So my dust shroud is almost completed. I have now completed the overhead mount with guide wires for stalibization. The shroud has been mounted to the overhead mount and counter weighted although I may need a little more weight to make it easier to lift. I have added the adjustment knobs although i am currently short by one.
The overarm duct was constructed using 4” ABS pipe. This setup was a little tricky. I had to use the bill pentz static calculator worksheet to figure out static pressures and air flows. I used the calculator to determine the static pressure of my current setup converted to a 5” duct. According to my previous measurements, the table saw was drawing about 1000 CFM from the cabinet so I know that I wanted the sum of two airflows to be 1000 CFM. I set up two worksheets. One for my 5” duct to the cabinet and one for the 4” overarm with the lengths of duct and the right number of transitions. I varied the airflows in the worksheet until the static pressures from each of the overarm and cabinet were equal but the airflows added up to 1000 CFM. When these pressures are equal, you maximize the airflow through the smaller pipe. My current setup will be giving something like 700 CFM and 300 CFM through the overarm.
Connecting this to the dust collection duct was a little easier than I originally anticipated. I used a 4” saddle and modified the saddle section by bending so it would saddle around a 6” duct. All I had to do is scribe the shape of the 4” duct opening onto the 6” duct and cut it out. THe saddle was screwed and duct tape was applied to seal the gaps.
I connected the shroud to the overarm and the overarm to the main duct using 4” clear pvc flex hose. The overarm duct has a 4” aluminum blast gate that is easy to reach from the front of the table saw. The overarm is able to fold down out of the way to allow for crosscutting wide pieces while still connected to the dust collector. I still haven’t tested the setup during cutting but turned it on long enough to determine that the amount of air flowing through the shroud is unbelievable compared to my vacuum setup…hopefully it all works.