Ducting

[Holsterguy]

Planning my new ductwork. Really hoping some of the collection gurus out there can help.
I have my tophat setup tucked in a corner out of the way, and planning to ditch the 2@4" splitter that came on the HF 2hp unit, and run a 5" main diagonally along the ceiling. The furthest tools away are- miter saw, radial arm saw, and contractor saw. Closest is router table, and Dewalt 735 planer about half way between.
I'm thinking- the main is going to be 20' (+-), do a 5" drop to each of the furthest machines (the table saw is getting revamped as in an old FWW article (issue #205). The other, closer machines, do 4" drops.
This sound OK, or am I really missing something?
Thank much.

[nucww]

I did the same setup about 5 yrs ago.  These are the things I did based on internet info and a flow meter on my system.
Need a blast gate at each tool.
Used metal hvac pipe.
All routing off the main 5" line should use Ys not T intersections.
They now have plastic 5" Ys reasonably priced.  I made mine from two straight metal pipes pipes.
Found 5" pipe at local wholesale distributor cheaper and better than box store
Use 4" drop downs at all tools.  maximizes velocity to counter gravity.  Actually your plan of 5" drop downs at the end of the run may have problems.  It may work close to the collector.
Minimize 90 deg turns
Used two adjustable 90 deg elbows set at ~45 to make a more gradual 90 deg turn
Tape all joints.  This added roughly 15 mph at the end of the run. For adjustable metal elbows tape each slip joint as well.
Minimize flexible pipe.
If the flow is weak at the tools on the end, you may want to try these:

change the HF impeller.  See internet for Rikon replacement.

[nucww]

Sorry the system send this before I was done.  I hit a tab for spacing but it went to post.
Try a Wynn filter for the top HF bag. Collects finer dust and has more flow area.
Look for possible leaks and tape them up.

[Holsterguy]

Thanks! Sounds pretty good/easy. Actually, woodcraft started selling 5" ys for really reasonable. I think 16$ each. I have one ordered just to see how well it "plays" with hvac pipe.
Just installed my tophat, and mounted the motor on a shelf above it, and it's exhausting straight outside.
Are you having any trouble with lifting up flow from machines?

[nucww]

The air flow that I have is sufficient to lift the chips.  I added the Rikon because I added a downdraft table near the DC.  For a Down draft table you need high CFM and this was an easy mod to get higher CFM.

[Holsterguy]

Ok, thanks. Think I'll start getting my pipe this weekend. Already have the 4".