# Dust Collection for Compound Mitre Saw



## TobiasZA

I have a question…. I am sure that many LJs' can help me. Now that my workshop build is nearing completion, I want to make a new Dust Collection "Box" for my De Walt DW708 Compound Mitre Saw. I have trawled the net and see any number of ideas. I am looking for an idea that REALLY works!! Every concept that I could find seems to have one or another shortcoming. Maybe some kind of venturi type of box is what I am leaning towards. The SCMS is in a permanent position in the shop, I don't do many compound cuts and I have a large space availalable behind the device.

Any offers?

Thanks in advance
Cheers
Tobiasza


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## Manitario

Is it a slider mitre saw? I found MS dust collection one of the most frustrating aspects of my shop; I use my MS a lot and it is the biggest dust producer. I tried a number of different blade shroud designs and different hood designs; they improved the dust collection but it was still poor. Eventually I upgraded my DC to a 5hp Clearvue; this pretty much solved all my MS dust collection problems. I have a simple hood with a 6" port; the increased airflow from the larger DC made the design effective.


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## TobiasZA

Hi. Thanks for the reply. Yes, it is a sliding compound MS. I am running a 5hp installed Dust extraction system with a large steel cyclone and plenum box with filter bags. There are some pics on my workshop page. Do you perhaps have a picture of your setup on your MS?

Cheers
Tobiasza


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## WhyMe

I made a very large dust shroud that I place behind the MS. It's made of 3/16 lauan using metal drywall corner bead and pop rivets to hold it together.


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## kdc68

*WhyMe*.....nice work !... from the second picture it looks like that shroud could swallow the Dewalt planer whole…...


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## wapakfred

I wish you the best of luck, and I'm fairly certain you'll won't meet your criteria of "really works". If the 708 is open under the blade it adds another place to catch dust; that's the way my Dewalt MS is made.


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## bigblockyeti

Given the light weight dust coming off the miter saw, it would also serve you well to use a dust collector instead of a shop vac as high air flow is much more important than being able to generate a high vacuum.


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## TobiasZA

Thanks very much for the replies. 
BBY: I am using a full DC system. see pics on my workshop page. 
Fred: The saw is not fully open under the blade, its more of a tiny shallow trough with an extremely small opening at the rear.
WhyMe: Nice work. Thanks for the pic.

I have a 4 inch port with blast gate going to the DC system. Somewhere I remember seeing a box that acted as a venturi, creating an area of faster air speed at the opening caused by the mid section low pressure of the venturi, just cant find the image. It seems to be a very sensible idea.
Cheers
Tobias


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## Whiskers

OOOh, this is a thread I can really get into, cause I'm faced with the same thing. I have a antique craftsman compound mitre saw that I use a lot. It came with this little bag that sticks out the back of the blade mech and I guess it was supposed to collect dust, but of course that is a fallacy cause the dust has no reason to travel up that path on it's own and into the bag since there is no natural airflow that way, however removing the bag and sticking a shop vac hose does wonders to cut down on the amount of dust it generates, but it still spits a ton of dust especially to the rear of the saw. I had envisioned a arrangement like Why4ne is using behind the saw, hooked to my 4" DC system with a router table style split that would suck air from behind and thru the weird blade thing. I've already bought a Rockler router table connector and associated fittings and hoses for connecting it all up. Why4me, I love your idea of using drywall corner material to join things up, I would have never thought of that. I actually have some of that on hand, but unfortunately it is already allocated to other purposes, but the stuff is so cheap it not a concern. I'm definitely going to watch this thread for a couple days for ideas.


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## WhyMe

I'll add a caveat. The dust shroud does a fair job of collecting the saw dust but is not perfect in anyway. I usually place it so the shroud is slightly tilted up so the saw dust that collects on the bottom has a tendency to slide down closer to the port to be sucked in. The use of the drywall corner bead was a one of those brain farts when I was trying to think of an easy cheap way to connect the thin lauan together. Obviously I could have used some same square strips of wood to connect the panels but I had the corner bead left over from some drywall work.


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## MR_Cole

I haven't done anything to mine yet, but I noticed that alot of dust goes sideways and down. Thus, the rear feet of the saw get covered. I'm thinking of doing a traditional dust hood for the rear, and then make a large chute under the saw that has cross-members to support the saw. Only issue is, I dont think my harbor freight dust collector can handle two 4" hookups.


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## TobiasZA

I agree that the dust coming off a mitre saw is light and small. The problem is that although it is quite contained in it's horizontal plane when doing a cut, but the vertical plane changes dramatically from the beginning of the cut to the end of the cut. Have a look at the following video that I found on YouTube, and let us know your thoughts





Cheers
Tobias


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## shawnmasterson

That is almost exactly how I intend to set up my DW slider when I finish my bench.


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## TobiasZA

Thanks Shawn. i am leaning towards this style of containment as well. Has anyone got any experience of this type of system?

Cheers
Tobias


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## Gene01

Mine is just a storage tub with a toilet flange on the bottom to connect to the DC hose. 
I have to be able to remove it to use tools behind the SCMS. That's why it's on a stand.
Mine's not perfect either. But, it contains MOST of the dust not caught by the saw's bag.


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## TobiasZA

Hi Gene, That is the kind of thinking that amazes me, extremely lateral thinking! Great idea for anyone who needs to move the capture box around often. I love the wooden knob, great touch. Thanks very much for sharing yet another angle on this thread. I shall look at plastic tubs and bins in a whole new way from now on!

Cheers
Tobias


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## craftsman on the lake

I'm on my third miter saw dust collection build and two things about collecting dust with a miter saw. Either you have a shroud that has a powerful enough dust collector connected to it that it can pull fast moving sawdust out of the air or you enclose the back, sides, and front of the hood to contain the dust so that it can be cleaned up later.

With dust hoods, the dust is ejected with enough force that it bounces out of the hood at you. Either suck it out or cover the front so it can't leave the area. Placing a suction vent at the bottom of a hood is almost meaningless. Half the dust bounces back into your face before it ever falls down to the suction port. Here's something I've done but still have not contained all the dust.


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## Finn

I made a diamond shaped hood, flat on top, with the front open , just enough to fit my DeWalt SCMS used at any angle. I have a six inch dust collector venting it at the bottom with a screen on it. It exhausts the light dust but not all the heavier sawdust, so I shovel it out of there every six months or so.


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## TobiasZA

Hi Jim, sounds interesting, do you have a picture at all please?

Cheers
Tobias


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## TobiasZA

Hi C on the L….. Thanks for your input. I am seriously of the opinion that the venturi effect can be successfully applied to a SCMS hood/box. I just don't know enough about venturi application, other than a very successful vacuum venturi that I had in my compressor line some years ago for my vacuum press.

Lets keep thinking

Cheers
Tobias


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## TobiasZA

This is a quote within a long discussion on the American Forestry Forum website:

_"In order to suspend particles in air, you need a lot of velocity.

In order to get velocity in a pipe, you have to overcome a lot of pressure loss-pressure increases as the square of the velocity. But you don't actually need much volume (CFM) because the pipes we use to move sawdust aren't that big.

In other words, the type of fan or blower you want is relatively high pressure, relatively low volume. A "squirrel cage" blower is just the opposite-low pressure and high volume.

You can make a venturi by blowing air through a largish pipe (e.g. 5" dia). At some point, reduce the diameter with a smoothly tapered reducer. Bring a small dust collection pipe into the side of the reduced pipe. Then expand the main pipe again back to its original size, using another smoothly tapered reducer.

It's counter-intuitive, but as the air speeds up through the smaller portion of pipe it reduces the static pressure. That will cause it to suck air and dust through the side pipe.

A gradual, smooth transition (reducer) is key to making this work. Abrupt changes in diameter cause high pressure losses an create turbulence that may destroy the venturi effect._

So if one creates a wide (horizontal) but very narrow (vertical) mouth across the entire width of the hood/box, then airspeed will be increased pre the mouth and will reduce to the normal air speed of the DC system post the mouth, or am I talking a whole load of rubbish??

Cheers
Tobias


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## rance

Search for "*FastCap* ChopShop Saw Hood". Looks like the best solution. You could even make your own.


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## TobiasZA

Thanks Rance. Interesting product. The Fastcap is more of an onsite device that can easily be erected and taken down quickly and moved. I am rather looking for a fixed solid walled system that would work with my central dust extraction system.

Take a look at the images on my workshop page, I want to incorporate proper extraction for all of my various workstations.

Thanks for your input

Cheers
Tobias


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## shawnmasterson

Though fastcap is a neat product, it really isn't a dust collection solution.
I wish the manufacturers would recognize they have a problem and need to address the real issue.


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## TobiasZA

Hi Shawn. I fully agree. 
Cheers
Tobias


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## PLK

I'm actually in the beginning stage of a miter saw station. I'll post to this in the next few days when it's closer to done. Adding a picture below. the saw station will go on the right of this cabinet 4 inches lower than the table height to be flush with the saws cutting surface. I'm building a dust hood with 2.5" shopvac hose hookup to the mack of the miter saw itself and a 4" line in the back of the dust hood for the 2hp dust collector.










Paul


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## TobiasZA

Hi Paul. Please keep us posted with pictures

Cheers
Tobias


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## TobiasZA

Hi
I have spent most of today trying out different things to achieve a decent dust collection off my SCMS. This was an unsuccessful day to say the least. The conclusion that I have reached is that the dust collection box/shroud/hood/container MUST travel with the saw in the horizontal plane and must be as close as possible to the unit.

Any thoughts…anyone?...

Cheers
Tobias


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## Finn

tobias….no picture. The hood, that I cobbled together, I made of MDF is diamond shaped as viewed from the top. I made it tall enough to clear the saw and about 4' wide. Trial and error got me the size of the opening required in the front. I put a flat thin plywood top (1/4") that I now find useful as a shelf. I caulked the joints and put some 1/4" screen over the dust collector intake that is in the bottom of the hood. I do not want a chunk of wood damaging my dust collector impeller.


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## TobiasZA

Hi Paul, tell me, does your hood move with the table ie left to right and vica versa?

Thanks
Tobias


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## HorizontalMike

To tell you the truth, I use a 5gal shopvac w/hepa filter, hooked up to a separator (Grizzly) a 30gal can as my dedicated DC for my 12in CMS. The high speed suction is low volume which is a perfect combination for this application. I swear this thing collects +95% of my MS cuts.


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## TobiasZA

Hi Mike. Thanks for sharing. I really want to give this my best shot…how to efficiently capture SCMS debris and dust….. I don't believe it to be impossible on a central system, I need to evolve the capture device….how?? I am not sure…....

Cheers
Tobias


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## DrDirt

*In order to suspend particles in air, you need a lot of velocity.

In order to get velocity in a pipe, you have to overcome a lot of pressure loss-pressure increases as the square of the velocity. But you don't actually need much volume (CFM) because the pipes we use to move sawdust aren't that big.*

I think they are looking at BLOWING air and not SUCKING

Very different processes. When blowing you have an air multiplier where pushing a small amount of air will cause a lot of air movement. sucking air not so much.

Picture it this way - when you have your hose on the discharge side of a shop vac - you can stand there and blow away dust like a leaf blower.

Hold your same hose in your shop connected to the vacuum side, and you see very very little air movement 10 feet away from the hose.

It is very hard to draw air at high speed over any distance. blowing is easy.


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## TobiasZA

Thanks DD. I understand this. So what do you think would be a solution?

Cheers
Tobias


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## PLK

He's my miter saw station, not even close to finished yet but got the miter cabinet built today and the dust collection done today.










The saw gets connected to the shop vac. The dust collector is the real key. I have a 4" line that runs to the bottom of the cabinet and a 7" x 4" opening that gets most of the dust. Between the shop vac and the DC running at the same time I bet I'm getting 90-95% of any dust that's produced.










It exceeded my expectations by A LOT!










The left table runs flush with the miters surface and fence. The saw swings left and right 50 degrees.


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## PLK

A bit blurry but this is the connection under the saw cabinet.










Paul


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## TobiasZA

Hi Paul. Really nice and neat job. Thanks for sharing

Cheers
Tobias


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## craftsman on the lake

A real trick is to get a large sliding miter saw dust free….. Those long sliders sticking out the back add to the complexity.


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## TobiasZA

Agreed, C on the L.

Defeat is not an option!!

Cheers
Tobias


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## PLK

The dust hood for my 10" slider would have been 4.5' wide by 4' deep which would have been fine if my shop wasn't approx 20' x 20'. Since I have a small shop I decided to go with the 10" non slider for a smaller footprint. If you have the room for it the concept is still the same you just need to have a LOT of room for the hood.

My slider will travel with me outside for off site jobs.

Paul


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## dbhost

I didn't catch if your saw is a slider or fixed…

Slliders are MUCH harder to collect dust from, and I won't lie, my dust hood isn't perfect, and it leaves plenty of chips / shavings in the base and on the saw, but I can actually "feel" the draw of the DC when using the miter saw, and I can actually watch streams of dust go in. I collect probably better than 90%.

http://daves-workshop.blogspot.com/2014/02/sliding-compound-miter-saw-dust.html

A couple of things that could make it better…

#1. A bit taller, I had to clearance the top in an arc to clear the hose, I didn't account for that.
#2. The entire hood could come up to just behind the fence. It ends too far back.
#3. The front could be enclosed between the sides and the saw itself closing off air space, forcing the collected air through a smaller opening.
#4. Figure out some way to make a ramp that slopes from just below the slide rails, and funnels dust into the port.

I don't (yet) have a particle counter, however, like I said, I feel the breeze when running the miter saw / dust colelctor, I am confident the fines are getting pulled in, a lot of the big stuff collects near / around the port. I made a few cuts with it OFF to test last night and the difference with / without is extreme. I think 90% is a very conservative number… I think with the changes I outlined above, I could get into the high 90s in capture.

No matter what you do, I somewhat suspect unless you use gravity to pull as well, the heavier dust / shavings are simply going to fall out of the air before they can make it to your port. That is unless you are running some monster DC with Jet engine suction… I just don't think with a normal hobby woodworking dust collection system, even a big 5HP cyclone you are ever going to be able to get 100%. It might be possible, and I would LOVE for someone to prove to me that it is possible… Because I would really LOVE to accomplish this…

A slider that does not have the rails behind the pivot like most do, would make things easier, but they are the exception rather than the rule. Hitachi has one that looks really good, and of course there is the Festool Kapex, but that is way out of my price range. For that kind of money I would be halfway to a Sawstop 3HP PCS…


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## craftsman on the lake

the video that I posted in a post way back at the beginning shows the features of my mitersaw stand with a 12" compound slider. My solution lets the hood be about 16" deep. It catches a lot of the sawdust.


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## TobiasZA

Hi DBH. My saw is a De Walt DW708 Slider. Thanks for your input, much appreciated. I would also love someone to show us exactly how to achieve 100% results. I am running a 5hp steel piped dust extraction system. Due to the design of my machine room, I have a lot of space behind the saw. After experimenting earlier in the week, I noticed that most of the particles that come back at me, are exiting the blade quite high,so…..what if I build a large catchbox that has an overhead rectangular port that travels with the axis of the head inside the box(the particles are already in the air) and another central port at the bottom?

Any thoughts on this
Cheers
Tobias


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## TobiasZA

C on the L…. Your flaps make a lot of sense

Cheers
Tobias


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## craftsman on the lake

Ya Tobias, even with a full dust collector sucking on a small area directly behind my 12" like I had previously, the dust still comes out at you if you have a hood behind it and will settle at the bottom and on the sides of the saw. That's why I said previously, you'd have to have super suction to get it all. For me, with my meager DC capabilities, containment within the hood then cleaning up later was the only way… for now. I've tried more than one time to design something.

The canvas in the front is hooked on like a curtain rod with rings but I find that it easily just flips up and over the top of the hood for cleaning. Spreading the curtains apart is only for when the saw moves to different angles.


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## TobiasZA

Thanks to everyone who offered advice and experience, I truly appreciate all the input. So far it seems that the "Woodnerd" appears to have licked to problem to the best extent.

See http://www.thewoodnerd.com/workshop/mitersaw.html

Has anyone built this collector and more importantly has anyone improved on it??

Thanks
Tobias


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## craftsman on the lake

He has a nice set up. To collect all the dust though he must have some serious suction. His input pipe looks to be at least 6" so it might be collected to a large vacuum unit. And, I'll even bet that when he turns his saw 45 degrees it doesn't all go up the chute. It would certainly be nice if it did though!


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## TobiasZA

C on the L… I agree. For me, to take 80-90% of the dust away during a 90 degree cut would suit me fine…I have no issue with a bit of cleanup here and there. I am using a 5hp with 4" ducting throughout cos that's what was available at the tine. In this case, bigger is definitely better

Cheers
Tobias


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