[_Ogre]

i just went thru installing a dc in my shop. your pic shows 6" hvac pipe first off it's very leaky, the long seam and all the joints on the segmented 90° and fittings leak like a sieve. not a problem in a heated house cuz leaks heat space. from my research pvc pipe is smooth and probably the best for your purpose. 2nd the harbor fright blower is to small for 6" pipe, the air velocity won't be enough to keep the dust/shavings in the airstream. plus the transition from 4" to 6" drops the speed of the air, similar to how the cyclone or thein baffle works. i'd recommend running all 4" pvc sewer pipe. you can't use more than one drop and have dust removal anyway. i'd also recommend not having drops come out of the bottom as any shavings from down stream can drop into the drop pipe.

as stated, i just went thru this and made my own blast gates and thein baffle. just the flex hose adapters can be quite a bit of cash at $10 each, i made mine for less than $1 each. my blast gates have proven to leak minimally and i automated the dc with switches at each blast gate. all in all i'm pretty happy with it
look thru my build for more on that woodworkingtalk.com/threads/dust-collection-ogre-style