6" vs. 4" dust collection duct

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!

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 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.

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.

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.

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

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.

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.

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!)

Quote:

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Originally Posted by 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

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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.

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.

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

Quote:

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Originally Posted by 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

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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

Quote:

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Originally Posted by Walt Stevens

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

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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.

Quote:

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Originally Posted by Shawn 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).

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

Quote:

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Originally Posted by Shawn Patel

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

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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

Quote:

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Originally Posted by Walt Stevens

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

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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.