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  1. #76
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    I'll let BobL respond in detail, but here is my experience.

    The losses from the machines and their hoods/shrouds is greater in my system than the losses from PVC pipe, including the bends.

    I used two 45 degree bends joined together instead of a single 90 degree bend. That seems to have helped. There is only one 90 degree bend in my main line, and I went a bit berserk with it (see pic) but it seemed to work well.

    IMAG0021.jpg

    My work to address hoods/shrouds can be found here ... https://www.woodworkforums.com/showth...ight=hoods+150

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  3. #77
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    Thanks John. Love the 90 bend. You must have run the shop out of 15's. But a bit expensive to do too many of them. My problem is lack of space to turn 180 degrees from DE exit to holes in the wall. Sorry about side on pic, still learning how to do posts.

    I know the machine end is the big issue but with 2hp hobby machine I'm trying to keep all the CFM I can.

  4. #78
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    Another question. I just realise that my planning has been locked into solid PVC near the DE and short bits of flex near the machine. What about using flex for gentle radius bends along the way?

  5. #79
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    Bob

    can you comment on the effectiveness of installing two 2 or 3 hp DCs in parallel?
    regards from Canada

    ian

  6. #80
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    My guess (and it is a guess) is that the flex would cause more losses.

    When I measured the air velocity in my system, the turbulence caused by the walls of the PVC pipe extended no more than 10-15 mm in from the wall. the remainder of the pipe cross section was uniform. My guess is that even the best flexy will create significantly mopre turbulence than that, and it would not need to be a great deal more before it impacted significantly on velocity and CFM.

    If you get a good optimisation of your 2 HP dusty done, and get 150 mm duct in, I am sure you will be amazed at the improvement in dust extraction.

    One of the important variables is the fan curve. Som fans are better than others at overcoming resistance caused by bends, flexy and etc, but this cannot be determined by static testing. Only dynamic testing reveals how well the fan performs in working conditions.

    However, I'd prefer to hear from BobL before drawing too many conclusions.

  7. #81
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    Quote Originally Posted by Rabbott View Post
    Another question. I just realise that my planning has been locked into solid PVC near the DE and short bits of flex near the machine. What about using flex for gentle radius bends along the way?
    The problem is to get a gentle arc requires using a longer length and smooth walled flex is rarely smooth so in most cases works out about the same as a 90 elbow. 2 x 45 bends is marginally better.

  8. #82
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    Quote Originally Posted by ian View Post
    Bob

    can you comment on the effectiveness of installing two 2 or 3 hp DCs in parallel?
    Blimey I just wrote a great long response and lost it so here is the condensed version.

    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.

    Two naked DC ports (each of which alone extracts X CFM) side by side connect to two separate DCs will not extract 2X CFM.
    This is because the two air streams will be fighting each other for the same air, this creates turbulence and reduces flow.

    To get the max air flow the two ports should be facing away from each other so they draw on difference hemispheres of air, or separated by around >5 and preferable 10 ducting diameters.

    However there are many WW circumstances where the air volumes are separated by a chamber or barrier where dual extraction would be beneficial.

    e.g. one to the swaggered above the table and one to the cabinet below
    BS - one above the table and one below, same for routers.
    For sanders (which are generally dreadfully blocked and restrict dust collection) run one attached to the machine and one above the machine.

    However I am not generally a supporter of two sets of ducting in any shed let alone a small DIY shop. It becomes very expensive and can restrict machine access.

    There are better uses for a second DC especially when long ducting runs are needed where it may be better to set each DC to service on end or side of a shed, this reducing duct lengths.
    I have designed several systems like this for forum members.

    The other sensible use is to use a second DC (if you already have it) as a general shed ventilator. Locate the sucking port as high as possible in the ceiling which is where all the fine dust goes and later precipitates out all over the shed. Run the ventilation while working and for sometime thereafter.

    However, do not go and buy a second DC just to be a ventilator. The same air flow can be obtained using a much lower powered exhaust fan.
    Last year I refurbished, modified and installed a 1/4HP variable speed squirrel cage fan I extracted from a skip at work.
    https://www.woodworkforums.com/f65/motor-conversion-start-189221
    This little sucker is very quiet and not having any filters uses very little power , it pulls ~1200 CFM at 50Hz and 1400 CFM at 60Hz.
    I installed it in the highest point in my celing primarily to vent hot exhaust gasses from my forge. However it is excellent at removing fine wood dust from the shed.

  9. #83
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    Bob

    Thanks for your reply. Could you also give me some advice regarding my previous post and photos (#75)? In particular, in the garden shed where I have put the DE space is very tight, so it is a trade off between having a straight vertical run of X distance, which i believe you recommend, but with 2 x 90 bends or using quite a bit of height to achieve 4 x 45 bends, which takes precedence?

    Thanks for all your many posts and info on the forum.
    David

  10. #84
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    Quote Originally Posted by Rabbott View Post
    My main query is which is more important, having a straight final run into the DE or avoiding 90 bends?

    If I set the DE outlet facing up, I can get about 1500 mm from inlet to the shed ceiling. I can either focus on a longer run with 2 x 90 bends or a shorter run with 4 x 45 bends. With a upwards facing DE I need a 180 loop. Or, I could point the inlet downwards and have a shorter run to the holes in the wall but also with sharp bends. I am planning on just connecting 6" flexible duct to the table saw when I use the it as it is only a short and fairly straight run.
    2 x 90 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..

    The straightness of the flex doesn't matter all that much so I'd be I'd be looking at using stormwater ducting for the table saw
    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?.

  11. #85
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    At the moment there is no guard. I'd like something like the Shark Guard but last time I looked there was a long waiting time. Maybe an articulated scoop? Have to sort out the cabinet outlet first. On the Laguna Fusion it's pathetic.

    Thanks for for the ducting equivalents. It's the first time I've seen such a clear comparison of straight and flex or bends. Very helpful.

    Any suggestion about having a certain length of straight pipe going into the DE?

  12. #86
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    Quote Originally Posted by Rabbott View Post
    At the moment there is no guard. I'd like something like the Shark Guard but last time I looked there was a long waiting time. Maybe an articulated scoop? Have to sort out the cabinet outlet first. On the Laguna Fusion it's pathetic.

    Thanks for for the ducting equivalents. It's the first time I've seen such a clear comparison of straight and flex or bends. Very helpful.

    Any suggestion about having a certain length of straight pipe going into the DE?

    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.

  13. #87
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    I can recommend one of these made from 10 mm polycarbonate. Not difficult to make and works well.

    IMAG0229.jpg

  14. #88
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    Thanks John

    Yes I had seen this in my reading of various posts but in my reply to Bob couldn't remember who to credit it to. Looks excellent and will certainly put on the to-do list. A far easier option than spending heaps on trying to import a Shark Guard. First however is enlarging Laguna Fusion outlet to 150 mm. I opened up the cabinet yesterday and found it half full of sawdust as the 2" hose from the throat had come off. This shares the 4" outlet so drastically reduces effectiveness of both.

    I have to have a large 180 U bend to get the 150 mm duct vertically from DE outlet (after modification as per Bob's plan) around and back down to the hole in the wall that then goes into the workshop at about the same level (see previous photo of tool shed). Do you have any advice about the choice of running the duct up to the shed ceiling, to give a longer straight run down into the dusty, and therefor have less turbulence, or have a shorter U, so less pipe distance but maybe more turbulence on entry. Bob say about 5 - 10 x duct diameter is ideal after junctions / bends etc. So 5 X would be 5 x 150 = 750 mm up and down so an extra 1.5 M of ducting. I have about 1.5 m clear from DE inlet and entry hole into the workshop which is on approximately the same level, vertically up to the ceiling of the tool shed which could be the top of the U bend.

  15. #89
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    Quote Originally Posted by Rabbott View Post
    Do you have any advice about the choice of running the duct up to the shed ceiling, to give a longer straight run down into the dusty, and therefor have less turbulence, or have a shorter U, so less pipe distance but maybe more turbulence on entry. Bob say about 5 - 10 x duct diameter is ideal after junctions / bends etc. So 5 X would be 5 x 150 = 750 mm up and down so an extra 1.5 M of ducting. I have about 1.5 m clear from DE inlet and entry hole into the workshop which is on approximately the same level, vertically up to the ceiling of the tool shed which could be the top of the U bend.
    Bob is the expert. However, based on the performance of my system I'd be less worried about the length of straight pipe and more concerned about bends, junctions and ports/shrouds. Some of my highest airflow readings are for machines with the longest runs, but the ports/shrouds are good. It is difficult to overstate the importance of the losses caused by the machines themselves, and their ports/shrouds. In my system that is where the big losses are. Next biggest are bends and flexy. Pipe length is at the bottom of the list of sources of losses. I'm pretty sure Bob will tell you that is what he would generally expect.

    Your biggest issue seems to be the ports for the table saw. Here are some pics of mine, which is a Taiwanese contractor saw around which I have built a cabinet. There is a sloped ramp under the blade that leads to a 150 mm duct. The duct is 150 mm all the way to that port. A 100 mm line comes off the line to the 150 mm line to the cabinet and is connected to the overhead guard, but the limiting factor is the riser on the guard, which has a cross section about equivelent to a 85-90 mm pipe. I am very happy with dust extraction, as noted in this video : https://www.youtube.com/watch?v=X5WE5t-9MqA

    IMAG0226.jpgIMAG0227.jpgIMAG0228.jpg

    Remember, it is necessary to ensure you get enough air into the cabinet. YouTube is full of videos showing blokes blocking all the holes in the cabinet, thinking that will help their dust collection when it does the opposite.

    If you do make your own overhead guard, which is highly recommended, I would change the design so that the front section you look through has no joint or seam at all, as noted in the next pic.

    O'head Blade Guard.jpg

  16. #90
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    Quote Originally Posted by John Samuel View Post
    . . . It is difficult to overstate the importance of the losses caused by the machines themselves, and their ports/shrouds. In my system that is where the big losses are. Next biggest are bends and flexy. Pipe length is at the bottom of the list of sources of losses. I'm pretty sure Bob will tell you that is what he would generally expect.
    Correct

    Your biggest issue seems to be the ports for the table saw. Here are some pics of mine, which is a Taiwanese contractor saw around which I have built a cabinet. There is a sloped ramp under the blade that leads to a 150 mm duct. The duct is 150 mm all the way to that port.
    Mine is similar except I inserted a thin Al sheet metal shallow inverted pyramidal hopper between the saw base and the legs. The apex of the hopper has a 6" duct which goes straight down and under the floor concrete floor - I inserted that under the concrete before the club was poured - one of the best things I have in my shed.
    There are then 5 , 90 bends (all are 2 X 45) and ~10m of ducting before that dust gets to the DC - so the flow is not as good as it could be, but it keeps the hopper completely empty of chips and is not the main source of the fine dust coming from my TS. The main source by far is still the blade guard. Like Johns my collection point is above the middle of the blade whereas it should be above the front. Someway I will change it. The good part about my guard is it is suspended from the roof so nothing is in the way at saw level height.

    Mine is a 3HP DC and Johns is a 4HP Clearvue so don't expect as good a performance as this. The 2HP will suffer more from bends and pipe runs than bigger units.

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