How it moves
The pad is mounted off-centre on the motor, so its centre travels a small circle — the orbit. It is also free to spin on that mount, so as it orbits it turns, and the path of any one abrasive grain keeps changing instead of retracing a fixed loop. That combination is what separates it from a sheet sander, whose rectangular pad moves in a fixed orbit only; see detail and palm sanders. Whatever the motion, the scratches still have to be removed grit by grit — that is in how to sand wood.
Reading the specifications
| Model | Orbit or stroke | Speed | Pad | Dust |
|---|---|---|---|---|
| Bosch ROS20VSC | Orbit diameter 3/32 in (2.5 mm); eccentric offset 3/64 in (1.2 mm) | 7,500–12,000 OPM, no load | 5 in, hook-and-loop | Microfilter canister; hose adapter for 1-1/4 or 1-1/2 in |
| DEWALT DWE6423 | Orbit diameter 3/32 in | 8,000–12,000 OPM | 4-7/8 in pad for 5 in discs; 8 holes | Locking bag; port for DEWALT extractors |
| Festool ETS EC 125/3 | Sanding stroke 1/8 in (3 mm) | 6,000–10,000 RPM | 5 in (125 mm) | 1-1/16 in (27 mm) extraction connection |
From Bosch's, DEWALT's and Festool's product pages. The orbit and speed figures are in each maker's own terms and are not directly comparable across rows.
- Orbit diameter, offset and stroke. Bosch publishes both an orbit diameter (3/32 in) and an eccentric offset (3/64 in) for one sander — the offset is half the diameter. Festool calls its figure a sanding stroke and says its 3 mm stroke is designed for superfine sanding. Before comparing two sanders' orbits, check that both makers mean the same measurement.
- OPM and RPM. Bosch and DEWALT give speed in OPM; Festool gives RPM; and DEWALT's manuals expand OPM as oscillations per minute where Milwaukee writes orbits per minute. Bosch also marks its figure as no-load. Treat each number as the maker's description of its own machine, not as a common scale.
- Variable speed. All three models above have a speed range rather than a single speed; the makers give the range, not a recommended setting for each job.
- Pad and discs. Pads are sized to a disc diameter (5 in on all three here; DEWALT's pad itself is 4-7/8 in) and attach by hook-and-loop. Hole patterns differ between makers — DEWALT's is 8-hole — and the holes in the disc must line up with the pad's for dust extraction to work, as Milwaukee's manual describes.
Equipment notePaid link
Random-orbit sander
DEWALT DWE6423
The sander whose sheet this section reads: DEWALT gives a 3/32 in orbit, 8,000–12,000 OPM and a 4-7/8 in pad for 5 in discs.
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Swirls, edges and brakes
Random motion does not make a sander mark-free. Bosch says the pad-dampening brake on its ROS20VSC helps prevent swirl marks — a maker's description of one feature — and technique, a worn or loaded disc, grit carried over from a coarser disc, and tipping the pad all leave marks of their own. Edges are rounded by a pad that overhangs them. Technique is in using a random orbital sander.
Dust
The models above collect dust three different ways: Bosch in a filter canister, DEWALT in a cloth bag, Festool through a hose connection to an extractor. They are not the same system, and a bag or canister is not a safety measure in itself. OSHA names exhaust at the point of sanding as the preferred control; NIOSH, testing an exhaust system it designed with a slotted pad, measured about a 90% reduction in emissions against the sander it compared it with — a result for that system, not a figure for any sander's built-in bag. Milwaukee warns that dust from sanding finishes such as polyurethane or linseed oil can self-ignite in the dust box: empty it often. How three of these sanders compare on dust, pad and speed, and what else to weigh before buying one, is in the sander buying guide.
Reading a random orbital sander's specifications
- Orbit, offset or stroke — and which the maker means
- Speed in OPM or rpm, no-load or not, and whether it varies
- Pad and disc diameter, attachment and hole pattern
- How it collects dust: bag, canister or hose port
- A pad brake, if the maker lists one
- Abrasives that fit — see choosing sandpaper
Sources
Every figure is the named maker's for the model named, in its own words. 'Orbit', 'stroke', 'OPM' and 'RPM' are not used consistently between makers — DEWALT's manuals, for one, expand OPM as oscillations per minute where Milwaukee writes orbits per minute — so figures are not compared across makers here.
- 1.
ROS20VSC 5 In. Random Orbit Sander/Polisher. Bosch.
Used for: The ROS20VSC's orbit diameter 3/32 in (2.5 mm), orbit radius 3/64 in (1.25 mm) and eccentric offset 3/64 in (1.2 mm); 7,500–12,000 OPM no-load; 5 in pad and industry-standard hook-and-loop discs; a pad-dampening brake Bosch says helps prevent swirl marks; a microfilter dust canister and an adapter for 1-1/4 or 1-1/2 in hoses.
- 2.
DWE6423 5-in Variable-Speed Random Orbit Sander. DEWALT.
Used for: The DWE6423's 3/32 in orbit diameter, 8,000–12,000 OPM, 4-7/8 in pad for 5 in discs with an 8-hole hook-and-loop pattern, a locking dust bag, and a port for DEWALT's dust extractors.
- 3.
Random Orbital Sander ETS EC 125/3 EQ-Plus. Festool.
Used for: The ETS EC 125/3's 1/8 in (3 mm) sanding stroke, which Festool says is designed for superfine sanding; 6,000–10,000 RPM; 5 in (125 mm) pad; 1-1/16 in (27 mm) extraction connection.
- 4.
DCW200 20V Max Brushless Quarter Sheet Sander, Instruction Manual. DEWALT.
Used for: The glossary in DEWALT's manual expanding OPM as oscillations per minute.
- 5.
M18 Random Orbit Sander 2648-20, Operator's Manual. Milwaukee Tool.
Used for: Milwaukee's definition of OPM as orbits per minute; dust from sanding coatings able to self-ignite in the dust box; hook-and-loop discs aligned with the pad's holes.
- 6.
Control of Dust Exposure for Random Orbital Hand Sanders (Engineering Controls Database). National Institute for Occupational Safety and Health.
Used for: A NIOSH-designed exhaust system with a slotted pad that reduced emissions by about 90% compared with the sander it was tested against.
- 7.
Wood Dust: Possible Solutions. U.S. Department of Labor, Occupational Safety and Health Administration.
Used for: Exhaust at the point where dust is produced as the preferred control for wood dust.
About this guide
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