Building a downdraft table...

[Josh Goldsmith]

I have read some posts talking about building downdraft tables. I also read that a few different people wanted to use furnace blowers. This got me thinking. I do HVAC (Heating Venting Air Conditioning) for a living. I constantly getting old furnaces and swamp coolers. I could get a motor for free but not sure how to build one. I saw a few different designs on the internet but i thought talking to people who actually use one could help me design a very efficient one. What CFM would you recommend? Can you over power it? What would you do different than yours? Any suggestions would be appreciated. It would be nice if you suck so hard that it would hold down your piece of wood that your sanding. Talk to you soon

[Matt Meiser]

Can you over power it?

Only if a) you so much suction that you can't remove the piece from the table or b) you turn your back and your workpiece disappears. :D

I think the bigger issue is filtration. Furnace filters, even good ones, are going to put the finest dust right back in the air unless you can vent it outside. My downdraft table is connected to my dust collection system which vents to the outside.

[Doug Jones]

Maybe like this;
1- Make a box
2- Cut hole for exhaust from blower
3- Mount blower and motor (don't forget cord hole)
4- Slanted top over blower
5- Make openings for filters (pleated reusable/ rinseable filters are best)

[Doug Jones]

6- Caulk all seams
7- Make slanted shelf on other half and caulk seams
8- Install casters, high enough off floor for exhaust to go
9- Make top to size
10- Make under trim to keep top from sliding and 1" holes

[Doug Jones]

Basicly it,,, at least this is how I did it.

And yes it does let a the real small dust particles back out into the air, but it also traps a lot more than you would think. I couldn't believe the amount of dust it trapped the first time I used it.
What I would of done different,,,, made sure the motor will last. Mine has already went down for the count.

[Rick Thom]

Josh, I built one a few years ago that connects to my 1 1/2 hp 1650 cfm dust collector, and it works pretty well.
The plans I had were for wall-hung but I just stick it on top of my work bench when I want it and connect it to mt DC.
It's a box 36 x 24 x 6" deep made out of 3/4 ply with peg board for the top surface. The botton is merely 1/4 masonite dadoed and caulked to the sides and ends forming a ramp for the larger dust. 4" fitting on end for dc connection.
The holes in the pegboard are relieved a bit with a countersink bit to aid airflow (both top and bottom side of board).
When I sand, the dc has enough suction that it certainly holds the board down and the majority of dust is captured. If it is a small item I am sanding, I merely put a scrap piece of ply or the like over the unused part of the top covering some holes and it increases the suction in those remaining open capturing more dust. When I am finished with it, I can just hang it on the wall out of the way because its pretty light and compact.
The sanding dust is very fine, particularly from hardwood with 220 grit or finer paper. I don't think normal furnace filter will handle it with the kind of airflow we are talking about.

[Dominick Giarraputo]

Just put one of those 3M micro fine filters behind your washable mesh filters to increase the amount of smaller particles being recirculated into the air. My father & I made a room dust filter that way and it works great. You can wash or repace the mesh filters several times before needing to replace the 3M filter.

[Jim Dunn]

I built mine like this. I wish I had made as tall as the table saw so I could use it for an outfeed table. But as it is built I can use it for my spindle sander setting on top and not have to use a step stool to reach it.:eek:

[Bob Dodge]

Hi Josh,

If you were to take a peek inside one of the small commercial downdraft tables, you find an axial fan, pulling roughly 1500-1800 cfm at 1725 rpm, and very low static pressure. Roughly 1" sp or so. 3/4hp motor.

http://www.denray.com/sample_page.php?machine=2634B&ind=1

You could build a nice table like Doug's, and run two,three, four blowers if you want. Those old residential blowers, are usually powered by 1/3- 1/4 hp motors. You don't want to push those too much, or you'll fry the motor. Better to use multiple blowers if you have access to a few.

On a table like the small Denray, the sides of the table are sloped as you can see in the pic. The dust falls into a trough, and into a waste drawer. That drawer is drawn and emptied manually.

A cartridge filter or two, would be fine for this application, because the filters are operating at such a low air velocity.

Good luck, Bob

[Al Lupone]

I just finished putting my downdraft/air cleaner table together. Platform on locking swivel castors. 32" x 60" size. One end is boxed in with the blower unit with 3 20 x 25 filters housed above the blower. They go from coarse to electrostatic ultrafine. On top of this is a 32" x 60" box made from 2 x6's. Used a sloping ramp inside made from 1/4" smooth white hardboard. The plywood sides on the ends extend up 1/4" to capture the 1/2" pegboard. I sized the closed box around the fan unit to leave me enough space to mount the other items. So far on one side I have the Delta belt/8" disk sanding center & my Delta planer. They are each mounted on 3/4 ply about 14 x 34". These ply bases are hinged on the 14" end using two 4" hinges from the top of the 2 x 6's. The tools are mounted offset enough to clear the 2 x 6's when I swing them under the downdraft box. There is enough room on the other open side for me to mount the 8" grinder I bought last month from Woodcraft. Just did that tonight. Since my Bosch benchtop saw & 1617 table router have a 37" height, I made the downdraft table 36 1/2" to also act as an outfeed table. My 100 yr old garage floors are a disaster. Without actually mounting the saw into the same table, there was no way to make them the same height AND keep them mobile.
I finished enlarging 450 of the pegboard holes tonite. First half at the fan end I made 1/2" Distant half I made 5/8". While my setup is not as good as a production ceiling mounted cleaner, it does make a visible difference. I took the compressor air hose & spent almost a half hour blasting in, on or under every surface to stir up all the dust. End result you could see the air getting cleaned & then look in and see everything collected on the filters. Another benefit is it really circulates the heat from the wood stove in the corner. I can also just slap down a piece of ply & have another work bench that I can also wheel outside.
Al
http://i33.photobucket.com/albums/d97/lobsta1/shop010a.jpg
http://i33.photobucket.com/albums/d97/lobsta1/shop009a.jpg

[Bart Leetch]

Just put one of those 3M micro fine filters behind your washable mesh filters to increase the amount of smaller particles being recirculated into the air. My father & I made a room dust filter that way and it works great. You can wash or replace the mesh filters several times before needing to replace the 3M filter.

Are you sure you wanted to say increase the amount of smaller particles being recirculated into the air?:)

[Hank Keller]

checkout workbench magazine. They had plans for one a few months back.

http://www.workbenchmagazine.com/main/wb289-sand01.html

Hank

[Dominick Giarraputo]

Quote! "Are you sure you wanted to say increase the amount of smaller particles being recirculated into the air?:)"

Bart, oops! I guess that wouldn't be the thing to do now would it!!:eek: :rolleyes:
Thanks for catching my mistake. I'm sure I was thinking "decrease" but typed "increase".

What can I say, I'm mentaly dislexic!

[Jeff Sudmeier]

I also use multiple filters in my air cleaner. I have yet to invest in washable filters, but I use a super cheap filter first, then a $10, then a $25. I have yet to replace the best filter, I replace the middle one every 6 mos and the super cheaps every month.

[Jim W. White]

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[Doug Jones]

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Why???????

[Jim W. White]

OK ...so trying to respond from a Blackberry is not all that effective.....

I built a downdraft using a furnace motor that I've been very happy with. It is very close in design to Doug's. It will not pull enough air to hold down work peices but it sure does a great job of keeping the fine dust out of your face; and I'm for anything that makes the sanding chore easier.

You can see some pictures and some details here:

http://myweb.cableone.net/jimnbeck/downdraft.htm