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Discussion Starter · #1 ·
Here is a downdraft box I just completed today for sanding with my ROS. I used the Rockler plan pdf. that I downloaded off their site .

http://go.rockler.com/tech/25077-Down-Draft-Ezplan2.pdf

I had a part of a sheet of prefinished 1/2"birch plywood I had bought and used for drawer sides. The box is pretty simple to build. I made my own perforated top pieces. I had built one years ago off the same plan, but they had small 1/2" holes and it cut the air flow so much ,I decided to make the holes 1' dia. spaced 1/4" apart.

I tried several drill bits to drill the holes and settled on the spade bit with the scoring ears on it.
I tried a Forstner type bit, and it cut OK from both sides, but it was slower, plugged up,was harder to exactly follow the pilot hole as the pilot point was so short.
The 2 auger type bits were the best cutters, but the threaded pilots would lift the material off table table fast.
The spade bit has a long tapered pilot that centers from both sides easily and the spurs do a good job of scoring the outside cut. I never would have guessed it ,but it worked best for drilling from both sides.

It took the longest to drill and finish all 278 holes.

The pictures tell the story.

Herb
 

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World's largest 'Whack-a-Mole' !
Again, Herb, beautifully crafted...have you put it to the test yet?
Just out of curiosity, why does it have to be so deep, top to bottom?
that's controlled by the thickness of the bed and the dia of the pickup..
 

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Herb...
you gonna put hardware cloth on the bottom side of the deck for small part loss control???
 

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Herb, that is a very nice build. You might have too many holes or the holes might be too big. My box is I think too big and the holes are too big. I have it hooked up to my big dust collector and it doesn't seem to be pulling enough air.

 

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David
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Nice, Herb. I went with my own design a year ago, still works great and with the DC hooked up it really pulls hard and will hold a piece in place if I block off the rest of the holes (easy to do).


David
 

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Hmmmmmm!!!

That sure looks like HF gray one handed clamps being used!!

Herb I thought that they went by the wayside a while ago.
 

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Discussion Starter · #8 ·
Hmmmmmm!!!

That sure looks like HF gray one handed clamps being used!!

Herb I thought that they went by the wayside a while ago.
I think you are right. The mini ones seem to hold fine, it is the large ones like the Irwins that don't hold good, and pinch your hands, good eye.
Herb
 

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Discussion Starter · #9 ·
Herb, that is a very nice build. You might have too many holes or the holes might be too big. My box is I think too big and the holes are too big. I have it hooked up to my big dust collector and it doesn't seem to be pulling enough air.

Haven't got it hooked up yet, so don't know how well it works. Might have to seal off some holes. I will pick up some fittings and flex to do a hook up this week.

The last one I made with 1\2" holes didn't do the job.
@stick 486
no hardware cloth

Thanks for all the comments, I will have some things to think about.

Herb
 

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Herb's project is a beauty. I wonder if you could make the box, then use one of the plastic or metal grids that go on flourescent light fixtures. Then have a couple of thin, rectangular masks with rectangular openings to lay over it, leaving openings just a little larger than the item being sanded? You could add a small chamber below the unit to slide in and store the masks out of harm's way. Just thinking.

I really like Stick's idea of, say a 1/4 or 1/3rd inch wire screen below the grid to strengthen it and catch dropped small parts. I'd also use very light weight materials wherever possible so I didn't get a hernia every time I hauled it out for use.

I think I'd put some very smooth material on the slanted boards to keep sawdust from hanging up on tiny rough spots.
 

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Discussion Starter · #12 ·
After reading this: Dust Collection Research - Downdraft Table

I am not sure it will even work.


I used the Rockler pdf.

25077-Down-Draft-Ezplan2.pdf



It is approximately 27X17X6".

No Hardware Clothe. What small parts are supposed to be able to fall into the box? this is for ROS sanding things larger than the holes. And since it is not made for cleaning the shop air en mass just for creating a negative pressure around a small area where I am sanding, and according to the article above will not work anyway, I may be able to cover part of the top,depending on the size of my piece to adjust the air flow. Thanks for all the comments,and suggestions, I should have done more research before I built this. It was a good exercise in drilling holes,though.:grin::grin:

Herb
 

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Nice build Herb. I built one similar to the one David shows a number of years ago. Since it's hooked up to my shop vac, I don't get a lot of downdraft when I sand smaller items. To remedy that, I just put a piece of plastic or some plywood, whatever is handy, to cover most of the exposed holes that are not around the piece that i'm sanding. That increases the airflow through the holes that are left uncovered. Works well enough to get most of the sawdust.
 
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Discussion Starter · #14 · (Edited)
Nice build Herb. I built one similar to the one David shows a number of years ago. Since it's hooked up to my shop vac, I don't get a lot of downdraft when I sand smaller items. To remedy that, I just put a piece of plastic or some plywood, whatever is handy, to cover most of the exposed holes that are not around the piece that i'm sanding. That increases the airflow through the holes that are left uncovered. Works well enough to get most of the sawdust.
I like that idea, I was thinking of a rubber mat like @TwoSkies57 ,Bill suggested too, to keep the material from sliding around also. I could make 2 top panels W/O holes too and just keep the middle one with holes,the others for spares.

I am hooking it up to my 3hp DC with 4" flex which has a lower velocity of air flow, but higher volume. I will figure out some way to get this thing to work.

Herb
 

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I like that idea, I was thinking of a rubber mat like @TwoSkies57 ,Bill suggested too, to keep the material from sliding around also. I could make 2 top panels W/O holes too and just keep the middle one with holes,the others for spares.

I am hooking it up to my 3hp DC with 4" flex which has a lower velocity of air flow, but higher volume. I will figure out some way to get this thing to work.

Herb
Herb, I have the same mat. I do most of my routing on the router table. When I make something like my oval cheese board with a large, curved routed goove to hold crackers and such I use my plunge router. That mat works great holding the piece so it doesn't slip around. I managed to tear my mat so I ordered a new one. Based on this thread I think I'll cut the old mat to use with the downdraft box. Mine is smaller than yours so I'm thinking of two sizes. One to cover half of the top and a second one to cover the whole top with a section cut out for sanding smaller pieces. I'll adjust based on the results.

With the size of your DC you shouldn't have much trouble with the sawdust. You may have a little collect on the top between the holes but a quick swipe with a workbench brush will clean it off. Since I'm using pegboard I have more space between much smaller holes so I do get some build up but it doesn't effect the sanding operaton.
 
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Discussion Starter · #16 ·
I well today I completed the downdraft box and all my fear were for naught, I works great. I do have a rubber pad for it coming, but might not even need it. I am happy camper ,it works way better than I had imagined. I did put side boards on it and they makes a big difference.

Herb
 

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Discussion Starter · #17 ·
Herb, I have the same mat. I do most of my routing on the router table. When I make something like my oval cheese board with a large, curved routed goove to hold crackers and such I use my plunge router. That mat works great holding the piece so it doesn't slip around. I managed to tear my mat so I ordered a new one. Based on this thread I think I'll cut the old mat to use with the downdraft box. Mine is smaller than yours so I'm thinking of two sizes. One to cover half of the top and a second one to cover the whole top with a section cut out for sanding smaller pieces. I'll adjust based on the results.

With the size of your DC you shouldn't have much trouble with the sawdust. You may have a little collect on the top between the holes but a quick swipe with a workbench brush will clean it off. Since I'm using pegboard I have more space between much smaller holes so I do get some build up but it doesn't effect the sanding operaton.
Barry, you might try enlarging some or all of your holes. The small holes actually cut down on the sir flow. Also they recommend beveling both sides of the holes to increase air flow. You can do that by just using a countersink.
Herb
 

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Discussion Starter · #18 ·
Tom, a Dust Collector is low velocity and high volume, a shop vac is just the opposite low volume high velocity A dust collector does not increase velocity when it is choked down, it has the same velocity and less volume. So if you say choke a 4" DC down to 2 1/2" you get the same as a 2 1/2" @ the same velocity as before but nearly 1/2 the volume as before.
You can tell by the sound of the DC. Leave the 4" wide open , it is loud making lots of noise, cover the end completely it is half as loud, because the motor and fan are not working hard moving air. Open your fingers and it is half again as loud,the motor and fan are working, but not full rate yet.
You can do the same with an amp meter on the DC line. Start up the DC with all the blast gates closed,(mine reads ) 9.6 a. everything closed, and 11.8 a. everything wide 0pen, which indicates it is working harder moving more air open and decreases when closed.
Herb
 

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Thanks Herb. Seems counterintuitive, but it is what it is. So my suggestion is not good so I removed it.
 

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Discussion Starter · #20 ·
I think that is because everyone thinks of a vacuum cleaner that is running at very high speeds compared to a 3750 rpm Dust collector, they are in the router motor range 10,000 rpm or more. And the number of fan blades on a dust collector are at least half what a vacuum cleaner fan has. So you have two different principles of moving a lot of air slowly and a small amount fast.

Herb
 
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