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6" vs 5" dust collection ductwork

7K views 47 replies 16 participants last post by  ibewjon 
#1 · (Edited by Moderator)
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.
 
#2 ·
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.
 
#6 ·
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.
 
#7 ·
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
 
#8 ·
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.
 
#9 ·
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.
 
#10 ·
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.
 
#11 ·
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
 
#12 · (Edited by Moderator)
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
 
#15 ·
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.
 
#18 ·
I have a 2 HP dust collector from Grizzly and used 6" steel duct all the way to most of my equipment. I also made my own wyes and sealed it all with a brush on duct sealer. (I am a retired sheet metal worker)

- Jim Finn
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.

- ibewjon
Either one of you guys interested in making some 12" x 12" x 6" wye's for me for a decent price? Would like to use 12" pipe for my new 10HP unit but, the cheapest spiral pipe wye's that I can find are $50 or so each in 12". My local HVAC supply house can not get 12" x 12" x 6" wye's or any other 12" wye's. Could use 6 wyes, 7×12" 90's and 8×12" blast gates, very expensive. LoL
 
#19 ·
Again…really appreciate all of your responses. Update…I have decided to use 5" metal ducts and attempt to fab my own wyes, etc. Used to work in HVAC so kind of know how to work with the metal ducts but appreciate any advice on that subject also. Yesterday, I increased the inlet on my HF DC from 5" to 6" because of the SDD outlet…it seemed to help the suction with my Rikon impeller and think the $12 spent on the flange and $5 on the rivets was worth it. BTW the depot has 5" duct 26 gauge at $3.22/ft in 2' sections…about 20% cheaper than anywhere else. https://www.homedepot.com/p/Master-Flow-5-in-x-2-ft-26-Gauge-Round-Metal-Duct-Pipe-26CP5X24/202191786
Still looking for a bargain on 90s and wyes or fabricating advice. Can't wait to not have to use my shop vac and respirator anymore!
 
#20 ·
Long radius 90's are a buy item for me. I have Oneida, but there are others. 90's are about $20. With the 5×5 x 4" she's at about $39, it will only take 4 to pay for a harbor freight spot welder. I will try to dig out my cardboard patterns and post for you to copy if you need me to. If you want them, tell me. I then made steel patterns out of some light guage duct that will wrap around the 26 guage.
 
#22 ·
Ibewjon…yes please post or email to me cbartle60@gmail.com…did you tape the seams or use mastic? I'm not much of a welder was thinking about using rivets do you think that'll be ok?

I've already asked sheet metal kid for a quote, but being the DIY guy that I am would prefer to make them and save the $. Thanks again I'm new to this site but loving it and can't thank you all enough for the help.

PS - bought a 14" Delta bandsaw in fantastic shape off craigslist…my wife is still fuming because I'm way over budget on my shop but just couldn't pass up that deal…been wanting a bandsaw for a long time!
 
#23 ·
Looking at sheet metal kid, I don't see a guage, but it is labeled as heating, cooling ductwork. Probably too thin for DC. Also, I don't see long radius 90's listed. And the wye fittings are dimension order for HVAC. If the parts come pre crimped, the inlet would be on the wrong end. I have not called them.
 
#24 ·
Looking at sheet metal kid, I don t see a guage, but it is labeled as heating, cooling ductwork. Probably too thin for DC. Also, I don t see long radius 90 s listed. And the wye fittings are dimension order for HVAC. If the parts come pre crimped, the inlet would be on the wrong end. I have not called them.

- ibewjon
The metal is 26 gauge. I don't quit follow the concerns you expressed, I purchased fittings from them and they work just fine on my system. That being said, I may have been lucky or simply unaware that there was/is an issue. My system is not too complicated. Two branches forking off the DC inlet, seven total blast gates (including a floor sweep), about 40 feet of duct work and about 30 feet of flexible pipe going to the various tools.
 
#25 ·
Looking at sheet metal kid, I don t see a guage, but it is labeled as heating, cooling ductwork. Probably too thin for DC. Also, I don t see long radius 90 s listed. And the wye fittings are dimension order for HVAC. If the parts come pre crimped, the inlet would be on the wrong end. I have not called them.

- ibewjon
The metal is 26 gauge. I don't quit follow the concerns you expressed, I purchased fittings from them and they work just fine on my system. That being said, I may have been lucky or simply unaware that there was/is an issue. My system is not too complicated. Two branches forking off the DC inlet, seven total blast gates (including a floor sweep), about 40 feet of duct work and about 30 feet of flexible pipe going to the various tools.
 
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