Ever since I got my shop marginally operational I've been fighting the DC arrangement around the disk/belt sander and the bandsaw. I finally tore out everything and re-piped it in a quasi permanent install:
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Sorry I didn't clean the mess up before I took the pics. I was just so ecstatic about finally solving this problem.
Since I went the cheap using standard HVAC ductwork I realized I was losing a good deal of the efficiency of the DC due to all the adjustable elbows and poorly sealed fittings.
So ...
I snooped around for ways to seal ductwork and found this mastic sorta stuff about as thick as yogurt. You wrap the fittings with a 'scrim' (I used fiberglass drywall tape) and daub the stuff on. I can assure you that it may be a bit more bother, once it's done it's infinitely neater and more permanent than duct tape. At least in my experience.
I've got most of the lower stuff sealed now and already I can see a difference in the amount of material pickup at each machine.