# Efficiency of Machine Sanding of Wood
## 4 Discussion  
In Figures 3-5, different rates of decline in sanding efficiency are observed. It seems that the rapid rate of decline in the sanding efficiency is related to the high initial efficiency (the greater the initial efficiency, the more rapid its reduction). This rapid rate of decline in sanding efficiency was observed with lower density samples, especially softwoods. A possible reason for the rapidly decreasing sanding efficiency (which occurs from 0.5 min to 3 min depending on grit size and species of wood) is that the spaces between the coated abrasive become clogged more quickly by wood dust. The weight loss of sample sets during sanding is uniform (Figures 6-8), which results from the fact that most of the experiment time takes place in the second blunting phase, for which such a course of the sanding process is characteristic. Additionally, in this way, the occurrence of a short time of the first blunting phase was emphasized. Moreover, in the case of most of the wood species, a third blunting phase occurred at the end of the experiment, when the vast majority of the sample mass had already been sanded. The rate of weight loss of the wood during sanding, as known to date, is generally greater for lower-density wood species; but the differences between the high-density species (oak) and the light softwoods (spruce, visible in the graphs) are slight. In addition, the lighter hardwood species (alder, walnut), in terms of wood removal rate, behave similarly to low-density softwoods. The conclusions of the scientific works to date indicating the effect of wood density resulted from comparisons of a mostly small number of species. [PERSON] et al. [23] compared parameters of sanding hard maple (_Acer saccharum_) (hardwood) and eastern white pine (_Pinus strobus_) (softwood). They mentioned wood species as one of the factors influencing the sanding results. The wood removal rate was twice as high for pine than for maple. [PERSON] et al. [21] considered only two hardwood species: European beech (_Fagus sylvatica_) and English oak (_Quercus robur_). With a slight difference in density (684 kg/m\({}^{3}\) for beech, 678 kg/m\({}^{3}\) for oak), they found significant differences between the wood removal rates of both species. [PERSON] and [PERSON] [25] also studied two hardwood species: Manchurian ash (_Fraximus mandshurica_), and birch (_Betula_ sp.). The density of wood samples in this study was respectively 620 and 470 kg/m\({}^{3}\). In this case, lower values of wood removal rates in all variants of the study were for the denser and harder Ashwood. [PERSON] and [PERSON] [26] used  
Figure 8: Average percentage weight loss of specimens sanded with abrasive belt P180. as many as 21 species (17 hardwoods and 4 softwoods) in the study on dust production during hand sanding. They found that the quantity of wood removed during sanding varied irreversibly with wood density. The results of these studies link the rate of the wood removed during sanding to the density and directly to the species of wood, regardless of whether it is softwood or hardwood. Therefore, to compare these two different types of wood, the total sanding times for all samples of each species were averaged. The calculated average values of these total sanding times for the six hardwood species and three softwood species separately are shown in Figures 9-11. Figure 10: Comparison of average results for hardwoods (beech, oak, ash, hornbeam, alder) and softwoods (pine, spruce, larch) species; P120 sandpaper. Figure 9: Comparison of average results for hardwoods (beech, oak, ash, hornbeam, alder, walnut) and softwoods (pine, spruce, larch) species; P60 sandpaper. The graphs in Figures 9-11 show that in all tested cases, the average sanding time of the samples of softwood species was lower than that of the hardwood species. The sanding times of the softwood species were: 2.5 min (P60), 5 min (P120), and 6.5 min (P180). For hardwood species, these times were 6.5, 7.5, and 8.5 min, respectively.