wrote:
Hi,

I'm about to buy a dust collector that has a 4" port. I've read some
posts that suggest not using 4" ducting in the shop but to use 5" or 6"
ducting and then reduce to 4" at the dust collector and at the
machines.


What is the point of going from a 4" port on the dust collector to 6"
pipeing? Is this more efficient?

Thanks

Alex

It's all about friction. The friction of the air moving along the pipe
walls slows the air down. The air has to move faster in the smaller
pipe than it does in the larger pipe, so friction losses are greater.
The air can speed up to pass through a short section of smaller pipe
without much loss. The longer the section of small pipe, the greater
the friction loss.

However, you must be careful not to use too large a pipe, or the air
will slow down too much in it and allow the chips to fall out. See
Bill Pentz's very informative web site
http://billpentz.com/woodworking/cyclone/Index.cfm

DonkeyHody
"If your only tool is a hammer, you tend to see every problem as a
nail." - Abraham Maslow