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Discussion Starter · #1 · (Edited)
So I was looking at some downdraft sanding box plans and then caught an idea floating in the old noggin, which as it turns outs is in my spell checker and is indeed a real word, go figure. Anyway I've been trying to figure out how to do dust collection on this and thought that I could build this sanding box and install one on top of my build. But then with gravity working as it usually does and this one being on earth and not the moon I thought maybe it should be on the bottom instead. Turns out I haven't committed the space above or below either way so it's open at this point. What I have at this point is a 6" PVC feed coming down to a https://www.amazon.com/Dust-Collection-Reducer-two-ducting/dp/B01DJMUIJ8 box. My original intention was to install a long 3" wide channel in the hood like a linear diffuser and feed it with the two 4" hoses but after seeing the downdraft sanding box it seemed less gooder. Yeah I know but I like that word and it's clean. Then this sanding box comes along and I think maybe make a custom size and drop it on top of the hood I built but that gravity thingy kept interfering with the physics of the whole idea and thought maybe I need to make one and put it in the base (bottom). I don't think I'm going to get 100% dust collection but would be happy at say 80-85%. I did cut some heavy plastic strips to hang down to restrict the opening needed for the saw to swing for full angles cuts but expect most cuts to be at 90 degrees anyway.

So thoughts, ideas, smart alec remarks? No really, I could use some additional brain power on this if you can spare it. The miter saw station is here. Actually after looking it's not so I have one attached. Okay maybe two. After a foot of snow I tend to get some cabin fever although my neighbor, did I mention having great neighbors is fantastic, just cleared the road and my driveway. Not going out anyway until my preop Dr's appointment tomorrow. Let Mother Nature and the expected 40 degree weather do it's thing. Refreeze is likely but the appointment in town is 2:15pm so I should be golden. But I digress........

I should mention that the DC is a CV1800 with a 6" PVC main line, 17" impeller, and 5 HP system.
 

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Nice looking miter station Steve. I have the same CV dust system, what fittings do you use to connect the 4” hose
to the duel 4” shut offs?
 

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Steve I don't know what the bottom of your saw looks like. Would it work to add a duct under the saw or is there too many openings in the saw base? If you could collect from the blade slot, I think you would catch much of the dust.
 

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I have a Bosch 10 inch sliding compound miter. My DC is mainly a shower curtain that fits most of the way around the saw, then gathers into a connector at the bottom. It works fairly well. I at some point will use some sheet aluminum attached to the blade 2.5 inch dust collection duct built into the saw. This will be formed into a "scoop" follows behind the blade. Hopefully, this will catch a lot of the dust before it hits the shower curtain. I'll use a hose clamp to hold it in place. Can't recall what saw had something like this "scoop", but some brand has this built in and inspired my shop-made solution. Always a good topic, given this is the worst sawdust producer in many of our shops.
 

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Discussion Starter · #5 ·
Nice looking miter station Steve. I have the same CV dust system, what fittings do you use to connect the 4” hose
to the duel 4” shut offs?
This ClearVue dual port is the same one I used on the router table except that one had separate blast gates for each branch. On the router table I used a 6" metal duct fitting to connect the 6" hose and the 4" hose connects directly to the ClearView ports. I also used Fernco connectors for the 6" main connection and at the table saw. That will be redone but at the rate the Postal service isn't delivering packages in my area it will likely be after I recover from my shoulder replacement surgery this coming Monday. Just can't have enough fun these days...I did order 6" to 4" Fernco reducers so hooking one of those directly up to the table saw should get me the closest direct connection rather than cutting into the saw base and installing a 6" connector.

I've almost talked myself into buying a good 3D printer just so I can make my own reducers. Everything I've seen commercially available have been like stack a 4" can on a 6" can. Where in my mind a good reducer should be cone shaped they have a 4" cutout in a 6" flat bottom. Doesn't make sense and it does create a ton of turbulence. I'm hoping the Fernco fittings will eliminate this but they are rubber and not sure if that will make a difference. Preference would be a smooth surface like PVC or metal. The PVC 6" to 4" reducers are shaped well but again the hose needs adapters to fit. The 6" hose fits snugly inside the PVC adapter but the 4" doesn't fit over or in. Thought just fired off, maybe I should paint the inside of the Fernco fittings before using them. That would give them a smoother surface, maybe?
 

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Discussion Starter · #6 ·
Steve I don't know what the bottom of your saw looks like. Would it work to add a duct under the saw or is there too many openings in the saw base? If you could collect from the blade slot, I think you would catch much of the dust.
The miter saw is the Dewalt DWS780

You would get some from the bottom but most goes out the back following the blade direction. What is hard to see from the pictures with the saw installed (bolted down) is that there is a hood around the backside of the saw and it tapers to reduce the inside dimension. The thought was that the smaller the area to collect the sawdust the easier it would be to accomplish. The top and bottom slant towards each other as do the sides so the back is a smaller rectangle than the front. Make sense? Sort of like this fitting except wood (MDF) and rectangular. The constructed hood had to be large enough to accommodate the depth and side to side movement of the saw for angled cuts. That determined the overall dimensions.
 

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I have a similar set up as you for my mitre saw. I only use it for 90 deg. cuts so I built a box around it with a removable door on the left side that extends to the saw blade ( I can still move the saw to the right for a mitre cut and remove the door to move it to the left if I need to). Then I cut an opening in the base that the saw is bolted to which is about 4" wide then built a 3 sided box around this opening. I connected the end of the box to the DC with a 4" pipe. I also attached a flex hose where the dust bag normally goes and connected this to the DC.

This is so effective that I only get a spoonful of sawdust outside the box. I also use it to collect dust off my 1" belt sander that has no way to attach dust collection to. I place the sander in front of the right side opening and there is so much air velocity that is sucks all the dust into the box around the mitre saw.
 

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Discussion Starter · #8 ·
Any chance you can post a picture? Sounds interesting but I'm a bit unclear as to it's shape.
 

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Here's some photos but it's difficult to show the opening under the saw. You can just barely see the opening in the photo taken inside the mitre saw box. There's some aluminum tape around the opening. This collector box is at the back of the large drawer under the saw. In fact I had to cut down the back of the drawer to allow for the collector box in order to be able to close this drawer. The 4" DC pipe attaches to the end of the collector box. Hope this helps explain what I did.
 

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You can't catch all the dust. Just put the pipe around the bottom somewhere and when finished sweep it to clean completely. ..
 

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If the DC had a hose going directly to the collection bag that is normally found on the Dewalt miter saw, would this not get a lot more than normal seeing as it’s suckimg air from there?
Have the hose split , one going directly to the saw, and the other to that catch basin .

Btw, Awesome looking miter saw station Steve
 

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Forgot to mention that I also found a cutting technique that tends to throw the sawdust back into the collector. It is to make a light, scoring cut as you pull the saw toward you, then complete the cut on the back stroke. The score creates a slight channel that directs the sawdust back. This has helped a lot. I don't have space for a saw station.
 

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I don't (yet) have a miter saw, but I have studied the various methods of dc. So far, this video shows the best I've seen.

I understand those that advocate for a large-area box to collect the sawdust after it's ejected past the saw, but that still leaves a lot of airborne nigh-invisible particles to breathe.

Stopping the sawdust at the closest point to the cut is the best and this video shows how this fellow did it quite simply.

This would be the method I would try. It's simple, easy to adapt to many saws, and doesn't require over-engineering as is very common in woodworking.

 

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At the expense of boring those of you who already know all this, thought I would throw in my
$ 0.02 worth of useless info.

In my not unsubstantial and varied readings and studies of air, oil and coolant flow pertaining to making my hot rodded Mustang faster and more reliable at the road course, there are many automotive systems that parallel dust collection. This includes cylinder head, intake and exhaust performance, aerodynamics (to do with generating downforce (or at least reducing/eliminating lift), coolant and oil flow inside the engine and within the cooling systems like coolers, radiators; braking system performance and air flow to cool them (duct work) etc etc.

When viewing the entire dust collection / shop vac / cyclonic scenarios and the difference between dust collector and vacuum cleaners, here are a few points I would like to mention:

The suction difference between the two systems makes a huge impact on the effectiveness (our only real concern being that it works) and efficiency of whatever it is we cobble together; flow potential and pressure vs volume..............that is the crux.

Elbow radius and neck down dimensions and curve design radically affect flow, as does the diameter and shape of the pipe / hose....smooth is good - ribbed is not. Insie outsie or outsie insie conncetions - think of the flow of air and the dust floating in the liquid.......yes Grasshopper..... air is a liquid.

Because dust collectors have very low pressure differential (suction) they require much greater unrestricted CFM of airflow. Going from a 4" to a 5" or 6" pipe on a D/C radically improves the performance over long runs - think HVAC systems with your furnace and a/c. This is why real dust collectors don't use bags - they may flow a ton for the first minute, but once they are full of dust, the outlet side of the D/C is restricted - meaning you can run sewer pipe, and your D/C system will still (not) suck......lol...see what I did there?

Here is my practical inclination to most of these highly complex problems and challenges.....without renting a wind tunnel (altho that is possible @ $2500/hr), doing your best on minimizing the compromises (like using Y adaptors not T fittings for example).

I figured that air flow can be controlled via waste gates - lots of times, less suction and more flow will actually pickup more of the dust - think air inlet on a router enclosure - not only from the top, but usually clean air to also draw across the router motor (to keep it cool) and to essentially create a main flow (river) of air the will then pull the additional air (and dust) along its path. Pls see Gr 3 level pic attached.

Reduce restrictions (on both sides of the pump; inlet and outlet; just like a cars engine) and reduce turbulence and you improve efficiency...........works on everything from air intakes, cylinder head flow, engine cooling and oiling systems, making your F1 car faster.......and improving your D/C effectiveness.

The challenge is to maximize the workings of whatever setup we are stuck with due to the various insurmountable factors - sooooo...... think about adjustability/variability to see what works best FOR YOUR SETUP.


Hoping this gets everyone thinking a little bit. Gotta say, I really enjoy being a (virgin) member on this forum, so much knowledge and skill set as well as friendly faces and comments.
 

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Great topic, Steve...
 

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I understand those that advocate for a large-area box to collect the sawdust after it's ejected past the saw, but that still leaves a lot of airborne nigh-invisible particles to breathe.
It's true that the big box design doesn't prevent particles from being thrown including fine particles but because of the mass differences due to the particle size only the heavier can actually reach "escape velocity". The invisible ones that are really harmful are also practically mass less. This means that once thrown they can't travel very far before they slow down to almost a standstill. A good analogy to what happens is when you throw a balloon compared to throwing a baseball. The pickup in the box is creating a wide low pressure zone that causes air in the room to move towards it. This would carry all the fine particles with it since they haven't moved far away from the saw. Just like one of those ceiling hung air filters will help clear a room, the big box will do the same thing so the one thing they should be good at is removing fine particles. Not to say that there are better solutions than just the big box.
 

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I saw a youtube demo where after a box type dc was used for the first time in the day. The lights were turned off and side-lighting was used. It looked like Hiroshima with fall-out.

If you have a big-box as your miter saw dc, try it for yourself. The larger particles aren't the problem; it's the almost imperceptible particles that linger and you breathe.

I'm not saying the box doesn't work; I'm saying it doesn't work well.
 

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Discussion Starter · #19 ·
I think one of the main takeaways here is that unless you're using an isolation chamber it's wise to use a mask regardless when doing such operations. Simply having a fine particle collection hung system and a DC isn't sufficient. My concern was and still is dealing with the majority of the sawdust and I think that's going to be the best it can be with this setup. The video link posted does well on a chop saw but maybe not as well on a compound miter saw where sliding action comes into play. If I were starting from scratch, and it's way too late for that, I'd build a containment system that could be mounted to the saw itself so that regardless of angle it would still be in the same fixed position. It would be mounted to the saw and not the station itself. Makes sense in my head......but that's not always a good place to work things out. At this point I simply don't have the room behind the saw to try that out. Moving that 5 cabinet assembly would be a major multi-person task and I simply don't have those resources.

The two opposing 4" ports should provide plenty of volume. One thing of note is I had my Shopsmith setup with the disk sander and took the 4" hood connected to the 4" hose on the CV1800 and although it did pick up some of the sawdust the very fine was certainly airborne. Both under and around the Shopsmith required vacuuming after sanding with the 60 grit paper. I think a smaller sized hood closer to the sander would have been a better solution. The hood was maybe 8" away. A smaller 4" diameter directed flared shaped coupling style fitting may have been a better collector and having someone direct it while sanding was being done likely even better. I tried what I had seen with some lathe operators but then again, like the miter saw, I think the intent was to capture as much as possible.
 

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This is an interesting thread. I enjoyed the guys uTube on his home made rubber collector around the miter saw. I bet it was exciting when the blade caught the rubber shroud! :surprise:
 
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