6" vs. 4" dust collection duct

[Daniel McCurdy]

Hey guys, I'm still working on setting up my shop and I've come to the point where I'm pretty sure where my tools will go for now.

I've done the rough math on how long the runs will be, bends, CFM requirements for the machines, etc. and I'd like some opinions on running 6" vs. 4" duct. I have a 2hp Grizzly DC 'rated' at 1550 CFM, which I plan to use on only one machine at a time. So my initial thought would be to take advantage of the power and air flow and run 6" to everything and make any nessasary modifications to dust ports like on the table saw.

My duct layout is pretty simple and probably won't exceed 50 linear ft. total. So the extra cost isn't as big of a deal.

I seem to get the impression from some sources that 4" duct just doesn't seem to get the amount of fine dust they'd like it to. Thing that I get mixed up on is that it looks like more people run 4" rather than 6".

I'm all ears!

[Chris Padilla]

Daniel,

First thing: have you decided to run metal duct or PVC duct?

I ran all my stuff in 6" PVC S&D (ASTM 2729 but SDR 35 works, too) and will carry that 6" as far as possible into the areas and equipment I wish to hook to. The key for DC is VOLUME of air which is why 6" tends to be pretty ideal for most cases.

One disadvantage with PVC is the lack of a 5" or 7" diameter size. You can only get it in 4", 6", 8" sizes. That may or may not be a big deal to you. For fittings, take a look at www.mcmaster.com (http://www.mcmaster.com) and do a search on "drain waste vent pvc" to get started with prices.

Also, do some searching here, this topic has been worked over pretty good.

[Prashun Patel]

People run 4" because it's easier and cheaper (less space, less cost of ductwork, availability of 4" flex, most tool ports are preconfigured for 4").

If I were you, I'd run a 6" main if feasible.

I wouldn't run 6" to the tsaw. I'd run 2x4" to the underside of the saw and above the blade guard respectively. For other tools if you'd prefer to run a single port, then reduce it as close to the tool as possible (or not at all).

If you need to use PVC, then make sure u ground it.

[Chris Padilla]

I run a main 6" right to my modified-from-4-inch-to-6-inch table saw sawdust door but I think it isn't the best place but I don't really want to invest time into making a shroud around the blade like the new PM2000 has or the SawStop has.

I will at some point in the future place an overblade protection/DC device on my TS.

[Greg Cole]

Nuther vote for 6"PVC trunk line and 4" branch drops to tools. Blast gates in appropriate places will provide pretty adequate air movement at the 50' run.
My longest run isn't more than 35 feet all told, and the JET I have is rated at 1200 CFM...works well for me.

Greg

[Ken Fitzgerald]

Daniel,

I paid Oneida to design my system. They spec'd 6 and went to 5" after the 90º bend at each downdrop. I have a 3 hp Super Dust Gorilla.

[Prashun Patel]

Chris-
I have a poorman's overblade dc that might work for you in the meantime: I tapped and bolted a 4" dc pipe strap to the front of my blade guard. Then I routed a 4" drop to the blade guard from my main. It clicks into the strap and catches a good amount of any spray (works especially well with mdf).

Two nice unanticipated effect:

1) It slips out of the strap easy so it makes it easy to vaccuum up the top of the saw after operations.
2) As stock is pushed through the guard to the blade, the front part of the guard tips down, bringing the hose close to the stock, keeping the port really close to the source.

But all this is only if you're an idiot like me still using the included cheap blade guard / splitter.

[Daniel McCurdy]

Sorry, didn't mention the material. Yes, I planned to use 2729 PVC...and yes, I'll be grounding it for sure!

I had thought about doing the 2 4" for the TS. I just wanted a more simple solution for the time being since I don't currently have an overhead hook up for it. I'll probably tackle that one later.

Its funny, I tried searching on the subject and just didn't seem to find what I was looking for. I guess there's a lot of times where things have to fitted around a certain existing criteria like room and budget. Room isn't an issue at all for the over all DC system, and I'd rather spend a little more on the larger stuff if its worth it.

I did purchase the Dust Collection Basics book by Shop Fox from Gizzly. Was very helpful, I'd recommend it. I just didn't understand why they seem to recommend running a main 6" line and then branch off to 4" (and then just have an additional 4" gate open to increase the CFM to the main line and keep the material moving along). Why not just run 6" right to the machine and increase the CFM there and collect more dust rather than pulling air from a different port that's not even in use? Doesn't seem to make sense to me. (Guess that's in a nut shell what I'm checking up on with this thread!)

[Daniel McCurdy]

Nuther vote for 6"PVC trunk line and 4" branch drops to tools. Blast gates in appropriate places will provide pretty adequate air movement at the 50' run.
My longest run isn't more than 35 feet all told, and the JET I have is rated at 1200 CFM...works well for me.

Greg

Hey Greg, thanks for the heads up. Just so it doesn't get confusing, I figured I have roughly 50' of duct to buy...not a 50' run. I mentioned that total to show that the $ difference isn't a big deal for me if 6" is that much of a better performance option.

[Lance Norris]

Daniel... here is a thread I started a couple weeks ago about improving the dust collection for a cabinet saw. The results have been dramatic.

http://www.sawmillcreek.org/showthread.php?t=76571

This might give you some ideas.

[Curt Harms]

I have a Penn State "2 h.p." D.C. with a Wynn filter. I ran 6" PVC, 6" homemade blast gates and 6" flex hose. At the end of the flex hose I put a PVC 6X4 reducer. My tools have 4" ports for the most part and I cut short pieces of 4" PVC for 'nipples' to slip the 4" end of the reducer over. The only machine that has 6" all the way is the table saw. Most of my tools are on mobile bases so using rigid pipe didn't work for me. Using 4" flex seems like it would cause loss of CFM & velocity due to friction and turbulence. I figured by going 6" flex I'd be moving as much air as 4" connections are capable of and it seems to work well.

HTH

Curt

[Walt Stevens]

Nuther vote for 6"PVC trunk line and 4" branch drops to tools. Blast gates in appropriate places will provide pretty adequate air movement at the 50' run.
My longest run isn't more than 35 feet all told, and the JET I have is rated at 1200 CFM...works well for me.

Greg

Greg,
I have the same DC unit and I'm just starting to plan a permanent duct system. Is the flow velocity through a 6" pipe high enough to keep larger stuff moving (as opposed to fine dust)? Also, I have a cyclone adapter on a trash can connected to the DC unit and I'm wondering if that reduces the effective flow?

Walt

[Curt Harms]

Greg,
I have the same DC unit and I'm just starting to plan a permanent duct system. Is the flow velocity through a 6" pipe high enough to keep larger stuff moving (as opposed to fine dust)? Also, I have a cyclone adapter on a trash can connected to the DC unit and I'm wondering if that reduces the effective flow?

Walt
What You may find is that with 6" in and out and the extra airflow, nothing will stay in the trashcan. It will all wind up in the DC bag.

[Chris Padilla]

Chris-
I have a poorman's overblade dc that might work for you in the meantime: I tapped and bolted a 4" dc pipe strap to the front of my blade guard. Then I routed a 4" drop to the blade guard from my main. It clicks into the strap and catches a good amount of any spray (works especially well with mdf).

Oooh, Oooh...I hear a PHOTO opportunity calling Shawn's name!! :D


But all this is only if you're an idiot like me still using the included cheap blade guard / splitter.

Actually, I think you're quite smart for keeping it on...most of use never even bolted them on when our saws were new...like moi.... :o

[Chris Padilla]

Also, I have a cyclone adapter on a trash can connected to the DC unit and I'm wondering if that reduces the effective flow?

Walt

Yes, anything that deviates from the nice straight, uniform cross-section, smoothed wall pipe will reduce air flow and increase turbulence and loss. This goes for wyes, elbows, reducers, tapers, flex, and anything else introduced to disprupt that nice straight, uniform cross-section, smoothed wall pipe. :)

Now, will it be noticeable? Hard to say unless you do a before and after apples to apples comparison.

[Walt Stevens]

What You may find is that with 6" in and out and the extra airflow, nothing will stay in the trashcan. It will all wind up in the DC bag.

That would be interesting! This all makes me wonder why the Jet DC and all of my machines have 4 inch ports. Looks like I have some modifying to do.

[Daniel McCurdy]

OK, here's a question.

If I were to make a new hood for my RAS and build in a 6" port, I could see how that will pull plenty of volume to move the dust through the larger pipe since the hood is wide open.

But on something like a TS, if I put in a 6" port, will there be enough access to air to pull the necessary CFM? In other words, would it be too choked off? Ultimately I know having the 2 4" would be better (one being over head), but in the meantime if I hook up a 6" and it can't draw enough volume, it won't be able to move along in the duct...if that's the case, I would think I'd be better off staying with 4" untill I get around to making an overhead hood.

[David Giles]

When Lance added a second 4" line, he essentially doubled the air flow. It shows that the restriction is a 4" hole anywhere along the duct including the equipment port. I got a similar improvement by replacing all 4" ducts and ports with 6" diameter. It was enough that a 1.5 Hp Jet blower became adequate. The 4" port acts like a half closed valve on a big diameter water line. The only way to move more water is to add pressure (bigger DC) or a bigger port (4" -> 6").

I do not find dust and chips dropping out in a 6" riser, even with my dinky blower.

[Daniel McCurdy]

When Lance added a second 4" line, he essentially doubled the air flow. It shows that the restriction is a 4" hole anywhere along the duct including the equipment port. I got a similar improvement by replacing all 4" ducts and ports with 6" diameter. It was enough that a 1.5 Hp Jet blower became adequate. The 4" port acts like a half closed valve on a big diameter water line. The only way to move more water is to add pressure (bigger DC) or a bigger port (4" -> 6").

I do not find dust and chips dropping out in a 6" riser, even with my dinky blower.

So there's enough open spots on the saw to feed the additional air volume needed for the 6"? I thought that there would be, but me thinking and someone else knowing is...well the reason I ask all the questions I do!

Thanks for sharing your experience!

[Curt Harms]

So there's enough open spots on the saw to feed the additional air volume needed for the 6"? I thought that there would be, but me thinking and someone else knowing is...well the reason I ask all the questions I do!

Thanks for sharing your experience!
I have a G1023. I had to stuff some foam between the table and cabinet and put magnetic sign material over the opening for the height adjustment wheel in order to get decent velocity thru the blade slot. At least on my saw air starvation was not an issue.

HTH

Curt

[Daniel McCurdy]

I have a G1023. I had to stuff some foam between the table and cabinet and put magnetic sign material over the opening for the height adjustment wheel in order to get decent velocity thru the blade slot. At least on my saw air starvation was not an issue.

HTH

Curt

Running 4" or 6"?

[Chris Padilla]

I have a G1023. I had to stuff some foam between the table and cabinet and put magnetic sign material over the opening for the height adjustment wheel in order to get decent velocity thru the blade slot. At least on my saw air starvation was not an issue.

HTH

Curt

I should do that on my Griz 1023Z but I'm too lazy to improve the DC on it right now. :)

Most TS are plenty leaky so there won't be any air starvation...no way!

[Jim Becker]

Well, lets' see...4" duct can handle about a maximum of 300-350 CFM...you just can't fit any more air in it physically at the given velocity. 6" duct can handle 600-800 CFM since the area is much larger. That should help you make your decision!

[Chris Padilla]

Sorry, didn't mention the material. Yes, I planned to use 2729 PVC...and yes, I'll be grounding it for sure!

I don't think there is any point in "grounding" PVC. It is quite difficult to do a good job grounding it so why even bother? No hobbyist shop is going to ignite sawdust...just won't happen.

[Paul Johnstone]

Sorry, didn't mention the material. Yes, I planned to use 2729 PVC...and yes, I'll be grounding it for sure!

I had thought about doing the 2 4" for the TS. I just wanted a more simple solution for the time being since I don't currently have an overhead hook up for it. I'll probably tackle that one later.

Its funny, I tried searching on the subject and just didn't seem to find what I was looking for. I guess there's a lot of times where things have to fitted around a certain existing criteria like room and budget. Room isn't an issue at all for the over all DC system, and I'd rather spend a little more on the larger stuff if its worth it.

I did purchase the Dust Collection Basics book by Shop Fox from Gizzly. Was very helpful, I'd recommend it. I just didn't understand why they seem to recommend running a main 6" line and then branch off to 4" (and then just have an additional 4" gate open to increase the CFM to the main line and keep the material moving along). Why not just run 6" right to the machine and increase the CFM there and collect more dust rather than pulling air from a different port that's not even in use? Doesn't seem to make sense to me. (Guess that's in a nut shell what I'm checking up on with this thread!)

Did you check the Bill Penz dust collection web page. It's excellent.

In short, run 6" as close as you possibly can to the tool.
The book probably said to use 4" drops off the main line because most people aren't going to go through the trouble of changing the size of their dust ports on their machines.

For a tablesaw, the ideal thing (at least in someone's opinion) is to split the 6" line into a 5" line going to the bottom of the cabinet, and then have a 4" going to the blade guard collection (I use a shark guard).

I have a dual drum sander with 2 dust ports. I ended up making them both 5", against recommendations.. but since the runs of 5" are very short (maybe 3 feet), I don't think it's a problem.. It seems to work ok.. but in general, they say to split a 6" to a 5" and a 4".. that's supposed to be the best balance.

[Greg Cole]

Greg,
I have the same DC unit and I'm just starting to plan a permanent duct system. Is the flow velocity through a 6" pipe high enough to keep larger stuff moving (as opposed to fine dust)? Also, I have a cyclone adapter on a trash can connected to the DC unit and I'm wondering if that reduces the effective flow?

Walt

Walt,
When I first installed my DC I found I had chips and shavings still int the DC ducting (el-cheapo corrugated 4" flex stuff) after letting the DC run for a minute after shutting off the planer or jointer. I found I got better results (ie no leftovers in the ducting) when using my planer & jointer if I actually left an additional blast gate partially open, meaning I was starving the DC for airflow. Since going to a 6" main, I can use just the blast gate hooked to the jointer or planer and keep the chips-shavings moving (no leftovers).
Installing the PVC is cheap and very easy. I'd highly recommend doing it the first time.

Greg

[Greg Cole]

That would be interesting! This all makes me wonder why the Jet DC and all of my machines have 4 inch ports. Looks like I have some modifying to do.

Hi again Walt,
You can remove the factory installed "wye" piece on the inlet port on your DC to find it's 6".

Greg

[Steven Wilson]

That would be interesting! This all makes me wonder why the Jet DC and all of my machines have 4 inch ports. Looks like I have some modifying to do.

Marketing. Woodworking machines should have DC ports, DC ports are 4", so lets slap a 4" port on them. That will work ok for chips but not for dust. If you want a machine with reasonable DC capabilities you need to look at machines designed for a more industrial environment where dust exposure limits are regulated. That's where you'll see the 5", 6" and larger ports on machines. Eventually that will make it's way down to our machines.

[glenn bradley]

That would be interesting! This all makes me wonder why the Jet DC and all of my machines have 4 inch ports. Looks like I have some modifying to do.

Most small units (like mine) have 4" ports. Larger units have 5" - 8" and generally make the concession of including an adapter to multiple 4" ports at the machine.

A recent review took a variety of machines and tested them. Some of the 4" machines that ran larger motors were tested with 6" duct and actually improved on short runs (interesting for the test but not long enough for most shops). None of the 4" machines were as good as even the smallest 6" machine but there is a lot of engineering involved outside of hose size ;-)

My Delta does fine with one machine at a time. It starts to suffer running the overarm and the cabinet on the TS but I adjust with the blast gates. A decent sized cyclone is somewhere down the road for me (I hope).

[Daniel McCurdy]

Did you check the Bill Penz dust collection web page. It's excellent.

In short, run 6" as close as you possibly can to the tool.



Yes, I did read quite a bit of it...and I'd agree with your summed up description. Seems the major point he was making that in his opinion, he doesn't think 4" gets the job done, so 6" should be used.

I'm pretty sure I'm going to go with 6". Just seems to me like that makes the most sense for my set up.

[Aaron Gatzke]

Chris, did you ground your pvc? I have heard differing opinions.
Thanks, Aaron.