Typically, to achieve this Japanese naguri (literally “beaten”) pattern in wood…
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…you’d need a sharp hand tool, patience and skill. It was traditionally done with a carving gouge or an adze, as seen in this photo:
Image: Wrath of Gnon
However, woodworker Takurou Seino (whose clever bowl we looked at here) has created a jig that allows you to do it with a trim router and a bowl bit.
By attaching an optional parallel guide, you can introduce a regularity to the pattern that would be impossible to achieve with hand tools:
Here you can see how Seino made the jig, or you can skip to the last quarter of the video to see how he uses it:
Seino has patented the design, and sells the jig for ¥6,000 (USD $41). Adding the parallel guide boosts the price to ¥9,600 (USD $65).
Source: core77