Quick answer: There are two kinds of orbital sander. A sheet (quarter-sheet or half-sheet) orbital sander vibrates a clamped piece of sandpaper in tiny circles – gentle, cheap to run, good for corners and light prep. A random orbit sander spins a round hook & loop disc while also moving it in an orbit, so the grain never repeats a path; it removes material faster and leaves no cross-grain swirls. For most woodworking, buy a 5" or 6" random orbit sander with variable speed and a vacuum port, and run gold hook & loop discs from 80 to 220 grit.
Sheet orbital sanders
The original "orbital sander" – also called a finishing sander, palm sander or quarter-sheet sander – has a square or rectangular pad that takes a quarter (or half) of a 9" x 11" sanding sheet, clamped at each end. The pad moves in very small circles at high speed, so it cuts gently and can't dig in. Because the pad has square corners, it gets into corners and against edges where a round disc can't. It's the tool for light sanding between coats, scuffing paint, prepping for sealer, and small pieces. It removes material slowly, and because every grain moves in the same tiny circle, it can leave faint swirl marks that show under stain if you push it.
Random orbit sanders
A random orbit sander has a round pad that spins on its axis while the whole pad orbits in an eccentric path. The two motions combined mean no grain crosses the same track twice – "random" – so it sands across the grain without leaving cross-grain scratches or the pattern of swirls a sheet sander can leave. It also removes stock much faster, which makes it the better choice for panels, tabletops and any surface bigger than a cabinet door. Discs attach with hook & loop, so a grit change takes two seconds and a part-used disc can go back on later; the dust holes in the disc line up with the pad and pull dust straight through to the vacuum. See hook & loop vs. PSA for how the attachments differ.
| Sheet orbital | Random orbit | |
|---|---|---|
| Abrasive | Quarter or half sheet, clamped | 5" or 6" hook & loop disc |
| Motion | Small fixed orbit | Spin plus orbit – random |
| Removal rate | Slow | Medium to fast |
| Swirl marks | Possible | Minimal with good technique |
| Corners | Yes | No |
| Grit changes | Slow – unclamp | Instant |
| Best for | Small parts, corners, between coats | Everything else |
What to look for
- Variable speed. Slow it down for finish sanding and delicate veneer, run it flat out for stock removal. A single-speed sander is always compromising.
- Dust extraction. A vacuum port and a matching hole pattern in the disc keep dust from being ground into the surface – which is what causes swirl marks. Even the bag helps; a hose is far better.
- Pad size. 5" is the standard and the widest disc selection; 6" covers more ground on big panels. Match your disc hole pattern to the pad.
- Orbit diameter. A 3/32" orbit is for fine finishing; 3/16" or larger removes more per pass.
- Grip. A palm grip is fine for a 5"; a 6" with a side handle lets you use two hands on large surfaces.
- Power source. Corded for unlimited run time, cordless for convenience (keep a second battery), pneumatic if the shop already runs compressed air – air DA sanders are the auto body standard.
Which discs
For wood, gold aluminum oxide hook & loop discs with an anti-load coating are the standard: 80 for leveling, 120 and 150 for smoothing, 180–220 before finish. For metal, auto body and heavy removal, ceramic discs cut faster and last far longer. Choose the hole pattern (no-hole, 5-hole, 8-hole, multi-hole) to match your sander's pad so the dust extraction works.
Getting a swirl-free finish
- Start the sander in the air, set it down flat, and keep it flat.
- Move about an inch a second in overlapping rows – don't rush, don't dwell.
- No downward pressure. Let the weight of the tool do the work.
- Step through the grits one at a time and vacuum between grits.
- Change the disc when it stops cutting; a loaded disc rubs and swirls.
- Lift the sander off while it's still running, then switch off.
Our guide to what to avoid with an orbital sander covers the mistakes behind every swirl mark and dip.
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Shop orbital and DA sanding discs in every grit and hole pattern.
