My outside-exhausting DC w/ baffle

[Dan Friedrichs]

I just finished setting my DC up to exhaust outside, so here's some pics.

Inside the grarag...*cough*cough* shop, there's 6" ASTM 2729 pipe to each tool. The pipe was just fitted together, and screwed through the fittings (no glue), so I can take it apart and re-arrange later (if wanted).

The main line goes through the "floor" into the crawlspace below the house. There, it's sucked into a 2HP Griz collector. I modified it by adding a Thien baffle below the existing input port, and by mounting a 6" piece of PVC to the top "outlet" (where the top bag would usually sit).

From there, the exhaust runs through another piece of 6" PVC to the wall of the crawlspace, where it goes through the wall, and vents outside the house.

I had to use 90* fittings on the exhaust because there wasn't room for 2 45*'s.

The Thien baffle is excellent. If you look at the last pic (showing the outlet on the side of the house), you'll see there's no dust on the rocks below (well, there's a little, but it's from sawing the 6" hole!). It all stays in the bag.

I'm going to replace the bottom bag with a plastic one, just so I don't end up with a fine layer of dust on everything in the crawlspace.

I'm also going to re-arrange the connections on the DC so that it hits the baffle/bag BEFORE the impeller, just incase I suck up any nails.

[Bruce Page]

Won't you be pushing all your heat outside come winter time?

[David Christopher]

Dan, thats pretty slick....I have the same DC..mine sits behind the shop. I took off everything and dump strait into a fox wire basket about 4 ft square....no bag no filter no seperater...6" from DC output to wire basket

[Dan Friedrichs]

Won't you be pushing all your heat outside come winter time?


Yeah, but my garage isn't heated, so I'm OK with it. My schedule rarely leaves me much time for woodworking during the winter months, anyways.

[Matt Benton]

Dan,

Unless you've done it somewhere else, you may want to put some wire mesh over the outlet to prevent small critters from getting into the DC...

[Ed Garrett]

Dan,

I'm pursuing a similar setup. How loud is the air blasting out of the exhaust port???

Sincerely,
Ed Garrett
Tallahassee

[Dan Friedrichs]

I'm pursuing a similar setup. How loud is the air blasting out of the exhaust port???


Good question. I have a neighbor whose backyard is about 20' from the exhaust port, so I was concerned about that. I'd estimate that it is maybe 1/2 as loud as a shop vac, or maybe 4x as loud as a dryer vent. It's definitely noticable, but I don't think it's loud enough that anyone would complain.

One thing you might consider is using something other than PVC for the exhaust piping. If you could find some of that flexible, insulated tubing they use to pipe HVAC around, I think that would be ideal. It's insulated, which might help deaden some of the noise, and it's flexible, so you could coil it a little before routing it outside, which would definitely deaden a good deal of the noise. The more the air as to turn corners, the less loud it will be.

[Jim Kountz]

So you have to crawl under the shop to empty the bag? Hows that working for ya?

[Myk Rian]

So you have to crawl under the shop to empty the bag? Hows that working for ya?
That's what I was wondering. I would rather duct the whole thing straight off the fan to the outside, and into a catch box. Just bypass the bags entirely.

The more twists, turns, etc. in a duct, the more noise will be generated by the turbulence. A smooth, straight duct is the most silent. I have 35 years experience on that matter.

[Mark Norman]

That's what I was wondering. I would rather duct the whole thing straight off the fan to the outside, and into a catch box. Just bypass the bags entirely.

The more twists, turns, etc. in a duct, the more noise will be generated by the turbulence. A smooth, straight duct is the most silent. I have 35 years experience on that matter.


+1, more turbulance = more noise.

I would also just pipe the stuff to the outside into some sort of containment such as a 55 gallon drum.

[Dan Friedrichs]

Ideally, it would just all go outside, but I live in a suburban neighborhood where that wouldn't fly.

Emptying the bag isn't a big deal - the crawlspace is actually under the house, which is higher than the garage, so it's only about a foot or so below the garage floor. Plus, I don't fill bags that often :)

I'm no noise expert, but it seems like there's two completely different things being talked about here:
First, the noise from the airflow itself. Certainly, more turbulence makes more noise.
Second, is noise generated at the impeller. In order to deaden this noise, you'd want to make the path non-straight, with massive interruptions in the path to absorb the sound energy. That's why people build "Z" shaped return ducts from their DC closets.

[Myk Rian]

Ideally, it would just all go outside, but I live in a suburban neighborhood where that wouldn't fly.
That's why the collection box.


I'm no noise expert, but it seems like there's two completely different things being talked about here:
First, the noise from the airflow itself. Certainly, more turbulence makes more noise.
Second, is noise generated at the impeller. In order to deaden this noise, you'd want to make the path non-straight, with massive interruptions in the path to absorb the sound energy. That's why people build "Z" shaped return ducts from their DC closets.
The impeller noise will still be transported down the tube. You won't get away from that, except by using a collection box to act as a muffler. The Z shaped duct will do nothing but impede the airflow, hence, less flow at the tools.

[Dan Friedrichs]

That's why the collection box.

No, that's what I meant - I would not get away with setting a collection box outside. The HOA would declare that it didn't match the decor :)



The impeller noise will still be transported down the tube. You won't get away from that, except by using a collection box to act as a muffler. The Z shaped duct will do nothing but impede the airflow, hence, less flow at the tools.

How does a collection box muffle sound? I think you're thinking of this like a car muffler, but it's entirely different. In a car, noise is created by the expansion of the air, thus the muffler acts as a place for the noise to be produced and absorbed prior to leaving the system. Here, the noise is not generated by the same means.

As the noise energy is transmitted through the tube/duct/whatever, the more barriers it encounters, the more energy from it is absorbed.

What you're suggesting is that if I place a speaker at the end of a straight piece of PVC pipe and measure the volume, then repeat with a pipe with several bends in it, I'll hear the same volume with both. Again, I'm no expert on this, but that seems intuitively wrong.

[Terry Stellman]

Dan,

I have the same dust collector and have wanted to vent mine outside also. Could you explain or better yet post a picture of what the top looks like that you connect to your 6" vent? How did you seal it? Thanks.

Terry

[Dan Friedrichs]

Dan,

I have the same dust collector and have wanted to vent mine outside also. Could you explain or better yet post a picture of what the top looks like that you connect to your 6" vent? How did you seal it? Thanks.

Terry

Sorry, I didn't take a picture of the top. It's really simple, though: I cut a piece of MDF into a circle that sits on a ridge along the top (if yours doesn't have a ridge, some bolts into the sides for the MDF circle to rest on would also work), and cut a 6" dia hole in the middle of that, which the PVC pipe goes into. I caulked the joints just to make sure no fines would escape.

If you're concerned about the stability of the piece of PVC sticking out of the top (ie - how to securely attach it to the MDF circle), there are lots of options:
-Use thick piece of MDF/ply and glue between the pipe and the MDF
-Heat the piece of PVC, then flare it out below the MDF
-Drive some screws through the pipe into the MDF

[Myk Rian]

I'm not going to get into an argument over this, like there happens to be in another thread on motor capacitors. I'm just telling you that a collection box will muffle the sound. It has nothing to do with how a car engine makes noise. Make it look like an air conditioner unit if there's an issue with aesthetics. And, as I previously stated, I have 35+ years experience with ducting. If that means nothing to you, then don't bother asking for advise on a forum.

No, that's what I meant - I would not get away with setting a collection box outside. The HOA would declare that it didn't match the decor :)



How does a collection box muffle sound? I think you're thinking of this like a car muffler, but it's entirely different. In a car, noise is created by the expansion of the air, thus the muffler acts as a place for the noise to be produced and absorbed prior to leaving the system. Here, the noise is not generated by the same means.

As the noise energy is transmitted through the tube/duct/whatever, the more barriers it encounters, the more energy from it is absorbed.

What you're suggesting is that if I place a speaker at the end of a straight piece of PVC pipe and measure the volume, then repeat with a pipe with several bends in it, I'll hear the same volume with both. Again, I'm no expert on this, but that seems intuitively wrong.

[Dan Friedrichs]

I'm not going to get into an argument over this, like there happens to be in another thread on motor capacitors. I'm just telling you that a collection box will muffle the sound. .....If that means nothing to you, then don't bother asking for advise on a forum.

Myk - I didn't ask the question, I was just making a suggestion to someone else. I'm also not trying to argue with you, I just don't understand what you're saying, so I'm trying to draw on your extensive experience to learn something.

What I don't understand is: What mechanism causes the use of a chip box to decrease the noise? The box needs to have some way for exhaust air to exit, right? Is it just holes in the sides? If so, how is that functionally different from just blowing all the exhaust (chips included) directly outside? Either way, you'd seem to have very nearly the same amount of noise damping.

Without baffles, I don't understand how any sound is absorbed. For instance, if we're in a room talking to each other, and I hold up a piece of MDF in front of my face, the same air flow occurs (roughly), but now I seem quieter to you because the MDF is interrupting and absorbing the sound energy. Without something to interrupt or absorb, what causes the volume to decrease?

[Keith Outten]

I have two shops that both use exterior chip boxes. One at CNU and my personal shop at home. Both shops have the DC inside (no filters or bags) and nothing but a 4" PVC pipe exiting the building directly into a chip box. The chip box at CNU is only about 20 feet from an asphalt sidewalk that is heavily traveled by students all day long and they don't even pay it any attention.

There is very little noise outside if all you are doing is exhausting the DC discharge, the chip box will definitely drop the noise level due to some acoustic filtering and don't forget that sound attenuates naturally...loses its volume as it moves away from the source. On the other hand don't think that a chip box can reduce the sound coming from your planner.

The noise level (very low level hum) at both chip boxes is low enough that you could hear someone next to you whisper.

I wouldn't recommend a 55 gallon drum, metal doesn't absorb sound nearly as efficiently as wood. I recommend a plywood box, make your chip box at least 6 foot long, 3 foot wide and about 2 foot tall which is the size of the chip box I have at CNU....it is the plywood shipping box that the ShopBot CNC router shipped in. All i did was paint it white and install a 6" dryer vent in the right side at the far end of the box. I use air conditioning filter material over the end of the vent, inside the box for a filter. The pipe from the DC pump is a straight piece about 6 feet long and runs through the wall directly into the box. I expect there are at least a hundred ways to disguise your chip box and make it look like a toy box, deck storage, etc.

If you search our Forums you will find pictures of this setup in another thread.

Let me remind everyone that The Creek is a friendly place, if you cannot be friendly your privileges here will be removed without warning. We are all here trying to help each other and some will disagree or prefer to take a different option than others recommend. Trying different methods is often how we learn new things. Failure has been one of my best teachers :)
.

[Prashun Patel]

Dan-
I'm curious. Have you noticed a noise reduction simply by venting outside vis-a-vis collecting inside? I can't tell from the exchanges above whether that's been the case.

Also, I'm probably just going to vent outside directly into a catch basin. Myk, and others, how to keep the splatter to a minimum?

[Dan Friedrichs]

Keith - Thanks for clarifying how your chip boxes work. The ones I've seen other people use have been much lower-tech (like a 55gal drum or a shipping crate without a lid, etc). I can see how a design like yours would reduce noise much more than a metal 55gal drum does :)

Shawn - I located my blower in a crawlspace, so that significantly reduced the motor noise. In the shop, the noise from the suction alone is quite a bit louder than I expected, but obviously much less than with the motor in the shop.

If you're concerned about noise, you might do some searching through this forum. IIRC, Mr. Becker posted some pics of his cyclone closet where he used a Z-shaped return baffle to successfully dampen the loudness of the return air. I can't seem to find the link to that thread, though... :confused:

[Prashun Patel]

Thanks for this, Ken (on many levels ;))

So, how do you empty your dust "coffin" (or should I say "caughin'") when it fills? Is it on wheels?

I hate having my bag inside, but I gotta admit, once I pop it out (and wipe all the spray from myself and sweep up all the dust that settles sinisterly [sic] at the bottom of the top bag waiting to fall on me at precisely this time) the lower bag is quite convenient to change vis a vis a plywood box.

Also, Keith, how did you make up the connection to the pump exhaust such that it can be removed easily.

[Prashun Patel]

Dan-
I'm nervous about drilling a 6" hole through my rim joist. Are you sure that's safe?

[Dan Friedrichs]

Dan-
I'm nervous about drilling a 6" hole through my rim joist. Are you sure that's safe?

No :) But once the subfloor is assembled and has flooring above it, I doubt the rim joist is actually bearing much load. I did my best to center the hole, but didn't worry about it beyond that.

[Nick Abbott]

I mounted my DC unit outside in a small shed attached to the back of my shop. A 4" pipe runs through the shop wall into a 55 gallon drum. The 4" exhaust extends out of the side of the shed about 12" above the ground with a 90 pointing at the ground. Around the exhaust port I built a plywood box that is about 24" square and 30" tall. The exhaust dumps inside this box and flows out under the 36"X58" platform that is the shed floor. The box around the exhaust air dump cuts the sound way down.

I have about a dozen sheets of Celotex sound board left over from a previous job. I lined the shed and the exhaust port box with a couple of sheets. This helps quite a bit. My exterior DC unit went from sounding about as loud as a running lawnmower (before the shed and exhaust box were built) to being a nice quiet muffled unit that bothers no one in the neighborhood.

[Charles Robertson]

I'm with Myk. Use 6" where you can, to your vac and as your exhaust pipe away from your vac. I used 6" thin wall sewer pipe as my exhaust line, 6" steel duct for my interior runs. as close to the equipment as possible. Yes, this will suck heat and/or cooling out of your shop, but who runs their vac continuously. A thought, small trailer- build a box on it to collect dust and shavings-6 sides with exhaust holes as needed, cover with towels to act as cheap filters, get rid of bags. This will also act as a muffler. My vac is out side in an attached closet, my exhaust runs 30 plus feet to a sawdust pile. I'm in the country, no noise problem. Use blast gates to select equipment. My shop is quiet and clean. This works for me, hope you can use some of this for your shop. Al Robertson