Wood machining properties of Australian plantation-grown eucalypts

10 This study assessed the moulding, drilling, turning, sanding, and routing properties of 11 seven plantation-grown hardwood species from southeast Australia to evaluate their potential 12 as a resource for the manufacture of high quality furniture and furnishings. Eucalyptus 13 grandis , Eucalyptus saligna , Corymbia maculata , Eucalyptus camaldulensis , Eucalyptus 14 sideroxylon , Eucalyptus cladocalyx , and Eucalyptus globulus were machined using different 15 tools, and the surface quality obtained was visually graded. A sanding sequence of 100-150 16 grit produced satisfactory surfaces for furniture manufacturing for most studied species. 17 Usually, a feeding direction against the rotational direction of the tool showed best results 18 and reduced incidence of corner breakout when routing. Overall, high-density plantation- 19 grown Australian hardwood species performed well during machining trials with the use of 20 appropriate parameters and cutting tools allowing overcoming some typical processing 21 difficulties for some species. The data obtained within this study will allow optimising the 22 machining process of plantation-grown wood in Australia and increase value from the current 23 plantation resource. 24

of mature wood at 12% MC according to Kingston and Risdon (1961); c Not available for 70 drilling; d Not available for turning; e Not available for sanding; f Not available for routing.   Spindle speed was set at 6000 rpm for both conditions. The specimens were fed 94 through the machine in order alternating through the species and graded. Two people using 95 sight and touch method graded the planed surface. A score was assigned to the worst defect 96 of each type: 5) Unacceptable with defect a lot beyond repair; 4) Unacceptable with defect 97 just beyond repair; 3) Fair with heavy sanding but undesirable; 2) Good with moderate 98 sanding but undesirable; 1) Very good with light sanding or no defect present. The pieces 99 scoring between 1 and 3 were considered acceptable.

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Drilling. Twenty-six samples 100 mm square and 20 to 35 mm thick were drilled using a 101 numerically controlled machining centre (Maka CNC-222 T, Germany). Five rows of ten 102 holes were bored in the face of each sample using six different drill bits were supplied by the 103 Leitz Company, Germany (Table 2). Blind holes were drilled to a depth of 15 mm. The drills 104 were set at 3,000 rpm and feed rate was 2 m min -1 . The holes were then graded: 1) Excellent 105 with no chipping; 2) Good with very slight chipping; 3) Fair with some chipping but 106 acceptable; 4) Poor with more serious chipping and unacceptable for seen surface; 5) Very 107 poor with severe chipping and unacceptable. was set-up to run at 6 m min -1 with a depth of cut of 0.5 mm. Each of the species was sanded 129 three times, removing 0.5 mm each time. The belt was removed after the first and the third 130 sanding pass and examined for the presence of clogging (Table 3). The surface finish 131 achieved was then evaluated using five different belt grit sizes: 80, 100, 120, 150 and 180.

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Two sanding programs were then tested: 100-150-180 and 80-120-180. Depth of cut was set 133 at 0.5 mm for 80 grit, 0.2 mm for 100 grit sandpaper and at 0.1 mm for 150-and 180-grit 134 sandpapers. Feeding was carried out at 6 m min -1 feed speed. The surface finish and the level 135 of fuzzing of the worst specimen from each set of four per species were each graded from 1 136 to 5 after each sanding program (Table 4). A specimen graded 1 for surface finish and 2 or 137 better for fuzzing would be considered acceptable. Extremely poor -cutter marks and defects still showing Extremely poor -excessive fuzzing, several sanding operations required a Based on Davis (1962).

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Routing. Routing trial was conducted using a numerically controlled machining centre 146 (Maka CNC-222 T, Germany). Samples were cut from selected boards and glued together to 147 make thirteen boards 200 mm square, and thickness from 23 to 35 mm. A series of cuts were 148 routed in the edges and face of each sample using four different HW bits (Table 5). Exterior 149 cuts were made on the quarter sawn face. The spindles were set to run at 16,000 rpm, and 150 rotated in a clockwise direction (viewed from the spindle). Feeding rate was 5 or 10 m min -1 151 depending on the trial.     Eucalyptus sideroxylon produced the best results when drilled with a variety of drill bits 208 ( Figure 5). Of the remaining species, the order from best to worst was Corymbia maculata, 209 Eucalyptus grandis, Eucalyptus saligna, Eucalyptus camaldulensis, and Eucalyptus globulus. 210 Examination of the entry of the holes showed that all species produced acceptable holes (i.e.    Five of the seven eucalypts were able to be turned well (Table 7). Eucalyptus 236 sideroxylon returned an 80% recovery of pieces graded 2 or better. The results were 237 considerably better than for the other species. All other species returned recoveries between 238 0% and 20% percent for pieced graded 2 or better. These pieces were considered to be 239 excellent, and would need very little reworking such as sanding. Eucalyptus saligna from 240 Mildura, Eucalyptus sideroxylon from Lake Hume, and Eucalyptus globulus from both Oxley 241 and Thurgoona returned 100% of acceptable pieces (Grade 3 or better). Eucalyptus grandis 242 from Mildura and Corymbia maculata from Lake Hume yielded in excess of 80% recovery.

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These pieces will require additional work, and are expected to sand to a satisfactory finish.

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Poor recoveries were obtained from Corymbia maculata from Shepparton and Eucalyptus  The only grit that left visible scratches on the surface of the timber was the 80 grit.

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None of the surfaces produced using the 100, 150 or 180 grit belts for any of the seven 262 species showed any visible scratches. The surface finish produced for all pieces was very smooth (grade 1). Eucalyptus cladocalyx, Eucalyptus sideroxylon and Corymbia maculata all 264 scored 3 for surface finish when sanded with 80 grit paper. These species were graded as 265 acceptable. Eucalyptus globulus scored 4 (poor). Eucalyptus grandis and Eucalyptus saligna, 266 scored 5 (extremely poor). These three species all had rough areas.

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No improvement in the fuzzing of the surface for Eucalyptus grandis past the 100 sanding 268 grits. The remaining species scored 2 or better for fuzzing using the 180 grit paper, indicating 269 that all of the surfaces were acceptable for finishing. For many species a sanding sequence of 270 100-150 grit produced good enough surfaces to be finished during furniture manufacturing.

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The only species that would benefit from sanding with a 180 grit paper were Eucalyptus 272 sideroxylon and Eucalyptus camaldulensis. 273 Sanding using a 100 grit belt would prepare the timber surface ready for sanding with 274 the finer belts. One pass would not produce a surface that would be acceptable for the 275 finishing of furniture. The critical factor here was whether the timber surfaces produced using 276 the 150 grit belt is satisfactory for finishing, or whether a further pass using the 180 grit belt 277 is necessary.

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There was a definite trend towards a feeding direction against the rotational direction 280 of the tool to produce the best finish. There was also a reduced incidence of corner breakout 281 using this method. The results of this trial indicated that there is no reason to cut with the tool 282 rotating in the same direction as the feed. with the feed, with most of the tools. When tool #3 was used to cut along the grain, good 287 surfaces were usually produced on all of the species. Eucalyptus saligna, Corymbia maculata, Eucalyptus globulus, Eucalyptus sideroxylon, and Eucalyptus cladocalyx all had a 289 perfect grade when cut in either direction. When the same tool was used to cut across the 290 grain, all species produced an acceptable surface. When cutting with the feed, all species 291 performed better than Eucalyptus regnans. When tool #1 and #2 were used to cut along the 292 grain, all species produced good surface, with tool #2 performing marginally better.

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Corner finish. The surface produced when cutting across the grain was not as good as 295 cutting along the grain, but still graded as acceptable. When cutting against the direction of 296 the feed of the wood, the edge finish was marginally better than for cutting with the feed.

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Cutting this way also resulted in half as many corner breakout defects. When tool #1 was 298 used to cut across the grain with the feed, only Corymbia maculata from Lake Hume,

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Eucalyptus sideroxylon, and Eucalyptus cladocalyx produced acceptable corners with all 300 other eucalypts returning unacceptable grade. The results for tool #2 were marginally worse.

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When tool #1 was used to cut across the grain against the feed, the results were better. All 302 species except Corymbia maculata from Shepparton and Eucalyptus globulus from Oxley 303 produced acceptable corners. Again, results for tool #2 were usually worse.

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Groove and breakout. When machining grooves across the grain, breakout was a problem at 305 the start and at the end with an average grade of 3.5 and 4.5, respectively. The only samples 306 to produce acceptable entry and exit breakout figures were Eucalyptus cladocalyx and 307 Eucalyptus grandis from Shepparton. The scores for mature Eucalyptus regnans were worse 308 than the average for the plantation species. Where possible, it would be recommended that 309 grooves across the grain be machined before any external cuts are made. On manually fed 310 routing machines, the breakout at the ends of the groove can be minimised by the use of 311 supporting (backing) pieces.

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This research confirmed that high-density plantation-grown Australian hardwoods can 315 perform well during moulding, drilling, sanding, and routing processes when the appropriate 316 tools and parameters are used, as demonstrated during the moulding and drilling trials.

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However, turning trials showed to be difficult for Eucalyptus cladocalyx, Eucalyptus 318 camaldulensis and Corymbia maculata from one location. For most species a sanding 319 sequence of 100-150 grit produced satisfactory surfaces for furniture manufacturing where 320 Eucalyptus sideroxylon and Eucalyptus camaldulensis could benefit from sanding with a 180 321 grit paper. A feeding direction against the rotational direction of the tool usually produced the 322 best finish when routing which also reduced incidence of corner breakout. The results of this 323 trial indicated that there is no reason to cut with the tool rotating in the same direction as the 324 feed. This project provides the technical information on machining of a number of potential 325 hardwood species which have met tree growth and primary processing requirements 326 regarding their potential for high quality furniture and furnishing products. The data obtained 327 within this study will allow optimising the machining process of plantation-grown wood in 328 Australia and increase value from the current plantation resource.