Downdraft Sanding Table

[Kyle Kaldor]

I'm working through my design of a downdraft sanding table and have a couple of ideas I'd like to bounce off all of you smart people.

I'm trying to create a "catch" for dust in a downdraft sanding table, somewhat like a cyclone would do.

Idea #1 just has a vertical panel before the filters.

Idea #2 has an angled panel before the filters. I was thinking this may allow the dust to settle better and not get sucked up into the filters.

What are your thoughts? See attachments. BTW, there's a lot of work left to do so keep the critiques to this portion please :D

Thanks,

Kyle

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[johnny means]

You'd be better off without the baffles and just put your port up high. The large open space will act more like a neutral vane than a bunch of constricted ducts. Either way your unlikely to get slow enough air flow for fine dust to settle.

[Ben Rivel]

Just as sort of "bigger picture" question, what are you intending to sand on this that you feel youd need a downdraft table to adequately capture the dust from? Something other than just using an RO on project pieces?

[Bill Orbine]

Do more filtration area and in stages like an over head air cleaner. You could take one of those and connect it to the table.

[Ted Phillips]

Also, don't forget to add an access panel or drawer at the bottom so you can empty the accumulated dust.

[Tom Bender]

The baffle will work on larger particulate and the angled baffle should be a little better. But most sanding dust is fine and will blow right past either.

You definitely need a good HEPA filter. A furnace filter is not going to be very effective with high dust concentration.

Put the bottom of your filter a couple inches off the chamber floor and figure on good sealing to keep dirty air from bypassing the filter.

[Peter Christensen]

To give you an idea of what a commercial table has in it. Work had a number of 4' x 6' Donaldson Downdraft Benches for the metal finishing department (grinding edges and surfaces of steel). They had 4 cartridges totaling 1000 square feet of filters and the company added a big HEPA filter to the outlet. The motor was 5 hp and drove a fan that seemed to be a cross between a squirrel cage and DC impeller moving about 3000cfm. Even with all that there was still some dust that ended up on the floor near the machine and floated to areas up to 50' away. You'll need lots of power and filter area so as to not restrict the airflow.

https://www.donaldson.com/en-us/industrial-dust-fume-mist/equipment/dust-collectors/cartridge/downdraft-bench/

[David Utterback]

It is not clear if the bonnet under the sanding table will result in equivalent flow (capture velocity) across the surface. I suggest you learn more about plenums as used in slot hood designs (not HVAC systems) to get the air velocity through the slots or circular holes appropriate for the volume of the plenum. Generally, the slot air velocity should be about 2 times the plenum air velocity. All these factors will need to be correct for the power and efficiency of the fan you will use.

For efficiency and ease of use, I would suggest slots through the table surface instead of circular holes. Pulling air through multiple small holes requires more power than long relatively narrow slots. The treatment of the of the edges of the slots or holes is very important to reduce frictional losses. A bell shape is the most efficient entry shape.

Let me know if you need additional information.

[Kyle Kaldor]

Just as sort of "bigger picture" question, what are you intending to sand on this that you feel youd need a downdraft table to adequately capture the dust from? Something other than just using an RO on project pieces?

That is mainly what I'd be using it for.

[Kyle Kaldor]

Do more filtration area and in stages like an over head air cleaner. You could take one of those and connect it to the table.

I have a homemade overhead air cleaner and I don't really like it. I'm not a fan of pulling the dust up into the air past my face and then having an exhaust port blowing the rest of the dusty air around. I'm actually planning to use the fan out of that in this table.

[Kyle Kaldor]

Also, don't forget to add an access panel or drawer at the bottom so you can empty the accumulated dust.

Ted, I didn't show this, but I'm actually also thinking about putting a 4" port to connect to my dust collector down in that area. Heck, I might even just scrap the entire design I have shown and just connect it to my dust collector.

[Bill Orbine]

I have a homemade overhead air cleaner and I don't really like it. I'm not a fan of pulling the dust up into the air past my face and then having an exhaust port blowing the rest of the dusty air around. I'm actually planning to use the fan out of that in this table.

I sorry if I haven't made myself clear..... I was suggesting that you could use the filtration unit under the table..... The unit draws air from the holes in you table. Make sense?

[Chris Parks]

I have never seen a DD that worked anywhere near properly but others may have. For a start large amounts of air flow is blocked off by the object being sanded and light dust from sanding operations floats as soon as it is created so in reality you need both an overhead hood and a DD capability and that requires serious amounts of air flow. If hand sanding Mirka do a nice unit that can be hooked up to a vacuum cleaner which does from all reports a reasonable job.

[Myk Rian]

I made a frame the size of my router table, and stretched chicken wire over it.
I just take the router and plate out, put the frame on the table, and turn on the DC.

[Peter Christensen]

Myk how big an object can you sand on your router/downdraft table? And how much air does your DC move?

[Martin Wasner]

I have never seen a DD that worked anywhere near properly but others may have. For a start large amounts of air flow is blocked off by the object being sanded and light dust from sanding operations floats as soon as it is created so in reality you need both an overhead hood and a DD capability and that requires serious amounts of air flow. If hand sanding Mirka do a nice unit that can be hooked up to a vacuum cleaner which does from all reports a reasonable job.

You need to use a proper downdraft table. Ours has a 48x72 table and flows 4000cfm. If there's something in the air, it came from somewhere else in the shop.

I still prefer it greatly over sanding with a vacuum.

[Chris Parks]

Heaps of air flow as I said above, way above what any hobbyist would find practical. I was asked to supply a CV Max to a start up chair manufacturer and we look at some sort of sanding station and DD table for finishing and after a bit of thought it was obvious we could get a better and cleaner result by venting a small room with the Max and the dust never got into the factory work area. It also could be used for spraying finish which was a bonus.