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PostPosted: Wed Feb 13, 2008 9:47 am 
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Charles was kind enough to offer these very nice plans to the OLF for use by its members.

Thanks Charles! [:Y:]

Greetings all,
Here’s a first draft of a Down Draft Table design.
I’ve tried to work around standard filter sizes (24 x 24) and readily available materials. For those of you without a table saw or limited panel cutting access you should be able to get 1/w sheet (2’ x 4’) pieces from your home improvement center and do a little splicing and cutting to length. I believe Home Depot calls them “handy panels”.
You can use 1x2 for the ledgers and spacers between and around the filters.

I’ve included the part # and website address for the filters that I have available locally. You may need to substitute according to your availability. The pre-filter catches all the big chunks and is relatively inexpensive to change using one will extend the life of the more expensive high efficiency unit. The 6” deep filter is a 95% efficiency unit (filters 95% of particles down to .05 micron).

My blower is one that I found at a yard sale for $15. Try your local HVAC supplier for a used unit. I scrounged a 1/3 hp motor and used a “link belt” (one of those red twisty adjustable kind). I’d guess it blows (or sucks) around 6-700 cfm.

The last element I plan to add is a shelf to put sanders and supplies on that is 2 or so inches thick and hollow. It will double as a manifold that I’ll plug my shop vac into the end of, and there will be a row of holes for the small diameter hose that my sanders use.
A row of air fittings for the sanders and plug strip will complete the rig. Maybe a strip lite on the bottom of the shelf would be nice too.

I’ll draw up the shelf next.
Attachment:
DDTable.pdf


Cheers!
-C


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PostPosted: Wed Feb 13, 2008 11:01 am 
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Thanks Lance!

One of these days I'll learn how to do the downloadable thing here on the OLF.

I'll get some refinements drawn up soon and send them along to whoever's interested, and as always, feel free to ask about materials and methods.

The grille top is a little tricky to make, but works much better than pegboard or ply with holes.
Sometimes you can find them used at building salvage outfits. They're used for cold air return floor grilles in older houses.

-C

PS one small typo I made- the "handy panels" are 1/4 sheets (2' x 4')

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PostPosted: Wed Feb 13, 2008 11:16 am 
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That looks great, Charles! I am thinking of incorporating a sanding table in one of my work benches, so this comes at a good time.

About the grille; what is it, exactly? And why does it work better than for example perforated plywood?

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PostPosted: Wed Feb 13, 2008 11:31 am 
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Thanks for that. Nice plan. I've got an old squirrel cage fan that might work great. Just a matter of finding the time one day.

Lance, these great looking plans must be worthy of going into the tools and jigs archives?

Thanks,
Danny


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PostPosted: Wed Feb 13, 2008 11:50 am 
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Hi Arnt,
In my experience the grille has a greater "open area" than holes in a panel. I've found that by the time you drill enough holes, in a piece of plywood, it gets too floppy. Don't ask how I know... The goal is to create the least amount of resistance a possible.
Anyway, in a nut shell the way to make one is to slot a piece of lumber, say a 2 x 6 or 2x8, cross grain with a 1/2" dado on the table saw with a mitre gauge or sled, or with a straight guide and a router. make the cuts 3/4" deep, or half way through. Space the slots with 1" of material remaining between them. Then rip the board into 1/2" wide strips. Next rip up some more solid stock into 1/2" x 1/2" pieces and fit them into the slotted pieces leaving a 1" gap between and voila! you've got a grill. I put 1/2" wide x 3/16" closed cell foam weather stripping on the top edges of all the grille edges to protect your working from getting "shop rash". The foam also keeps the work from sliding around.

-C

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PostPosted: Wed Feb 13, 2008 12:52 pm 
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For the downdraft table I made a couple days ago, I dado'd the top with 1/4" wide slots, 1/2" apart. I left a 1-1/4' wide center support area. 5/8" plywood, and it's plenty stiff, still, yet there seems to be a good enough flow. To d it again, I would consider a 3/8" dado slot, though... I topped it all with soft foam weatherstripping.

Mine's 24x26"x8". I connect it to the DC with the 4" inlet, but I will plumb it permanently via two 5" ducts leading to the main 7" trunk line to the DC. that should have enough vacuum t actually hold the guitar body firm to te table, i suspect <g>

I was going t do a table like your plans(nice plans, BTW!), but decided my DC can pull more air than a furnace blower anyhow, and this takes up much less space. If I didn't have the huge DC already, I'd go the blower route...


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PostPosted: Wed Feb 13, 2008 2:01 pm 
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Woo Hoo, I got a compliment from Grumpy.
Now I can DEFINITELY retire!!!!
-C

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PostPosted: Wed Feb 13, 2008 2:45 pm 
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I have 3 (or 4? I'll have to dig around in the shed) pretty big blowers with 3 phase motors that I bought at an auction at a shipyard about 5 years ago, I've been planning to use one of those in a sanding table (I would like to use one of the others and build a Pentz style cyclone around it, when I get around to it...). They have seen a lot of use, but I have tested them so I know they work and boy do they move a lot of air!

Thanks for the tips on the grilles guys, most appreciated!

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PostPosted: Wed Feb 13, 2008 3:58 pm 
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Oops, spotted a typo in my grille making description- the cross pieces are 1/2 x 3/4 to fit the notches.
-C

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PostPosted: Thu Feb 14, 2008 9:55 am 
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This could very easily be adapted to do double duty as a room air filter, something that I have in the works (parts acquisition stage). I've been thinking about how I want to set it up, and I think that doing double duty with a DDT would be great!

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PostPosted: Mon Feb 18, 2008 12:09 pm 
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Mario, will you pull the table off that "sucker" and show us the insides? Is it just an open box with the 4" DC inlet on the side, or is it plumbed to the center to even out the draw? I've seen so many versions of a down-draft table, I'm not sure what actually works, aside from having enough CFM to pull the feathers off a chicken at 20 paces.


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PostPosted: Mon Feb 18, 2008 1:39 pm 
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No baffles at all. I considered some, but decided to try it out first. It works well enough...

I will be setting it up permanently, where it will be hooked up directly to the main trunk(7") of the dust collector via a pair a 5" steel ducts. Once I have that amount of flow, I may want to add baffles. If i do, i'll keep y'all posted. But so far, the big empty box concept works...


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