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Thread: More dust collection questions

  1. #1
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    More dust collection questions

    The quest for better dust collection practices continue.

    Some of you use Fein or Festool (or shopvac) into your ROS. Others have tapped into the central dust collection system.

    The concern on using the central DC, is that it might not be high enough pressure (or vacuum level) for the small dia hose/passages of the sander.

    Has anyone validated this with data? A 15" impeller on a 5hp motor does pull a pretty good vacuum. And vacuum is related to vane tip velocity (and perhaps secondarily vane shape, curvature and angles).

    It is not obvious to me that the central DC system would have lower vacuum pressures than a shop vac system. Are there published curves? (central DC usually can find a pressure/volume curve, is there anything like it for the vacuums?)

    Variable speed to control the vacuum level is another concern. Some crack a blast gate. Others run wide open anyway. It 'may' be, to get the DC motor running on a part of the curve that doesnt over draw current, means cracking a blast gate elsewhere and this drops the vacuum level. Maybe, just depends on where it is at on the operating curve.

    But I am mostly interested in factual data on the vacuum levels of the shop vacs as a starting point.

  2. #2
    I connect my PC ROS to my DC system and see no sanding dust on my work piece. The sander has an internal fan that pulls the sanding dust into the collector if the collector is installed, so there should be no problem with even minimal air flow through a small diameter hose.
    Lee Schierer
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  3. #3
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    Some cyclone systems, such as a few models from Oneida, are specifically designed to be able to work more effectively with high static pressure situations like CNC machines and some smaller port tools. These setups sense what's going on and adjust speed, etc., accordingly, but still "live" on air flow, however. IMHO, hey are not going to be an overall great solution for small hand-held electrics like a Festool, Fein or similar extractor will provide as those vacuum systems are designed for very high SP and limited air volume.
    --

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

  4. #4
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    Quote Originally Posted by Jim Becker View Post
    those vacuum systems are designed for very high SP and limited air volume.
    Yes, this is my question. What design attributes, specifically, make the vacuums better than a central DC.

    Is it static pressure capability? If so, what level of SP is needed? And what is the actual SP of a DC? Has anyone compared the SP of their cyclone to the SP of their vac with an actual guage? (some years ago I shopped for home vacuum cleaners armed with a vacuum guage - interestingly the one that worked the best was not the one with the highest SP, air flow was also needed)

    Does any one have DATA showing any of these attributes? Or have specific design parameters/values required?

    I get that the vacs are designed 'specifically to complement the sander'. But that could mean anything (especially after marketing gets involved), so was wondering what it means from a technical performance perspective.
    Last edited by Carl Beckett; 01-01-2019 at 5:49 PM.

  5. #5
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    The nature of the blowers in the vacuum vs the dust collector are different. The former excels at providing higher pressure with low air volume...you can't get much air in a 1.5-2.5" port/hose. The latter performs best at low pressure and high air volume which is why you always see the advise to use larger duct. More air fits in it is the simple reason. (it's more involved than that, but...)

    DC doesn't "have" SP...static pressure is a "restriction" attribute of the pathway between what you're trying to clear dust/chips from and the devices you're using to do that collection. It tends to be a higher number with small ports and hoses/duct because so little air can fit in that network at one time. That's why "specifications" for a collector often reference CFM (cubic feet per minute) number "at" such and such static pressure. CFM, which is the measure of air volume moved will change as the actual static pressure varies with the situation. Hence, the need for a fan curve to properly evaluate and compare one DC to another. (most mass market tool makers do not provide fan curves...probably because for marketing purposes, providing an impressive CFM number makes their machine look nice, but is at the same time un-achievable once actual duct work and tools are attached)

    There are a number of threads here which get into things and there are also some web sites that are well known technical discussions of dust collection principles.

    The shortest conclusion, however, is that small hand-held electric tools with small ports are best served by a "vacuum" type setup for dust extraction and larger tools with large ports and large diameter duct work networks are best served by a fit for purpose dust collection system.
    --

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

  6. #6
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    Hi, I used an Oneida cyclone for dust extraction from a ROS for years, it worked great at dust collection ( I would keep an additional port open to allow air flow for the cyclone).

    The issue was that some of the very fine dust would wind up plugging the filter so I stopped doing that and use a Festool vacuum now for that operation. Obviously with the vacuum I don't have that problem and emptying the cyclone bin is much nicer now that I don't have that very fine dust in there. (No point putting a HEPA filter on a cyclone to provide good shop air and then put puffs of fine dust in the air when emptying the barrel).

    Regards, Rod.

  7. #7
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    I have no doubts that my cyclone would be adequate at the very least pulling the dust from my ROS, however I cant imagine a time when Id rather have my 3HP dust collector running instead of my small, portable, quiet CT vac.
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