Black & Decker 3 in. x 21 in. Belt Sander

I brought this sander into my shop for a run of weekend projects—truing up outdoor furniture parts, cleaning up rough deck boards, and fitting a few tight interior trim patches. It’s a compact 3 x 21 belt machine with a 7-amp brushed motor, a low profile, and a nose that slips close to adjoining edges. After several weeks of mixed use on pine, cedar, and some stubborn maple, here’s how it behaved.

First impressions and setup

Out of the box, the sander feels light for its size at about 8.3 pounds, with a shape that naturally wants to ride flat. The three-position handle adjusts quickly and makes a real difference in stance—palm-down for horizontal work, angled for vertical surfaces, and tucked when squeezing into tight spots. The included medium-grit belt is a reasonable starting point for general cleanup, though I immediately grabbed an 80-grit belt for faster material removal and a 120-grit for finishing passes.

Belt tracking required some attention at first. Like most compact belt sanders, the tracking knob is sensitive; a quarter-turn is a big adjustment. I let the machine run on a scrap board for a minute and made micro-adjustments until the belt stayed centered at speed. It held well after that, though I continued to check it before each session.

Design and ergonomics

The best part of this design is its low, flush profile and angled front. It lets you get the platen close to a vertical surface—face frames, deck posts, door jambs—without the housing in the way. There’s also a retractable hood that exposes the top of the belt. That sounds like a gimmick, but it’s genuinely useful for nibbling into corners or working the underside of an overhang where the nose alone can’t reach.

I like the compact body for one-handed steadying while the other hand guides the handle. Balance is decent; it doesn’t feel nose-heavy unless you’re using the very tip aggressively. Vibration is present but not fatiguing for short to medium sessions. Noise is typical belt-sander loud—hearing protection is smart.

Power and material removal

At 7 amps, this is a mid-powered, single-speed machine. On softwoods and construction lumber, it removes stock quickly with an 80-grit belt and keeps pace without bogging down. On hardwoods like maple or oak, it’s still capable, but you’ll need to let the machine do the work. If you lean hard, the motor will respond with more heat than speed, and you’ll glaze belts faster than you make progress.

The sweet spot is steady, even pressure with a slow, overlapping pass. On edge-glued panels, I used diagonal passes to flatten glue lines before switching to finer grits. For painted doors and deck boards, it stripped finishes efficiently with a coarse belt, though the final surface still benefited from a follow-up with a random-orbit sander.

There’s no variable speed, which limits finesse on delicate veneers or thin edge banding. It’s manageable—start with a higher grit and keep it moving—but if you spend a lot of time on fine furniture parts, a variable-speed unit is nicer to live with.

Getting into tight spots

The angled nose is the feature that earns its keep. I used it to flush-sand deck fascia to mitered corners and blend proud rails to stile faces. The retractable hood is a smart addition; pulling it back exposes the top run of the belt, which let me clean up the underside of a countertop overhang and sand inboard of a corner without going at it with a file.

Because the front roller is small, it concentrates pressure at the nose. That’s great for control, but it also means you can overdo it and dig divots if you stay in one place. Light touch, short strokes, and frequent checks against a straightedge are the move.

Belt tracking, changes, and technique

Tracking stability is decent once set, but it likes periodic tweaks. My setup routine that worked best:
- Clamp a scrap board, run the sander at full speed, and adjust tracking in tiny increments.
- Let it run for 10–15 seconds between adjustments; the belt often recenters slightly as it warms.
- Re-check after changing grits or if you shift pressure between the nose and the body mid-pass.

Belt changes are straightforward, and releasing tension makes it easy to swap grits mid-task. I had the best surface results with 80 → 120 → 150 grit progression, then switching to a random orbit sander at 180/220 to remove cross-grain scratches.

One caution on tension: overtightening the belt to “lock in” tracking can do more harm than good. It increases stress on the rollers and bearings and doesn’t really solve drift that comes from uneven pressure. Keep tension at the recommended level and correct with the tracking knob instead.

Dust collection and cleanup

The onboard bag captures a fair amount of coarse dust, but like most small bags on belt sanders, it struggles with fine sanding dust and clogs if you push too hard. Empties are frequent on larger jobs. I had better luck connecting a shop vac using a universal hose adapter; with extraction, the surface stayed cleaner and belts lasted longer.

Plan on wearing a dust mask regardless. If you’re working indoors on anything other than a quick touch-up, hook up to a vac or set up a fan to move air away from your face.

Heat, durability, and build quality

Under normal, steady use on softwood and moderate hardwood tasks, heat buildup stayed reasonable. During prolonged sessions on dense maple with 80-grit and firm pressure, the housing around the roller area did get notably warm, and I caught a faint hot-plastic smell once. Backing off pressure and giving the tool a brief rest solved it. This is a reminder that this is not a heavy-duty, all-day flooring sander. It’s a compact, budget-friendly machine best used with a light hand.

The housing is plastic, which helps keep weight down and makes the tool easier to maneuver vertically, but it also means it lacks the thermal mass and rigidity of magnesium or cast housings found on pro-grade sanders. If your work involves regular, aggressive stock removal on hardwoods, that’s where a heavier-duty tool with a more robust build will pay off over time.

On the positive side, the flush design and moving parts felt tight and consistent after a few weeks. The belt stayed aligned with routine checks, and the handle adjustment remained solid with no play.

Where it fits in the shop

This sander shines as a homeowner and DIY workhorse: smoothing deck boards, cleaning up shop-made cabinets, tuning exterior doors, knocking down glue lines, and blending joints where a plane can’t reach. It’s light enough to use vertically without fighting it, and compact enough to sneak into places larger sanders can’t.

If you’re a pro doing stair treads, countertops, or slab-leveling day in and day out, you’ll want more power, better dust extraction, and a housing designed for continuous duty. For everyone else—especially if you pair it with a random-orbit sander for final finish—the DS321 covers a lot of ground for the footprint and price.

The bottom line

Strengths:
- Low-profile, flush design and angled nose truly expand where you can sand
- Respectable material removal for a 7-amp unit when you let it work at its pace
- Adjustable handle adds real control on vertical surfaces and in tight spaces
- Retractable hood is useful, not a gimmick

Trade-offs:
- Single-speed limits finesse on very delicate work
- Tracking needs careful setup and occasional tweaks
- Dust bag is merely okay; best with a vac hookup
- Plastic housing warms up with heavy pressure on dense hardwoods

Recommendation: I recommend this sander for DIYers and occasional users who value access and control over brute force. It’s a practical, budget-friendly tool for general carpentry, outdoor projects, and shop tasks where a belt sander saves time. Use light pressure, keep belts fresh, and add a shop vac, and it performs reliably within its lane. If your work is predominantly hardwood flattening or you expect all-day duty, step up to a heavier, pro-grade model with variable speed and a more robust build.