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  1. #16
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    Nov 2007
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    melbourne australia
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    To deal with hand sanding dust I recommend one of these: MIRKA 70x125mm YELLOW hand sanding block



    – Mallee Agencies

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  3. #17
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    Jan 2014
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    Sydney Upper North Shore
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    Interesting discussion. There is another thread where it was said that even a Clearvue wouldn’t make a down draft table functional.
    What sort of flow would be required and what HP machine would be required?

  4. #18
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    Feb 2006
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    Perth
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    Quote Originally Posted by Lappa View Post
    Interesting discussion. There is another thread where it was said that even a Clearvue wouldn’t make a down draft table functional.
    What sort of flow would be required and what HP machine would be required?
    It depends on the size of the table but most problems are usually because of the issues I described in my previous post, holes too small, wrongly positioned so they get mostly covered up etc.

    If a Clearvue is connected to a down draft table with 6" ducting and the table top is well configured it should be able to pull 1000 CFM from above or around the table.
    Given that power tool fans put out between 1/10 and 1/20th of that air flow the ClearVue should easily keep up.

    On machines like routers it won't catch all the chips because the velocity of any chips will be greater that the air speed even near the holes but it's not really meant for these, it's meant for fine dust. Thats why I suggest attaching hoses from power tools direct into the 6" ducting outlet of the table

    Chip scatter can be constrained with curtains and chips landing on the table can easily be swept into slots located near the edge of the table.

    One more feature to add to down draft holes is to make them all "mini bell mouth hoods" for more efficient air collection.

  5. #19
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    Apr 2013
    Location
    Mornington Peninsula
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    70

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    Lappa - I got the impression from the other thread that the clearvue/downdraft table works really well for hand sanding or picking up residual dust from a mechanical sander connected to a dust collector...

    Leigh


    Sent from my iPad using Tapatalk

  6. #20
    Join Date
    Jun 2005
    Location
    Helensburgh
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    7,696

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    Many Years ago I was asked to supply a cyclone for a chair maker and he built a small enclosed cabinet/room that was ventilated with a CV Max. He did that after everything they tried to reduce the dust hazard from hand sanding failed building the cabinet fixed the problem. Most DD tables in a hobby workshop would take up about the same floor area as one of the cabinets in the link below. Because it is not a blast cabinet changes could be made to suit the use of sanding, my mate made one out of plywood using perspex/acrylic for viewing.

    hand blasting cabinet - Google Search
    CHRIS

  7. #21
    Join Date
    Aug 2007
    Location
    Saskatoon, SK, Canada.
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    1,436

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    Quote Originally Posted by Lappa View Post
    Interesting discussion. There is another thread where it was said that even a Clearvue wouldn’t make a down draft table functional.
    What sort of flow would be required and what HP machine would be required?

    The aerospace company I used to work for had about eight downdraft tables when I worked there. Six were dry and two were wet, the dust drawn through a water bath. They also had a couple dozen side draft filter units to make a filter booth/room to capture the dust from the parts too big for tables. They were used for grinding aluminium, steel and titanium parts. Separate areas for different metals.

    The dry tables were the bigger of these with 4 filters of about 1,000 square feet of filtration. Maintenance added HEPA filters to the outlets for better filtration. Look at the data sheet and you'll see they used a 5 hp backward inclined airfoil impeller (more efficient than the ones in most DC's including the CV's) pulling 3,000 CFM. That number is likely the impeller alone, just like the advertised DC's sold to woodworkers. The operators were using disc and belt grinders along with a variety of die grinders. If they put the work closer to the middle and positioned the work and tools so they threw the dust and sparks towards the middle of the table they work reasonably well at grabbing it. Often though they put the part near the edge and let the dust and sparks fly to the right or beside them to the floor. Naturally they don't work as well like that.

    The wet tables were the big back to back pair with a 10 HP impeller drawing the air from both tables at the same time. Go to the bottom of the page to another page with a picture of it from the side. They were better designed at the table because they were enclosed on the top and three sides, helping to contain the dust. The air drawn down was pulled through the water and then up into the middle chamber hitting inclined, what looked like sloped slabs of corrugated foam, filters. The water running back to the tank below and the air passing through to the impeller and then across the top which was then directed down as an air curtain across the open front, helping to contain the dust over the table. They worked really well but aren't something easily made to use at home even if you did have a ton of room. I was never around (worked evenings) when maintenance changed the water and removed the sludge so don't know what was done to get the air pulled through the water on the table side to the filters to get the dust to mix with the water.

    The booths/room were were a bank of a dozen 5 HP impeller units forming the wall about 36' long with the same impellers as the downdraft tables (same brand) with 4 filters totalling 800 square feet each, so 9,600 square feet total. It was about 15' or 18' wide with plastic strip curtains on the 3 open sides stopping a couple feet from the floor to let the air in. There were 3 to 6 people working in it depending on the parts, wing ribs, fuselage frames etc. They were very good at keeping the dust contained but the people inside had to wear masks all the time and they floor needed sweeping of the heavier particles at the end of shift.

    Watching those units being used over the years taught me that containing the dust to where you are working, curtains, is important and just as important, is to as much as possible, direct the dust towards the suction area of the table. So if routing for example route the edge away from the front of the table where you stand in a direction that throws the chips to the back. Same applies to sanding etc. Setting up walls or curtains as Bob has done makes a huge difference. I just don't like the air pulled up near my face on the way to the fan. Sorry Bob.

    Once upon a time I took a couple 16" diameter fans that came from natural gas ceiling heaters in the plant at work that had burned through the heat exchanger cores. Same kind of axial flow fans you would see in paint booths, greenhouse and barn ventilators. I put them in the wall behind my fathers lathe to remove the sanding dust. They grabbed all the dust and a lot of the shavings, blowing them into the woods behind his shop. You could see the sanding dust come off a bowl and make a fast 90º turn and go straight to the fan. No good in the winter but in the summer would be the best way to capture all the dust from a sanding table in front of them. Most of your continent would be effective year round. If you are lucky enough to live far from people they would be the best and simplest method of handling the dust.

    Pete

  8. #22
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    Feb 2006
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    Perth
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    Quote Originally Posted by QC Inspector View Post
    Same applies to sanding etc. Setting up walls or curtains as Bob has done makes a huge difference. I just don't like the air pulled up near my face on the way to the fan. Sorry Bob.
    If you mean my fume hood, remember I'm sitting or standing outside the fume hood and the extractor fan is at the back of the fume hood so the fumes are not going straight up past my face but upwards and away from me. And there's 1600 CFM sweeping in around my head and body and in from the sides. I should wear my wearable particle detector one day while I'm welding.


    Here's across section of the setup.

    Screen Shot 2020-05-12 at 7.20.04 am.png

    Most of our standard lab fume hoods where we use far nastier stuff than welding fumes had a similar design, but were only 800 CFM. These were 900mm wide across the front and were semi enclosed with either acrylic or PC sides.
    Screen Shot 2020-05-12 at 7.24.45 am.png

    For ultra clean lab work we used HEPA filtered almost fully enclosed air fume hoods with either acrylic or PC sides and backs. These used a HDPE down draft table so that clean air was constantly swept down over the work and a PC screen further separated the operator from the work. These hoods were 900 - 1200 mm wide across the front. The HEPA delivered 800 CFM and the extractor was adjusted to draw ~700 CFM through the down draft hood table so that ~100 CFM of HEPA filtered air deliberately spilled out past the operator. This removed the possibility pf the operator contaminating the sample.

    Screen Shot 2020-05-12 at 7.40.36 am.png
    When nasty acids were use we did the work towards the middle back of the hood so that the acid vapours would not spill into the lab. If someone left a beaker too close to the edge of the down draft table the acid sensor in the room would squawk.

    Since the lab air itself is fully HPEA filtered, and dirtiest things in the labs where the operators, for unattended (eg ON) experiments we would run the extractor at slightly above 800 CFM so that nothing escaped into the lab.
    Attached Images Attached Images

  9. #23
    Join Date
    Jan 2014
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    Sydney Upper North Shore
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    Quote Originally Posted by Ambrosia View Post
    Lappa - I got the impression from the other thread that the clearvue/downdraft table works really well for hand sanding or picking up residual dust from a mechanical sander connected to a dust collector...

    Leigh


    Sent from my iPad using Tapatalk
    I was referring to this statement, even though you said you were using a Clearvue.

    I am still not convinced as nice as that looks, fine dust floats as soon as it is released and to capture it takes a LOT of air and I don't know of a hobby DE that could do that”

    i like the look of your setup and I’ll probably build something similar and utilise the collection box under my home built table saw.

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