Dust Collection Pipe Size

[BKind2Anmls]

I have quite a bit of 4" PVC pipe and fittings. In my current shop, I attempted to use it to set up a dust collection system but had little success.

In my new shop I would like to collect dust efficiently and all that I have read from books and dedicated sights and heard from the forums is that 6" pipe is the way to go and it will improve pickup dramatically. Therefore, I figured I would have to bite the bullet and buy all new 6" stuff.

What I am wondering, however, is that if 6" pipe is the best pipe to install, why don't any woodworking stores offer it? Does anyone have any ideas about this? Especially those members who actually own or work in a woodworking store? It seems that with all the talk about 6" stuff being so hard to find, if it was truly an improvement the stores would add it to their inventory.

Thanks

 

[Herebrooks]

Hi Susan: My experience has been that 4" pipe is sufficient unless you have very long runs(like 25' or more). Perhaps your CFM(cubic feet per minute) is not enough from your dust collector. I have used metal 4" in my first shop and 4" thin walled PVC(Much cheaper) in my second. In my current studio I have two collectors(one on each side of my shop) so I don't have pipe running across the ceiling. I use 4" clear flex pipe with the wire molded into it and ground the wire to the collector so I don't get static shocks. Your probably humid enough in SC so this doesn't happen. I'm in Asheville where it gets pretty dry in the winter.
Not to mention that 6" is very expensive. Duct tape the fittings rather than glue them in case you have to make changes.
Bill

 

[McRabbet]

If your intent is to capture fine dust generated by your larger tools, then you need to have about 800 cfm at the source of the dust. In general, 4" duct is not capable of carrying that flow, so 6" is recommended. The longer the duct runs, the more turns it has the more flex you use and the capacity of your dust collector all impact flow. Here is a section on Duct sizing quoted from Bill Pentz' website that gives you some guidance:

Ducting Diameter affects the amount of airflow just like the size of the pipe and water valve size affects water flow. Unlike a shop vacuum that generates roughly ten times the pressure, air from our blowers will not do a good job of squeezing around obstructions or through small openings. As a result size has everything to do with how much air you can move at a given pressure. We must size our ducting correctly. If made too small it kills our airflow needed for good fine dust collection. If made too large it does not maintain the airspeed in the ducting to avoid plugging and a buildup of dust piles. This makes sense as a garden hose would empty a city water tank far slower than a 6" diameter pipe because the garden hose is too small. We control water flow by opening and closing our faucet, meaning add just one constriction in the line and it can kill our flow. Opening the faucet wide gets you a flow limited by the size of the pipe. Getting a larger central storage tank has little effect unless you put it higher in the air where it can generate more pressure. As with water, getting a bigger blower with more horsepower does little good if the airflow is too restricted by the size of the ducting, tool ports, hoods, and duct openings.

For instance a 1.5 hp dust collector that can move a maximum of 1100 CFM moves far less air than that maximum depending upon what sized ducting we use. This typical small shop dust collector blower only generates 4" to 6" of pressure when working. With the added overhead of our filter and minimum ducting, that pressure is only ample to move about 800 CFM when hooked up with a short piece of 6” flex hose. That pressure will only pull about 550 CFM when connected with 5” flex hose and only about 450 CFM when hooked up with 4" flex hose.

Whether you have a modest 1/2 HP 600 CFM blower to a roaring 5 HP maximum 2300 CFM blower you need to balance the ducting size. We constantly trade off our ducting size to move the right air volume at ample speed with minimum resistance. To get the needed 800 CFM that larger tools need for good fine dust collection through a 4" duct or hose you need about 9,000 FPM that takes a monster impeller and huge motor. That's why knowledgeable woodworkers use 6" ducts and 6" flex right to their larger machines even with portable dust collectors. Without a monster blower, if your duct is smaller than 6" to your larger machines, then it will not move enough air to capture the fine, most unhealthy dust. The best you can hope to do is make your system a little more efficient.

I have used 4" PVC from a small DC and know that it doesn't collect the fine stuff from my tablesaw, even when it is the only device connected. I have a ClearVue Cyclone like the one in the Spring Raffle but it is still only partially installed (a long story filled with procrastination, a shoulder injury and laziness). I bought 10' lengths of 6" Sewer & Drain PVC (ASTM D-2729; white, with bell coupling ends) and associated fittings from a plumbing supply in upstate SC a little over 2 years ago for my replacement ductwork -- it is light in weight, plenty rigid and easy to cut and install. I'll avoid any 90* bends, using two 45* els with a short segment of straight pipe to reduce the drag on airflow. Most fittings can be found at Lowe's, but they only carry the heavier SDR35 (light green; with gasket end or bell end) S&D pipe in most of their stores. It costs double the price of the thinner, white S&D pipe even though both have the same outside diameter, so the fittings work with either. Do not use any Tee's or 90's that you find; use 6" Wyes for branches and paired 45's like I described. I made my own tool ports from plywood and a short section of 6" pipe or 1/2 of a slip coupling glues into the plywood.

You asked why the stores don't carry it? Heavy marketing for the small DC system in the one-car garage means more profit despite lower efficiency. You really need at least 2 HP blower and sub-micron filters to get the best efficiency -- the ClearVue is 5 HP and draws 1,400 CFM.

 

[Travis Porter]

The woodworking stores don't sell it because it isn't something people buy from there very much, and the markup they would have to put on it would make it way overpriced. If you notice, you don't see Cyclones or other larger dust collection systems in the woodworking stores. Basically, you have to order or find a supplier for the pipe and fittings. If you go with metal, you can find the pipe at Lowes or HD, but I would NOT use the fittings (wyes, elbows, etc) as they are too tight of a radius for dust collection. If you go with plastic, for 6" you will need to go to a plumbing supply most likely.

 

[merrill77]

What I am wondering, however, is that if 6" pipe is the best pipe to install, why don't any woodworking stores offer it?

Because most woodworkers who install dust collection systems are interested in keeping the shop clean, rather than keeping their lungs clean. If your purpose is to minimize the mess and cleanup effort while you work, a $200 DC and 4" pipe will do fine.

If your purpose is to remove dust that can be harmful to your lungs, then you need to move at least 800cfm at the tool - and have appropriate dust collection shrouds. To move that much air any significant distance, you need at least 6" ducts and a well designed impeller paired with the proper motor. If you don't want to be replacing expensive filters frequently, then you need a cyclone, too, preferably one that has been proven independently (e.g. ClearVue). If this is your purpose, then you should read the Bill Pentz site - someone else provided a link.

Chris

 

[BKind2Anmls]

Thanks for your responses. I have read Pentz' sight several times. I want dust collection so I don't have to spend two hours cleaning for every two hours sawing. I have a nice Delta air cleaner hanging from the ceiling for the fine stuff so I am interested in Chris' observations that 4" will keep the shop clean.

I may go ahead and try my 4" stuff again since I have the blast gates, Ys, etc and it will be a long time before I could afford to buy any 6". I have a 2 HP Delta that I was going to put outside the shop for noise. However, if I did that my runs would be more than 25'. Maybe I'll try a design that puts it in the center of the shop and make my runs out from it like an octopus. I can probably get away with 4" pipe then. The shop is noisy anyway when a saw is on. Dust collection is my absolute least favorite part of designing a shop but it will be the one I appreciate most once its up and running.

 

[McRabbet]

Susan,

Just remember that any dust that your ceiling air cleaner captures is also getting to your lungs. I always wear a filter-equipped respirator whenever I use my ROS or stationary sander or other fine dust producers. This one is under $18 from Grizzly with OSHA-approved filters (they also have $9 VOC filters for this unit). It is particularly important to add this layer of protection when working with woods that have known toxic or irritant effects like Black Walnut. Sorry to rant, but I met an older woodworker several years ago that died from lung cancer caused by his failure to protect his lungs from Walnut dust for several years.

View image in gallery​

 

[Travis Porter]

Start with what you have and expand out. I believe your 2 HP collector has a 6" inlet. As you have the time and money work from the collector out with 6" pipe. It will make a LOT of difference. I used to have a 2 HP Jet collector and when I did it, the difference was amazing.

 

[Gotcha6]

The Delta air cleaner on the ceiling will be helpful, but many of us have made air filter tables for dust that stay closer to the source. Using an old furnace fan and pleated furnace filters, I made one as a supplemental table/outfeed that has 2 - 20 x 20 filters, 2 fan speeds, and wheels. It really helps about the fines and my plans are to eventually turn it into a sanding downdraft table as well.
Lowe's carries the DWV grade PVC pipe and fittings I used for my DC system. It is thinner wall thickness and thereby less expensive than Schedule 40 which is overkill for DC service. If you use the long sweep bends and combinations it will greatly increase efficiency.
My pet peeve with DC piping is that a lot of the gates & adapters sold by the DC manufacturers don't readily fit the aforementioned pipe sizes.

 

[richlife]

The woodworking stores don't sell it because it isn't something people buy from there very much, and the markup they would have to put on it would make it way overpriced. If you notice, you don't see Cyclones or other larger dust collection systems in the woodworking stores. Basically, you have to order or find a supplier for the pipe and fittings. If you go with metal, you can find the pipe at Lowes or HD, but I would NOT use the fittings (wyes, elbows, etc) as they are too tight of a radius for dust collection. If you go with plastic, for 6" you will need to go to a plumbing supply most likely.

I agree with Travis about the fittings, but I got a steal on elbows at a flea market. To overcome the tight radius, I used two elbows for each 90* turn (45* each ). A little extra work and extra sealing required, but I ended up with all metal main branches and flex only at the tools. Rich