Koyo Professional Grade Spherical Knob Cutter

While concave cutters are designed to make a flush cut on a branch, the spherical knob cutter features a rounded, cup-like blade shape. This allows you to scoop out the wood tissue around a knob or scar, creating a concave depression that heals over smoothly without leaving a protruding bump.

While it is professional-grade, it is accessible to anyone serious about bonsai maintenance. Just be aware that because the steel is incredibly sharp and designed for aggressive material removal, it is best to practice on scrap wood or less critical branches until you get a feel for how much material the tool removes.

Yes, high carbon steel is prone to oxidation. To keep the blades in top condition, wipe them clean of sap and moisture after every use, and apply a light coat of camellia oil or a similar rust-preventative oil before storing the tool in a dry place.

Absolutely. Because this is a high-quality Japanese tool, it is designed to be sharpened. You will need a small, specialized stone or a diamond file to maintain the inner curve of the spherical blades, as standard flat sharpening stones won't reach the cutting edge effectively.

This size is a standard, versatile length for most bonsai work. It provides enough leverage for removing knobs on medium-to-large trunks while remaining maneuverable enough for detailed refinement work on smaller branches.