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UNIVERSITI PUTRA MALAYSIA

CHARACTERIZATION OF MACHINING DEFECTS IN WOOD

PLANING OPERATION

SAEID REZA FARROKHPAYAM

FH 2010 2

CHARACTERIZATION OF MACHINING DEFECTS IN WOOD PLANING

OPERATION

By


Thesis Submitted to the School of Graduated Studies, Universiti Putra Malaysia,

in Fulfilment of the Requirements for the Degree of Doctor of Philosophy

April 2010

ii

Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfilment

of the requirement for the degree of Doctor of Philosophy

CHARACTERIZATION OF MACHINING DEFECTS IN WOOD PLANING

OPERATION

By


April 2010

Chairman: Jegatheswaran Ratnasingam, PhD

Faculty: Forestry

The objective of this study was to evaluate the effect of some machining factors on

the machinability of selected Malaysian hardwoods and to quantify the major types

of machining defects in the planing operation. The study aims to reveal the

relationship between the types of surface defects generated after planing with the

variable factors. It also studies the sanding process as an indicator to reveal loss

thickness (yield) after the planing process on defective planks.

For this research, three wood species, Rubberwood (Hevea brasiliensis), Melunak

(Pentace spp) and Dark Red Meranti (Shorea spp) were chosen based on their

machining characteristics, commercial position in the local and global market, and

their usage as a solid material in the furniture industry. 50 clear samples of each

wood species, for each treatment, in a uniform moisture content (10%), of the final

size of 19 by 102 × 910 mm, were machined by a planer unit, Weinig Unimat 23E

using only the bottom spindle of the machine. The cutterhead had 4 knives with a

iii

diameter 120 mm, rotating at 6000 revolutions per minute (RPM). The depth of cut

(0.8, 1.6 and 2.4 mm) and feed rate (8, 12 and 16 m/min) were the experimental

variables, while all other factors were kept constant. The surface quality of the

individual sample was examined both visually, and sense of tactile to classify the

samples into five grades based on the amount and severity of defects present, as

given in the standard (ASTM, D 1666 – 87).

In every instance, 60 percent or more of the samples were defect-free, and the

slightly defective pieces outnumber the more seriously defective ones, by a wide

margin. An in-depth analysis of the samples surfaces, machined under the three

parameters of processing, found that among these three factors, depth of cut had the

most significant effect on torn and fuzzy grain. This research also revealed that the

combination of feed rate, depth of cut and wood species used had no significant

effect on the surface quality of samples.

This research showed that the planing operation as a part of wood products

manufacturing can influence the quantity or volume of product parts manufactured

from a given amount of lumber and labor by affecting the processing yield. The

proper machining factors in relation to the wood species used decreases the surface

defects. These defects results in increasing labor cost, machining cost and loss of

wood material. Therefore, the optimal condition for planing operation of the three

Malaysian woods to produce the best yield was realized at the minimum of depth of

cut, and maximum cutting marks number per millimetre.

iv

Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia

sebagai memenuhi keperluan untuk ijazah Doctor Falsafah

SIFAT KECACATAN-KECACATAN PEMESINAN DI DALAM OPERASI

PENGETAMAN KAYU

Oleh


April 2010

Pengerusi: Jegatheswaran Ratnasingam, PhD

Fakulti: Perhutanan

Objektif penyelidikan ini adalah untuk mengkaji kesan beberapa faktor pemesinan

spesies kayu keras Malaysia terpilih dan mengesan jenis-jenis kecacatan major

akibat pemesinan pada proses pengetaman. Penyelidikan ini juga mengkaji perkaitan

di antara jenis kecacatan permukaan selepas proses pengetaman dengan beberapa

jenis factor, serta mengkaji proses pelicinan sebagai indikator untuk mengemukakan

kehilangan hasil selepas proses pengetaman pada permukaan sampel-sampel yang

cacat.

Kayu Getah (Hevea brasiliensis), Melunak (Pentace spp) dan Meranti Merah Tua

(Shorea spp) adalah spesies kayu yang telah digunakan di dalam penyelidikan ini.

Pemilihan spesies kayu-kayu ini adalah berdasarkaws kepada sifat-sifat pemesinan,

kedudukan komersil di pasaran tempatan dan luar negara dan penggunaanya sebagai

bahan mentah utama di dalam industri perabot. Sebanyak 50 sampel bagi setiap

spesies kayu ini telah diuji. Sampel-sampel ini yang mempunyai kadar kandungan

air (10%), dan bersaiz 19mm X 102mm X 910m, telah dimesin dengan

v

menggunakan unit mesin pengetam, Weinig Unimat 23E, dengan hanya

menggunakan spindal bawah yang mempunyai 4 mata pisau, berdiameter 120 mm,

pada kelajuan 6000 revolusi per minit (rpm). Kedalaman pemotongan adalah 0.8, 1.6

dan 2.4 mm dan kelajaam pemotongan adalah 8, 12 dan 16 m/min, dimana kedua-

duanya faktor ini merupakan factor berubah, manakala faktor-faktor yanag lain

adalah dikekalkan seragam. Kualiti permukaan setiap sampel telah diperiksa dengan

mata kasar dan secara fizikal, untuk diklasifikasikan kepada lima gred bergantung

kepada jumlah dan jenis kecacatan yang terhasil, seperti yang tertera dalam standard

ASTM, D 1666 – 87.

Secara umum, 60 peratus atau lebih daripada sampel-sampel didapati bebas dari

kecacatan, dan hanya sebilangan sampel-sampel yang mempunyai kecacatan yang

sederhana, manakala sampel-sampel yang mempunyai kecacatan yang sangat tinggi

adalah sangat jarang.

Analisis yang mendalam pada permukaan sampel-sampel yang telah dimesin dengan

menggunakan tiga proses parameter tersebut menunjukkan bahawa hanya faktor

kedalaman pemotongan mempunyai kesan yang tinggi pada ira koyak dan ira serabut

, berbanding dengan faktor-faktor yang lain.

Selain itu, penyelidikan ini turut mendedahkan bahawa kombinasi di antara kadar

pemotongan, kedalaman pemotongan dan spesies kayu yang digunakan tidak

mempunyai kesan ketara terhadap kualiti permukaan sampel-sampel. Penyelidikan

ini menunjukkan bahawa operasi pengetaman adalah sebahagian daripada proses

pembuatan produk kayu yang mempengaruhi kuantiti atau jumlah produk yang

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dihasilkan, selain daripada jumlah kayu dan tenaga kerja melalui hasil yang

diperolehi. Faktor pemesinan yang bersesuaian dengan spesies kayu yang digunakan

akan mengurangkan kecacatan pada kualiti permukaan. Kecacatan ini akan

menyebabkan peningkatan tenaga kerja, peningkatan kos pemesinan dan kerugian

kayu. Keadaan optimum operasi pengetaman bagi tiga jenis kayu Malaysia ini, untuk

mendapatkan hasil yang terbaik boleh dicapai pada kedalaman pemotongan yang

minimum dan jumlah pemotongan per mm yang maksimum.

vii

ACKNOWLEDGEMENTS

Obviously a project like this requires the assistance (and understanding) of many

people. I want to thank all of them.

I would like to thank Associate Professor Dr. Jegatheswaran Ratnasingam, my

supervisor, for mentoring me thoroughly during this research project.

I would also like to thank members of my supervisory committee, Associate

Professor Dr. Edi Suhaimi Bakar, Associate Professor Dr. Tang Sai Hong, and Ir.

Fuad Abas, for their advice and support.

Acknowledgement is given to the Forestry Faculty, Universiti Putra Malaysia, Wood

Industry Skills Development Centre (WISDEC) and Zabol University for providing

me with the opportunity to conduct my research.

And finally, a word of thanks to my wife, Maryam for going along with me.

viii

I certify that a Thesis Examination Committee has met on 14 April 2010 to conduct

the final examination of Saeid Reza Farrokhpayam on his thesis entitled

‖Characterization of Machining Defects in the Wood Planing Operation‖ in

accordance with the Universities and University Colleges Act 1971 and the

Constitution of the Universiti Putra Malaysia [P.U.(A) 106] 15 March 1988. The

Committee recommends that the student be awarded the Doctor of Philosophy.

Members of the Thesis Examination Committee were as follows:

Name of Chairperson, PhD

Professor Mohd Hamami Shahri

Faculty of Forestry

Universiti Putra Malaysia

(Chairman)

Name of Examiner 1, PhD

Professor Nabuchi Tadashi

Faculty of Forestry


(Internal Examiner)

Name of Examiner 2, PhD

Dr. H‘ng Paik San

Faculty of Forestry


(Internal Examiner)

Name of External Examiner, PhD

Associate Professor Barbara Ozarska

Department of Forest and Ecosystem Science

The University of Melbourne

Australia

(External Examiner)

________________________

BUJANG BIN KIM HUAT, PhD

Professor and Deputy Dean

School of Graduate Studies


Date:

ix

This thesis was submitted to the Senate of Universiti Putra Malaysia and has been

accepted as fulfilment of the requirement for the degree of Doctor of Philosophy. The

members of the Supervisory Committee were as follows:

Jegatheswaran Ratnasingam, PhD

Associate Professor

Faculty of Forestry


(Chairman)

Edi Suhaimi Bakar, PhD Associate Professor

Faculty of Forestry


(Member)

Tang Sai Hong, PhD

Associate Professor

Faculty of Engineering


(Member)

_______________________________

HASANAH MOHD GHAZALI, PhD

Professor and Dean

School of Graduate Studies


Date: 15 July 2010

x

DECLARATION

I declare that that thesis is based on my original work expect for quotations and

citations, which have been duly acknowledged. I also declare that it has not been

previously, and is not concurrently, submitted for any other degree at Universiti

Putra Malaysia or at any other institutions.

_______________________________


Date: 1 May 2010

xi

TABLE OF CONTENTS

Page

ABSTRACT ii

ABSTRAK iv

ACKNOWLEDGEMENTS vii

APPROVAL viii

DECLARATION x

LIST OF TABLES xiv

LIST OD FIGURES xvi

LIST OF ABBREVIATIONS xx

CHAPTER

1 INTRODUCTION 1

2 REVIEW OF LITERATURE 9

2.1 Wood Machining Processes and Value-Added Wood

Products Industry 9

2.2 Overview of the Wood Machining Process 12

2.2.1 Orthogonal Cutting 13

2.2.2 Peripheral Milling 20

2.3 The Planing Operation and Its Importance 25

2.3.1 The History and Evolution of the Planer 27

2.3.2 Surface Quality of Planed Wood 29

2.4 Factors Affecting the Planing Operation 33

2.4.1 Workpiece Factors 34

2.4.2 Tool Factors 41

2.4.3 Machine Factors 44

2.5 Machines and Tools 48

2.6 Machining Defects and Its Economics Effects 52

2.6.1 Rough Mill Yield 53

2.6.2 Cost 57

2.7 Common Types of Wood Machining Defects and Their

Causes 59

2.7.1 Fuzzy Grain 60

2.7.2 Raised Grain 63

2.7.3 Chipped Grain 66

2.7.4 Chip Mark (Chip Print or Chip Bruising) 68

2.8 Wood Species 71

2.8.1 Rubberwood 72

2.8.2 Dark Red Meranti 79

2.8.3 Melunak 87

3 RESEARCH METHOD 95

3.1 Introduction 95

3.2 Scope of Tests and Research 96

3.3 Materials 99

xii

3.4 Sampling in Experiments 100

3.4.1 Planing Test 101

3.4.2 Sanding Test 112

3.5 Equipments 115

3.5.1 Planing Machine 116

3.5.2 Sanding Machine 118

3.6 Data Acquisition 119

3.6.1 Evaluation of Planing Defects 120

3.6.2 Evaluation of Samples after Sanding 124

3.7 Statistical Analysis 127

4 RESULTS AND DISCUSSION 133

4.1 Moisture Content and Density 133

4.2 Evaluation of Planing Test Results 134

4.2.1 Comparative Planing Properties Based on

Defect-Free Percentage 134

4.2.2 Comparative Averages of Defective Pieces Based

on Type of Defect 137

4.3 Frequency of Types of Defects Related to the Factors 140

4.3.1 Raised Grain Frequency in Different Species 141

4.3.2 Torn Grain Frequency in Different Species 143

4.3.3 Fuzzy Grain Frequency in Different Species 144

4.3.4 Chip Marks Frequency in Different Species 146

4.3.5 Raised Grain Frequency in Different Depth of Cut 148

4.3.6 Torn Grain Frequency in Different Depth of Cut 149

4.3.7 Fuzzy Grain Frequency at Different Depths of Cut 151

4.3.8 Chip Marks Frequency at Different Depth of Cut 153

4.3.9 Raised Grain Frequency at Different Feed Rate 154

4.3.10 Torn Grain Frequency at Different Feed Rate 156

4.3.11 Fuzzy Grain Frequency as the Different Feed Rates 158

4.3.12 Chip Marks Frequency at Different Feed Rate 159

4.4 Effects of Test Factors on Surface Quality 161

4.4.1 Main Effect of the Factors with Normal

Distribution on Surface defects 162

4.4.2 Main Effect of the Factors without Normal

Distribution on types of defects 166

4.4.3 Interaction Effect of Factors on types of defects 172

4.5 Relationship Description of Yield Loss and the factors

combinations 176

4.5.1 Depth of Cut and Feed Rate combinations on

Rubberwood 178


Dark Red Meranti 180


Melunak 182

4.5.4 Comparative Sanding Results for the Three

Wood Species 184

xiii

5 CONCLUSIONS AND FUTURE WORK 186

5.1 Conclusion 186

5.2 Future Work 189

REFERENCES 191

APPENDICES 202

BIODATA OF STUDENT 230

LIST OF PUBLICATIONS 231

xiv

LIST OF TABLES

Table Page

2.1 Machine – process classification 12

2.2 Differences characteristics between orthogonal and peripheral milling 25

2.3 Machine factors and tool wear 44

2.4 Mechanical and machining properties of Rubberwood 80

2.5 Mechanical and machining properties of Dark Red Meranti 85

2.6 Mechanical and machining properties of Melunak 92

3.1 Commercial names for the test wood species 100

3.2 Properties of the samples 103

3.3 The range of indicator weights 108

3.4 Machining condition for the planing 110

3.5 High Speed Steel tools composition 111

3.6 Technical information of moulder used in this research 116

3.7 Technical specifications of the sander used in this research 119

3.8 Data set showing scores given by researcher to the severity of defects on

specimen‘s surface 130

4.1 Physical properties of the samples 134

4.2 Occurrence of planing defects on the samples 135

4.3 Relative freedom from defects 136

4.4 Occurrence of planing defects types in treatment components 138

4.5 Frequency of raised grain in different species 141

4.6 Frequency of torn grain in different species 143

4.7 Frequency of fuzzy grain in different species 144

4.8 Frequency of chip marks in different species 147

xv

4.9 Frequency of raised grain in different depths of cut 148

4.10 Frequency of torn grain in different depths of cut 150

4.11 Frequency of fuzzy grain in different depths of cut 151

4.12 Frequency of chip marks in different depths of cut 153

4.13 Frequency of raised grain in different feed rates 155

4.14 Frequency of torn grain in different feed rates 156

4.15 Frequency of fuzzy grain in different feed rates 158

4.16 Frequency of chip marks in different feed rates 159

4.17 One-sample Kolmogorov-Smirnov test 161

4.18 Analysis variance results 162

4.19 Ranks of different wood species for type of defects 167

4.20 Ranks of different depths of cuts for type of defects 170

4.21 Ranks of different feed rates for type of defects 171

4.22 Means for combination of the feed rates and wood specie 173

4.23 Means for combination of depth of cuts and wood specie 173

4.24 Means for combination of depth of cuts and feed rates 174

4.25 Means for combination of depth of cuts, feed rates and wood species

used in this research 175

4.26 The result of the sanding test 177

4.27 Average loss thickness in sanding process on Rubberwood samples 179

4.28 Average loss thickness in sanding process on Meranti samples 181

4.29 Average loss thickness in sanding process on Melunak samples 183

xvi

LIST OF FIGURES

Figure Page

2.1 Approximate value increase of 1 board foot of lumber 11

2.2 Two basic forms of machining 12

2.3 Geometry of orthogonal cutting 14

2.4 Force nomenclature in orthogonal cutting 15

2.5 Actions of cutting tools in forming various types of chips in orthogonal

cutting of wood 18

2.6 Terminology applicable to peripheral-milling cutterhead 23

2.7 Cutting with and against the grain 39

2.8 Cutting direction in wood machining 40

2.9 Basic tool geometry 42

2.10 Effect of rake angle on the planing quality of wood species 43

2.11 Rotary machining process 50

2.12 Effective factors on productivity in wood machining processes 54

2.13 Example of fuzzy grain 60

2.14 Example of raised grain 64

2.15 Example of chipped grain 67

2.16 Example of chip mark 69

2.17 Rubberwood (Hevea brasiliensis) 72

2.18 Hevea brasiliensis - Transverse section 77

2.19 Hevea brasiliensis - Radial section 78

2.20 Hevea brasiliensis - Tangential section 79

2.21 Dark Red Meranti (Shorea curtisii) 81

xvii

2.22 Shorea curtisii – Transverse section 84

2.23 Shorea curtisii – Tangential section 87

2.24 Shorea curtisii – Radial section 88

2.25 Melunak (Pentace triptera) 89

2.26 Pentace triptera - Transverse section 91

2.27 Pentace triptera - Tangential section 94

2.28 Pentace triptera - Radial section 94

3.1 Flow line for planing and sanding tests 98

3.2 Overview of research 99

3.3 Sample of the marking of sawn timber 102

3.4 Diagram for sawing Lumber samples into smaller samples for

planing tests 104

3.5 Permissible number of cuts with depth of cut 0.8 on a 19 mm

thickness board 106

3.6 Diagram for total number of samples for planing test 106

3.7 Planing the samples with bottom spindle 109

3.8 Planing samples randomly and continuously 111

3.9 Diagram to choose samples for sanding test 113

3.10 The grain belts configuration used in this study 114

3.11 Defect removing by sanding process 115

3.12 Conventional planing and moulding machine 117

3.13 Wide-belt Sander machine 118

3.14 Planing grades Nos. 1 and 5 121

3.15 Fuzzy grain in Rubberwood, grades Nos. 2, 3, and 4 122

3.16 Torn grain in Melunak, grades Nos. 2, 3, and 4 123

3.17 Chip mark in Dark Red Meranti, grades Nos. 2, 3, and 4 124

xviii

3.18 Raised grain in Rubberwood, grades Nos. 2, 3, and 4 125

3.19 A sample of data sheet to record planing test result 126

4.1 Effect of depth of cut and feed rate on percentage of defect-free samples 137

4.2 Averages of different types of defects 139

4.3 Percentage of types of defects in different treatment components 140

4.4 Various raised grain degrees in three wood species 142

4.5 Various raised grain degrees in three wood species 144

4.6 Various fuzzy grain degrees in three wood species 146

4.7 Various chip marks degrees in three wood species 147

4.8 Various raised grain degrees in three depths of cut 149

4.9 Various torn grain degrees in three depths of cut 150

4.10 Various fuzzy grain degrees in three depths of cut 152

4.11 Various chip marks degrees in three depths of cut 154

4.12 Various raised grain degrees in three feed rates 155

4.13 Various torn grain degrees in three feed rates 157

4.14 Various fuzzy grain degrees in three feed rates 159

4.15 Various chip marks degrees in three feed rates 160

4.16 Mean comparison of total error between different depths of cuts levels 164

4.17 Mean comparison of total error between different feed rates levels 164

4.18 Mean comparison of total error between different wood species 165

4.19 Fuzzy grain on Rubberwood a) before sanding, b) after sanding 179

4.20 Effect of depth of cut and feed rate on loss thickness for Rubberwood 180

4.21 Chip marks on Meranti a) before sanding, b) after sanding 182

4.22 Effect of depth of cut and feed rate on loss thickness for Meranti 182

4.23 Torn grain on Melunak a) before sanding, b) after sanding 184

xix

4.24 Effect of depth of cut and feed rate on loss thickness for Melunak 184

4.25 Comparison of loss thickness on three wood species in planing process 185

xx

LIST OF ABBREVIATIONS

2D Two Dimensions

3D Three Dimensions

ANOVA Analysis of Variance

ASME The American Society of Mechanical Engineers

ASTM The American Society for Testing and Materials

CBP Cement Bonded Particleboard

cm Centimeter

CRD Complete Randomized Design

DIN The German Institute for Standardization

DMRT Duncan Multiple Range Test

DRM Dark Red Meranti

FSP Fiber Saturation Point

HSS High Speed Steel

ISO The International Organization for Standardization

JIS Japanese Industrial Standards

kg Kilogram

KS Kolmogorov-Smirnove

kW Kilowatt

LDS Laser Displacement Sensor

m Meter

Mbf One thousand board feet

MDF Medium Density Fiber

http://en.wikipedia.org/wiki/Japanese_Industrial_Standards

http://en.wikipedia.org/wiki/Board_foot

xxi

min Minute

mm Millimeter

MOE Modulus of Elasticity

MOR Modulus of Rupture

MPa Mega Pascal

MTC Malaysian Timber Council

RPM Revolutions Per Minute

N Newton

s Second

USD The United States dollar

α Rake Angle

β Sharpness Angle

γ Clearance Angle

µm Micrometer

CHAPTER I

INTRODUCTION

Wood is one of the most versatile materials known to humans. Wood is used to

produce a diverse range of products and services that the society relies upon for

many activities. From building houses to manufacturing furniture to printing books,

wood has become a key resource. In this context, the forestry and wood industry is

still one of the major engines of the Malaysian economy. Wood industry exports in

Malaysia during 2007 rose nearly 60% to USD6 billion, compared with the figures

from 10 years ago. Furniture exports stood at USD1.9 billion, and the furniture were

exported to more than 160 countries, with the largest market, the US, receiving about

USD2 billion worth of exports (Pillay, 2008).

Wood machining processes have gained great importance in recent years due to the

short supply of wood, and the increasing environmental awareness among users and

manufacturers. Wood machining techniques that are in use emphasizes on the

maximum utilization of wood, especially to produce finished products, which helps

in reducing wastage. As the world becomes more attuned to the competing

requirements of resource sustainability, industrial economics and the environment is

better off with better utilization of wood resources. One of the keys to a more

effective use of wood is the development of a vigorous secondary manufacturing,

sometimes called value added industry, which results in finished products. The

success of secondary manufacturing of wood products is dependent on effective

machining processes.

2

Usually, the outcomes of wood machining processes are heavily influenced by

workpiece surface quality considerations. Tool sharpness requirements as well as

machine feed and speed parameters often influence the workpiece surface quality.

Research on surface quality measurement technology is being aimed at identifying

and quantifying defects associated with the machining processes. The degree of

roughness of a surface often affects the way the material itself is used. In general,

surface irregularities can cause misalignment and part malfunctions, excessive

loading over small areas, friction and lubrication problems, general finish and

reflectivity problems, as well as other catastrophic failures.

Although surface quality for wood products has been a key issue since woodworking

first began, the level of precision required does not approach the level that is found

in metal working. This has been due, in part, to wood's inherent dimensional

instabilities. The other main reason is that many common uses for wood did not

require exceptional surface finishes, as compared to many metal applications. The

evaluation of surface irregularities in wood is, however, important to assure proper

fit of machined parts for gluing, acceptable surface finish for furniture, and as a

methodology to evaluate the accuracy of the manufacturing process.

The last reason has become even more important in recent years due to the increased

cost of raw materials, the increased production costs, and the higher production

speeds available. Any deviations in expected product quality can quickly cause

significant economic losses. There has also been a trend toward tighter tolerances for

many forest products industries. An example of this would be the lamination of

wood, or wood-based products with plastic films or ultra thin veneers. Even the

3

slightest irregularity on the surface will show up through the top laminate (Lemaster,

2004).

In wood products manufacturing, the quality of the wood surface requires much

more attention, since wood has several unique characteristics such as complex

natural composites, visco-elastics, hygroscopic, anisotropic, fibrous, porous and

inherent natural defects. These characteristics, combined with the machine variables,

complicate the production of machined wood surface with an acceptable quality.

Planing and moulding is a complex and subtle machining process that has much in

common with milling and grinding of metals. These metal machining processes,

have however been widely studied. In contrast to the vast amount of research and

publication for metal machining, the planing of wood has received little attention

(Jackson et al., 2001).

Determination of surface quality of wood is a complex process influenced by the

heterogeneous structure of the wood, kinematics of the cutting process, and

machining conditions. Machining properties of woods are directly related to

machining defects such as fuzzy grain, chip mark, raised grain, chipped grain, etc.

(Davis, 1962; Hernandez et al., 2001; Malkocoglu et al., 2006). Wood materials

exhibit a wide range of defects due to biological as well as machining-related causes.

In some cases there is no clear distinction between biological causes of poor surface

quality as opposed to machining related causes. An example of this is the

phenomenon of raised grain; wherein the growth rings of the wood structure are

elevated from the normal wood plane, creating a series of raised areas (lines) on the

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