Advice on miter saw dust collection port size

I recently bought a new (and hopefully last) miter saw - the Bosch 12 inch slider. I have a 3HP cyclone DC with 6 inch pipes in my shop. I made a larger rubber shroud to replace the original and so far have only used the saw DC port connected to one of my shop vacs until I can get it permanently connected to the larger system.

I intend to branch off and connect a smaller (probably 2 1/2 inch line) to the saw port and a larger line to a shroud that I'll be making to cover the area near the bottom of the saw. My dilemma is the size of the line going to my home made shroud. I know that a full 6 inch line will give me more CFM and a 4 inch line will give me more velocity. I'm not sure which will work better in this application and am looking for advice/comments. Sorry if this topic has been covered before; I have read a lot of threads on miter saw dust collection already.

6" or 5" would be my choice for the shroud over 4" no question. It's not about "velocity"; rather, it's about moving volume of air. My shroud has a 5" drop and I get reasonably acceptable collection...at least as much as you can actually collect from a miter saw that likes to spit debris in multiple directions.

Are you going to connect the smaller line to a branch of the dust collector or run a little shop vac on it in addition to the shroud? I'm planning out the exact same scenario right now. I am thinking I'll do 6" on the shroud.

I originally had the small port on the back of mine connected, but now just have a 45 degree elbow on it that directs anything coming out the blade guard port into the shroud. It's much less cumbersome when I am cutting at angles and less complicated. All of the DC air flow is focused on the hood that way.

6" on mine, and wouldn't want smaller.

Jim and Tom, thanks for your inputs and confirming my original thought that the full 6 inch line would be better. And Jim, I like your idea of just having the small saw port point in the direction of the shroud. I'll have to look at possibly redesigning the Bosch port though since it pretty much points north.

I just put a PVC 45º elbow on the end of the blade shroud port of my Delta CMS so that it wasn't pointing "up" during a cut.

I've got a 4" Y with a 4 inch line to the shroud and a 2 1/2 one on my DeWalt 12" slider and it does okay. I have low expectations from this and it is by far the most inefficient setup in the shop. Perhaps I'll try it with a 6" line and see.

And a related question... (I'm not sure what the etiquette is about highjacking a thread or if each question should be in a new thread...) When connecting the dust shroud to the DC, is it better to split up the 6" main and have 2 4" going above and below the shroud, or use a PVC 45º elbow as Jim was saying and just connect the 6" directly to the base of the shroud?

Are you guys attaching the 6" DC hose to the top or bottom of the shroud? Seems like the top would be better for the fine dust?

I'll post these pictures again, since they're already in the gallery here. I built this over ten years ago, as a prototype, thinking that I would make any changes needed. I've never needed to change anything, and it's still in use. It's 1" deeper, front to back, than the saw by itself.

There is a 6" duct under a built in plenum under the back. There is a slot all along the back of the top of the plenum. No dust, even fine dust, gets back out the front. We can even use it in a finished house with no worries about dust on anything in the house.

DC is a 3hp four bagger that rolls in, and out, of regular doorways.

Thanks. But I don't understand the "slot all along the back of the top of the plenum" part. Also, would a single 6" duct be necessarily better on the bottom part? Due to my layout, it might be better to connect it on the side...

My 6" port has a large square HVAC fitting on the bottom of the shroud which has a 6" port on it. The 2" port on the saw has a vac hose long enough to travel into the sq HVAC fitting. Anything that doesn't find its way into the opening gets brushed into the sloped opening on the bottom. Dave

Jean-Claude, I think the slot along the back just makes sure there is suction all across the back of the box to cover any direction the sawdust was headed. That PVC elbow directs most of the heavy sawdust down towards the slot. I don't know if it mattered or not, but seemed like a good thing to try when I made that first "prototype". It worked so good from the start that I never had any reason to try it a different way. I can't say if it's necessary or not, but since this one works so well, if I built another one, it would be the same way.

My duct comes in from the bottom only for the reason that my setups are always temporary (sometimes up to two years, but typically around one), so ductwork is just laying on the floor inside whatever house we're working on.

6" to an HVAC register boot. I put a couple of sheetmetal wings on the boot to help capture the dust. The saw is able to swivel and tilt it's entire range with this setup. I ran 4" to a 4" x 2.5" adapter to the factory port on my Hitachi. I split the 2 from a 6" line.

https://farm1.staticflickr.com/719/2...d2c4c20a_o.jpg

https://farm1.staticflickr.com/775/2...401fa69a_o.jpg

I directed mine into a stud cavity with a 6" at the bottom. No collection at the saw port, it just spits into the stud cavity using an old rubber 90 from my dad's old Dewalt RAS..

Thanks. I also have many long term "temporary" setups...:)

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Originally Posted by John Ziebron

I recently bought a new (and hopefully last) miter saw - the Bosch 12 inch slider. I have a 3HP cyclone DC with 6 inch pipes in my shop. I made a larger rubber shroud to replace the original and so far have only used the saw DC port connected to one of my shop vacs until I can get it permanently connected to the larger system.

I intend to branch off and connect a smaller (probably 2 1/2 inch line) to the saw port and a larger line to a shroud that I'll be making to cover the area near the bottom of the saw. My dilemma is the size of the line going to my home made shroud. I know that a full 6 inch line will give me more CFM and a 4 inch line will give me more velocity. I'm not sure which will work better in this application and am looking for advice/comments. Sorry if this topic has been covered before; I have read a lot of threads on miter saw dust collection already.

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John, is this saw the Glide saw? I made a shroud that captures near enough to everything for my Glider and can post pics if needed.

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Originally Posted by Chris Parks

John, is this saw the Glide saw? I made a shroud that captures near enough to everything for my Glider and can post pics if needed.

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Chris, yes, this is the Bosch 12" glide saw. It replaced my DeWalt DWS780 when I needed more room. I'd love to see some pics of your shroud.

John, my apologies for the delay but here it is. The one big draw back is that the saw cannot be rolled fully left and right but the offending bits of the shroud could be hinged or even made removeable if needed. I am using a CV1800 to power the hood through a single 6" duct and it collects nearly everything. I put it on a sliding base as the fences each side are fixed and if I use a sub fence on the saw I can wind it in or out to line up the fences. All dust goes in the bottom and drawn out the top so it needs a good dust extractor to make this hood work. The curved plenum is made from 3mm MDF, I made a rough form, wet the MDF and clamped it to the form for a few days to dry. The bottom inlet must be sized to at least match the area of a 6" duct. Any questions or if I can be of further help please ask.

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I don't have a miter saw and wasn't going to reply to this thread but thought I'd go ahead and show the set-up my radial arm saw since it is a somewhat similar concept.

I installed a rather basic collector with a 4" port at the bottom connected to a Grizzly 2hp dust collector. Prior to this, my wall and floor was covered with sawdust after any use and after the modification I only have minimal sawdust, primarily in front of the fence. I would think that anything 4" or up would have a good chance of giving good performance (depending on the design), though anything below might be questionable.

I've attached a few pictures to show the set-up. Please excuse the blade that is on the saw and it is pretty rough. I occasionally work with reclaimed wood and prior to stacking & storage I will remove unusable and nail-filled sections, so use an old blade to save wear and prevent damage to my better blades.


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Chris, thanks for posting all the pics and explanation. I really like your design and will now plan on going that route. I especially like that even though the collection area is at the bottom and the DC duct is at the top the saw is still very close to the wall (the reason I bought the Bosch).

The idea of having some forward/aft movement to accommodate a sacrificial fence is also very good. I always use 1/2" MDF for such fences. So instead of using a knob and threaded rod I would use a couple of 1/4" pins on that forward cross piece and have 2 holes (1 set on each side) drilled 1/2" apart on the base. That would make my changeover faster and my big hands wouldn't have to fumble around with a knob under the slider since you really have to adjust it at 0 degrees.

My one question would be about your factory dust chute. I see that you have the original 90 degree rubber fitting on yours. If you are cutting a 45 or greater miter to the right does some sawdust escape from that fitting being so close to the left front of the shroud?

It doesn't seem to cause any problems but I will remove it and see what happens. I did have it hooked up to the plenum of a previous hood with a small hose but the whole hood was a hopeless case converted from when I had a different saw. I move the sliding base with a cordless drill on the nut, it was very handy doing the initial fence set up to get it spot on. My bench fences are sitting on pins so I can lift them off and use the benches as needed.

Thanks Chris. Staring at the pictures again I realize now that you don't have to have the saw at zero to adjust for your sacrificial fences. You just have to adjust them to be even with the extra cabinet fences on the left and right side.

And I like your side bracket to hold the clamp. Makes access to it easy but keeps it out of the way when not used.

I'm not familiar with the electrical system in Australia but it appears you may have changed the plug on the saw. That was one of the first things I did on mine. Power tools like this that draw a lot of current have heavier gauge wire making the cord heavy to the point where the factory straight in plug won't stay in the outlet very well. I think it's somewhat of a safety hazard and could lower the performance of the tool due to a poor connection. This is now the third tool I have with a heavy cord that I've changed the plug over to a 90 degree one.

John, the electrical plug is standard in Oz, we use 240V single phase for all single phase and 415V for all three phase. if you want the original picture files PM me your email address and I will send them to you.

Just an observation: While trimming out my son's house with painted MDF, it became apparent that 4" or 6" stock sawed while laying flat spewed dust all over, while if cut standing vertically, dust almost shot exclusively into the dust collection chute. Also (not a surprise) cutting wood vs MDF, dust tended to be directed to the chute in a much more controlled manner.

I just plumbed the whole shops this summer. Went with the Dust Deputy XL since DC has a 6" port. I did a 6" to the cabinet behind my miter saw (also to TS and Jointer). I can hold my hand up to the opening and feel the air flowing in.