Generation Mechanism and Quantitative Evaluation of Fuzzy Grain on Planed Surfaces of Hinoki (Chamaecyparis obtusa)

An orthogonal cutting experiment of air-dried hinoki (Chamaecyparis obtusa) was conducted and the fuzzy grain recognized as a whitish cluster on the finished surface was extracted by digital image data processing. The relative area of fuzzy grain took the maximum values of 6 to 10% for the contact angle of annual rings (phi) of 0 degrees, decreased as the contact angle increased, then took the minimum values of 3 to 4% for the angle of 45 degrees and finally increased in accordance with the contact angle. It was revealed from SEM observation that the cluster of fuzzy grain consists of cells around the ray that were scraped off in the cutting, but not separated as complete chips, were crashed by the travelling cutting edge, and were finally raised up from the wood surface after the cutting. The conformation of the cluster changed characteristically in accordance with the contact angle of annual rings. It was also revealed that the number of AE (Acoustic Emission) events detected in the cutting process correlated positively with the relative area of fuzzy grain.