dust collection plenum for multiple machines?

[Dave Burson]

Ok dust collection question- almost finishing up shop and my last station I am putting in is a large multiple table saw (3) and router table station. I planned for this when building shop so ran 6” pvc under the concrete to this area. The three cabinet T-saws are laid out with two bolted together side/side, and one sitting opposite on other side of an outfeed table that’s soon to be built. The router table will be built into outfeed table, and the PVC pipe comes up from ground under the middle of the router table, thus trying to keep any dc piping very low in design. With four machines I am trying to design best way to distribute the air. I remember seeing someone designed a plenum of sorts with a gate on each exhaust port but no experience in this regard.

So 2 questions-
1. Anyone have one or seen one designed that is efficient in both effectiveness and space consciousness? Pictures would be extremely helpful.
2. The DC is already hard wired with several on/off switches throughout the shop, with one being on each table saw. But I am hoping use some sort of auto on blast gate on this plenum. Ideas /input for that?

Appreciate your input. TIA! Dave

[james manutes]

Do you have a powerful enough DC to support 6" ducting w/ multiple machine's ? I wouldn't have had the main trunk come up under a machine . This line must split somewhere , w/sweeping elbow's , wye's , and automated blast gates , which will eat up some space . I don't think a box or plenum is the way to go , just for the resistance . three wye's in a row is a "manifold" that could work . I'd start on my bench with some fittings and see what that tells you . We all know to use as little Flex as possible . Just dive in and see. I was surprised the cubic ft. that was taken up by the ducting itself , especially the corners , drops , etc.

[Marc Fenneuff]

A shop-made plenum on the suction side of the blower is going to impose a huge penalty on airflow. I'd see if you could find (or have fabricated) a "3-legged" "Pants Wye" with a blast gate on each leg. That would keep the overall size potentially small enough to work behind/beside your 3 saws. Use a regular Wye for the router table.

[John Lanciani]

Take a look here; https://sawmillcreek.org/showthread.php?139804-Dust-collection-install&highlight= There a couple of pics of the plenum I built.

[Andy D Jones]

I would be concerned that the air velocity in a plenum could drop below that which maintains the sawdust in suspension. Since your DC pipe is below the floor, however, you could make the bottom of the plenum tapered/sloped so that even if dust falls out of the airflow, it can continue downhill along the bottom of the plenum to the DC pipe at the bottom.

However, the fact that airflow is going to slow down in the plenum, then speed up again in the pipe, means a significant pressure drop across the plenum will occur, reducing overall airflow. Whether this is a problem depends on the rest of the ducting, and how big a blower is on your DC.

-- Andy - Arlington TX

[Jim Becker]

Wyes and individual blast gates would be how I'd handle this situation...it may be tricky doing that, however, if the duct back to the DC is coming up out of the floor in the middle of the machines that are all ganged together. Operating the blast gates may be tricky, too!

[Dave Burson]

Take a look here; https://sawmillcreek.org/showthread.php?139804-Dust-collection-install&highlight= There a couple of pics of the plenum I built.


Thanks John, those look great. I see you have the 3hp Oneida, did you notice any noticeable loss/efficiency in using this? I have the Oneida 2HP, and am considering upgradin to something bigger, maybe one with the smart boost to give it all the "juice" needed , but... hoping to put that off to see what I get out of what I use.

[Jim Becker]

I have the older Oneida 2hp (7" inlet) and it performs very well for single machine use. I've gotten away with acceptable performance for quick jobs on other tools when my CNC is running, too, although that's clearly not the best idea for anything requiring more intensive collection. So I'll say that your idea to consider one of the newer, higher air flow and/or smart units isn't a horrible idea at all if you can fund it.

[Terry Therneau]

I did exactly that with a pod of tools, and it worked very well. 5" of rise on average (I scribed to a sloped bit of floor), 2x6 covered with 3/4 ply. I'm taller, and like my table saw up a bit more so was very happy with the dimensions. There was a Unisaw, Atlas table saw, Delta HD shaper, and a router table. Each serviced by a closable opening into the plenum. 6" pipe came down from the ceiling along side a post (which is, unfortunately, dead center in the shop and structurally critical) and into the plenum. (The Atlas to the right of the Uni, sharing a common fence, acted as right side support. Shaper behind the Uni acted as outfeed. Router table filled 1/2 of the fourth quarter of the square.)

This was sealed fairly carefully to the floor. Basic conservation of mass dictates that if there is one 6" pipe coming in, and only one 6" gate open to a machine, and no leaks, that air in must equal air out. I saw no loss in suction. I took it down a few months ago in a "new machine, completely rearrange the shop" exercise, and the inside of the plenum was sawdust and air tunnels. Most of the 6 year's production must have gone on to the collector, however; because I still filled up the bin regularly.

I have seen this argument that a plenum will lose suction multiple times, and I've never understood how an empty box can violate physics. If there are leaks then all bets are off, of course.
Terry

[Marc Fenneuff]

You’re talking about mass but the discussion with DC is about static pressure loss. 50’ of straight round duct directly off the impeller will have a lower flow than at the collector due to the friction of the air moving in the duct. Just a 90* elbow imparts the equivalent of many feet of straight duct. All transitions are supposed to be as gentle as possible to maintain CFM and a plenum with a bunch of corners violates that guideline.

[james manutes]

The way it was explained to me , a box or plenum can introduce turbulence in the box , much like snow swirling around as it comes off the back of a semi- trailer . Not much , but adds to the total the DC must overcome .

[John Lanciani]

Thanks John, those look great. I see you have the 3hp Oneida, did you notice any noticeable loss/efficiency in using this? I have the Oneida 2HP, and am considering upgradin to something bigger, maybe one with the smart boost to give it all the "juice" needed , but... hoping to put that off to see what I get out of what I use.

The pics show v2 of my plenum setup and it works quite well; v1 was much more crudely designed with the gates being vertical instead of set at 45 deg. I don’t get any accumulation of dust or chips in the plenum and with the 3hp collector I get plenty of volume at the tools to pick up all of the dust.

[Terry Therneau]

Yes, I was guilty of ignoring turbulence, and will stand corrected in that regard. Any transition from round to square, square to round, sharp corner, etc. adds to that. In my case the plenum is 5.5" x 6' x 5.5', so it was a bit more like a stream into a big lake, then out the other side. The corners and edges are far enough away not to matter as much. The big advantage was convenience and a little more height for my machines. Behind the scenes is an older 5HP Oneida cyclone with 6" ducting (used, from a retired business) so I could afford some inefficiency. The 16" planer uses it all though (and fills the bin in a heartbeat!)

[Marc Fenneuff]

Behind the scenes is an older 5HP Oneida cyclone with 6" ducting (used, from a retired business) so I could afford some inefficiency.

Yes! We all have a CFM budget to work with, a bigger engine gives you a bigger budget.

[Dave Burson]

I have the older Oneida 2hp (7" inlet) and it performs very well for single machine use. I've gotten away with acceptable performance for quick jobs on other tools when my CNC is running, too, although that's clearly not the best idea for anything requiring more intensive collection. So I'll say that your idea to consider one of the newer, higher air flow and/or smart units isn't a horrible idea at all if you can fund it.

TY Jim! I agree about the 2hp. Just hoping for a little more boost out of it so as toy be able to suck both sides of the TS, and the router, and ... works ok but not enough juice to power anything with any significant loss or inefficiencies, like a plenum either I'm guessing.

[Jim Becker]

TY Jim! I agree about the 2hp. Just hoping for a little more boost out of it so as toy be able to suck both sides of the TS, and the router, and ... works ok but not enough juice to power anything with any significant loss or inefficiencies, like a plenum either I'm guessing.

Indeed. But also keep in mind that DCs don't "suck" so much; rather than move large volumes of air at a given speed and that's what moves the material...air flow. Pressure is low compared to a vacuum like a shop vac or what you use in your home for floors. The more air a DC can move, the better the performance for dust collection. Duct size and design is very much in play around that, too, because bends and hose add fictional loss that inhibit air flow.

[Michael W. Clark]

If you are trying to connect multiple machines together, the design of the connection and the ducting needs to be such that your velocity in the system is sufficient to keep the material suspended, not dropping out. This will depend on your collector and how many points are operating at a time. If only one machine, then put a gate on each branch and use wyes to connect them of the same diameter.

The pressure loss in a plenum depends on a lot of things such as acceleration losses and how your branch connections are connected to it. A wye would be less loss than a branch stabbed into a flat side for example.

The main thing is don't let material collect in the ducting or plenum. If you cut through a nail, it makes a spark and it will drop out in the plenum. It could catch any dust in there on fire. If this is between machines and hard to get to, could make for a challenging situation.

[Tom Bender]

Hi Dave
How many dust ports are you wanting to connect? 3 saws and a router + how many overhead collection points. How many of those will you run at the same time?

It's going to be tricky to get enough good fittings and blast gates into the space under the saws.

Blast gates might be operated mechanical with rods and levers or with cables.

A way to clean out the ducts might be helpful. Maybe a cap you could pull off.