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  1. #61
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    Diagram of my saw table now loaded - Post 52

    Cheers

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  3. #62
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    I will be putting it on a mobile base but I'm not sure how much that would raise it off the ground. Probably buy the 400+ kg model from Timbecon.

  4. #63
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    Looking at my diagram Doug, what would you change re air entry points?

  5. #64
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    Quote Originally Posted by Lappa View Post
    Looking at my diagram Doug, what would you change re air entry points?
    Nothing right now Lappa, I will have a look in the morning.

    It is now 12:30 on 3 January here. You guys are three hours behind us so you want to play, I want to sleep.

    I have just been out in my shed working on this:
    20170103_002608.jpg

    It's a piece of Mango stump I got from Mapleman a couple of years ago to turn into a weatherstation. The other side will probably be the side on display but I sanded the back side tonight just to make sure I was not casting aside the best bit after it is sanded.

    ANyway with my bad back, I have to alternate between standing and sitting and walking around and lying down so I will surely have some time to look at your diagram tomorrow.

    Cheers

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

  6. #65
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    Quote Originally Posted by Lappa View Post
    Looking at my diagram Doug, what would you change re air entry points?
    Hi Lappa,

    I finally get a chance to sit and reply. My day did not go how I thought it would. I found out that H&F had one only hydraulic and pneumatic workshop cranes left. I had been trying to get one for over a month and they had been out of stock for a while. My day changed to drive to the other side of the bay, bag the crane, take home and assemble.
    A351 | HPC-1T Pneumatic & Hydraulic Engine Crane | For Sale Sydney Brisbane Melbourne Perth | Buy Workshop Equipment & Machinery online at machineryhouse.com.au
    Now I can lift heavy things with my compressor instead of my back. Happy days!!

    Anyway, to your tablesaw.

    I love the snorkel.

    Do you use the saw outside of the table? If no, than would you consider removing the safety guard? It serves no purpose in the table other than to make dust extraction trickier.

    I am guessing the extraction port is where it is to line up with the dust chute which is probably attached to the blade guard. No blade guard - no dust chute. And no need to put the extraction port where it is in the diagram.

    So lets put the air intake at the front of the cabinet pretty much where it is and then encourage maximum airflow over the blade by putting the extraction port in the back of the cabinet also in line with the blade. This should help by maximising the extraction of the entrained invisible dust so that less dust makes it back out of the saw cabinet.

    The more you can extract below the table the less that needs to be dealt with by whatever above table dust extraction you use.

    How does that sound?

    Cheers

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

  7. #66
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    That's a nice looking unit. Years of bending over vehicles, lifting heavy bits like cyl. heads off blocks etc. etc. and I've got the typical mechanics back so these days anything that helps lifting is a blessing. One thing I've seen that I don't like on some engine cranes are the wheels. I usually find they are hard, too small and prone to jamming.
    Anyways, back to my table saw. Thanks for the "look over" the diagram. The saw stays in the table.
    When I first built the table, the saw had to be manually raised and lowered by removing the front panel and using the same adjustments as you did when using the saw in its normal manner. It was a right royal pain in the butt. I also had no dust collection - just a plastic tray in the base of the cabinet under the saw. The majority of chips were always thrown to the back RH corner of the cabinet so when I added a dust port for the VC, I placed it there. I then made a screw assembly so I could raise and lower the saw from a wheel at the front of the cabinet. This effectively divided the bottom of the cabinet into two. It runs from the front to the back. I then added a Pickup to the dust chute hole in the saw blade cover and connected it to another VC with a port at the front. I put two 50mm ports near the top of the LH side near the snorkel, to get some air movement across the cabinet towards the dust port. The majority (probably 70%) of left over chips etc that are not taken out by the VCs went to the RH side.

    When I added the 150mm port. I put it in the same place as the VC port, removed the flexible pipe from the dust chute port on the saw and pointed the pipe directly at the new port.
    If I was to place the port at the back, it couldnt be put near the bottom as the saw raising mechanism would block it.
    When you say to remove the blade guard, is it just the spring loaded one or the complete aluminium housing that is attached by 4 screws to the saw body?

    table saw with lift.JPG

    Cheers
    Attached Images Attached Images

  8. #67
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    Originally Posted by LappaRe air inlet/entry ports. Should they be equal to or larger than the machine outlet ports or doesn't it matter if they are oversize?

    Just doing some calcs. now my 150mm outlet port is connected to my saw table.
    Quote Originally Posted by BobL View Post
    If by an "air inlet/entry port" you mean the air inlet port into a machine cabinet then the area should be greater.
    As important is location and shape.
    Location wise the ideal placement is in the cabinet opposite the outlet
    An inward facing rounded lip will help reduce resistance especially if the size of the inlet is constrained by the machine itself.
    After seeing the diagram of your saw I can now see what you were driving at.

    If the shape of the air inlets and outlets are different, then using "equal areas" is not appropriate and it becomes important to look at the actual flow through each shape

    For example, your 550 x 35 mm inlet slot has a cross section of 19250 mm^2 while the 150 (154?) mm outlet duct has a cross sectional area of 18627 mm^2 .
    One would this expect that as the slot has a larger area than the duct that more air would be able to flow through through the slot.

    However, this is not the case as the 35 mm width is quite restrictive.
    To determine the minimum area/dimensions of the slot one can look at the theoretical flow using ab air flow calculator.
    It turns out that at around 700 cfm a 550 mm long slot needs to be 48 mm wide to have the same pressure loss (hence loss of flow) as a 154 mm diameter duct.

    I use the following pressure drop calculator as I found it's results agree closely with some experimental testing
    Pressure Drop Online-Calculator
    One needs to know something about the properties of air and pipe roughness to use it correctly.
    It is much easier to use its results comparatively rather than absolutely, i.e. just change the minimum number of parameters and compare the pressure drops

    Of course the calculator does not take into account the profile/shape of the edges of openings which can be as significant as the shape.

  9. #68
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    I finally got around to making the BMH former for the 6" ducting.

    Here is the setup during the "cool down spin cycle"
    IMG_1876.jpg

    It takes a bit longer to form the bell mouth.
    The former is bigger and needs more heat, there's more plastic diameter wise, and the radius of curve of the edge is 37.5 mm so lengthwise its stretched a bit more as well.
    I took it slowly the forming part took about 8? minutes

    IMG_1877.jpg

    Here's the former, and the finished hood.
    It came off very easily with two taps of a wooden mallet because the rim of the BMH was stretched to be slightly bigger than the former
    IMG_1878.jpg

    Comparison with not quite fully formed 4" BMH - all my good 4" ones are at the men's shed
    IMG_1879.jpg


    Final diameter measurement was 224 mm (should be 225) so it shrank about 1 mm on cooling down.
    Next time will over stretch it by a few mm.
    IMG_1880.jpg

  10. #69
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    That turned out great Bob! What a brilliant idea.

  11. #70
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    Quote Originally Posted by bueller View Post
    That turned out great Bob! What a brilliant idea.
    I suppose you will be wanting some? We can make some on saturday if you like.

  12. #71
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    Hi,

    I received a few emails asking for help with this thread. Please for give the Imperial units as I am on the wrong side of the pond and untrainable at my age... So I'll jump right in...

    This discussion kind of bounces around between hoods and ports ignoring a lot of things that have much greater impact on our dust collection efforts. Most traditional tools either come with no fine dust collection or marginal collection for sawdust and chips. To get good fine dust collection many tools need containment around all dusty areas, much better hoods, and plenty of airflow. For instance my 36" long 6" wide belt sander came with an end cap collection hood with a port sized to fit on a 2.25" diameter vacuum hose. When connected to my big 100+ water column inch shop vacuum it got pretty good sawdust collection. Hooking this up through a reducer to my dust collector moved so little air, there was no effective dust collection. My dust collection system only provided about 7 water column inches of pressure, so this lacked the pressure to collect hardly at all through the small port. I had to remake a new hood with a full 6" diameter port before the collection with my dust collector was as good as it was with shop vacuum. Although that got the visible sawdust, my particle meter showed there was still a long way to go. That belt launched fine dust all over the exposed sides and top surface. I had to contain that whole unit in its own cage to keep from launching fine dust all over. In addition to this containment, we also need to properly build our hoods and ports. If we look at the air flow going into the end of a straight pipe, we quickly see that sucked air comes from all directions so the air behind and to the sides crashes into the air coming in the front creating a lot of turbulence which can significantly reduce our overall flow. Ideally hoods and ports should always use a bell shaped curve (hyperbolic) to remedy turbulence from the sides and back. At the same time if you measure airflow with a flat 6" port versus one with a nice proper curve, the amount of resistance measures in the tenths of a water column inch versus ten to twenty times more for hoods with the wrong shape.

    So here are many of the basics again summarized.

    1. Chip collection collects the same sawdust and chips we would otherwise sweep up with a broom. Most small shop stationary tools need two things before they have good chip collection, upgraded hoods and ample airflow. Our blades, bits, cutters and sandpaper often launch dust filled air streams at a speed of over 100 miles an hour, but dust collectors typically only move air at about 40 miles an hour. That race is always lost by our dust collection systems unless we start by upgrading tools to contain the dust with hoods that control, direct and deliver the fast moving dusty air streams for capture. With good hoods most small shop tools get pretty good chip collection with just 350 cubic feet per minute (CFM) airflow moving at least 4000 feet per minute (FPM) in vertical ducts and at least 3000 FPM in horizontal ducts.

    2. Fine dust collection assures that our air quality stays below accepted standards and is much harder to do. Still, it is easy and affordable to get good fine dust protection. The best protection is to wear a good properly fit NIOSH approved respirator mask with dual HEPA quality cartridges and work outside or with our main doors open a bit and a strong fan blowing out a side door or window to create a good airflow through our shops to keep the fine dust from building. Our particle counters show for best protection we need to put on our respirator mask and start venting our shop before we start making fine dust and both the mask and fan need to stay on for about a half hour after we stop making fine dust. Still, it is not that hard to get good fine dust collection which is what my web pages share in considerably more detail.

    a. Wood is made up of dried very fine tubes that are extremely fragile, so every time we touch wood with our blades, bits, cutters and sandpaper at a microscopic level we shatter these tubes launching millions of particles that are so fine they are invisible without magnification. These particles are also so light they can be moved with the lightest airflow and will stay airborne in normal room air currents.

    b. OSHA testing shows on average every twenty pounds of sawdust collected also generates enough fine dust to cause 15,119 typical two-car garage sized shops to fail an EPA (or EU indoor air quality test). Think about this. Missing 1% still releases enough airborne dust to cause 151 typical shops to fail an air quality test.

    c. Worse, unless fine wood dust gets wet it lasts nearly forever. Our particle meters show that even making a long perfect spiral using a razor sharp hand plane launches enough fine dust to peg meaning max out many particle counters.

    Decades of research show to get good fine dust collection we have to start by even better tool hoods and also have to move enough air to pull in the fine dust before normal room air currents blow this dust all over. It takes right at three times more total airflow to collect the fine dust as it does to get good chip collection. For the more engineering inclined we need at least 50 feet per minute out to about 15.25 inches in every direction around the working portions of our tools translating to about 1000 CFM at most major small shop stationary tools. Blower technology is mature meaning blowers of the same type, size and speed from all the more reputable blower makers all move nearly the same air. The blower air tables show it takes at least a 3 hp dust collector with a 14" diameter impeller turning at 3450 RPM to move this real 1000 CFM. Because a cyclone burns up more hp it takes a 5 hp motor turning at least a 15" diameter impeller at 3450 RPM to move this same air. For those with the 2750 RPM motors add one inch to the blower wheel sizes. For what it is worth, some of the highest resistance levels in our dust collection systems are caused by poorly made or engineered hoods.

    Air at dust collection pressures is more like water and will barely compress at all, so any small duct, undersized hood, restriction or obstruction and act like a partially closed water valve and limit the flow in the whole system. 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. A 1" diameter duct only moves 22 CFM; 2" moves 87 CFM, 3" moves 196 CFM, 4" moves 349 CFM, 5" moves 545 CFM, 6" moves 785 CFM and 7" moves 1069 CFM. Bottom line to get the real 1000 CFM required most need to use all 7" or larger diameter duct or use oversized blower wheels that generate the extra pressure needed to pull more air through smaller diameter pipe.

  13. #72
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    Thanks for your input Bill.

    Quote Originally Posted by bill pentz View Post
    This discussion kind of bounces around between hoods and ports ignoring a lot of things that have much greater impact on our dust collection efforts. .
    A specific discussion of hoods and ports is the intention I started this thread, there are plenty of other threads in the dust forum repeatedly raising the other topics you have mentioned but very few on the topic of ports and hoods.

    Ever since your good work in the last few decades there has slowly been an increase in use of efficient dust collector machinery and larger ducting while the matter of ports and hoods has largely been ignored and increasingly become the elephant in the dust collection corner. In my visits to many sheds I increasingly see large DCs and Cyclones using 6" ducting only to be stymied at the business end of the collection with tiny dust ports, choked cabinets and a very poor understanding that a naked hood or pipe end is a major impediment to flow.

  14. #73
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    Quote Originally Posted by BobL View Post
    I suppose you will be wanting some? We can make some on saturday if you like.
    That would be awesome if you have the time when we catch up. I'm still dead keen for Saturday you are, looking forward to it!

  15. #74
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    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

  16. #75
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    Thanks for the input Bill.
    Reading this statement

    Quote Originally Posted by bill pentz View Post

    Air at dust collection pressures is more like water and will barely compress at all, so any small duct, undersized hood, restriction or obstruction and act like a partially closed water valve and limit the flow in the whole system. 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. A 1" diameter duct only moves 22 CFM; 2" moves 87 CFM, 3" moves 196 CFM, 4" moves 349 CFM, 5" moves 545 CFM, 6" moves 785 CFM and 7" moves 1069 CFM. Bottom line to get the real 1000 CFM required most need to use all 7" or larger diameter duct or use oversized blower wheels that generate the extra pressure needed to pull more air through smaller diameter pipe.
    In essence you are saying you achieved 1100 CFM using a 1 HP dust collector with 7" piping - correct?
    Was the dust collector one of the common designs that probably the majority of people on this forum with dust collectors (as against vacuum cleaners) use ie. this design or similar

    IMG_0250.jpg

    or was it a 1 hp unit mounted atop your cyclone.
    If it is similar to the picture above, did you run 7" pipe all the way to the 14" impellor blade then 7" out from the impellor housing to a 7" inlet on the filter assembly?


    Cheers and thanks for taking part
    As Chris had stated, 7" pipe is virtually unobtainable in solid PVC.

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