buckets on the vacuums in the wood shop seem to fulfill their purpose: large wood chips collect in the bucket while finer wood dust is caught by the bag in the vacuum.
It was my hope that the separator would do this on the aluminum vacuum too, but it does not. Dust remains intermixed with the aluminum in the bucket, while lots of large chips and even non-trivial pieces end up in the vacuum body. The latter shred the bag, especially since it is weakened by moisture. We use lubricoolant for many aluminum cuts, so we vacuum up wet aluminum frequently.
This vacuum is still a huge improvement over the old one for one reason: hose size. Aluminum chips are stringy and tangle up; they constantly clogged the old vacuum’s small hose. That hasn’t been a problem anymore.
But the bag is absolutely a no-go and the separator just takes up space. Getting rid of the latter and shortening or even removing the top piece will gives us back some flexibility in storing it too.