Ducting and Blast Gates for Shop Dust Collection: Pipe Sizing, Static Pressure, and Multi-Machine Runs

A dust collector's rated CFM is measured at the collector itself, not at the far end of a shop full of ducting and machine ports — and it's entirely possible to own a genuinely capable collector and still get weak suction at your CNC router or table saw because the ducting between them is undersized, has too many restrictive fittings, or is trying to serve multiple machines through gates that don't seal properly. This guide covers actually designing a duct run: pipe sizing, static pressure losses, and blast gate placement for a shop running more than one dust-producing machine off a single collector.

Why Duct Sizing Matters More Than Collector Size

Airflow through ducting faces resistance (static pressure loss) from pipe length, every elbow and fitting, and any reduction in diameter — and that resistance compounds fast. A collector rated for strong CFM at zero static pressure can lose a large fraction of its real-world performance to a long, narrow, elbow-heavy duct run, which is why two shops with identical collectors can have very different actual performance at the tool. Oversizing main duct trunk lines relative to your collector's actual capability doesn't help either — air velocity has to stay high enough (generally cited around 3,500-4,000 feet per minute for wood dust) to keep dust and chips suspended in the airstream rather than settling out and clogging the duct.

Sizing the Main Trunk and Branches

Duct DiameterTypical UseNotes 4 inchSingle small tool branch (router, small sander)Common branch size for lower-CFM tools; don't run as a shared trunk for multiple machines 5-6 inchMain trunk line feeding 2-3 machine branches, or a single high-CFM machine like a CNC router or table sawThe practical sweet spot for most single-collector home/small shops 7 inch+Larger multi-machine trunk lines, cyclone-based systemsOnly worth it if your collector's rated CFM actually supports the larger diameter at usable velocity

As a rule, keep branch duct diameter equal to or smaller than the trunk line it feeds from, never larger — a branch wider than the trunk it draws from can't be adequately served no matter how good the trunk sizing is.

Minimizing Static Pressure Loss

Every 90° elbow costs meaningfully more static pressure than a shallower-angle fitting covering the same direction change — two 45° elbows in sequence typically lose less pressure than one 90° elbow, even though the total direction change is the same. Keep duct runs as short and as straight as your shop layout allows, and avoid flexible hose for anything beyond the last few feet connecting to a mobile or vibrating tool — corrugated flex hose has dramatically higher static pressure loss per foot than smooth rigid or semi-rigid pipe, and a shop with long flex-hose runs is very often the same shop complaining about weak suction at the far machine.

Blast Gates

A blast gate is a manual (or automated) shutoff at each machine's branch line, kept closed except at the machine currently in use — this concentrates all of the collector's airflow at whichever single branch is open, rather than the collector's suction being divided (and weakened) across every branch simultaneously. A shop running multiple machines off one collector without blast gates is one of the most common causes of "my dust collector isn't strong enough" complaints, when the actual problem is airflow being split across open branches that aren't even in use. Metal or well-sealed plastic blast gates outperform cheap gates that don't seal fully closed, since even a small gap at a closed gate bleeds off real airflow from the branch that's actually working.

Automated Blast Gates

For a shop with more than two or three machines, automated blast gates (solenoid or motor-actuated, triggered by a current sensor on each tool's power circuit) remove the need to manually open and close gates every time you switch tools, and ensure a gate never gets left open by mistake on a branch not in use. This is a meaningful quality-of-life upgrade once a shop grows past a couple of machines, though it's an added layer of complexity and cost that's not necessary for a one- or two-machine setup where manually managing two gates is trivial.

Grounding and Static

Plastic ducting can build up static charge from dust and chips moving through it at velocity, and in dry conditions this can produce a genuinely startling (and in rare cases with fine combustible dust, hazardous) static discharge. Running a grounding wire through or along plastic ducting, bonded to a real earth ground, is a cheap and standard mitigation — metal ducting is inherently conductive and just needs to be bonded and grounded at one point in the run.

Safety

Fine dust from wood (especially MDF) and certain other materials is a genuine respiratory hazard independent of ducting design; proper duct sizing improves collection efficiency but doesn't replace the need for adequate filtration at the collector itself (see the site's dust collection setup guide for filter tier selection) or a respirator for operations that still generate airborne fines despite good collection.

Good ducting design is the difference between a dust collector that performs on paper and one that actually keeps a multi-machine shop clean at the point of cut. Size the trunk to your collector's real CFM, keep runs short and gentle on turns, and add blast gates the moment a second machine shares the system — it's the single highest-leverage change most shops can make without buying a bigger collector at all.

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