Question for you Dust collector duct gurus

[Paul Johnstone]

I'm running 6" ductwork from my collector. It's a Clearview cyclone.

I am going to branch the ductwork on a Y at the tablesaw.

On my table saw, I am going to have a blade guard dust collector (excalibar). The hose on the blade guard starts at 4" and eventually reduces to 3".

I was going to run a duct to the bottom of the saw (the other branch of the Y).

I was thinking about running 6" duct to the bottom of the saw and using a blast gate at the Y to reduce the flow so that air goes into the blade guard. The benefit of this setup is that when I'm not using the blade guard (like dado blade) , I can open the restricting blast gate and get a full flow to the bottom of the saw.

My concern though is that when I am using the blade guard, will the 6" duct be too wide? My intuition says I'll take a performance hit but is it even worth worrying about?

[Harold Beck]

Bill Pentz' site gives some ideas for dust collection at various types of components. For a table saw he recommends a 3.5" to the top and a 5" to the bottom collection point.

Hope that helps,

HB

[Jim O'Dell]

Paul, I've got the Clear Vue also, and I have piped in a 4-6-6 wye on the down tube from the ceiling down to the TS. I branched mine off at the ceiling level, so the 4" goes parallel, with another 45 degree ell, at about 5' off the floor level. I'll pipe this to the future overhead guard. My belief is that even with both open, there is only so much that is going to go through the 6" pipe leading to all of this. Certainly a blast gate would allow you to control the flow, just so you don't over work the motor. Everyone says to get a clamp on volt meter to monitor the consumption of the motor. I'll be doing that when I get the interior finished up in the shop. Having a blast gate on both lines to the TS would be a good idea. Jim

[glenn bradley]

I use the gate to my below saw duct to adjust the flow. This gives me a variable amount of flow at the blade guard (both feeds are gated but the guard is generally full off or on). This has been working well.

[Bob Spare]

I use the gate to my below saw duct to adjust the flow. This gives me a variable amount of flow at the blade guard (both feeds are gated but the guard is generally full off or on). This has been working well.

Have the ClearVue, (not installed yet) given advise on another forum use blast gates above and below and adjust the gates to your wishes. Made sense to me.

[Jim Becker]

Bill Pentz' site gives some ideas for dust collection at various types of components. For a table saw he recommends a 3.5" to the top and a 5" to the bottom collection point.

This is how mine is set up, relatively speaking, and it works well. The idea is to balance the air "availablity" with the capacity of the duct for that air.

[Bob Dodge]

Paul,

Whenever you operate both legs of a wye, the static-pressure in both branches will balance automatically. For example, a 6x4x4 wye pulling a total 800 CFM, will draw 400 CFM through each leg. When you use a 6x6x4 wye, the 6" branch has to pull a LOT more air because resistance is much lower. The suction-pressure in the 4" branch will drop. With 800 total CFM at the drop, your ratio may be somewhere around 675 CFM at the base, and 125 CFM at the overarm(rough example). With a 6x4x4 configuration, you'll re-balance that suction, and you'll flow perhaps 550 CFM at the base, and 250 CFM at the overarm guard. Again, those figures are NOT for your specific dc, but merely an example of what happens.

Using a blast-gate to control the flow at the base is fine, "if" you are only looking at "clean" airflow, however, with dirty air, you want to be sure that you're not choking it down to the point where you'll get velocity issues in the 6" riser. For example, let's assume you're choking that 6" base-branch to 600 CFM. Your velocity in the 6" riser(between base and the wye), will be 3057 FPM. You want 4000 FPM, minimum.

Now, you have a fairly strong dc on your hands, and you'll flow a lot more air than the example I gave you, but, you still don't want to go overboard on the sizing of your base branch. Does your saw have a dust-ramp?

When I bought my UniSaw, I assumed I'd get rid of the included 4" hood that came with the saw and upgrade to a 5" hood. My saws' cabinet has a rear port, measuring roughly 7.5" x 3.5". The 4" hood that came with the saw, is a flared hood, roughly 8" wide, by 4" tall, with a 4" port. I tried that hood since I already had it on hand. I immediately ditched the idea of going with a larger hood. The saw was spotless inside. There simply was no need to go to a larger hood. The dc I use is a small industrial 2 HP single-stage from Pyradia/Belfab, with 12.5" impeller.

My recommendation to you is, try your present hood to see if you're getting satisfactory results. If you have to up-grade for any reason, do not go with more than a 5" hood, or your overarm-guards' suction will suffer.

Bob

[Bob Dodge]

One more point Paul,

Increasing the airflow at the base when you're not using the overarm guard, is redundant. You're obviously going to set-up your pipes in such a way that you'll be getting all the dc you want at the base, even when you use the overarm. There's simply no reason to increase that airflow, when you close-off the oa-bc. Simply closing it off, will already give you more suction at the base anyway.

Bob

[Paul Johnstone]

Thanks for everyone's input and explanations.. I think based on this advice, I will follow Bill's recommendation and use 5" on the bottom.
Thanks for the explanation Bob of the reasoning behind this.

I was trying to be cheap and avoid buying 5" ductwork, but it won't be that bad, as I'll only need 10' or so.

Unfortunately, I have a contractor's saw, so DC doesn't work too well with my old setup. I'm going to make some more mods to it, in hopes of improving things.