twistsol wrote:High CFM is what pulls in the fine particles. High suction allows you to pick up the larger chips etc. Shop vacs are typically high suction, whereas dust collectors are high CFM. If I had to choose between the two, go with the high CFM since you can go back and get the heavy dust later. The fine and ultra fine dust will migrate everywhere and is what gets into your lungs and can cause health issues.
According to the chart in the following Wood Magazine article, nearly all WW machines require at least 350 CFM.
Yeah, but they are running 4" or larger ports on modern table saws for those recommendations. I am not an air engineer, but I think you will struggle to get that CFM (350) going through a 2 1/4" port on a Shopsmith. If it did, at those air velocities, it would whistle like crazy (over 10,000ft/min air stream). I think that small port is too restrictive for that airflow, but I haven't tried testing it. The relation is FPM=CFM/duct area, but I don't think this holds as an absolute equation, i.e. I think the smaller the port, the more turbulence takes over and raises SP for a high airflow.
You really have to look at the speed of the airstream, NOT the airflow. The reason Wood mag and others talk about 350 CFM (airflow) is because on a 4" port that equates to 4,000ft/min air speed (Bill Pentz recommendation).
P.S. I don't know the answer here, i.e. what the maximum air speed or airflow is into a 2 1/4" port. What I do know is that every fan/blower has a set of design curves (SP versus airflow). Just because you have a 1000CFM rated DC hooked up to a Shopsmith, doesn't mean that the blower is pulling 1000CFM through that 2 1/4" port! Depending on the resistance (SP) connected to the DC, it could be running at much less than 1000CFM (can calculate this if you have the fan curve and know the SP). Any 2 1/4" vacuum hose is very restrictive as is the 2 1/4" dust port on the tool. This is why I think a large DC might be overkill for a Shopsmith (if you are not running duct work). It might be rated for 1000CFM, but only able to move 200CFM through the 2 1/4" opening on the saw guard perhaps...