static bearings 58 oer the indirect benets of: improved hard-part machined surface texture; greater compo- nent accuracy and precision; coupled with increased tool life. While, due to the fact that hydraulic fuild is virtually incompressible, if an interrupted cut occurs for any reason, the tool can later pick-up exactly where the interruption occurred thereby eliminating the os- tensibly termed ‘witness marks’ on the machined sur- face. Great demands for increased spindle power are not necessary, as typical D OC ’s are ≈0.75 mm, coupled to small feedrates. With for example, the cutting data for a φ12 mm, hard-turned part, might be by utilising a spindle speed of 4,500 rev min –1 , which equates to a surface speed of ≈170 m min –1 . is is well within the capabilities of some turning centres today, that have spindle speeds of 10,000 rev min –1 . As one can gather from this discussion, hard-part turning and thread- ing (Fig. 251a) is principally concerned with saving money, by removing additional and now, superuous operations from the overall product’s cycle time. It has been reported by industrial-users, that by utilising a hard-part turning strategy, then the total time to com- plete the component has been reduced by up to 75%, when compared to the traditional approach, of: rough- turning; then heat-treating; and nally cylindrically grinding. is latter process of cylindrical grinding, can still be valid where extremely tight tolerances are to be held, coupled to when high-quality surface texture demands are to be met. Oen, both for large-batches, or if continuous production runs are necessary, for ei- ther hard-part nished turning, or when cylindrical grinding, they require critical dimensional tolerances to be held across certain diameters, or indeed, for their lengths. In this metrological situation, a ‘receiver gaug- 58 ‘Hydro-static bearing performance’ , is characterised by three factors, these are its: load-carrying capacity; oil ow-rate; and pumping power. e magnitudes of the hydro-static coe- cients depend very much on the pad design, such that: W = a f A p p r Q = q f W/A p × h 3 / µ P = p r Q = H f (W/A p ) 2 × h 3 / µ Where: W = Load on the bearing (N); Q = Volume ow-rate of oil (m 3 s –1 ); P = Pumping power (N × m s –1 ≡ W);a f = Pad load coecient (dimensionless); q f = Pad ow coecient (dimen- sionless); H f = Pad power coecient (dimensionless, because H f = q f /a f ); A p = Pad area (m 3 );p r = Oil pressure in the recess of the pad (Pa); h = Film thickness (m); µ = Dynamic viscosity of the oil (Pa.s). (Source: Mott, 1985) ing’ unit specially-congured to measure such part dimensional features can be built-up from modular units and its associated instrumentation (Fig. 252). Not only can this custom-built receiver gauge assem- bly (Fig. 252b), simultaneously measure many compo- nent features quickly, but through the instrumentation unit (Fig. 252a), ‘Statistical Process Control’ (SPC) can be employed to up-date the whole process through ‘closed-lop’ feedback to the machine’s controller. is up-dating will automatically modify the tool osets, thereby minutely adjusting the process and as such, re- ducing variability in the process to a minimum. Parts can be loaded into the adjacent ‘receiver gauge unit’ , via a gantry-robot (Fig. 250e), or alternatively by a ‘dedi- cated robotic device’. Once held in the robot’s gripper, the nished hard-turned/-ground part, is manipulated into the desired orientation by its axes, then steadily lowers the completed workpiece onto the component support plates within the receiver unit. In the case of Fig. 252b, the centres will automatically engage with the centre-drilled holes, slightly liing the compo- nent to its measuring height, prior to the measuring heads progressively moving forward to contact each machined component’s surface feature – for automatic measurement and control. .. Hard-Part Milling Introduction Until relatively recently, the application of HSM by milling of hardened die and mould steels was consid- ered something of a ‘black-art’. is is not the case, as by adhering to some basic machining principles and guidelines the whole process becomes a somewhat: straightforward; predictable; and a protable activity. In eect, there are three primary machining meth- ods utilised to produce hardened dies and moulds, although it should be stated that the die/mould con- guration, along with its respective hardness will de- termine which technique, or combination of processes produces the optimum manufacturing route. However, notwithstanding these circumstances, the primary methods can be classied as follows: 1. ‘So machining’ – milling – this is where the part is ‘roughed-out’ prior to its hardening heat treatment. e technique of ‘so-machining’ is normally con- sidered when milling large workpieces, or com- ponents requiring deep-cuts, or wide features – such Machining and Monitoring Strategies Figure 251. Hard-part machining operations undertaken on many components by through-hardening, hard-facing or by surface-hardening heat-treatment; are acceptable. [Courtesy of Sandvik Coromant] . Chapter Figure 252. In-process gauging, used for up-dating the cutting process voiding ‘tool-drifting’ during a production run. [Courtesy of Mahr/Feinpruf ] . Machining and Monitoring Strategies as that depicted in Fig. 251b. Aer rough-milling, any semi-nishing and nishing operations can be undertaken in the hardened condition, 2. Hard-part milling – this is mainly where small-di- mensional parts, or components requiring the pro- duction of shallow-cut features that can be readily milled (e.g. threads – Fig. 251a; gears and hobs – Fig. 251c) – in the hardened state, 3. Electrical discharge machining (EDM) – is usually utilised when the part incorporates thin features, requiring deep cuts, thus the EDM process may be the only practical solution to this problem. Hard-Milling – Tool Selection and Replacement For most die and mould operations, selecting the ap- propriate cutter geometry is important, with many op- erators choosing ball-nosed end mills (Fig. 249 – bot - tom right) for such hard-part milling work. Such geometry is chosen for rouging and nishing oper- ations, because the tool’s large radius dissipates both the heat, while ‘spreading’ the cutting forces across its longer cutting edges. Additionally, the ball-nose end mill enables the user to cut closer to the net shape of the part’s geometry at high speeds and feeds. When a part incorporates wide and at areas across its base – needing to be milled, a corner-radiused tool should ideally be utilised aer the surface has been roughed- out with the ball-nosed tooling. e logic behind em- ploying the corner-radiused tool for nishing, is that with its smaller radius it cannot dissipate the heat and forces as readily as the ‘ball-nose’ , this is why it is usu - ally used for semi-nishing/nishing operations when hard-part milling. If a square shouldered part feature is needed, then a ‘square-ended tool’ is only used aer the ‘ball-nose’ has roughed-out the component’s fea- ture – leaving the minimum of stock to be removed. is ‘square-ended’ cutter – due to its sharp corner, has a tendency to chip/fracture, since it acts as a ‘stress- raising source’ for the heat and cutting forces. Tool rigidity is important, with the tool’s shank being much larger in diameter to that of the cutting diameter. With ball-nosed cutters, a small dra an- gle of about ½° is employed for additional strength, while the tool’s neck is usually slightly-relieved when HSM milling straight walls. In both of these cases, the tool’s projection from its holder should be kept to a minimum – to improve its intrinsic rigidity. Returning briey to the former case of the cutter having a dra angle. Another reason for the ½° dra angle when ma- chining dies and moulds, is that if for example, when the hardened die has a dra angle of 5°, the cutters modied relief should be ½° clearance, producing an included angle of cutter body relief of 4½°. During machining a die cavity (Figs 246 – bot - tom right and 249b), the excessive heat that is gener- ated modies the part’s surface topography, which in turn, reduces component accuracy. One technique to minimise such heat generation and retention while milling, is by controlling the radial step-over (i.e. pick- feed) distance for adjacent tool paths – when taking ‘parallel cuts’ 59 (Fig. 84c). is radial step-over is the distance between the centrelines of successive paral- lel cuts ‘a e (p) ’ – shown in Fig. 247b. erefore, for ball- nosed roughing-out operations, this radial step-over should ideally be between 25 to 40% of the cutter’s diameter. Conversely, for nish-milling – for a given cusp height on a at surface, the radial step-over can be calculated, as follows (Fig. 247b): Radial step-over (mm) = √4( a p × D e ) – 4 (a p 2 ) Where: cusp height is the chordal deviation – nish tolerance, thus, a p = cusp height (mm), D e = tool diam- eter @ a set D OC (mm). Cusp height (mm) = D e/ 2 – √ (D e 2 – a e (p) 2 )/4 Where: a e (p) = radial step-over (mm). (Sources: adapted from Sandvik Coromant, 1994; Ma- carthur, 2001) Since, the radial step-over determines the length of time each cutting edge spends in the actual cut, in conjunction with the amount of time it has to cool, prior to re-entering the following cutting-pass. is in eect, simplistically determines the quantity of heat that will accumulate in both the tool and the ma- chined workpiece. So, when the radial step-over is too wide, the heat builds-up in the cutter’s edge, due to the fact that there is insucient time for it to conduct the heat away, before it re-enters the following cut. While, smaller step-overs can facilitate ‘almost’ a continuous cooling action, which limit’s the heat generation and its 59 ‘Parallel cuts’ – when milling, are sometimes referred to as ‘lace cuts’. If they are not parallel – such as when pocket-mill- ing a triangular feature, where parallel cuts would be ineec- tive, then the technique here is to utilise variable step-over cuts, termed: ‘non-lace cuts’.(Source: Smith et al., 1993) Chapter retention, allowing a slightly higher cutter rotational speed to be programmed. A suitable coating selec- tion for example, on a cemented carbide cutter, will also enable higher speeds to be realised. In hard-part milling operations, coatings, such as: titanium car- bonitride (TiCN) can withstand temperatures up to 400°C, comparing this to titanium aluminium nitride (TiAlN), which can withstand cutting temperatures of up to 800°C, indicates for many hardened alloy steel dies and moulds, the latter coating makes for a wiser choice in these production circumstances. e selection of speeds and feeds will also aid in controlling heat build-up. With large chip thicknesses helping to remove heat build-up in the tool and work- piece. When chip loads are too light, the heat quickly builds-up – as edges tend to rub the surface being milled, which in turn, aects tool life and may create ‘white-layering’ in the sub-surface in steel-based prod- ucts. So using the largest possible chip loads improves through-put of parts. By way of illustration, if the chip load per tooth should be 0.2 mm, but instead it is only 0.05 mm, then a workpiece that normally takes around 18 minutes to machine, will now actually take 72 min- utes. is increased time means the tool’s edge will now spend 400% longer in-cut. Flood coolant should not be used when adopting an HSM milling strategy for hardened metals (>40 HR C ). In the USA some industrial trials were conducted into milling such hardened workpieces and, it was reported that by not using ood coolant then tool life was in- creased by 500% – on average. ese trials including various methods of coolant delivery, via: through- the-tool coolant holes; coolant grooves; coolant hoses; and for normal- and high-pressure coolant applica- tions; in all cases the tool life was reduced. e main problem with the various forms of coolant delivery it would seem, is the result of the cemented carbide tooling suering from ‘thermal-shock’ , creating by the high tool/chip interface temperatures and the im- mediate ‘quenching-eect’ of the coolant application – this ‘thermalcycling behaviour’ occurring at very fast rates. Nonetheless, work-hardened chips in the cut- ting vicinity must still be evacuated from deep recesses and pockets to avoid the ‘recutting eect’. By using an air-and-mist application – close to the tool’s edge, this will provide a means of swarf removal, while produc- ing some ‘token’ cutting edge lubrication – assuming that ‘coolant-eect’ permissible exposure levels (PEL’s) can be safely dealt, thereby with minimising potential health hazards. Any decisions concerning tool replacement will de- pend on the users machining needs, with the tool fail- ure generally being apparent by the naked eye, or un- der low optical magnication – simply observing the cutting edges to determine the ‘wear-patterns’. In-cut, a worn tool’s edges will tend to emit a dull ‘red glow’ 60 , this indicates that excessive forces and heat are being generated in the cutting zone, shortly leading toward a rapid and catastrophic tool failure condition. is ‘vis- ual glowing eect’ is initially usually conned to the 60 ‘Tooling – glowing red’ , this temperature-induced machining condition has been widely reported. Trent, 1984, stated: ‘Under very ex- ceptional conditions, when cutting fully hardened steel, or certain nickel alloys at high speed, chips have been seen to leave the tool red hot* – i.e. a temperature of over 650°C’. *is term ‘red hot’ – relating to temperature is somewhat vague, as shown in the chart, for: Variation of colours with temperatures – tempering, stress relief and hardening: Colour: °Fahrenheit: °Celsius: Colour: °Fahrenheit: °Celsius: Colour: °Fahrenheit: °Celsius: Straw yellow 430 220 Light blue 590 310 Faint red 950 510 Light brown 465 240 Grey 615 325 Dark red 1150 620 Brown 520 270 Grey-purple 660 350 Dark cherry 1175 635 Purple 545 285 Grey-blue 705 375 Cherry red 1300 705 Dark blue 565 295 Dull Grey 750 400 Bright cherry 1470 800 NB Temperatures above are either slightly rounded-up, or -down. Conversion: °Celsius = 5/9 (°F - 32) (Sources: Avner, 1974; Bofors, 1981) Machining and Monitoring Strategies cutting edge corners – where high stresses and tem- peratures are generated, which can be precisely tem- perature-monitored by thermographic equipment 61 , or simply rather crudely, by naked eye observation – with the machine tool’s lights turned out! So, by applying the correct tooling in a consistent and repeatable manner, becomes a vital factor for any form of predictability with all hard-metal machining applications. is is also particularly true for any form of hard-part: drilling; reaming; and tapping opera- tions; where these production processes oer serious challenges to the cutting edges, as the bulk hardness of the workpieces increase to >40 HR C . 9.10 Ultra-Precision Machining Introduction In the last few years, there has been a momentous drive toward producing components and indeed assemblies, signicantly more minute than was previously the case. e demand might be to locate and align mechanical parts together in much closer proximity, or perhaps, oering improved functionality and providing en- hancement of power-to-weight ratios necessary for electronic micro-circuitry. In fact, the adjacent circuit dimensions for nanometric electronic devices can have a proximity to each other of: 0.000006 mm (i.e 6 nm ≡ 6 × 10 –9 m). 61 ‘ermography’ , utilises the infra-red radiation emitted by a temperature-induced body. ese thermographic cameras, oer considerable benets to any form of actual temperature- monitoring applications. ermal gradients, hot-spots and heat losses can be observed – by ‘line-of-sight’ measurements – during actual machining operations. ey can also be used to assess temperatures in electrical cabinets, servo-motors, ballscrews, etc., for actual condition monitoring of the ma- chine tools. (Source: Smith et al., 1996) NB Typical temperature ranges for thermographic cameras are: –40°C to >2,000°C with a thermal sensitivity of 0.08°C, making then ideal for some forms of tool temperature moni- toring – assuming that the chip-stream is away from the cam- era’s lens. (Source: Flir Systems™) e challenges for the whole of the ultra-precision manufacturing industries, are to be able to make and supply miniscule devices that will meet these latest de- sign objectives. Before, discussing the tooling require- ments and machining techniques necessary to pro- duce these diminutive parts, oen with a high volume demand. It is worth trying to comprehend the ‘true dimensional size and scale’ of these miniature compo- nents and assemblies. Previously, the term ‘hair’s breadth’ was oen quoted as a very minute dimensional size, but if one looks at Fig. 253a, here, the large circle is sup- posed to represent the diameter of an actual hair – for comparison. Although even here, a hair is not of uniform diameter. In some very simple comparison tests undertaken about 6 years ago (Smith, 2002). He plucked one of his own hairs from his head – that he could not really aord to miss!, plus four more from several other people in the vicinity! en, he located this group of hairs within an scanning electron mi- croscope (SEM) chamber and simply measured them. e surprise was that they varied quite considerably, ranging from the smallest hair: at φ30 µm to that of the largest hair at: φ100 µm. So, the diagram (Fig. 253a) in- dicating that the hair’s size was ≈φ89 µm is somewhat misleading as a form of measurement criteria, as we will begin to appreciate, that the dierence of a few ‘microns’ can be excessively out-of-tolerance in some ultra-precision components and assemblies. Even the previous high-accuracy value of a ‘micrometre’ – oen simply termed the ‘micron’ this dimensionally-being 10 –6 m (i.e. illustrated against the hair for comparison in Fig. 253a), which is not considered and exceptional dimensional size to ‘hold’ in today’s ultra-precision machining world. In fact, the technical challenge now and into the future, is not one of the actual manufac- ture of these parts (Fig. 253b), but measuring them, as the old statement, that: ‘We make it, then measure it, at ten times this accuracy’ , does not hold true any- more. We are ‘almost routinely’ of late, making ultra-pre- cision components at the ‘atomic levels of resolution’ , so how can one measure sub-atomic sized components at the ‘absolute limits’ of today’s metrological instru- mentation? is form of ‘innitesimal measurement’ , is where the term ‘uncertainty of measurement’ really does become and important factor. ere are so many variables in the actual manufacturing process that can inuence the overall dimensional sizes of critical fea- tures with these miniscule components. Chapter Figure 253. Micro- and nano-machining of parts is a big challenge for both today and tomorrow. Machining and Monitoring Strategies e term ‘ultra-precision machining’ – that is its accuracy and precision, really does need to be more clearly stated 62 . Many people wrongly surmise that ‘ul- tra-precision manufacture’ only refers to very minute components, but one can also relate to a large-scale di- mensional workpiece, that has certain features for ex- ample, its machined diameter, or face (Fig. 257b), to- gether with its overall manufactured width, or length (Fig. 254 – top), to these ultra-precision dimensions. In recent years, the distinct challenges with respect to ‘micro-machining’ manufacture have been reason- ably successfully overcome, but ‘nano-machining’ (10 –9 m) and indeed, ‘pico-machining’ (i.e. 10 –12 m), is now distinctly on the horizon (i.e see Fig. 254, for an indication of the relative ‘sizes and scales’ demanded – of late. ese latter machining operational strategies, oering simply massive challenges in terms of the: • Production environments – controlling and moni- toring the temperature, humidity atmospheric pres- sure, cleanliness and dust ingress, together with any oor- and air-borne vibrational eects, 62 ‘Accuracy’ , here and to make it more readily understood, will be stated in distinct two ways, thus: ‘Accuracy’ , can be established by the dierence between the actual position of the machine’s slide and the position de- manded by the CNC, or: ‘Accuracy’ , is the conformity of an indicated value to a true value (i.e. an actual, or accepted standard value – this being a qualitative term only).So, the accuracy of a control system can be expressed as the: Deviation, or dierence between the ultimately controlled variable and its ideal value – usually in the steady-state, or sampled instants. ‘Precision’ , on the other hand, is: e degree of discrimina- tion with which a quantity is stated – e.g. a three digit nu- merical, discriminates among 1000 possibilities. NB Precision* is oen contrasted with accuracy. For exam- ple, a quantity expressed with 10 decimal digits of precision, may only have one digit of accuracy. (Source: Smith, 1993) *Bell (1999) states that: ‘Precision’ , is a term meaning ‘neness of discrimination’ , but is oen misused to mean ‘accuracy’ , or ‘uncertainty’. Its use should be avoided if possible – accord- ing to Bell. So if this latter statement is the actual situation, then some singular confusion reigns, when we use the word ‘precision’. In eect, we should always say: ‘accuracy and pre- cision’ , as uniquely and simply metaphorically-depicted in the well-known Archery: ‘Target analogy’ – for arrows hitting a target, thus: Wide arrow scattering, but centred (on average) on the ‘gold’ – accuracy, Arrows o target centre (i.e. from the ‘gold’), but closely grouped – precision, Close arrow grouping on the ‘gold’ – accuracy and precision. (Source: Oakland, 1986, Smith et al., 1993) – – – – – – • Work-holding security, part restraint; manufac- turing with its potential for component distortion – perhaps achieved by some form of ‘cryogenic ma- chining’ , together with monitoring tool wear the component, • Retrieval of parts once manufactured – this collec- tion operation of minuscule machined parts aer manufacture is not without problems, as at best, they will be almost invisible to the naked eye (i.e see some of these ‘larger parts’ manufactured in Fig. 253b), • ‘True’ dimensional measurements – of such ma- chined part’s actual features, need to be measured perhaps when in-situ as it is being manufactured, or later, when any distortions through subsequent handling and temperature eects have been nulli- ed. ese major manufacturing and measurement prob- lems will have to be addressed in the relatively near- future, if these latter ‘invisible to the naked eye’ parts some of which being beyond the visible spectrum for our sight are to be dealt with outside the ‘research environment’ and into actual ultra-precision produc- tion. .. Micro-Tooling Introduction e question oen posed when considering mi- cro-tooling, is: ‘What constitutes a micro-tool?’ For example, some automotive engineering companies might consider micro-tooling to be <φ0.95 mm, while others in say the aerospace industries, would set an arbitrary level at <φ0.55 mm, conversely, in the medi- cal and optical industries they would be more in- clined toward diametral values of <φ0.06 mm. So in eect, it all depends upon a company’s ‘working-di- mensional criteria’ , rather than an actual dimensional size. Micro-tooling – such as endmills, are currently commercially available in the USA, that have been manufactured to φ0.006 mm (i.e ≡ 6 µm), sitting quite nicely within the ‘micro-machining dimensional tol- erance zones’. Contrast this to other company’s, who would even consider ‘nano-machining’ to operate with workpiece dimensional features set at <0.025 mm (i.e ≡ 25 µm)! So, there is even some confusion as to what constitutes either: ‘micro-’ or, ‘nano-tooling’ and the re- spective features that they might adequately machine. So, as a ‘start-point’ , if we average these (above) three Chapter Figure 254. Relative dimensional sizes and scales, for: • machining of accurate and presicion parts or • equated to their respective measurement. [Source: Smith, et al., 2002] . Machining and Monitoring Strategies industrial-versions of what constitutes a ‘micro-tool’ , we obtain the following dimension for ‘our tooling’: <φ0.95 + 0.55 + 0.06/3 (mm) = ≈<φ0.52 mm, or by sim- ply and conveniently rounding-down, let us consider in our discussion, that any form of ‘micro-tooling’ is to be set at, or below: φ0.5 mm. e geometric features of any ‘micro-tools’ cannot simply be considered as minute version of ‘macro-tool- ing’. More specically, we simply do not just scale- down say, a φ12 mm drill, then manufacture its geom- etry as a micro-tool of, for example: φ0.25 mm drill (Fig. 255a). Micro-tools have to be ‘engineered’ to pro- vide eective chip evacuation, this is particularly rel- evant when hole-making (Fig. 255b), yet remain rigid enough to withstand the cutting forces generated and not fracture under these conditions. In the following sections concerning this review on micro-tooling, the production processes of: drilling; milling; and boring tools; will be briey mentioned. Micro-Drills and Drilling Probably the most signicant dierence when about to utilise these minuscule tools, compared to their macro-drilling counterparts, is that an operator can- not even see what size they are, without suitable visual magnication! is means that a micro-drill’s careful handling – of these fragile tools, plus their safe stor- age are vital. Micro-drills require correct containment and appropriate labelling, allowing them to be readily identied. Due to their minute diameters, micro-tool- ing require rotational speeds of ≈100,000 rev min –1 in order to obtain the correct peripheral speeds, thereby minimising the cutting forces acting on the micro- geometry of the cutting edges. So that the minute geometric features of the cutting edges are maintained (Fig. 255b), it is desirable to have a very ne carbide grain structure 63 – to strengthen the tool’s edges. If just the smallest amount of uncontrolled lateral force oc- curs, it can cause either tool edge fracture, or instigate complete breakage. us, if a micro-tool’s edge is just slightly chipped then this in itself may not adversely 63 ‘Micro-tooling materials’ , cemented carbide’s increased ri- gidity over other tooling materials, makes is susceptible to fracture. A good substitute micro-tool material is M-35 co- balt steel, it is a compromise between carbide drills and those manufactured of M-2 and M-7 HSS. Heat generated drilling holes, will ‘roll’ a drill’s edge, thus it becomes: dull; ploughs; and breaks. Cobalt improves drill ‘red-hardness’. aect cutting, but a 5 µm edge-chipping on a φ100 µm tool will radically modify the tool’s geometry and seri- ously impair its cutting performance. is miniscule cutting edge modication can cause the tool to break, or damage the part’s features – requiring very careful handling of such micro-tooling, in order to obtain the optimum cutting performance. A drill’s feature that needs to be modied from that of its comparable ‘macro-drilling’ equivalent, is the drill’s web ( i.e. see Fig. 47- bottom), this being the cen- tral portion of the tool that extends axially along the ute – gradually thickening as the distance increases from the tool’s point. So for a micro-drill, the web is proportionally thicker, because there has to be some ‘core-strength’ to a micro-tool. By way of illustration, on a micro-drill a web of say just 25 µm is simply not robust enough, as such, it would not work. To reduce a micro-drill’s stress and prevent it from binding in the hole, a back-taper 64 is purposely ground – playing a major role in drilling eciency. While, another mi- cro-geometric consideration for these minute drills is its cutting edge sharpness, becoming of critical impor- tance as the relative tool diameter gets smaller – this being a limitation to eective micro-machining. For example, on a macro-drill, if the cutting edge has a 25 µm cutting edge radius, it is considered somewhat sharp, but this would hardly be the case for a micro drill. Moreover, on a micro-drill if the cutting edge radius is 10 µm and it is taking a 2 µm chip load, its not just considered as ‘dull’ , but it is highly-negative raked! e PVD-coating process on micro-drills can be successfully accomplished, if the drill is manufactured with a reduced width of edge preparation, thus main- taining its sharpness (i.e by way of illustration, Fig 18 shows typical ‘edge-preps’ for macro-cutting inserts). In any form of micro-drilling operation, very high spindle speeds are necessary, for example, if a φ0.2 mm micro-drill is utilised, then the spindle speed should be ≈80,000 rev min –1 , in order to prevent the creation of high drill thrust and torque forces, which might 64 ‘Micro-drill back-taper’ , this is where a slight decrease in the drill’s diameter is being specically peripherally-ground, decreasing in size from the drill point up to and toward the shank. NB Back-taper on a micro-drill is generally relieved by be- tween: 5 µm and 13 µm; because the ute’s lengths are usually <25 mm. Conversely, on a ‘macro-drill’ this back-taper lies be- tween: 13 µm and 25 µm per 25 mm of length. Chapter . Micro- and nano -machining of parts is a big challenge for both today and tomorrow. Machining and Monitoring Strategies e term ‘ultra-precision machining – that is its accuracy and precision,. grouping on the ‘gold’ – accuracy and precision. (Source: Oakland, 198 6, Smith et al., 199 3) – – – – – – • Work-holding security, part restraint; manufac- turing with its potential for component distortion. sizes and scales, for: • machining of accurate and presicion parts or • equated to their respective measurement. [Source: Smith, et al., 2002] . Machining and Monitoring Strategies industrial-versions