Need Help with dust collection planning

[Tony Roun]

Hi All,

I am finally getting around to installing a dust collection setup. I have a 2HP 220v jet dust collector, and my plan was to vent directly outside with no filtration. I don't have any CO concerns since this is in an outbuilding so I just need to remember to crack the door at the other end of the shop, and neighbors are not of concern since I am on acreage. The dust collector has a 6" inlet and a 5" outlet. I have everything in my shop that would need dust collection is on wheels except for my table saw and my miter saw. Everything on wheels would be able to easily plug in within 6 feet of the blower motor. I located the miter saw only a few feet from the dust collector, and the table saw is only about 8-10 feet away.

Ideally, I was hoping to keep the cost of this system down, and was thinking that 4" sewer PVC pipe would be pretty easy for me to use. My concerns are that a lot of what I have read on this forum and others sites suggests that 6" is really needed in order to capture enough CFM to pull the really fine dust out. If I used 4" sewer pipe, my plan was to come vertical up off the table saw, then over the 8-10 feet over to the dust collector and then down. I am guessing that the total length of that run would be 18 feet or so. So do you think I will be OK using 4" or should I really invest in 6" for the run? I wasn't sure if a 4" pipe would starve the blower motor, but the fact that I am going directly outside with no filtering should help a lot. Please help me as I am sort of stumped with all of the variables.

Thanks so much.

[James Gunning]

The amount of air that can physically flow through a 4" pipe is less than half of that which can flow through a 6" pipe. I have proved this for myself using only a 1HP blower. I also converted my machines to 6" pickups or used a manifold with smaller multiple pickups that approximates the area of the 6" pipe. An example would be both under-table and over-arm pickups on a table saw. To be truthful, a 2HP blower using the 6" pipe will still leave some of the airborne dust floating around. You really need a 3-5HP blower with a 14-16" impeller generating around 800-1000 CFM at the pickup to capture most of the airborne dust generated. For that you would also need a 7-8" main line, if you have ducting to each machine. Not all of us can manage that, but optimizing what you have is easily possible.

With the ability to vent outside, you have an ideal situation to maximize what you already have. Get some kind of a cyclone. My suggestion (and I have no connection with Oneida) would be their SDD XL. The cyclones sold on eBay have gotten good reviews and would work well also. The best solution would be a Clearvue, but also one of the most expensive. Hook it up to vent outside, and use 6" pipe to do the connections. (your 5" outlet from the blower is fine as is) Modify your machines to have 6" pickups. No sharp 90 degree turns (use wide radius turns) , as little flex pipe as possible, sealed well. Keep the runs as short as possible, and use smooth walled pipe.

[Tony Roun]

Thanks for the response. Prior to doing the appropriate research into this topic I had purchased a home-made cyclone from a friend that should work well, only issue is that it is really setup for 4" and would likely be easier starting over if I ended up migrating to 6". Additionally, I had bought a package of 4" flex hose for all of my connection points for equipment. Hence my desire to make 4" work, but shame in me for not doing the research first.

Can an I ask an ignorant question... If I ran a 6" main duct in PVC or metal, and then branched off at the machines with 4" flex hose, would the 4" be too constrictive and lose any benefit of having the 6" main duct?

I still need to do more reading on the metal vs PVC question too.

[Roger Green]

I would run 6" all the way to the machine.

[James Gunning]

Tony,

The short answer to your question about using a 6" main and 4" branches is: it did not work for me. I tried using a 6" to 4" transition and it was obvious that the flow was noticeably restricted compared with just the 6" pipe alone. Kind of like the flow restrictors used in plumbing and hydraulic systems. All that is required is a small disk to change the flow rate. That was the discovery that prompted me to enlarge the pickup ports on my machines to match the 6" pipe.

Look at it this way. A 4" pipe cross section has about 12.56 sq. in. A 6" pipe cross section has about 28.27 sq. in. Dust collectors/cyclones are all about maximum air flow at low pressure. The larger pipe will flow way more air.

A 4" system will work, after a fashion, but would capture and carry far less dust than the 6" system. Both will probably pick up most of the chips. For that matter, so will a broom and dustpan. Health is the reason that capturing the dust is important. The sub-micron dust that settles in our lungs and coats everything in the shop is what we are really worried about.

Also, avoid the use of flex hose as much as possible. The internal friction due to turbulence will reduce the air flow more than smooth wall pipe. If flex is necessary, use the shortest piece possible. Either PVC or metal works fine for ducting.

[John K Jordan]

Splitting the 6" to 4" works for me at certain machines: bandsaw (split into three 4"), lathe (works well for sanding dust), and 22-44 drum sander. I reduce one 4" to use a long shop vac hose for cleanup and it works fine too (I open an adjacent 4" blast gate some to get plenty of air flow in the main 6" horizontal run - about 40')

Here is a ClearVue splitter at the lathe at the left side of the picture - 6" to two 4" blast gates:
lathe_PM_Jan17_IMG_5751.jpg

I think machines like table saw and jointer need 6". I carry the portable planer outside.

My DC is a 5hp ClearVue cyclone - I have no idea if the extra HP has made a difference in how well the 4" works. I haven't measured the airflow or pressure either. I do know the inside of the bandsaw is always clean and the particle counting air quality monitor doesn't go crazy when I use the drum sander. I personally would not use a 4" main. The 6" S&D PVC pipe is not all that much more than the 4"

JKJ

[Tony Roun]

OK, thank you all for your help so far on this thread. I am going to go with 6" metal duct (26 gauge), and increase the size of my ports at my machines to 6" as well.

Last decision is whether or not I even need to mess around with a cyclone separator, or just blow it all outside. There is nothing behind my shop where I would be venting other than some woods. I guess I am sort of leaning toward just venting direct without a pre-separator so that I get maximum draw with the 2HP blower. Thoughts?

[James Gunning]

Tony,

Any separator you use will cause an increase in static pressure and will reduce the amount of air that the blower will flow. There is always some cost to a separator. If you have a suitable situation, just venting all the chips and dust outside works OK. Realize that at some point you will have a pile of chips under your blower exhaust that will need to be dealt with. Maybe just raking it into the woods and letting it rot will suffice. All you need to do is just route the outlet hose through the outside wall. You wouldn't need the part of the DC for the filter and collection bags at all. I would think a piece of smooth pipe 5 or 6 feet long to move the chips a short distance from your building might be a good idea.

[John K Jordan]

...I would think a piece of smooth pipe 5 or 6 feet long to move the chips a short distance from your building might be a good idea.

From the way some farmers handle manure and compost, a sloped concrete pad with block walls would constrain the pile somewhat from spreading all over the area and mixing with the dirt/gravel when removed. The "stall" could have doors or be open on the front to allow a front end loader bucket to scoop easily. Bringing the pipe in high then aiming it straight down could focus the chips and sawdust.

I've become a concrete convert for easy cleanup. I just put in a concrete floor for my new peacock house.

peacock_concrete_IMG_201702.jpg

JKJ

[Larry Frank]

While a 6" pipe is great, your velocity decreases. With smaller dust collectors, you may have insufficient air speed to keep all the dust moving. There is a trade-off with pipe size, velocity and cfm. Using larger diameter pipe will reduce static pressure losses and slightly increase flow. Just because it has more than twice the area, it will not give you twice the flow.

I get adequate air flow with my l larger dust collector with the 4" ports at the machine(>700 cfm).

[Tony Roun]

Larry, thank you for your response and thoughts.

It is safe to safe that I am confused about overall duct sizing relative to the 2HP dust collector that I have. I have heard and read I need six inch pipe to move enough volume of air to get the fine stuff, then I hear that 2HP is not sufficient for 6" pipe and I should consider downsizing the duct size to 5" or 4". Does anyone know of a chart or some visual that correlates DC horsepower to duct size? I am going with metal so 5" or 6" is fine with me.

[Larry Frank]

Wood Magazine in March 2008 had a chart showing which dust collectors were good with 6" duct. I found a copy of the article online.

Do a Google search for "182dustcollectors"

[James Gunning]

Tony,

This is a subject that has lots of controversy swirling around it. The website by Bill Pentz contains lots of well researched information and could be considered the best source out there. If you look at the table toward the bottom of this page: http://billpentz.com/woodworking/cyc...cs.cfm#HowMuch labeled "Hobbyist Fan Table for Shop With Ducting, Cyclone and Cartridge filters" you can get a quick estimate of how your 2HP blower should fare with 6"or7" pipe. Realize that this chart has a list of assumptions "the fine print". Two of the assumptions are a cyclone and a fine filter. If you duct everything outside using just the blower, your airflow will be higher. Also, notice that there is no provision for 4" pipe. The reason for that is the airflow through a 4" duct drops below any of the standards considered as adequate. Also, realize that Bill Pentz sets a high standard because he has a life threatening allergy to wood dust. His intent is to provide an airflow standard that is attempting to collect the fine dust cloud generated at the source machine as well as the larger chips. In CFM terms, he found that about 800 CFM at the source machine was generally adequate to collect the fine dust. More CFM is always better in this case.

It is possible to get a high airflow through a 4" pipe. However, it requires a very smooth, short, pipe with few or no restrictions and a very large blower and impeller, well beyond the 2HP one you have. The power tool manufacturers did not do the woodworking community any favors by making 4" pickups a standard for most machines. I don't know why that size was selected, it could have been design consideration, but more likely money, since the 4" duct is cheaper. Hard to say in each case, but it's obvious that 6" is where it needed to be to get any decent airflow from the smaller blowers. I realize that in some cases a 4" pipe might be the only size that would fit in a certain application. Many are very reluctant to do any surgery on their machines to enlarge a 4" pickup to a 6". I don't blame them, I didn't want to do that either. I was able to work around that issue in some cases by using manifolds that have multiple pickup hoses that roughly total the 6" size. This post shows how some of my machines were adapted: http://www.sawmillcreek.org/showthre...pipe&highlight=

In the end, each of us does what he prefers, and can afford. The information is out there, it's up to us to decide how to apply it to our individual shops. I defer to Bill Pentz because he is a trained engineer and due to his health scare devoted years of study and money to a subject that nearly all of us have no training or deep understanding of. Lots of reading on the Pentz website, but if you wade through it, you will get a much better understanding of the dust collection problem.

[Tony Roun]

James, thanks again for the thoughts. I have read a lot from Bill's website but had not come across the chart that you pointed me to. OK, it looks like 6" will work OK (but not great) if I avoid filtering and chip separating, but I would benefit from upgrading to 3HP dust collector at some point down the road, and the 6" duct will work fine for that too. I was surprised to see the comments Bill wrote about PVC having less friction than steel duct work and would be better for air flow if all else was the same.

Thanks again.

[James Gunning]

Tony,

I can understand the PVC argument. The interior of the pipe and fittings is smooth with no joints or ridges inside the pipe like the metal piping. There are metal pipes with an interior as smooth as PVC, but at a very high cost.

In dust collection you can't have a blower too big. Sort of the same argument as never having too many clamps. The only time I would think the blower is too big would be if it's lifting tools right off your bench. If I had the room and the ability to use a stationary DC, I would have a Clearvue. 5HP cyclone. For now, I'll make do with my 1HP blower on a metal SDD and wear a dust mask when I'm generating dust. That plus keeping the garage open with a fan blowing through all the time keeps things aired out on my end.