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  1. #106
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    Cheers Bob. Before installing the new junction, I took a manometer reading on the open 150mm duct and read 3.5".

    With the new junction installed, including the blast gate, I still read 3.5", so I am not moving any more air with the additional 2 x 100 ducts. Surprising ? I guess not.

    I then reassembled the shroud and connected everything up.



    (Picture sans flexi duct LHS).

    Of course, it soon became evident that while doing a marginally better job down at the base, it still wasn't as I would like, given all the experimentation.

    I then started to play with blocking off part of the 150mm top port, and could hear the velocity increase through the lower ducts. A couple of test cuts, and my upper capture from the saws port seemed adequate, and the pickup at the bottom better also.

    I am now radiusing the lower ports with rasp and file in an effort to reduce turbulence, and setting up the top duct "permanently", rather than just friction fit in the hole.

    I plan to have a play around with "eye lids" over the ports to mix the flow, but still maintain the 3.5" w.c.

    We shall see what happens eh ?
    Glenn Visca

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  3. #107
    Join Date
    Feb 2006
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    Perth
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    Quote Originally Posted by Glenn.Visca View Post
    Cheers Bob. Before installing the new junction, I took a manometer reading on the open 150mm duct and read 3.5".
    With the new junction installed, including the blast gate, I still read 3.5", so I am not moving any more air with the additional 2 x 100 ducts. Surprising ? I guess not.
    The 6" further rack along the line limits the total amount of air that can be moved. The idea of the 3 inlets is to collect it from a wider pattern.

    Of course, it soon became evident that while doing a marginally better job down at the base, it still wasn't as I would like, given all the experimentation.
    I wasn't expecting there would be any eye opening differences in performance.

    [QUOTE]I then started to play with blocking off part of the 150mm top port, and could hear the velocity increase through the lower ducts. A couple of test cuts, and my upper capture from the saws port seemed adequate, and the pickup at the bottom better also. I am now radiusing the lower ports with rasp and file in an effort to reduce turbulence, and setting up the top duct "permanently", rather than just friction fit in the hole. I plan to have a play around with "eye lids" over the ports to mix the flow, but still maintain the 3.5" w.c./QUOTE]

    Yep blocking off some ports to get more air collected from the others is all part of the game.

  4. #108
    Join Date
    Jan 2001
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    Langwarrin, Victoria, Australia
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    Well, I think this will be the last post for this thread ... unless I have an epiphany.

    I don't think I can improve things much beyond where I am at now.

    So to recap.

    10 Cuts through structafloor - no DC running.
    IMAG0935.jpg

    10 Cuts through structafloor - top 150mm duct only.
    IMAG0936.jpg

    10 Cuts through structafloor - top 150mm duct plus 2 x 100mm ducts each side.
    IMAG0946.jpg
    Note the dust pattern and the clear section extending to the left and right of the little ducts. This is clear testimony to BobLs advice to radius duct ports - as its quite clear it has a dramatic positive effect on air pickup.

    I had some A4 sized plastic project sheets that I picked up from Spotlight many months ago that I taped (gotta love duct tape) to the shroud in an attempt to remove dead air and generally improve flow. They seem to have a positive effect.

    Having consumed them, I cut up some old manila folders to make some more gentle curves heading up to the main duct.

    I ended up adding eyelids to all 3 ducts, while still maintaining 3.5" w.c. to get to the end result.
    IMAG0947.jpg

    IMAG0948.jpg

    After making the cuts, a little blast with the compressor nozzle, and we pick up the remaining dust.

    All in all, pretty happy now.
    IMAG0949.jpg

    I also took some current readings.

    DC disconnected from ducting (but bags and filter bags on). 5.1A

    All ducts closed. 2.5A

    All ducts opened. 5A

    With SCMS port open. 4.8A

    Can someone tell me what this means on a motor rated at 9.6A. I note the metal inlet to the D.C. is a tad less than a full 150mm PVC duct. Say around the 140mm range. Does this present possibility to replace that inlet with a full 150mm ?

    Bob thanks very much for your ideas and recommendations.

    Others who replied - thank you too ..

    Those who viewed - I hope this little endeavour provided some ideas for your future endeavours.

    If anyone would like some sketchup drawings of the junction box - send me a PM with your email address - and I will gladly send through.
    Glenn Visca

  5. #109
    Join Date
    Oct 2013
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    New Zealand
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    I've been keeping an eye on this thread and would like to say thank you for sharing the data and all the photos! Very informative and gives me a bunch of idea for when I get around to building something similar.

  6. #110
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    Quote Originally Posted by Glenn.Visca View Post
    I also took some current readings.
    DC disconnected from ducting (but bags and filter bags on). 5.1A
    All ducts closed. 2.5A
    All ducts opened. 5A
    With SCMS port open. 4.8A

    Can someone tell me what this means on a motor rated at 9.6A. I note the metal inlet to the D.C. is a tad less than a full 150mm PVC duct. Say around the 140mm range. Does this present possibility to replace that inlet with a full 150mm ?.
    The motor on the DC7 would almost certainly be used on a range of Machinery and the 9.6A represents a nominal current that the motor can run at more or less continuously under load.
    Remember a high load on a DC is when it does it's most work i.e. moving lots of air.
    When a DC is blocked it cannot move air and so it just moves the same air around inside the impeller housing

    The fact that the motor is not drawing close to its 9.6A rating also means it is not developing its full 3HP - in other words it is somehow being restricted.
    This is not that unusual for DCs like the DC7 which is an older DC design and with its tortuous impeller to filter bag housing path, and like you said the 140 mm entry, is probably causing this.

    Even though the 140 mm intake is only ~7% smaller in diameter than a 150 mm intake and only 15% smaller in area, in terms of air flow it will be ~25% less efficient than a 150 mm diameter duct.

    The generic 2HP (DC3 equivalent, rated at 7.7A) DC that I modified in this thread https://www.woodworkforums.com/f200/generic-2hp-dc-171247 started out (with no bags or filters) drawing 5.2A. (1.6HP).
    Removing, the whole (300 mm diam) impeller inlet front, and the outlet between the Impeller and filter housing resulted in the motor drawing 6.2A or 1.97HP.
    After I modified the impeller to a bigger bell mouthed entrance, and less restrictive exit it drew 5.4A - not a whole lot better than 5.2A but consistent with an improvement in flow

    For comparison my 3HP DC draws around 9.2 A with all ports open and about 6.8 A with all ports closed.

    It's a lot of trouble but it would be worth seeing what current the motor draws with the whole front of the impeller removed and the S-bend impeller to bag bousing removed.
    If you decide to do this the current should be watched carefully to make sure it does not exceed the rating or it will over heat the motor.
    I won't happen right away and you will have more than enough to turn it off if required.

    Going back to the current draw by the DC7 motor when your SCMS ports only are opened, the fact that it drops to 4.8 A from 5A with all ports open.
    Is that for with or without the eyelids?

  7. #111
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    Thanks again Bob. I am going to answer your questions a little backwards.

    Quote Originally Posted by BobL View Post
    Going back to the current draw by the DC7 motor when your SCMS ports only are opened, the fact that it drops to 4.8 A from 5A with all ports open.
    Is that for with or without the eyelids?
    Same / same. When I was placing the eyelids, I closely watched the manometer to ensure that I didn't change W.C. (we call this tuning... )


    Quote Originally Posted by BobL View Post
    It's a lot of trouble but it would be worth seeing what current the motor draws with the whole front of the impeller removed and the S-bend impeller to bag bousing removed.
    If you decide to do this the current should be watched carefully to make sure it does not exceed the rating or it will over heat the motor.
    I won't happen right away and you will have more than enough to turn it off if required.
    You piqued my interest, so I went back and did a comprehensive test - save for removing the S Bend housing (but I think you will see some interesting things from the data below).

    First off, the inlet ID is ~150mm at the impeller side, however, there is an internal lip in the steel inlet (presumably to give some strength, that reduces the effective size to ~140mm. There is a bullseye in there too.

    The impeller O/D is ~290mm from blade edge to blade edge, with the internal core being ~135mm.

    The blower outlet to the S Bend is 160x120mm, as are each of the bag chutes off the S-bend. So, by my theory, this means my max inlet to match those outlets would be 156.35mm.

    I ran two series of tests, first as I progressively deconstructed the D.C., and then as I reassembled I ran them again. Now, you may recall that in another thread, I had asked my mother (who very sadly passed away on August 31st ( ) to make me some calico bag inserts for the collection bags in an effort to minimize chips rattling around the inside of the collection bags and puncturing them. During the "Test 2" round I removed those bags, and I must say, I also gave the filter bags a clean out too. To say they were grotty is well ... ahem ... ahem ... and but of an understatement.


    Description Test 1 Test 2
    All Closed 2.45A 2.53A
    All Open 4.77A 5.06A
    SCMS (with eyelids on) 4.55A (W.C. 3.5") 4.77A (W.C. 4")
    SCMS (with eyelids off 4.55A 4.77A
    At impeller with inlet ON, bags and filters ON 4.6A 4.8A
    At impeller with inlet OFF, bags and filters ON 5.7A 5.9A
    At impeller with inlet off, bags and filters OFF 5.94A to 6.00A


    I also noticed during my final "all closed" test, I could see air moving around inside the now clear collection bags. Clearly I have more of a leak somewhere that I haven't yet taped. There are only 2 places left which I will have to get to soon.

    What all this tells me is that I can generate some improvement by changing the inlet to a 150mm duct. Could possibly go a little larger, but its not going to gain anything while the blower outlet and the S-Bend is the size it is.

    Gee I wish I had a pitot tube or an anemometer. But anyways, these tests still speak volumes.

    Cheers,
    Glenn Visca

  8. #112
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    Thanks Glen, very comprehensive and getting a little clearer.

    OK so the benefit of
    - cleaning the bags is demonstrated by the fact that the current drawn using cleaned bags is close to the current with no bags.
    - going to a 150 mm inlet is also worthwhile. I wouldn't bother to go any larger as your 150 mm ducting is the limiting step.

    I was still perplexed as to why the motor is not drawing more current with the impeller entry and the bags off.
    But now I realise that the impeller is just under 12" in diameter which is the same as the DC3 impeller.
    This tells that even if a 3HP motor is used that impeller size only requires ~2HP to run at full speed anyway.
    It terms of performance the only benefit of the DC7 over a DC3 is then twin bags which are worth having because they reduce construction and increase flow.
    This is worth knowing as some members have asked me if that impeller/combo would be suitable for converting to a cyclone but unfortunately that impeller size is too small.

    RE: Eyelid pressures. The reason I asked about this was although the visual suggests the eyelids keep chip better under control they may compromise total air flow and not be so effective at fine dust control. But the fact that the pressure drops and currents are the same for eyelids and no eyelids indicates that air flow is not a problem.

    Thanks for doing those tests they are very informative.

  9. #113
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    Not at all Bob .. thanks heaps to you!
    Glenn Visca

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