I posted this on another forum awhile back, but thought more folks might be interested:
I always had what I thought was inadequate dust collection from my Delta DJ-20 jointer, despite using 6" duct and a 3 hp DC. Though not excessive, I always had chips coming off the sides of the cutter and some on the floor under the cabinet. When I removed the jointer from the cabinet awhile back I happened to look closely at the rectangular dust chute that runs from under the cutter head to the rectangular port at the front of the cabinet- it did not have a top!!!! It was a three sided, open-topped, chute! Most of the air being sucked by the DC was probably coming from the open-bottom cabinet and not from around the cutter head!!
I figured that can't be good for suction, so I enclosed the top with a piece of ply. I would expect this might be a problem with many jointers, especially the clones. Check it out, you might be surprised!
Here are pics showing what I mean by an open-topped chute and my solution.
The rectangular chute angles down from upper right to the discharge at the front of the cabinet at the lower left.
Those are the fingers of the hand I inserted into the chute outlet that are sticking out where there is no top on the chute.
Plywood chute top. Since the sides of the chute were taller than the cutter head opening and the port on the front of the cabinet, I sized the top so it would fit inside the walls of the chute:
Screws through the chute sides hold the plywood top in place:
A view from the discharge port at the front of the cabinet showing the new plywood chute top installed: