I'm reading "Bill's Place" (Bill Pentz) and his writeups on what does or
doesn't constitute an effective dust collection system. He insists that
4" ducting is woefully inadequate for safe dust collection. He writes
that 6" is what is needed.

His writeup gets fairly technical and sounds very convincing. But of
course, using 6" ducting greatly increases the cost of the ducting for
my workshop.

Are there other opinions on this or do people pretty much agree that 4"
ducting is inadequate?

Jack