## 3 Results and Discussion  
The results of the sieve analysis of sawdust sucked off from the frame saw PRW-15M and the chips sucked off from the machining centre SCM Tech Z5, and AX320 Pinnacle from birch shavings with and without heat treatment, are shown in Tables 4-6. By comparing the proportions of the individual sawdust fractions of the PRW-15M frame saw (Table 4), it can be stated that there are no differences in the proportions of the sawdust fractions of natural birch wood and thermally treated birch wood. The distribution of chip fractions according to the distribution is symmetric, with the largest fraction in the grain size range of 0.250-0.500 \(\upmu\)m.  
Analyses of the shavings of individual sawdust fractions indicate that coarse and medium coarse fractions over 0.5 mm in size from the sawing process of both untreated and treated birch wood on the PRW-15M frame saw belong to the category of polydisperse fibrous materials, rod-shaped with significant elongation in one dimension. The agreement between the granulometric composition of the steam-saturated wood vapor at a temperature of \(t=125\)-135 \({}^{\circ}\)C and the granulometric composition of the native birch wood chips predicts that the thermal treatment of the birch wood does not affect the chip formation process. This finding is similar to the results of temperature analysis in the process of drying beech timber by low and high temperature regimes on sawdust grain size presented by [PERSON] et al. [37]. Microscopic analysis of the chip shape of the fractions below 500 \(\upmu\)m indicates that the chip size of these fractions by their shape belongs to the group of isometric chips. Chips having approximately the same dimension in all three directions. Circularity is in the range \(\Psi=0.7\)-1.0. The proportion of fractions of chip extracted from the machining centre AX320 Pinnacle (Table 5), is similar to sawdust from the PRW-15M frame saw. Chips from machining centre AX320 Pinnacle did not show any significant effect of birch wood thermal treatment on the particle size except for the increased proportion of fine fraction of thermally treated birch wood, which increased from 2.1% to 4.4% for thermally treated birch wood mode I, and to 5.5% for the thermally treated wood mode II. From the chip shape aspect, only chips of a coarse fraction above 1 mm are fibrous chips. Medium and fine fraction chips are isometric chips with a circularity value in the interval: \(\Psi=0.7\)-1.0. The chips formed at the SCM Tech Z5 machining centre (Table 6) differ according to the proportion of the individual fractions compared to the sawdust formed by sawing the birch wood on the PRW 15M sash gang saw. The coarse fraction chips above 2 mm make up to 2/3 of the total chips produced. Similar representation of the fractions of beech, maple, and oak wood chips at the SCM Tech Z5 machining centre at a removal of \(a_{\text{e}}=3\) mm and a feed speed \(v_{f}=3\) m\(\cdot\)min\({}^{-1}\), and at feed speed \(v_{f}=5\) m\(\cdot\)min\({}^{-1}\) reported by: [PERSON] and [PERSON] [38]. With the feed speed decreasing at this machining centre when milling wood as the authors stated [39], the share of the coarse fraction is increasing at the expense of the medium coarse fraction. The chip shape of the coarse fraction corresponds to the shape and size of the layer to be cut. Medium and fine fractions of birch wood chips with or without thermal treatment are isometric chips. A comparison of the dust fraction of the extracted sawdust from the PRW-15M frame sawing machine and the chips extracted from the CNC machining centres suggests that the smallest chips in the extracted bulk wood mass are chips of size \(a=32\)\(\upmu\)m (Figure 6). Fractions below 30 \(\upmu\)m (thoracic dust or respirable dust) were not detected by measurements.