Guide to workshop dust control
Whether you have a tiny basement shop or a spacious “Garage Mahal” with plenty of room to work, you probably could benefit from a new or improved dust-collection system. Dust and chips from machining and sanding operations add clutter to your work area, and can damage your lungs, as well.
Unfortunately, setting up a system can seem perplexing, what with complicated terms, such as fan curve, static pressure, cubic feet per minute (cfm), and airflow velocity. Then there are those calculations required to determine the proper dust collector, duct sizes, and system layout.
But don’t give in to frustration and the dust. We’ll simplify it all for you. To do that, we worked with a dust-collection expert: Jeff Hill, an engineer with Oneida Air Systems, a leading maker of dust-collection equipment. We traveled to WOOD® magazine reader John McCausland's shop in Jamestown, Pennsylvania. There we analyzed John’s dust-collection system to see how well it performed and where we could make improvements. See “Performance—by the numbers” below to learn how we tested the system. We learned a lot from this shop visit, and so will you.
Following that, we’ll distill all the technical mumbo-jumbo into a few basic rules of thumb that you can use to size your ducts and collector and lay out a customized system with only a minimum of calculations. We’ll show options in ductwork and fittings to help you get started.
One man’s system: a case study
John McCausland taught woodworking, metalworking, and drafting for 30 years. So he knew a thing or two about what he needed when he designed and built his new shop in 1998. The 26x28' space, shown in the opening photo above, and in the floor plan, below, provides John a place to pursue his hobby when not working as a ranger at a nearby state park.
John built his system using off-the-shelf components, and was happy with its performance. We knew the system worked, but we wanted hard data to see its strengths and weaknesses. We asked: “How can it be even better?”
Let’s start with the collector
A 3-hp dust collector with four bags powers John’s system. To save space and reduce noise, John installed the collector in a shed attached to the shop, shown in the photo below. He ran the main duct through a hole in the wall, just below the peak of the vaulted ceiling.
Placing the dust collector outside the shop brought another benefit. The machine’s stock bags filter only particles 20 microns and larger. But it’s the fine particles 20 microns and smaller that are most hazardous to breathe. To capture them before the air returns to the shop, John cut holes in the wall that separates the shed from the shop, and added frames that hold four high-efficiency furnace filters.
Our expert says: The dust collector does the job, but isn’t performing to its full potential. With stock filter bags, it musters only 736 cfm. The collector is rated at 1,800 cfm, which it probably can’t achieve, but it’s still short of the mark. The motor generates only about 60% of its maximum amperage (14 amps at 220 volts) due to ductwork inefficiencies.
Jeff agreed that mounting the collector outside the shop saves space and reduces noise. But, he adds, “Why filter the air twice? Replacing the 20-micron bags with 1-micron bags would eliminate the small dust, and make the filters unnecessary.”
John also could install a cyclone system in place of the current collector. A cyclone captures the big chips and most of the fine dust in an easy-to-empty tub. Therefore, the filter bags don’t clog as quickly, and John will only face the mess of cleaning them every few months or so, rather than every few weeks.
We couldn’t install a cyclone that day, but, following Jeff’s advice, we did install four 1-micron bags on John’s collector. Airflow increased by more than 300 cfm due to the bags’ greater airflow capability. That means the motor can pull more air and produce more of its potential power, as demonstrated by the increased amp draw.
Performance—by the numbers
To get an idea of how well John’s dust-collection system worked, we started by drilling a small hole in the main duct, just beyond where it comes through the wall. That allowed Jeff Hill to insert the pitot tubes for two different gauges: one that measured airflow in cubic feet per minute (cfm), and one to check static pressure (sp), as shown in the photo above. Using an ammeter, we also measured the motor’s amperage draw, below. See the results in the table following.
We took readings under three conditions: First, with all the blast gates open to check the system’s maximum achievable flow. Next, we closed off all gates except the radial-arm saw to determine maximum flow farthest from the collector. Finally, we tested with just the bandsaw’s gate open to determine flow at the most-restrictive port.
The first sets of numbers show performance with the collector‘s stock 20-micron filter bags. Performance was adequate everywhere but at the bandsaw. The second set reflects the impressive improvements made by installing 1-micron polyester felt bags.
Duct dos and don’ts
Because the price was right, John used HVAC (furnace-style) pipes to create the ducts in his dust-collection system. All the pieces consist of 26- and 28-gauge galvanized steel.
Our expert says: Snap-lock HVAC pipe works fine, and is economical. But Jeff prefers 24- and 26-gauge galvanized steel for any ducts larger than 4" because it’s strong enough to resist being sucked flat by a powerful collector. Never use lightweight 30-gauge or dryer-vent pipe. Even a modest collector can do them in.
Where ducts intersect and turn, John used short-radius elbows and tee fittings designed for HVAC use. These increase resistance in the system, preventing it from moving all the air it could.
Our expert says: These fittings really hinder the performance of John’s system. Fittings designed for dust collection would get the most from his collector, or possibly allow using a smaller one.
For best airflow, elbows should bend at a gentle radius—at least 11⁄2 times (1.5x) the diameter of the pipe. The radius of HVAC elbows usually equals pipe diameter (1x). Where pipes join, wye fittings allow air and chips to flow through the transition with little turbulence.
Duct sizing in John’s system is straightforward, starting with the 6"-diameter main line. A 5" branch, shown in the photo above, serves the floor sweep, and has two additional 4" branches that serve the tablesaw and spindle- and belt/disc sanders. At another point on the main, a 5" branch feeds in from the planer (with a 4" offshoot to the jointer). All other branch lines are 4" diameter.
John connected all of his machines to the ductwork using flexible hoses. Even machines he doesn’t move around, such as the thickness planer and jointer, connect this way to simplify hookups and prevent machine vibration from rattling the ductwork. In most cases, the flexible hoses are less than 3' long.
John’s bandsaw represents one exception to this rule. It’s connected to the 4" branch line with approximately 8' of 2"-diameter flexible hose, as shown in the photo below. This small hose fits the bandsaw’s stock, under-table port.
Our expert says: The long, small-diameter hose greatly reduces the cfm of airflow at the bandsaw, yielding marginal dust pickup. Always run the largest appropriate hose as far as possible, then reduce it to a smaller port size only at the end. Better yet, modify the machine, if you can, to accept a larger port.
John’s system serves him well, removing chips effectively, even if lacking in efficiency. There’s room for improvement, as we pointed out. But this case proves that, if you understand the basics, you can control workshop dust. Now, let’s check out some rules for setting up a dust-collection system in your shop.
System Setup: What you need to know
To design your own system, you’ll have to consider many factors, such as what machines you’ll connect, where to place them, what size dust collector to buy, and what type and size duct system you’ll need. Thankfully, you can build a great system following a few rules of thumb:
Note: The following rules may yield a system with more power than you actually need, but too much power is better than too little. Plus, an oversized system can handle future expansion.
Step 1. Find airflow needs
Start the process by determining how much air your tools need. Find the airflow requirements of each machine you’ll connect to the system, and the corresponding duct size necessary using Chart 1, below.
Step 2. Lay out the ducts
Now lay out your duct system on paper, keeping the following in mind:
• Position the air-hungry machines closest to the collector.
• The largest duct diameter required from Chart 1 determines the minimum size of your system’s main duct. (The collector you choose in step three will influence this as well.)
• Whenever possible, build branches that serve more than one machine.
• Make duct runs as short as possible, minimizing the number of bends.
Plan the shortest, straightest runs you can because every bend and foot of duct adds air resistance, known as static pressure loss, shown in Chart 2, below.
After you’ve laid out a tentative duct system, determine the static pressure loss for each branch using the chart. Be sure to include the equivalent footage for 45° wyes and 90° elbows. For each branch you also need to include whatever amount of the main duct exists between that branch and the collector.
Note: Each foot of flexible hose equals 3' of rigid duct, so include these runs in the total. Also, port designs vary, so it’s tough to calculate their static-pressure loss. To be safe, add 1.5" for each port on the branch.
As an example let’s say you have a 6" straight main duct. At 14' from the collector, a 45° wye branches into a 4" line to the tablesaw. That branch is 12' long with two 90° bends, and connects to the saw with 3' of flexible hose. Here’s the static pressure loss for that branch:
The branch with the greatest total static pressure loss is the one that determines what your dust collector will have to overcome. If you ever run your system with two blast gates open at the same time, add both totals to get your static pressure loss.
Step 3. Choose a dust collector
Now you can buy a collector. Each should be rated by horsepower, cfm, and a maximum static pressure. Eliminate any collector with fewer than 1.5 hp. Smaller, portable machines generally lack the power needed for a built-in system.
The cfm rating will be shown prominently, but the static pressure rating is more important. The number must be higher than the highest loss in your system, calculated in Step 2, to prevent chips and dust from settling in the ducts.
You’ll also need to know the highest airflow value (determined in Step 1) to find the minimum cfm rating you should purchase. Don’t be surprised if the dust collector that meets your static-pressure needs is rated at about double the cfm any of your machines requires. Manufacturers often rate cfm with no ducts attached, so their ratings are higher than you’ll get in real-world use. (To learn more, see our dust collector review from issue 140.)
Your dust collector also needs to accommodate the largest diameter duct in your system. In fact, a good rule of thumb is to make your main duct the maximum size your dust collector can accept.
Options for ductwork and fittings
You’ve sized your collector and planned the duct layout, now you need to choose what ducts and fittings to use. You have a lot of options. See “Ductwork and fittings selector” below.
Even with the process simplified, setting up a dust-collection system takes planning. If you prefer to have someone else do the calculations described here, the companies below can help. Oneida Air Systems, for example, will design your system, applicable toward the purchase of a cyclone or ductwork.
Once you’ve made all the decisions and bought your components, temporarily connect the ducts and fittings, and then check how well everything works. When the system performs to your satisfaction, screw, glue, or rivet the components together; seal the seams with tape or caulk; and start making sawdust. You won’t have to clean it up.
These companies provide information and products for setting up a dust-collection system in your shop:
Air Handling Systems, Inc.
Ductwork/hose, fittings, accessories, design assistance 800/367-3828
American Fabric Filter Co.
High-efficiency filter bags 800/367-3591
Grizzly Industrial, Inc.
Dust collectors, ductwork/hose, fittings, accessories, filter bags, design information 800/523-4777
Oneida Air Systems, Inc.
Cyclone systems, ductwork/hose, fittings, accessories, filter bags, design assistance 800/732-4065
Penn State Industries, Inc.
Cyclone systems, dust collectors, ductwork/hose, fittings, accessories, filter bags, design information 800/377-7297
Ductwork and Fittings Selector
• Designed specifically for dust collection, and therefore the most efficient.
• Available only through specialty suppliers, such as industrial supply catalogs and online retailers. See the sources at the end of the article.
• Costlier than HVAC-style.
• Used in professional shops and ruggedly built.
• Fittings are designed to maximize airflow and material movement in system.
• The spiral style is very rigid and has a smooth seam to minimize resistance.
• May be available in a wider range of diameters.
• Fittings generally work with metal, pvc, or plastic pipe.
• Flexible metal duct can make gentle bends around obstructions.
• Designed to move air only, not solid materials, such as dust and chips, so less efficient overall than the industrial components above.
• Readily available at any home center in 24- or 26-gauge steel.
• Priced economically.
• Easy to assemble and install using screws or rivets.
• No wye fittings available, just tee-style. Choose flared tees over straight tees.
• No long-radius elbows available, short-radius only.
• Fittings generally work with metal, pvc, or plastic pipe.
• Designed to move liquids, but capable of carrying air, dust, and chips.
• Readily available in any home center or hardware store.
• Economical in 4" sizes.
Note: Use "Schedule-35" type (drain, waste, vent), not "Schedule-40."
• Diameters larger than 4" may be difficult to find and costlier.
• Easy to cut, assemble, and install using special adhesive, screws, or rivets.
• We recommend grounding to prevent static buildup in system.
• Long-radius elbows and wye fittings are available, but only fit pvc pipe.
• PVC is quieter than metal.
• Designed for dust collection at lower cost less than industrial metal.
• Only available through ductwork suppliers and woodworking retailers.
• Flexible hose available in black or clear.
• Plain flexible hose is economical, type with spiral wire costs more.
• Flexible plastic hoses join rigid ducts to machines and fit around obstacles.
• Flexible hose is well-suited to temporary use and for runs that get disconnected when not in use (such as an across-the-floor run to a tablesaw).
• Spiral-wire hose provides crush-resistance and simplifies system grounding.
• Static pressure loss of flexible hose is approximately 3 times higher than rigid pipe, so it is not well suited for building an entire system.
• Clear-plastic rigid ductwork allows views of blockages in ducts. Usually smaller in diameter, this style requires pvc “sleeves” to connect with fittings.
• Absolutely necessary for controlling airflow in any dust-collection system serving multiple machines.
• Available through ductwork and woodworking retailers in plastic or cast aluminum styles.
• Moderately priced.
• Blast gates allow you to close off airflow at individual machines or branches to maintain optimum airflow to the machines being used.
• Half gate can be inserted at any point in duct by cutting a narrow slit.
• Blast gates generally fit inside-diameter of any pipe or hose above, though they may require gaskets to achieve a tight seal in non-matching applications.