Dividing a 6" duct in 4

J

Jonathan

New member
Hey all,

I am going to try a different style of dust collection for my compound miter saw. I mostly see people building hoods around the saw with a dust pick-up behind the blade and a larger one for the hood. I want to try doing more collection at the source, by placing a collection point behind the blade, another under the blade, and a small rectangular hood/scoop on each side of the blade. That's a total of four pick-ups that I need to split off from a single 6" main. My question is what diameter should I use? 2", 3", or 3.5"? I'm assuming I'll use a 6/4/4 wye for the initial division, and then further reduce each 4" line. Each time I divide the line and add more flex hose, I'm assuming I'm increasing resistance quite a bit, so I'm guessing that I need four 3" hoses mated up to the 6" main.

Thanks,

Jonathan
 
Well one way to tackle the problem is to calculate the area of a 6 inch pipe, which is 28.27 inches. As long as your total cross sectional area remains at or below 28.27 square inches you should be okay. You can search MarkFerraro posts on this very issue. I cannot seem to find the post, but I posed the question of how much air return did I have to allow for my sound closet and got some outstanding help from Baba Brown and McRabbet. This new version of the forum is hard for me to use or find things.
 
Thank you for your contributions to the ClearVue Forums. Is this the post you were referring to?
http://www.clearvuecyclones.com/for...01-sound-isolation-closet-return-air-question

We're sorry to hear that the new forum layout has been an adjustment. The upper search box will only search the current forum you are in by default. If you wish to search all forums, click on the Forums tab or the Home breadcrumb and then enter your search criteria.

CVCSupport
 
Jonathan,

I agree with MarkFerraro but wish to add that by my way of thinking keeping the total cross sectional of all 4 branches around that of 6” pipe (28.27 square inches) is important. Reducing the total cross sectional area of all four mitre drops much below 28.27 square inches could reduce air velocity in the dust collection pipe back to the cyclone. I agree that four 3”-diameter pipe to the mitre saw is the right size. My reasoning is as follows...

Reducing the 6” to a pair of 4” pipes reduces the 28.27 square inches cross sectional area to 25.12 square inches. The 25.12 square inches now becomes the target, since the 6” x 4” x 4” wye reduction cannot be recovered.

Branching each 4” pipe (cross sectional area = 12.56 square inches) into a pair of pipes means each pipe coming out of the 4” pipe would need a cross sectional area of 6.28 square inches. This cross sectional area suggests a pair of hoses from a single 4 inch pipe would have a diameter of 2.8”. Therefore, choosing four pipes to the mitre saw each with a diameter of 3” is about right.

The way in which the 6” pipe to a pair of 4” pipes reduction is made can drastically affect air flow. Making the transition from 6” to a pair 4” pipes using a fitting like the Woodstock T23830 - 6" x 4" D/C Adapter from Grizzly Tools would go a long way in preserving air flow. This style of wye fitting has the pair of 4” nipples molded directly into the 6” leg. A 6” x 4” x 4” wye followed by a 4” x 4” x 4” wye fitting would reduce air flow to that of a single 4” pipe, less than half of that otherwise available from a single 6” port, potentially significantly reducing velocity in the main 6” trunk to the cyclone. The same reasoning applies to the 4” reduction to the pair of 3” pipes.
 
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