Why do almost all use 6" flex at ends of their duct runs?

[Kevinmk_37]

Starting to buy the last pieces to assemble the duct runs. I noticed that the norm is to run 6" solid to about 4 feet of the machine and then run flex the last distance. Since flex has greater loss than solid I would think everyone would want to go solid all the way. Do they use flex to make hook up easier or is it that they want to be able to move the machines? I am sure its more expensive putting several fittings into the end of the run vice flex pipe but it would be better to cry once and have better performance.

Some of my big machines will never move so I was leaning towards running solid including a dreaded 90* bend at the very end but don't know how challenging that will be.

Looking for some thoughts from those who have already completed the job.

 

[McRabbet]

I would use a Fernco 6" x 6" connector at the end of the four foot run to get the main duct horizontal and then use 6" pipe and fitting to all of your blast gates; i.e., all solid pipe. Your can continue solid pipe to the machine ports if they never move (avoiding sharp elbows at all costs), or use the shortest segment of flexible duct that you can to connect to the port. I made 6" ports for my table saw and jointer from plywood and half of a PVC coupling glued into it and then connect a short piece of flex to the blast gate serving those ports. My flex runs are shorter than four feet.