Cross-finishing sanding wood-based panels

At its in-house Technical Centre, Steinemann analyzed how cross-finishing affects the surface quality of medium-thickness MDF panels in order to identify differences in sanding results when using a fine sanding head with angular orientation (N-head; N-sanding = fine sanding with oriented heads) and without (G-head; G-sanding = fine sanding without oriented heads). The change in surface roughness at different fine sanding angles was evaluated.

To determine the influence of cross-finishing on a sanded surface, two different grit sequences were selected. In the first sanding run, 25 MDF panels were calibrated with grit size P60. The feed rate was 60 m/min., stock removal was 0.1 mm. Five panels each were then processed at a fine sanding angle of 0°, 4°, 6°, 8° and 10° with grit size P100, where the panels were run through fine sanding twice. The same trial was then conducted with the grit sequence: P80 for calibration sanding and P100/P100 for fine sanding.

The roughness of each panel was measured at 5 different locations. The diagram in Figure 1 shows the means of these measurements, taken on five panels for each different fine sanding angle, and for each of the two trial runs (2 x 25 measurements).

The effects of the fine sanding angle, tested with grit sequences 60/100/100 and 80/100/100, are visualized in the diagram. The trend is unmistakable: The greater the fine sanding angle, the lower the level of roughness of the sanded panels. These results demonstrate the positive influence of Steinemann’s cross-finishing method.

Figure 1: Influence of cross-finishing on the roughness of a sanded MDF panel

Grit sequence

Figures 2 to 4 show the surface of the sanded panels 60/100/100 (K/N/N). The images show the change in surface roughness from calibration sanding with grit size P60, to the second fine sanding run with grit size P100. This example is based on a fine sanding
angle of 6°.

Figure 2: Surface after calibration sanding (P60)
Figure 3: Surface after the first fine sanding run
(P60/P100 – fine sanding angle 6°)
Figure 4: Surface after the second fine sanding run
(P60/P100/P100 – fine sanding angle 6°)

The change in the sanded panel is clearly visible: The surface structure becomes more homogeneous from calibration through to the second fine sanding run, though deep scratches are still visible. This is attributable to the grit sequence: When using a P60 belt for calibration sanding, the grit marks are so deep that they cannot be entirely eliminated, even by the second fine sanding run (see our March report on grit sequence).

Figure 5 shows that selecting a different grit sequence – P80 for calibration sanding and P100 for fine sanding – results in a significantly better surface finish with no deep grit marks.

Figure 5: Panel sanded with P80 for calibration sanding and P100 for fine sanding

In summary, as the visible results indicate, the best strategy is to skip as few grit sizes as possible when selecting the grit sequence.