Downdraft table - suction?

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Simon Magennis
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Joined: Sat Jan 07, 2012 7:51 am
Location: Menorca. Spain.

Downdraft table - suction?

Post by Simon Magennis »

Check my logic please.

I will be making myself some sort of downdraft table in the near future. The simplest option is just to plug in one of my workshop vacuum cleaners. However these are very noisy but I don't have anything else at the moment. So that is step one. But there may be a later "Plan B".

"Plan B" would be to get a motor separately and build some sort of suction unit which brings me to the basic question. Is this logic correct: to reduce noise, a larger fan and motor and bigger diameter tubing is the key? If so any suggestions about appropriate motors.

As I am in Europe the usual US assumptions about motors and filters related to "furnaces" don't apply. We don't have the things. (Heating is based on pumped water to radiators and whole house aircon in so far as it exists is not central and ducted but rather based on mini-splits where an external unit is connected to multiple internal units with a liquid for heat exchange.)

Thanks.

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Bob Gramann
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Re: Downdraft table - suction?

Post by Bob Gramann »

The vacuum won’t pull much volume. It’s suction will be unnoticeable if your table is more than a few inches square. You are right about the noise. Bigger fan, wider ducts means less noise. Have you considered a simple box fan? It pulls a lot of air.

for illustration only: https://www.homedepot.com/p/Lasko-20-in ... /100405665

Carl Dickinson
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Re: Downdraft table - suction?

Post by Carl Dickinson »

The point of the downdraft table is to collect the dust. The vac might work but something like this might work better, https://www.harborfreight.com/13-gallon ... +collector. It will still be noisy though. I've got my dust collector in an outside shed but needed some sort of return air venting to keep the conditioned air inside the shop.

David King
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Re: Downdraft table - suction?

Post by David King »

I built mine twenty five years ago using a smallish 1/5hp squirrel cage blower from Granger. It's relatively quiet and moves a LOT of air for the Amps. The problem is that that air is very concentrated and moving at a high velocity at the output and you need the diffuse that and spread it around to a large filter area. It's the same issue at the intake where you want and even down flow over the work area which again involves making air pathways from all corners towards the inlet near the center. The work surface is a simple lattice of wood strips with spacer blocks between them about the size of a guitar. That is hinged to the bench and directly under it is a prefilter of 25mm foam filter media. Around the sides of the bench are 6 16" x 20" x 1" pleated furnace filters to remove the fine dust before it exits.
To be honest i never use the thing because I find any noise to be distracting and I really don't need it because I long ago stopped using power sanders and so don't kick up much dust at all with hand sanding. A small, 3 speed box fan like Bob is suggesting with a fiberglass insect screen on the front and a deep pleated polyester media on the back would take care of you to whatever level of purity you can afford filter-wise.

Alain Lambert
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Location: Trois-Rivieres, Quebec

Re: Downdraft table - suction?

Post by Alain Lambert »

A fan from an old kitchen range hood or a bathroom fan would be relatively quiet and move a lot of air.

Simon Magennis
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Re: Downdraft table - suction?

Post by Simon Magennis »

The fan in our kitchen extractor is so loud that we scarcely ever turn it on. :-) When we replace it, I will not be re-using it for this.

Alain Lambert
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Location: Trois-Rivieres, Quebec

Re: Downdraft table - suction?

Post by Alain Lambert »

Sometime, these fans are loud because the air passage is restricted. When running with a lot of "air room" they calm down. This is assuming this is not a bearing problem or vibration problem.

Simon Magennis
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Joined: Sat Jan 07, 2012 7:51 am
Location: Menorca. Spain.

Re: Downdraft table - suction?

Post by Simon Magennis »

Carl Dickinson wrote:
Sun Sep 27, 2020 3:06 pm
The point of the downdraft table is to collect the dust. The vac might work but something like this might work better, https://www.harborfreight.com/13-gallon ... +collector. It will still be noisy though. I've got my dust collector in an outside shed but needed some sort of return air venting to keep the conditioned air inside the shop.
I had a look for something like this at the UK Axminister Tools site. (https://www.axminstertools.com/eu/machi ... extractors) That got me to think that maybe getting a chip collector would be a good option and maybe something like dust deputy as well and replacing the bag filter with a cylinfrt filter too.

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