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  1. #16
    Join Date
    Apr 2008
    Location
    Southern Riverina
    Posts
    139

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    Thanks Bob, all understood except the last bit.

    I have no bags or filters at all. Perhaps I've used the word 'separator' incorrectly? I'm referring to the steel ring that the bag and filter normally attach to, that contains a rudimentary cone and directs the incoming air into a vortex. My understanding was that this was intended to help separate the heavier particles (which fall into the bag) from the lighter ones (which head up into the filter), in much the same way as a cyclone does.

    My fan blows directly into one of these rings for the reasons I explained above, but the ring has no filter on top amd only a short tube of shade cloth below. All chips and dust and air form a vortex in the ring and are ejected down through the tube onto a compost pile below.

    My (probably flawed) reasoning for adding the ring at all was that the air entering it via the factory (rectangular, tangential) port might be no more troubled than if it were simply exiting the raw impeller housing into free air, and it provides a convenient, ready made solution for directing everything where I want it to go.

    Obviously I could remove it, and either leave the blower exit totally naked or fabricate some kind of chute with an appropriate flare to reduce turbulence if you thought that would deliver better results?

    I'll try and add some pics later - just because I've used a thousand words doesn't mean I've explained anything!

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  3. #17
    Join Date
    Nov 2016
    Location
    USA, Indiana, West Lafayette
    Posts
    188

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    That steel ring you called a 'separator' is usually called a collector ring or bag holder. I call it a separator ring. As far as I'm concerned your nomenclature is absolutely correct.

    The problem with using it for expansion and direction change is the high cost in static pressure of rotating the air. There's no advantage to that rotation for your use.

    A simple elbow would have much lower pressure loss, but the high velocity can cause some "splash" of the debris when it hits the pile. To decrease the velocity expand directly out of the fan and then turn. You could use HVAC duct. It doesn't have to round, a simple fabricated box like duct will do fine.
    Dave

  4. #18
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    27,756

    Default

    OK that makes sense.

    I'd just put a Bell mouth hood or flare on the exit

  5. #19
    Join Date
    Apr 2008
    Location
    Southern Riverina
    Posts
    139

    Default

    Pic for fun:
    TS-dust-01.jpg

  6. #20
    Join Date
    Apr 2008
    Location
    Southern Riverina
    Posts
    139

    Default

    Thanks for the advice, I will ditch the ring and rotate the impeller housing through 90 degrees so it blows straight down and add a short, nicely flared chute.

    Bob, does this change your opinion of my setup? I was really hoping that the low resistance on the output side, coupled with nice open ports and no flexy on the input side, might get the 3HP motor working hard enough to justify its use over the cheaper 2HP unit?!

  7. #21
    Join Date
    Jun 2005
    Location
    Helensburgh
    Posts
    7,696

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    The absolute best dust control I know of on a router table was done by opening the area around the cutter and using a venturi effect to extract with through the table top. It is shown here....Yet another Router table build.
    CHRIS

  8. #22
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    27,756

    Default

    Quote Originally Posted by Dusty Dave View Post
    Thanks for the advice, I will ditch the ring and rotate the impeller housing through 90 degrees so it blows straight down and add a short, nicely flared chute.

    Bob, does this change your opinion of my setup? I was really hoping that the low resistance on the output side, coupled with nice open ports and no flexy on the input side, might get the 3HP motor working hard enough to justify its use over the cheaper 2HP unit?!
    Yes it makes sense now.

    The main advantage of the 3HP over a 2HP is it should handle the higher currents resulting from the increased flow caused by reduced back restriction. However, in such a situation would still be carefully monitoring the currents and the motor temp to see that they do not go too high. The currents should be OK when connected to a restricted machine but may be a problem when used in open port situations like turning. If the motor only gets slightly hotter then adding a fan to the outside of the motor might be worth considering?

    Don't forget you can't change the speed of these SP motors. They will both spin (minus some small slippage) at the speed determined by the mains power frequency. When the flow is restricted on either the input or output sides there will be more cavitation and turbulence inside the impeller housing which produces less overall flow.

    If you want a real increase in performance/flow then the impeller needs to be spun faster, so something like a 3P motor and a VFD is needed. That's what I have done on my setup.

  9. #23
    Join Date
    Apr 2008
    Location
    Southern Riverina
    Posts
    139

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    Thanks Chris, that's awesome inspiration! I was already thinking along the lines of some of it - ie, getting away from flexy stuck in the back of the fence, and improving the below-table cross-flow extraction - but MandJ really takes it to a whole new level!

    Thinking cap back on...

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