Be careful when claiming "X" number of CFM in your dust-collection
system.

The CFM figures provided by most vendors who do not deal in industrial
systems sold to large commercial companies (those companies have
engineers who can spot phony specifications a mile away) use CFM
like Detroit uses "horsepower" in automobile engines. There is no
industry-standard set of conditions under which CFM is measured for
consumer goods, which means the company can invent any scheme they
want to get the highest CFM reading they can. As long as they can
prove that the machine moves that many CFM under conditions they
created, they aren't open for fraudulent representation.

Caveat emptor: "Let the buyer beware".

The only way to measure CFM and static pressure accurately is by using
a pitot tube inside the duct with a manometer or Magnahelic (R) gauge
setup. The numbers published by sellers of consumer-oriented dust
collectors have little connection to how the system will perform in
a real shop environment.

If you want to really understand dust collection, and how CFM relates
to having a safe shop, visit Bill Pentz's dust-collection web site at

http://cnets.net/~eclectic/woodworki...lone/index.cfm

Bill has designed a very effective cyclone dust collection unit with
recommended motor, impeller, blowers, etc.

I manufacture kits for the cyclone and blower housing, based on his
design. That info is on the same site at

http://cnets.net/~eclectic/woodworki...larkesKits.cfm

There is a lot more to proper and effective dust collection than most
people realize. Time invested in learning can pay off many times over
in protection of your health. Wood dust can become fatal for some
woodworkers and I don't like taking those kinds of chances.

Clarke