EFFECTS OF MACHINING CONDITIONS ON SURFACE ROUGHNESS IN PLANING AND SANDING OF SOLID WOOD

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INTRODUCTION 1. UVOD
In wood fi nishing, roughness refl ects faults on a wood surface as a result of the operations carried out in production.These faults are repeated with a low probability and periodically.Control and monitoring of surface roughness is required to maintain product quality at the same level throughout the production, as this property affects wood adhesion and changes can increase loss.After solid wood undergoes machining by sawing, planing, sanding, etc., it becomes a fi nal product.Wood fi nishing is an important factor in determining the economic value of the fi nal product.Accordingly, surface roughness is a defi nitive property for measuring the success of the wood fi nish.
Surface roughness can be evaluated quantitatively and qualitatively.Each approach has advantages and disadvantages, such as a slower speed, sensitivity, and the accuracy of results (Malkocoglu, 1999).There are various methods of surface roughness measuring in the area of woodworking.Lumber surface roughness can be measured with an airfl ow method (Porter, 1971).An imaged light and needle-scan can also measure surface roughness (Peters, 1970).It is thought that surface roughness in industrial applications can be easily done with a light-sectioning shadow scanner method (Sandak, 2005).However, the stylus trace method has emerged as the most suitable and applicable method in the measurement of surface roughness (Peters, 1971;Faust, 1987).Stumbo (1960) mentioned that a decrease in surface roughness will occur with an increase in the cutter speed and number of teeth in cutting saws.An increase in surface roughness will occur with an increase in feeding speed.When planing and milling softwood species compared to hardwood species, roughness is greater when cutting perpendicular to the grain than when cutting along the grain.In general, worn cutters increase surface roughness.With regards to average roughness values, approximately the same values are obtained in directions perpendicular to the grain and along the grain (Steward, 1970).
Roughness of various tree species has been investigated.Gurleyen (1998) studied surface roughness in the planing of beech (Fagus orientalis L.), scotch pine (Pinus sylvestris L.), sessile oak (Quercus petreae L.), and black locust (Robinia pseudoacacia L.).Demirci (1998) studied oriental beech (Fagus orientalis L.), scotch pine (Pinus sylvestris L.), oak (Quercus petreae L.), and black locust (Robinia pseudoacacia L.) in the machining of massive wooden material with circular saws.Ors et al. (1999) studied the planing and sanding operations of planed and sanded massive wooden material using oriental beech and Scotch pine.Kantay et al. (2001) studied the surface roughness of sliced veneer boards from tree species of walnut (Juglans regia L.) and oriental beech (Fagus orientalis L.) in Turkey.Ünsal et al. (2002)  ) and aspen (Populus tremula L.) with a stylus trace method.Malkocoglu (2007) investigated planing properties and surface roughness of oriental beech (Fagus orientalis Lipsky.)grown in the Eastern Black sea region, Anatolian chestnut (Castenea sativa Mill.), black alder (Alnus glutinosa), Scots pine (Pinus sylvestris L.) and oriental spruce (Picea orientalis (L.).It was observed that using veneer with tough surfaces in plywood production reduced adhesion quality (Faust, 1986).Hiziroglu  This study investigated and evaluated surface roughness through planing and sanding experiments for several hardwood and softwood species commonly used in Turkey.

Wood material 2.1. Uzorci drva
Various species of softwoods and hardwoods were used for the experiments.European black pine (Pinus nigra Arnold) and cedar of Lebanon (Cedrus libani A. Rich), as two softwood species, and Sessile Oak (Quer-cus petraea Lieble) and black poplar (Populus nigra L.), as two hardwood species commonly used and grown in Turkey, were selected as experimental material for the study.The samples were all randomly selected from naturally grown wood in Istanbul and Kutahya in Turkey.The wood was conditioned at a temperature of 20 ± 2 °C and 65 ± 5 % to a moisture content of about 12 %.30 specimens (25 x 102 x 910 mm) were used for each planing and sanding test according to ASTM standard D 1666 (2004) (ASTM International, 2004).

Performance of planing and sanding experiments 2.2. Provedba eksperimenta pri blanjanju i brušenju
Planing experiments were carried out using a TORK brand K500-X250 model thickness planer at the facility of the Istanbul University, Forestry Faculty of Furniture and Wood Machining.Thirty test samples with the dimensions 25 x 102 x 910 mm and a wood moisture content of 12 % were made from each tree species.As stated in the above said standard (ASTM D-1666), the cutting depth was 1.6 mm for all the cuts.The properties of the cutting tools used in the planing tests are presented in Table 1.
A wide-belt caliber sander, Melkuc Kombi 650 model, for calibrating and sanding of wood based panels was used for the sanding experiments.The cutting speed in sanding operation was set to 5.5 m/min.The samples previously used in the planing experiments with dimensions of 20 x 102 x 910 mm were fi rst sanded with 80 grain sandpaper and then with a 120 grain.

Roughness measurement 2.3. Mjerenje hrapavosti
The measurement of surface roughness was done according to protocols in TS 6956 EN ISO 4287, TS 971, and TS 2495 EN ISO 3274.An instrument for measuring surface roughness, Mitutuyo Surfjet SJ 301, was used for the determination of surface roughness by a contact stylus trace method.
Measurements were made in two different directions, perpendicular and along the grain.Gaussian fi lter type was used.Sampling length was 2.5 mm and the evaluation length was L t = 12.5 mm.Cut-off length was 2.5 mm.Surface roughness values were measured with a sensitivity of ± 0.01 μm.Tool measurement speed was 10 mm/min, the diameter of the measurement needle was 4 μm, and the needle tip 90°.Care was taken to have a measurement environment around 18 °C -22 °C, away from noise sources, and without vibration.The tool was calibrated before the measurement and the calibration was checked at established intervals.Arithmetic mean and standard deviation were used for the evaluation of the specifi c gravity and the number of annual rings per cm.In the evaluation of roughness results, correlation analysis, analysis of variance (ANOVA), and also a t-test were employed to investigate whether there is a signifi cant difference between the roughness values with respect to the applied measurement directions.
A total of 8 roughness measurements were conducted on 4 fi xed points established on each machine in directions perpendicular to the grain and along the grain on 30 planed samples.A Ra (average roughness) value was used in the evaluation of results of roughness measurement.
There is a very weak correlation between roughness, a dependent variable, and the number of annual rings per cm and the specifi c weight, an independent variable, at 0.097 and -0.038, respectively.However, a strong positive correlation is observed between the number of annual rings per cm and the specifi c weight, an independent variable at 0.804.The data obtained from the experiments is given in Table 2.
Figure 1a below shows roughness values along the grain for various machining conditions and tree species.Figure 1b shows the roughness perpendicular to the grain.Figure 1c provides the mean of the roughness values perpendicular to the grain and along the grain in the form of a graph.
Table 3 provides average roughness values, standard errors based on tree species, and lower and upper limits based on a 95 % confi dence limit.
With respect to tree species, oak had the highest roughness average with 6.780 μm, followed by black poplar with 6.338 μm.With regards to the upper and lower limits of tree species based on a 95 % confi dence level, the confi dence ranges of pine and cedar of Lebanon intersect.When roughness values are studied based on machining conditions, the highest average  than the roughness value along the grain).Figure 2 shows the average roughness values (Ra) along and perpendicular to the grain based on tree species in the form of graphs.Ra of poplar is 1.6077 μm higher than that of pine.The average roughness value Ra of poplar is also 1.5048 μm higher than that of cedar of Lebanon.However, Ra of oak is 0.4417 μm units higher than that of black poplar.The Ra of pine is 2.0494 μm less than that of oak.Although the Ra of pine is 0.1029 μm less than that of cedar of Lebanon, there is no signifi cant difference between the two.In other words, pine and cedar of Lebanon may roughness values were found in Run 1 and sanding, and the average roughness values for Run 3 and Run 1 exhibited close values when the upper and lower limit values of the Run 3 and Run 1 are studied based on a 95 % confi dence level, the limit values for both runs overlap.It was determined that the machining conditions of Run 4 had the lowest roughness average.
With regards to measurement direction, there was a signifi cant difference between the measurement values along the grain and measurement values perpendicular to the grain (the average of the roughness values perpendicular to the grain is 1.553 μm higher According to statistical analysis results, the Ra for Run 2 was by 1.1737 μm higher than for Run 1.Although Ra for Run 1 was by 0.0218 μm higher than for Run 3, there was no signifi cance between them (Sig: 1,000) and Run 1 and Run 3 can be put into the same group with regards to roughness averages.While the value of Ra for Run 1 was by 0.2375 μm higher than for Run 4, it is by 0.2677 μm less for sanding.The Ra for Run 2 exhibited a signifi cant difference since they were higher compared to all the other machining conditions.The Ra for sanding conditions have a slightly higher Ra compared to all the other machining conditions except for Run 2. Sanding machining condition can be shown as a separate group with regards to Ra.At the same time, although Ra for Run 3 was by 0.2158 μm higher than for Run 4, these two machining conditions are shown under the same group with regards to roughness averages.
According to the statistical analysis results, there was no signifi cant difference in roughness with regards to measurement directions.Figures 3a, 3b, 3c, and 3d show the roughness graphs under machining conditions for Runs 1, 2, 3, and 4 based on measurement directions and tree species.
Figure 4 presents a roughness graph under sanding condition based on measurement directions an d tree species.

ZAKLJUČAK
As a result, Sessile Oak showed the roughest surface in wood machining operations.According to the roughness measurement results for black poplar, surfaces with the highest faults and the roughest surfaces occurred in the sanding operation.Although it was expected that black poplar would have smoother surfaces during sanding, since the machining method affects surface quality, an increase in the roughness was observed.It is believed that this result is signifi cantly affected by the type of procedure.Cedar of Lebanon exhibited values close to black pine with regards to average roughness, displaying the lowest average roughness values amongst the tree species studied.The values for black poplar and sessile oak were found to be higher.Cedar of Lebanon was in the same group as black pine in regards to surface roughness and exhibited the highest roughness value.
et al. (2013) determined surface roughness in the sanding of pine (Pinus strobus), borneo camphor (Dryobalanops spp.) and meranti (Shorea spp).Zhong et al. (2007) evaluated surface roughness in various commercially produced composite panels including particleboard, medium density fi breboard (MDF), and plywood in addition to ten different solid wood species which are commonly used in furniture production.Skaljic et al. (2009) determined surface roughness values of planed beech-wood (Fagus L.), oak -wood (Quercus L.) and fi r-wood (Abies alba Mill.) specimens.

Figure 1a
Figure 1aRoughness values along the grain for various machining (cutting type) conditions and tree species 1b Roughness values perpendicular to grain for various machining (cutting type) conditions and tree species 1c Mean Roughness values for various machining (cutting type) conditions and tree species Slika 1. a) Vrijednosti hrapavosti uzduž vlakanaca za različite uvjete obrade i različite vrste drva; b) vrijednosti hrapavosti okomito na vlakanca za različite uvjete obrade i različite vrste drva; c) prosječne vrijednosti hrapavosti za različite uvjete obrade i različite vrste drva studied the surface roughness of massive parquets from oak and oriental beech in Turkey using a stylus trace method.Ilter et al.

Table 3
Aver age roughness values, standard errors based on tree species and lower and upper limits based on 95 % confidence limit Tablica 3. Prosječne vrijednosti hrapavosti, standardna pogreška za pojedinu vrstu drva, donja i gornja granica za interval pouzdanosti od 95 % Figure 2Graphs of average surface roughness along and perpendicular to the grain based on tree species Slika 2. Prosječna hrapavost površine istraživanih vrsta drva uzduž vlakanaca i poprečno na njih μm be gathered together under the same group with regards to roughness value.The Ra values for black poplar and oak are higher than those for the other tree species.