In the picture in the previous post about cup centers you will note that the dust collector pick-up has a shroud or frame around the opening. When I upgraded from my dust distributor system to an actual dust collector system I purchased “Woodshop Dust Control” by Sandor Nagyszalanczy (yup, that’s spelled correctly) as a guide. In the book Sandor recommends surrounding any free openings (as opposed to a fixed pick-up as found on, say, a planer) with a frame to increase efficiency. The frame reduces the amount of air being drawn from behind the boot therefore increasing the amount drawn from the front – where you want it. This works exceptionally well; so much so that I am going to increase it from the recommended 2″ minimum to 3″ to see what happens. At times it gets in the way but moving it out of the way has never put it out of range.
If your dust pick up is simply an open ended duct, your collector is not being used anywhere near it’s capacity. The heating boot – which can be horizontal or vertical – probably doubles the volume of a simple duct opening (you can also go too big) and the frame doubles that. I highly recommend Sandor’s book which is available on line through Lee Valley Tools. My guess is that about 99% of the home-shop dust collectors out there are under-used due to undersized ducting (probably 4″ PVC, right?). Units around 1000 – 1200 cfm (2-3 hp) will require 6″ horizontals with 5″ verticles. Elbows should be long radius (2-45’s will do) and tee’s should be 45/wye combinations. I took the time to build a cyclone to make it a two-stage system; it works so well that hardly any fines reach the filter. Rebuilding my system was the best thing I ever did. The time spent has been paid back many times in reduced clean up time, my shop is a much safer environment and it’s just a lot nicer to work there.
As always, I encourage your comments and questions, so please refer to the tag line at the bottom of the article to post a comment.