On Planing Machine Engineering Characteristics and Machined Timber Surface Quality

Abstract

Rotary machined timber surfaces exhibit small waves orthogonal to the timber feed direction resulting from the intermittent engagement of the cutting tool with the timber. These surface waves are typically less than five micrometres in height and when regularly spaced at 1 mm width characterize a good quality machined surface. Variations in the regularity of these surface waves are considered as surface defects. Machined timber surfaces produced by planing and moulding machines are a typical case. These surfaces will often exhibit waviness defects caused by inaccurate contact between the tool tip and the timber being cut. There are a number of different vibration sources on these machines. The primary cause of surface waviness defects has been found to be forced vibration, although inaccurate cutter servicing and relocation are also factors. The work presented in this paper concentrates on phenomena caused primarily by forced structural vibration. Systematic engineering and wood machining investigations are applied to a special purpose instrumented test rig so that correlation between vibration data and observed waviness defects can be established. The surface assessment of machined timber is carried out using a special purpose contact based surface tracing instrument. The engineering design and manufacturing influences that lead to unacceptable surface waviness variation effects are discussed.