By Martin Harris.

Overarm Dust Collection for Table Saws

Overarm dust collection puts a pickup right over the table saw blade, usually built into a blade guard that hangs from an arm or boom, with its own hose to the collector. It catches the fine dust the top of the blade throws up toward you, which the cabinet port under the table cannot reach. Run it together with the cabinet port, and split your airflow between the two with gates or a wye.

My main table saw dust collection guide covers the cabinet side and overall CFM targets. This page goes deeper on the part above the table: why it matters, the commercial and shop built options, hose sizes, and how to balance the two pickups.

Why the cabinet port misses the fine dust

On a table saw, the top of the blade spins toward you. The teeth at the front come down into the wood, pass under the table, and come back up out of the kerf at the back of the blade. Most chips fall into the cabinet, where the port can pull them away. Some dust stays with the teeth as they come up through the table, and the blade flings it forward over the top toward the person feeding the board.

That stream above the table is mostly fine dust. Bill Pentz, who has written about fine dust capture for many years, points out that particles you can see settle fairly fast, while the fine particles under 10 microns stay in the air. A cabinet can look clean after a cut while a cloud of fine dust has already left the saw. I cover the health side in is sawdust dangerous.

Suction also falls off quickly with distance. Pentz calculates that even a 6 inch duct moving 785 CFM only holds the 50 FPM needed to pull in fine dust out to about 13.42 inches from the opening. The cabinet port sits well below the table, far from the top of the blade. A pickup inches above the blade is in the right place.

Commercial blade guard collection options

Overhead collection comes in three general forms. Many modern saws ship with a blade guard that has a small dust port. Aftermarket guards bolt to the saw's splitter or riving knife and offer bigger ports. Full overarm systems hang the guard from a separate arm so nothing sits behind the blade.

• Stock guard with a small port. Some stock blade guards come with a small dust port sized for a shop vac hose. A port that small will not carry much air from a dust collector.
• Floating overarm guard. The SawStop Floating Overarm Dust Collection Guard (TSG-FDC) fits SawStop's ICS, PCS, and CNS saws. Its published specs list a 4 inch outer dust tube, a 3 inch inner tube, a guard 3-1/2 by 18-1/2 inches, and a minimum of 400 CFM. The support legs attach under the extension table, so the arm reaches over from the side.
• Splitter mounted aftermarket guards. Shark Guard, which makes guards for many older and contractor saws, offers 2-1/2, 3, and 4 inch dust ports. Its port size page says the 2-1/2 inch port suits a shop vac and can work with a dust collector of at least 1.5 HP through a 4 to 2-1/2 inch reducer, though that is not ideal. It calls the 4 inch port the one designed for dust collectors and says it likely gives the best overall collection.
• Boom mounted hoods. The PSI Woodworking TSGUARD hangs a clear dust hood from a boom that its listing says extends up to 83 inches, can mount to the ceiling, swings out of the way, and connects to standard 4 inch hose.

A safety point on all of these. A dust hood and a blade guard are different things. A guard is built to keep your hands away from the blade. A hood is built to catch dust. Before you take off your saw's stock guard to fit an overhead unit, confirm the maker sells the new unit as a blade guard for your saw. If it is only a hood, keep the stock guard on or use a proper guard with it. Keep the riving knife in place either way.

Building a DIY overarm boom

A shop built boom is a reasonable project if you already have a proper guard, or you want to add a collection hood above a guard. The idea is to hang a clear hood over the blade from an arm mounted to the ceiling, a wall, or a post beside the outfeed table, then run hose along the arm.

1. Pick the mounting point. A ceiling joist directly above the blade gives the cleanest arm. A post beside the saw works if the ceiling is too high or finished.
2. Build or buy the arm. The arm must hold the hood steady without drooping. Use a stiff material, and support it at the mounting end with a solid bracket into framing.
3. Make the hood. A narrow clear box, open on the bottom, sized to cover the blade and a few inches in front and behind, is enough. Put the hose port on top or at the back.
4. Add height adjustment. The hood should sit just above the workpiece. A sliding post with a lock knob lets you set it for each board thickness.
5. Make it swing away. Some cuts need the space above the table clear. A pivot at the arm lets you move the hood aside instead of taking it down.
6. Secure against drops. Add a stop so the hood cannot fall onto a spinning blade if a lock knob slips.
7. Check clearance with the saw unplugged. Raise the blade to full height and tilt it to full bevel. The hood must never touch the blade in any position.

Route the hose along the arm with gentle bends, and support it so it does not pull the hood down. Rigid pipe along the ceiling with a short flex drop to the hood loses less airflow than one long flex hose from the floor.

Hose sizing for the top pickup

Duct size decides how much air a hose can carry while keeping the dust moving. Air speed in feet per minute equals CFM divided by the area of the pipe in square feet. Using that formula and a 4,000 FPM target, here is how much airflow each size carries:

Source: 4, 5, and 6 inch figures from Bill Pentz's dust collection basics page. The 2-1/2 and 3 inch rows are calculated with the same CFM equals FPM times area formula.

Keep the flex part of the top hose short. Oneida's static pressure data puts 1 foot of 4 inch flex hose at about 0.280 in. w.c. (inches of water column, a measure of resistance) at roughly 4,000 FPM, nearly the same as 5 feet of rigid 4 inch duct at 0.285. An overarm hose that snakes 10 feet across the floor costs a lot of airflow. My best dust collection hose guide covers smooth wall options for the flex you do need.

Splitting airflow between the top and the cabinet

Two open pickups share one collector's air. Look at the table above: two 4 inch hoses open together have a combined area of about 0.175 square feet. To keep both near 4,000 FPM, the collector has to deliver about 700 CFM at the saw. Many 1 to 2 HP collectors cannot do that through a real duct run, so plan the split around what you have.

• Collector on the cabinet, shop vac on the guard. This is the simplest split for a small shop. The shop vac's high suction suits a small guard port, and the collector keeps all its airflow for the cabinet. You do need both machines running during a cut.
• One branch, a wye, and two hoses. Run a 5 or 6 inch branch to the saw, then split with a wye into a 4 inch cabinet hose and a smaller guard hose. A smaller top hose takes a smaller share of the air.
• Two gates on one saw. Put a blast gate on each pickup. Open both for cuts that throw a lot of dust above the table, like ripping, and close the top gate for cuts where the guard is swung away. See my guide on how to install blast gates for placement.
• Throttle the top. Shark Guard notes that a 4 inch guard port can pull hard enough to pick up small offcuts, and suggests a blast gate to regulate it. Partly closing the top gate sends more air to the cabinet.

To balance the two, start with both gates fully open and make a few rip cuts. If dust spills out the bottom of the cabinet or piles up inside, close the top gate a little. If dust sprays forward off the blade, open the top more or move the hood lower. A strong light shining across the table from the side makes the fine dust easy to see. My 4 inch vs 6 inch dust collection comparison helps if you are deciding what branch size to run to the saw, and my complete guide to small shop dust collection covers sizing the collector for it.

Seal the cabinet first

When you add a top pickup, the cabinet gets less air. That makes cabinet leaks matter more. Close up large openings like the gap around the tilt mechanism or an open motor cover, while leaving the motor its cooling air as the saw's manual requires. A zero clearance throat plate also helps, since it leaves less room around the blade for dust to blow up through the table. The better the cabinet holds suction, the less air it needs, and the more you can send to the top.

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