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Thread: Dust collection

  1. #16
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    Interesting thread with some good ideas. However, I am confused. I have no idea how "venturing effect" has anything to do with benefits when you reduce the size of the duct. I understand what it is and the differential pressure issues. But how this could help with dust collection is really unclear.

  2. #17
    Quote Originally Posted by Larry Frank View Post
    Interesting thread with some good ideas. However, I am confused. I have no idea how "venturing effect" has anything to do with benefits when you reduce the size of the duct. I understand what it is and the differential pressure issues. But how this could help with dust collection is really unclear.
    It's "Venturi", similar to that employed by spray painting guns. A large volume of air passing an opening creates a negative pressure in that opening, drawing liquid (or solids like dust) up into that stream of passing air.

  3. #18
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    Larry, it's only a benefit at the actual machine port and is certainly limited. But the reason I mention it is because folks can still benefit from a larger drop to the machine even when the port is smaller. It's a not a huge benefit, but it's still real. Quite often changing the physical port on a machine is not a trivial task..
    --

    The most expensive tool is the one you buy "cheaply" and often...

  4. #19
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    I agree that in some cases it is not really an advantage to change the port on a machine. I get more than enough airflow through the 4" machine ports with my 5 hp Dust collector.

    When you reduce going from say a 5" hose to a 4" port, I still have no idea why the term venturi is applied. It is not like a spray gun where you are using it to suck paint up.

  5. #20
    Jim a small correction. You said in post 15 that 6" duct has nearly 4 times the area of 4" duct. It is a little over twice. 4" = 12.57, 6" = 28.27 & 8" = 50.27, so it is about 4 times the cross sectional area of 4".

  6. Quote Originally Posted by Peter Christensen View Post
    Jim a small correction. You said in post 15 that 6" duct has nearly 4 times the area of 4" duct. It is a little over twice. 4" = 12.57, 6" = 28.27 & 8" = 50.27, so it is about 4 times the cross sectional area of 4".
    Aside from the cross sectional area, the other thing to keep in mind is the ratio of perimeter to cross sectional area and the boundary layer depth, where a smaller pipe will have more frictional resistance and higher proportion of airflow affected by the boundary layer. So just matching area between several smaller pipes to a larger one will still produce more resistance and lower airflow in the multiple smaller pipe system. Hence, 3 x 4" pipes are probably closer to equivalent to one 6" as a ball-park.

    Cheers, Dom

  7. Quote Originally Posted by Jim Becker View Post
    Larry, it's only a benefit at the actual machine port and is certainly limited. But the reason I mention it is because folks can still benefit from a larger drop to the machine even when the port is smaller. It's a not a huge benefit, but it's still real. Quite often changing the physical port on a machine is not a trivial task..
    Agreed, and I believe it's a common, and flawed, misconception / rule of thumb, that if you have a 4" port you immediately throttle the airflow like a tap in an incompressible water based system. It will reduce the airflow and create some turbulence that further reduces airflow if the transition is abrupt, yes, but it's still far better to have 6" right up to a 4" port than to run even a short length of 4" ducting; which very quickly adds a heap of resistance at the flow rates (circa 1000cfm) that 6" and 5hp can otherwise provide.

    Just try breathing through a full straw and then through a very short slice of straw - completely different animal.

    Cheers, Dom

  8. #23
    A lot of great ideas, I think I'll have to get something like a harbor freight with a upgraded filter or a jet 1100 with the filter top. I would have to roll it around. I'm planning on spending about 7k on tools. I can't get to much woodworking done if half my budget is spent on dust collectors, ducting and hanging air filters. I'm glad I learned so much from you guys. I would have just run a cheap duct collector at one end of my 50' long shop and run a bunch of 4" ducting. I would have spent a lot of money (for me anyhow) on a system that wouldn't work☺

  9. #24
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    Quote Originally Posted by Peter Christensen View Post
    Jim a small correction. You said in post 15 that 6" duct has nearly 4 times the area of 4" duct. It is a little over twice. 4" = 12.57, 6" = 28.27 & 8" = 50.27, so it is about 4 times the cross sectional area of 4".
    Thank...mental error. I'll correct the original post.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  10. #25
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    Brian,

    I'll second the suggestion that, no matter what you do, you get one of these:

    3m.jpg

    They're the cheapest, best way to protect your lungs by far. This one is $28 with P100 particulate filters. It is surprisingly comfortable even with glasses and hearing protection. I do not mind wearing it even for long periods.

    Also, if you're considering a canister filter to replace a filter bag, check out Wynn Environmental. I bought one of their filters to retrofit an old portable DC and it really eliminated a lot of airborne dust without reducing airflow.

    Finally, if you go the cheap route, consider getting a super dust deputy from Oneida. It's a substantial upgrade for not a lot of money. If you have room, go on Craigslist and find a 55 gallon drum to place under the cyclone instead of buying one from Oneida. There's a guy near me who always has 35 and 55 gallon drums for $25. It's easy to cut a hole in the lid to attach the cyclone.

    Good luck.


  11. #26
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    Quote Originally Posted by Brian W Evans View Post
    Brian,

    I'll second the suggestion that, no matter what you do, you get one of these:
    3m.jpg
    After years of using the 3M respirators in the 6000 series someone here (was it you?) recommend I try one of the 7502 models and I did. I love it, even more comfortable than the 6200 and 6300 models I'd bought for years. It's here: https://www.amazon.com/gp/product/B008MCUT86 I think these are the filters I use but somewhere I bought a quantity for cheaper: https://www.amazon.com/3M-2097-Parti.../dp/B00328IAO0

    You can get also get filters for volitiles and full face respirators. These are good for finishes. I use the full face model with volitile filters for spraying chemicals around the farm, these, I think (although I paid about $10 for two): https://www.amazon.com/gp/product/B0013A7MBQ

    JKJ

  12. If 7k is your total budget then fair enough. If it's just the start of longer term spending I'd still suggest spending the $2500 on a good cyclone setup, less without filters and venting directly outside (and better if climate control is not required).

    Of course it's your money, health and hobby so do what's right for you. I just know that from personal experience, going from a useless 2HP single stage to the Clearvue, it would now be the very last powertool I would part with if forced to choose.

    Cheers, Dom

  13. I recently retired and have been reorganizing my 2-car garage workshop into a more permanent woodworking shop.
    Having lots of free time to spend on piddling and now having the potential to be spending much more time in the shop has made dust collection become something I am more interested in.
    The dust collector I have is an old Delta AP400 which is rated at 600 or 650 cfm.
    A long time ago, due to clogging with planer chips I removed the impeller protection cross that was inside the 4" inlet.
    It made it work a lot better but if you accidentally suck a towel into it the impeller will get bent.
    My impeller can be bent back into shape, that may not be true for more powerful machines and if the impeller is cast aluminum it will most likely break vs bending, so even though removing the impeller protection has anti-clog benefits it also has drawbacks.
    Like almost everyone else with a single stage dust collector emptying the bag is just about the worst job there is.
    Quite some time ago I put a trash can separator in front of the dust collector, I built mine with a ~30 gallon metal can from HD using a 90* elbows I already had on the inlet and outlet of the lid.
    The separator works good for keeping the collector bag empty, but it has huge hit on the airflow.
    I keep it there because emptying that bag is such a pain.
    Moving a Rockler 20ft Dust Right hose from tool to tool works good enough to collect almost all of the shavings from the planer and jointer.
    It works pretty good on the 4" bench top belt sanders.
    I have an old Delta 36-714 tablesaw and the bottom of it will fill up with sawdust. There is a small area near the dust port that stays clear but opening the saw and pushing the pile to the port is required every so often.
    As I write this I wonder if it's even worth moving the hose to the tablesaw during use, I might as well just let the sawdust pile up and then suck it all out periodically since I have to do that anyway.


    Okay....
    So with time to burn I figured the first thing to do was to get an idea of how things were really working in my dust collekction setup.
    I bought an inexpensive anomometer during the Christmas sales to see what kind of cfm I was getting through the system and to have an idea if any changes I make actually improve the performance.
    Please don't get bogged down with the the absolute readings I obtained.
    With the instrument I have and using a consistent methodology the readings are what they are and on a comparison basis though they show significant drops in the airflow by adding the trash can separator, blast gates, flex hose. Bending the flex hose also reduces the airflow.


    Summary of what I have and measured.
    HoldPeak HP-846A anomometer.
    Dust collector Delta AP-400 1HP.
    New 48" tall singed felt filter bag.
    33 gallon metal trash can with seams and handle mounting holes caulked.
    90* plastic elbows on inlet and outlet of trash can lid.

    CFM measurements:
    AP-400 inlet 780 cfm (yeah I know it's a 650 cfm dust collector)
    Trash can elbow inlet 498 cfm
    Blast gate manifold 380 cfm

    4” x 20’ Dust Right hose extended 270 cfm (oddly extension doesn't seem to matter)
    4” x 10’ clear flex hose. 250 cfm
    4” x 13’ metal duct and 4’ flex hose. 240 cfm




    With a single Dust Right 20' hose attached directly to the trash can I measure 350 cfm.
    FWIW I have had the Dust Right hose for a few months and it does not do the slinky collapse nearly as well as it did initially.



    More piddling around:
    I thought the airflow might improve with only one 90 elbow in the lid so I swapped in a straight hose coupler.
    It separates so much better when using two 90 elbows in the lid vs one elbow and one straight coupler. It doesn’t matter if the single elbow is on the inlet or outlet, lots of stuff blows through the trash can. I never even measured the cfm, I just reinstalled the 90* elbow.
    I didn't expect a blast gate manifold to affect the airflow as much as it did.

    I disassembled that and went back to just having the Dust Right hose connected to the trash can.


    I don't know if this adds any better perspective about airflow losses than looking at the vendor websites that have calculators and design tools.
    Making some measurements on my own setup certainly was an eye opener for me.


    On another forum I talked about my experience using the anomometer and someone asked a very good question.
    Is the goal to have a clean looking shop or to have dust control ?


    I think it takes a considerable investment of money and design to achieve dust control.
    I also think a considerable amount of money can be spent on trying to achieve dust control and still not meet that goal.
    With an entry level dust collector (even being hamstrung by the trash can) you can collect the sawdust and shavings and have a shop that looks tidy.



    Attached Images Attached Images

  14. #29
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    I do not believe anything to do with the fan anemometer. IMHO Getting 780 cfm with a 1 HP dust collector makes no sense at all.

  15. Quote Originally Posted by Larry Frank View Post
    I do not believe anything to do with the fan anemometer. IMHO Getting 780 cfm with a 1 HP dust collector makes no sense at all.
    It makes sense if the fan anemometer is placed in front of the duct/inlet, blocking the inlet area, forcing the air velocity to increase, measuring at only the highest velocity point in the center and then multiplying by the unblocked area. But the numbers would be hugely inflated / wrong.

    I tester a 2HP single stage with pleated filter, using a hot wire probe across a 6" test duct, and measured 300cfm with about 3ft of 4" hose

    Cheers, Dom.

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