- Email: [email protected]
Effect of machining on surface roughness of wood
ARTICLE IN PRESS
Building and Environment 41 (2006) 1074–1078 www.elsevier.com/locate/buildenv
Effect of machining on surface roughness of wood Murat Kilica,, Salim Hiziroglub, Erol Burdurlua a
Department of Wood Products Industrial Engineering, Hacettepe University Ankara, Turkey Department of Forestry, 303-G Agricultural Hall, Oklahoma State University, Stillwater, OK 74078, USA
b
Received 9 July 2004; received in revised form 22 April 2005; accepted 3 May 2005
Abstract The objective of this study is to evaluate effect of various machining techniques on the surface roughness of beech (Fagus orientalis) and aspen (Populus tremula) lumber. Surface characteristics of sawn, planed, and sanded samples of both species were determined employing a stylus type profilometer. Average roughness (Ra ), mean peak-to-valley height (Rz ), core roughness depth (Rk ), reduced peak height (Rpk ), and reduced valley depth (Rvk ) roughness parameters were used to determine surface characteristics of the samples. Based on the results of statistical analysis, measurements taken from the surface in tangential and radial directions of both species did not result in significant difference at a 95% confidence level. However, significant statistical difference was found between surface characteristics of aspen and beech samples, machined with four different ways in both grain orientations. This study suggests that stylus method can be successfully used to evaluate and distinguish variations on the surface of wood, due to grain orientation and planning and sanding. Data generated in this study can be used as a quality control tool for further processes such as finishing or gluing of wood from two species. r 2005 Elsevier Ltd. All rights reserved. Keywords: Surface roughness; Beech; Aspen; Sawn solid wood; Sanding
1. Introduction Surface quality of solid wood products is one of the most important properties influencing further manufacturing processes such as finishing or strength of adhesive joint. Laminated lumber with smoother surfaces will have better glueline resulting in higher strength properties. Surface roughness of wood can be affected by various factors such as annual ring variation, wood density, cell structure, and latewood/earlywood ratio. Type of machining used during production, raw material characteristics of work piece or a combination of both these parameters are responsible for surface quality of the final products and in determining its cost. Increased cutting speed or rpm results in an improved surface quality of wood products [1–3]. Planed surface Corresponding author.
E-mail addresses: [email protected] (M. Kilic), [email protected] (S. Hiziroglu). 0360-1323/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2005.05.008
characteristics of solid wood is a function of machining quality, which is directly related to knife marks per cm and not by cutterhead speed alone [4,5]. Sandmarks are also important parameters influencing the quality of the surface as a function of grit size and any variation from a certain expected degree of surface quality of wood will result in cost increase and waste of raw material. Surface irregularities on solid wood traditionally are not recognized as much as for other engineered surfaced materials. Although the surface roughness of wood can readily be determined in technical terms, given a representative or numerical reading of the surface topography no accepted standard method has been established for this purpose Several methods are available but have not found widespread use in the industry. Stylus, optical profilometer, image analyses techniques using a video camera, pneumatic, ultrasonic, and microscopy are some of the methods used to evaluate surface roughness of wood products [6–10]. Each of them has some disadvantages and some
ARTICLE IN PRESS M. Kilic et al. / Building and Environment 41 (2006) 1074–1078
disadvantages over each other. Stylus method has been used to determine surface roughness of solid wood and wood composites in the past studies [11–14]. One of the main advantages of the stylus method is to have actual profile of the surface and standard numerical roughness parameters, which can be calculated from the profile. Any kind of irregularities and magnitude of roughness on a surface can be objectively quantified by this method. Therefore, in this study a fine stylus method was employed to determine surface roughness of machined wood samples prepared from two species.
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with a maximum width capacity of 60 cm, feed speed of 8 m/min, revolution of 6000 rpm, and nose width of 40 mm. The planes cutterhead had three knifes. A set of four samples was sanded on a drum-type sander using 60- and 80-grits sandpaper. Each sample was run once through the sander using a sanding speed of 22 m/min and sanding pressure of 6 kg/cm2. Table 1 shows sampling schedule. A schematic representation of Rk, Rvk, and Rpk roughness parameters is illustrated in Fig. 2. Once all machining processes were completed, the samples were conditioned in a computer-controlled climate chamber
2. Methods and material Ten trees were harvested for the experiments. Each tree was sawn on a portable sawmill with circular saw using live-sawing pattern. Saw diameter, number of tooth, kerf, revolution, and feed speed were 30 cm, 28, 0.32 cm, 6000 rpm, 6 m/min, respectively. Sixteen boards without any knots, defects, or any grain distortions were prepared for the tests. Average density of the samples were 0.70 g/cm3 for beech and 0.40 g/cm3 for aspen. Table 1 displays average diameter at breast height (dbh), age range, density, and sampling schedule for both species. The lumber was first air dried to 30–35% moisture content before they were dried in a laboratory type kiln to 10% target moisture content. Dried lumber was trimmed to 150 cm long and 15 cm wide and 2 cm thick samples with tangential (flatsawn) and radial grain (quarter sawn) orientations for the surface roughness measurements. Sawn, planed, and sanded surfaces of the samples with two grain orientations were used for the experiments. The test design considered surface characteristics of sawn, planed, and sanded with 60- and 80grit sandpaper small lumber. Each machining was carried out for tangential and radial grain directions of both beech and aspen as illustrated in Fig. 1. Four samples were selected for each machining application. The samples were planed using a laboratory-type planer
Fig. 1. Schematics of the tangential and radial surfaces. (not scaled).
Fig. 2. Definitions of Rk , Rvk , and Rpk parameters [16].
Table 1 Sampling schedule Tree number
Species and density (g/cm3)
DBH (cm)
Age (yr)
Number of sample
Number of surface measurement Radial
Tangential
1 2 3 4 5
Beech 0.70
35 38 35 30 34
140 142 143 126 149
16 16 16 16 16
20 20 20 20 20
20 20 20 20 20
1 2 3 4 5
Aspen 0.40
50 45 44 35 50
20 20 21 22 20
16 16 16 16 16
20 20 20 20 20
20 20 20 20 20
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Fig. 3. Surface profilometer used in this study.
with a temperature of 20 1C and relative humidity of 65% for 2 weeks prior to the tests. A fine stylus-type Mitutoya Surftest SJ-30 equipment consisting of the main unit and the pick-up was used to evaluate surface characteristics of the samples (Fig. 3). The pick-up has a skid-type diamond stylus with 901 tip angle and with a 5 mm tip radius. The stylus traverses the surface at a constant speed of 1 mm/s over 12 mm tracing length converting vertical displacement of the stylus into an electrical signal. A representation of surface can be obtained in the form of a graph. Fig. 4 shows typical surface roughness profiles of tangential beech sample machined with a different equipment. The equipment was checked every 100–120 measurements by using a standard reference plate with an average roughness (Ra ) of 3.02 and 0.48 mm. The device uses a digital filtering to separate the surface profile into two profiles, waviness and roughness profiles. A cut-off length of 3 mm, a parameter that differentiates roughness and waviness profiles from each other, was used for the measurement. Five roughness parameters, average roughness (Ra ), mean peak-to-valley height (Rz ), core roughness depth (Rk ), reduced peak height (Rpk ), and reduced valley depth (Rvk ) were used to analyze quantitatively surface quality of the samples. Ra and Rz are the most commonly used parameters in stylus method. In addition to these two parameters, Rk family parameters were also used to get a more detailed information about the surfaces of machined samples. Ra and Rz parameters are discussed in the previous studies [11,15,16]. However, description of Rk , Rvk , and Rpk are illustrated in Fig. 2.
3. Results Results of the surface roughness values of machined samples are presented in Tables 2 and 3 and Figs. 5 and
Fig. 4. Typical surface profiles of machined samples of beech in tangential grain orientation.
6. Based on statistical analysis, no significant difference was observed between surface roughness characteristics of tangential and radial machined surfaces of beech and aspen samples at a 95% confidence level. For example average roughness values of planed tangential and radial samples of aspen had 7.05 and 7.36 mm, respectively. The difference between two values as a function of grain orientation is only 4.3%. Sanded surfaces of both species resulted in lower values of above differences, ranging from 2.2% to 4.3%. Sawn surfaces of two different species had larger differences of Ra values due to less homogeneous surface as compared to those of both planed and sanded samples. Rz and Rk parameters also followed this trend. In general when roughness parameters of two species machined differently were compared to each other, significant differences were determined at a 95% confidence level. Beech had Ra values of 11.05, 7.90, 8.20 and 5.80 mm in tangential direction for sawn, planed, 60-grits sanded and 80-grit sanded samples, respectively. On the other hand aspen had 10.7, 7.05, 6.68, and 4.63 mm, for the above parameters which are significantly lower than those of beech. This finding can be related to the anatomical structure of beech [17]. Although both species are diffuse porous, pores and rays of beech are larger and more
ARTICLE IN PRESS M. Kilic et al. / Building and Environment 41 (2006) 1074–1078
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Table 2 Average roughness of aspen samples Roughness parameters (mm)
Sawn surface Tangential
Planed surface Radial
Sanded surface 60-grit
Sanded surface 80-grit
Tangential
Radial
Tangential
Radial
Tangential
Radial
Ra
10.7 (1.28)
13.26 (1.54)
7.05 (1.16)
7.36 (0.60)
6.68 (0.37)
6.99 (0.78)
4.63 (0.63)
4.50 (0.26)
Rz
84.6 (13.99)
94.74 (12.71)
61.62 (8.51)
66.80 (7.38)
58.77 (7.49)
67.49 (8.42)
43.34 (9.10)
45.10 (8.9)
Rk
25.35 (3.05)
27.55 (3.43)
20.24 (3.29)
21.07 (1.91)
21.11 (1.47)
23.54 (1.50)
13.96 (1.00)
13.48 (0.69)
Rpk
10.57 (1.51)
13.13 (1.85)
7.12 (1.08)
8.80 (1.59)
7.27 (1.16)
8.16 (1.24)
4.69 (0.56)
5.45 (0.75)
Rvk
18.5 (3.89)
25.69 (7.52)
16.19 (6.8)
14.9 (3.02)
12.60 (1.38)
13.77 (1.53)
7.34 (0.63)
8.12 (0.71)
Numbers in parentheses are standard deviations.
Table 3 Average roughness of beech samples Roughness parameters (mm)
Sawn surface Tangential
Planed surface Radial
Tangential
Radial
Sanded surface 60-grit
Sanded surface 80-grit
Tangential
Tangential
Radial
Radial
Ra
11.05 (2.6)
12.77 (3.7)
7.90 (0.57)
8.90 (0.85)
8.20 (0.75)
6.90 (0.70)
5.80 (0.52)
5.63 (0.54)
Rz
100.10 (21.60)
101.74 (17.83)
63.45 (11.10)
69.60 (9.00)
68.33 (12.06)
74.24 (12.50)
59.10 (9.38)
52.81 (10.59)
Rk
27.55 (3.43)
33.59 (8.55)
12.94 (1.99)
17.24 (2.45)
22.69 (2.70)
24.91 (2.03)
16.26 (1.13)
18.30 (1.41)
Rpk
13.13 (1.85)
13.65 (2.15)
7.58 (1.33)
8.85 (1.06)
8.22 (1.08)
9.01 (1.30)
6.67 (1.06)
6.39 (1.07)
Rvk
25.69 (7.52)
28.34 (4.66)
16.10 (2.61)
19.41 (4.61)
16.88 (1.89)
14.40 (1.63)
10.58 (0.92)
10.77 (1.22)
Numbers in parentheses are standard deviations.
Fig. 5. Average values of Ra , Rk , and Rz parameters of aspen samples.
Fig. 6. Average values of Ra , Rk , and Rz parameters of beech samples.
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noticeable as compared to those of aspen. Therefore, aspen resulted in lower values of roughness parameters indicating smoother surfaces in both radial and tangential grain orientations than those of beech. The differences in roughness values between two species were more prominent in the case of Rz and Rk parameters which also had a similar trend. Although Rpk and Rvk did not show as much difference as other parameters used in the study for aspen and beech, they had similar trends with Ra , Rz and Rk . As can be seen Fig. 2 Rpk and Rvk parameters are related to peaks and valleys of a surface. In a previous study, both parameters were used successfully to evaluate surface roughness of wood composites [11]. However, they might not be very useful to distinguish surface characteristics of solid wood due to its non-uniform surface. Based on the Ra , Rz and, Rk values determined from the surface of both species, roughness of the samples significantly improved with increasing grit size of sand paper as can be observed from Tables 2 and 3. It appears that five roughness parameters can be used to evaluate surface roughness characteristics of solid wood surfaces, machined with different methods according to the findings in this work. It should be noted that Rpk and Rvk are not as stable as the other three parameters in the case of sawn and planed surface. However if the surface is sanded, both parameters can also be accurately employed to identify the surface characteristics of machined solid wood.
4. Conclusion In this work, effect of various machining of beech and aspen lumber on their surface roughness characteristics was investigated. In the light of preliminary results of this study, a stylus method can accurately be used to evaluate surface roughness of machined samples of both species. It is suggested, in further studies to consider more than one grit size of sandpaper in order to attain a better understanding of the effect of sanding on board surfaces. Surface roughness of the samples exposed to different relative humidity levels and other machining
properties of such species could be evaluated to provide an initial data for finishing applications.
References [1] Lemaster RL, Beall FC. The use of dual sensors to measure surface roughness of wood-based composites. Proceedings of the ninth international symposium on non-destructive testing of wood. MD, Wisconsin:Forest Products Society; 1993. p. 123–130. [2] McKenzie WM. Fundamental aspects of the wood cutting process. Forest Products Journal 1960;10(9):447–57. [3] Mitchell P, Lemaster R. Investigation of machine parameters on the surface quality in routing soft maple. Forest Products Journal 2002;52(6):85–90. [4] Davis EM. Machining and related characteristics of United States hardwoods. Washington, DC: Technical bull. no. 1267. USDA; 1962 68p. [5] Wengert EM, Lamb FM. A handbook for improving quality and efficiency in rough mill operations. Princeton, WV: R.C. Byrd Hardwood Technology Center; 1994 107p. [6] Akbulut T, Hiziroglu S, Ayrilmis N. Surface absorption, surface roughness, and formaldehyde emission of Turkish medium density fiberboard. Forest Products Journal 2000;50(6):45–8. [7] Drew WE. Surface texture measurement errors: stylus type instruments. Quality 1992:41–4. [8] Faust TD. Real time measurement of veneer surface roughness by image analysis. Forest Products Journal 1987;37(6):34–40. [9] Funck JW, Forrer JB, Butler DA, Bruner CC, Maristany AG. Measuring surface roughness of wood: a comparison of laser scatter and stylus tracing approaches. Proc. of the Soc. of PhotoOptical Instrumentation Engineers, Bellingham, Washington 1992;1821:173–83. [10] Stumbo DA. Surface texture, measuring methods. Forest Products Journal 1963;12(7):299–303. [11] Hiziroglu S. Surface roughness analysis of wood composites: a stylus method. Forest Products Journal 1996;46(7/8):67–72. [12] Hiziroglu S, Suchsland O. Linear expansion and surface stability of particleboard. Forest Products Journal 1993;43(4):31–4. [13] Peter CC, Cumming JD. Measuring wood surface smoothness: a review. Forest Product Journal 1970;20(12):40–3. [14] Ostman BAL. Surface roughness of wood-based panels after aging. Forest Products Journal 1983;33(7/8):35–42. [15] ANSI. Surface texture (surface roughness, waviness, and lay) B46.1. New York: The American Society of Mechanical Engineers; 1985 43p. [16] Mummery L. Surface texture analysis. The handbook. Muhlhausen, Germany: Hommelwerke; 1993 106p. [17] Hoadley B. Identifying wood. 1990. Newton: The Taunton Press Inc.; 1990 CT 06740.
Building and Environment 41 (2006) 1074–1078 www.elsevier.com/locate/buildenv
Effect of machining on surface roughness of wood Murat Kilica,, Salim Hiziroglub, Erol Burdurlua a
Department of Wood Products Industrial Engineering, Hacettepe University Ankara, Turkey Department of Forestry, 303-G Agricultural Hall, Oklahoma State University, Stillwater, OK 74078, USA
b
Received 9 July 2004; received in revised form 22 April 2005; accepted 3 May 2005
Abstract The objective of this study is to evaluate effect of various machining techniques on the surface roughness of beech (Fagus orientalis) and aspen (Populus tremula) lumber. Surface characteristics of sawn, planed, and sanded samples of both species were determined employing a stylus type profilometer. Average roughness (Ra ), mean peak-to-valley height (Rz ), core roughness depth (Rk ), reduced peak height (Rpk ), and reduced valley depth (Rvk ) roughness parameters were used to determine surface characteristics of the samples. Based on the results of statistical analysis, measurements taken from the surface in tangential and radial directions of both species did not result in significant difference at a 95% confidence level. However, significant statistical difference was found between surface characteristics of aspen and beech samples, machined with four different ways in both grain orientations. This study suggests that stylus method can be successfully used to evaluate and distinguish variations on the surface of wood, due to grain orientation and planning and sanding. Data generated in this study can be used as a quality control tool for further processes such as finishing or gluing of wood from two species. r 2005 Elsevier Ltd. All rights reserved. Keywords: Surface roughness; Beech; Aspen; Sawn solid wood; Sanding
1. Introduction Surface quality of solid wood products is one of the most important properties influencing further manufacturing processes such as finishing or strength of adhesive joint. Laminated lumber with smoother surfaces will have better glueline resulting in higher strength properties. Surface roughness of wood can be affected by various factors such as annual ring variation, wood density, cell structure, and latewood/earlywood ratio. Type of machining used during production, raw material characteristics of work piece or a combination of both these parameters are responsible for surface quality of the final products and in determining its cost. Increased cutting speed or rpm results in an improved surface quality of wood products [1–3]. Planed surface Corresponding author.
E-mail addresses: [email protected] (M. Kilic), [email protected] (S. Hiziroglu). 0360-1323/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2005.05.008
characteristics of solid wood is a function of machining quality, which is directly related to knife marks per cm and not by cutterhead speed alone [4,5]. Sandmarks are also important parameters influencing the quality of the surface as a function of grit size and any variation from a certain expected degree of surface quality of wood will result in cost increase and waste of raw material. Surface irregularities on solid wood traditionally are not recognized as much as for other engineered surfaced materials. Although the surface roughness of wood can readily be determined in technical terms, given a representative or numerical reading of the surface topography no accepted standard method has been established for this purpose Several methods are available but have not found widespread use in the industry. Stylus, optical profilometer, image analyses techniques using a video camera, pneumatic, ultrasonic, and microscopy are some of the methods used to evaluate surface roughness of wood products [6–10]. Each of them has some disadvantages and some
ARTICLE IN PRESS M. Kilic et al. / Building and Environment 41 (2006) 1074–1078
disadvantages over each other. Stylus method has been used to determine surface roughness of solid wood and wood composites in the past studies [11–14]. One of the main advantages of the stylus method is to have actual profile of the surface and standard numerical roughness parameters, which can be calculated from the profile. Any kind of irregularities and magnitude of roughness on a surface can be objectively quantified by this method. Therefore, in this study a fine stylus method was employed to determine surface roughness of machined wood samples prepared from two species.
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with a maximum width capacity of 60 cm, feed speed of 8 m/min, revolution of 6000 rpm, and nose width of 40 mm. The planes cutterhead had three knifes. A set of four samples was sanded on a drum-type sander using 60- and 80-grits sandpaper. Each sample was run once through the sander using a sanding speed of 22 m/min and sanding pressure of 6 kg/cm2. Table 1 shows sampling schedule. A schematic representation of Rk, Rvk, and Rpk roughness parameters is illustrated in Fig. 2. Once all machining processes were completed, the samples were conditioned in a computer-controlled climate chamber
2. Methods and material Ten trees were harvested for the experiments. Each tree was sawn on a portable sawmill with circular saw using live-sawing pattern. Saw diameter, number of tooth, kerf, revolution, and feed speed were 30 cm, 28, 0.32 cm, 6000 rpm, 6 m/min, respectively. Sixteen boards without any knots, defects, or any grain distortions were prepared for the tests. Average density of the samples were 0.70 g/cm3 for beech and 0.40 g/cm3 for aspen. Table 1 displays average diameter at breast height (dbh), age range, density, and sampling schedule for both species. The lumber was first air dried to 30–35% moisture content before they were dried in a laboratory type kiln to 10% target moisture content. Dried lumber was trimmed to 150 cm long and 15 cm wide and 2 cm thick samples with tangential (flatsawn) and radial grain (quarter sawn) orientations for the surface roughness measurements. Sawn, planed, and sanded surfaces of the samples with two grain orientations were used for the experiments. The test design considered surface characteristics of sawn, planed, and sanded with 60- and 80grit sandpaper small lumber. Each machining was carried out for tangential and radial grain directions of both beech and aspen as illustrated in Fig. 1. Four samples were selected for each machining application. The samples were planed using a laboratory-type planer
Fig. 1. Schematics of the tangential and radial surfaces. (not scaled).
Fig. 2. Definitions of Rk , Rvk , and Rpk parameters [16].
Table 1 Sampling schedule Tree number
Species and density (g/cm3)
DBH (cm)
Age (yr)
Number of sample
Number of surface measurement Radial
Tangential
1 2 3 4 5
Beech 0.70
35 38 35 30 34
140 142 143 126 149
16 16 16 16 16
20 20 20 20 20
20 20 20 20 20
1 2 3 4 5
Aspen 0.40
50 45 44 35 50
20 20 21 22 20
16 16 16 16 16
20 20 20 20 20
20 20 20 20 20
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Fig. 3. Surface profilometer used in this study.
with a temperature of 20 1C and relative humidity of 65% for 2 weeks prior to the tests. A fine stylus-type Mitutoya Surftest SJ-30 equipment consisting of the main unit and the pick-up was used to evaluate surface characteristics of the samples (Fig. 3). The pick-up has a skid-type diamond stylus with 901 tip angle and with a 5 mm tip radius. The stylus traverses the surface at a constant speed of 1 mm/s over 12 mm tracing length converting vertical displacement of the stylus into an electrical signal. A representation of surface can be obtained in the form of a graph. Fig. 4 shows typical surface roughness profiles of tangential beech sample machined with a different equipment. The equipment was checked every 100–120 measurements by using a standard reference plate with an average roughness (Ra ) of 3.02 and 0.48 mm. The device uses a digital filtering to separate the surface profile into two profiles, waviness and roughness profiles. A cut-off length of 3 mm, a parameter that differentiates roughness and waviness profiles from each other, was used for the measurement. Five roughness parameters, average roughness (Ra ), mean peak-to-valley height (Rz ), core roughness depth (Rk ), reduced peak height (Rpk ), and reduced valley depth (Rvk ) were used to analyze quantitatively surface quality of the samples. Ra and Rz are the most commonly used parameters in stylus method. In addition to these two parameters, Rk family parameters were also used to get a more detailed information about the surfaces of machined samples. Ra and Rz parameters are discussed in the previous studies [11,15,16]. However, description of Rk , Rvk , and Rpk are illustrated in Fig. 2.
3. Results Results of the surface roughness values of machined samples are presented in Tables 2 and 3 and Figs. 5 and
Fig. 4. Typical surface profiles of machined samples of beech in tangential grain orientation.
6. Based on statistical analysis, no significant difference was observed between surface roughness characteristics of tangential and radial machined surfaces of beech and aspen samples at a 95% confidence level. For example average roughness values of planed tangential and radial samples of aspen had 7.05 and 7.36 mm, respectively. The difference between two values as a function of grain orientation is only 4.3%. Sanded surfaces of both species resulted in lower values of above differences, ranging from 2.2% to 4.3%. Sawn surfaces of two different species had larger differences of Ra values due to less homogeneous surface as compared to those of both planed and sanded samples. Rz and Rk parameters also followed this trend. In general when roughness parameters of two species machined differently were compared to each other, significant differences were determined at a 95% confidence level. Beech had Ra values of 11.05, 7.90, 8.20 and 5.80 mm in tangential direction for sawn, planed, 60-grits sanded and 80-grit sanded samples, respectively. On the other hand aspen had 10.7, 7.05, 6.68, and 4.63 mm, for the above parameters which are significantly lower than those of beech. This finding can be related to the anatomical structure of beech [17]. Although both species are diffuse porous, pores and rays of beech are larger and more
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Table 2 Average roughness of aspen samples Roughness parameters (mm)
Sawn surface Tangential
Planed surface Radial
Sanded surface 60-grit
Sanded surface 80-grit
Tangential
Radial
Tangential
Radial
Tangential
Radial
Ra
10.7 (1.28)
13.26 (1.54)
7.05 (1.16)
7.36 (0.60)
6.68 (0.37)
6.99 (0.78)
4.63 (0.63)
4.50 (0.26)
Rz
84.6 (13.99)
94.74 (12.71)
61.62 (8.51)
66.80 (7.38)
58.77 (7.49)
67.49 (8.42)
43.34 (9.10)
45.10 (8.9)
Rk
25.35 (3.05)
27.55 (3.43)
20.24 (3.29)
21.07 (1.91)
21.11 (1.47)
23.54 (1.50)
13.96 (1.00)
13.48 (0.69)
Rpk
10.57 (1.51)
13.13 (1.85)
7.12 (1.08)
8.80 (1.59)
7.27 (1.16)
8.16 (1.24)
4.69 (0.56)
5.45 (0.75)
Rvk
18.5 (3.89)
25.69 (7.52)
16.19 (6.8)
14.9 (3.02)
12.60 (1.38)
13.77 (1.53)
7.34 (0.63)
8.12 (0.71)
Numbers in parentheses are standard deviations.
Table 3 Average roughness of beech samples Roughness parameters (mm)
Sawn surface Tangential
Planed surface Radial
Tangential
Radial
Sanded surface 60-grit
Sanded surface 80-grit
Tangential
Tangential
Radial
Radial
Ra
11.05 (2.6)
12.77 (3.7)
7.90 (0.57)
8.90 (0.85)
8.20 (0.75)
6.90 (0.70)
5.80 (0.52)
5.63 (0.54)
Rz
100.10 (21.60)
101.74 (17.83)
63.45 (11.10)
69.60 (9.00)
68.33 (12.06)
74.24 (12.50)
59.10 (9.38)
52.81 (10.59)
Rk
27.55 (3.43)
33.59 (8.55)
12.94 (1.99)
17.24 (2.45)
22.69 (2.70)
24.91 (2.03)
16.26 (1.13)
18.30 (1.41)
Rpk
13.13 (1.85)
13.65 (2.15)
7.58 (1.33)
8.85 (1.06)
8.22 (1.08)
9.01 (1.30)
6.67 (1.06)
6.39 (1.07)
Rvk
25.69 (7.52)
28.34 (4.66)
16.10 (2.61)
19.41 (4.61)
16.88 (1.89)
14.40 (1.63)
10.58 (0.92)
10.77 (1.22)
Numbers in parentheses are standard deviations.
Fig. 5. Average values of Ra , Rk , and Rz parameters of aspen samples.
Fig. 6. Average values of Ra , Rk , and Rz parameters of beech samples.
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noticeable as compared to those of aspen. Therefore, aspen resulted in lower values of roughness parameters indicating smoother surfaces in both radial and tangential grain orientations than those of beech. The differences in roughness values between two species were more prominent in the case of Rz and Rk parameters which also had a similar trend. Although Rpk and Rvk did not show as much difference as other parameters used in the study for aspen and beech, they had similar trends with Ra , Rz and Rk . As can be seen Fig. 2 Rpk and Rvk parameters are related to peaks and valleys of a surface. In a previous study, both parameters were used successfully to evaluate surface roughness of wood composites [11]. However, they might not be very useful to distinguish surface characteristics of solid wood due to its non-uniform surface. Based on the Ra , Rz and, Rk values determined from the surface of both species, roughness of the samples significantly improved with increasing grit size of sand paper as can be observed from Tables 2 and 3. It appears that five roughness parameters can be used to evaluate surface roughness characteristics of solid wood surfaces, machined with different methods according to the findings in this work. It should be noted that Rpk and Rvk are not as stable as the other three parameters in the case of sawn and planed surface. However if the surface is sanded, both parameters can also be accurately employed to identify the surface characteristics of machined solid wood.
4. Conclusion In this work, effect of various machining of beech and aspen lumber on their surface roughness characteristics was investigated. In the light of preliminary results of this study, a stylus method can accurately be used to evaluate surface roughness of machined samples of both species. It is suggested, in further studies to consider more than one grit size of sandpaper in order to attain a better understanding of the effect of sanding on board surfaces. Surface roughness of the samples exposed to different relative humidity levels and other machining
properties of such species could be evaluated to provide an initial data for finishing applications.
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