The Design Development of the Sliding Table Saw Towards Improving Its Dynamic Properties

Home , Circular saw, Panel saw, Spindle (tool), Table saw

applied sciences

Review The Design Development of the Sliding Table Saw Towards Improving Its Dynamic Properties

Kazimierz A. Orlowski 1,* , Przemyslaw Dudek 2, Daniel Chuchala 1 , Wojciech Blacharski 1 and Tomasz Przybylinski 3

1 Department of Manufacturing and Production Engineering, Faculty of Mechanical Engineering, Gdansk University of Technology, 80-233 Gdansk, Poland; [email protected] (D.C.); [email protected] (W.B.) 2 Rema S.A., 11-440 Reszel, Poland; [email protected] 3 Institute of Fluid-Flow Machinery, Polish Academy of Sciences, 80-233 Gdansk, Poland; [email protected] * Correspondence: [email protected]

Received: 15 September 2020; Accepted: 15 October 2020; Published: 21 October 2020

Abstract: Cutting wood with circular saws is a popular machining operation in the woodworking and furniture industries. In the latter sliding table saws (panel saws) are commonly used for cutting of medium density fiberboards (MDF), high density fiberboards (HDF), laminate veneer lumber (LVL), plywood and chipboards of different structures. The most demanded requirements for machine tools are accuracy and precision, which mainly depend on the static deformation and dynamic behavior of the machine tool under variable cutting forces. The aim of this study is to present a new holistic approach in the process of changing the sliding table saw design solutions in order to obtain a better machine tool that can compete in the contemporary machine tool market. This study presents design variants of saw spindles, the changes that increase the critical speeds of spindles, the measurement results of the dynamic properties of the main drive system, as well as the development of the machine body structure. It was proved that the use of only rational imitation in the spindle design on the basis of the other sliding table saws produced does not lead to the expected effect in the form of correct spindle operation.

Keywords: sliding table saw; spindle; critical rotational speed; static stiﬀness; dynamic properties; noise; sawing of wood composites

1. Introduction Cutting wood with circular saws is a popular machining operation in the woodworking and furniture industries. Its popularity is mainly due to the fact that in this method of cutting relatively simple and cheap tools are used, usually saws and disc cutters with small dimensions. In the furniture industry, sliding table saws (panel saws) are commonly used for cutting of medium density fiberboards (MDF) [1], high density fiberboards (HDF), laminate veneer lumber (LVL) [1], plywood [2] and chipboards of different structures [3]. The most demanded requirements for machine tools are accuracy and precision, which mainly depend on the static deformation and dynamic behavior of the machine tool under variable cutting forces [4]. Sliding table saws (panel saws) should guarantee the user straightness of the kerf in the longitudinal direction, perpendicularity of the kerf to the sawn board surfaces, a smooth kerf surface after cutting, as well as lack of washboarding [5] on the sawed surface. In sliding table saws, the blade of the collared saw is rigidly fixed to the driving spindle [6–9]. The qualitative effects of the sawing process depend on the static and dynamic properties of the entire structure of the machine

Appl. Sci. 2020, 10, 7386; doi:10.3390/app10207386 www.mdpi.com/journal/applsci Appl. Sci. 2020, 10, 7386 2 of 12 tool, and the cutting system consists of a machine tool, clamping system, a workpiece and a tool. Hu Wan-yi et al. [10] presented the results of empirical works devoted to the noise generated by the sliding table saws during idling. The generated noise has three main sources: air flow around the saw blade and in the suction system (aeromechanic noise), and the noise depending on the structure of the machine tool. Noise caused by mechanical vibrations can result from unbalance of the main saw blade system, eccentricity of the main spindle, incorrect assembly and loosening of the bearing, which are could be caused by wear of bearings race-ways [10]. Vibrations and noise in machine tools are always present simultaneously, hence, if the vibrations are at a lower level, the noise is also lower [11]. For example, self-exciting chatter vibrations have a particularly negative effect on the cutting process effects, a state of the workpiece (waviness, roughness), a machine tool life and tool condition, as well as on the efficiency of machining. In addition, they accelerate spindle-bearing wear and cutting-edge wear (it is not only faster, but even catastrophic). Furthermore, they make it difficult to obtain the required surface quality and cause excessive noise [12]. The manufacturers of sliding table saws tend towards improving sawing accuracy by minimizing the vibration level and noise of their machine tools, and thank to that growing their competitiveness at the market. Nasir and Cool [13] have done a very thorough review of the literature in which they have shown that the studies of sawing processes are the subject of numerous studies in many scientific centers. Kvietková et al. [14] reported on the results of the effect of number of saw blade teeth on noise level during transverse cutting of beech wood. However, the tests were not conducted on the sawing machine, but with the use of the power tool. For this reason, the expected noise level when using similar circular saw blades on a panel saw is likely to be completely different. The same power tool Kminiak et al. [15] applied in the research on the quality of a machined wood surface while transverse cutting of European beech (Fagus sylvatica L.). Very often, experiments of cutting with circular saw blades are conducted on the special laboratory stands, e.g., cross-cutting of green spruce and beech wood [16], or cutting process with feeding in the longitudinal direction of modified beech wood (Bendywood Candidus Prugger Sas, Bressanone, Italy), DMDHEU (1.3-dimethylol-4.5-dihydroxyethyleneurea) (Wood Biology and Wood Products, University of Goettingen, Goettingen, Germany) and Lignamon (a name of ammonia-treated compressed beech wood) [17]. The publication by Mandic et al. [18] was found among the reports from the numerous studies on the process of cutting with circular saws conducted on a sliding table saw. These authors were the few who carried out their empirical research of power consumption and the acoustic emission (AE) on the panel saw the type Minimax CU410K machine tool (SCM Group, Rimini, Italy), and the material to be cut was laminated particle board. Surface roughness produced by rip sawing with circular saw of MDF was evaluated by Aguilera [19] using a stylus technique. In that research while in climb cutting mode the surface roughness was slightly better if the cutting speed was higher. The findings of work by Aguilera and Barros [20] lead to the conclusion that the sound pressure (measured with microphones) generated in the process with circular saw blades is closely related on satisfactory levels of correlation with the surface roughness. The samples were machined in a single-spindle shaper machine. However, in both cases described in works [19,20], the research was carried out on a single-spindle shaper machine, which is much stiffer than a panel saw. Therefore, it would be difficult to expect similar results when cutting MDF boards on a panel saw. Since, there is the carcinogenic nature of wood dusts [21], the saw dust extraction systems of sawing machines have been also examined in terms of their efficiency [22,23] and acoustic emission [23]. Due to its low inherent stiffness, the circular saw is one of the weakest elements of the machine tool system. Hence, vibrations of the sawblade and any roughness of the cutting surface must be limited. Cutting vibration can be suppressed by uncoupling the two vibration modes of the same nodal diameter number by using outer slots in the saw blade [24,25] and creating high saw body damping using inner slots filled with viscoelastic resin [26]. The behavior of the circular saw blade also depends on its design [27,28]. Nevertheless, the reduction of the transverse vibrations of the saw blade can be obtained if it operates below the value of the critical rotational speed [6,29,30]. Appl. Sci. 2020, 10, 7386 3 of 12

Appl. Sci.Dietrych 2020, 10, [ 317386]states that the ability to perform tasks correctly by the new designed machine3 of tool 13 can be evaluated on the basis of quality indices, which include expected life of the machine, reliability, precision and low level of emitted interference (vibration and noise). For a panel saw the objective function should be comparable toto the the cutting cutting accuracy accuracy it it achieves. achieves. An An illustration of the causal relationship betweenbetween these these mentioned mentioned quality quality indicators indicators and and vibrations vibrations is shown is shown in Figure in Figure1. Too 1. much Too vibrationmuch vibration activity activity of the of machine the machine tool (panel tool (panel saw) saw) will awillﬀect affect durability durability (expected (expected life), life accuracy), accuracy and andreliability reliability [11,32 [11,32]. Therefore,]. Therefore, at the at stage the stage of designing of designing and testingand testing the prototype, the prototype, it is necessaryit is necessary to ﬁnd to findthe sources the sources of vibration of vibration and noise. and Such noise. activities Such activities are called are vibroacoustic called vibroacoustic construction constructio (emission)n (emission)diagnostics diagnostics [11,32]. [11,32].

Figure 1. Quality indices of the machine tool and their relation to vibrations, where: MPC—machining Figure 1. Quality indices of the machine tool and their relation to vibrations, where: MPC—machining process conditions; Q1, Q2, Q3, Q4—quality indices. process conditions; Q1, Q2, Q3, Q4—quality indices. Based on the observations, it can be assumed that most manufacturers in the design process use statisticalBased and on comparativethe observations, methods it can [33 be], whichassumed rely that on rationalmost manufacturers imitation of practically in the design proven process sawmill use statistdrivesical of similar and comparative design, similar methods size and [33 similar], which kinematics, rely on rational taking into imitation account of development practically proven trends sawmillin a given drives group of of machine similar tools. design, similar size and similar kinematics, taking into account developmentThe aim oftrends this study in a given is to presentgroup of a newmachine holistic tools. approach in the process of changing of the sliding tableThe saw aim design of this solutions study inis orderto present to obtain a new a betterholistic machine approach tool in that the canprocess compete of changing in the modern of the slidingmachine table tool saw market. design This solutions review presents in order design to obtain variants a better of saw machine spindles, tool changesthat can in compete increasing in the moderncritical speeds machine of spindles, tool market. measurement This review results presents of the design dynamic variants properties of saw of the spindles, main drive changes system, in increasingas well as thethe developmentcritical speeds of of the spindles, machine measurement body structure. results of the dynamic properties of the main drive system, as well as the development of the machine body structure. 2. Spindle and Main Driving System 2. Spindle and Main Driving System 2.1. Design Variants of Main Spindles 2.1. Design Variants of Main Spindles In North America, a system with circular saw blades having a spline in the inner hole working withIn a spindleNorth America, having an a system external with spline circular is common saw blades to circular having sawing a spline machines in the inner for primary hole working wood processing,with a spindle especially having [an7]. external The second spline way is common of embedding to circular the saw sawing blades machines on the spindlesfor primary of sawing wood processing,machine tools, especially common [7]. in The Europe, second is by way ﬁxing of embedding them with the the fastening saw blades collars on the [29 ,spind34]. Inles this of casesawing the machineoperation tools, of the common saw must in Europe, be at a rotational is by fixing speed them lower with the than fastening their critical collars speed, [29,34 guaranteeing]. In this case the operationstable operation of the saw of the must tool be [29 at]. a However, rotational thespeed clamping lower than of the their saw critical with the speed, help guaranteeing of collars allows the stablefor multi-saws operation to of place the tool saws [29 on]. Ho thewever, spindles the with clamping little distances of the saw between with the them. help Moreover,of collars allows the latter for multisolution-saws is commonlyto place saws used on in the format spindles saws with where little the distances cutting torquebetween is them. most oftenMoreover, transmitted the latter by solutionfriction between is commonly the mounting used in collarsformat and saws the where saw blade the cutting [8,29,35 ].torque Orlowski is most and often Dudek transmitted [35] analyzed by frictionthe development between the of themounting main spindles collars and of the the sliding saw blade table [8,29,35 saws for]. Orlowski the last quarter and Dudek century. [35] analyzed the development of the main spindles of the sliding table saws for the last quarter century. In the last decade of the twentieth century, the long spindles with ratio of the supports spacing L to the inner diameter of the front bearing d of about 12.7, were mounted in the format saws [36]. Appl. Sci. 2020, 10, 7386 4 of 12

Appl. Sci.In 2020 the, last 10, 7386 decade of the twentieth century, the long spindles with ratio of the supports spacing4 of 13 L to the inner diameter of the front bearing d of about 12.7, were mounted in the format saws [36]. This type of solution is be still found in the sliding table saw DMMS-40 Classic (REMA S.A., Reszel, This type of solution is be still found in the sliding table saw DMMS-40 Classic (REMA S.A., Reszel, Poland, Figure 2a), in which the traditional V-belt has been displaced by the PK belt (v-ribbed belt). Poland, Figure2a), in which the traditional V-belt has been displaced by the PK belt (v-ribbed belt).

(a) (b)

FigureFigure 2. 2. LongLong main main spindle spindle in in the the sliding sliding table table saw saw DMMS DMMS-40-40 Classic Classic (a, (a, REMA REMA S.A. S.A.)) and and short short main main spindlespindle ( (aa)) view view from from motor motor side side in in the sliding table saw Fx550 (b)),, REMA S.A S.A..

InIn 2006, 2006, Altendorf showedshowed atat thethe Drema Drema Fair Fair in in Poznan Poznan a newa new generation generation of slidingof sliding table table saws saws F45 F45Elmo Elmo (Altendorf, (Altendorf, Minden, Minden, Germany) Germany) [37 ],[37 with], with a short a short main main spindle, spindle, with with a L/ da ratioL/d ratio of about of about 3 [38 3]. [Since38]. Since then, then, the the market market has has been been supplying supplying mainly mainly short-wheeled short-wheeled spindles spindles drivendriven mainlymainly with a a rearrear-wheel-wheel transmission. transmission. This This kind kind of of the the design design was was applied applied in the in sliding the sliding table saws table types saws as types follows: as follows:Fx3 (after Fx3 modernization (after modernization Fx550 [39 Fx550], f. Rema [39], SA, f. Rema Reszel, SA, Poland), Reszel, UNICA Poland), 400 UNICA (f. Griggio, 400 Cadoneghe,(f. Griggio, Cadoneghe,Italy—company Italy closed– company in 2018) closed [40], in K 2018 700S) (f.[40 Felder], K 700S Group, (f. Felder Hall Group, in Tirol, Hall Austria) in Tirol, [41 ]Austria) and PF 400S[41] and(f. Rojek, PF 400SCastolovice,ˇ (f. Rojek, CzechČastolovice, Republic) Czech [42 Republic)]. Each of [ the42]. aforementioned Each of the aforementioned saws has a stepped saws has main a steppeddrive, in main which drive, the in change which of the rotational change of speed rotational depends speed on depends the position on the of position the PK belt of the in PK the belt belt intransmission. the belt transmission. There are There usually are solutions usually solutions with three with pairs three of pulleyspairs of orpulleys less often or less with often four with pairs four of pairspulleys. of pulleys. Nevertheless, Nevertheless, the most the modern most modern solution solution seems to seems be the to variant be the withvariant a continuously with a continuously variable variabledrive, such drive, as insuch one as of in the one design of the variants design variants of the F45 of sawthe F45 [37]. saw [37].

2.2.2.2. Static Static and and D Dynamicalynamical P Propertiesroperties of of S Spindlespindles TheThe use use of of only only rational rational imitation imitation in in the the design design on on the the basis basis of of the the other other table table sliding sliding saws saws producedproduced does not not lead lead to to the the expected expected effect effect in in the the form form of of correct correct spindle spindle operation, operation, and and this this mainly mainly concernsconcerns the the possible possible exceeding exceeding of of the the to tool’sol’s lateral lateral run run out out value. value. Too Too much much lateral lateral runout runout of of the the saw saw bladeblade can can be be a a source source of of additional additional force force excita excitationtion for for the the tool, tool, which which can can cause cause unwanted unwanted machining machining errorserrors as as a a result. result. Errors Errors of of this this type type are are not not very very visible visible when when cutting cutting individual individual thin thin wood wood composite composite panels,panels, however, however, very often these materials materials are are cut cut in in packages packages and and then then the the errors errors on on sawn sawn surfa surfacesces cancan be be more more observable, observable, especially especially in case of top boards in the package. TheThe correctness of of the the spindle spindle design design can can be determined be determined based based on analytically on analytically determined determined speeds speedscritical, critical, which which seems seems to be to a be rational a rational approach, approach, especially especially for for circular circular sawing sawing machines. machines. In the the literatureliterature [[8,438,43],], it it can can find find recommendations recommendations to calculate to calculate the values the values of spindle of spindle critical critical rotational rotational speeds ncr from the Equation: speeds ncr from the Equation: s 1 n = 300 , (1) cr f1 ncr  300 max , (1) fmax where: f max is a maximum deflection of the spindle in cm (determined on the front or rear end of the where:spindle). fmax The is a calculated maximum critical deflection rotational of the speedspindle should in cm satisfy (determined the inequality: on the front or rear end of the spindle). The calculated critical rotational speed should satisfy the inequality:

nncr(1.5 2) work , (2) where: nwork is a working rotational speed of the spindle, rpm. Appl. Sci. 2020, 10, 7386 5 of 12

Appl. Sci. 2020, 10, 7386 5 of 13

The short spindle of the sliding tablencr saw( Fx31.5 (before2)nwork modernization,) presented at work [34] can (2) develop working speeds of 3500, 4500 and≥ 6000 min÷ −1, depending on the location of the PK belt in where:beltn workpulley.is a Thi workings type of rotational solution appeared speed of in the this spindle, machine rpm. tool in 2011 [38]. On the spindle, Ø 450, TheØ 350 short or Ø 300spindle mm circular of the sliding saw blades table can saw be Fx3 clamped (before with modernization) the Ø 125 mm diameter presented flanges, at work which [34 ] can 1 developdefines working the rotation speeds speed. of 3500, On 4500both andsides, 6000 the minspindle− , dependingwas supported on theon 6206 location 2RS1 of Explorer the PK belt(SKF) in belt pulley.bearings This type and ofthe solution ratio L/d appeared= 2.6. Deformation in this machine calculations tool were in 2011 carried [38]. out On with the the spindle, use of Ø450,the Finite Ø350 or Ø300Element mm circular Method saw (FEM blades) in which can betheclamped spindle model with was the loaded Ø125 mmon the diameter rear end flanges,by a force which Fs-d from defines the rotationthe shaft speed. drive, On which both was sides, determined the spindle using was the supported available software on 6206 of 2RS1 the Explorercompany (SKF)SKF (is bearings an acronym for Svenska Kullagerfabriken, Swedish Ball Bearing Factory, SKF Sweden AB, Göteborg, and the ratio L/d = 2.6. Deformation calculations were carried out with the use of the Finite Element Sweden) [44]. The circular saw blade at the front end was loaded, with forces which values and Method (FEM) in which the spindle model was loaded on the rear end by a force F from the shaft location were determined according to the work [8], assuming that full rated engine powers-d of 7.5 kW drive,is whichavailable was in the determined cutting zone. using the available software of the company SKF (is an acronym for Svenska Kullagerfabriken,Computations of maximum Swedish deformations Ball Bearing of the Factory, Fx3 (Figure SKF Sweden3) and Fx550 AB, (Figure Göteborg, 4) saw Sweden) spindles [44]. The circularwere carried saw out blade as static at thestructural front endlinear was analyses. loaded, In both with models forces linear which tetrahedrons values and type location elements were determinedwith a fully according structured to the mesh work of 1 [ 8mm], assuming size (the mesh that of full elements rated engine was not power refined) of were 7.5 kW applied. is available The in the cuttingmodel zone.assumed one degree of freedom in the form of the possibility of rotation in relation to the Computationsspindle axis, which ofmaximum in the machine deformations tool’s coordinate of the system Fx3 (Figure it is the3 )Z and axis. Fx550 Moreover, (Figure it was4) saw assumed spindles werethat carried both out of the as bearing static structural supports are linear cylindrical analyses. and In do both not allow models for lineartranslational tetrahedrons displacement type elementsin X and Y directions, but only allow for rotation in the relation to the axis Z. In computations, the material with a fully structured mesh of 1 mm size (the mesh of elements was not refined) were applied. properties of spindles were as follows: Young’s modulus 205 GPa, Poisson’s ratio 0.28. The model assumed one degree of freedom in the form of the possibility of rotation in relation to the In Figure 3, the resultant deformation of the spindle in the Fx3 sawing machine caused by the spindle axis, which in the machine tool’s coordinate system it is the Z axis. Moreover, it was assumed cutting forces and by the force Fs-d, for the operating speed nwork = 3500 min−1 is presented. The that bothmaximum of the deflection bearing supportsof the spindle are cylindrical in this case andwas doequal not to allow 0.034756 for translationalmm. Based on displacement the obtained in X and Yresults directions,, it was but found only that allow forfor the rotation two lowest in the rotational relation speeds to the axis of the Z. saw In computations, spindle the condition the material propertiesdescribed of spindles by Equation were (2) as is follows:not satisfied. Young’s For that modulus reason, 205the model GPa, Poisson’sof the spindle ratio was 0.28. redesign.

Appl. Sci. 2020, 10, 7386 6 of 13

The new spindle model was calculated with the support diameters equal to Ø 35 mm (under 6207 2RS1 Explorer bearing), increasing the L/d ratio to 3.0, according to SKF recommendations for optimum spacing of spindle supports [45]. Due to the predominant influence of the forces from the drive, the diameter of the rear end was also increased. In Figure 4, the resultant deformation of the spindle in the Fx550 sawing machine caused by the cutting forces and by the force Fs-d, for the operating speed nwork = 3500 min−1 is presented. The resulting deformation values for the changed spindle turned out to be smaller [34], which resulted in the higher ncr/nwork ratios for each case of rotational speed (Figure 5). An improved spindle of the new type (Figure 2b) was implemented in the table sliding saw Fx550. Moreover, in the latter machine tool to increase the sawing aggregate rigidity of the panel saw, the stiffness of the motor plate guiding was increased, and simultaneously rolling guides with higher rigidity were used [38].

Figure 4. The resultant deformation (in mm) of the spindle in the Fx550 sawing machine caused by the Figure 4. The resultant deformation (in mm) of the spindle in the Fx550 sawing1 machine caused by cutting forces and by the force Fs-d, for the operating speed nwork = 3500 min− . the cutting forces and by the force Fs-d, for the operating speed nwork = 3500 min−1.

6000

4500

spindle speed, rpmrotationalspindle 3500

0 0.5 1 1.5 2 2.5

ncr/nwork

Fx550 Fx3

Figure 5. Ratios of critical rotational speeds to working rotational speeds revolutions ncr/nwork of spindles of table sliding saws Fx3 (an old applied solution) and Fx550 (a currently applied design) (Rema SA), where vertical bold lines indicate the limits of the recommended values of the ratio

ncr/nwork.

3. Dynamic Properties of the Machine Tool

3.1. Dynamic Properties of the Main Driving System Some selected problems concerning the empirical research of the saw cutting unit of the table sliding saw were described by Orłowski et al. [34]. Cempel [32] expressed that the diagnosis should be limited to one definite industrial case with using repeated methodology. This recommendation was due to the certainty that setting standards of diagnosis is too risky [32]. Before performing of vibroacoustic empirical tests the researcher should consider which parameter should be measured in a given case. The vibration velocity is a common choice, but not always the right one, because the better option is often measuring of displacements or accelerations [32]. Appl. Sci. 2020, 10, 7386 6 of 13

While the review of the spindle designs, it was observed that the position of the driving wheel on the spindle may be different, therefore, numerical calculations were additionally performed to demonstrate the effect of the pulley position on the spindle with increased rigidity [46] on its critical rotational speeds. The results of the calculations showed that for this type of rigid spindle, in each of theAppl. analyzed Sci. 2020, 10cases, 7386 of the wheel position, the critical rotational speed was approximately 14,400 min6 of− 121 and the ratio of ncr/nwork ≈ 2.4. In Figure3, the resultant deformation of the spindle in the Fx3 sawing machine caused by 1 the cutting forces and by the force Fs-d, for the operating speed nwork = 3500 min− is presented. The maximum deflection of the spindle in this case was equal to 0.034756 mm. Based on the obtained results, it was found that for the two lowest rotational speeds of the saw spindle the condition described by Equation (2) is not satisfied. For that reason, the model of the spindle was redesign. The new spindle model was calculated with the support diameters equal to Ø35 mm (under 6207 2RS1 Explorer bearing), increasing the L/d ratio to 3.0, according to SKF recommendations for optimum spacing of spindle supports [45]. Due to the predominant influence of the forces from the drive, the diameter of the rear end was also increased. In Figure4, the resultant deformation of the spindle in the Fx550 sawing machine caused by the cutting forces and by the force Fs-d, for the operating speed 1 nwork = 3500 min− is presented. The resulting deformation values for the changed spindle turned out to be smaller [34], which resulted in the higher ncr/nwork ratios for each case of rotational speed (Figure5). An improved spindle of the new type (Figure2b) was implemented in the table sliding saw Fx550. Moreover, in the latter machine tool to increase the sawing aggregate rigidity of the panel saw, the stiFigureffness 4. ofThe the resultant motor platedeformation guiding (in was mm) increased, of the spindle and in simultaneously the Fx550 sawing rolling machine guides caused with by higher

rigiditythe cutting were used forces [38 and]. by the force Fs-d, for the operating speed nwork = 3500 min−1.

6000

4500

spindle speed, rpmrotationalspindle 3500

0 0.5 1 1.5 2 2.5

ncr/nwork

Fx550 Fx3

FigureFigure 5. 5. RatiosRatios of of critical critical rotational rotational speeds speeds to to working rotational speeds revolutions ncrcr//nwork ofof spindlesspindles of of table table sliding sliding saws saws Fx3 Fx3 (an (an old old applied applied solution) solution) and and Fx550 Fx550 (a (a currently currently applied applied design) design) (Rema(Rema SA), SA), where where vertical vertical bold bold lines lines indicate indicate the limitsthe limits of the of recommended the recommended values values of the ratio of thencr / rationwork .

ncr/nwork. While the review of the spindle designs, it was observed that the position of the driving wheel 3.on Dynamic the spindle Properties may be of di thefferent, Machine therefore, Tool numerical calculations were additionally performed to demonstrate the effect of the pulley position on the spindle with increased rigidity [46] on its critical 3.1.rotational Dynamic speeds. Properties The of results the Main of the Driving calculations System showed that for this type of rigid spindle, in each of 1 the analyzed cases of the wheel position, the critical rotational speed was approximately 14,400 min− Some selected problems concerning the empirical research of the saw cutting unit of the table and the ratio of ncr/nwork 2.4. sliding saw were described≈ by Orłowski et al. [34]. Cempel [32] expressed that the diagnosis should be3. limited Dynamic to Propertiesone definite of industrial the Machine case Tool with using repeated methodology. This recommendation was due to the certainty that setting standards of diagnosis is too risky [32]. Before performing of vibroacoustic3.1. Dynamic empirical Properties oftests the the Main researcher Driving Systemshould consider which parameter should be measured in a givenSome case. selected The vibration problems velocity concerning is a common the empirical choice, research but not ofalways the saw the cuttingright one, unit because of the table the bettersliding option saw wereis often described measuring by Orłowski of displacements et al. [34 or]. Cempelaccelerations [32] expressed [32]. that the diagnosis should be limited to one definite industrial case with using repeated methodology. This recommendation was due to the certainty that setting standards of diagnosis is too risky [32]. Before performing of vibroacoustic empirical tests the researcher should consider which parameter should be measured in a Appl. Sci. 2020, 10, 7386 7 of 12

givenAppl. Sci. case. 2020 The, 10, 7386 vibration velocity is a common choice, but not always the right one, because the better7 of 13 Appl. Sci. 2020, 10, 7386 7 of 13 option is often measuring of displacements or accelerations [32]. VibrationVibration diagnosticdiagnostic experimentalexperimental analyzesanalyzes havehave beenbeen carriedcarried outout onon thethe sawsaw cuttingcutting unitunit ofof thethe modernizedmodemodernizedrnized tabletable slidingsliding sawsaw Fx3Fx3 (currently(currently Fx550)Fx550) (f.(f.(f. REMAREMA S.A.,SS..AA..,, Reszel,Reszel, Poland).PolandPoland).). The The circular circular sawsaw bladeblade withwith mainmain dimensionsdimensions Ø300 Ø 300 × 3.23.2 × 30 and numbernumber ofof teethteeth zz == 96 was mounted onon thethe spindlespindle blade with main dimensions Ø 300 ×× 3.2 × 30 and number of teeth z = 96 was mounted on the spindle with collars of Ø 125 mm. The measured rotational speed of spindle was nwork = 5128 rpm. The place with collarscollars ofof Ø125Ø 125 mm. mm. The The measured measured rotational rotational speed speed of of spindle spind wasle wasnwork nwork= 5128= 5128 rpm. rpm. The The place place of theofof the the accelerometer accelerometer accelerometer (A in (A (A Figure in in Figure Figure6) installation 6) 6) installation installation was also was was the also also measuring the the measuring measuring point position, point point position, position, and was and and located was was onlocatedlocated the top onon ofthethe the toptop main ofof thethe body mainmain of body thebody spindle ofof thethe system.spindlespindle Thesystem.system. Fluke TheThe 810 FlukeFluke vibration 810810 vibrationvibration tester (f. testertester Fluke, (f.(f. Everett, Fluke,Fluke, Washington,Everett,Everett, Washington,Washington, DC, USA) USA)USA) was was usedwas usedused to measuring toto measuringmeasuring of the ofof accelerations thethe accelerationsaccelerations in the inin X, thethe Y, X,X, Z axes,Y,Y, ZZ axesaxes which,, whichwhich are axes areare ofaxesaxes the ofof machine thethe machinemachine tool co-ordination tooltool coco--ordinationordination system systemsystem (Figure (Figure(Figure6). 6).6).

Figure 6. A view of the saw cutting unit of the modernized table sliding saw Fx3 with a position of Figure 6. A view ofof thethe sawsaw cutting cutting unit unit of of the the modernized modernized table table sliding sliding saw saw Fx3 Fx3 with with a position a position of the of the accelerometer A, where: X, Y, Z – axes of the table sliding saw co-ordination system [47]. accelerometerthe acceleromete A,r where: A, where:X, Y, X, Z Y,—axes Z – axes of the of tablethe table sliding sliding saw saw co-ordination co-ordination system system [47]. [47].

TheThe vibrationvibration testertester FlukeFluke 810810 automaticallyautomatically convertsconverts thethe receivedreceived accelerationacceleration signalssignals intointo aa waveformwaveform plotplot (Figure(Figure7 7a)a)7a) and andand creates createscreates vibration vibrationvibration velocity velocityvelocity spectra spectraspectra (Figure (Figure(Figure7 b).7b).7b). The TheThe latter latterlatter feature featurefeature is isis a aa disadvantage,disadvantage, since,since,since, the thethe person personperson conducting conductingconducting the thethe tests teststests has hashas practically practicallypractically no nono inﬂuence influenceinfluence on onon the thethe way wayway the thethe test testtest is performed,isis performed,performed, and andand the thethe results resultsresults are areare processed. processed.processed.

((aa)) ((bb)) Figure 7. Waveform of the acceleration signal (a) and vibrational velocity spectrum of the signal (b) of FigureFigure 7.7. WaveformWaveform ofof thethe accelerationacceleration signalsignal ((aa)) andand vibrationalvibrational velocityvelocity spectrumspectrum ofof thethe signalsignal ((bb)) the modernized table sliding saw Fx3 in the measurement point (Figure6) in Z axis [47]. ofof thethe modernizedmodernized tabletable slidingsliding sawsaw Fx3Fx3 inin thethe measurementmeasurement pointpoint (Figure(Figure 6)6) inin ZZ axisaxis [47][47]..

TheThe changeschanges ofof componentcomponent velocitiesvelocities vvjj inin functionfunction ofof timetime tt,, cancan bebe computedcomputed onon thethe basisbasis ofof The changes of component velocities vj in function of time t, can be computed on the basis of vibrational velocity amplitudes (Figure7b) [ 47]. The Root-Mean-Square (RMS) values of vibrational vibrationalvibrational velocityvelocity amplitudesamplitudes (Figure(Figure 7b)7b) [[4747].]. TheThe RootRoot--MeanMean--SquareSquare ((RMSRMS)) valuesvalues ofof vibrationalvibrational velocities were calculated for each measurement axis of the modernized table sliding saw Fx3. In the velocitiesvelocities werewere calculatedcalculated forfor eacheach measurementmeasurement axisaxis ofof thethe modernizedmodernized tabletable slidingsliding sawsaw Fx3.Fx3. InIn thethe next step, the total vibrational velocity for the measurement point was computed from the equation nextnext step,step, thethe totaltotal vibrationalvibrational velocityvelocity forfor thethe measurementmeasurement pointpoint waswas computedcomputed fromfrom thethe equationequation asas follows:follows: q as follows: 2 2 2 vΣ(RMS) = vX(RMS) + vY(RMS) + vZ(RMS) , (3) 2 2 2 2 2 2 (3) v RMS  vX RMS  vY RMS  vZ RMS , (3) v RMS  vX RMS  vY RMS  vZ RMS ,

FigureFigure 8 8 presents presents RMSRMS valuesvalues of of vibrational vibrational velocities velocities in in directions directions of of XX,, YY andand ZZ axesaxes of of the the cocoordinationordination system.system. InIn FigureFigure 88,, thethe valuevalue ofof thethe resultantresultant RMSRMS ofof vibrationalvibrational velocityvelocity SigmaSigma waswas alsoalso Appl. Sci. 2020, 10, 7386 8 of 12

Appl. Sci.Figure 2020,8 10 presents, 7386 RMS values of vibrational velocities in directions of X, Y and Z axes of8 of the 13 coordination system. In Figure8, the value of the resultant RMS of vibrational velocity Sigma was also shown. The The analyzed analyzed values values in in three three directions directions XX,, YY and Z were measured at thethe measurementmeasurement point (Figure 66).).

Figure 8. RRoot-mean-squareoot-mean-square values values of of vibrational vibrational velocities velocities in in directions directions of of XX,, YY andand Z axes of the modernized tabletable slidingsliding sawsaw Fx3Fx3 co-ordination co-ordination system system measured measured at at the the measurement measurement point point (Figure (Figure2a) 2a)together together with with a resultant a resultant Root-Mean-Square Root-Mean-SquareRMS RMSof vibrational of vibrational velocity velocity Sigma. Sigma.

Due to the use in literature the different diﬀerent criteria values for making an assessment of the new machine tool [ 32] in the analyzed investigation were determined two values: RMS amplitude of the total vibrational velocity and the peak value (amplitude). Obtained Obtained values values from from experimental experimental test are presented in Table 1 1.. BothBoth BlakeBlake andand ŁŁączkowski ˛aczkowskiare are guidedguided byby thethe values of the peak amplitude [3232].]. However, for for both both standards, standards, the the experimental experimental values values obtained obtained are are evaluated evaluated differently diﬀerently (Table (Table 1).1 A). Asimilar similar situation situation can can be be observed observed for for the the other other two two machine machine tool tool evaluation evaluation standards: standards: ow ownn standards standards of the the American American diagnostic diagnostic company, company (IRD, (IRD Machanalysis Machanalysis Limited, Limited Maharashtra,, Maharashtra, India), India) and the, and British the Britishcompany company VCI Ltd VCI (Strabane, Ltd (Strabane Great, Great Britain). Britain) In this. In case,this case, both both standards standards base base their their assessment assessment on onthe the value value of of the theRMS RMS. Unfortunately,. Unfortunately, the the evaluation evaluation of of the the examined examined main main spindlespindle systemsystem of the modernized table sliding saw Fx3 based on the experimental experimental data received is again divergent for both standards (Table 1 1).). TheThe presentedpresented analysisanalysis showsshows thatthat therethere areare nono unequivocalunequivocal criteriacriteria forfor assessingassessing the conditioncondition ofof the the examined examined machine machine tool. tool. Moreover, Moreover, the the choice choice of assessment of assessment criteria criteria can very can oftenvery oftenbe more be more or less or subjective. less subjective.

Table 1. Experimental values of vibrational velocities with diagnostic evaluation on basis of a few Table 1. Experimental values of vibrational velocities with diagnostic evaluation on basis of a few diagnosis standards. diagnosis standards. RMS v v RMS of Vibrationalof Vibrational Velocities, Velocities, vΣ Σ PPeakeak V Valuealue of of V Vibrationalibrational V Velocities,elocities, vmaxmax mm s 1 mm s 1 mm·s−1 · − mm·s· −1− ExperimentalExperimental Results 2.08 3.27 2.08 3.27 Results Range RMS of vibrational velocities for Range RMS of vibrationaldiagnosis, velocities mm sfor1 diagnosis, mm·s−1 · − StandardsStandards DiagnosisDiagnosis oror *range*range peak peak value value of vibrational of vibrational velocities, velocities, mm·s−1 mm s 1 IRD Mechanalysis Admissible 2–4· − VCI IRDLtd. MechanalysisGood Admissible1.27– 2–42.54 Blake VCI Ltd.Admissible Good*2.20 1.27–2.54–6.00 Łączkowski Good *2.50–6.30 Blake Admissible *2.20–6.00 3.2. DynamicŁ ˛aczkowski Properties of the Machine T Goodool Body *2.50–6.30 In the sliding table saw Fx550, which is the follower of the circular sawing machine Fx3, a new machine frame body made of steel sections connected with special lockers and welded was applied (Figure 9). In the previous version of the machine tool body, there was a solution which based on a set of bent body parts connected (mainly welded) with flat steel plates. The new design of the machine Appl. Sci. 2020, 10, 7386 9 of 12

3.2. Dynamic Properties of the Machine Tool Body In the sliding table saw Fx550, which is the follower of the circular sawing machine Fx3, a new machine frame body made of steel sections connected with special lockers and welded was applied (Figure9). In the previous version of the machine tool body, there was a solution which based on a set Appl. Sci. 2020, 10, 7386 9 of 13 of bentAppl. body Sci. 2020 parts, 10, 7386 connected (mainly welded) with ﬂat steel plates. The new design of the9 machineof 13 tool bodytool body has muchhas much more more sti ﬀstiffnessness of of the the machine machine structure in in comparison comparison with with the thepanel panel saw sawFx3, Fx3, and thattooland kindbodythat kind ofhas the ofmuch the body bodymore can canstiffness be be met met of only onlythe inmachine in the the highest-classhighest structure-class in panel panelcomparison saws. saws. with the panel saw Fx3, and that kind of the body can be met only in the highest-class panel saws.

FigureFigure 9. General 9. General view view of of the the frameframe body of of the the sliding sliding table table saw saw Fx550 Fx550.. Figure 9. General view of the frame body of the sliding table saw Fx550. ThisThis body body solution solution has has given given a spectaculara spectacular reductionreduction of of the the resultant resultant peak peak values values (amplitudes) (amplitudes) This body solution has given a spectacular reduction of the resultant peak values (amplitudes) vΣ ofv theΣ of vibrationalthe vibrational velocities velocities (Figure (Figure 10 10)) measured measured at the point point #4. #4. The The measurement measurement point point #4 was #4 was situatedvsituatedΣ of in the each invibrational each case case in velocitiesin the the middle middle (Figure on the10) the bodymeasured body wall wall whichat the which waspoint wasparallel #4. parallelThe to measurement the tomain the spindle main point axis. spindle #4 wasThe axis. situated in each case in the middle on the body wall which was parallel to the main spindle axis. The The valuevalue ofof thethe vibrationvibration velocity for for the the new new solution solution is issignificantly signiﬁcantly below below the thepermissible permissible minimum minimum value of the vibration velocity for the new solution is significantly below the permissible minimum valuevalue recommended recommended by Łby ˛aczkowski[ Łączkowski32 [32].]. value recommended by Łączkowski [32]. Tytuł wykresu Tytuł wykresu

3.5

]

1 -

s 3.5

]

- 3 s

3 2.5 2.5 2 2 1.5 1.5 1 1 0.5

Vibrational velocity [mm velocity Vibrational 0.5

0 Vibrational velocity [mm velocity Vibrational 0 #4 #4 Fx3 Fx550 Fx3 Fx550

Figure 10. Resultant peak values (amplitudes) of the vibrational velocities vΣ measured on the frame Figure 10. Resultant peak values (amplitudes) of the vibrational velocities vΣ measured on the frame Figurebody 10. atResultant the measurement peak values point(amplitudes) #4 of the sliding of table the vibrational saws Fx3 and velocities Fx550. vΣ measured on the frame bodybody at the at measurementthe measurement point point #4 #4 of of the the sliding sliding tabletable saws Fx3 Fx3 and and Fx550 Fx550.. Testing the unloaded machine tools of both Fx3 and Fx550, maintaining tool setting, machining TestingparametersTesting the were unloadedthe unloaded carried machine out machine in industrial tools tools of of both conditionsboth Fx3Fx3 and in Fx550the Fx550, frame, maintaining maintaining of the project tool tool setting, POIR.01.01.01 setting, machining machining-00- parameters were carried out in industrial conditions in the frame of the project POIR.01.01.01-00- parameters05888/15 were (in carried Polish out Program in industrial Operacyjny conditions Inteligentny in the frame Rozwój, of the project Smart POIR.01.01.01-00-05888 Growth Operational /15 05888/15 (in Polish Program Operacyjny Inteligentny Rozwój, Smart Growth Operational (in PolishProgramme Program). Measurements Operacyjny of noise Inteligentny were done Rozw withó thej, Smart use of the Growth integrating Operational sound level Programme). meter Programme). Measurements of noise were done with the use of the integrating sound level meter Measurements(SON-50) (f. of Sonopan, noise were Bialystok, done with Poland) the use in of the the points integrating according sound to the level International meter (SON-50) Organization (f. Sonopan, (forSON Standardization-50) (f. Sonopan, (ISO Bialystok,) standard Poland) (ISO 7960:in the 1995) points [48]. according At the locationto the International of the microphone Organization in the Bialystok, Poland) in the points according to the International Organization for Standardization (ISO) foroperator Standardization position (about (ISO )1.5 standard m over the(ISO hall 7960: floor 1995)) for the[48]. sliding At the table location saw Fx3of the the microphone noise on the inidling the standardoperatorwas at (ISO the position level 7960: of (about 1995)77.5 dB 1.5 [48 whereas m]. over At the inthe case locationhall of floor Fx550) of for it the the was microphonesliding 73.5 dB. table The saw inresultant theFx3 operatorthe noise noise determined on position the idling as (about 1.5 mwasan over av aterage the the level from hall of ﬂoor)all 77.5 measurement dB for whereas the sliding points in case tablewas of Fx550 as saw follows: it Fx3was for the73.5 Fx3 noisedB. equalled The on resultant the to 79 idling dB noise and was determined for atFx550 the was level as of anequal average 74.6 dB.from all measurement points was as follows: for Fx3 equalled to 79 dB and for Fx550 was equalThanks 74.6 dB. to: a new body of the sliding table saw Fx550, a modernized stiffer spindle, a stiffer system of theThanks electric to: motor a new plate body guiding of the sliding[38], and table a steady saw Fx550 PK belt, a strainingmodernized system stiffer th espindle described, a stiffer sliding system table of the electric motor plate guiding [38], and a steady PK belt straining system the described sliding table Appl. Sci. 2020, 10, 7386 10 of 12

77.5 dB whereas in case of Fx550 it was 73.5 dB. The resultant noise determined as an average from all measurement points was as follows: for Fx3 equalled to 79 dB and for Fx550 was equal 74.6 dB. Thanks to: a new body of the sliding table saw Fx550, a modernized stiﬀer spindle, a stiﬀer system of the electric motor plate guiding [38], and a steady PK belt straining system the described sliding table saw Fx550 has been a source of the general noise on the idling at the level lower about 5 dB in comparison to the sliding table saw Fx3.

4. Conclusions This review’s objective was to present a new holistic approach in the process of changing the sliding table saw design solutions in order to obtain a better machine tool that can compete in the contemporary machine tool market. Based on the review, it can be concluded that:

In modern design solutions of sliding table saws, the main circular saw blades are clamped by • means of collars on spindles with a short support spacing with a ratio of the supports spacing L to the inner diameter of the front bearing d of about 3. It ought to be emphasized, that excessive increase in the diameter of the front bearing d and simultaneous striving for the optimum support spacing is not possible with the sliding table saws, as every manufacturer aims for the smallest possible dimensions of the cutting unit. To evaluate the dynamic properties (behavior) of the spindle it is useful to determine their critical • values of rotational speeds. The maximum deformations determined in static structural linear analyses showed that in the case of the Fx550 saw spindle they are 10 smaller in comparison × with the spindle of the Fx3 saw, which made it possible to estimate critical speeds, which satisfied the inequality presented in Equation (2). The use of only rational imitation in the spindle design on the basis of the other sliding table saws • produced does not lead to the expected effect in the form of correct spindle operation, and this mainly concerns the possible exceeding of the tool’s lateral runout value. The errors on sawn surfaces caused by the tool’s lateral runout value can be more apparent • especially in case of top wood composite boards (MDF, HDF, LVL, plywood or particle boards) in the sawn package. An application in a new machine frame body of steel sections connected with special lockers • instead of the solution which based on a set of bent body parts between flat steel plates resulted in lower noise values of around 5 dB during idling. If the noise of the machine tool is decreased and simultaneously vibrations are at lower • level, hence, it could be expected higher accuracy of sawing which is especially important in furniture production. Experimental values of vibrational velocities (RMS or peak value of vibrational velocities) • on basis of a few diagnosis standards allowed us to classify the examined main spindle system of the sliding table saw Fx550 as good or admissible design solution from the point of its dynamics.

Author Contributions: Conceptualization, K.A.O., P.D. and W.B.; methodology, K.A.O., W.B. and D.C.; investigation, K.A.O., W.B., P.D., D.C. and T.P.; writing—original draft preparation, K.A.O., D.C.; writing—review and editing, K.A.O., D.C. and T.P.; supervision, K.A.O.; project administration, K.A.O. All authors have read and agreed to the published version of the manuscript. Funding: It is kindly acknowledged that this work has been carried out within the framework of the project POIR.01.01.01-00-05888/15, which has been financially supported by the European Regional Development Fund. The authors would also like to acknowledge the company REMA S.A. in Reszel (Poland), which is the beneficiary of the project. Acknowledgments: It should be acknowledged that the sliding table panel saw Fx550 has been awarded with the MTP Gold Medal of DREMA 2017 in Poznan, Poland. The role of Eng. Karol Duchnicz from Eaton Truck Components Sp. z o.o., ought to be acknowledged for his valuable guidance in spindle modelling. Conflicts of Interest: The authors declare no conflict of interest. Appl. Sci. 2020, 10, 7386 11 of 12

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