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  1. #1
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    Default SCMS Dust Extraction

    Hi Folks,

    after finishing the majority of work on my study, its time to start on the shed.

    I am seeking some advice on dust extraction for my sliding saw - and wonder what collective wisdom I haven't captured after reading many of the posts on this forum.

    Attached is an image of my proposed SCMS area in the shed.

    SCMS Station - 20140801.PNG

    I plan to have a 6" opening in the hood, and another 6" opening coming up under the table (which should be under the sliding rods on the saw). On the right is the main duct that will head back to the DC (which is a Hafco DC7 - rated at 2400CFM - at the impeller I figure). Don't pay too much attention to the particular fittings chosen (like the Junction rather than "Y" etc. - I just wasn't able to find any schematics of "Y"s to help the sketchup drawing).

    Will having duct top and bottom cause "competition" in the airflow and thus unwanted turbulence ?
    What do folks use as a blast gate on 6" duct ?
    Am I better off with 2 x 4" rather than 2 x 6" ?

    All comments appreciated.....
    Glenn Visca

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  3. #2
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    Quote Originally Posted by Glenn.Visca View Post
    I plan to have a 6" opening in the hood, and another 6" opening coming up under the table (which should be under the sliding rods on the saw). On the right is the main duct that will head back to the DC (which is a Hafco DC7 - rated at 2400CFM - at the impeller I figure).
    There is no way that a DC7 generates 2400 CFM as it comes off the showroom floor..
    That measurement is a industry standard measurement fudge that measures the air speed in the middle of a duct but with no filters/bags and 8" ducting on a good day with the full wind behind it. The limiting factor is the size of the main ducting which means that about half the rating is possible provided 6" ducting is used, or maybe 1600 cfm if 8" ducting is used.

    Will having duct top and bottom cause "competition" in the airflow and thus unwanted turbulence ?
    Yes the two air streams will usually conflict with each other.
    For fine dust control (think "gas like" behaviour) it's usually better to have unidirectional air flow. i.e. one 6" duct at the back will be best

    Some times two narrower higher speed air intakes in critical places like collection ports close to the blade can capture more coarse chips but you will capture less fine fine this way.

    What do folks use as a blast gate on 6" duct ?
    make youw own or but the Clearvue ones ($22 ea I think)

    Am I better off with 2 x 4" rather than 2 x 6" ?
    A 4" port can at best capture ~400 cfm while a 6" port can capture ~1200 cfm but it depends what these feed into and whether you want fine or coarse duct control.
    If you are feeding into only 4" ducting then both are is a waste.
    If its 6" ducting 2 x 6 is also a waste.
    2 x 6" only works if you are using 8" ducting but see also above

    If you are not using 6" ducting that will be your biggest limitation.

  4. #3
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    I haven't done a final rig-up on mine yet, but in a test run I found that using a shop-vac fitted to the saw's internal system, and a 2hp DE with 5" outlet sitting behind the end of the cut left very very little dust behind. I'm using 5" because I'm restricted to that by the Thicky/Jointer "difficult" European size.

    This is set up without any kind of hood in place - I just don't like the way they get in the road, block light and vision etc.

    The 5" outlet will need to be able to move it's position to cope with mitre cuts, so I'm thinking rare earth magnets and a steel plate will do the job there.

    Placed like this, the two airstreams don't compete much because they are running in the same direction apart from a last minute slight change of direction, and the 5" duct is slightly behind and slightly to the right or left of the intake for the saw (up the back of the blade of course).

    One day, a smart manufacturer will be "turned on" and make a moulded intake that fits neatly around the back of the cut so that a 4, 5 or 6" hose can be attached. This dual extraction system works very well on a number of tools (SCMS, Table Saw, Router Table in my case).

    By using remote control power sockets I can fire up the two extractors at the same time with one button - not a fan of tool triggered extraction either - I prefer to choose how long it runs for and for several repeat cuts on the SCMS I can just leave them both running continuously. This is actually less noise aggravation because they are a constant noise rather than stop-start-stop-start-stop-start-stop-start-stop-start-stop-start-stop-start-stop-start which is probably not too good for the motors anyway.
    Regards, FenceFurniture

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  5. #4
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    ALL SCMS on the market has very small dust port. Only reasonable dust port I have seen is on the Omga where the dust port is 100mm. But Omga does not make SCMS, they make mitre saw, some of their mitre saw has blade diameter of 370mm.

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    I wasn't as clear as I could have been - an additional dust port so that two extractors can be used.
    Regards, FenceFurniture

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  7. #6
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    Hey Bob, thanks for the reply ... I thought that might be the case, so I will stick to a single 6" duct under the table, and then use my trusty pool hose on the built-in port to direct the majority of the dust right down into the duct. Its quite amazing how effective that little bit of hose is at simply directing the flow.

    Quote Originally Posted by BobL View Post
    There is no way that a DC7 generates 2400 CFM as it comes off the showroom floor..
    Understood. I included this purely as an indicator that I wasn't using a 60 year old preloved Electrolux.


    Fence Furniture ... do you have a particular brand of remote power point you use ? Where did you get them ? Might be a good addition for my DC (although - need to consider the magnetic switch).
    Glenn Visca

  8. #7
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    Quote Originally Posted by Glenn.Visca View Post
    ... do you have a particular brand of remote power point you use ? Where did you get them ? Might be a good addition for my DC (although - need to consider the magnetic switch).
    Mine are from Aldi but I'm not sure I can receommend them these days - 3 of 8 have failed. Maybe better off getting the Kambrook ones from Bunnings. They will take 10, or maybe 20 sockets on the one remote. My research shows that you buy the RC itself with 3 sockets from Bunnings (or it might have been Masters) and get the rest of the sockets from eBay. Major gouging if you go the other way around, for some bizarre reason.

    If you have a zero volt release switch then you have to work around that because they will be useless otherwise.
    Regards, FenceFurniture

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  9. #8
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    Just a thought. I recently posted my mitre saw enclosure Here's a link in case u haven't seen it already: https://www.woodworkforums.com/183643...st-extraction/

    I have found that a single 6" port right behind the blade gives me pretty much total dust extraction.

    Maybe u can adapt this idea into your design?

  10. #9
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    Hi john,

    Yours was one of the posts I reviewed before drafting my design, but my scms will be against a wall, which limits me to either top or bottom.

    But, I have certainly used parts of your hood as inspiration. My hood design is very approximate until I get the saw into place and can measure all of the boundaries.
    Glenn Visca

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    What about 1x 6" port through the right side about level with the existing dust port, instead of 1 top and 1 bottom?

  12. #11
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    It's an option john.

    I think I need to wait now until the saw is in place so I can work out all the boundaries in the various positions.

    Obviously I want to capture as much as possible in all positions.

    Thanks to all for comments.
    Glenn Visca

  13. #12
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    Quote Originally Posted by Glenn.Visca View Post
    Hi john,

    Yours was one of the posts I reviewed before drafting my design, but my scms will be against a wall, which limits me to either top or bottom.

    But, I have certainly used parts of your hood as inspiration. My hood design is very approximate until I get the saw into place and can measure all of the boundaries.
    Hi Glenn:

    If you have reviewed John's setup then you might have seen mine as well which I shared on his thread. I am absolutely amazed at how much more effective airflow is achieved through larger diameter ducts. I shouldn't be (amazed), as BobL and other knowledgeable guys have explained the theory again and again for our benefit. But now that I have experienced the difference between 3", 4", 5" and 6" ducting, I wish I had 5" and 6" flex/ducts to all machine ports!

    I have approx. 5" (or 140mm) flex at the back bottom left of my SCMS, and a 6" (or 150mm) flex at the right forward part of the shroud. I like my shroud set up, although if I were to do it again, I would not use butterfly nuts for the moveable top, but perhaps use some rare earth magnets. I can still do that in future.

    I positioned the two large ports as far apart as possible and on opposite sides of the shroud. I don't know if there is turbulence due to competition between the two? Probably.

    Anecdotally, it seems that the back one gets a lot of the big chips, while the front one gets the fine dust. When I turn the machine for a mitre joint towards the right, i.e. front of machine turned left, back of the machine angled to the right, the big chips end up more at the back right of the shroud rather than going down the 5" port. I'm not too worried about this as BobL/Pentz/etc. say to be more worried about the fine dust, not the chips. Before my current dust collection shroud, I could see dust choking the whole shop. Now I do not. Of course, that does not mean that the finest (invisible) dust has been captured, but according to the theory (i.e. large airflow, big ducts, ports close to the action, etc.), I hope that it has been an improvement.

    Anyway, I wish you all the best and look forward to your pictures in due course!
    Warm Regards, Luckyduck

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    Whatever you do definitley use the machines dust port as well. I find with a shop vac on my Makita SCMS it removes around 80% of the dust.

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    Quote Originally Posted by Burnsy View Post
    Whatever you do definitley use the machines dust port as well. I find with a shop vac on my Makita SCMS it removes around 80% of the dust.
    Thanks Burnsy. I agree that the shop vac gets a lot of the big chips. I still use my Festool CT36 on my SCMS, even with the big ports in place. Seems very effective. My big concern with my shop vac though is that I fear that it is no longer (perhaps never did?) capturing the finest dust. I can't remember the details, but I'm pretty sure BobL or someone else on the forum did some tests on real-world shop vacs and found that they leak (badly).
    Warm Regards, Luckyduck

  16. #15
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    Quote Originally Posted by Burnsy View Post
    Whatever you do definitley use the machines dust port as well. I find with a shop vac on my Makita SCMS it removes around 80% of the dust.
    Good idea but while it removes 80% of the mass of dust it probably only removes 8% of the total number of particles.

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