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Thread: DC chip vs fine dust collection

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  1. #1
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    DC chip vs fine dust collection

    I keep seeing it repeated (and repeated and repeated) that you need more cfm to collect the fine dust than the larger chips. Can anyone point me to where this is documented, not just who originally repeated it? Or at least a calculation of why. My rational brain would suggest the opposite. Table saw as a case in point. The tip speed of a 10" blade at 4000 rpm is 119 miles per hour. The blade produces chips and dust of varying size, presumably ejected at 119 mph. Grab a handfull of chips and a handfull of sanding dust and see which you can throw the farthest. Wouldn't the heavier chips travel further, just as a baseball will travel further than a shuttlecock when hit by a bat? Wouldn't it be more difficult to collect the fast moving chips? With my DC running, I am more likely to see chips at my feet than fine dust in the air when I am not able to use my table top collector. Nuts, I'm confused...help me out here.

  2. #2
    Everything you said is correct.

    But people worry about the finest dust because it can be inhaled deep into the lungs, where it stays.

    So whatever very fine (respirable) dust is missed poses a health risk. The chips just sit on the floor.

    I know many don't agree with me, but I do not think you need large cyclones and 6" piping to get the finest dust. 1-1/2 horse single-stage DC's (with good filters) combined with air cleaners do an excellent job of keeping the air clean. Cleaner than the air outside, or in my office.

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    Quote Originally Posted by Dan Hintz View Post
    Don't worry, Phil, we all love you
    LOL, where did everyone go?

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    We think you're great in fact!

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    Crickets.......



    LOL.


    IMHO, while collection at the source is vital (and sadly, many of our tools are designed poorly in this regard), I've been fascinated by watching my Dylos Air Quality Meter over the past few months.

    As much as my 5HP Oneida cyclone can remove at the source (and this is vitally important), when using the table saw or especially the drum sander, the particles in the room quickly reach unacceptable levels. What quickly makes these go down is the overhead air cleaner.

    I often wondered whether buying the air cleaner was money well spent. Since being able to measure the environment with the Dylos meter, I don't work without the overhead cleaner on. And at high speed when sanding, for sure.

    The air cleaner gets the particle count down to approximately 100 when running. The ambient air in the shop is normally 500. And with the sander running (hooked up to the cyclone and an additional 4" port sucking in surrounding air), the air can easily get up to 15,000 particles (measured 30 feet away !!!!!)

    So again, IMHO, get the best dust collection you can swallow purchasing, modify (enlarge) the ports to 6" if possible (usually is) but save enough in your budget for an air cleaner.

  7. #7
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    It's an interesting question Alan as to whether it's realistically possible on most operations even at high CFM and with enough effort on careful hood set up to capture all the dust produced. The answer technically has to be no, in that the chances are that something escapes - but the big question is how much actually needs to.

    It's got to be very situation and machine specific - both in terms of what works by way of hooding/capture arrangements, the dust system set up and the machine type/size. And that's before we start talking about cyclone separation and filter retention.

    Wonder if there's any chance of some government money to do some testing and figure it out???

    ian

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    Hi Alan, I also have a Dylos, an Oneida cyclone with HEPA filter, and no ambient air cleaner.

    When I come into the shop the air is around 500 counts, run the cyclone for 10 to 15 minutes, down to 100 or less.

    I will admit that the only power sanding I do is a ROS with a festool vacuum, I mostly scrape or hand plane for a finish process.

    My only dust producing machine in any amount is the sliding table saw and it has a blade shroud and overhead guard, which makes an enormous difference.

    The important thing is to measure and make sure you're doing well, buying the Dylos was a great decision...........Regards, Rod.

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    I was wondering if I could convince Rod Sheridan (or others) to take a Dylos reading in a carpeted area of their home with a normal amount of foot traffic. I am very curious about the relativity and meaningfulness of the various Dylos readings in the shop environment. I am also curious about the cost of running my 5hp cyclone for 10-15 minutes just as an aircleaner....I assume it to be reasonably high given current electrical costs in my area. I may just do that and post the findings sometime.

  10. #10
    Alan, that is a very interesting data point. I don't have any way to measure air quality. But I do have an overhead air cleaner. After turning off the dust source about how long does it typically take to get the particle count down?

    I am wondering because I don't like running the overhead air filter . It is a little loud and most of my time in the shop is spent quietly with hand tools. I would prefer to turn it off after it has done it's job.

    Lets see a little back of the envelope calculation: my garage is 22x22x11 = ~5k ft^3. My Jet says it moves ~1k ft^3/minute. So it will process the volume of air of my garage in ~5 minutes. But how much of that is just the same filtered air being recirculated? Would nee a lot more math to improve the accuracy and lots depends on how efficiently the air moves around the shop. And also the efficiency of the filter. Looks like mine is only 85% at 1 micron. So I am probably looking at 3-4x the time to get the count down.

    Thanks!!
    Salem

  11. #11
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    So it seems that using the Dylos particle counter explodes one myth that seems to get repeated over and over, the one that says that the ambient air cleaners are nothing but "dust blowers". And wasn't that term coined by one of the gurus of dust collection?

    Personally I am happy that I have one of those dust blowers, as I can't tell you how much dust my DC DIDN'T catch yesterday when I made at least a dozen 5 cut method tests trying to zero out my table saw sled. Using a sled to take a sliver off a cut is one of those operations that table top collection sucks at, particularly when you can't use your Shark Guard.

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    Pardon my disagreeing Ole, but i don't think anybody has (that i've seen anyway) ever said that a functional ambient cleaner doesn't help clear the air. The objection that gets raised time and again is that they by definition can't function until the air we're breathing is full of dust, that we end up breathing this dust until the air has cleared, and that consequently it's inadvisable to design a system to require the use of one.

    Bill Pentz and lots of others routinely instead steer people towards their targeting a system and hooding arrangements that capture the dust at source.

    The other issue that Bill has raised that militates against using an ambient cleaner is that leakage means that you end up with a shop layered with dust. Dust that gets stirred up every time you move, and which can easily result (if the reported numbers are true) in particle counts much like those caused by machines with poor dust collection.

    It's all very well taking a Dylos reading after the count has dropped and consoling yourself that it's fine. The issue is that (a) the medical limits are very low (they typically specify dust limits in terms of steady levels (1 - 5mg/m3 or better) maintained over an 8hr day), and (b) you take a significant hit while waiting for this to happen. The standards are presumably pitched as low as they are they are for some reason.

    The 'dust blower' comment or whatever that i saw related to recirculating systems fitted with filters that allow the fine dust to blow straight through - because the media fitted is too coarse to catch fines. This targeted the older style bag filters that used a fabric with large openings. It's applicable too to good quality filters that have started to pass dust as a result of wearing out or being damaged.

    The tougher question is whether or not a properly functioning high CFM system can capture the dust in all possible cutting situations. The answer to that one is presumably that 'it depends'. Depends if nothing else on having hooding arrangements that work for the task in hand....

    ian
    Last edited by ian maybury; 01-28-2012 at 10:27 AM.

  13. #13
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    Guess you can count me in as one of those whose DC systems are woefully inadequate as I also have an overhead dust blower arounder. At least that's what I'm surmising from all of these repeatitive posts........in 500 words or more......in every dust collection thread on this forum.

    Me, I'll stick to contributors like Phil Thein, who use logic and common sense in their approach, instead of nebulous, ambiguous references and run on sentences that come to no conclusions.

    I'd much rather spend my time in the shop actually woodworking than spending every spare dollar and moment trying to calculate and acquire the ultimate DC system.

    What was that term again? Oh yea, post purchase rationalization.

  14. #14
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    Quote Originally Posted by Joe Leigh View Post

    Me, I'll stick to contributors like Phil Thein, who use logic and common sense in their approach, instead of nebulous, ambiguous references and run on sentences that come to no conclusions.
    What you are doing is what everyone in this life does, cherry pick the information to suit yourself. Stick to your guns and don't let anyone tell you any different, they are your lungs so you should be responsible for them.
    Chris

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  15. #15
    Quote Originally Posted by Ole Anderson View Post
    So it seems that using the Dylos particle counter explodes one myth that seems to get repeated over and over, the one that says that the ambient air cleaners are nothing but "dust blowers". And wasn't that term coined by one of the gurus of dust collection?
    I think BP was referring to the 30-micron bag DC's as dust blowers.

    Although he did say air cleaners take hours to work. Here (source: http://billpentz.com/woodworking/cyc...conversion.cfm):


    Many wrongly think all you really need to protect yourself from fine wood dust is a good mask. A good mask only protects you while working. Few leave their masks on long enough. Using an air cleaner or even a modest sized exhaust fan takes about six hours to clean your shop air amply to take off that mask.
    IMHO, the Dylos meters exploded a bunch of myths. The particle counters have done a great job exposing a lot of what was once thought to be gospel as little more than marketing hype.

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