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DIY Dust Control Devices for the Home Wood Shop
CONTENTS: Foreword:

Effective control of wood dust is an essential element of any woodworking shop. Inhalation of wood dust can cause serious health problems and the woodworker must minimize exposure to this hazard.


DISCLAIMER:

The reader assumes all responsibility and liability associated with the hazards of woodworking. The author has no control over how a reader will act as a result of obtaining information in this article. The author shall not be responsible for any errors or omissions that may be present in this article. Accordingly, the author shall assume no liability for any damages or harm incurred by a reader or any other person as a consequence of any information presented in this article.

This article is directed toward a hobbyist audience and is not intended for application in a commercial, institutional, or industrial setting. Commercial and institutional woodshops are generally governed by a complex set of worker safety regulations, such as those mandated by OSHA. Satisfying the compliance of such regulations is beyond the scope of this article.


THE HAZARDS OF WOOD DUST AND WHERE IT CAN BE CONTROLLED

There are generally three "points" at which wood dust can be controlled:

    1. At the source;
    2. In the air (airborne dust); and
    3. At the point of breathing (mouth/nose).

Minimizing dust at the first point, its source, is the preferrable and most logical means of control, as this prevents the dust from being distributed around the shop in the first place. This is most effectively accomplished by using a good dust collection system. A dust collector, which is essentially a specialized vacuum cleaner of sorts, draws dust away from its source in woodworking machinery. Hoses are connected to the woodworking machines to collect the generated dust. The dust is drawn into a filtration system, typically a filter bag or cannister, where it can be routinely emptied. Dust collectors are rated by motor power (in HP), and by the volume of air that can be passed through the machine (cubic feet per minute - CFM). Dust collectors are also rated by the smallest diameter of particles that can be trapped in the filter, the diameter being expressed in microns. One micron is 1/1000th of a millimeter. The lower the number of microns stated, the smaller the particle that can be removed (and the better the system). Ideally, your system should be capable of filtering down to 1 micron, and there are many such models available at reasonable cost.

The second point of the dust problem is when some of the dust becomes suspended in the air. This creates a breathing hazard, and also results in contamination and a possible fire hazard when the airborne dust settles onto surfaces. Airborne dust can be removed to some degree by using room air filtration devices.

Abatement at the third point can be accomplished by means of a good respirator mask. The cheap paper dust masks found in stores offer little protection; they can allow dust particles up to 30 microns or more in diameter to pass through. Avoid these and purchase a high-quality NIOSH/OSHA approved filtration mask capable of filtering particles down to 1 micron or smaller. These can be purchased for about $30-$50. The better masks have replaceable filter elements. AO Safety makes high-quality respirators that are readily available from many tool suppliers. If you do any finishing, consider purchasing a mask that also filters mists and fumes. Don't forget to keep an extra set of replacement filter elements on hand.

This article will provide some design guidance for building a sanding downdraft table and a room air filtration unit. These devices will help remove some of the dust found at the first and second points, respectively.

Keep in mind that these devices will not remove all of the wood dust from these points, and that they should never take the place of a good respirator. A safe woodworker will take steps to control dust at all 3 points.


WHY YOU NEED MORE DUST CONTROL THAN IS OBTAINABLE WITH DUST COLLECTORS ALONE

While a good dust collector is capable of removing the majority of dust created by many woodworking activities, there are some instances where a dust collector cannot remove it all, or it is difficult to attach to the work area. This is the dust that "gets away." Perhaps the best example of this is the dust created by sanding.

Sanding is a task that generates large quantities of fine dust that is comprised of wood particles and ejected abrasive grit. Due to the inclusion of abrasive particles, this kind of dust is particularly dangerous to breathe. My sanders have dust bags, neither of which is able to catch more than a fraction of the generated dust. The majority of this dust finds its way into the air (and onto everything in sight). What is needed is a means of limiting this airborne dust.


Sanding Downdraft Table

A sanding downdraft table is essentially a work surface that incorporates a means of drawing away sanding dust for collection. A downdraft table can be as simple as a benchtop-mounted box with a pattern of holes in the top surface, which can then be connected to a shop vacuum or dust collector. When the vacuum or dust collector is activated, downward air flow draws dust away from the work piece during the sanding operation. Most of the dust passes through the holes in the surface and to the vacuum or dust collector.

If you don't have a dust collector to utilize a bench top downdraft table, you can build a self-contained table. The design of this version is similar to that discussed above, except that a filter and blower are incorporated into the device. An old furnace blower fan and some good 1-micron furnace filters (such as 3M FiltreteTM) work quite well. The filters can be periodically removed and vacuumed clean, or replaced.

Below are some photos of a self-contained downdraft table I built several years ago:


Kevin Brady's DIY downdraft table. Constructed from 1/2" MDF. Mounted on casters for mobility.

View of the top surface. Top is 1/4" masonite bonded to 1/2" MDF.

Inside view of the downdraft table. Dust is drawn downward and settles into the dust collection compartment on the left side.

View of the dust collection compartment and filter. Accumulated dust is easily removed with a shop vac.


View with blower housing cover removed. Filter is easily removed for cleaning or replacement.

Downdraft table is powered by an old furnace blower.

Grooves routed into top surface to provide a better path for moving dust.

Download my sketch in PDF for this downdraft table. (Caveat -- it's a rather crude drawing.)

Alternatively, here are the plans for the benchtop downdraft table, to be connected to a dust collector or shop vacuum.

Both sets of plans require the free Adobe Reader.


Room Air Filtration Unit

A room air filtration unit is a device that draws dust-laden air inward, passes it through a filter, and ejects clean air out. At its best, a room filter is capable of filtering a portion of the dust suspended in the room's air. It is by no means a replacement for dust collection at the source, and certainly not a replacement for using a good respirator mask. But a well-designed room filter can greatly reduce the amount of airborne dust in a shop.

There are many good commercial room air filtration units available that are designed for small woodworking shops. Jet, Delta, Penn State Industries, and JDS Tools offer decent units for hobbyist use, for around $200-$300 or so.

But why pay that kind of money when you can build your own for a fraction of the cost? For around $75-$100, you can construct a good air filtration unit in an afternoon.

How Much Filtration is Necessary for Your Shop?

This mostly depends on the size of your shop. When HVAC engineers design a heating or air conditioning system for a building, they design based on the building's air volume in cubic feet, and how rapidly the air is to be cycled through the system - how many times the building's air is "exchanged" per hour.

When designing a room dust filter, you can apply a similar approach. Calculate the room's air volume: length X width X height in cubic feet. Then determine how many times per hour to exchange the air. An exchange value of 6 to 8 times per hour is a reasonable rate. More is better, as a faster rate means less dust will accumulate and settle. Let's do an example.

My shop is in my 2-car garage. The dimensions are 24' X 24' X 9' ceiling height. The volume is thus 5184 cubic feet. I want to design for an air exchange of 8 times per hour. That means I will cycle the entire volume of the shop's air 8 times an hour - about once every 7.5 minutes.

I must now determine how many cubic feet per minute (CFM) that will be necessary to meet my design requirements. I will be cycling 5184 cubic feet of air per 7.5 minutes, thus 5184 divided by 7.5 yields a rate of just under 700 CFM.

However, this value of 700 CFM is at an ideal rate of flow. Since I will be passing the inbound air through filters, and since filters restrict the free flow of air, some adjustment is needed in order to determine the rated blower fan capacity. Without getting into the tedious fluid dynamics involved, we can approximate by a factor of about 2 and select a blower fan rated at a free-flowing rate of around 1400 CFM. That will provide an adequate amount of "headroom" so as to yield a realistic 700 CFM under the load of air passing through the filters.

Of course, this is a simplification; there are other factors that will affect the air flow, such as filter size, area of the exhaust aperture, direction of air flow, etc. However, this formula should provide a good estimate. In fact, the blower formula can be simplified as such:

Rated Fan CFM = Room Length X Room Width X Room Height ÷ 3.75

Applying the above formula to my garage volume, I calculate: 24 X 24 X 9 ÷ 3.75 = 1382.4 ≈ 1400 CFM

Once you have determined the rated CFM required of your fan, it's just a matter of buying a suitable fan. You could use a furnace blower, and you might be able to pick up a used one fairly cheap from a local HVAC contractor, or perhaps a yard sale. Another option, one that I had used in the construction of my filtration unit, is to purchase an attic fan from a home improvement center. These attic fans are inexpensive, costing around $25-$30 or so, and are rated for moving 1000 or more CFM.

Original DIY room air filtration unit. Below are some photos of the room air filtration unit I built several years ago:


Kevin Brady's DIY first air filtration unit. The enclosure was constructed from scrap particleboard salvaged from a discarded ping-pong table.

Back view of unit, showing filters at the intake.

Pull-switch for actuating the blower, a 1500 CFM attic fan.

View of filter side, with retaining door open. The unit uses 2 stages of filtering.

The first stage of filtering is comprised of two general-purpose furnace filters.

Behind the two filters in the first stage is a separator frame. The separator frame is 2" thick, with wire mesh on each side. Turbulence created within this space causes some of the dust that has passed beyond the first stage to precipitate here.

Behind the separator frame is the second filtration stage, which is comprised of a 1-micron Filtrete furnace filter. This stage traps most of the fine dust that has passed through the first stage.

Side hatch for accessing the fan. As you can see, a small amount of dust passes through the filters and collects here. This hatch provides access for periodically cleaning the fan and motor.

Hindsight is 20/20.

That was my first (and so far, only) DIY room filtration unit. Looking back, I would have done some things differently in my design. I would have foregone the scrap particleboard (even though it was free) and opted to construct the enclosure from something much lighter, like 1/2" plywood. I didn't enjoy lifting the behemoth up to the ceiling.

More importantly, I would have designed it to filter air from all directions by mounting filters on all 4 sides of the box, and porting the filtered exhaust air out the top or bottom. As it is now, the unit is primarily effective in filtering dust that is present in the air behind the unit. Even so, the unit does remove a good portion of the airborne dust, which is evident when I frequently clean the filters. In any case, I hope the photos above give you some basic idea for building your own filtration unit.

After mulling all of this over for some time I started really thinking about a design for an improved room air filter. And so another weekend project took form. Read on....


UPDATE:
ROOM AIR FILTRATION UNIT ... BIGGER AND BETTER

If a little is good, more is better, and so I set out to design and build a filtration unit with twice the air volume and better filtration. This new one would have filters on all four vertical sides. I disassembled the previous unit described above and cannibalized some of the parts to build the more powerful and more efficient filter unit. The old filtration unit was very heavy, due to its 3/4" particleboard construction. It used a single 1500 CFM attic fan. I bought a second fan and a sheet of 1/2" Baltic Birch plywood to build a dual-fan 3000 CFM unit. Here is the story...

FREE plans! Download the NEW & IMPROVED dimensional drawings in PDF for this air filtration unit. A big THANK YOU to Eric Heidel for taking the time to polish up my old, crude plans and make these oustanding drawings!


It pays to get good filters. I chose furnace filters that would capture dust particles down to 1 micron, such as 3M's FiltreteTM filters, or equivalent. Sure, they're expensive, but you can clean them with a shop vacuum and reuse. Don't waste your time with the cheap 30-cent fiberglass filters, as they are of little effectiveness and will allow much of the particulates to pass through.

Here is the frame of the enclosure under construction. I used 1/2" Baltic Birch plywood for the entire enclosure. One 60" X 60" sheet was all I needed for the entire project. I used a pneumatic crown stapler with 1" staples and wood glue to join the parts. I considered making a cutout to mount a filter on the bottom as well, but I was concerned that the structure would not be as strong. So I stayed with the 4-side filter configuration.

A close-up view of one of the corner columns, showing the channels for retaining the 1" thick filters.

Since I didn't have a compass large enough to draw the 15" circles for cutting the two apertures in the top panel, I had to improvise. I used a thin strip of wood with a small hole for the pencil and pivoting about the center on a sheet metal screw.

I used a jig saw to cut the two apertures. I inserted the fans to ensure that the apertures were of proper size to snugly fit the fan shrouds. But no matter how good you are with a jig saw, there is bound to be a small gap around the shrouds. Therefore, when mounting the fans, I sealed the shrouds with a bead of silicone caulk.

The enclosure, ready for mounting the fans and the electrical connections.

The wiring assembly. I used an ordinary 15 amp single pole switch to actuate the fans. Note the internal connection of the fans at the metal junction box. Make sure these fans are properly grounded and that a 3-prong grounded plug is used to connect power. The unit is powered by 125VAC.

View of the unit suspended from the ceiling with the fans mounted. I had salvaged the attic fan from the previous unit, and bought another similar fan at a home center store.

Inserting the filters. Due to to the dimensions of the enclosure, I was able to use larger filters (16X25) for the sides, and 16 X 20 filters for the ends of the enclosure.

Small latches made from narrow strips of hardwood are turned inward to retain the filters.

Here is the room air filtration unit, suspended by chains from the ceiling and ready to run. Although much larger than the old unit, it actually weighs less (about 50 lbs.), due to the lightweight plywood construction. The unit filters air from all 4 vertical sides, and exhausts clean air upward from the top of the unit.

A strip of paper towel held near the filters shows that the unit is drawing air inward. This is a test you can use periodically to check the filters. If the paper strip doesn't draw inward, it's a good sign that the filters are becoming clogged and need to be removed for cleaning with a shop vacuum.

Size matters. This unit, capable of filtering 3000 CFM of air, works like a champ. It removes a substantial portion of airborne dust from my shop. The total cost of the components used in the construction of the unit was about $125 - about half the price of the anemic units you find in the stores.


DIY DUCTING AND MACHINE CONNECTIONS FOR DUST COLLECTION

If you are considering adding a dust collection system to your shop, I recommend the book, Woodshop Dust Control, by Sandor Nagyszalanczy. This book is an excellent technical reference that thoroughly covers just about every aspect of dust reduction in a home shop or small commercial shop. It's 15 bucks well spent.

Good dust collection machines are made by Jet, JDS Tools, Penn State Industries, and Delta. I ordered a 1-1/2HP, 1250CFM single stage dust collector from Penn State for just under $300 plus about $60 shipping. It is a well-made machine and I am quite pleased with its performance. It will easily handle dust collection from two machines and filters dust particles down to 1 micron.

When my dust collector arrived and I initially set it up, I used the 50 feet of flexible tubing that came with the unit (free from Penn State with the purchase of the dust collector!). I merely strung the tubing along the ceiling of my home shop, and quickly discovered that this was going to be unsatisfactory. The flexible tubing drooped down from the ceiling and was a bit unwieldy. Not to mention the fact that 50 feet of corrugated flexible tubing tends to impede the flow of air somewhat. I decided to construct a metal ducting system along the ceiling, choosing to use the flexible tubing only for the drops from the ceiling duct. I went to Menard's and bought a bunch of 26 gauge, 4" diameter galvanized steel stove piping and various elbow and tee fittings. A crimping tool is handy to have for this operation. I constructed a length of metal ducting that I suspended a few inches below the ceiling of my shop. I then had to retrofit dust ports onto the woodworking machines that didn't already have them - namely my table saw, jointer, router table, miter saw, and thickness planer. I have a cheap Delta benchtop belt/disc sander that has two dust ports of an unconventional 1-1/2" diameter. I have no idea how I'm going to adapt that, but I'll think of something.

Below are some pictures of my dust collection endeavors:


The 1.5HP, 1250CFM dust collector I ordered online from Penn State Industries. The unit is dual voltage and comes wired for 125V. I opted to rewire it for 250V.

A view of one of the 4" hose drops (foreground).

I used 4" galvanized stove ducting for the duct runs. Connecting the lengths of ducting with the various elbow and tee connectors is a snap; a couple sheet metal screws in each joint holds the components in place. I wrapped each joint with metallized duct tape and suspended the ducting a few inches below the ceiling with steel wire.

Jumper wires are connected to provide electrical continuity from the flexible tubing to the galvanized ducting. The black flexible tubing contains steel spring wire for rigidity - this wire also provides a good ground path. Good grounding of dust collection ducting is essential to reduce the risk of static discharge, which can cause a dust explosion under some conditions.

I connected a vertical galvanized duct downward from the ceiling and connected its lower end to the dust collector inlet with a short length of 4" flexible tubing.

I adapted a plastic dust hood to my jointer using 3M double-sided foam tape. No need to drill holes for screws.

A view of the jointer with the 4" dust collection hose connected.

I adapted a dust port onto my Delta table saw. I cut a 16"x19" piece of 1/2" Baltic Birch plywood and mounted a 10"x10" table saw hood in the center. I then mounted the plywood/hood assembly horizontally under the apron of the saw and connected a short length of 4" flexible plastic tubing.

I connected the other end of the tubing to a 4" plastic splice coupling which passes through a piece of plywood mounted across two of the table saw's side legs.

A shop vacuum crevice tool mounted on the back side of my router table fence makes a good dust extraction point. A 4" to 2.5" adapter allows connection of the dust collection hose.

I built a dust collection port for my cheap, crappy Delta miter saw. This saw creates a lot of dust and very little of that dust makes its way into the cloth bag, thereby necessitating my kludgy dust collection scheme. I constructed a small box-like enclosure, with a jointer dust hood mounted on the top surface of the enclosure, just under the miter saw's table.

I used a short length of 4" tubing to connect the dust hood with a 4" plastic splice coupling which passes through the right side of the enclosure. This system does not catch all of the dust generated by the miter saw, as some of it is ejected from the top of the cut by the rotation of the blade. Nevertheless, it helps quite a bit. In this front view you can see the short length of tubing connecting the dust hood with the exhaust port at right.

Of all my power tools, the benchtop planer produces the most chips and saw dust. After planing a stack of lumber I would literally be wading in mounds of wood shavings. I kludged a 4" dust port onto a piece of 1/4" plywood which I pop riveted to the metal shroud on the exit side of the planer. It works quite well, with only a small amount of shavings falling to the floor. But I must make sure all the other blast gates are closed, as this little planer demands the dust collector's full power.


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