View Single Post
  #21   Report Post  
Posted to rec.woodworking
Brooks Moses
Posts: n/a
Default 4" vs 6" ducting for effective dust collecting

Art Greenberg wrote:
On Sun, 22 Jan 2006 20:07:12 -0700, mywebaccts (at) wrote:
Are there other opinions on this or do people pretty much agree that 4"
ducting is inadequate?

It depends. The article on Bill's site tries to explain why and when to choose
a particular size. You can't ignore the physics behind what's going on without
reducing efficiency.

Look at the velocity needed to keep the dust suspended in the airstream. If
you don't have that velocity, the dust will settle out in the pipe. Velocity
is a function of CFM and pipe cross-section. FOr a given CFM, making the pipe
larger (larger cross section) will result in lower velocity. At some point,
you end up with a situation where the dust never makes it to the blower.

Yeah, I was about to point out: it's very possible to have pipes that
are too big for your blower!

If the blower is pulling the same volume of air, the airspeed in a 6"
pipe will be half that of the airspeed in a 4". If you don't have a big
enough blower, then that can be a problem.

- Brooks

The "bmoses-nospam" address is valid; no unmunging needed.