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Downdraft / Outfeed Table

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Project by HickoryHill posted 03-01-2015 09:31 PM 4566 views 51 times favorited 32 comments Add to Favorites Watch

This thing really sucks……but doesn’t. I’ve had this on my list to build for probably the last 6 or 7 years and finally got around to building it over the month of February.

About 6 years ago I acquired an old 4 speed commercial furnace blower from my uncle when he was doing a HVAC remodel for his church. The 20amp outlet is first in line and I use it to connect sanders to. This then feeds the 60 minute spring wound timer which control the 3 switches that are wired to Low, Med/Low and High speeds.

Overall dimensions are; 49 ½”W x 34 3/8”D x 33 15/16”H.

The top is ¼” peg board and air/dust is drawn down through and across angled plywood to the downdraft chamber where it passes through a 20”x20”x1” Filtrete 600 pleated filter and then through a Filtrete 1900 pleated filter. Air comes out a 14”x14” cold air return vent. Most the time I can get away using the lowest speed during sanding. It also seems to work well as a shop filter. Makes me wonder if I need the ceiling mounted shop filter anymore. The peg board rests on 1/16” thick aluminum angle iron and is just held in by gravity and the weight of the loose peg board top. Thus I can easily change out the filters as needed without any tools.

The cabinet carcass is ¾” pre-finished birch ply from Menards. While great for shop projects, be careful sanding it as the veneer face is very thin. Door fronts and all trim is walnut we got in at work and I had milled up. I was planning on using strips to maple to hide the plywood edges at each end of the cabinet but ended up making essentially the equivalent of angle iron out of the walnut and pin nailed it on the edges. I think it dresses it out nicely. The top is framed in ¾” walnut and is spaced off the carcass by ¾” ply to make a 1 ½” overhang. My thinking was maybe I would need clamp something to it at some point. It doesn’t make too bad of a work surface either.

All the drawers are 12”W x 22”L with the top two being 5 3/8”D and the bottom being 10”D. The drawers are made of ½” Baltic birch ply and are simply rabbeted corners with glue. For the bottoms I used ¼” birch ply. All ride on 100# ball bearing slides. The top drawer has a front to back divider and individual dividers to create spaces for 5” orbital sander discs. The middle drawer is routed for a center divider but only has a full width divider in it to create a front and back section.

The cabinet rides on swivel casters with the two front ones being Total Lock casters, locking both the wheel and the spin of the caster. The casters are 3 ½” Colson Series 2 Performa with Delrin Bearing casters from the Caster Depot. They are rated at 225# per caster. I have used these casters on probably 11 different projects here and at work.

Overall I am very happy with its performance and love the outfeed function of it as well.

ENJOY

Added 3/2/2015:

When I attached the fan to the cabinet I was worried about squeaks/etc caused by the blower and cabinet rubbing together so I installed a 3/4” high density rub strip around the opening and then used rubber washers for the screws holding the unit to the cabinet. As well to help hold up the blower of the floor of the cabinet I did use some more rubber stripping there as well.

Added 3/3/2015:

Added 3/8” slots every 3” on center (last picture)

-- Jim, Michigan





32 comments so far

View woodchuckerNJ's profile

woodchuckerNJ

1153 posts in 1094 days


#1 posted 03-01-2015 09:41 PM

Your holes are too small, you are starving that heater blower.
Make your holes larger and watch that thing pull the fines down even more, and clean the air too.

-- Jeff NJ

View HickoryHill's profile

HickoryHill

213 posts in 3606 days


#2 posted 03-01-2015 10:44 PM

Jeff, how much bigger you think? Double? They are 1/4” right now.

-- Jim, Michigan

View McDustmaker's profile

McDustmaker

52 posts in 755 days


#3 posted 03-01-2015 11:29 PM

I really like your down draft/outfeed table. You really did a great job. I am curious about woodchuckerNJ’s comments and hope he replies back.

-- Richard, Temple, GA.....If I smell of sawdust then I was having fun

View Bulkhead's profile

Bulkhead

16 posts in 993 days


#4 posted 03-01-2015 11:54 PM

I love that project! I like the storage space I have under my outfeed table at the moment, but I would swap it for this dust collection/outfeed table..

Really like the results

(those drawer pulls look familiar!)

View hoss12992's profile

hoss12992

3831 posts in 1353 days


#5 posted 03-02-2015 12:36 AM

That is really cool. Love the design that you came up with on it. Great job

-- The Old Rednek Workshop https://www.facebook.com/theoldrednekworkshoptn

View Cweatherl's profile

Cweatherl

43 posts in 908 days


#6 posted 03-02-2015 12:46 AM

Very nicely done! I very well may copy some of your design for my outfeed table. :-)
I’d suggest making your holes bigger as well. Or, at least opening the airflow area so that the fan motor doesn’t burn up from lack of air. What is the surface area of the blower output? You should try to equal this area with your air intake holes and the area they add up to.

-- If you look for the bad in mankind expecting to find it, you surely will. Abraham Lincoln (1809 - 1865)

View woodchuckerNJ's profile

woodchuckerNJ

1153 posts in 1094 days


#7 posted 03-02-2015 01:38 AM

The size of the holes would depend on the cfm of the blower.
I had made a table for a shop vac, and 1/4 was too small.

I now have a DC that I connect to it, and my holes for that are 3/8 each and it still starves the DC. But again, it depends on how many holes and whether it is currently starved. Take the top off, does the unit slow down.
But I also have a blower that I may decide to use, as I am looking to get a downdraft table and an air cleaner out of it.

I can tell you that 1/4 will not allow you to move nearly the volume of air that the blower is capable of.
If your blower speeds up while the top is on, and slows down when you remove it, you are starving your blower for air.

The easiest way to get there is to start enlarging the holes 1/8 inch at a time. You don’t want the panel to hold much suction to the table. So if it is holding to the table with some force, you are starving the blower. Keep opening holes. I suspect somewhere around 3/8 to 1/2 for that many holes, but I don’t actually know.

Let us know what you find.

-- Jeff NJ

View HighPointWW's profile

HighPointWW

49 posts in 955 days


#8 posted 03-02-2015 10:44 AM

Very nicely done! And having a multi-function station is a very smart way to go!

View b2rtch's profile

b2rtch

4822 posts in 2508 days


#9 posted 03-02-2015 11:25 AM

Very nice, where did you find the switch?
I used a similar blower to make me a shop air clearer.
I have another blower to someday do the the same thing that you did.
I had hard time finding a switch for my shop air cleaner.

-- Bert

View HickoryHill's profile

HickoryHill

213 posts in 3606 days


#10 posted 03-02-2015 12:26 PM

b2rtch: I just picked it up at Menards. I know Lowes has them as well, so HD should too.

The outlet on the face their is really smaller than the 14×14 cover I put on it. I wasn’t thinking and cut the opening to match the blower, but actual opening for the blower is approx. 9×13.

So, 9×13 = 117 sq in of output area.

The peg board has 24×46 1/4” holes, so to me that’s 24×46*.25 = 276 sq in. (Am I thinking wrong?)

I don’t recall noticing to much of a change in sound when placing the peg board on, but I will have to check again when I get home tonight.

-- Jim, Michigan

View KelvinGrove's profile

KelvinGrove

1396 posts in 1372 days


#11 posted 03-02-2015 01:07 PM

Jim,

It does look like your math is off. a 1/4 inch hole (.25) is .25 X .25 X .785 (or .125 X .125 X 3.14 if you prefer) = 0.049. Then (24 X 46) X .049 = 54.1. That is about 20% of what you were thinking.

And Jeff is on the right track as to increasing the air flow. As for the holes, think of it this way:

If you have a 6 inch square post and a hole that is 6 inches square only one post will fit in the hole. If you double the size of the hole (to 12 X 12) it takes four times as many posts to fill it up. (round posts and holes work the same way) So while doubling the size of the hole from .25 to .5 may not seem like much, it is actually four times the open area.

Not to get too deep into it, a hole with a .5 inch circumference will have better flow than .25 holes for another reason. As the air is pulled into the hole the edge of the hole creates friction and back pressure (just like water running into a sink with a clogged drain.) When you double the size of the hole you have four times as much open space but only twice as much edge creating the friction. For the same reason, a thick top will have more friction than a thin one. The more distance the air has to pass through the hole the more surface area there is to create friction.

If you can remove the top you might want to consider making your own which has slots running transverse to your aluminum stiffeners rather than holes. You might be able to drop a 1/4 flush trim bit through one of the existing holes and “connect the dots”

After seeing how you put this together I have added it to my favorites. I am planning one of these right now.

-- Tim P. Calhoun GA. If traffic is passing you on the right, YOU ARE IN THE WRONG DAMN LANE.

View HickoryHill's profile

HickoryHill

213 posts in 3606 days


#12 posted 03-02-2015 01:27 PM

Oh yeah, I knew that…....using Pi, but was in a hurry before work. I had completely run that through my head earlier too. So you have your math right.

3/8” holes would yield us 121 sq in.
1/2” holes would yield us 216 sq in.

Tim: You mean grooves on the underside running perpendicular to the aluminum angle iron?

-- Jim, Michigan

View KelvinGrove's profile

KelvinGrove

1396 posts in 1372 days


#13 posted 03-02-2015 01:31 PM

Tim: You mean grooves on the underside running perpendicular to the aluminum angle iron?

- HickoryHill

Actually, slots all the way through. It would look more like the exhaust vent cover you see on the first picture of the unit. Far more open space that way.

-- Tim P. Calhoun GA. If traffic is passing you on the right, YOU ARE IN THE WRONG DAMN LANE.

View b2rtch's profile

b2rtch

4822 posts in 2508 days


#14 posted 03-02-2015 01:34 PM

“The peg board has 24×46 1/4” holes, so to me that’s 24×46*.25 = 276 sq in. (Am I thinking wrong?)”
Years ago I spent several week analyzing and trying to improve the cooling systems on very large mining equipment.
One of the many things we looked at, was different style of front grille and side panel openings on the engine compartment and in front the of the radiator.
We found out that the effective area for air laminar flow though a round home is about 25%, everything else is lost to turbulence.
So if you take the total area of holes that you calculated (276 sq in) the effective area for air flow is probably about 25% of that or 69 sq in

-- Bert

View bondogaposis's profile

bondogaposis

4020 posts in 1811 days


#15 posted 03-02-2015 02:32 PM

I love this project. I have been wanting to build a combination outfeed/downdraft table for some time now. This gives me some great ideas.

The peg board has 24×46 1/4” holes, so to me that’s 24×46*.25 = 276 sq in. (Am I thinking wrong?)

Yes I believe your calculation is a bit off. The area of a 1/4” hole is not .25”. The area of a circle is Pi r squared.
So it is .125” squared x pi = .049 sq in So back to your original calculation 24×46 x .049 = 54 sq in

-- Bondo Gaposis

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