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6" vs 5" dust collection ductwork

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Forum topic by JETJock60 posted 06-13-2019 11:19 PM 715 views 0 times favorited 40 replies Add to Favorites Watch
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JETJock60

9 posts in 39 days


06-13-2019 11:19 PM

Topic tags/keywords: dust collection question

I’m in the process of setting up my dust collection system. I have a Harbor Freight DC (I know, I know it’s cheap but it’s all my budget allows and I’ve have had it for a few years). I did recently upgrade the impeller to the 12” Rikon and increased the input to 6” by opening it up with a 6” flange. In addition, I will be venting it to the outside and adding in a cyclone. My question is this…the Super Dust Deputy I just bought has a 5” input. Is 5” sufficient as the main trunk line or should I install 6”? I’m having a problem sourcing 5” PVC and wyes for a decent price, so I’m considering putting in 6” with 4” runs close to my tools. I’ve read that reducing from 6” to 5” on the inlet side is a bad idea, so I’m not sure what to do here? When the budget allows I will eventually get a DC with more power. BTW – the new impeller and larger intake made a significant difference in the suction on the bargain DC.


40 replies so far

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DRWard

14 posts in 101 days


#1 posted 06-13-2019 11:50 PM

Let me preface my comments by being up front with the fact that I am by no means an expert on topic of dust control. That said, I recently “hard piped” the DC system in my basement shop (prior to that I would simply drag a hose from tool to tool). Prior to running the pipe, I read everything I could find on the subject. What I was able to discern is that the pipe size is primarily determined by the inlet size of your DC inlet (in my case it is 5”). Furthermore, I learned that it is best to maintain that dimension for as long as possible before reducing the pipe to 4”, which is the diameter found on most shop machines. Scaling up or down will reduce the overall efficiency/effectiveness of your system. Regarding sourcing 5” PVC pipe and fittings, I experienced the same issue. I finally decided to go with 5” snap lock metal ductwork (I sourced this from Oneida), I sourced the 5” metal fittings (Wyes, 90, 45 and 5” to 4” reducers) from the Sheet Metal Kid. The Sheet Metal Kid produces an excellent product at a very competitive price. Overall, I am very pleased with the my system.

-- Donn, North Carolina

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Rayne

1209 posts in 1962 days


#2 posted 06-14-2019 12:12 AM

Don’t increase main line. Find a local HVAC company and you’ll probably find your 5” snaplock ducts and fittings. I found one here locally, is 26ga, and it’s cheaper than PVC.

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ibewjon

685 posts in 3215 days


#3 posted 06-14-2019 12:52 AM

5” steel, 26 guage is the only way to fly. 6” is too big for a small DC. I have a 2hp and 5” pipe. Venting outside is no good if you heat or cool your shop.

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JETJock60

9 posts in 39 days


#4 posted 06-14-2019 01:07 AM

You guys are great! Thanks so much for replying so quickly. I honestly hadn’t even considered metal ducts, but definitely will research prices tonight. Sounds like 5” is the way to go. Thanks again! Will post a picture once it’s finished.

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pintodeluxe

5954 posts in 3235 days


#5 posted 06-14-2019 03:03 AM

I went with 6” metal mains and 4” metal pipe close to the tool. This allowed me to special order 26 gauge HVAC from Home Depot (cheapest option of all).

My Tempest cyclone has a 6” inlet though. So I guess if you’re set on the dust deputy, you’ll be limited to 5” pipe. Metal pipe is better than PVC for sure.

Good luck with it.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

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fly2low

86 posts in 519 days


#6 posted 06-14-2019 06:55 AM

Not sure that metal is “surely” better than PVC. PVC has a lower coefficient of drag compared to metal. 4 inch and 6 inch pipe and fittings are easy to source and easy to work with. 5 inch is found in the unicorn department.
The only issue with PVC is grounding, and it is not a real issue

-- Rich Gig Harbor, WA

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ibewjon

685 posts in 3215 days


#7 posted 06-14-2019 01:21 PM

26 guage 5” is easy to purchase. Just look beyond the big boxes. 6” is 50 percent larger than 5”, so you need a DC that is 50 percent larger. Most machines don’t have the airflow needed to work with 6”. Don’t forget to use long radius 90’s, or 2-45degree elbows. And seal all snap Lok joints the length of the pipe and all joints. And not trying to insult anyone’s intelligence, but the pipe joints for DC go opposite of a furnace. I have seen a couple systems installed wrong, opposite of flow direction.

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cmyers

1 post in 3114 days


#8 posted 06-14-2019 03:50 PM

I’m in the same boat as JETJock60. My early PSI Tempest 2HP cyclone has a 5” inlet. I’m about to reorganize my workshop, and as part of that will be running new pipes for the DC. After considering various options with 6” vs 4” thin wall PVC, I think that I’ll look at using 5” metal duct and reduce to 4” at the machines.

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ibewjon

685 posts in 3215 days


#9 posted 06-14-2019 04:15 PM

Depending on the number of Y’s you need, I paid for my HF spot welder with the savings from making my own. I can make any y, even make a double y, 5” or 4” tap, for the price of 1 1/2 pieces of 2’ long snap Lok. Then paint with duct sealer, which should be done with bought fittings as well.

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fivecodys

1437 posts in 2058 days


#10 posted 06-14-2019 04:19 PM



Let me preface my comments by being up front with the fact that I am by no means an expert on topic of dust control. That said, I recently “hard piped” the DC system in my basement shop (prior to that I would simply drag a hose from tool to tool). Prior to running the pipe, I read everything I could find on the subject. What I was able to discern is that the pipe size is primarily determined by the inlet size of your DC inlet (in my case it is 5”). Furthermore, I learned that it is best to maintain that dimension for as long as possible before reducing the pipe to 4”, which is the diameter found on most shop machines. Scaling up or down will reduce the overall efficiency/effectiveness of your system. Regarding sourcing 5” PVC pipe and fittings, I experienced the same issue. I finally decided to go with 5” snap lock metal ductwork (I sourced this from Oneida), I sourced the 5” metal fittings (Wyes, 90, 45 and 5” to 4” reducers) from the Sheet Metal Kid. The Sheet Metal Kid produces an excellent product at a very competitive price. Overall, I am very pleased with the my system.

- DRWard

Yep. I did the same thing. 5” snap lock duct from Oneida. The fittings were pretty pricey but for my small system this all works very well. I vent the “Exhaust” outside after it passes through the SDD. No visible fine dust on the plants in the flowerbed so I’m happy.

https://www.lumberjocks.com/projects/388617

-- When you leave your shop for the night, make sure you can always count to 10.

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Ocelot

2275 posts in 3060 days


#11 posted 06-14-2019 05:12 PM

Grizzley has had 5” plastic components (Ys, Gates, ports). I bought a few when I “designed” my hard-piped system which I still haven’t installed. I plan to have some 5” from the planer, which has a 5” port on it. Other parts will be 4” with a main trunk 6” square.

Note that not all DC components of the same nominal size will fit together nicely.

As for 5” vs 6” round, The cross-section of 6” is 44% larger (6×6)/(5×5) = 1.44. Don’t worry about pi, it cancels.

Anyway, there are two factors to consider:
CFM – volume of air per unit time. More is better. Generally, a bigger pipe will allow higher CFM.
Velocity – speed of the air. More is better. Generally, a bigger pipe will have lower velocity.

If the velocity is too low, the dust will fall out of the airstream and begin to clog the pipe, but this is a self-limiting thing. As the pipe gets a little accumulation in it, the velocity increases so that accumulation stops (usually).

As long as you have adequate velocity to keep the dust/chips in the airstream, bigger pipe is better.

I personally wouldn’t worry about 6” if that’s what you can get for a good price. 6” will allow higher CFM (at the tool) than 5”, but with reduced velocity in the pipe

My plan is to use 6” square trunk lines, which I can fabricate out of used alumalite signs. The problem with square is keeping the pipes from collapsing. If I ever do it, I’ll post about it, but that’s my plan. 6” square is 25% more cross-section (roughly) than round. I’m not worried about dust settling in the pipe.

-Paul

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ibewjon

685 posts in 3215 days


#12 posted 06-14-2019 07:16 PM

5” steel. It works.

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ibewjon

685 posts in 3215 days


#13 posted 06-14-2019 07:17 PM

Square heat duct gas turning vanes to help at the corners. Try that with chips. I think square duct will work about as good as square wheels.

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pintodeluxe

5954 posts in 3235 days


#14 posted 06-14-2019 09:53 PM



Not sure that metal is “surely” better than PVC. PVC has a lower coefficient of drag compared to metal. 4 inch and 6 inch pipe and fittings are easy to source and easy to work with. 5 inch is found in the unicorn department.
The only issue with PVC is grounding, and it is not a real issue

- fly2low

The constant static shocks that are an issue with PVC kept me from even considering plastic. Even too long of a 4” flex hose will produce an irritating level of static discharge. I’ve experienced this on a stationary oscillating sander. It felt like I was getting shocked about a thousand times a minute. But, since I have metal pipe, I just grounded the spiral wire of my flex hose and it fixed the problem.

By the way, when I purchased special order 26 gauge pipe from the big box store, it was actually cheaper than PVC.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

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ibewjon

685 posts in 3215 days


#15 posted 06-14-2019 10:14 PM

I have heard a hundred ways to ground PVC. The problem is, you can not ground an insulator. Wrapping foil tape or bare wire around it actually acts like a capacitor and builds up a bigger charge. It is awfully hard to convince some people. STEEL!!!

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