really... is 4" PVC "good enough"?

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Forum topic by rieferman posted 01-12-2011 09:14 PM 1160 views 0 times favorited 6 replies Add to Favorites Watch
View rieferman's profile


39 posts in 2893 days

01-12-2011 09:14 PM

I’m new to this forum but have been lurking for awhile. This is a very active board with a lot of great posts, so kudos on that. I hope I can contribute positively too.

Now, down to business..

I understand the math and calculations and science that says I should use 6” PVC for plumbing my harbor freight 2 hp dust collector. I get it, it’s better.

I also understand the math that says that the free 4” PVC and fittings that I received is much better on my single income budget than un-free 6” PVC.

SOOOOO… For those of you with 4” hard plumbed to each machine (i.e. centralized DC, NOT moved from machine to machine) using a similarly powered dust collector (I have built a thien baffle into my system) is 4” pipe “good enough”? I mean, in the real world where I reside, has your experience with this type of setup be pretty positive, or is it a totally worthless step to take? (side note: I will be wearing a respirator while working, so I’m looking to pickup chips not the “fine dust” per se).

-- New to woodworking, old to barn fixin'

6 replies so far

View Paul C.'s profile

Paul C.

154 posts in 3447 days

#1 posted 01-12-2011 09:22 PM

I think so, yes. But – wear a mask.

My 4 in system grabs all the chips fine, but I am leery of the fine dust.

View live4ever's profile


983 posts in 3212 days

#2 posted 01-12-2011 09:33 PM

Welcome to LJ.

I’ve been researching the same thing lately, and am in the process of doing exactly what you’re wanting to do.

I haven’t come across anything that says it WON’T work or is a waste of time. There are plenty of people using both 4” pipe and 6” pipe successfully, even though the calculations suggest that 4” won’t give enough CFM at the machine and that 6” won’t keep the airspeed high enough to keep dust and chips in suspension.

Basically, using EITHER 4” or 6” pipe is pushing the limits of this DC in different directions (assuming a long run of 20-30ft), and you have to try to make up for that in as many different ways as you can. Here are the ways people are doing that, and I plan to make a lot of these modifications to my own setup:

1) A cartridge upgrade from Wynn.

2a) A stovepipe mod, which replaces the gray flex hose between blower and bag ring with smooth metal – see NBeener’s recent forum post


2b) Building a new shopmade carriage/platform for the motor that mounts it vertically, such that the blower has a straight, few inch, shot into the bag ring. The saved space also provides room for a Thein trashcan separator. One thing to note about the Thein separator – it will probably eat up much of the performance gains made by the other mods – so you have to decide how important chip separation is to you.

3) Designing your ductwork system carefully, replacing all 90 degree turn with gradual 45 degree bends. Placing blast gates at branch points to minimize wasted airflow. Reducing lengths of flex hose as much as possible.

For me, the trouble of all of these mods isn’t that bad – less trouble than trying to source, buy, and piece together 6” pipe and fittings. YMMV.

-- Optimists are usually disappointed. Pessimists are either right or pleasantly surprised. I tend to be a disappointed pessimist.

View PurpLev's profile


8547 posts in 3850 days

#3 posted 01-12-2011 09:40 PM

I have 4” PVC ‘permanent’ duct (permanent as in all machines are stationary including DC, but it’s temporary as we are still renting). I set it up with 4” PVC because of cost factor and I know sooner than later we will be moving and I don’t want to spend too much on something that will have to be removed and most likely not reusable in another location. that said – the machines at the ends of my runs leave a lot to be desired. If you are doing it and want to be done with it and not planning on replacing it ever again – go with 6” from the get go.

the 4” ‘works’, but not as good as it could be. esp. for the finer particles.

-- ㊍ When in doubt - There is no doubt - Go the safer route.

View NBeener's profile


4816 posts in 3376 days

#4 posted 01-12-2011 09:55 PM

Agreed with the prior posts’ advice.

4” will work, in your case.
6” will work better.

If you go the 4” route, then … all the other things that create static pressure losses become MORE important:

- the straightest runs you can make, with the fewest bends, angles, and elbows
- the shortest runs you can make
- straight pipe, using only the shortest lengths of flex hose you can manage

Added CFM from a dust collector is a lot like make-up: it can hide a million little mistakes ;-)

My last mile of DC hose was a 28’ section of flex-hose – NOT very smooth on the inside.

Last night, I replaced it with a 20’ section of hose that is nearly as smooth on the inside as PVC piping would be.

I noticed a fairly substantial difference in suction.

I also noticed a BIG difference, when I replaced the HF DC OEM bag with a Wynn Filter.

And another fairly sizable increase—as mentioned above—when I did the “stovepipe modification,” sealed any leaky points, shortened the length of the run FROM my DC TO my chip separator, and switched THAT hose from flex to 4” galvanized steel duct pipe, and sealed the joints really well.

With what you propose, I would think something like a chip separator could induce enough static pressure loss that you might get a fair amount of dust and shavings AT your machines.

6” pipe might solve that.
A higher HP DC, with more CFM might solve that.
Meticulous attention to the above—minimizing static pressure losses—might solve that, too.

See what I mean ? :-)

Good luck !

-- -- Neil

View rieferman's profile


39 posts in 2893 days

#5 posted 01-12-2011 10:00 PM

Live4ever, I agree with the modifications you suggest. I built a stacked assembly where the thien baffle is directly in the ring that comes with the unit. I exhaust outside and have minimal bends, so restrictions are at a minimum. Picture attached (note, these pics are before cutting the exhaust through the wall)

edit: side note, my setup sucks through the bag (rather than sucking through a barrel)... this is for ease of discarding dust when it fills up.. just remove and tie up/toss out. This setup would implode the bag when the DC is turned on, so the bag is lined with a mesh cage skeleton (made of some spare fence material I had laying around) that is easily shimmied out of the bag when it comes time to empty. Just put the cage in your next bag, attach, go.

Purplev, In case it makes a difference, my farthest run is by far my bandsaw at probably about 35 feet of ducting. 2nd furthest is my planer at 25 feet. 3rd is my drill press at 20 feet. And my table saw, jointer, and miter saw are all about 15 feet.

-- New to woodworking, old to barn fixin'

View Raymond's profile


676 posts in 3929 days

#6 posted 01-12-2011 10:02 PM

All my machines are hard plumbed, about 20 ft for the machine the farthest away. That is the table saw. Works great for me. I have the HF 2HP dust collector

-- Ray

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