Dust collection question

[rusty]

Have a 10" craftsman table saw, 10" dewalt chop saw, future 15" grizz helicle planer, future 8" jointer. Probably too much for the 5 gallon bucket dust collector setups. Will probably go with a fixt cyclone setup with overhead pipes and blast drop downs. All these will be within 20' square area.
How much CFM would be needed, and do I need grounding for the pipes?
thanks

 

[Mike Davis]

The 15 inch planer will be the biggest draw, size for that and the rest will be covered. I never run more than one machine at a time.

From Bill Pentz:

1. In spite of the exaggerations, citing maximum airflows and testing tricks all major brand name small shop dust collectors and cyclones sized over 1.5 hp provided the 350 cubic feet per minute (CFM) needed for good chip collection but no dust collector under 3 hp or cyclone under 3.5 hp provided the 1000 CFM airflow that our vendors who guarantee air quality established that we need for good fine dust collection.

 

[JimD]

Let's take grounding first. The theory that supports grounding is based upon a fear that wood dust can burn or explode. Grain silos explode occasionally from dust. But wood dust does not. It is theoretically possible but getting the right dust/air ratio is very very difficult. The dust level would be too high for you to breathe. So from a scientific standpoint, there is a near zero risk of an ungrounded system. I've never grounded mine and never worried about it.

Mike cites an excellant source in Bill Pentz. He does actual research and posts very useful information. The tricky thing about Bill is he has an extreme allergy to dust. Not just wood dust but all kinds of dust. So his input is basically consistent with what you need to do if you have a bad allergy like he does. I think he may also believe that his allergy was caused at least in part to not using better dust collection earlier.

I will never own a 3hp cyclone. I have no allergy to wood dust. There is other data showing that much more modest systems do pretty well. I like Matthias Wandel's research using a Dylos dust meter, for instance, and some of the posts on other websites.

I don't like the way my shop vac is working with my new SawStop, as I expected, and will probably buy the "2hp" harbor freight DC and put a super dust deputy on it and discharge outside. I will still use my shop vac for the smaller tools. I think my air quality will be good enough for me. I think it will be similar to the air quality in my house (which would also have to improve if Bill Pentz lived in it).

 

[Bas]

The CFM question is tricky. It's not just how much air the dust collector can move, but at which static pressure ("suction"). This chart from 2014 shows a comparison between machines. The longer the pipe and the more turns you have between the machine to the collector, the bigger the motor and impeller need to be.

For a shop your size, with the equipment listed, I'd go with a 3HP machine such as this one from Grizzly. You can also look for something more compact but there is a trade-off of course in performance.

These machines will perform far better than the typical 1.5HP single stage collectors. I previously had the Harbor Freight model, with Wynn canister filter and trashcan separator. It worked OK, but only when attached directly to the machine, using fixed pipe and blast gates caused too much of a drop in static pressure to catch the finer dust. No such problems with my current cyclone system.

Provided you remember to actually connect the hose to the saw. And remember to turn it on. And open the blast gate

I use PVC pipe, and plastic hose from the blast gate to the machine. I've not had any issues with static electricity. There has been quite a bit of discussion on static buildup, metal vs PVC, etc. The bottom line is that there are zero reports of someone having blown up their shop because they didn't ground the pipes. You would need massive amounts of fine dust as well as massive air movement to generate those conditions. Think industrial equipment and fine bread flour.

 

[JimD]

Here is a link to some of Matthias's measurements and comments on wood dust:

https://woodgears.ca/dust/dylos.html

Matthias's DC is not 3hp or bigger. But he is reporting essentially indoor air quality with it running, including for small particles. He is not the only one. Sawmill Creek organized a group buy on Dylos meters several years ago. You can find threads from their use on their website.

One thing you definitely do not want to do is to operate a cheap DC, like the Harbor Freight unit I will probably buy, with the bags it comes with. It will collect chips but it will blow the fine dust that may be an issue for you all over the place. I believe it is literally better to do nothing than to do this. Felt bags are definitely better and not that expensive. I think that is the minimum.

But in terms of how much do you need to do - big cyclone system, possibly with air filtration too - or small DC with decent fitration it depends on your goals. If you put extra special filters on your HVAC system due to allergies or other issues, you need the big system. If you do not need those kind of protections in your house to stay healthy, I do not see where you need them in your shop.

 

[Rwe2156]

My experience is planers and jointers (or any machine that makes shavings) are actually easier to collect than machines that make dust like saws. The average CFM requirement at the machine is around 350 but air speed is also important. That is influenced by static resistance (pipe diameter) and blower capacity. The most common mistake I see guys make is undersized ducts. 4" pipe is definitely not going to get it (already made that mistake).

Since that is not a huge shop, I would suggest you take a look at the Harbor Freight 2HP collector (on sale now). I've read quite a few posts that guys have had good luck with them. Ttake it apart and couple the blower to a cyclone. Get rid of the cheap bag and add a canister type filter or vent outside.

I used 6" SD PVC pipe for my ductwork. That is another area where you can save $$$. I have had static issues I run a wire from the metal blast gate to round on an outlet. Seems to help.

Any brand name cyclone set up is going to cost at 10X as much.

 

[rusty]

Good idea using a modded 2hp harbor freight model. Since it comes with the 4" inlets/outlets how did you change over to 6" pipe?

 

[Rwe2156]

I don't have the HF mine had a 4" Y splitter there's a 6" outlet on housing. I just removed the splitter and ran 6" flex to the cyclone.

The super dust deputy comes with 5" outlets you can use an adapter to go to 6" ducts.

 

[Plunkett]

Do you then change the dust ports on your machines to 6" as well, or is just your ductwork at 6"? I think I read Pentz say upgrading to 6" at the machine is a lot better, but again, not sure by what standard!

I don't have the HF mine had a 4" Y splitter there's a 6" outlet on housing. I just removed the splitter and ran 6" flex to the cyclone.

The super dust deputy comes with 5" outlets you can use an adapter to go to 6" ducts.

 

[rusty]

Good information, 6" main from D.C. with 4" drop downs with blast gate to each machine.
Was going to also put in an dust devil or equivalent device.

 

[JimD]

DCs move lots of air but not if there is significant resistance. Shop vacs are very different, moving small amounts of air but doing so even when there is significant resistance. So the idea of using larger pipe with a DC to increase airflow is valid. But you do not want to get too big and have the velocity of the air in the duct fall to the point that the dust will not remain suspended to the separator. Six inch is probably not big enough for this to happen but seems pretty large for the HF DC. You will raise the cost significantly relative to 4 inch S&D and all the pieces will probably have to be special ordered. But it still may be a good idea, at least for a trunk line. But with a one man shop and using one tool at a time, the benefit of a 6 inch trunk reducing to 4 inch drops isn't terribly apparent to me. The loss in the system is still the resistance times the distance so the bigger trunk will increase airflow but as soon as you restrict it at the tool, that resistance will drop the airflow throughout the system. Very few tools have more than a 4 inch dust port.

I also struggle with the concept of a really large DC to make sure you get the fine dust. The easiest material to move is the fine dust. But I guess that also makes it the easiest material to escape the DC suction. But if it escapes, it won't be floating around long if you leave the DC on. My little shop is 2688 cubic feet. If a DC moves even 269 cubic feet per minute, it would cycle all the air in 10 minutes. I think the real airflow will be closer to twice that meaning all the air gets filtered in 5 minutes. So if I quit generating for something on the order of 5 minutes, the DC will then filter out any residual dust in about 5 minutes. That doesn't make me think I need a separate air filter. It also seems consistent with the Dylos readings Matthias and others report from their shops.

To me it all comes down to your sensitivity. If you cannot take a slightly elevated dust level for a few minutes, you need a much bigger system than if you are less sensitive. It isn't really a matter of whether your system will remove the fine dust. It will if your filter is fine enough. It is just how quickly will it get it. With a 110V system, some may escape and have to be removed as the DC cycles all the air in the shop. That doesn't seem like a terrible or unacceptable situation to me, but I am not terribly sensitive to wood dust (at least at this point).

 

[Rwe2156]

Do you then change the dust ports on your machines to 6" as well, or is just your ductwork at 6"? I think I read Pentz say upgrading to 6" at the machine is a lot better, but again, not sure by what standard!

I ran the 6" as close to machine as possible, then reduced to 4" from blast gate to machine.

I realize theoretically 6" all the way is better, but 1) I wasn't anxious to get into modifying machines and 2) after using it for several years, it works fine the way it is.

 

[golfdad]

Rusty Im in Archers Lodge area also.. Feel free to drop me a PM . You can come take a look at how mine is set up