# dc confusion overload



## dstew (Sep 27, 2014)

I have been in the technical electronics and electrical field for over 35 years and worked on CNC , PLC and laser equipment and everything else.
I have never been so confused in all my life as I am about DC systems.
I have read many forums info along with Bill Pentz's info. I had one of the last units Bill and his son made, I never got it all installed before I lost my shop to a fire. I want to replace it and was looking at Griz 0441 or the CV unit . I have 3hp jet cabinet saw, 20" planer, 8" jointer, 24" wide belt sander, 14" bandsaw, osc spindle sander few other small machines. My shop is in a 30' x 65' x 12' high polebarn but I am keeping machines in 30' x 28' area. The runs to the planer ,wide belt and tablesaw will be the closest
to DC. I am not done rebuilding the shop yet so the layout is not set in stone. My confusion starts with people saying to run 6" main line instead of the 8" that the manufacturer states a long with many other issues. Things important are to be able to collect the fine dust so moving the most air is important but some info I have read has said neither unit will work if to big or to small of pipe is used. Some use the 6" as it is cheaper and easier to get but what about 8" oem says it is set up for. At this point I am not even sure what to ask so any suggestion would greatly be appreciated. Thanks for time and ideas


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## jdonhowe (Jul 25, 2014)

Okay, let me take a stab at it, but let me stress that I am not an air flow professional, by any means.

Bottom line first: with your planned DC, I agree that for your setup 8" duct work is the way to go. I also agree with everything else you said, and your thought process, but allow me to give my slant on the topic.

As I see it, the most important factor is air flow, essential for getting dust picked up by the system, and also for good separation, particularly for fine particles. Air speed is needed to keep the dust moving once picked up, so it doesn't get hung up in the duct work.

The larger the duct work area, the better air flow is maintained. I liken it (perhaps wrongly) to passing electrical current through large and small diameter wires: 12 gauge wire will carry more current than 16 gauge, with less loss. So, especially with a large shop, you want the largest diameter duct you can get, to minimize duct-related lose of air flow.

The dilemma is that as the duct size increases, air speed decreases:

Airspeed(fpm) = Air flow(cfm)/duct area(sqft)

So, there is greater likelihood of dust dropout in the duct. I think this is what's behind the notion that ducts can be either too small (air flow suffers) or too large (air speed suffers).

According to Bill Pentz and others, 3000 fpm is adequate air speed for horizontal duct runs. Using as an example the Grizzly G0441, with stated 1654 cfm, if my math is correct, with 8" ducts:

area= pi*r^2 = pi*(0.33)^2 = 0.35 sqft;

1654/0.35 = 4738 fpm, which more than exceeds recs. Actually, 10" ducts would give you 3000 fpm, assuming you believe Grizzly's claimed air flow.

I think the recommendation for 6" ducts is primarily based on cost:
6" is cheaper and more readily available (HD, Lowes, e.g.) than 8". Also, most hobbyist woodworkers, such as myself, can't afford the high performance DC system you're planning on getting. Many, for example, go with the HF DC- cheaper than the Grizzly, but for which even 6" duct probably gives less than desirable airspeed.

Just my .02; good luck!


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## dstew (Sep 27, 2014)

Thank you very much for your explanation as I had all this info good and bad churning around and around in my head till I knew nothing. It helps to have someone get you down the right road again. I talked to Bill back in 2005 and we talked about his health issues from wood dust and I thanked him for all his knowledge , time and personal expense for helping us (woodworkers) have a safe environment to enjoy our hobby. He is a great guy who unfortunately has been taken advantage of by the unethical and unmoral individuals out there for economic gain. I just would like to have a good system that will capture the most dust for what I spend the money for as we all have been exposed to many toxins in the work place over our
working career. No need to add to this at home so wear your PPE at home. 
Be safe and thanks again


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