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  1. #1
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    Dust collection

    I've just purchased a hobby CNC machine and attempted to surface the spoilboard (MDF) obviously loads of dust and so a face mask. Whilst the surfacing was going in I held a 1200watt domestic vacuum near to the cutter to remove the dust but its still going everywhere.
    I assume a dust shoe would help contain the dust, but are there any advantages to using a shop vac rather than a domestic vacuum

  2. #2
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    Re: Dust collection

    A conventional shop vac and a domestic vac are going to be about the same when applied to collecting chips/dust from a CNC (thats to say, not good). And MDF dust is the worst. If you're going to get serious about doing CNC work, best to bite the bullet and get (or assemble your self) a 2 stage, dedicated dust collection system. Think 1 HP minimum. And keep the flex hose as short as possible. You'll thank yourself in the end.

  3. #3

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    Re: Dust collection

    here is a link to a project I did converting a Dyson DC22
    the newer Dyson Ball are better to use.
    you can pick up faulty ones of marketplace gumtree etc as parts or complete.

    https://www.thingiverse.com/thing:3821185



    Now I use Brushless DC motors like this.
    Some come with a driver and information how to start them up.
    Some you need to get a 3 or 4 wire BLDC driver

  4. #4

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    Re: Dust collection

    Modification I am working on now is to redirect the exhaust air back into the dust shoe to lift and agitate chips and dust from the cutter and re cyclone any super fine particles that are not caught in the separator.

  5. #5
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    Re: Dust collection

    I have actually got a simple cyclone collector attached to my vac at the moment, unfortunately, either with or without this, the dust just goes everywhere and the vacuum is 1200 watts which I think is over 1 hp. The pipe between the vacuum and the collector is about 600mm (2ft) and the pipe from the collector is about 4 meters (13 ft) and 50mm (2in) diameter

  6. #6
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    Re: Dust collection

    If your motor will tolerate it, try enlarging your pipe to move more air. Also, shop vac (brush type) motors are typically rated at peak output. Conventional motors on dust collection systems are rated differently.

  7. #7

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    Re: Dust collection

    A member of another group I am a part of made a YouTube Cyclonic Dust Separator mod from a cheep Amazon Shop Vac, there are a few on YouTube and this mod will apply to most in not all of them.
    The problem he was having was that fine dust from cutting plywood and mostly MDF was clogging his HEPA filter and still getting out over his workshop.
    More so due to poor design of the cyclonic separator, A dust deputy etc would have dramatically reduced this, but nowhere near as much as a Dyson Mod.
    I suggested to him to get and insert a Dyson Cyclonic head of a local clasifieds like Gumtree or Craigslist

    The following are snipets from our discussions.

    From this Shop Vac.


    Link to YouTube Video for Mod he followed.
    https://www.youtube.com/watch?v=c19NzKRkv7E

    Before adding the Dyson mod


    Finally he locally sourced a burnt out Dyson, this was a bit of a task as people dont throw out good appliances in Norway.
    After he supplied me with the details of his build and the Dyson he acquired, this was the mod I suggested tor him.

    This is the Dyson head he got, I made annotations how to mod it


    These was the my installation suggestions to him


    Also the Dysons are a multi stage separator, the one he acquired was a 2 Stage series
    The outer part where the hose comes in is the first stage single Cyclone.
    The centre tube I am indicating is the fine collector for the inner 2nd stage Cyclones this MUST be atmospherically separated from the 1st Cyclone chamber and main collection canister.
    when you remove and examine the waste canister you will notice an inner seal for the 2nd stage.


    With the bottom cowling removed you can see the inner 2nd stage with 6 smaller cyclone's in parallel.


    Due to height constraints of his finished dust extractor, after disassembly and cleaning we found that we could just leave the top cowling off and it can still be screwed together.


    Added a Gasket


    For the time being he just tapped the 2nd cyclone collection chamber


    Make sure there are no flat areas or obstacles that will deflect or slow down air stream velocity entry into the cyclonic chamber should be smooth and progressive.



    All Done and ready to test.


    He tested the Dust collector on his CNC router 3D carving MDF with a .25 Tapered Ball .
    And the results are in....

    The main collection bin.


    Bottom of Dyson Cyclone, 2nd stage fine particle canister.


    Inside 2nd Stage Canister after removing cover, this is the super fine dust that ends up on everything.


    Top Half of Shop Vac HEPA filter compartment and top of Dyson head.

  8. #8

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    Re: Dust collection

    All of my builds are now based on the Dyson Ball Cinetic head, its a 3 Stage Cyclonic Separator.
    They have the little rubber nozles on the end of the cyclone cones that are supposed to vibrate keeping the cone end clear and better fine particle separation.




  9. #9

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    Re: Dust collection

    This is a smaller version from a Dyson portable Stick vacuum with a 12V 20W cordless Vacuum motor.
    This unit performs very well, however it only collects 80-90% of the chips it wont pick up larger heavy chips.
    However this is not a problem as it picks up the super fine problematic dust and fine chips.



    Some of my testing.
    In this test I just have the bottom of the 2nd stage taped up.
    Not the dust is being agitated in the collection chamber.
    https://www.youtube.com/watch?v=UCgXRDQCQPk

    Here I have an extended collection chamber for the 2nd stage cyclones
    Also note the main collection chamber dust is being agitated.
    https://youtu.be/cUA0wVxBwzo

    In the next Video I have added 2 components.
    1st. I have added a Horizontal Disc attached to the base of the 2nd Stage collection canister, this stops the dust being picked up and swirled around by the vortex in the main collection canister.

    2nd I have added a balanced trapdoor that closes when empty but opens wen there is dust in the 2nd stage collection chamber.
    When the dust extractor is powered up the vacuum is pulled on the inner 2nd stage first pulling the balanced trap door closed starting normal operation.
    Downfall was that any fine particles collected remaining in the 2nd chamber get sucked out and released into the room.
    Working on adding a solenoid etc that closes the door as a part of the start process.
    https://youtu.be/ncpb77rSZQ4

    I am working on another modification to the dust shoe so the Dust collector expelled air is returned to the dust shoe to blow onto the job and get recycled back through the dust collector returning any fine particles for collection.
    and as a stage 2 I will be introducing a length of wire up the centre axis of the vacuum tube as a corona negative ion emitter to force fine particles to clump and make separation more efficient.

    This was the motor I used for this unit.

  10. #10
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    Re: Dust collection

    Just found out how to upload photos. This is what I have at the moment
    Click image for larger version. 

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    Tha vacuum is a 1200w bagged. The bag is quite heavy fabric which is clean(washed).
    The dust bucket Is a 5 gallon wine container with an internal "skeleton" to stop it collapsing. The cyclone was something I picked up of ebay. The Dyson cyclone looks a lot more sophisticated with the multi stage separation.
    It does work quite well when collecting chips or using to Pick up rubbish from the floor and not much gets to the vacuum itself,I can put my hand over the end of the tube and it will stick to it no problem. it just doesn't seem Capable of collecting the fine mdf dust either with or without the cyclone attached.
    Dec0ywhat type of dust shoe are you using. I think this may be the first thing I need to sort out, as I think the cutter is throwing and lifting the mdf dust too high for the vacuum to collect

  11. #11
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    Re: Dust collection

    Hi - Cyclones can be very simple, the longer the cone the better the extraction. Dyson have the problem of making a small extractor that can be carted around a home so they have lots of small cones. The "cyclone" with the cylinder will not work well as there is no velocity gradient in the system. Since in the case of a home or workshop extractor that space is not really an issue you can make a long cone with tangential entry and an exit central tube that comes down into the cone a bit and it will be very effective. If your into math there are many videos and descriptions on how to design these things. Its standard engineering stuff and taught in 2nd year eng.... They are generally clear for entertainment value you could make one from 3mm MDF or 2mm plastic quite easily...Peter

    cyclones work via 3 mechanisms 1) gravity pulls particles down. If a particle is small enough to float around in a room then a cyclone can't separate it and a filter is required. Some mdf dust is like this 2) air velocity creates drag on the particle and moves it along the ducting, when it comes into the cyclone it hits the cone wall and slows down, gravity pulls these particles down and they go the bucket 3) They can also reenter the air vortex but at a lower level. The air velocity is slower at the bottom of the cone then the top of the cone, they hit the wall again (due to the circular acceleration pushing them outward) and slow down again. At some point the drag is less then the gravity force and the particle falls out of the vortex into the bucket.

    There are horizontal cyclones as well to save space, but verticals are more common...

  12. #12

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    Re: Dust collection

    peteeng
    Re: Dust collection
    Hi - Cyclones can be very simple, the longer the cone the better the extraction. Dyson have the problem of making a small extractor that can be carted around a home so they have lots of small cones. The "cyclone" with the cylinder will not work well as there is no velocity gradient in the system. Since in the case of a home or workshop extractor that space is not really an issue you can make a long cone with tangential entry and an exit central tube that comes down into the cone a bit and it will be very effective. If your into math there are many videos and descriptions on how to design these things. Its standard engineering stuff and taught in 2nd year eng.... They are generally clear for entertainment value you could make one from 3mm MDF or 2mm plastic quite easily...Peter
    Hi Pete I have to disagree with some parts of your explanation of the cyclonic separation principles,
    In Basic theory this is correct, however a single large or 1 stage system heavily relies on exhaust fine particle filtration.

    The design of the Dyson is not a problem more so limitations of the collection canister capacity and operation cycle time as far as small cones ill get into that shortly.

    "The "cyclone" with the cylinder will not work well as there is no velocity gradient in the system." is a misleading statement, the design of the cyclone chamber is relative to the overall requirement taking into account the particle size and weight required to be separated.
    Many shop dust extractors are based on a simple canister/cylinder design.

    cyclones work via 3 mechanisms 1) gravity pulls particles down. If a particle is small enough to float around in a room then a cyclone can't separate it and a filter is required. Some mdf dust is like this 2) air velocity creates drag on the particle and moves it along the ducting, when it comes into the cyclone it hits the cone wall and slows down, gravity pulls these particles down and they go the bucket 3) They can also reenter the air vortex but at a lower level. The air velocity is slower at the bottom of the cone then the top of the cone, they hit the wall again (due to the circular acceleration pushing them outward) and slow down again. At some point the drag is less then the gravity force and the particle falls out of the vortex into the bucket.

    There are horizontal cyclones as well to save space, but verticals are more common...
    To expand on Cyclone design, in theory any particle that is denser can be separated however some factors will effect efficiency.
    Vertical Cyclones are more efficient separating particles with greater density utilising downward gravitational force, Horizontal can be used where particle density is close like fine MDF dust.

    Conical Cyclone design is the better preferred design for mixed SIZE practical separation focusing on smaller particles.

    You are close on its operation, the thing most dont understand is how the particles are trapped its not just gravity.

    When the air and particles enter the Cyclone their accelerated along the wall of the Cyclone.
    The centrifugal force pushes heavier particles to move to the outer walls of the Cyclone.
    The walls start to converge to form the funnel progressively reducing the diameter of the cone, the Air velocity is fairly constant combined with the smaller diameter causes a faster spiral with more centrifugal force pushing particles to the wall.
    As the Air approaches the bottom of the cyclone cone it inverts and starts moving upward in the same circular direction.
    The inertia of the denser heavier particles forces them downward into the catchment receptacle.
    Fine particles in suspended in the inner cyclone continue to be pushed outward and may pass into the outer cyclone and moved back downward along the wall and collected.
    Clean air is then passed out the top of the cyclone.

    Most commercial designs are based on a single tall narrow cyclone with a cartridge filtration for the output.

    Bag style shop dust extractors use a large Cylindrical Canister as its first stage to separate large dense particles like chips etc..

    The Dyson Principal
    The Dyson uses up to 3 tiers or stages of Cyclones in Series.


    1. Dust Enters the bottom cylindrical Cyclone that is also the main catch canister.
    2. Air with medium-fine micro particles enters the centre column and is passed into the 1st layer of medium size cyclones that separates medium and fine particles.
    3. This in turn is passed to the next layer of smaller Cyclones that filters majority of fine particles, by this stage most if not all particles are trapped.
    Dyson also use a HEPA filter but this rarely gets cleaned.
    The biggest problem with the Dyson is the catch canister size, if it overfills past the fill line its efficiency is dramatically reduced.

    If you where to get 4-8 Dyson heads and place them in parallel on you're larger shop dust extractor air out you may dramatically reduce the time between filter cleaning or even eliminate it

    Their are other techniques that can be applied to separate finer particles;
    Introducing static electricity to clump particles making them larger and recirculating back through the cyclonic separator.
    Water atomisers to clump particles etc.

  13. #13
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    Re: Dust collection

    Hi Decoy - thanks for expanding the explanation. Its difficult to explain things succinctly in this sort of forum. better to see a video. Regards Peter

    https://www.youtube.com/watch?v=LwGXu4e6T1A

  14. #14

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    Re: Dust collection

    Quote Originally Posted by peteeng View Post
    Hi Decoy - thanks for expanding the explanation. Its difficult to explain things succinctly in this sort of forum. better to see a video. Regards Peter
    Totally agree it is a very difficult subject to convey as so much goes on in what initially appears to be a very simple process.
    This is one of the better explanation videos, however the part I find that many over look, including this video is the the relevance of cone length or height and more importantly the inversion process that occurs at the base of the cone.

    The presenter is inaccurate with his statements of;

    1. 5:10 Suggests that the inertia of denser/heavier particles cause them to hit the wall slow down and gravity causes them to fall downward out of the reject port.

    2. 6 :30 presenter state's "its a common misconception that centrifugal force separates the particles from the gas stream".

    - Does not discuss the relevance of cone length.
    - Does not identify or describe the importance of cyclone inversion

    The length of the cone has multiple functions
    1. It gives centrifugal force time to move/push particles outward toward the wall in the downward traveling spiral.
    2. lighter air molecules/particles being lighter are displaced towards the centre of the cone and draw upward by the inner cyclone.
    3. Gives centrifugal force time to push denser particles from inner to outer cyclone.
    4. Length of cone is relative to air velocity and particle size, if its to long the inversion will occur to high from base of cone reducing efficiency.

    Its a combination of centrifugal force moving particles outward toward the wall of the cone, wall friction inside the cone is undesirable, its inertia that keeps the denser heavier practical's moving in the downward spiral trajectory along/parallel to the wall.
    Dense particle concentration should be at its highest at the bottom of the spiral/cyclone.

    The MAGIC happens when the cyclone inverts..
    The base of the Cyclone has a receptacle and is air tight/sealed to the cone
    As air and dense particles accelerate toward the bottom of the cyclone, Air pressure builds up inside the receptacle and base of cone causing the cyclone to invert.
    At the full inversion point a combination of inertia and gravity forces denser/heavier particles to leave the inverting stream and collect in the receptacle.

    He did touch on Serial and Parallel use

  15. #15
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    Re: Dust collection

    Hi Decoy - without starting a war of words - particles hitting the wall and slowing down is a very important part of the process. Cones do erode over time so this effect can't be neglected. Centrifugal force per se does not separate the particles, it moves the particles out to the wall where they hit the wall and slow down. Some particles stay in the downward vortex and separate as you explain either from the primary vortex, the base of the vortex where it changes direction or the upward inner vortex, These go around and around until they separate (or not then its into the filter)

    Heres a very good video in Korean (wish my lecturers were as good as this guy) the maths is in maths... Peter

  16. #16

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    Re: Dust collection

    Quote Originally Posted by peteeng View Post
    Hi Decoy - without starting a war of words - particles hitting the wall and slowing down is a very important part of the process. Cones do erode over time so this effect can't be neglected. Centrifugal force per se does not separate the particles, it moves the particles out to the wall where they hit the wall and slow down. Some particles stay in the downward vortex and separate as you explain either from the primary vortex, the base of the vortex where it changes direction or the upward inner vortex, These go around and around until they separate (or not then its into the filter)

    Heres a very good video in Korean (wish my lecturers were as good as this guy) the maths is in maths... Peter
    I do not see the link?

    I have watched many videos and read many papers, there is no one place that goes in depth into the processes.
    Always happy to engage in any discussion with anybody who has similar interests, like you said as long as it doesn't lead into a war of words..

    If you are ok to continue in the discussion I am as well.
    Happy to listen to what you know and evaluate or compare.

  17. #17
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    Re: Dust collection

    Hi Decoy - You have started me down the path of reviewing my uni stuff. There are a few theories used to design cyclones and these days you can do it with CFD as vorticity is now handled quite well. Here is an article with some of the maths and the link that I thought I had included. I have been helping the local mens shed set up a new dust extraction system. Initially it was going to be a filter tower 5.5m high 1.2x2m footprint. I thought this was over the top. So the search for cyclones started. I have settled on one that does not need a filter, is highly recommended by users and fits a space that we would prefer it to be rather then create a skyscraper at our front door. Peter

    https://www.youtube.com/watch?v=1SsbSxbalFo

    https://clearvueoz.com.au/clearvue-cvmax/

  18. #18
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    Re: Dust collection

    No scientific theory to add to the discussion here, but I will offer my observations from experience. I purchased an older Torit cyclone for my woodworking shop in the early '80s. It came from a business that made mortuary stones. More specifically, they were sand blasting the lettering into the stone marker and using the cyclone to collect the debris. What caught my attention was the pattern of wear.

    Current thinking at the time of the cyclone manufacture was to extend the lower part of the cone well into the collection box (a part of the enclosed system) by as much as a foot or more. This was evident from the images in the operating manual that came with the device. I couldn't really be sure how far it extended because much of the lower cone was gone. The aggregate effect of granite particles circulating thru the system was most evident at the bottom of the cone. Whether that was because of the concentration of the stone particles there, because of centrifugal force, or a combination of both, I can't say. The upper cylindrical exhaust pipe that extended into the cyclone was intact and showed little wear. Just my observations.

    Thanks for the discussion.

  19. #19

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    Re: Dust collection

    the inner tube in Peteeng Korean YouTube picture is marked R2 will not come in contact with harsh solids.
    The intake is at the top marked Hc or Bc once in there and it debris or particles pass the tangent of the radius will rub along the walls of most entire length/height of the cone, where most of the abrasive marble etc will concentrate along the wall at the bottom of the cone.
    What you are seeing in the picture where RC is marked is all you need into the collection receptacle.

  20. #20

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    Re: Dust collection

    Quote Originally Posted by peteeng View Post
    Hi Decoy - You have started me down the path of reviewing my uni stuff. ]


    Here is a link to ALCHE whitepaper on cyclonic Separation, the video I linked is presented in the whitepaper.
    These guys do a very good presentation, being a Chemical Engineering Academic Site, would be of higher credibility.

    Recommended viewing.
    I just subscribed to their YouTube channel, it has lots of very good engineering and process videos content.


    https://www.aiche.org/academy/videos...-demonstration

    https://www.youtube.com/watch?v=2pm54ayF3TA

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