Just bought a used Jet 1200cfm DC to replace my little 650cfm jet. The 1200 comes with a cloth lower bag, my old 650 had a clear plastic bag and I kinda like the plastic better. If I switch the 1200's cloth lower bag with a plastic one, am I hurting the performance?
I would replace BOTH the upper and lower bags, upper with a canister filter, and lower with a plastic bag. You will improve your performance quite noticeably...
So if a pleated filter isn't in my budget just yet, can I still use a plastic bottom bag with a cloth upper bag?
I built a separator last year, it works great.
(http://i282.photobucket.com/albums/kk246/seajai/2009_0622seperator0001.jpg)
I run large amounts of cedar through my planer and the best way to tell if my drum is getting full is seeing the few bits of shavings in the plastic bag. But my new Jet 1200cfm DC has a cloth bag, so I wont be able to see the chips getting into the bag, which is why I want to get rid of the cloth bag and go to plastic.
Assuming your 1200 CFM Jet dust collector is a Jet DC-1200 bag model, that has 30 micron bags (might as well just put a box fan in front of a pile of dust and blow it around...), you REALLY need to take those bags off and put something that actually works on there. A clear plastic lower bag is fine, and if a canister filter isn't in your budget, you REALLY need to at the very least get a 1 micron felt bag up top. HOWEVER, it is likely you will lose some suction because of the plastic bag and only one bag on a system that had started with 2 very porous bags to begin with...
Highland Hardware sells a 1 micron bag http://www.highlandwoodworking.com/shakerfeltpolyestermicronfilterbag20x32.aspx (http://www.highlandwoodworking.com/shakerfeltpolyestermicronfilterbag20x32.aspx) for $29.99
IF you want the best filtration and flow that you can get out of that dust collector, I would suggest saving up a few more bucks and getting the canister though...