Beads of sweat collect on my brow whenever I hand out belt sanders during the boat building classes I teach. In the wrong hands these powerful tools can easily do more damage?like sanding through the hull of a boat in seconds?than good. The same is true for belt sanders on the jobsite. A racing abrasive belt under a rookie's guidance might spell disaster for those built-ins, stair parts, or custom oak doors. After years of using these tools for installing finish work and building boats, I've learned that getting a good, flat finish is about control, and control comes from skill, experience, and good tool design.
While we can't do much about your skill and experience, we did test seven 3x21-inch belt sanders: the Bosch 1274DVS, Craftsman 27725, DeWalt DW431, Hitachi SB75, Makita 9903, Porter-Cable 352VS, and Ryobi BE321 Type II. We looked for the good design features that'll help you achieve a flat, smooth surface and good performance: nice balance, comfortable handles, straight tracking, easy adjustments, and good finish quality. We also looked at power for knocking off tough materials like paint.
I worked the sanders for a month on site and in my shop on both hard and softwood projects. I used them to surface glued-up stock, remove paint and varnish, resurface a maple countertop, sand a badly weathered deck railing, and clean hardened epoxy off boat building projects. I also built a jig to test how well they reached inside corners and edges. To keep things fair, I used the same brand of 40-, 80-, and 120-grit belts on all seven machines.
Design and Ergonomics
Body Styles and Handles. There are two distinct body styles in this test: low profile and traditional. The Bosch, Ryobi, and Craftsman units have motors in-line with the belt and their handles are at the far ends of the tools. The result is a long, narrow, and low-profile tool, about 1-1/2 inches more narrow than the more traditionally designed DeWalt, Hitachi, Makita, and Porter-Cable tools. These four higher-profile, more traditional designs have motors that spin transverse to the belt. Their handles also are above the belt rather than at the ends of the tool, a design resulting in a wider but shorter sander.
Though I've always used belt sanders with the traditional layout, I like the low-profile tools' balance and feel, especially for working wide, flat surfaces like a glued up panel or hardwood floor repair. The Bosch in particular is light, nicely balanced, and has well-shaped handles. Of the more traditional tools, the Porter-Cable and Makita units have exceptionally comfortable handles and well-distributed weight, although the Porter-Cable is a bit heavy. I found the DeWalt's handles a little too close together, making the tool uncomfortable to hold.
Flat Tops. The Bosch, Craftsman, Ryobi, and higher-profile Makita sanders have flat tops so you can flip them belt-up for use as stationary tools. This is great for shaping small parts or working to a scribe line. Each of these sanders worked great when I used them upside down to work the edge of a piece of trim. This position also was excellent for minor adjustments to little pieces of base molding that I had to fit over a threshold. You can even put an edge on a chisel or flat bar for rough work with the tools in this position.
Fences. Fences turn these belt sanders into proper little sanding stations that are great for installing built-ins, trim, or boat interiors. You can already use the Bosch belt-up, but to get even more utility out of it, the company sells optional accessory fences and hold-downs. DeWalt sells similar fences and hold-downs, making it the only traditionally designed unit with this accessory package.