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  1. #91
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    Quote Originally Posted by BobL View Post
    I assume you are prepared to install two independent sets of 6" ducting thru the shed?
    If not then the limit is that 6" ducting can only carry a maximum of about 1250 CFM. It matters naught if one or 2 3HP DCs are hooked up in parallel 6" can still only move 1250 CFM.
    I was thinking along the lines of using a single 8 inch pipe (call it 64 units of area), which via a Y junction and say a metre of a tapered ducting) would connect to two 2hp units running in parallel. My thinking was that after allowing for boundary effects, the effective area of an 8in duct is approximately 2x the effective area of 6in duct.
    Would two 2 hp units separated connected to a manifold, be able to move sufficient air along an 8 in duct.



    The other "option" that comes to mind is to fit a 1 hp blower immediately adjacent to a major dust producing major machine to evacuate the machine and "pressurize" the duct so that a 2hp unit at the filter / bag end has oomph to move the required volume of air.
    regards from Alberta, Canada

    ian

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  3. #92
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    [QUOTE=ian;1902725]I was thinking along the lines of using a single 8 inch pipe (call it 64 units of area), which via a Y junction and say a metre of a tapered ducting) would connect to two 2hp units running in parallel. My thinking was that after allowing for boundary effects, the effective area of an 8in duct is approximately 2x the effective area of 6in duct.
    Would two 2 hp units separated connected to a manifold, be able to move sufficient air along an 8 in duct. [QUOTE]

    Inside the Y junction where the air splits in two the air streams going to the two DC will fight each other for the limited supply of air. This will create turbulence and reduce flow through both of them.
    The limitations are the 2HP Generic 2HP 4" inlets - this limits the flow to about 400 CFM.
    It's difficult to determine what the turbulence will do using 2 x 2HP DCs but you wont get 2 x 400 or 800 CFM, probably around 650-700 CFM.

    It would make far more sense to modify the 2HP Units along the lines of my recommended Mod in the Sticky at the top of the dust forum.
    After modification using 6" ducting generates >850 CFM

    OK you might want to connect 2 MODIFIED 2HP DCs, each around 850 CFM, to an 8" duct, but because of what I said above you won't get 1700 CFM maybe 1400 CFM - which is theoretically equivalent to the smaller ClearVue.

    However, dust extraction is not just about total CFM moved. It's more about what can the impeller deliver under restrictions imposed by ducting, junctions, machines and bags. The 2HP bags are small and quite restrictive (much more so that the twin bags on big 3HP units) and as the load increases a machine with a bigger well made impeller like a Clearvue will move more air under load than a twin 2HP setup as described.

    Despite what I said I would still provide very good flow and you could guarantee >1000 CFM
    BUT - is t worth it?
    You need 2 x 2HP DCs
    They need to be modified according to my recommendations
    Then you need to use 8" ducting, expensive, especially junctions - then you need to open up machines to 8" ducting EEEK - some machines don't have enough space to accommodate 6" ducting.
    More floor space needed
    More noise generated
    And 2 x 2HP DCs would use ~ 15A in total versus about 9A for a 3-4HP DC - this demonstrates the better efficiency of a bigger impeller.
    That 6A difference doesn't sound like much but it sure adds up.
    Lets say 6A x 240V X 26c/kWhr = 37c/hour MORE to run.
    20 hours a week x 52 weeks a year = $390 a year.
    It would not take many years to buy the ClearVue.

    Even if you already had 2 or 3, 2HP DCs, like I said previously, it would makes more sense to modify the machines and use them judiciously on separate sets of machines with 6" ducting.

    The other "option" that comes to mind is to fit a 1 hp blower immediately adjacent to a major dust producing major machine to evacuate the machine and "pressurize" the duct so that a 2hp unit at the filter / bag end has oomph to move the required volume of air.
    This definitely won't work. A 1HP simply doesn't move enough air. It would only pull about 400 CFM from a machine. A standard 2HP can pull 600 cfm BUT the 1HP is in like so it throttles the flow and all you will end up with is somewhere between 400 and 600. It would be better to just used the 2HP Unit.

  4. #93
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    Quote Originally Posted by BobL View Post
    20 hours a week x 52 weeks a year = $390 a year.
    It would not take many years to buy the ClearVue.
    Jeezuzzzz wouldn't i love 20 hrs of shed time a week!! And how much shed time involves having the dusty running? maybe 10% I think?

    How long to pay for the clearvue at $39 per year? and I am being generous here! Come on, I spill more beer than that.

    Cheers

    Doug
    I got sick of sitting around doing nothing - so I took up meditation.

  5. #94
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    Quote Originally Posted by doug3030 View Post
    Jeezuzzzz wouldn't i love 20 hrs of shed time a week!! And how much shed time involves having the dusty running? maybe 10% I think?
    How long to pay for the clearvue at $39 per year? and I am being generous here! Come on, I spill more beer than that.
    Cheers

    Doug
    It sounds like you are not running your DC for anywhere near as long as you should.
    If you are only running it while a machine is cutting or sanding then you will always have high fine dust levels in your shed.
    It depends on the size of the shed but for a 6 x 4 x 2.4m shed, to minimise exposure to fine dust I would run a 2HP for at least 10 minutes after the each light/small/short dust making activity and for at least 20 minutes after each heavy dust making activity. For most woodworking that involves machinery means basically leaving the DC running after the first dust making activity until you leave the shed..
    For a 3HP DC those times can be halved because it grabs more dust at the source,

    Besides
    - some retired blokes do 40 hours plus.
    - it also depends what you are doing - turning means DC should be on ALL the time
    - same for sanding and routing.

    I haven't been doing much wood work for the last few years but today I ripped docked and sanded about 20, 1.8m long pine boards. Then I sanded a kiddies cot with lots of dowel rungs, and then did a but of turning - all up the DC would have been running for ~6 hours.

    I really should remember to switch the DC off when it is just being used as a shed vent as I now have a 1/4HP squirrel cage fan located high up near the roof line - it draws ~1200 CFM but draws less than 1A.

  6. #95
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    Quote Originally Posted by BobL View Post
    It sounds like you are not running your DC for anywhere near as long as you should.
    If you are only running it while a machine is cutting or sanding then you will always have high fine dust levels in your shed.
    It depends on the size of the shed but for a 6 x 4 x 2.4m shed, to minimise exposure to fine dust I would run a 2HP for at least 10 minutes after the each light/small/short dust making activity and for at least 20 minutes after each heavy dust making activity. For most woodworking that involves machinery means basically leaving the DC running after the first dust making activity until you leave the shed..
    I run the dusty for a while after the machine stops. There are two "bathroom" style exhaust fans that run from when I go into the shed until I leave or sometimes until the following morning (sometimes by design and sometimes due to absent-mindedness).

    My recent - extremely heavy dust generating activity - wearing out my old thicknesser cutterhead prior to installing the helix one, has been done outside the shed where the prevailing breeze deals with the dust. When I use my lathe it is generally in the undercover outdoor entertaining area/carport, which has good airflow. Now that the weather is getting warmer and daylight saving has started, it is nice to spend a bit of time working outdoors of an evening anyway.

    When I moved into this shed a couple of years ago, it was very dusty. I cleaned it up for the good of my health. It has remained extremely clean since, without any effort apart from sensible dust management practices. I have had no need to attach a brush to a stick and sweep the walls and rafters like I had to when I moved in.

    Cheers

    Doug
    I got sick of sitting around doing nothing - so I took up meditation.

  7. #96
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    Quote Originally Posted by doug3030 View Post
    I run the dusty for a while after the machine stops. There are two "bathroom" style exhaust fans that run from when I go into the shed until I leave or sometimes until the following morning (sometimes by design and sometimes due to absent-mindedness).
    Thats good that you leave them on all the time. All axial fans that feel like they move a lot of air, but some of that air is recirculated air that goes back through the fan so the total movement is not as high as it feels. This is why Squirrel cage or impeller fans are much better at moving air. Axial fans perform very poorly under restriction so the first thing I would do is remove any grille or guard. This increases the flow but also increases the recirculation within the fan. The most efficient Axial fans are those with wide blades that overlap significantly and have the minimal gap between the blades and the outer housing.

    My recent - extremely heavy dust generating activity - wearing out my old thicknesser cutterhead prior to installing the helix one, has been done outside the shed where the prevailing breeze deals with the dust. When I use my lathe it is generally in the undercover outdoor entertaining area/carport, which has good airflow. Now that the weather is getting warmer and daylight saving has started, it is nice to spend a bit of time working outdoors of an evening anyway.
    I wouldn't be relying on working outside as a way to get around dust exposure. I lost my sense of smell for 6 weeks in 2002 working outside with MDF. For heavy dust generation if you cannot do anything else I would recommend at least wearing a mask.

    When I moved into this shed a couple of years ago, it was very dusty. I cleaned it up for the good of my health. It has remained extremely clean since, without any effort apart from sensible dust management practices. I have had no need to attach a brush to a stick and sweep the walls and rafters like I had to when I moved in.
    That sounds more like an indictment of the previous owner than the cleanliness of your practices.
    Anyone who needs to sweep walls and rafters really does have a problem.
    I'm rarely talking or worrying about dust that can be seen, which is very difficult to manage even when one has access to fine dust measuring gear.

  8. #97
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    Quote Originally Posted by BobL View Post
    I wouldn't be relying on working outside as a way to get around dust exposure. I lost my sense of smell for 6 weeks in 2002 working outside with MDF. For heavy dust generation if you cannot do anything else I would recommend at least wearing a mask.
    *sigh* Yes Bob. I thought it would go without saying that I wear safety glasses, hearing protection and respiratory protection as appropriate to the activity, inside the shed or outside.

    That's almost like telling me to be careful not to put my fingers on the blades.

    Cheers

    Doug
    I got sick of sitting around doing nothing - so I took up meditation.

  9. #98
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    You have done a wonderful job of maximising your saws effectiveness and dust control. A lesson for newbies like me. Top duct I'll follow you guidelines.

    Bottom duct is a bit trickier. The cabinet has a slightly sloping floor and a 4" outlet that can be easily modified like Bob's and your plans but it also has a 2" duct coming from a cowl under the blade to join the 4" outlet by a junction taking up the top 1/2 of the 4" outlet. I'll put in a more acutely sloping floor and a 6" outlet plus a collector on top but not sure what to do with 2" duct. Pass it out through cabinet and join via a y junction or leave it open to drop into the bottom and then the 6" duct?

    Sorry pic appears to be on it' side. Don't know why as original was OK.
    Attached Images Attached Images

  10. #99
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    The 2" ducting from the blade cowl is there to stop bits from falling onto the motor and belt because the 4" dust collection is so crap at doing this. The cowl clutters the inside of the cabinet rather badly and increases the ejection of fine dust from the blade above the table. I would remove the cowling completely. If you have 6" ducting the air flow will keep that area MUCH cleared than before.

    However there is a small risk that a piece of wood may fall through from above table and get jammed between the belt and pulleys. To reduce that risk I run a zero clearance throat plate and only swap it out for angled cuts (i.e. hardly ever). An alternative is to build a small cover for the belt.

  11. #100
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    Thanks Bob just the advice I was looking for. I'm away from home at the moment but will look seriously at this when I get back. And duct/cowl on top as per John's design.

  12. #101
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    Bob I have been reading this thread and others for ages but still find it hard to bring it all together when planning my own system. The quotes/info below are gems that are hidden in pages of general blurb. It would be fantastic if you and or others could bring some of these guidelines for beginners together as a sticky or at the start of this thread. It might also save you from repeating the same things over and over to newbies like me.


    Quote Originally Posted by BobL View Post
    2 x 90º bends will generate a pressure loss equal to ~10 ft of straight duct or 3.5ft' of flex so you can work out which is best
    I suspect there won't be much in it and I would just do what is easiest..

    9 ft of flex will reduce airflow about 10% of your air flow whereas 9ft of straight pipe will reduce it by 3%.
    How are you dealing with the saw guard?.
    Quote Originally Posted by BobL View Post
    A basic guideline to maintain smooth (minimal turbulence) air flow is that there should be 5 (and preferably 10) duct diameters between junctions and bends.
    The DE itself is classified as a junction
    In practice in a DIY shed this is very difficult so you do the best you can.
    Normally it would be better to go bigger and use a bigger bell mount but its not advisable for the ducting entering a standard type impeller to be more than half the diameter of the impeller otherwise the impeller will not develop its proper pressure differential. '



  13. #102
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    Quote Originally Posted by Rabbott View Post
    Bob I have been reading this thread and others for ages but still find it hard to bring it all together when planning my own system. The quotes/info below are gems that are hidden in pages of general blurb. It would be fantastic if you and or others could bring some of these guidelines for beginners together as a sticky or at the start of this thread. It might also save you from repeating the same things over and over to newbies like me.
    Yeah I agree, I must have written some of this stuff over and over again. Maybe when I retire from my retirement I should write something.

  14. #103
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    Quote Originally Posted by Rabbott View Post
    Bottom duct is a bit trickier. The cabinet has a slightly sloping floor and a 4" outlet that can be easily modified like Bob's and your plans but it also has a 2" duct coming from a cowl under the blade to join the 4" outlet by a junction taking up the top 1/2 of the 4" outlet. I'll put in a more acutely sloping floor and a 6" outlet plus a collector on top but not sure what to do with 2" duct. Pass it out through cabinet and join via a y junction or leave it open to drop into the bottom and then the 6" duct.
    Difficult to see much from the pic ... but do you need that cowl and 2 in duct at all? If the air is flowing in the right direction (which requires some thought about where it gets into the cabinet, its path through and out of the cabinet) and there is enough of it at the appropriate velocity, could it be done away with/replaced with something simpler? I am concerned that the cowl and the 2 in duct could be restricting airflow past the blade and into the duct.

  15. #104
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    Good idea. I'm away at the moment but when I get back home will have a closer look and post some better pics. Good to draw on your experience.

  16. #105
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    Several people have PMed me about the generic 2HP DC mod, especially how this thread is a WIP and cluttered with additional info, and said they would like to see the mod summarised into one or 2 posts.
    So here goes.

    Start by removing the large impeller intake flange and use it as a template to draw a replacement (size and screw locations) onto material, as per the white piece in this photo.
    The Generic 2HP DC-6inchinlet-jpg
    You can use sheet metal (as per photo) or MDF for the replacement flange,

    The hole in the middle of the flange is NOT the OD of the ducting but OD + OD/2, so for 6" ducting the hole is ~9" in diameter
    An adapter flange is then made from some thicker material the central hole of which has an curved edge opening that is OD on the outside to OD + OD/2 on the inside.
    This is known as a "Reverse Bell Mouth Port"
    My adapter flange as shown in the above photo is made from 32 mm thick Melamine.

    On the inside it looks like this - this is not a REVERSE bell mouth port (air flows from narrower to wider opening) but a normal Bell Mouth Port (air flows from wider to narrower opening) as used to collect dust while turning. The curves are the same for both ports


    Cross Section wise Bell mouth ports looks like this - in this case the machine cavity is the impeller cavity
    6" port upgrade for a 15" Thicknesser-bellmouthport-jpg

    Here is another view showing the step for smooth transition of the 6" duct to inner curved edge.
    The Generic 2HP DC-joinedup3-jpg

    To be theoretically correct I should have used thicker (37.5+ mm) melamine but it is not critical as long as there is a nice fat curved entry way - in the case of the 2HP impeller no wider than OD + OD/2 otherwise the performance of the impeller will be compromised..

    The above will no little to improve the air flow unless the following is also undertaken.

    Remove the whole impeller from the DC and remove the outlet flange (usually plastic)
    Make a stand and outlet flange adapter that will enable the impeller to be held up close to the filter bag housing like this

    The Generic 2HP DC-combo2-jpg
    Above is how I did mine but it could just as easily be made using MDF like this one below by Jonno
    5in Flex or 4in DWV pipe?-image-7-jpeg

    With the outlet flange adapter molter to the filter bag housing the hole in the bag housing can then be accurately marked out.
    Remove the outlet adapter flange and cut out the opening with a thin kerf cutting wheel on an angle grinder
    The Generic 2HP DC-hole-jpg

    Block up the old round filter bag housing inlet - this is how I did mine.
    The Generic 2HP DC-holepatch-jpg

    Finally seal everything up as air tight as possible using an appropriate sealer.
    You may need to use foam or rubber gaskets to fill large gaps.

    The air flow obtained with this mod is a significant improvement over the original DC and well worth doing.

    Back to TOC.
    Last edited by BobL; 5th March 2020 at 02:02 PM.

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