applied sciences

Article Comparative Study on CNC Routing Methods for Transposing a Traditional Motif from Romanian Textile Heritage into Furniture Decoration

Antonela Lungu , Mihai Ispas, Lumini¸ta-MariaBrenci, Sergiu Răcă¸sanand Camelia Co¸sereanu*

Faculty of Furniture Design and Wood Engineering, Transilvania University of Brasov, B-dul Eroilor, nr. 29, 500036 Brasov, Romania; [email protected] (A.L.); [email protected] (M.I.); [email protected] (L.-M.B.); [email protected] (S.R.) * Correspondence: [email protected]

Abstract: This paper presents experimental research on the Computer (CNC) routing of a traditional motif collected from ¸Tara Bârsei (Transylvania region) using two methods, namely, engraving (Engrave) and carving (V-Carve). The analysis of the CNC processes includes the calculation of the path lengths, an assessment of the processing time and wood mass loss, and an evaluation of the tool wearing by investigating the tool cutting edge on a Stereo Microscope NIKON SMZ 18 before and after processing the ornament on wood. An aesthetic evaluation of the ornament routed on wood, using both the engraving and carving methods, is also conducted, whilst a microscopic analysis of the processed areas highlights the defects that occurred on the wood surface depending on the tool path.   Keywords: CNC router; textile heritage; stereo-microscopy investigation; traditional motif Citation: Lungu, A.; Ispas, M.; Brenci, L.-M.; R˘ac˘a¸san,S.; Co¸sereanu, C. Comparative Study on Wood CNC Routing Methods for Transposing a 1. Introduction Traditional Motif from Romanian Textile Heritage into Furniture As in many other cultures in the world, the textile heritage from Romania is proof of Decoration. Appl. Sci. 2021, 11, 6713. cultural expression, and it has to be well preserved for the next generations. Unfortunately, https://doi.org/10.3390/app11156713 the objects in this category may be subjected to degradation risks due to their advanced age and sometimes improper conservation [1]. Actual digital technologies supported by Academic Editor: Giuseppe Lazzara graphics programs, computer-aided design (CAD), and computer-aided manufacturing (CAM) allow for the replication and transfer of valuable motifs found on old textiles Received: 21 June 2021 onto modern ones [2], thus contributing to their preservation. In light of the Framework Accepted: 20 July 2021 Convention on the Value of Cultural Heritage for Society (Faro Convention), a “New Published: 22 July 2021 heritage” is about to rise up, and it pertains to the use of the past in the present and its renewal into the future [3]. Taking advantage of modern technologies, creative industries, Publisher’s Note: MDPI stays neutral such as fashion, ceramics, the textile industry, the furniture industry, and others, are able to with regard to jurisdictional claims in transpose old traditional motifs onto new objects, preserving them in new forms. published maps and institutional affil- Computerized Numerical Control (CNC) routers in the furniture industry offer the possi- iations. bility of decorations on the wood surface, importing the vector file made with graphic software, which renders the drawing of the original motif, or by converting 2D digital images into 3D representation through developed applications, such as Visual C++ software [4]. The sculpting process on a CNC router is based on optimization of the milling parameters, selection Copyright: © 2021 by the authors. of the right tool, and the processing method. The majority of scientific papers investigate Licensee MDPI, Basel, Switzerland. the quality of routed surfaces by measuring the roughness parameters [5–9] or by applying a This article is an open access article mathematical model to adjust the feed rate depending on the surface quality along with the distributed under the terms and cutting direction and species of wood [10], or genetic algorithms on CAM software [11]. The conditions of the Creative Commons spindle speed of 14,500 rpm and feed speed of 2 m/min for CNC routing and wood Attribution (CC BY) license (https:// had as low effect values for the roughness parameter Ra (average surface roughness measured creativecommons.org/licenses/by/ as the arithmetic averages of the absolute values for all deviations of peaks and ridges) for 4.0/).

Appl. Sci. 2021, 11, 6713. https://doi.org/10.3390/app11156713 https://www.mdpi.com/journal/applsci Appl. Sci. 2021, 11, 6713 2 of 12

a conventional way of cutting [5]. In the case of CNC milling of and wood, 10,000 rpm for spindle speed and 5 m/min for feed speed were recommended for a minimum value of Rz (the average maximum peak to valley of five consecutive sampling lengths within the measuring length) roughness parameter, whilst for wood, a feed speed of 7 m/min and spindle speed of 18,000 rpm were found to be optimal [6]. Minimum Ra and Rz values were obtained for a spindle speed of approx. 17,000 rpm and a feed speed of 2 m/min in the case of CNC milling of Cedar of Lebanon [7]. Numerous studies were conducted to evaluate the tool wear or the effect of tool wear on the machining process for various species of wood or wooden-based materials [12–17]. Tool wear has a great influence on the quality of the product, its accuracy, and productivity. The measurement of the cutting edge profile gives indications about the tool wear level. It can be performed automatically [12] or by chemical, microscopic, and hardness analysis of the cutting knife. Indirect methods can also be used, such as the measurement of the electrical current consumption or the measurement of the sound pressure during processing. Both are higher when the tool wear increases [13]. Measuring Ra and Rz roughness parameters after successive CNC milling of pine wood, it was determined that, for the anti-wear coated tools, the values of the roughness parameters are higher in the phase of initial wear than those of an uncoated tool, but with increased wear, the situation is reserved and the roughness parameters for coated tools decreased to lower values than the initial ones [14]. Research on the correlation between the tool wear and cutting forces in the machining process of the Aleppo pine have shown that the edge recession occurred at a cutting length of 850 m, with abrupt wear at about 200 m [17]. The research presented in this paper shows the process of transposing a traditional motif taken from the textile heritage originating from the SE region of Transylvania from

Romania (named T, ara Bârsei) on the wood surface, as decoration such as for furniture, using a three-axis CNC router for the milling process. Two methods of transposing the motif were applied: engraving (Engrave) and carving (V-Carve), using V-Grooving Router Bit tool with an angled tip of 90◦. Linux CNC version 2.7.0. software was used to simulate the machining process and the tool path for the two variants of the ornament. wood was used for the experiment, and twenty successive ornaments were machined and executed for each variant of the model. The wear of the tools was determined by scanning electron microcopy of the tool cutting edge before starting the CNC milling process and after the ornaments were processed twenty times both by engraving and carving. A visual evaluation of the processed ornaments was conducted from the aesthetic and qualitative points of view, and details of the areas where wood fuzziness occurred were highlighted by stereo-microcopy analysis.

2. Materials and Methods The traditional Romanian ornamentation is rich in geometric representations, charac- terized by a delicate refinement. The present research uses the plant motif from Figure1 for the experiment, which is originally stitched in a cross technique on the sleeve of a traditional woman’s blouse from the village of Bran, where Dracula’s castle is located. The ornamental composition, subjected to the laws of symmetry and alternation, contains the motif of the clover leaf, the “water wave” pattern, and the fir leaf. All traditional motifs in Romania have a symbolic value. Thus, the clover suggests the magic number three, which exists in many ritual practices and generally protects human life, and the four-leaf clover is considered to bring luck [18]. Flowing water means a crossing, a test, and thus represents the passage, the flow of life, and the flow of time [19]. The fir tree can be assimilated with the tree of life, which is the backbone of the world. It is present at weddings and funeral rituals, and when it is represented with seven rows of branches, those are the seven heavens [20]. This popular motif with symbolic value was collected as a picture from the particular owner of the original blouse (Figure1a) and then rendered in vector format using the professional vector graphics software CorelDRAW X17 (Figure1b). The file was Appl. Sci. 2021, 11, x FOR PEER REVIEW 3 of 12

Appl. Sci. 2021, 11, x FOR PEER REVIEW 3 of 12

Appl. Sci. 2021, 11, 6713 from the particular owner of the original blouse (Figure 1a) and then rendered in vector3 of 12 format using the professional vector graphics software CorelDRAW X17 (Figure 1b). The filefrom was the then particular imported owner in AutoCAD of the original LT 2017 blouse (Figure (Figure 1c) and 1a) transferred and then to rendered the 3-axis in CNC vector router,format ISEL using GFV the type, professional German production,vector graphi wicsth software a maximum CorelDRAW spindle speed X17 (Figureof 15,000 1b). rpm. The thenfile was imported then imported in AutoCAD in AutoCAD LT 2017 LT (Figure 20171 (Figurec) and transferred 1c) and transferred to the 3-axis to the CNC 3-axis router, CNC ISELrouter, GFV ISEL type, GFV German type, German production, production, with a maximumwith a maximum spindle spindle speed ofspeed 15,000 of 15,000 rpm. rpm.

(a) (b) (c)

Figure 1. Traditional (motifa) from Ţara Bârsei subjected to the present(b) research: (a) the picture of the textile(c) object, (b) the digital vector format drawing, and (c) the contour of the ornament used by the CNC router for milling the maple wood surface.FigureFigure 1. 1.Traditional Traditional motif motif from from ¸Tara Ţara Bâ rseiBârsei subjected subjected to the to presentthe present research: research: (a) the (a picture) the picture of the textileof the object,textile (object,b) the digital(b) the vectordigital format vector drawing,format drawing, and (c) the and contour (c) the ofcontour the ornament of the ornament used by the used CNC by routerthe CNC for router milling for the milling maple the wood maple surface. wood surface. The contour of the ornament (Figure 1c) was CNC machined in two ways: the first one wasThe the contour engraving of the method ornament (Engrave), (Figure for1c) which was CNC a constant machined depth in twoof the ways: cut at the 3 mm first wasone applied wasThe the contour to engraving both of closed the method ornament contours (Engrave), (Figure and open for1c) whichcontourswas CNC a constant of machined the drawing; depth in oftwo the the ways: second cut at the 3 one mmfirst waswasone the appliedwas carving the toengraving method both closed (V-Carve),method contours (Engrave), which and can open for be which contours applied a constant ofonly the for drawing; depth closed of contours, thethe secondcut at with 3 onemm variablewaswas theapplied depths carving to between both method closed 1 (V-Carve), mm contours to 3 mm which and for open can thebe surfacecontours applied and of only 3the mm for drawing; closedfor the contours,thecontour. second The with one othervariablewas processing the depthscarving betweenparameters method 1 (V-Carve), mm of the to 3 CNC mm which forrouter the can surfacewere be applied the and spindle 3 only mm speed forfor theclosed of contour. 15,000 contours, rpm The otherand with feedprocessingvariable speed depths of parameters 6 m/min. between of the1 mm CNC to router3 mm werefor the the surface spindle and speed 3 mm of 15,000for the rpm contour. and feed The speedotherTwenty processing of 6 m/min. maple parameters (Acer pseudoplatanus of the CNC L.) router wood were panels the withspindle dimensions speed of 15,000of 300 rpm mm and × 200feed mmTwenty speed × 11 mm,of maple 6 m/min. a moisture (Acer pseudoplatanus content of 11%,L.) and wood a mean panels density with dimensions of 615 kg/m of3 were 300 mmused× 3 for200 the mm Twentyexperiment.× 11 mm,maple Due a moisture(Acer to its pseudoplatanus homogeneous content of 11%, L.) structure wood and a mean panelsand color density with compared dimensions of 615 kg/m to other ofwere 300 species mm used × 3 offor200 wood, the mm experiment. maple × 11 mm, wood a Due moisture is recommended to its homogeneouscontent offor 11%, carving. structure and a mean and colordensity compared of 615 kg/m to other were species used offor wood, Thethe experiment.tool maple type wood chosen Due is to recommended for its homogeneousthe experiment for carving. st ructureis CMT and Orange color comparedV-Grooving to otherRouter species Bit of wood,The tool maple type wood chosen is recommended for the experiment for carving. is CMT Orange V-Grooving Router Bit angled angled◦ 90° (Figure 2). These double cutting edge CMT bits offer a large range of woodworking90 (FigureThe tool2). possibilities, Thesetype chosen double making for cutting the cleanexperiment edge CMTcuts in bitsis the CMT offer panels. aOrange large They range V-Grooving are of made Routerof super Bit possibilities, making clean cuts in the panels. They are made of super strength Fatigue strengthangled Fatigue90° (Figure Proof ®2). steel These with double Tungsten cutting carbide-tipped edge CMT cutting bits edgesoffer a[21]. large range of Proofwoodworking® steel with possibilities, Tungsten carbide-tipped making clean cutting cuts in edges the panels. [21]. They are made of super strength Fatigue Proof® steel with Tungsten carbide-tipped cutting edges [21].

Figure 2. CMT Orange tool, V-Grooving Router Bit 90◦, code 715.095.11. Figure 2. CMT Orange tool, V-Grooving Router Bit 90°, code 715.095.11. 2.1. Method to Analyse Tool Wear Figure 2. CMT Orange tool, V-Grooving Router Bit 90°, code 715.095.11. In order to study the initial (abrupt) tool wear, twenty panels were used for CNC routing the ornament on the surface, and for each panel, the Engrave method was applied

on one face and V-Carve on the other face. Two new V-Grooving 90◦ router bits were used for CNC milling of the wood surface: one for the Engrave method and the other for the V-Carve method. Before starting to process the ornaments on wood panels, the cutting Appl. Sci. 2021, 11, 6713 4 of 12

edge was studied using the stereo-microscope NIKON SMZ 18, with a zoom ratio of 18:1 and zooming range between 0.75× and 13.5×. The total magnification of the microscope used to investigate the tool cutting edge was 120×. The stereo microcopy investigation was repeated after each new milling operation of the ornament on the wood surface for both CNC machining methods.

2.2. Simulation of Tool Path The tool path was automatically calculated by the software Linux CNC version 2.7.0., a free software that runs under the Linux operating system. It was used together with the 3-axis CNC router. The software offers the possibility to simulate the machining process and to visualize the tool path and the data related to it: the length of the trajectory and the estimated processing time.

2.3. Method to Analyze the Wood Ornaments Produced An investigation of the wood ornaments was conducted by comparing the two variants obtained by the Engrave and V-Carve methods from two points of view: the aesthetic one, following similarity with the original motif, and the quality of the processed surface analyzed by stereo-microscopy in the areas where wood fuzziness occurred. Wood mass loss after CNC machining the ornaments with the Engrave and V-Carve methods was also determined by weighing each panel before and after milling the wood. Wood mass loss may be correlated with the processing time in terms of productivity.

3. Results The results obtained in the experiment are presented in Table1.

Table 1. Recorded results for the Engrave and V-Carve methods.

Mass of Removed Wood 1, Processing Time, in No. Method Tool Path, in m/Panel in kg/Panel min:s/Panel 0.038 1 Engrave 19.165 39:03 (0.005) 0.014 2 V-Carve 49.741 59:48 (0.002) 1 Average value calculated for the 20 panels on which experiment has been conducted. Values in the parenthesis are standard deviations.

3.1. Tool Wear The wear occurred after processing the ornament twenty times on maple wood. This aspect was highlighted by the stereo-microscopy investigations. The tool cutting edge wear was not visible at the stereo-microscope after processing the ornament three times, but after milling the fourth panel, small changes were observed on the tool cutting edge (zone W, Figure3; zone W rotated by 90 ◦, Figure4). Comparing the initial aspect of the tool cutting edge and the final one (after twenty uses), visible modifications occurred, both when the Engrave method (Figures5 and6) and the V-Carve method (Figures7 and8) were applied. Appl. Sci. 2021, 11, x FOR PEER REVIEWA and B circled areas in Figures5–8 were identified as the more affected zones of the5 cutof 12

edge, where its shape was modified as the result of the wear process.

Figure 3. Zone W of the investigation on the wear of the tool cutting edge. Figure 3. Zone W of the investigation on the wear of the tool cutting edge.

Figure 4. Zone W rotated by 90° for the investigation of the wear of the tool cutting edge.

(a) (b) Figure 5. Zone W of the Engrave tool (120× magnification) on a stereomicroscope: (a) initial; (b) after twenty uses. A and B circled areas are the more affected one because of the wear process

(a) (b) Figure 6. Zone W rotated by 90° of the Engrave tool (120× magnification) on a stereo-microscope: (a) initial; (b) after twenty uses. A and B circled areas are the more affected one because of the wear process. Appl.Appl. Sci.Sci. 20212021,, 1111,, xx FORFOR PEERPEER REVIEWREVIEW 55 ofof 1212

Appl. Sci. 2021, 11, x FOR PEER REVIEW 5 of 12

Appl. Sci. 2021, 11, 6713 5 of 12 FigureFigure 3.3. ZoneZone WW ofof thethe investigationinvestigation onon ththee wearwear ofof thethe tooltool cuttingcutting edge.edge. Figure 3. Zone W of the investigation on the wear of the tool cutting edge.

FigureFigure 4.4. ZoneZone WW rotatedrotated byby 90°90° forfor thethe investigatioinvestigatio nn ofof thethe wearwear ofof thethe tooltool cuttingcutting edge.edge. Figure 4. Zone W rotated by 90◦ for the investigation of the wear of the tool cutting edge. Figure 4. Zone W rotated by 90° for the investigation of the wear of the tool cutting edge.

((aa)) ((bb)) (a) (b) FigureFigure 5. 5. ZoneZone W W of of the the Engrave Engrave tooltool (120(120×(120×× magnification)magnification)magnification) on on a a stereomicroscope:stereomicroscope: ( ((aaa))) initial;initial;initial; ( (b(bb))) after afterafter twenty twentytwenty uses. uses.uses. A AA and andand B BB circledcircled areasareas areare thethe moremore affectedaffected oneone becausebecause ofof thethe wearwear processprocess circledFigure areas5. Zone are W the of more the Engrave affected tool one (120× because magnification) of the wear process.on a stereomicroscope: (a) initial; (b) after twenty uses. A and B circled areas are the more affected one because of the wear process

((aa)) ((bb)) (a) (b) FigureFigure 6. 6. ZoneZone WW rotatedrotated byby 90°90° 90◦ ofof thethe the Engrave Engrave tooltool (120×(120× (120× magnification)magnification)magnification) onon on aa a stereo-microscope:stereo-microscope: stereo-microscope: (( (aaa))) initial;initial; initial; (( (bb))) afterafter after twentytwenty twenty uses.uses.Figure AA 6.andand Zone BB circledcircled W rotated areas areas by are are 90° the the of more morethe Engrave a affectedaffectedffected tool oneone (120× becausebecause magnification) ofof thethe wearwear on process.process. a stereo-microscope: (a) initial; (b) after twenty uses. A and B circled areas are the more affected one because of the wear process. The circles in Figures5–8 indicate the zones where the differences are more visible (A and B circled areas). After twenty uses, the tools used for engraving and carving have blunt and rounded edges compared with their initial states in zone W and zone W rotated by 90◦, especially for the tool tip area. The wear process looks more pronounced for the second case, where the tool cutting edge was used for carving (V-Carve), as seen in Figures7 and8. Even if the tools were new, irregular contour of the cutting edge was noticed at the microscopic level before starting to use the tools for CNC routing the maple wood panels. Instead, the traces of sharpening the cutting edge were visible at this stage for zone W (Figures5 and7). The contour of the cutting edge became more regular after twenty uses of the tools, especially Appl. Sci. 2021, 11, 6713 6 of 12

Appl. Sci. 2021, 11, x FOR PEER REVIEW 6 of 12 Appl. Sci. 2021, 11, x FOR PEER REVIEW 6 of 12

when the V-Carve method was applied (Figures7 and8), but the traces of sharpened knife disappeared, replaced by a blunt-knife appearance.

(a) (b) (a) (b) Figure 7. Zone W of the V-Carve tool (120× magnification) on a stereo microscope: (a) initial; (b) after twenty uses. A and BFigure circled 7. areasZone are W ofthe the more V-CarveV-Carve affected tooltool one (120(120× because× magnification)magnification) of the wear onon process. aa stereostereo microscope: microscope: ( a(a)) initial; initial; (b (b) after) after twenty twenty uses. uses. A A and and B Bcircled circled areas areas are are the the more more affected affected one one because because of of the the wear wear process. process.

(a) (b) (a) (b) Figure 8. 8. ZoneZone W W rotated rotated by by 90° 90◦ ofof the the V-Carve V-Carve tool tool (120× (120× magnification)magnification) on on a a stereo-microscope: stereo-microscope: ( (aa)) initial; initial; ( (bb)) after after twenty twenty Figure 8. Zone W rotated by 90° of the V-Carve tool (120× magnification) on a stereo-microscope: (a) initial; (b) after twenty uses. A A and and B B circled circled areas are the more a affectedffected one because of the wear process.process uses. A and B circled areas are the more affected one because of the wear process 3.2. ToolThe Pathcircles in Figures 5–8 indicate the zones where the differences are more visible (A andThe B circlescircled inareas). Figures After 5–8 twenty indicate uses, the the zones tools where used thefor engravingdifferences and are carvingmore visible have In Figures9 and 10, the tool path simulated by Linux CNC version 2.7.0. software blunt(A and and B circled rounded areas). edges After compared twenty with uses, their the inittoolsial used states for in engravingzone W and and zone carving W rotated have is represented. The dashed line represents the trajectory traveled when idling, and a byblunt 90°, and especially rounded for edges the tool compared tip area. with their initial states in zone W and zone W rotated continuous line represents the path traveled during processing. With an interrupted red by 90°,The especially wear process for the looks tool more tip area. pronounced for the second case, where the tool cutting line, the shape and dimensions of the wooden piece are presented. edge Thewas wear used process for carving looks (V-Carve), more pronounced as seen infor Figures the second 7 and case, 8. Evenwhere if thethe tool tools cutting were new,edge irregularwas used contourfor carving of the (V-Carve), cutting edgeas seen was in noticedFigures at7 andthe microscopic8. Even if the level tools before were startingnew, irregular to use thecontour tools offor the CNC cutting routing edge the was maple noticed wood at panels.the microscopic Instead, thelevel traces before of sharpeningstarting to usethe thecutting tools edge for CNCwere routingvisible atthe this maple stage wood for zone panels. W (Figures Instead, 5 the and traces 7). The of contoursharpening of the the cutting cutting edge edge beca wereme visible more regular at this stageafter twentyfor zone us Wes (Figuresof the tools, 5 and especially 7). The whencontour the of V-Carve the cutting method edge was beca appliedme more (Figures regular 7 afterand 8), twenty but the us traceses of the of sharpenedtools, especially knife disappeared,when the V-Carve replaced method by a was blunt-knife applied appearance.(Figures 7 and 8), but the traces of sharpened knife disappeared, replaced by a blunt-knife appearance.

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3.2. Tool Path 3.2. Tool Path In Figures 9 and 10, the tool path simulated by Linux CNC version 2.7.0. software is In Figures 9 and 10, the tool path simulated by Linux CNC version 2.7.0. software is Appl. Sci. 2021, 11, 6713 represented. The dashed line represents the trajectory traveled when idling, and7 of a 12 represented. The dashed line represents the trajectory traveled when idling, and a continuous line represents the path traveled during processing. With an interrupted red continuous line represents the path traveled during processing. With an interrupted red line, the shape and dimensions of the wooden piece are presented. line, the shape and dimensions of the wooden piece are presented.

FigureFigure 9.9. ToolTool pathpath whenwhen milling with thethe Engrave method is is applied. applied. Figure 9. Tool path when milling with the Engrave method is applied.

Figure 10. Tool path when milling with the V-Carve method is applied. FigureFigure 10.10. Tool pathpath when milling with th thee V-Carve method is is applied. applied. The calculated tool path by the Linux CNC software was 19,165.4 mm when the The calculated tool path by the Linux CNC software was 19,165.4 mm when the EngraveThe method calculated was tool applied path and by the49,741.4 Linux mm CNC when software the V-Carve was 19,165.4 method mm was when applied the Engrave method was applied and 49,741.4 mm when the V-Carve method was applied Engravefor CNC methodrouting. was Calculating applied andthe whole 49,741.4 length mm whenof the thepaths V-Carve for the method twenty was processed applied for CNC routing. Calculating the whole length of the paths for the twenty processed forornaments, CNC routing. there was Calculating a route with the 383.3 whole m length length offor the engraving paths for and the 994.8 twenty m length processed for ornaments, there was a route with 383.3 m length for engraving and 994.8 m length for ornaments,carving. Similar there research was a route on Aleppo with 383.3 pine m concluded length for that engraving dge recession and 994.8 occurred m length at fora carving. Similar research on Aleppo pine concluded that dge recession occurred at a carving.cutting length Similar of research 850 m, with on Aleppo abrupt pine wear concluded at about 200 that m dge [17]. recession occurred at a cutting lengthcutting of length 850 m, of with850 m, abrupt with wearabrupt at wear about at 200 about m [20017]. m [17]. Appl.Appl. Sci. Sci. 20212021, 11, 11, x, 6713FOR PEER REVIEW 8 ofof 1212

3.3.3.3. Wood Wood Ornaments Ornaments Investigation Investigation AA first first evaluation evaluation of of the the ornaments was conducted byby comparingcomparing thethe twotwo variantsvariants transposedtransposed ontoonto thethe wood wood surface surface with with the originalthe original motif. Themotif. visual The investigation visual investigation revealed revealedthat the textilethat the motif textile transferred motif transferred by CNC milling by CNC on the milling maple woodon the surface maple lookswood different surface looksdepending different on depending the method on applied: the method Engrave applie ord: V-Carve. Engrave or In V-Carve. Figure 11 Ina, Figure the ornament 11a, the ornamentlooks crowded looks whencrowded applying when the applying Engrave the method. Engrave In themethod. second In case, the second when the case, V-Carve when themethod V-Carve was method used (Figure was used11b), (Figure the ornament 11b), th processede ornament on theprocessed wood surface on the resembled wood surface the resembledoriginal motif the original more. motif more.

2 1

3

(a) (b)

FigureFigure 11. 11. TheThe CNC CNC routed routed ornaments: ornaments: ( (aa)) using using the EngraveEngrave method;method; ( b(b)) using using the the V-Carve V-Carve method. method. Areas Areas marked marked with with 1, 1, 2 and 3 were identified to be characterized by pronounced wood fuzziness. 2 and 3 were identified to be characterized by pronounced wood fuzziness.

StudyingStudying the the ornaments ornaments processed processed by th thee two methods,methods, threethree zoneszones wherewhere woodwood fuzzinessfuzziness occurred occurred after after processing processing the the orna ornamentment by the EngraveEngrave methodmethod onon thethe woodwood surfacesurface were were highlighted. highlighted. These These zones zones are are mark markeded in Figure 1111a,a, andand theythey werewere assigned assigned thethe numbers numbers 1, 1, 2, 2, and and 3. 3. These These zones zones were were subjected to aa stereo-microscopystereo-microscopy analysisanalysis with with 22.5×22.5× magnificationmagnification and and compared compared to to similar similar zones zones of the V-Carved ornament.ornament. TheThe imagesimages areare presented presented in Figures 1212–14–14 for for the the Engrave Engrave method method (a) (a) and and for for the the V-Carve V-Carve method method (b). (b).The The arrows arrows indicate indicate fuzzy fuzzy grains grains onthe on woodthe wood surface, surface, more more numerous numerous and largerand larger in size in sizethan than on theon the variant variant of the of ornamentthe ornament for which for which the Engrave the Engrave method method was used.was used. Appl. Sci. 2021, 11, 6713 9 of 12 Appl. Sci. 2021, 11, x FOR PEER REVIEW 9 of 12 Appl. Sci. 2021, 11, x FOR PEER REVIEW 9 of 12 Appl. Sci. 2021, 11, x FOR PEER REVIEW 9 of 12

(a) (b) (a) (b) FigureFigure 12. 12.Detail Detail 1 from1 from Figure Figure(a) 8 subjected8 subjected to to stereo-microscopy stereo-microscopy analysis analysis withwith 22.522.5×× magnification:magnification:(b) (a ()a ornament) ornament obtained obtained Figureby the 12.Engrave Detail method:1 from Figure detail 8 fromsubjected the pictureto stereo-mic (left)roscopy and the analysis image with 22.5×22.5× magnification:magnification (a(right) ornament); (b) ornament obtained byFigure the Engrave 12. Detail method: 1 from detail Figure from 8 subjected the picture to stereo-mic (left) androscopy the image analysis with 22.5 with× 22.5×magnification magnification: (right ();a) ( bornament) ornament obtained obtained byobtained the Engrave by the V-Carvemethod: method:detail from detail the from picture the picture (left) and(left )the and image the image with with22.5× 22.5× magnification magnification (right (right); (b).) ornament bybyobtained the the V-Carve Engrave by the method: V-Carvemethod: detail method:detail from from detail the the picture from picture the (left picture ()left and) and( theleft image)the and image the with image with 22.5 with×22.5×magnification 22.5× magnification magnification (right (right). (right); (b).) ornament obtained by the V-Carve method: detail from the picture (left) and the image with 22.5× magnification (right).

(a) (b) (a) (b) Figure 13. Detail 2 from Figure(a) 8 subjected to stereo-microscopy analysis with 22.5× magnification:(b) (a) ornament obtained FigureFigureby the 13. 13.EngraveDetail Detail 2 method:2 from from Figure Figure detail8 subjected8 fromsubjected the to pictureto stereo-microscopy stereo-mic (left)roscopy and the analysis analysis image withwith 22.522.5×22.5×× magnification:magnificationmagnification: (a(right ()a ornament) ornament); (b) ornament obtained obtained Figure 13. Detail 2 from Figure 8 subjected to stereo-microscopy analysis with 22.5× magnification: (a) ornament obtained bybyobtained the the Engrave Engrave by the method: V-Carvemethod: detail method:detail from from detail the picturethe from picture (theleft picture )( andleft) the and(left image )the and image with the image 22.5 with× withmagnification22.5× 22.5× magnification magnification (right );(right (b )(right ornament); (b).) ornament obtained byobtained the Engrave by the V-Carvemethod: method:detail from detail the from picture the picture (left) and(left )the and image the image with with22.5× 22.5× magnification magnification (right (right); (b).) ornament byobtained the V-Carve by the method: V-Carve detail method: from detail the picture from the (left picture) and ( theleft image) and the with image 22.5 with× magnification 22.5× magnification (right). (right).

(a) (b) (a) (b) Figure 14. Detail 3 from Figure(a) 8 subjected to stereo-microscopy analysis with 22.5× magnification:(b) (a) ornament obtained Figureby the 14.Engrave Detail method:3 from Figure detail 8 fromsubjected the pictureto stereo-mic (left)roscopy and the analysis image with 22.5×22.5× magnification:magnification (a(right) ornament); (b) ornament obtained Figure 14. Detail 3 from Figure 8 subjected to stereo-microscopy analysis with 22.5× magnification: (a) ornament obtained Figurebyobtained the 14. EngraveDetail by the 3 V-Carvemethod: from Figure method:detail8 subjected from detail the from to picture stereo-microscopy the picture (left) and(left )the and analysis image the image withwith with 22.522.5× ×22.5× magnificationmagnification: magnification (right (a )(right ornament); (b).) ornament obtained by the Engrave method: detail from the picture (left) and the image with 22.5× magnification (right); (b) ornament byobtained the Engrave by the method: V-Carve detail method: from detail the picture from the (left picture) and the (left image) and withthe image 22.5× withmagnification 22.5× magnification (right); (b ()right ornament). obtained obtained by the V-Carve method: detail from the picture (left) and the image with 22.5× magnification (right). by the V-Carve method: detail from the picture (left) and the image with 22.5× magnification (right). Appl. Sci. 2021, 11, x FOR PEER REVIEW 10 of 12

Appl. Sci. 2021, 11, 6713 10 of 12

4. Discussion 4. DiscussionFor this research, a traditional Romanian motif taken from textile heritage was transposedFor this as research, an ornament a traditional on maple Romanian wood panels motif by taken CNC from machining textile heritagewith two was different trans- posedmethods: as anengraving ornament (Engrave) on maple and panels (V-Carve) by CNC using machining the V-Grooving with two Router different Bit methods:angled at engraving90°. The comparison (Engrave) andbetween carving the (V-Carve)two processing using themethods V-Grooving included Router a visual Bit angledanalysis at of 90 the◦. Theappearance comparison of the between processed the ornament two processing in the two methods variants, included followed a visual by a analysisstereo-microscopy of the appearance of the areas of thewhere processed fuzzy gr ornamentains occurred in the after two milling variants, the followedwood; a tool by awear stereo-microscopy assessment by ofmicroscopic the areas where investigatio fuzzy grainsn of the occurred tool cutting after milling edge after the wood; twenty a toolsuccessive wear assessment millings of byornaments; microscopic and investigationa calculation of of the the tool tool path cutting and edge of the after mass twenty of the successiveremoved wood millings during of ornaments; the millingand process a calculation and their ofcorrelation the tool path with and the ofprocessing the mass oftimes. the removedThe woodvisual duringanalysis the revealed milling that process the andornament their correlation looked totally with different the processing when it times. was engravedThe visual or carved analysis by the revealed CNC thatrouter. the The ornament carved looked ornament totally looked different more when similar it was the engravedoriginal motif. or carved In addition, by the CNCthe microscopic router. The investigation carved ornament showed looked large more and similarnumerous the originalwood fuzzy motif. grains In addition, on the engraved the microscopic surfaces, investigation thus bringing showed another large advantage and numerous to the V- woodCarve fuzzymethod. grains on the engraved surfaces, thus bringing another advantage to the V-CarveThe method.tool wear was highlighted by microscopic analysis of the tool cutting edge, whereThe blunt tool and wear rounded was highlighted edges were by compared microscopic with analysis their ofinitial the toolstate cutting after the edge, ornament where blunthad been and processed rounded edgestwenty were times. compared with their initial state after the ornament had beenIt processed is found twentythat the times. wear of the tool used for engraving is 37.5% for the cutting area (see FigureIt is found 5) and that 26.7% the wear for the of tip the area tool (Figure used for 6). engraving For the tool is 37.5%used for for V-Carve the cutting milling, area (seethe wear Figure is5 41.2%) and 26.7%for the for cutting the tip area area (Figure (Figure 7),6 ).while For thefor toolthe tip, used it forwas V-Carve 42.8% (Figure milling, 8). theThese wear data is show 41.2% that, for the in the cutting case areaof milling (Figure with7), whilethe Engrave for the method, tip, it was the 42.8% wear (Figure of the tool8). Thesewas less data pronounced show that, than in the that case in of the milling case of with V-Carve the Engrave milling. method, The explanation the wear of is the related tool wasto the less length pronounced of the thantool thatpath infor the the case two of V-Carveapplied milling.methods The (approx. explanation 19.2 m is when related the to the length of the tool path for the two applied methods (approx. 19.2 m when the Engrave Engrave method was applied and 49.7 m when the V-Carve method was applied). method was applied and 49.7 m when the V-Carve method was applied). It was also noticed that, when milling with the Engrave method, the wear affects the It was also noticed that, when milling with the Engrave method, the wear affects the cutting edge area more, while when milling with the V-Carve method, the wear cutting edge area more, while when milling with the V-Carve method, the wear percentage percentage of the tool tip is higher. This can be explained by the different contact areas of the tool tip is higher. This can be explained by the different contact areas between the between the tools and wood for the two cases, with the difference being the interior tools and wood for the two cases, with the difference being the interior surface of the surface of the ornament, where the cutting depth varies between 1 mm to 3 mm, and the ornament, where the cutting depth varies between 1 mm to 3 mm, and the tip of the tool is tip of the tool is involved in the milling process. involved in the milling process. Correlations between tool path lengths calculated for twenty processed ornaments, Correlations between tool path lengths calculated for twenty processed ornaments, their corresponding processing times, and masses of the removed wood are presented in their corresponding processing times, and masses of the removed wood are presented in Figure 1515..

(a) (b)

FigureFigure 15.15. ComparisonComparison betweenbetween thethe EngraveEngrave and V-CarveV-Carve methodsmethods appliedapplied toto CNCCNC routingrouting ofof anan ornamentornament onon aa maplemaple woodwood surface:surface: ( a(a)) correlation correlation between between the the mass mass of of removed removed wood wood and and tool tool path path length; length; (b) correlation(b) correlation between between the tool the path tool path length and processing time. length and processing time. Appl. Sci. 2021, 11, 6713 11 of 12

5. Conclusions The results of the present research show that the tool path is longer when applying the V-Carve method than for the Engrave method, and this aspect resulted in a longer processing time for the V-Carve method, as seen in Figure 15b. Instead, the mass of the wood removed during the routing process is higher when applying the Engrave method than when applying the V-Carve method. This can be explained by the constant cut depth of 3 mm for the Engrave method compared with the variable cut depth between 1 mm and 3 mm for the V-Carve method (3 mm only for the contour), resulting in a higher volume of wood removed in the first case. The longer tool path in the case of applying the V-Carve method, correlated with a longer processing time, is a drawback of this method in terms of productivity. Choosing the right method to be applied in CNC routing of ornaments similar to that used as an example in this research is a compromise between appearance, surface quality, and productivity. Being a furniture ornament, the aesthetic and the quality of the processed surface should be considered, so the V-Carve method is more advantageous from these points of view.

Author Contributions: Conceptualization, A.L., M.I. and C.C.; methodology, M.I. and C.C; software, A.L., L.-M.B. and S.R.; validation, A.L., M.I., L.-M.B., S.R. and C.C.; formal analysis, M.I.; investigation, A.L., L.-M.B. and C.C.; resources, A.L.; data curation, C.C.; writing—original draft preparation, A.L. and C.C.; supervision, C.C.; project administration, A.L.; funding acquisition, A.L. and C.C. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable. Acknowledgments: The authors thank Dan Petrea for his work with milling processing, Melania Cristea for her help in measuring the weight of the panels and tools, and Gabriel Boriceanu for providing the photos with the model. Conflicts of Interest: The authors declare no conflict of interest.

References 1. Ilie¸s,D.C.; Herman, G.V.; Caciora, T.; Ilie¸s,A.; Indrie, L.; Wendt, J.; Axinte, A.; Diombera, M.; Lite, C.; Berdenov, Z.; et al. Considerations Regarding the Research for the Conservation of Heritage Textiles in Romania. In Waste in Textile and Leather Sectors; Körlü, A., Ege University, Eds.; IntechOpen Limited: London, UK, 2020. [CrossRef] 2. Doble, L.; Stan, O.; Suteu, M.D.; Albu, A.; Bohm, G.; Tsatsarou-Michalaki, A.; Gialinou, E. Romanian traditional motif—element of modernity in clothing. IOP Conf. Ser. Mater. Sci. Eng. 2017, 254, 172009. [CrossRef] 3. Fairclough, G. The Value of Heritage for the Future. In Heritage in Society. Cultural Policy and Management (KPY); Yearbook 3; Ünsal, D., Ed.; Istanbul Bilgi University Press: Istanbul, Turkey, 2012; pp. 34–41. 4. Sood, S.; Duvedi, R.K.; Bedi, S.; Mann, S. 3D representation and CNC machining of 2D digital images. Procedia Manuf. 2018, 26, 10–20. [CrossRef] 5. Pinkowski, G.; Szymanski, W.; Nosowski, T. Analyses of surface roughness in selected wood species after machining on a CNC woodworking centre. Ann. WULS SGGW For. Wood Technol. 2012, 79, 164–169. 6. Çakiro˘glu,E.O.; Demir, A.; Aydin, I. Determination of the Optimum Feed Rate and Spindle Speed Depending on the Surface Roughness of Some Wood Species Processed with CNC Machine. J. Anatol. Environ. Anim. Sci. 2019, 4, 598–601. [CrossRef] 7. Hazir, E.; Koc, K.H. Optimization of wood machining parameters in CNC Routers: Taguchi orthogonal array based simulated angling algorithm. Maderas Cienc. Tecnol. 2019, 21, 493–510. [CrossRef] 8. Sütcü, A.; Karagöz, Ü. Effect of machining parameters on surface quality after face milling of MDF. Wood Res. 2012, 57, 231–240. 9. Supadarattanawong, S.; Rodkwan, S. An Investigation of the Optimal Cutting Conditions in Parawood (Heavea Brasiliensis) Machining Process on a CNC Wood Router. Kasetsart J. (Nat. Sci.) 2006, 40, 311–319. 10. Gawronski, T. Optimisation of CNC routing operations of wooden furniture parts. Int. J. Adv. Manuf. Technol. 2013, 67, 2259–2267. [CrossRef] 11. Krimpenis, A.A.; Fountas, N.A.; Mantziouras, T.; Vaxevanidis, N.M. Optimizing CNC wood milling operations with the use of genetic alghorithms on CAM software. Wood Mater. Sci. Eng. 2014, 11, 102–115. [CrossRef] Appl. Sci. 2021, 11, 6713 12 of 12

12. Ohuchi, T.; Murase, Y. Milling of wood and wood-based materials with a computerized numerically controlled router V: Development of adaptive control grooving system corresponding to progression of tool wear. Wood Sci. 2006, 52, 395–400. [CrossRef] 13. Aguilera, A.; Meausoone, P.J.; Rolleri, A.; Barros, J.L.; Burgos, F.; Aguilar, C. Advances on indirect methods to evaluate tool wear for Radiata pine solid wood . Wear 2016, 350–351, 27–34. [CrossRef] 14. Pinkowski, G.; Szymanski, W.; Gilewicz, A.; Krauss, A. Impact of the wear of the cutting edge on selected parameters of the surface geometric structure after wood milling. Ann. WULS SGGW For. Wood Technol. 2009, 69, 187–191. 15. Keturakis, G.; Lisauskas, V. Influence of the Sharpness Angle on the Initial Wear of the Wood Milling Knives. Mater. Sci. (Medžiagotyra) 2010, 16, 205–209. 16. Porankiewicz, B. Theoretical simulation of cutting edge wear when milling wood and wood based products. Wood Sci. Technol. 2006, 40, 107–117. [CrossRef] 17. Aknouche, A.; Outahyon, A.; Nouveau, C.; Marchal, R.; Zerizer, A.; Butaud, J.C. Tool wear effect on cutting forces: In routing process of Aleppo pine wood. J. Mat. Process. Technol. 2009, 209, 2918–2922. [CrossRef] 18. Antonescu, R.B. Dic¸tionarde Simboluri ¸siCredin¸teTradi¸tionaleRomâne¸sti; Edi¸tiedigitală, Direc¸tiade cercetare, eviden¸tă a patrimoni-

ului cultural mobil, imaterial ¸sidigital; Institutul Nat, ional al Patrimoniului: Bucures, ti, România, 2016; p. 661. 19. Semne Cusute. Available online: https://semne-cusute.blogspot.com/2012/07/motive-unda-apei.html (accessed on 5 June 2021). 20. Semne Cusute. Available online: https://semne-cusute.blogspot.com/2012/07/bradutul.html (accessed on 5 June 2021). 21. CMT Orange Tools. Available online: https://www.cmtorangetools.com/eu-en/industrial-router-bits/v-grooving-router-bits- 90deg (accessed on 5 June 2021).