Get the Right-size Random-orbit Sander
To get to the bottom of the issue, we put nearly a dozen tools through extensive head-to-head testing in the WOOD® magazine shop.
For starters, don't expect the more expensive 6" sanders to deliver a finer finish. All of the sanders, regardless of size, left a scratch-free surface on wood when sanded to 220 grit. (We tested each model with Klingspor's PS33 and Mirka Abranet hook-and-loop sanding discs on pine, red oak, and cherry.)
Likewise, larger sanders have no inherent advantage when it comes to dust collection. In fact, the 5" sanders did a better job when sanding narrow parts, such as face frames, because the dust-collection holes sit closer to the center of the pad, as shown above, staying on or nearer the wood. So how do they differ? Read on to find out.
5" models: Lean, light, effective
Size and shape:Nimble and with its center of gravity directly over the pad, a typical 5" sander weighs 2–3 lbs less than a 6" model, making it easy to control with one hand. No wonder few models have handles for two-hand use.
Sanding speed: As a rule, these models just can't match the fast stock-removal rate of 6" sanders. So expect to spend 30–50% more time using a 5" machine versus a 6" model for the same job.
What it will cost you: Good news here—you can get a top-performing 5" random-orbit sander for $60 to $90. Plus, 5" sanding discs cost 10–25 cents less per disc than 6" ones, and you can buy them just about anywhere.
Where it shines: Because of its top-side palm grip and lighter weight, you'll tire less using a 5" random-orbit sander, especially on vertical surfaces. (On flat horizontal surfaces, you simply guide the tool while its weight rests on the wood.) And, the more-effective dust collection when sanding narrow pieces will leave you breathing easier.
6" sanders: Brawny, fast, pricey
Size and shape: Most 6" sanders have larger motors than 5" models, adding weight, but not necessarily vibration. All have pistol-grip handles with triggers and stubby front handles for two-handed use. Using it one-handed feels more awkward than with a 5" sander.
Sanding speed: At maximum speed, the pads on 6" sanders spin about 2,000 rpm slower than 5" models. Nevertheless, the 30%-larger pad size gives 6" sanders a decided advantage in removing stock quickly.
What it will cost you: Electric 6" sanders sell for $115 to nearly $300. Because you'll use fewer discs to do the same work, disc costs over time should be about the same as for a 5" sander. You'll likely have to go to woodworking or tool specialty stores, catalog retailers, or online to buy them.
Where it shines: Bigger is better when it comes to sanding broad surfaces, such as tabletops, cabinet sides, and doors.