Mike_D_S595 posts in 2667 days #1 posted 12-14-2017 03:48 PM Ok, I did the maths… First off, I found this from the Wood Magazine review article which included the W1685: Then I did an overlay match to produce a matching fan curve. Then I laid out a several size options for ducting using mixes of 4”, 5” and 6” following the basic guide image like in the Oneida tutorial with one 90 deg elbow at the tool and two 90 deg elbows to the cyclone. Cross referenced CFM against the fan curve plot and computed velocity in the main duct. So you can review all those setups. All of them potentially work from a CFM perspective, but a few of them are certainly marginal to bad on velocity in the mains. A note on the math, I used published SP loss numbers for 3500 CFM from the Grizzly manual. Pressure loss is strongly related to flow velocity. So actually, the higher velocity in the 4” will actually increase pressure loss, so the actual CFM in the 4” might actually be slightly below 400 in the actual balanced system. On the contrary, reduced velocity in 5” and 6” cases would lower SP loss, raising effective CFM and velocity. So there needs to be a bit of judgement call, but you’re not going to go from 450 CFM to 600 CFM or from 2500 FPM to 3500 FPM. It becomes a question of how marginal the difference is. Depending on what you are going to do exactly, you may never notice any problems. And if your heavier chip generators (jointer, planer, lathe, etc) are close to the DC it’ll be more in your favor. If It were me, I’d go for the 5” branch and mains options followed by 4” branch with 5” mains and try to bring down the SP losses some. Doing things like allowing a longer lead in to the cyclone by using two 45 deg elbows and a longer straight transition run, changing the tools to all have 5” ports if possible, etc should all help to bring down the SP losses slightly. But in all cases, I’d avoid 6” mains as you just don’t have the power to keep the velocity up. Regards,Mike -- No honey, that's not new, I've had that forever......

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