Quick Dust Collection Question

[Josh Baldwin]

Hey guys so I think I know the answer to this, but I figured you guys would know better than me.

I'll be setting up my new garage shop in a few weeks or so. I'm running a ClearVue 1800 with 6" ducting across the ceiling dropping down to each tool. For most of the tools with 4" ports I'll just be dropping the 6" down to a 4" and then using a 4" iVac automated blast gate and then 4" flex hose connected to the tools.

Now for the SawStop I'm going to bring the 6" down and then split it into a 2" for the overarm blade guard port and a 4" for the cabinet port. Do I really need to split this from a 6" or can I taper it down to a 4" and then split it to the 2" and 4"? The reason I ask is because the damn iVac 6" blast gate is $250 vs $100 for the 4" blast gate. Will this make a big difference?

One bonus question that I'm trying to figure out as well:

How small should I be willing to go before I should just use my Bosch Dust Extractor? So for let's say my Ridgid Oscilating Sander which has a 2.5" opening. I'm assuming that would starve the dust collector and not be smart. Is that correct? Is it totally fine for all of my 4" tools?

As always any help is greatly appreciated.

[John Lanciani]

Split the 2" off before a 4" blast gate and just leave it open. With a dust collector that big you need the volume anyways as a single 4" open isn't enough flow.

[David Walser]

Josh -- WRT your last question, use your Bosch Dust Extractor for your smaller tools. A shop vacuum, like your Bosch, uses suction, not air flow, to capture dust. A dust collector, like your ClearVue 1800, uses air flow, not suction, to capture dust. (Yes, there is an obvious relationship between 'suction' and 'air flow'. For the sake of this discussion, let's assume they were completely unrelated things.) With a small port, such as those found on powered hand tools, such as a track saw or random orbital sander, the port is just too small to move a large volume of air. Thus, a vacuum works best with small ports and a DC works best with large ports. Your Ridgid Oscillating Sander falls in a grey area where either a DC or vacuum might work. In my experience with the Ridgid Oscillating Sander, my vacuum works better than my DC. But then, I'm using a rather large shop vac (lots of vacuum) and an underpowered DC at the end of a long run of duct. YMMV.

WRT your other questions, you may want to give us more information. A lot depends on the length of your duct runs and how many branches and drops you will have. Still, I will point out that by using a blast gate at the end of each drop, just before the flex duct, a lot of your ClearVue's capacity will be consumed in maintaining low pressure in all those unused duct runs. For this reason, your system will be more efficient the closer to the DC you put your blast gates. Your machine may have plenty of capacity and the location of blast gates is a non-issue in your situation. It's NOT a non-issue in most situations.

[Jim Becker]

I see no harm to the 6" drop to the table saw/overarm location and the 6/4/3 split. (You will likely need to use a 6/4/3 wye and adapt the hose for the overarm accordingly...at least I did when I set similar up years ago) A gate on the over-arm branch is certainly optional and it could be left open as John mentions, but honestly, I would not (and did not) do that because of noise, despite the real fact that it can makeup for other 4" drops in the system. If time allowed, I'd honestly work on getting larger ports on tools so that the drops didn't have to be restricted, with the intermediate solution of keeping the drops large until right before the gate and connecting hose.

[David L Morse]

...I will point out that by using a blast gate at the end of each drop, just before the flex duct, a lot of your ClearVue's capacity will be consumed in maintaining low pressure in all those unused duct runs. For this reason, your system will be more efficient the closer to the DC you put your blast gates...

I don't understand "capacity will be consumed". If there are no significant leaks, and thus no air flow, exactly what "capacity" is being consumed?

[Jim Becker]

I agree with you....closed branches have no real effect on performance. Only the open gate(s) have material effect.

[Robert Engel]

Sounds like an excellent system.

+1 on using dust extractor for hand tools and sanders.

[Josh Baldwin]

I see no harm to the 6" drop to the table saw/overarm location and the 6/4/3 split. (You will likely need to use a 6/4/3 wye and adapt the hose for the overarm accordingly...at least I did when I set similar up years ago) A gate on the over-arm branch is certainly optional and it could be left open as John mentions, but honestly, I would not (and did not) do that because of noise, despite the real fact that it can makeup for other 4" drops in the system. If time allowed, I'd honestly work on getting larger ports on tools so that the drops didn't have to be restricted, with the intermediate solution of keeping the drops large until right before the gate and connecting hose.

Hey Jim thanks for the input as always. So you said the 6/4/3 split would be ok, but what about 6 to a 4 and then a blast gate and then the 3/4 split off? Would this be worse than the blast gate at the 6 and then the 6/4/3 split? Also, regarding getting larger ports on tools. I'm not sure how to go about that. How would I do that on a Dewalt planer or router box that have 4" ports? Thanks.

[Josh Baldwin]

Split the 2" off before a 4" blast gate and just leave it open. With a dust collector that big you need the volume anyways as a single 4" open isn't enough flow.

Thanks for the reply John, that's a good point. I'll have to think about the noise Jim mentioned and see if that makes sense for this setup.

[Josh Baldwin]

Josh -- WRT your last question, use your Bosch Dust Extractor for your smaller tools. A shop vacuum, like your Bosch, uses suction, not air flow, to capture dust. A dust collector, like your ClearVue 1800, uses air flow, not suction, to capture dust. (Yes, there is an obvious relationship between 'suction' and 'air flow'. For the sake of this discussion, let's assume they were completely unrelated things.) With a small port, such as those found on powered hand tools, such as a track saw or random orbital sander, the port is just too small to move a large volume of air. Thus, a vacuum works best with small ports and a DC works best with large ports. Your Ridgid Oscillating Sander falls in a grey area where either a DC or vacuum might work. In my experience with the Ridgid Oscillating Sander, my vacuum works better than my DC. But then, I'm using a rather large shop vac (lots of vacuum) and an underpowered DC at the end of a long run of duct. YMMV.

WRT your other questions, you may want to give us more information. A lot depends on the length of your duct runs and how many branches and drops you will have. Still, I will point out that by using a blast gate at the end of each drop, just before the flex duct, a lot of your ClearVue's capacity will be consumed in maintaining low pressure in all those unused duct runs. For this reason, your system will be more efficient the closer to the DC you put your blast gates. Your machine may have plenty of capacity and the location of blast gates is a non-issue in your situation. It's NOT a non-issue in most situations.

Hey David thanks for the all the info. Yea it's mainly the tools like the Ridgid Oscillating Sander that I wasn't sure about. Sounds like the vacuum might be the smarter option and also cheaper/easier to setup. I'll probably have about 7 drops and my plan was to put the blast gate pretty high up, maybe 8 feet off the ground with 12 foot ceilings. At least that's what I was thinking, but now some people are saying to keep the 6" as long as possible and as close to each machine as possible before tapering down to the 4" blast gate/flex hose. A lot to think about, my brain is going to explode! Haha

[Jim Becker]

Hey Jim thanks for the input as always. So you said the 6/4/3 split would be ok, but what about 6 to a 4 and then a blast gate and then the 3/4 split off? Would this be worse than the blast gate at the 6 and then the 6/4/3 split? Also, regarding getting larger ports on tools. I'm not sure how to go about that. How would I do that on a Dewalt planer or router box that have 4" ports? Thanks.

I would not split off after you're already at 4". You'd be wasting the benefits of the 6" drop significantly.

[David Walser]

When I was designing my system, I discussed my plans with the good folks at the Blast Gate Company. (Great company to deal with, by the way.) My original designs had the blast gates at the end of each drop, just before the flex duct running to each machine. I was told I would get better performance if I moved the blast gates closer to the DC. The explanation provided was the one I gave earlier.

Think of it this way: Sometimes we may think if a 4" duct is better than a 2.5" pipe, a 5" duct must be better still. And, if a 5" duct is better, an 8" duct must be better yet. Of course, this isn't (always) true. It's not just the volume of air that matters. Velocity also matters. The DC's that most hobbyist woodworkers have simply cannot effectively use an 8" duct effectively. There were be plenty of CFM, but the air will move too slowly to pick up the dust and chips in that large a space. Similarly, if the impeller were blowing out the window of a small closet, you could detect a small breeze from the air being drawn through the closet and out the window. On the other hand, if the impeller were blowing out the upper window of a high school gym, you wouldn't feel a thing. Bottom line: All those drops and branches increase the 'size of the duct' or 'size of the room' through which the impeller is pulling the air.

Again, I've not run any experiments myself nor have I any real world data. I'm basing these comments on a source I believe to be reliable. And, I'll add, the comments are consistent with what I've read, including here on Sawmill Creek.

PS: Sorry for the delay in replying. I started to reply and forgot to hit "post". My bad.

[Jim Becker]

David, that's a good point. My gates are actually up higher and closer to the "main" in my shop. The one for my drum sander is actually at the ceiling height, but fortunately operable with my long fingers.

[Michael W. Clark]

Be careful with 6" drops and a lot of 4" ducting going to the machine. For a 6", you need about 800 CFM to keep 4000 FPM velocity. (I would think you want 4-5K FPM velocity for most hobby systems). To get 800 CFM in the 6", you have to pull it through the 4", so that velocity would be ~9200 FPM so the losses would be extremely high. If you just have a short transition from 4-6", that's probably OK as you get some static pressure regain in the transition. It may be best to have another 4" gate open so you have 2 at a time open or have a bleed on those lines.

As for blast gate location, I can only think of 2 reasons to put them closer to the collector. First, the less duct you have under negative pressure (the duct between the gate and your collector) the less duct there is to leak and reduce flow at the source you are collecting from. If all your duct is done properly, then this is a non-issue. The other reason to locate gates high is to keep them away from operators. In an industrial system where all branches are operated at the same time, the blast gates are used to balance the airflow between branches and they are locked in position with the set screw. If they are located low, then operators will move them and get the system out of balance. We locate them in the ceiling so they are not as easy to access.

If you have auto gates, put them where it makes most sense for your installation. If doing manual gates and only operating one tool at a time, put them where they are not a trip hazard (the blades are sharp!) and you can easily access them. Installing them with the blade horizontal makes them stay open/close without using the thumb screw. The negative pressure from the system should pull the gate blade up tight to the housing to minimize leakage.

When talking system performance, flow and pressure are coupled together, you can't separate them. The difference in pressure causes the CFM to flow. The amount of CFM, and pressure required to flow this CFM, determines fan HP for a given fan type. This is all inter-related. Sure CFM is needed to collect the material, but if you don't have the fan HP to deliver the SP to cause this CFM to move into the hood and carry the dust to the collector, then you don't get the collection you wanted at the source or the material doesn't make it to the collector.

I assume you have a 5HP Clearvue so HP is probably not your concern. I would make sure you have plenty of open area so you don't starve it or have material settling in the duct.

[John C Bush]

Hi Josh,
For my SS I have 6" ceiling mounted duct reduced to 4" for an autogate then a 4 x 4 wye for a flex hose drop to the saw base and the other to the Shark Guard mounted on the riving knife. I had a 2 1/2" drop initially and it didn't pull much dust so I changed to 4" and added a gate at the guard. I remove the Guard and hang it on a bungy and close the gate when in the way for narrow rips. I find I dodn't use the overblade guard much--just when doing a lot of ripping.