The workhorse sander for most tradesmen is the 5-inch-diameter random-orbit sander. Thanks to its ability to hog off stock with a coarse grit disk and leave a smooth, finished surface with a fine grit, this single tool has replaced the old progression of belt sander to half-sheet finish sander for many. It doesn't replace all sanders for all applications – but truth be told, it has replaced a lot of them over the past few decades.
The random-orbit sander gets its wide range of capabilities from its action. The sanding pad is connected to a free spinning bearing, which is mounted off-center to a flywheel driven at full motor speed. This design gives the pad a full-diameter spinning motion along with a small wiggling action known as the orbit. The amount of orbital action is determined by how far off-center the pad is mounted and is called the orbit size.
Under no-load conditions, the combined motion is relatively uniform, and a dot marked on the sanding pad often traces what looks like a spirograph pattern. But once the pad touches the work the equilibrium is broken and the tool moves more randomly, changing rotation speed and orbit shape in response to varying pressure from the user. Random-orbit sanders can remove material quickly because a lot of area is covered by the sanding disk every second; and they can leave a nearly swirl-free finish with the finest grits because their eccentric rotation doesn't follow the same path, so the scratch pattern is truly random.
A mechanical pad brake built into each tool adds enough friction to keep the pad from free-spinning up to full motor rpm; the brake is a wear part that eventually needs to be replaced. Earlier electric random-orbit sanders were made without pad brakes, similar to pneumatic models, but they were tricky to handle when lifted off the work surface. At rpm of 10,000 or more, a sanding disk could land on the work as aggressively as a grinder, and a free spinning disk was apt to fly off the pad violently and could nearly jerk the tool out of your hand.
Of the many random-orbit sanders on the market, we narrowed our test selections down to the newest 5-inch electric models with variable-speed settings, hook-and-loop sanding pads, and on-board dust-collection containers. The variable-speed setting lets you fine-tune the sander's performance for different materials and abrasives.
Slower speeds, our testers noted, reduce heat when sanding plastics, decrease pitch buildup on disks when sanding knotty pine, and help the grit dig in better on oily woods like teak. For most sanding, though, our testers use the top of the speed range, occasionally making slight adjustments down from the maximum to improve troublesome vibration harmonics. All of our comparative testing was done at the highest speed setting for consistency, and as a result should be pretty accurate for the single-speed versions of these sanders too.
Hook-and-loop sanding disk attachment is the most common system for electric random-orbit sanders. The disks are reusable and easy to change, and are said to run cool because of the slight air space between the disk and the pad. Some of these sanders can be fitted with a smooth pad for use with pressure-sensitive adhesive (PSA) disks, which are typically thinner and less expensive.
When testing these tools side by side, we evaluated ergonomic concerns like switch access, grip comfort, and vibration, as well as control and performance factors like how gently a sander "landed" on the work, how smoothly it tracked on the work while sanding, and the relative effectiveness of its dust-collection features.
But the most important test result was sanding quality – how evenly and completely each pass of the tool actually sanded the wood. Evenness can be described as the density of the scratch pattern created by the sander, and completeness as how effectively that pattern was spread by the entire disk surface. When these two elements – evenness and completeness – are well coordinated, the sanding grit contacts every last bit of the work surface uniformly and blends its scratch pattern in fewer passes, making the work ready for the next-finer grit sooner and helping that finer grit cover and remove the previous coarser scratches completely. Yes, random disk movement is essential for a fine finish, but a more consistent scratch pattern is easier to blend and cover in fewer passes than one with wild looping arcs. Viewed this way, sanding quality equals sanding efficiency.
Porter-Cable turned in the best sanding results consistently, with the fastest and most uniform finishing. A strong new motor design gives the tool a body shape that took some getting used to, but the results cannot be denied.
Festool took second with very refined but slower performance in a comfortable lightweight tool. Bosch earned third place with all-around high-quality sanding, comfort, and features. Competent sanders by Makita, Milwaukee, and Hitachi occupy the middle tier, followed by the less preferred DeWalt and Ridgid models. And trailing them all is the Craftsman sander.
Karsten of Karsten Balsley Woodworking and Kerry Stoen of Westwoods of Boulder contributed to this test; both are career custom woodworkers in Boulder, Colo.