With that intro.
Several months ago I bought a 1600CFM dust collector from Harbor Freight. I knew the 1600CFM was "optimistic." When it arrived what I had was a dust collector with two very porous (30+ micron) bags, one to collect and one for the "filter." So in effect there were two very porous filter bags. I replaced the collection bag with a black plastic bag and the filter with a "shaker felt" bag from Highland Hardware. Filtration increaded dramatically, CFM dropped even more dramatically. I now had about a 600CFM dust collector - at $149.95, still not a bad deal.
However, I decided to upgrade the system a bit. Lo and behold! CFM is now up to about 1200.
Here is the upgrade, (total cost about $60.00)
I ordered to collector rings (Part #33) for my dust collector (model # 45378) at $14.35 a piece for a total of about $32.00 when s/h is added. I ordered another "shaker felt" filter bag from Highland Hardware for $29.95, about $34.00 with s/h.
I then built a box 21w X 42L X 5H box, divided it on the top into two squares with a 5" cross piece, then put 2 1/2 wide peices around the inside of each opening and triangular corner blocks to give me two octagonal openings about 16"w. On the botton of the box i located a similar opening in the center of the bottom. Then put two pieces of 1/4 luan between the bottom frame and the upper ends to give me a slope for the dust to slide down into the collection bag.
Then I mounted the box to the collector on the dust collector with angle braces and caulked the joint. I took the two new collectors, cut most of the inlet off of one and cut slots in the other inlet, then slid one inside the other and screwed them together with sheet metal screws. I then mounted the two collectors over the top holes, secured with angle braces and caulked. Then attached the bags in their respective places and turned it on. Worked like a champ. Total cost for a moveable 1200CFM dust collector, about $220.00 (dust collector, collectors, bag)