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Dust collection is easiest to size before you buy a collector or run ductwork. A table saw and a planer can both make a large mess, but their airflow needs depend on the tool’s ports, the duct route, and whether both machines will run at once. Use the figures below as a planning method, then check your tool manuals: a machine’s published airflow requirement takes priority over a rule of thumb.
Start with the machine, not the collector’s headline number
Find the dust port diameter and any recommended airflow in the saw or planer manual. If the manual gives a required flow, use that as your target at the machine. Collector ratings are often stated as free-air airflow—the best-case figure with little or no duct attached. Bends, long runs, small hoses, filters, and a full collection bag all reduce delivered airflow.
If no airflow figure is provided, use these practical planning ranges: about 350–450 cubic feet per minute (CFM) for a table saw with a 4-inch port, and about 400–600 CFM for a small or medium planer with a 4-inch port. A planer with a 5-inch port may need roughly 600–800 CFM. These are working estimates, not guarantees; chip ejection and hood design make a difference.
Estimate airflow from duct size
Air needs enough speed to carry chips through horizontal ductwork. A common target for wood chips is around 3,500–4,000 feet per minute (FPM) in branch duct. Multiply the duct’s cross-sectional area by air speed to estimate the needed CFM:
CFM = duct area in square feet × air speed in feet per minute. For a round duct, area is about 0.00545 × diameter in inches squared. At 3,500 FPM, a 4-inch duct has an approximate target of 305 CFM; a 5-inch duct, about 477 CFM; and a 6-inch duct, about 687 CFM. Actual systems lose pressure along the way, so the collector must deliver the target airflow at the tool, not merely at its inlet.
These figures help catch obvious mismatches. A collector intended for 600 CFM cannot provide that flow through a long, restrictive 4-inch hose just because the inlet is 6 inches wide. Likewise, a large duct may carry chips well but still need a collector with enough airflow and static-pressure capability to overcome the system’s resistance.
Compare the two machines
| Machine and connection | Planning airflow | Typical concern |
|---|---|---|
| Table saw, 4-inch port | 350–450 CFM | Dust escaping above the blade if only the cabinet port is connected |
| Planer, 4-inch port | 400–600 CFM | Chips piling up in the hood or clogging a small hose |
| Planer, 5-inch port | 600–800 CFM | Collector or duct too small for the larger outlet |
Planers often produce a sudden, heavy stream of chips. A collector that seems adequate for light table-saw trimming may bog down when feeding a wide board. A saw, meanwhile, can throw fine dust above the table even when its lower cabinet is well connected. An overhead blade guard with a dust port can capture more of that dust, but it adds another branch and may reduce flow if both ports run at once.
Choose a collector and duct layout
For one machine at a time, a small shop may do well with a portable collector rated around 600–1,000 CFM in free air, provided its performance curve and duct setup support the required flow at the tool. A portable woodworking dust collector is often the lower-cost choice for short runs and one or two machines. Check the manual’s airflow or performance curve rather than treating the largest number on the box as delivered CFM.
For a longer fixed duct system, several machines, or a planer with a 5-inch port, compare larger collectors with published performance curves. A dust collector with a published performance curve makes it easier to judge airflow at the resistance your system will impose. Do not assume that a bigger motor alone means better collection; fan design, filter condition, and duct layout matter too.
Use smooth metal duct for fixed runs where practical, and keep the run short, with few bends. Flexible hose is useful at the machine, but long corrugated sections add resistance and can trap chips. Avoid reducing a 5-inch planer outlet to 4 inches immediately unless the tool maker allows it and your collector can still maintain adequate flow.
Decide whether to run both tools at once
If you use the saw and planer separately, size the system for the more demanding tool and close the unused branch with a blast gate. If both may operate at once, add their airflow targets: a 400-CFM saw and a 600-CFM planer imply about 1,000 CFM at the machines before accounting for duct losses. That usually calls for a larger system than either machine alone.
Blast gates only help when they seal reasonably well and are positioned where they are easy to reach. A gate left partly open wastes airflow. If the system serves multiple branches, use a dust-collection blast gate at each branch and open only the machine in use. Avoid relying on a narrow Y-fitting or a series of sharp elbows to split the flow.
Test for common failures
Run the planer with a typical cut and watch the chip stream. Chips spilling from the hood, backing up in the hose, or lingering inside the machine point to poor capture or a blockage. At the table saw, inspect both the cabinet and the area above the blade. A clean cabinet does not prove that airborne dust is controlled.
Check for a clogged filter, a full bag, a crushed hose, leaks at joints, and a gate that is not fully open. Each can reduce airflow enough to turn a borderline setup into a poor one. Fine dust that escapes the collector is also a health hazard; use an appropriate filter and wear a well-fitting respirator when conditions call for it. A dust collector is not a substitute for safe cleanup: do not use compressed air to blow settled dust around the shop.
When choosing between a cheaper portable collector and a larger fixed system, match the purchase to the actual duty. For short duct runs and one machine at a time, the cheaper option can be entirely adequate. Pay more when you need the airflow for a larger port, long ductwork, simultaneous use, or reliable chip capture during heavy planer cuts.