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Thread: DC chip vs fine dust collection

  1. #31
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    Quote Originally Posted by Ole Anderson View Post
    Thank you. Yes, I have seen the "dust blower" analogy applied both to ambient air cleaners and to older bag style dust collectors. Maybe we ought to start referring to what we are speaking of as a "dust management system" that would include respirators, dust collection systems, machine "hoods", ambient air cleaners, shop vacs and the trusty broom and dust pan. Any one of those alone will never provide us with an acceptable dust level as far as our lungs are concerned, you really need every one of those in order to address the problem.
    I have thought this for some time but couldn't come up with a term for it, kudos to you for doing so. I think someone should do a Sawstop on the dust recycling industry for that is what most of us do, recycle the fine dust. I reckon someone should lobby the govt to ban any device that does not trap and hold the very finest particles, end of story.
    Chris

    Everything I like is either illegal, immoral or fattening

  2. #32
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    There is something to be said for the galoots that just use a froe, chisels and planes, they don't spend much time arguing about dust collection.

  3. #33
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    Quote Originally Posted by Ole Anderson View Post
    There is something to be said for the galoots that just use a froe, chisels and planes, they don't spend much time arguing about dust collection.
    But just ask about sharpening. Dave

  4. #34
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    +1 to what Dave said about the need for everybody to (carefully, and with discrimination) apply the information that's about (which tends to come in mixtures of accurate, patchy, incomplete or downright misleading depending on where you look) to their own situation.

    The bottom line i have to think is that viewed through a 21st century consumer lens the position is pretty unsatisfactory - but the upside is perhaps the opportunity it leaves open for those prepared to put the work and thought in to knock the problems down one by one to come up with a very good system at reasonable cost......

    I'm impressed by the way that despite some vigorous discussion that we've as a group managed to stay polite and on the message. Thanks guys.

    What was that about another dust system topic???

    ian
    Last edited by ian maybury; 01-29-2012 at 6:38 PM.

  5. #35
    Let's keep the govmt out of woodshop dust collection. They are busy trying to figure out how to keep the dust down on dirt roads.

  6. #36
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    Steve made some very good points in addressing the OP's question. It takes more energy to capture the larger particles if they escape the hooding. Sometimes the smaller particles can be drawn back into the hood if they are on the "fringe" (technical term) of being captured or not. The velocity generated by the hood at the point of dust capture ultimately determines how good the hood will perform. The capture velocity has to be enough to overcome any fan effect from rotating parts and draw the dust into the hood. The required capture velocity for larger particles is higher than that of smaller particles (generally speaking) due to their mass and velocity. The more enclosing the hood is, generally the better job it will do and the less CFM it will require (EU TS's with riving knives and hoods in close proximity of the blade do a better job of dust collection). However, the more enclosing the hood, the more that access to the cutterhead is limited.

    The performance of a hood drops off drastically as it is moved away from the dust producing source. If the distance from the hood to the source is doubled, the CFM requirement will approximately quadruple to maintain the same capture velocity and similar hood performance.

  7. #37
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    Michael, Bill P talks about the effective dust collection at the end of the duct but I can't recall him differentiating between light and heavy particles/debris. I have termed this area for my own purposes to catchment bubble. IIRC the catchment bubble for a 150mm/6" duct is about 13". Very good point about the difference between heavy and light material. As for dust being dragged and pushed by moving blades etc, turn a bandsaw on and using a bit of wood gently push some saw dust close to the blade and watch what happens and keep in mind this is very low speed device. The dust is pushed away by the airstream quite strongly and shows what must be happening many times more strongly with a TS or router table
    Chris

    Everything I like is either illegal, immoral or fattening

  8. #38
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    I do not know which cleaner are the best but I do know that if the sun are shining thru. the window at the right angle that you can see the dust in the air even in a clean house , the best way to remove all of the dust would be to turn the house or workshop inside out during a rain storm

  9. #39
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    Ray, no one says all the dust can be captured but no one says we have to breath it all either.
    Chris

    Everything I like is either illegal, immoral or fattening

  10. #40
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    Quote Originally Posted by Chris Parks View Post
    Ray, no one says all the dust can be captured but no one says we have to breath it all either.
    I think the $64,000 question is who clean is "clean enough" and what is the most cost effective and straight forward way to accomplish that "clean enough". Unfortunately, there is very little straight forward about the whole proposition except in the minds of those that feel they have the answers. Some of them probably do but the difference in solutions probably means all of them don't.
    Of all the laws Brandolini's may be the most universally true.

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    Your bandsaw weighs more when you leave the spring compressed instead of relieving the tension.

  11. #41
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    I have to admit that after years of thinking I was invincible it is now comforting to see the Dylos under 1000 and to turn on the DC when the numbers spike- sometimes into the tens of thousands- and leave the shop for 15 minutes and return to numbers below 1000 again. Don't know what that means in real life but I was born without a sense of smell so I don't have any survival skills to identify bad air. Carrying the oxygen tanks for my Dad gave me time to realize that the price difference between a great system with testing equipment- Dylos and Anemometer- and my previous mediocre one was less than $1K. Of course I found some used components because that is half the fun so most of the cost was in bigger piping and fittings. It also gave me the excuse to find more machines. Dave

  12. #42
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    No question but that it's a classic example of a scenario where the devil is always in the detail - get the engineering wrong/change the circumstances to something outside of design assumptions and no matter how many of the spec boxes you tick you're still not going to have a high performing system.

    It's basically the reason why those of us that are engineering types sometimes get accused of negativity and pernickdtyness - it's born of the knowledge (gained through hard experience) that a workable (it's still not necessarily going to be perfect) solution requires that every single issue/variable is knocked down in turn.

    Unlike in e.g. marketing where once you have something that sounds vaguely correct you can backfill the gaps with some bluster. That's before mentioning that there isn't even full or reliable performance documentation available for most dust system equipment anyway, with the result that we're each left to apply 'judgement' and hope for the best in many cases.

    It's worsened by the fact that it takes instrumentation to know whether or not a decent job is being done (that we don't necessarily sense what's going on) - and by the fact that the regulatory limits that do exist are (a) based on complex medical and statistical analysis which may or may not be an accurate predictor of outcomes, and (b) regulations that only set out technical/system requirements in broad brush terms.

    Particle counters are great, but there's potentially complexity in there too. The regulated TLV/daily exposure limit is about 1mg/m3, but this is for wood dust of all particle sizes produced by cutting operations. The very fine dust that is most risky comprises it seems only a very small proportion of that produced in such operations, meaning that the permitted quantity of very fine dust in the air we breathe is very low indeed. (a small part of the 1mg/m3 above) A particle counter is (a) going to have to work at these very low levels of fine dust (which they seemingly do), (b) because it samples a specific range of particle sizes may ignore large quantities of other sized particles in the air, and (c) isn't as a result all that easy to correlate with the above regulated exposure limits..

    Maybe the conclusion to be drawn from all of this is that it's the sort of situation where the chances of running everything to ground with absolute certainty are pretty slim. That we always roll the dice to some degree in engaging in an activity like woodworking. (as in most of life - you pays your money and you takes your pick) It on the other hand suggests that while these systems are never perfect that it's very clearly wise to get on with it - to do all we reasonably can to maximise the performance.

    It's tempting to get frustrated with all of the uncertainty and lack of black and white information, and to as a result decide 'a pox on all their houses' and do little or nothing about protecting ourselves - but that sounds just a little too brave to my mind....

    ian

  13. #43
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    Quote Originally Posted by Chris Parks View Post
    Michael, Bill P talks about the effective dust collection at the end of the duct but I can't recall him differentiating between light and heavy particles/debris. I have termed this area for my own purposes to catchment bubble. IIRC the catchment bubble for a 150mm/6" duct is about 13". Very good point about the difference between heavy and light material. As for dust being dragged and pushed by moving blades etc, turn a bandsaw on and using a bit of wood gently push some saw dust close to the blade and watch what happens and keep in mind this is very low speed device. The dust is pushed away by the airstream quite strongly and shows what must be happening many times more strongly with a TS or router table
    Chris,
    The catchment bubble is dependant on several factors and can't necessarily be related to duct size. It depends on CFM, hood design, required capture velocity, etc. As you say, the spinning blades provide a fan effect. This would effect the catchment bubble either in a positive or negative way depending on where the hood is located and how it is configured. We typcically design the hood first to determine CFM required, then size the duct to maintain conveying velocity for the material.

  14. #44
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    Van, what do you use for a dust system? yes at this stage of development we see all types of answers but it will settle down. When the car was first invented there were all types of that also, electric, steam, petrol etc. Those that don't believe in it are quite entitled to their views and good on them. Everyone must make their own judgement for better or worse and if the consequences of that are ill health later in life they have no choice but to stand by their decision as they made it. I put that in the category of smoking, same thing. Those that think they have the answers may well be wrong but better to have done something than nothing and in the process advancing the knowledge in all probability. Since I have been involved in this stuff I have heard numerous stories of people losing their livelihood due to wood dust and regret not doing something about it, the only issue there is that for the small shop there was no equipment and less knowledge than now. It is only in relatively recent times that wood dust problems have been exposed for what they are and I think that the internet has been the main vehicle that has done that. I would never criticise anyone for not taking what I consider the necessary steps to safeguard their health, everyone makes their own choices in this life. I might try and persuade them but in the end it is their choice.

    What has happened over the last few years is that there is more tolerance for the view that dust extraction is a necessity, I believe when Bill Pentz started his crusade he was pilloried quite extensively but these days there is a view he was the pioneer and is the living reference for all this stuff. I doubt that the same amount of criticism would be forthcoming to anyone who espouses the same views these days and that is how it should be.
    Chris

    Everything I like is either illegal, immoral or fattening

  15. #45
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    Ian, the dylos 1100 pro displays two counts. 2.5 micron and larger and .5 micron. Both move up and down with some consistency and while not totally scientific it does create a frame of reference when compared to outside and inside the house air. Helps with the guesswork. Dave

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