I needed a small dust separator for my MPCNC, so I made a top hat out of 4" PVC pipe. It's attached to the lid of a 2.5 gallon jar. Seems to be working ok. The inlet is a 1" pvc coupler. I rough cut the radius on my band saw, and then wrapped sand paper around the 4" pvc, and sanded until I had a good tight fit. It's attached with PVC cement, and holding well.
How are you attaching the hose to your MPCNC?
I like this idea for my drill press too. I have a small, wall mounted vacuum there, which fills quickly.
Using this https://www.thingiverse.com/thing:2797108
Oh, and I should update and say this works really well, unless you are doing linear pocketing and running parallel to the grain. When I do that, it ends up taking out long strips which clogs the baffle. Clogs the hose though too. If I do peel for pocketing strategy, I have no issues.
In your first post you mention using a 4" PVC pipe. Looking at the photos the pipe appears to be larger, maybe 8". Can you please confirm the correct size? Maybe you meant to say 4" radius.