Short answer: keep the dust foot, and judge your vacuum by the airflow it holds at the tool rather than the motor label. Capture happens at the cutter, where a collector-class extraction point does the work; a machine enclosure only catches what the foot misses. On a 120 V outlet, a vacuum sold as 5 hp holds roughly 95 CFM [160 m³/h] at working suction — enough for chips under a snug skirt, short of deep cuts. Work through the checks below in order and you will know which fix your shop actually needs.
What the dust pattern tells you
Read the machine straight after a ten-minute cut, before you change anything. Each pattern points at one cause:
- Chips spraying off one side of the cutter point to a skirt gap or a shroud lifted off its seat. Close the brush to about 1/4 in [6 mm] off the surface and reseat the shroud.
- A grey film on the table an hour after the cut points at fine dust: it is either passing the filter or escaping capture, and those need different fixes.
- Strong suction against your palm at the hose end but weak pickup at the foot points to restriction or a leak between canister and cutter — packed chips, a loose lid gasket, an open drain cap.
- Capture that fades over a fifteen-minute job points to a loading filter or a canister past half full.
- A cloud hanging in the cut on deep or fast passes points to a volume shortfall at the tool, the class mismatch worked out below.
Five patterns, five causes. On a desktop router the volume shortfall is the most common, so start there.
The causes, most likely first
- The vacuum is a pressure machine doing a volume job. A shop vacuum develops 50 to 90 in of water [12–22 kPa] of suction and pushes its air through a 2 in [50 mm] hose at around 100 CFM [170 m³/h]. Chip capture at a foot wants the two-stage collector class, about 350 CFM [595 m³/h] at the cutter as a floor. Nothing downstream fixes that mismatch.
- The path leaks or restricts. Ten feet of 2 in hose, two sharp bends and a half-full canister eat the flow the foot does get.
- The filter passes fines. A standard cartridge returns the 1–5 µm fraction to the room, which reads as dust everywhere even with perfect pickup at the cutter.
- The spindle shroud is off. Its job is to close the volume around the cutter; with it removed the same airflow sweeps roughly twice the area and capture velocity halves.
- No machine enclosure. Last on the list, because it only matters once the four above are fixed.
How to check each cause
Isolate the machine first, so the spindle cannot start while your hands are in the work envelope. Then work down the checks:
- Measure velocity at the foot inlet with a hot-wire anemometer. A 2 in hose has an area of 3.14 in² [0.0218 ft²], so 4,000 fpm [20 m/s] measured there is 4,000 × 0.0218 = 87 CFM [148 m³/h]. That number against the target settles whether you have a class problem.
- Repeat at the vacuum's inlet. An inlet at 4,000 fpm with the foot at 1,500 fpm [7.6 m/s] means more than half your flow is lost in between: seat the lid gasket, close the drain cap, clear packed chips, shorten the hose.
- Flashlight-test the filter. Run the vacuum alone for five minutes in a dark shop with a beam across the exhaust 6 in [150 mm] away. A visible plume means fines are passing the filter or the canister seals.
- Check the skirt and shroud fit. The brush should ride within 1/4 in of the surface, and the shroud should seat without distortion. If it fights you on and off, check its orientation and burrs on the seating faces before trimming anything.
- Lay a dust survey. Black card beside the gantry, ten-minute cut, look at 30 minutes and again next morning. Particles under 10 µm settle slowly, so the morning film is the honest one.
The same velocity-times-area arithmetic is what you would use to check a replacement enclosure fan's airflow; an anemometer earns its keep twice in one shop.
Checking the 5 hp vacuum against the target
The inputs:
- The outlet: 120 V, 15 A branch circuit, what a desktop machine plugs into.
- The label: 5 hp, a developed peak rather than a continuous rating.
- The constants: 1 hp = 746 W, and standard fan arithmetic, air horsepower = CFM × inches of water ÷ 6,356.
- The collector-class target: 400 CFM [680 m³/h] at the cutter.
- The vacuum's working point: about 80 in of water [20 kPa] at suction.
The arithmetic:
- 5 hp × 746 W/hp = 3,730 W; 3,730 W ÷ 120 V = 31 A. A true continuous 5 hp draws about double what the 15 A outlet supplies, so the label cannot be continuous power.
- The outlet's real ceiling: 120 V × 15 A = 1,800 W ÷ 746 W/hp = 2.4 hp of input.
- Allow a generous 50 % for motor and fan losses: 2.4 × 0.5 = 1.2 hp of air power.
- Flow that supports at working suction: 1.2 hp × 6,356 ÷ 80 = 95 CFM [160 m³/h].
- The collector class spends less at the target: 400 CFM × 4 in of water ÷ 6,356 = 0.25 hp.
Result: your vacuum has roughly five times the air power and a quarter of the flow, because it is built to drag a small volume through a 2 in hose and a fine filter. The collector moves its volume through a 4 in [100 mm] duct at about 4,600 fpm [23 m/s], inside the 3,500–4,500 fpm [18–23 m/s] the ACGIH Industrial Ventilation transport-velocity tables set for holding wood shavings in suspension. Pressure and flow trade along the machine's curve — pressure alone is not a complete answer for gas flow — and the foot lives on the flow end of it.
Decision: at 150 CFM at the tool or below, keep the skirt at 1/4 in and take lighter passes. Full-depth cuts in solid wood need the collector class. An enclosure makes up none of the missing volume; it catches the tail.
The fix, by what you measured
| What you found | The fix |
|---|---|
| 87–150 CFM at the foot, dust escapes on deep cuts | Move to a two-stage collector with 4 in duct; keep the foot |
| Foot reads about half the inlet reading | Seat the lid gasket, close the drain cap, clear packed chips, shorten the hose |
| Plume at the exhaust in the flashlight test | Fit a HEPA cartridge (99.97 % at 0.3 µm) or duct the discharge outdoors |
| Chips escape one side only | Close the skirt to 1/4 in and reseat the shroud; both cost nothing but time |
| Grey film persists with capture fixed | Add containment, next section |
When a full enclosure earns its floor space
Build one when the morning film still appears after capture is fixed. That film is fines the filter returned or the foot missed on the far side of the cut, and containment catches them. Size the port for turnover: a bay of 36 × 30 × 24 in [915 × 760 × 610 mm] around a desktop machine holds about 15 ft³ [425 L], and at the collector-class flow it changes its air 27 times a minute, about 1,600 times an hour. That holds the box slightly negative, so every gap is an inlet rather than an outlet — the opposite of the positive-pressure scheme used for clean-room cabinets, so be clear which one your machine's spec means.
For the build itself, CNC dust containment enclosure design covers full-machine housings, and small CNC dust enclosure design for chip control covers desktop-scale panels, ports and viewing windows. An enclosure with no extraction of its own just becomes the dustiest shelf in the shop.
Keeping the control cabinet out of the dust
The film that settles on your table also settles on the controller. House the electronics in a Type 12 cabinet — dust, dirt and dripping liquids — and check the door seal with a paper strip: if it slides out with the door latched, replace the gasket. Ratings here are manufacturer ratings; ours are built to the type and are not UL listed. The NEMA enclosure types guide gives the full ladder, and a dust-resistant switch enclosure for a wood shop covers door and gland choices for exactly this air.
If the box needs a size and cutouts the catalog does not carry, custom enclosures are built to your drawing and delivered in 10 business days, counted from your approval of the drawing, and the enclosure selector narrows the choice first. One thermal note if a drive moves into that sealed box: drives carry a 40 °C [104 °F] ambient rating, and a stainless wall sheds only about 3.7 W per m² per kelvin, so size the enclosure for the heat at the same time.
Stopping it coming back
- Baseline the foot velocity the day the system works — say 4,000 fpm — and clean the filter when it falls 20 %, to 3,200 fpm [16 m/s].
- Put a drop-out separator between foot and vacuum. Two-stage separation keeps chips out of the filter, so the flow holds all day.
- Sweep to a standard: NFPA 654 flags a wood-dust layer 1/32 in [0.8 mm] deep over 5 % of a room's floor as the housekeeping limit for combustible dust.
- Remember why the fines matter: OSHA's fallback limit for particles not otherwise regulated is 5 mg/m³ of respirable dust over an eight-hour shift, and that fraction is exactly what a bypassing filter returns.
Enclosures for this job
Catalog sizes that suit the job this article answers, picked from its subject; open one for its full specifications.
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 12 × 10 × 6 in | 304 stainless | 12 x 10 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 20 × 16 × 8 in | 304 stainless | 20 x 16 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 24 × 20 × 8 in | 304 stainless | 24 x 20 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Is a 5 hp shop vacuum enough for dust collection on a desktop CNC?
Judge it by airflow, not the label. On a 120 V, 15 A outlet the continuous input tops out near 2.4 hp, so 5 hp is a developed peak; the same machine holds roughly 95 CFM at 80 in of water. That captures chips with the skirt within 1/4 in of the surface; full-depth cuts in solid wood need the two-stage collector class.
How do I tell whether the dust foot is capturing before building an enclosure?
Run a ten-minute cut, then lay black card beside the gantry and check it at 30 minutes and again next morning. Particles under 10 microns settle slowly, so a fresh grey film by morning tells you fine dust is passing the filter or the capture zone. No film within 12 in [300 mm] of the cutter means the foot is doing the job.
Can I run the machine without the spindle shroud if it is hard to install?
Refit it and fix the seating instead. The shroud closes the volume your airflow has to sweep; removing it roughly doubles that open area and cuts capture velocity about in half. Check orientation and burrs on the seating faces before trimming anything, and keep whatever guard function it provides.
What stops the fine dust a shop vacuum returns to the room?
A HEPA cartridge, defined as 99.97 percent capture at 0.3 microns, plus latched canister seals. A standard filter passes the 1 to 5 micron fraction that stays airborne for hours, which is the film you find in the morning. Alternatively, duct the discharge outdoors through a 4 in wall port.
