# Thoughts on Dust Collection Please



## RobNY (Oct 9, 2013)

I am currently working on building my shop and have bought a used Grizzly 3 HP Cyclone Dust Collector with a 8" main connector. The main run will be over 40' and figure something like 55' or so total to the machines. It had come with some 6" Northfab piping what I am wondering is should I use 8" as main pipe instead? Either way I will be stuck buying a bunch of piping no matter what. My thought is it would be better to use 8" as the main pipe with 6" pipe used pointing down that I split into 2 4" flex to the machine. Is this the best way to approach it or is there a better way? Thanks.

-RobNY


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## woodnthings (Jan 24, 2009)

*it's science not an art...*

http://billpentz.com/woodworking/cyclone/ducting.cfm#pipe_size

Go to this site and you will find:


*Pipe Size* Always use the largest diameter duct that your blower can use with the least number of restrictions. If your ducting is too small, then it instead of your blower defines the CFM that your system can provide at your machines to pick up the dust. If your ducting is too large you might not maintain the airspeed needed to keep sawdust and chips from building up and blocking your ducting. You need about 3000 feet per minute (FPM) airspeed to keep light sawdust moving horizontally and about 3800 FPM to move it vertically. Air engineers target their designs to maintain about 4000 FPM to keep the dust entrained (moving). FPM is simply CFM divided by the area of the duct in square feet instead of inches (144/sq. in.). If you do the math for the 1000 CFM we need at our larger tools and the 4000 FPM airspeed we need to keep our vertical runs clear, most small shops should run at least 7" duct. This sized duct is rare and the more commonly available 8" duct is so large we end up with the airspeed falling so low our vertical runs plug. My personal solution has been to use 6" duct which will normally only carry about 790 CFM, and to get that to over *1000 CFM by using an oversized impeller of at least 15" diameter* running at 3450 RPM. This makes for more noise but results in great fine dust collection. It also means my whole system of mains and down drops ends up using 6" duct.
So unless you move up to a larger impeller and increase the air speed, things won't work right. Read all you can stomach on this site and you'll find your answer.

Some dust collector sites offer planning:
http://www.pennstateind.com/store/ductwork-planning-service.html

http://www.oneida-air.com/static.asp?htmltemplate=static/shop_plan_design.html


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