DC Branch Ducts Diameter

[Edward Weingarden]

My Oneida V3000 3hp cyclone DC is due to arrive today. I'm planning the duct runs and have read info on how to size the branch ducts. The basic layout will be a main duct running diagonally along the ceiling, with branches coming off to the machines. The longest run will be about 35'.

The info I'm reading differs with respect to the size of the branch ducts. I don't recall if it was from the Oneida site, or Bill Pentz's write-up, but my understanding was that I should run 6" ducts to the machines (when possible), even modifying the machine if it has a 4" port. I've also read the book by Sandor Nagyszalanczy. The charts in the book indicate that I should be running 4" branch ducts to most of the machines. I understand the aspects of maintaining the appropriate CFM while having an appropriate air velocity. As of right now I've purchased 6" PVC duct only. Of course I can get 4" and 6" to 4" Y's. Can someone help to clarify the proper branch duct sizing for me. Thanks.

[Peter Christensen]

Sandor's book was first published in 1996 with a revision in 2002. So the data is based on older industrial information when the goal was to get rid of the chips and most of the visible dust. Hence the 4" recommendations. The 6" recommended now is to also get rid of the dust that does the most harm to your body, the invisible dust down to less than a micron. Go with the 6" and open up your machines wherever possible to the same.

[Julie Moriarty]

Oneida has a tutorial to help size ductwork.

[Edward Weingarden]

Peter - thank you for your input. Julie - thank you for pointing out the tutorial.

On a separate but related note, I have a Grizzly 17" band saw with one dust port (at the base) which is an integral part of the base; it is not a plastic port which can be removed. The port under the table is also integral to the machine. It seems that I will have to live with those 4" ports unless I cut the metal ports out of those areas, something that I am hesitant to do. My Grizzly table saw has a removable 4" port but the opening has a combined small diameter hose going to the under-blade "funnel", while the remainder of it is a square opening into the base of the cabinet. Again, it seems that I will have to live with that arrangement. If anyone has any suggestions about those two tools, please chime in. Thanks.

[Jim Becker]

Typical hookups for a large band saw that has two 4" ports (cabinet and under table) would be a 6" drop to the machine and a wye to the two 4" ports. That covers about the same area as a single 6" drop if you look at the chart in the sticky thread above.

[Joe Jensen]

When looking to modify your machine ports it's important to figure out the port size at the point of dust collection and not just the connector on the side of the machine. Most machines have a larger connector on the cabinet than port at the point of dust collection. Where ever possible you need to enlarge at the point of collection. If the opening at the bit or blade is only a 2" port, no matter how big the duct is you will get very low airflow. As a point of reference, my Sawstop ICS had a 4" duct on the side of the cabinet but in reality at the blade shroud inside it was about 2". My current Felder large sliding table saw has a 5" port on the side of the machine which connects internally to a 4" flex hose which connects to an opening that the equivalent to a 3" round port. Sadly I can't modify either machine as the openings are in the cast iron blade shrouds.

[Peter Christensen]

Accepting undersized or minimal at best ports in a machine defeats the purpose of making a better DC system in the first place. There is always a way to add another port for extra suction from the cabinet. It must also be remembered that to get that suction additional air into the cabinet is needed. Like sucking on a milkshake straw when a cherry is plugging the bottom. There is usually an access door to crack open if you don't want to make more holes.

There are small particle counters available for about $50 that will show you if your improvements are helping and at least tell you when it's safe to take take off your mask.

https://www.ebay.com/sch/i.html?_fro...nitor&_sacat=0

[Edward Weingarden]

Peter - excellent point about allowing more air flow through the cabinet.

[Larry Frank]

Rather than just talk port sizes, I have measured actual flow and the determined if I needed to open up the ports larger.

If I am getting 600-700 cfm with 10" static pressure, do I need to open the ports on my Sawstop PCS?

[Peter Christensen]

From every thing I’ve read you can’t get much over 400cfm through a 4” pipe. So if you’re using one of the anemometers with a fan to measure the air flow then that would explain the high numbers you got. A hot wire anemometer would give more accurate readings.

[Larry Frank]

Sorry Peter but where did you get your information about 400 cfm and what test did you run to confirm that.

For your information, I used a hot wire anemometer and ran many tests on my system to test various ports and create a performance curve. I published my data and methodology on this forum.

I am running a Oneida Dust Gorilla with a 15" impeller and 5 hp motor.

I have also published information concerning the poor accuracy when using a fan type anemometer.

[Josh Kocher]

Your V3000 has a 7" inlet I believe, have you considered a 7" main? Dropping to 6" for the branches? My 2hp Oneida has a 7" main that later splits and tapers to a 6"... I have a pretty short run so probably doesn't make a huge difference... but your 35' might start to see a worthwhile improvement... worth looking to see if it's viable.

I have a 6" to my bandsaw that splits to 2*4" and it's okay... I used to think it was pretty good... but there's quite a bit of dust on the table esp. resawing...
If I'm doing a lot of work on the bandsaw I set up an extra 4" flex hose that comes off a separate multipurpose drop in the centre of my shop. It seems to help of I clamp it on a good spot...

[Chris Parks]

Sorry Peter but where did you get your information about 400 cfm and what test did you run to confirm that.

For your information, I used a hot wire anemometer and ran many tests on my system to test various ports and create a performance curve. I published my data and methodology on this forum.

I am running a Oneida Dust Gorilla with a 15" impeller and 5 hp motor.

I have also published information concerning the poor accuracy when using a fan type anemometer.

Link to published information?

[Larry Frank]

Chris...you have questioned me before and we went thru several messages back and forth. I posted the information on this forum. It is also posted on Lumberjocks under RedOak49 blogs.

I will ask you again Chris to post information about your system along with how you have performed testing. Sharing the information would help others to evaluate their systems. What dust collector are you running?

[Chris Parks]

Sorry for asking and I withdraw the request. You attempted to start a PM dialogue which I will never participate in and I ended it very smartly by refusing to answer. I haven't got any information on my system so asking is not going to get you very far but you offered the information that you had so I asked for a link within this forum. My apologies for upsetting you.