Blade thinning is the process of removing material from the sides of a blade and then re-polishing the surface to a factory finish. Blade thinning is beneficial and often necessary at some point in the lifespan of knives that are used regularly. Most people only re-sharpen their knives by removing material at the edge of the blade, the bevel above the edge becomes larger over time as it creeps up the blade. A wide bevel is an indicator the blade has become too thick, and it will not cut as well as it did when it was new. Blade thinning is also essential when repairing blades that have chips and recurves.
Thinning is best performed by knife manufacturers and professional repair shops like ours, by people experienced with temperature control (overheating and tempering the steel is a risk that should be mitigated in the process). Thinning can be accomplished at home using waterstones, but the process is laborious and the results are rarely as uniform as can be accomplished with machines. Some knives, such as those made by Anryu Knives and Kurosaki Knives, are designed to better accommodate this process at home. Such knives, known for their “wedge” grinds, can be thinned regularly to avoid periodic lapses in performance.
A vast array of machines and abrasives are suitable to accomplish blade thinning. Because of this, achieving the same finish as the factory that made the knife is unlikely. Many Japanese factories use large stone grinding wheels and buffing wheels to accomplish the job. We use a variety of abrasive belts that run on sanders modified with proprietary radial platens that simulate the action of the Japanese wheels and help prevent overheating the steel during the process. While some people advocate for regular thinning each time a knife needs sharpening, we recommend the process only when a blade is disproportionately thick near the edge. If a knife doesn’t cut well after restoring it’s bevels, thinning may be in order.