How do I determine sufficient dust suction?

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Forum topic by Elizabeth posted 04-08-2013 11:22 PM 3427 views 0 times favorited 14 replies Add to Favorites Watch
View Elizabeth's profile


817 posts in 3142 days

04-08-2013 11:22 PM

Topic tags/keywords: dust collection question

I have a mix of metal ducting and plastic dust hose in my shop.

I have a Laguna 2HP dust collected with a 6” inlet, and the ducting goes to 4” before running to my bandsaw. The bandsaw is the closest machine to the collector on the system. Here’s a slightly old photo showing the basic setup:

I have also added a wye to the bandsaw connection, with a 2” branch coming off so I can collect dust from directly underneath the table in addition to the back of the machine.

This week I am adding an 18” bandsaw to the system. The two bandsaws will be located next to each other, and I am going to use the same basic ducting run for both bandsaws. I will add a wye which will turn the run into two 4” runs, one for each bandsaw.

Add to this the fact that the 18” bandsaw already has two 4” ports on it – one at the back of the machine and one under the table.

So to recap: one bandsaw has a 4” port and a 2” port, and one bandsaw has two 4” ports.

My question is about whether I can have both machines run off the same blast gate without too much of a loss in suction. I have a choice of attaching the blast gate BEFORE the split, immediately off of the metal ducting on the ceiling, or getting a second blast gate and attaching them somewhere within the plastic ducting runs closer to each machine. I’d rather have just the one gate, for cost and ease of access reasons. The suction of the system seems pretty good, but I don’t know if having the two bandsaws “active” on the dust system at once will have an adverse effect to the efficiency of the system.

Thoughts? Should I just try running one of the bandsaws with a gate to a different tool intentionally left open elsewhere, to simulate the airflow and see what happens?

14 replies so far

View AandCstyle's profile


3052 posts in 2256 days

#1 posted 04-08-2013 11:41 PM

I am not an expert, so FWIW. I would try to get a 6” line to the BSs and have a separate blast gate for each one. The reason is that the new BS has 2 4” ports and your line is only 4”, that means that the BS needs about 24 square inches of air and you are only supplying half that. A 6” line would supply about 27 square inches of air. You may be okay with separate blast gates since BSs generate small light particles (unlike a planer), but in my experience, the dust collection isn’t that great with BS. I wouldn’t even trying the single BG solution. HTH

-- Art

View kdc68's profile


2657 posts in 2276 days

#2 posted 04-08-2013 11:51 PM

Elizabeth...Well I would think you would suffer a lot of suction loss from your 2hp collector if you have 4 ports (3 of them 4”) open at once. If it were me, I’d spend the extra $$ and have a separate gate for each pair of ports to each saw. Close off the dual ports with a blast gate to the saw not in use to take advantage of the CFM from your DC for the saw in use …I’m sure you get better advice from someone familiar with you particular Laguna DC system….

BTW You have an awesome shop setup!!!

-- Measure "at least" twice and cut once

View Manitario's profile


2630 posts in 2882 days

#3 posted 04-09-2013 02:38 AM

I think that you will experience too great of a loss of suction with leaving the the 4 ports open. I have a 5hp dc and I usually only leave 2 ports open at a time…

-- Sometimes the creative process requires foul language. -- Charles Neil

View Elizabeth's profile


817 posts in 3142 days

#4 posted 04-09-2013 04:36 AM

Thanks guys. For now I have dug out my Dust Right hookups from Rockler and will use them to hook up one saw at a time till I can get more gates etc for the system.

View JoeinGa's profile


7736 posts in 2006 days

#5 posted 04-09-2013 11:56 AM

I dont have a DC in my current shop, but I just wanna say that I am amazed at how CLEAN your shop is! What a nice place to work in that must be!

-- Perform A Random Act Of Kindness Today ... Pay It Forward

View Fred Hargis's profile (online now)

Fred Hargis

4986 posts in 2492 days

#6 posted 04-09-2013 12:06 PM

I want to echo the awesome shop comments. But to your question: good DC requires moving huge amounts of air. Now, you have a 4” line going to the BS, which at best will move maybe 400 CFM, then you was thinking of spitting that (~200 CFM per branch) and then that would split again. Get the picture? Bandsaws don’t generate huge amounts of dust, but the dust they do throw is the smaller stuff (harder to capture, requires more CFM). So, go with whatever temporary setup you can, but long term planning should include an upgrade to the duct size to get maximum performance.

-- Our village hasn't lost it's idiot, he was elected to congress.

View Elizabeth's profile


817 posts in 3142 days

#7 posted 04-09-2013 07:20 PM

Thanks guys. I will have one saw at a time on the system, and I spoke with my Woocraft guy (who helped me design the system last year and also sold me the Rikon) just now. He says “I just spoke with Rikon. They recommend about 1000 cfm at the unit. Given that you have a 1600 CFM collector and short runs you should be close. I think the fastest option for you would be to put in a Y and test the saw. Rikon seemed to think you would be ok given the length of run. Let me know how it goes. We could increase the 4” line that you have above the garage door fairly easily.”

View MrRon's profile


4769 posts in 3242 days

#8 posted 04-09-2013 07:46 PM

I would definitely have a blast gate for each machine. Sucking air from two open sources will result in an overall loss of suction. I hear everyone talking about CFM and no mention of “velocity”. Velocity is what will pick up fine dust. If the velocity is not high enough (duct size too large), large particles will settle out of the air stream and could cause a blockage. You need both velocity and CFM; CFM to move large amounts of sawdust and velocity to keep it moving along.

View MrRon's profile


4769 posts in 3242 days

#9 posted 04-12-2013 07:46 PM

I’ll bet your hair stands up on end when you walk under the metal duct from the bandsaw.

View Elizabeth's profile


817 posts in 3142 days

#10 posted 04-12-2013 07:54 PM

Not that I’ve noticed…should walking under it bother me?

By the way, I’ve run the machine and resawn a log; no dust inside the machine afterward, though there was a lot left over on the table. So it looks like the suction will be sufficient for one machine on the 4” line.

View kdc68's profile


2657 posts in 2276 days

#11 posted 04-12-2013 11:01 PM

Elizabeth....Glad to read that you figured out the blast gate senario….Gotta keep that very well set up, organized, and clean shop dust free

-- Measure "at least" twice and cut once

View John Ormsby's profile

John Ormsby

1285 posts in 3736 days

#12 posted 04-12-2013 11:46 PM

A 6” duct system usually needs a 5 hp cyclone or bigger in order to be efficient. You should only use the equivalent of a 6” diameter port configuration for the outlets. 6” to 5” would be the smallest reduction combined.
It is a matter of physics. The type of impeller is also important. Your bends look good.
You most likely would need separate blast gates for the two saws. One would service the 4” 2” setup and the other the two 4” ducts brought into a wye at the gate.

-- Oldworld, Fair Oaks, Ca

View pmayer's profile


1028 posts in 3064 days

#13 posted 04-13-2013 07:51 AM

If you are using a long section of flexible hose currently as a workaround, you might not get the results that you are expecting. Flex hose kills air flow in a dramatic way. I have a 5 HP cyclone (rated at 1800 CFM) that draws 1000-1300 CFM from tools hooked up with a single 6” port (varies depending on static pressure), and 600-800 CFM on my 4” ports. On one 4” port where I was getting 850 CFM, I added a 20’ section of flex hose and measured it at roughly 500 CFM.

So, keep in mind the major penalty for flex. You are still probably better off than you would be leaving several ports open, but you might not be as far ahead as you expect.

-- PaulMayer,

View Kennyl's profile


58 posts in 1861 days

#14 posted 05-20-2013 10:52 AM

First what an impressive shop you have,you may want to consult with oneida or clear vue for the utmost way to get the most from your system.I just skimmed over some comments about blast gates which are important to have at each machine again what a nice looking shop much nicer looking than mine but I am working on it.

-- Kennyl

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