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  1. #76
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    Apr 2003
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    Gold River, California
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    Quote Originally Posted by Chris Parks View Post
    Bill, I have been aware of the 7" duct being superior for some time and have mentioned it here in posts but the problem is 7" is unobtainable for all intents and purposes in Australia.
    Chris,

    You are absolutely right and are seeing the same problem I had to address back in early 2000, except I had already landed in the hospital so was motivated to find a real solution. After upgrading to finer filters on my dust collector, adding a cartridge filter, building my own cyclone, and installing all 4" ducting, nothing worked well, so tired of playing dust collection instead of doing wood working I stupidly threw money at the problem. I installed the top magazine rated cyclone system with vendor designed and supplied ducting plus their finest most expensive filter. I hated that system the day it was turned on. Airflow and collection were far worse than my prior system. It came configured with 1", 2" and 3" down drops to attach to my smaller hand held tools that worked so poorly I immediately stopped using them and went back to my big shop vacuum. All other machines got a single 4" down drop and those also worked dismally. The graduated main that went from 8" to 4" looked impressive, but built up huge piles in the duct that when the larger gates were opened these piles slammed down the duct so hard they blew apart my aluminum taped duct joints and destroyed my expensive fine filters. It had so many problems I decided to junk it and go with a commercial system. Instead, less than three months later I was in the hospital with a severe allergic reaction, most likely to the cocobolo, teak, rosewood, red cedar and ebony I used making Christmas gifts.

    All our small shop vendors, magazines, dust collection books, and even forum folks said this system I already installed the best we had in the industry, but it did not work. Everyone assumed that a dust collection system able to suck up sawdust, chips and even tape measures would more than suck up the fine dust we can move with the lightest breath. This sounds logical but is dead wrong. I got all tested and was educated by the experts. Fine dust is so light that it stays airborne in normal room air currents, plus it leaks from all over our machines, so unless we upgrade tool hoods and move about three times more air than it takes for good chip collection room air currents will spread the fine dust before it can be collected. The expert advice called for my shop needing a 7.5 hp or 10 hp 3450 RPM motor turning at least a 16" diameter material handling impeller and all 7" diameter down drops and 8" mains. Only 6" or 8" diameter duct was readily available and affordable, plus my shop panel was maxed out and could not power more than a 5 hp motor. After a lot of research and some experimentation, I came up with having to use an oversized blower that moved a real 1200 CFM through 6" duct. Then I discovered all standard cyclones pass 100% of the under 30-micron sized airborne dust particles into our fine filters which quickly loads them up and ruins them, so I came up with a new cyclone design that is independent medical school tested to separate 99.9% of the fine dust down to 4.7-microns. I shared my results and building plans for anyone who wants to build one for their own personal use, but do no permit folks building them for sale except Clear Vue who has that exclusive contract.

    So either use an oversized blower or use all 7" sized duct... I chose the oversized blower. Most use standard blowers and 6" duct so measured results all tend to perform at about the 785 CFM range.

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  3. #77
    Join Date
    Apr 2003
    Location
    Gold River, California
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    46

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    Quote Originally Posted by Lappa View Post
    In essence you are saying you achieved 1100 CFM using a 1 HP dust collector with 7" piping - correct?
    Lappa,

    No, I don't know how to get those kinds of flows from a 1.5 hp dust collector. I oversaw three sets of magazine tests for dust collectors. Jet and Delta consistently tested as not only the best performing major brands of dust collectors, but also were the only ones with fan curves that showed someone actually engineered their blowers. All of the rest of the 1.5 including the few who claim 2 hp but only draw amps consistent with a 1.5 hp unit tested well below the 1100 CFM maximum airflow. Inspection showed poorly designed impellers, blower housings and especially poor blower outlets and transitions. We tested all the blowers detached from the dust collectors with no filters and ducting except a special oversized test pipe that had a large control valve that let us adjust the size of the opening which also adjusts pressure. At maximum opening the Jet got a real 1100 CFM, but when we added back on the filters, etc. working performance dropped to between 785 and 550 CFM over the normal filter resistance range. In fact, virtually all tested at about half the working airflow of what we measured as maximum. The added resistance of using 4" down drops, 4" diameter duct/flex hose, or 4" tool ports dropped working airflows into the 350 CFM range. So no, I know of no viable way to get a real 1100 working airflow from traditional dust collectors.

  4. #78
    Join Date
    Feb 2006
    Location
    Perth
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    Quote Originally Posted by bill pentz View Post
    At maximum opening the Jet got a real 1100 CFM, but when we added back on the filters, etc. working performance dropped to between 785 and 550 CFM over the normal filter resistance range. In fact, virtually all tested at about half the working airflow of what we measured as maximum.
    Thats more or less I see with the generic 12" Impeller 2HP DCs that are very commonly used here is Australia.
    The impeller comes standard with a single 4.5" inlet spilt into two 4" inlets and an outlet of equivalent area to a 6" duct but it usually connects to the filter bag housing via a 5" duct.

    Opening up the impeller inlet to accept a 6" duct, the naked impeller can generate ~1100 CFM but as you so often ay Bill, the fan curve that stymies these small impellers
    Attaching a clean needle felt filter drops the 1100 to 850CFM (pleated filter does 925 CFM).
    These 2HP units can only handle short runs of ducting and minimal junctions AND the machinery has to be opened up to reduce resistance.

    Many DIY'ers in Australia operate in small shops with only one 10A circuit (16A breaker) available and especially in rented situation will not be able to use more than 2HP of DC power. For them this is the only DC option available.

  5. #79
    Join Date
    Jan 2014
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    Sydney Upper North Shore
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    4,464

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    Bill,

    in your first post you stated, and I quote
    "My 1. hp dust collector is one of the better and tests with a maximum airflow of 1100 CFM, but what happens to that airflow when I use smaller than 7" diameter ducting is scary."

    From that statement it would be normal to assume you had a 1.hp dust collector that achieved 1100 CFM with 7" ducting would it not.

    Now you saying you don't?

    I'm confused

  6. #80
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    Feb 2006
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    Perth
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    Quote Originally Posted by Lappa View Post
    Bill,

    in your first post you stated, and I quote
    "My 1. hp dust collector is one of the better and tests with a maximum airflow of 1100 CFM, but what happens to that airflow when I use smaller than 7" diameter ducting is scary."

    From that statement it would be normal to assume you had a 1.hp dust collector that achieved 1100 CFM with 7" ducting would it not.

    Now you saying you don't?

    I'm confused
    I think he meant 1.5HP ?

    Bear in mind it's unrestricted. I have a 1/3 HP squirrel cage fan that moves 1600 CFM and and 1/4 HP that moves 1200 CFM but as soon as a small restriction is placed in the flow it drops dramatically.

  7. #81
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    Feb 2006
    Location
    Perth
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    In Fletty's shed thread over it the Shed forum there has been a discussion about PVC flanges and I got to thinking - there's not a lot of difference between BMHs and flanges so I modified a 100 mm BMH former to have a much narrower radius of curvature and guess what - it works.

    Th shoulder is not perfectly square which is what would be ideal for a blast gate.
    However - I have a plan to make another former with a completely square shoulder and then put the rounded shoulder flange on that and use more of a point source of heat to just heat the outside of the shoulder and push the curve into the corner = all this happens of course while the lathe is suing it ~60 rpm.
    IMG_1924.jpg

    Here's what the front looks like compared to a 100 mm BMH (top) - not that different to the standard commercial 100mm floor drain flange
    IMG_1923.jpg

    I've rub out of former material and will need to go down to the milling yard and pick up some short ~250 mm diameter logs.

    I can see I'm going to end up with a library of formers,
    100 mm BMH
    100 mm flange - slight round
    100 mm square shoulder flange
    And repeat for 150 mm

    I will need some more face plates!

  8. #82
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    Feb 2006
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    Perth
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    Quote Originally Posted by BobL View Post
    Th shoulder is not perfectly square which is what would be ideal for a blast gate.
    However - I have a plan to make another former with a completely square shoulder and then put the rounded shoulder flange on that and use more of a point source of heat to just heat the outside of the shoulder and push the curve into the corner = all this happens of course while the lathe is turning it @ ~60 rpm.
    I found a 150 square piece of Tuart on the midden and turned up a 90º square shouldered former for the partially formed 100 mm flange.

    The first flanges I made above have a radius of curvature at the shoulder of about 12 mm (CF the BMH which have a 25mm radius)

    Using the square shouldered former and a focused hot air gun the best I could convert these to was ~7.5mm radius of curvature.

    I think it needs something like a hot metal shoulder or push from the outside of the PVC shoulder to push the soft PVC into the 90º former shoulder

  9. #83
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    Feb 2006
    Location
    Perth
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    Just cross linking a post on bandsaw dust extraction in Hand Tools and machinery forum to this thread.
    More bandsaw dust extraction ideas.

    That post discusses this arrangement for under table extraction.
    More bandsaw dust extraction ideas.-img_1919-jpg

  10. #84
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    Feb 2016
    Location
    Canberra
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    5,124

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    I like the linkage and how it's moveable.

  11. #85
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    Feb 2006
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    Perth
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    Quote Originally Posted by woodPixel View Post
    I like the linkage and how it's moveable.
    Thanks WP, The hex socket closest to the door will be replaced by a knob of some kind as this is the one that has to be loosened to drop the BMH do the door can be opened.
    Wa using it yesterday and and its working well.

  12. #86
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    Feb 2006
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    Perth
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    Was talking to a bloke from the mens shed this morning and he suggested not worrying about trying to get the shoulder square and just bog up the gap produced by rounded shoulder with "no more gaps".
    Think I might give that a try before tackling squaring the shoulder.

    Flange1.jpg

  13. #87
    Join Date
    Oct 2014
    Location
    South Australia
    Posts
    86

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    @ Bob,
    Just trying to catch up with what you have on the bandsaw.
    So your using a bell mouth at the guides under the table, are you still using the cut out pipe at the back of the table in conjunction with this?
    If so, are you using a third extraction point anywhere?
    Cheers,

  14. #88
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    Mar 2005
    Location
    Camden, NSW
    Age
    74
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    3,576

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    Quote Originally Posted by BobL View Post
    Was talking to a bloke from the mens shed this morning and he suggested not worrying about trying to get the shoulder square and just bog up the gap produced by rounded shoulder with "no more gaps".
    Think I might give that a try before tackling squaring the shoulder.

    Flange1.jpg
    Hi Bob, if you are referring the 'flange' application not the 'BMH' application then I don't think there's any need to square up the junction anyway? Just make sure that the inserted 150mm pipe is cut square and inserted all the way to the face and then the inner surface of the duct blocks off the discontinuity?

    fletty
    a rock is an obsolete tool ......... until you don’t have a hammer!

  15. #89
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    Feb 2006
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    Perth
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    Quote Originally Posted by mase View Post
    @ Bob,
    Just trying to catch up with what you have on the bandsaw.
    So your using a bell mouth at the guides under the table, are you still using the cut out pipe at the back of the table in conjunction with this?
    If so, are you using a third extraction point anywhere?
    Cheers,
    I've tried just about every combination
    Currently I use 3 extraction points.
    A One under table with a BMH as shown in post #83 above which does most of the work.
    B The original dust port at the front top of the cabinet, this does the least of all 3 points
    C The original dust port at the bottom right of the cabinet - this vents the cabinet but very little duct gets there anyway because the under table point is so effective.

    Because B is sort of redundant I'm looking to move that one back above the cutting operation.


    Quote Originally Posted by fletty View Post
    Hi Bob, if you are referring the 'flange' application not the 'BMH' application then I don't think there's any need to square up the junction anyway? Just make sure that the inserted 150mm pipe is cut square and inserted all the way to the face and then the inner surface of the duct blocks off the discontinuity? fletty
    Not quite - Remember I'm using ducting to make the flange and I can't insert regular ducting inside a piece of ducting - well not without stretching it first but then I'm not sure the stretched ducting would cope with being stretched further into a flange. Joining to ducting would require a coupler of some sort or an expanded piece of ducting.

  16. #90
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    Mar 2005
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    Quote Originally Posted by BobL View Post
    Not quite - Remember I'm using ducting to make the flange and I can't insert regular ducting inside a piece of ducting - well not without stretching it first but then I'm not sure the stretched ducting would cope with being stretched further into a flange. Joining to ducting would require a coupler of some sort or an expanded piece of ducting.
    Good point! A split ring only the length of the radius, would have the same effect but of course reduce the inner diameter by the thickness of the duct wall. I'm still using my last few 150mm electrical conduit bell mouths, built like battleships!
    a rock is an obsolete tool ......... until you don’t have a hammer!

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