Stability of thermosmoothed and precision planed solid wood surfaces

The outer cell layers of a machined solid wood surface usually collapse and compact during processing due to the cutting forces. This layer is called deformation zone. The deformation zone is excessively instable, varies with temperature and MC variation of the environment. Usual surface investigations like surface roughness or surface tension measurements provide only few and indirect information about the status of the deformation zone, although this is the layer to adhere. Suggestion is made to consider the behaviour of the deformation zone during wetting instead of single parameters, in order to better characterize the status of the surface and its expected reaction when treated with water based materials. In this research, the focus has been on describing the behavior of the deformation zone of precision planed and thermosmoothed solid wood surfaces during wetting with distilled water. An individual wetting procedure has been developed, whilst surfaces have been characterized by 3D roughness measurement. The evaluation has been performed after defining the convenient roughness parameter as indicator of surface topography changes of the deformation zone due to wetting. Based on indicators sequence has been set among wood species and machining types regarding the answer given by their deformation zone to wetting. Although the two cutting methods offer the smoothest machined surface, their stability to wetting with water differs considerably. The deformation zone of precision planed surfaces has been proven to be more stable than the one of thermosmoothed surfaces. Black locust preserved its stability even when thermosmoothed.