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Thread: Overhead Dust Collection for TS - Optimum Hose Size

  1. #1
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    Overhead Dust Collection for TS - Optimum Hose Size

    After years of struggling with inadequate/non-existent DC, specifically TS overhead, I've finally made the decision to upgrade (hopefully) from a Delta 760 DC and 4" flexible hoses for my 1-bay garage setup.


    A major goal is TS overhead dust collection for my lungs. I'm uncertain as to what size piping I should be considering, and therefore cannot filter through all the options available for retail purchase:


    1. 4" reduced down from the (planned) 6'' main
    2. 2.5" reduced down from the (planned) 6" main
    3. 2.5" from a dedicated shop vac (least preferred due to needing to turn on two sources)


    Given the three possible scenarios, which would likely provide the best overhead DC for the TS?


    For the curious - I just purchased the Harvey G700 during their BF sale. This unit checks a lot of boxes for me: small form factor, duct location (not wanting overhead), and ease of waste bag cleaning.


    TIA
    Last edited by Mike Shields; 11-28-2021 at 2:55 PM.

  2. #2
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    Mine is a 4" flex hose (coming off a 6-5-4 wye) then there is a 4" to something smaller adapter (can't remember what size exactly) that connects directly to the shroud.
    There is a very fine line between “hobby” and “mental illness.” - Dave Barry

  3. #3
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    I'm not following your plan. The Delta 50-760 DC comes with a 4" inlet. Are you planning to upsize to 6" main? The restriction at the inlet will negate any larger pipe or hose in the system.

    2.5" hose is for vacuums, not dust collection. The difference being vacuums (shop vacs) work on high differential static pressure and dust collectors work on moving air (CFM). The smallest hose you should be looking to use is 4" and then no more than 5 feet.

    You mentioned "upgrade (hopefully)" and "(planned) 6" main". What dust collector are you hoping to get to support the 6" main?

    What tablesaw do you have? What size ports are on the cabinet and on the guard?

    The rule of thumb is the the outlet of the wye or the size of the trunk needs to have the same or more square inches as the sum of the square inches of open gates. If the cabinet is 4" and the guard is 2.5" (add the sq.in. and then convert back to dia inches to get 4.71"), then a 4x2.5x5" wye (or a 5x5x5 wye with a 5-4 and 5-2.5 reducers) is required. If the wye is 4x2.5x4, then there is no "extra" capacity to pull from the 2.5 and the small port (with its higher SP losses) will essentially be starved (stalled, overwhelmed; choose your word) and do nothing.
    Last edited by Anthony Whitesell; 11-28-2021 at 3:53 PM.

  4. #4
    So a couple of things:
    1) No matter what you do, it's going to be difficult to capture all the dust from a table saw, because the blade throws it all forward at about 100 MPH, average dust collector is about 40 MPH.
    2) Always use as large a pipe as possible, until you're forced to reduce it.
    3) Avoid flex pipe whenever possible.

    Most table saws have a 4" inlet, which is a design compromise, you're actually better off with a 6" if you can fit it. Hard to tell without knowing which saw you've got.

  5. #5
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    Quote Originally Posted by Anthony Whitesell View Post
    I'm not following your plan. The Delta 50-760 DC comes with a 4" inlet. Are you planning to upsize to 6" main? The restriction at the inlet will negate any larger pipe or hose in the system.
    Not true. If you have a 1/4" nozzle at the end of your garden hose, you will be very disappointed with a 1/4" hose. Think about. I am only calling it as I see this fallacy repeated way too often.

    I have a 3" SharkGuard on my G1023, bigger than a 2.5" vac hose but more manageable than a full 4" hose. I have a 5" on my cabinet bottom, enlarged from the stock 4" hole using a bellmouth inlet.
    NOW you tell me...

  6. #6
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    I have a 6" main with wyes to 4" drops to the cabinet and to a Shark Guard. With this setup, a zero-clearance throat plate, and closing off some of the openings in my cabinet saw I am able to cut MDF without adding any fines into the air. I have a mildly underpowered 2HP DC with PVC ducts kept as short and straight as possible. I monitor my shop air quality with a Dylos and I love not needing a respirator for most operations at the table saw.

  7. #7
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    Quote Originally Posted by Ole Anderson View Post
    Not true. If you have a 1/4" nozzle at the end of your garden hose, you will be very disappointed with a 1/4" hose. Think about. I am only calling it as I see this fallacy repeated way too often.
    Nothing false about it. Think about it. If the DC has a 6" inlet with 6" piping and the machine has a 4" port, then you can open a gate to pull more air to (re)gain FPM in the 6" trunk. If the DC has a 4" inlet with a 6" piping and the machine has a 6" port, opening another port will do nothing for the CFM. The restriction at the DC inlet (4") cannot be over come.

    To your analogy, this is not a 1/4" nozzle on a 1/4" hose. It is a 3/4" hose on a 1/4" spigot. Even if the 1/4" valve is 100% open, the flow in the larger hose will never exceed what you could get from a 1/4" hose. (not factoring in losses due to static pressure) FWIW, around here most garden hoses are 5/8" or 3/4". When I had to redo some plumbing in my basement, I changed the pipe and spigot from 1/2" to 3/4". I get a whole lot more water out the end of the hose now!

  8. #8
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    Just my opinion, worth what you paid for it.

    The delta has a 6" inlet they neck down immediately to two 4" ports as their common rockler/woodcraft consumer base is running flex hose off the shelf from their dc to the tool. Its the impeller size that makes the most difference in those single stage machines and the filter loss and filter size, material type, and its volume capacity that limit the design.

    You need to do the work backwards (or to many is backwards from how they think it should be done). Look at your tools, plan your route to your dust collector, do the math on the static pressure you are introducing with that setup (runs and fittings and pipe types all have a calculation), and THEN buy a machine with the capability to overcome that static pressure while keeping a 800-1000cfm level or so so the chips stay in flight.

    Read Air handlings documentation pdf on sizing your duct work or Sandor's book on Woodshop dust control if you are just using a smaller setup. They have the math you need.

    I run a 12"-10"-8 mainline with mostly 8" drops (I guess one 6" drop too) off wyes and then neck down to the largest ports I can at my machines. My mainline is at 17' up. I keep my jointer and planer fairly close to the machine although, while not ideal, my furthest machine is a Large shaper with above and below table 6" collection and it still has zero issue. Again do the math first and then provide what you need in the machine. I have a 12' tall 10hp cyclone with 4029 cfm. I run Nordfab ductwork. Shop is 2560sq 40X64.

    Most folks start with just buying a cheap dust collector first and are doomed from the start.

    Above my bench I run dust extractors (festool shop vacs) and collect the small tools dust from hand sanders with that.

    I run 8" to my table saw and collect with a large overblade setup (4"-3"), and in cabinet and also in cabinet shroud around lower blade. But again, I have the ductwork capacity a and the machine to support that ductwork.

    I would not put a 2.5" hose off a 4" mainline off a lousy dust collector and its Wye - at least I would not be shocked when the dc is lousy. I also would not hook a 6" pvc mainline to a 650cfm junk dust collector easier just because I saw it on the internet. Another I question is 650cfm dust collectors that folks randomly hook up these wannabe cyclone right angle garbage can lids and think well I am keeping my filter from clogging. Issue is the math was never done to figure out the additional static loss and reduction in cfm you are adding to your setup. The machine cant handle that additional static pressure you just introduced and keep ships in flight.

    For folks wondering I have $1400 in my DC and $1500 in the ductwork - all bought used except a half dozen pieces I need specifically. I had the power infrastructure already to power the setup (3ph). To me $3K is cheap at this level of performance but its not for everyone I know. It will run anything I want or will ever need, and is modular to do just that as well easily. Ill also note I run a separate DC on my CNC that can run for hours and hours.

    Again, I just control my own shop. Just have to make me happy. You do you. Glad folks have Dust collection thoughts.
    Glad its my shop I am responsible for - I only have to make me happy.

  9. #9
    Bill, you make some very good points. The op has already chosen a dust collector though and has to work within its limits.

    Given a 6" main duct and assuming based on convention that the tablesaw has a 4" connector in the cabinet, you could have a 4" drop to the overhead hood. The two 4" hoses are approximately the same cross sectional area as the 6" main.

    Cabinet saws are particularly bad for dust collection as most rely on picking up the dust after it has dispersed into the base. The sliding table saws I have used are much more effective as they typically have a pickup closely coupled to the blade in line with the air stream coming off it. I cobbed a similar dust chute on my old Unisaw out of sheet metal attached to the arbor and some flex hose routed through the cabinet side, which was quite effective. Not all saws are suited to this approach but it is worth thinking about. The dust coming off the top of the blade is annoying and gets your attention but the bulk of the problem is below the table.

  10. #10
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    Quote Originally Posted by Anthony Whitesell View Post
    Nothing false about it. Think about it. If the DC has a 6" inlet with 6" piping and the machine has a 4" port, then you can open a gate to pull more air to (re)gain FPM in the 6" trunk. If the DC has a 4" inlet with a 6" piping and the machine has a 6" port, opening another port will do nothing for the CFM. The restriction at the DC inlet (4") cannot be over come.

    To your analogy, this is not a 1/4" nozzle on a 1/4" hose. It is a 3/4" hose on a 1/4" spigot. Even if the 1/4" valve is 100% open, the flow in the larger hose will never exceed what you could get from a 1/4" hose. (not factoring in losses due to static pressure) FWIW, around here most garden hoses are 5/8" or 3/4". When I had to redo some plumbing in my basement, I changed the pipe and spigot from 1/2" to 3/4". I get a whole lot more water out the end of the hose now!
    I misread your comment thinking the Delta 50-760 was a tool not the dust collector. His proposed Harvey G700 DC is 2 hp, 1100 cfm max and has a 6" inlet, therefore 6" piping would be adequate, although going to a 7" main if he has long runs would not be out of the question, even with a 6" inlet, it depends on the fan curve. 800 cfm for TS top and bottom collection is pretty standard. 800 cfm in a 7" main gets you 2993 fpm velocity which will move chips along nicely in a horizontal run. A 6" for vertical runs will be appropriate as you will see a velocity of 4074 fpm but at a cost of higher friction losses.
    NOW you tell me...

  11. #11
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    I have a 6" duct going to the cabinet base & a 2.5" flex that drops down from an OH 6" duct for the blade guard. Dust collection is just about perfect, top and bottom. This is backed up by a particle counter that sets on a shelf behind me when operating the saw.


    The only time I've been able to detect any dust escaping is when cutting off less than a kerf width. Then a ton of dust squirts out the side of the guard. It's an annoyance that I will get around to fixing. Some day. I tell myself.

  12. #12
    I am installing a stationary dust collector but my older system may be similar to yours. It is a 2 HP Oneida portable. I too struggled with a simple way to connect to both the SawStop Floating Overarm Guard and cabinet base. Both base and overarm are 4”. I chose a Powertec 6x4x4 wye and 4” flex for my temporary connection. It works reasonably well. It gets most chips and keeps Dylos readings below 1000 counts per minute for fine particles in the air. I also run two whole shop air filters while milling so your situation may be different. I don’t have good photos in my phone of the set up. Here is a pic of the overarm latch with the wye in the background.
    93BD99D9-01F8-4E38-9BF3-2FC11BEA37DB.jpg
    Here is the saw. Again the flex connection was not the intended subject.
    7BE3FB75-8ACF-4D45-BEDE-0DE7C43B8C8D.jpg
    The duct size question is very difficult from an engineering perspective. Flow in a both branches of a wye is complicated and does not resolve to simple constant flow loss coefficients like a single flow path of pipe and elbows. I have a branched flow calculation but I had to simplify the loss in the wye. You have simplified the problem considerably by reducing the number of choices. Common sense and engineering agree that flow will seek the path of least resistance. I would try to keep resistance as equal as possible between the branches. You will want 350-450 CFM for a guard like mine and the same for the cabinet. So use 4” to both. If your guard has a smaller inlet than 4”, you will have to reduce down to the guard’s port but minimizing the resistance in the connection to wye is the best you can do. You could put a blast gate on the cabinet or seal up the cabinet to restrict the flow on that path but that reduces overall flow which defeats the purpose of sucking the maximum air away from the operator.

    Your Harvey G700 is different than most collectors in that it has variable speed. It can generate a lot more head and flow than a conventional fixed speed collector by increasing RPM of the blower. Your table saw with two ports is pretty much the same as running two tools at once. At 2HP, the maximum speed will be needed to operate both ports for serviceable collection of chips and dust.

    i look forward to seeing how your installation turns out.

    I think
    Attached Images Attached Images

  13. #13
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    All the replies are very much appreciated.

    I'm strictly a hobbyist, but my health is a major concern as I get older. While I would like to believe this will be my end-game DC install, years of reading about this topic suggest that will not be the case. The information provided in all the replies will definitely help me towards reducing some errors.

    Buying the Harvey G-700 was the easy part. The ducting will (should) be fairly simple: 6" main (the G700 size) with a 12' run with a wye for the 4" to the Sawstop and a 4" to the overhead. TBD what overhead I'll buy, as I'm not totally convinced there is a "best" solution regardless of price - I primarily want effective DC not a guard...not going there. I'll then run another wye of the 12' main line with something that will allow moving a line between my router table, jointer, and planer that sit along the opposite wall.

    G700 set to ship Dec 10. Calling a duct supplier as soon as I hit "post quick reply".

    Thanks,

    Mike

  14. #14
    Mike, I built an overarm. I experimented with 4" and 2 1/2" hoses without a doubt the 4" hose was markedly better, which kinda makes sense, but I had a thought maybe increased suction with smaller hose, not proven out.

    A further comment on overhead DC. In my work, at least, I've found there many times I can't use it even it I wanted to, such as: when using a sled, a miter gauge, tenon jig, or any rips less than 2" wide (or wide enough to get a push stick between hood and fence, and you're forced to use push sticks rather than push shoes.

    My point is 75%-80% of the time its impossible to collect table top. I suppose a device could be made for a sled, but....

    So, DC is only as good as when you can use it. The rest of the time, you go with PPE, air filtration, and a well ventilated shop when possible.

    I was looking at the SawStop 4" overarm, but after using it a while, I'm glad I made my own.

  15. #15
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    I have a small slider with above the table and below the table extraction.

    Below table is a 5", the splitter mounted guard is a 2 1/2" which connects to the 2" port on the guard.

    It works well because the guard is very narrow, maybe 3/4" wide at the blade. Dust collection is good on the machine.

    If i use the overarm mounted guard, it has a port that the 2 1/2" hose fits inside, collection is good on this, just not quite as good as the other guard due to lack of airflow with a smaller hose.



    Regards, Rod.

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