3" or 4" pipe for dust collection

[Kasey Miller]

Hey everyone I know there is already a lot of discussion on this topic already but I'm having trouble deciding if there will be a big difference between using 3" or 4" pipe for my dc. I currently have a 1 1/2 hp dc. I am going to discharge everything outside. I know with the bigger pipe I will have more volume of air to travel through the pipe. But am I going to see a big difference between the two different sizes. Also I am just doing woodworking stuff whenever I get free time so I am not out woodworking 8 hrs a day or anything. Just looking for advice and people's opinions. Thanks

[David Kumm]

4" minimum, 5" might even be better. Dust collectors need larger pipe, shop vacs smaller. Dave

[Ole Anderson]

Here, bigger is definitely better.

[Steve Peterson]

It really depends on what you are attaching to the DC. You could start with the duct size of your machines. My 6" jointer has a 4" port. My lunchbox planer has a 4" port with a 2.5" adapter, so they obviously thought that some people would be hooking it up to a shop vac. My tabletop sanders have 2.5" ports, but would be better if I expanded them to 4" ports. I use a 6" port when I am sanding at the lathe. I use two 4" pipes to my bandsaw and connect it to a 6" trunk.

Flex hose most commonly comes in 2.5", 4", and 6" sizes. Each one is approx. twice the cross section of the next size. 4" pipe has about 1.75X the cross section as 3" pipe. I think you would be much happier with the extra airflow with 4" pipe.

Steve

[James Gunning]

Go with larger pipe. The amount of air that can flow through a pipe when using a dust collector (note: not a shop vac or similar) is pretty much related to the cross section of that pipe. For example, a 3" pipe has 7.065 square inches of cross section, a 4" pipe has 12.56 square inches of cross section, and a 6" pipe has 28.26 square inches. As you can see there is a significant increase in sectional area with a much smaller increase in diameter.

I used to use 4" pipe and went to 6". There was a dramatic, very noticeable increase in the amount of air my DC flows. The other big factor is the type of pipe. Smooth is much better than flex, and minimize the bends and restrictions. I also refitted my machines with 6" ports (or used multiple smaller ports feeding into the 6") so there was not a restriction to the airflow right at the source.

[Kasey Miller]

Does the suction lessen with the larger pipe or does it increase it more since there is more airflow. Also can you run to much pipe for it were it will lessen the suction. Thanks again for everyone's responses

[John Donhowe]

Okay, Kasey, let me thrown in my .02. First, don't get hung up about the suction. DC's are designed to create a lot of airflow, since that is ultimately what's needed to pick up dust. Static pressure (vacuum, or the "suction" I think you refer to) is relatively low, and to my knowledge is measured in a closed DC system (air intake is completely blocked). By contrast, a shop vac can produce high static pressure (suction), but at low airflow. DC's are best for large tools (table saws, jointers, planers; shop vacs better for small, hand held tools: routers, sanders.

Air speed (feet per minute) is sometimes perceived as "suction", and not to be confused with air flow (cubic feet per minute). A given air flow passing through a smaller pipe will have a higher air speed. However, smaller pipes have a lot more resistance to air flow than larger pipes- just as it's harder to sip through a skinny straw than through a wide bubble tea sized straw. Also, the longer the pipe, regardless of size, the greater the resistance, and lower the airflow. As long as the air speed is sufficient to keep dust particles moving within the pipe, the loss of air flow by going to smaller pipe is not worth the performance cost. So, go with the larger pipe.

If for some application you're finding that air speed (perceived suction) is too small, you can add a reducing adapter (say 4" to 3" or 2-1/2") at the collection end of the pipe/hose to increase air speed to help with dust pick up, without paying the performance penalty of having narrow pipe the whole run.

[Kent A Bathurst]

Kasey -

Let me ask a couple very simple questions:

What is the pipe diameter on your DC infeed flow? Outfeed flow?

Is there a reason you don't want to continue those designed diameters?

[Kasey Miller]

My dc is a 1/2 hp with 6" inlet and 4" outlet. Thw impeller is 11" to 12" not sure if that matters or not. I really don't want to use 6" pipe due to the expense of the pipe. Thanks again guys very helpful info.

[Roger Feeley]

I have a central DC and used 4" plastic pipe throughout. I will be moving soon and will take the pipe with me but I plan to run a main 5" pipe down the center of the shop and branch off with the 4" to individual machines. I will use flexible hose for the final 4' or so to each machine and then reduce as needed at the very end.

[Bud Millis]

Kasey,

When I had my HF dust collector setup I used 5" from the planer and jointer to the DC. Planing wider pine boards or boards with big shavings would clog up the pipe. I would go with at least 6" dia. You can reduce/enlarge the pipe - I did that on the jointer from 4" to 5".

[Kasey Miller]

Thanks everyone for your opinions and how you did your shop. I think I am going to go with the 4".

[paul cottingham]

Do the math sometime. Calculate the area of a 3" circle. Then calculate the area of a 4" circle. That is the difference in the amount of air you can pull through. Air flow is king.

[Mike Chalmers]

Kasey,

When I had my HF dust collector setup I used 5" from the planer and jointer to the DC. Planing wider pine boards or boards with big shavings would clog up the pipe. I would go with at least 6" dia. You can reduce/enlarge the pipe - I did that on the jointer from 4" to 5".

Wow. I can't imagine how that would happen. I had a similar set up with 5" from my 20" planer and never saw anything that would be remotely similar to a clog. Was the wood wet?

[Larry Frank]

Reading some of the posts makes me wonder a bit. While everyone seems to think that going to larger pipe is the answer, it is not always correct. Going to a larger pipe makes sense if you have a large enough dust collector. You need a minimum air speed to move dust and chips. If you fall below that speed, you can get clogs. Bill Pentz has a great website that covers this issue. He also has some real world test results concerning the HF dust collect.

A 5 or 6" pipe needs a dust collector with sufficient capacity to maintain air flow speeds.