DC duct sizing

[Kevin Cackler]

I am using the duct sizing guide at https://airhand.com/designing/ to size our ducts appropriately. I have identified our 'main' machines and have increased the ducts appropriately as these main machines enter the main trunk.

My issue/question is that we have a corner of our shop that contains only one 'main' machine but contains 4 other non-main machines. Each of these machines has a 4" port. The way I currently have the system designed, the one main machine in this corner connects to the trunk and the trunk size increases at that point. But the 4 other machines in this corner tie into this main machine's branch and the duct DOES NOT increase in diameter. If I'm reading that sizing guide correctly, this is what we're supposed to do. The duct only increases in size when a main machine enters the trunk. If I am reading that guide correctly, and I have 5, 4" machines all feeding into one little 4" duct, that seems like a lot for that duct to handle. Granted, we will only be using at most 3 of them at once, but even so, it seems like a lot for it to deal with.

So should we increase this duct to 5 or more inches to accommodate the multiple machines that feed into it? But then I worry that we won't have a high enough CFM due to the increased duct size.

I'm probably making this more complicated than it needs to be, but we're dropping $5k+ on our little dust collection system and I want to make sure we do it right.

[Chris Padilla]

Very generally speaking, going to a larger duct is usually better. Most machines will do better with a 6" line over a 5" line and even better than a 4" line.

If I follow you correctly, it sounds like you have 5 machines each with 4" ducts and that feed into a 4" duct that then feeds into the trunk. And you plan to run at least 3 of these at a time. The 5 4" into 1 4" that then feeds into the trunk sounds like a bad design to my ears.

First, separating each of the 5 4" into their own ducts that feed into the trunk would be better.

Second, increasing each of the 5 4" to something larger will usually be better.

Personally, I like to take at least 6" duct to each machine and do the following:
(1) I will modify the dust port on the machine to accept 6" OR
(2) I will take the 6" as far as possible before tapering down to something smaller OR
(3) I will split the 6" duct into 2 4" ducts (for example, the cross-sectional area of a 6" pipe is just a bit more than 2 4" pipe cross-sectional areas) and connect those to the machine (this is good for a table saw with a blade shroud in the cabinet and one above the blade)

Now all this depend on your DC and its impeller size and the trunk size, etc. I think if you have a decent cyclone and 14"+ impeller, that using at least 6" is pretty darn good if you don't want to think too hard. A larger impeller like in the 16"+ size likely benefit from a larger trunk (8", for example) with 6" drops.

If you can provide more details on the overall system, we can provide more succinct answers.

[Kevin Cackler]

I knew that 4" stuff sounded off. The Airhand.com guide says that if your machine has a 4" port, then the manufacturer has determined that a 4" branch will support the machine. And that a branch should only be upsized if it's part of the trunk, where a "main" machine enters the trunk, and a "main" machine is your worst case scenario of which machines are operating at one time.

I'm having my much more artistically talented wife draw up a rough floorplan which will hopefully clear things up a bit.

[Chris Parks]

I knew that 4" stuff sounded off. The Airhand.com guide says that if your machine has a 4" port, then the manufacturer has determined that a 4" branch will support the machine. And that a branch should only be upsized if it's part of the trunk, where a "main" machine enters the trunk, and a "main" machine is your worst case scenario of which machines are operating at one time.

I'm having my much more artistically talented wife draw up a rough floorplan which will hopefully clear things up a bit.

A machine manufacturer has determined what is best..........I can hear the laughter form here. No machine manufacturer to my knowledge has even the vaguest idea of what good dust control is.

[Rod Sheridan]

A machine manufacturer has determined what is best..........I can hear the laughter form here. No machine manufacturer to my knowledge has even the vaguest idea of what good dust control is.

Hi, I have a saw/shaper and a jointer/planer.

Both came with airflow requirements for the machines, and a certificate of conformance for dust collection performance.

There are many manufacturers who actually design in dust collection................Regards, Rod.

P.S. That said, I agree with you in general, if you have a machine with a 4" port, it's most likely that the port is too small and the manufacturer didn't desin in dust control.

[Jim Becker]

I knew that 4" stuff sounded off. The Airhand.com guide says that if your machine has a 4" port, then the manufacturer has determined that a 4" branch will support the machine.

What it really means is that the machinery manufacturer has just done what they've done "forever" despite more attention to what's required to fully evacuate dust and chips from machines in recent years. The tools have 4" ports because they have always had 4" ports, in other words. It sounds like Air Handling's guide hasn't changed at all, either. Note, I'm not saying that a 4" port isn't appropriate for a specific machine; I'm only saying that it's not universal as it might appear to be since so many machines just happen to have 4" ports "just because". Consider that many folks have "kicked things up a notch" on table saws by up-sizing the port, having a hood around the blade and simultaneously support over-arm dust collection from that same larger hookup. The results are usually compelling.

I agree with Chris that feeding multiple machines at the same time requires you to insure that the drop supporting multiple machines is adequately sized to handle the air flow required for the number of open ports at one time. So if you have two 4" ports that share a drop, the drop, itself, must be sized to adequately support the air flow that will allow the presumable 400-500 CFM max that can flow through a 4" port times the number of ports. And, of course, the blower on the collector needs to be adequate for the task, too. A 6" drop servicing two 4" ports "likely" will work ok (without doing the math). Designing duct for a shop that has multiple simultaneous machines/workers is a lot more complicated than designing a duct work system for a one-person operation!

[Kevin Cackler]

Knowing that the branch needs to be upsized to support potentially more than one 4" port does answer one of my primary concerns. Laying everything out was the hard part. Resizing things is easy in comparison!

I appreciate everyone's input. I'm going to go resize things on my own and report back here so I can find out what else I did wrong, lol

Thanks guys

[Jim Becker]

If you keep in mind that it's all about "volume", it will be easier for you to visualize what needs to be done even before any of the math gets tackled. The volume of two machine ports is what it is and the drop that supports them simultaniously has to accommodate that fact.

[Kevin Cackler]

Here is a bird's eye view of our floorplan as it currently stands. Due to ceiling height restrictions (Only 12') I would like to keep things in the wall-ceiling corners as much as possible. We also have to contend with an overhead door that we need to go around, as well. The miter stations have no DC right now, so that is open ended. We will probably build a plywood hood and shove a 6" duct into it but I'm sure someone here will have a better idea if that one is stupid.

If someone could help me by providing the pipe layout, I can do the work of piecing it together. I just want to make sure that we don't have to tear anything apart to clear a clog down the line.

Our worst case scenario is probably both table saws, the planer, and the jointer/a shaper running at any given moment, though it's certainly possible that we might have the edge sander, the big shaper, the jointer, and then planer going at once, as well.

The DC isn't mounted anywhere yet, and can move freely along that front wall, so long as it's not over the garage door really. We have a roll off on that side of the shop that we had intended on dumping into, however.

Any and all help is very much appreciated!

[Ole Anderson]

Due to ceiling height restrictions (Only 12') I would like to keep things in the wall-ceiling corners as much as possible.
Any and all help is very much appreciated!

The problem with putting the duct in the wall/ceiling corner is that the wyes will point down the wall. That can result in chips/offcuts falling down the unused downstream wyes as debris passes the opening on the bottom of the duct. Best if you can locate the duct just far enough away from the wall to align the wye opening horizontal then add a long radii sweep to take the pipe down the wall. Man, I wish I had 12' instead of under 8' ceiling height.

[Kevin Cackler]

Never even thought of that, Ole! Very good point, though. We will definitely move things out a bit. Thank you

[Chris Parks]

I'm probably making this more complicated than it needs to be, but we're dropping $5k+ on our little dust collection system and I want to make sure we do it right.

What dust extractor is going to drive this system?

[Kevin Cackler]

It's a 5HP grizzly motor from this guy http://www.grizzly.com/products/5-HP...ollector/G0672

[Dominik Dudkiewicz]

Wow, if you want to run a couple of table saws, shaper, and a planer or sander running concurrently I would suggest you'd want approximately 3000cfm - approx 800cfm to each machine. For that you would want something like a 10-12" main trunk with 6" drops to each machine. You would want to plan the ducting and position of the machines to get the relative flow required to each machine (some require more, some less) and you would need to keep at least 3 ports open all the time to ensure you maintain enough cfm and velocity in the main trunk to prevent buildup. It's not a quick thing to work out if you want to do it right and if you are running a production shop I'd suggest taking the time to get it right. You are going to want a 10hp + system i'd expect.

Sorry out and on a phone right now so a detailed response is not easy.

Cheers, Dom

[Chris Parks]

At that price I would be buying a cyclone, either Oneida or Clearvue and you will not have to deal with bags which don't filter worth a damn, leak and have to be cleaned and emptied. As a guess a CV Max would have the largest flow capacity or their new metal version which may flow more.