Scrub plane throwing you a curve?
Q: I've found all kinds of information on how to sharpen regular plane blades, but how do I go about sharpening the curved iron of a scrub plane?
A: Scrub planes feature a blade with a curved end to quickly hog off large amounts of material when thicknessing lumber by hand. This curvature presents a challenge when sharpening, particularly if you're accustomed to relying on a honing guide. But by following these simple steps, you can master the technique for sharpening a scrub plane blade. As you learn, keep in mind that scrub planes are roughing tools, so there's no need to obsess over achieving the perfect edge as you would with a smoothing plane.
To sharpen a new scrub plane iron, start by flattening the back of the blade, just as you would for an ordinary plane iron. A mirrorlike polish isn't necessary, but you'll want to remove any factory grinding marks from the back of the blade near the cutting edge — a task you'll perform only once.
With the back flattened, turn your attention to the curved bevel. Set the blade down on a medium (1000-grit) sharpening stone so that it rests on the bevel. Tilt the blade slightly forward and back until you feel the flat of the bevel register against the surface of the stone. Scrub plane irons have a relatively wide bevel, making it easy to feel. Tilt the blade up just a little from this position to concentrate your sharpening effort on the cutting edge of the bevel.
Lock your wrists to hold this angle and, while maintaining contact with the sharpening stone, swing the blade from side to side in small arcs, working the entire width of the bevel with each swing. To prevent wearing the stone unevenly, work the blade over the entire length of the stone. Check your progress frequently, and when you notice an even microbevel along the cutting edge, switch to a finer stone (6000 to 8000 grit) and repeat the process to refine and polish the edge.