Machining and Monitoring Strategies Part 10 ppsx

Figure 255. Some typical micro-tooling: drills and boring tools.
Machining and Monitoring Strategies 
otherwise lead to premature tool breakage. While an-
other note of concern when micro-drilling is its pene-
tration rate. If too high a drill feedrate is programmed,
then the micro-drill will immediately fracture. Some
micro-drilling manufacturing companies either rec-
ommend a single-ute assymetric drill geometry – al-
lowing high chip loads, coupled with an ecient chip
evacuation process, conversely, another approach is to
increase the number of drill utes, but this may cause
chip evacuation problems with ‘sticky’ workpiece
materials. At present, micro-drills can normally drill
holes with L/D ratios of 5:1, but it is anticipated that
these L/D ratios will soon be up to 10:1. In any micro-
drilling operation, the rst few revolutions of the drill
are crucial (Figs. 49 and 50), as the drill’s point expe-
riences eccentric forces as it enters the cut, with any
workpiece irregularities causing the drill to ‘walk’ – re-
sulting in its bending, breakage, or at the very least
some ‘helical wandering’ (i.e axially – see Fig. 70) as
the drill penetrates into the part. In order to mini-
mise the eccentric forces as a micro-drill enters a hole,
many micro-drilling manufacturers recommend that a
pilot hole (Fig. 50b) of between 1-to-2 drill diameters
deep is produced, utilising a short and rigid pilot drill.
A pilot drill’s point angle (i.e. see Fig. 46 – top) should
have an included angle that is either identical, or
greater than that micro-drill producing the nal hole.
If smaller included angles were selected, as the drill en-
ters the pilot drilled hole, this causes the micro-drill’s

cutting edge to chip. is tool wear-eect is because,
as the micro-drill’s more shallow point angle initially
contacts the previous pilot-drilled hole – with its more
acute angled geometry, as the micro-drill enters work-
piece, this contact will take place at the outer edges of
the lips before the drill point touches the hole’s surface.
In lieu of a pilot-drilled hole, then begin the feedrate
at somewhat less than the nishing feed, or perhaps,
utilise a ‘pecking-drilling action’ – drill to a predeter-
mined depth, partially withdraw the drill, then drill
deeper into the workpiece, once more partially with-
draw the drill, then repeat this sequence. ‘Pecking’ has
the further benet of avoiding dwell at the bottom of a
‘blind hole’ , this being an important surface integrity
feature with work-hardening materials.
Hole tolerances that have been satisfactorily micro-
drilled in a range of workpiece materials are of the
order: ± 5 µm, with tolerance-in-roundness (TIR) of
<2.5 µm. By utilising coolant delivery at high pressure,
either through-the-drill, with the ‘larger drill sizes’;
or alternatively ood coolant for minute micro-drills;
usually allows a 30% increase in cutting speeds coupled
to extended drill life. Although care should be made
when utilising through-coolant drills
65
, as their small
coolant hole diameters will simply clog unless the cool-
ant has been passed through some form of micro-ltra-
tion unit, to remove ‘nes’ and other types of potential
clogging debris.

Micro-Mills and Milling
Over the last few years, with the advances in cutting
tool materials in combination with that of cutting tool
technology, has led to signicantly smaller milling
cutter diameters with more complex geometries be-
ing produced (Fig. 255-bottom le). In fact, several
important technologies have developed during the last
decade to assist the cutting tool manufacturers to cater
for the micro-machining industries. Probably the most
important of these new technology applications is the
design and development of very high accuracy six-axis
CNC tool grinding machines, having temperature con-
trol and coolant condition monitoring – these being
key elements in the cutter-grinding process. Grinding
tolerances held by these machines on say, an φ0.12 mm
ball-ended end mill, must be within <2.5
µm (TIR).
Complementary to these multi-axes CNC grinders,
has been the improvements in diamond grinding
wheel technology, in conjunction with appropriate
grinding wheel metrological inspection techniques,
that have contributed to the signicant advancement
in micro-tool manufacturing quality and productivity.
Whilst continuing our discussion on the cutting tool
material front, micro-milling cutters are now being
produced from extra-ne grain cemented carbides, al-
lowing sharp cutting edges in conjunction with good
milled surface nishes. For example, one Japanese mi-
cro-tooling manufacturer oers a standard range of
‘micro-mills’ , from:

φ5 µm to φ55 µm; in incremental
65 ‘Ethanol’ , is an alternative applied lubrication strategy, to that
of either the usual water-based ood coolant method, or by
through-the-tool delivery. Here, ethanol is a form of alcohol,
occurring naturally in the sugar fermentation process, its
benets are that it has less-than-water viscosity, enabling it to
penetrate into the tool/chip interface in a superior fashion to
that of other coolants. Ethanol is usually delivered to the cut-
ting zone in the form of a spray-mist. While another bonus
of the application of ethanol is its low evaporation point, giv-
ing it eciency in cooling and as a lubricating agent for tool
spindle speeds (i.e. of up to and including) >60,000 rev min
–1
.
Moreover, ethanol simply evaporates and this eect negates
any disposal costs, while it provides a slight ‘chilling-eect’ on
the part, minimising thermal growth problems on miniature-
sized components.
 Chapter 
sizes of 25 µm. is range includes four-ute square-
ended cutters (i.e. similar to the one depicted in Fig.
255 – bottom le), together with ball-nose end mills,
plus some customised micro-mill tooling.
Complementary to these micro-milling cutters, are
their respective toolholders
66
, which must hold and
securely contain the tool’s shank in an accurate and
precise manner. Any form of tool runout when held
in the toolholder must be kept to absolute minimum.

e toolholder’s importance in the micro-milling op-
eration is oen overlooked, at the user’s peril! By way
of illustrating this fact, if one has a two-ute φ0.5 mm
end mill then the chip-load will be <0.010 mm tooth
–1
.
So, if the micro-mill has a runout of 5 µm, the cutter
is only utilising one of its utes – by a factor of 100%.
is micro-mill’s runout condition, leads to cutter in-
stability coupled with a poor milled surface situation,
with the potential for either reduced tool life, or break-
age. Micro-milling tool deection and its subsequent
breakage when utilised for micro-machining opera-
tions, are principally caused by three main factors,
these are:
1. Micro-machining creates a substantial increase in
the specic energy, as the chip thickness decreases
– meaning that here, as the chip gets thinner with
smaller D
OC
’s, the micro-mill is subject to greater
resistance, when compared to that of ‘macro-mill-
ing’. Moreover, it is almost as if the workpiece mate-
rial becomes harder during micro-machining. is
resistance force to machining here, is strong enough
to exceed the bending strength of tool – even prior
to any wear occurring, leading to tool breakage.
A method of minimising tool breakage and prevent-
ing its occurrence, is to ensure that the chip thick-
ness is smaller than the radius of the tool’s edge,

2. During micro-milling, a sharp rise in the cutting
forces and stresses resulting from chip-clogging
may cause tool breakage – when say, utilising a two-
ute cutter, each cutting edge removes chips from
the machining vicinity by only a half rotation of the
tool. Likewise, if chip-clogging occurs – within a
few micro-tool revolutions, the cutting forces and
66 ‘Micro-milling/-drilling toolholders’ , are typically manufac-
tured with taper-/face-tments of the : ISO 15 to 30, or HSK-
E25 to 32 types. A typical range of micro-toolholders, might
cover tool shank sizes in a range from: φ0.5 mm to φ2 mm, in
0.01 mm increments. With ‘matching micro-tooling’ , to typi-
cal tolerances of: <+0/-4 µm, with these micro-tools typically
being, for example, rated @ 40,000 rev min
–1
, having a runout
of <3 µm @ 4xD.
bending stresses increase beyond the limit of the
tool’s bending strength, thus causing it to break. A
possible solution to this problem, is to utilise alter-
native tooling materials such as micro-grained M-2
HSS, as they are more exible and as such, they can
tolerate any likelihood of chip-clogging in a more
compliant manner than their cemented carbide
counterparts,
3. While micro-machining very ductile workpieces,
micro-mills can lose cutting eciency as a result of
BUE – this results in increased lateral pressure (i.e.
as feeding occurs) on the micro-mill, causing it to
slightly deect. is increasing tool deection due

to the presence of BUE, increases the stress gener-
ated with every cutter rotation, quickly causing the
micro-tool to break. is well-known BUE phe-
nomena is termed: ‘extensive stress-related break-
age’ , which could possibly be minimised by adopt-
ing a somewhat more ecient and benecial cutting
uid lubrication strategy.
NB Due to these (above) micro-tooling related
phenomena, many of the latest micro-milling ma-
chines are equipped with sensors to dynamically-
measure and monitor the cutting forces acting on
the micro-mills.
Micro-Boring Tools and Internal
Machining Operations
e production problems of drilling small holes in
workpieces is a big challenge, but this is nothing com-
pared to that of the technological complexity of bor-
ing very minute holes and other internal features in
components. Some tooling manufacturers oer insert-
style tools that are specically-designed to bore-out
small hole diameters, even down to just ≈φ0.3 mm.
A typical micro-boring tool is illustrated in Fig. 255c
(i.e. ≈φ0.3 mm), where the main features of the tool-
ing are explained. In the enlarged diagram of a mi-
cro-boring insert geometry schematically illustrated
in Fig. 255 – middle right (i.e. for a ≥
φ0.7 mm boring
insert). is particular micro-boring insert geometry,
is designed for both boring and proling operations
into holes of ≥φ0.7 mm, although the clearance (‘t

max
’)
will only cope with shallow prole-depth features, be-
fore fouling on the tool’s shank. Micro-tool stiness is
quite high and occurs due to the enlarged shank di-
ameter, allowing reasonably large L/D ratios of >10:1
to be bored – which is remarkable, considering the
minute size of these insert’s. Other micro-machin-
Machining and Monitoring Strategies 
ing
67
operations that can be undertaken include (Fig.
255 –
middle-right): grooving; threading; face-groov-
ing; back-boring (i.e. not depicted).
Some important micro-machining factors need to be
addressed, prior to boring-out previously drilled holes
with these micro-boring tools (Fig. 255c), such as:
•
Setting the micro-boring tool at the hole’s centre
height (Fig. 255d – top) – this is the most impor-
tant preliminary step when about to commence a
micro-boring operation. A micro-boring tool that
is incorrectly set below the hole’s centre-height (Fig.
255d –
bottom) – adversely aects its performance
in several ways. It could foul on the curvature at the
bottom of the pre-drilled hole, through a reduced
edge clearance angle (primary relief). Moreover,
the ‘tool fouling’ causes the insert to rub against

the hole impeding the cutting action, which in
turn, creates vibration causing the insert’s tip to be
‘driven-down’ still further below centre. As a conse-
quence, the tip is forced deeper into the workpiece
material – due to the radial sweep of the bore. us,
as the top rake angle is increased – relative to that of
the workpiece, the clearance angle is reduced. is
geometric change in the micro-boring tool’s geom-
etry, causes the insert to ‘snatch, or grab’ material
rather than cut it, which then increases vibration,
so tool breakage will shortly ensue,
NB Due to the minute dimensions of these micro-
tools
68
, it is very dicult to set the tool exactly on
67 ‘Micro-machining’ , has been dened according to a dierent
approach, namely, concerning the actual workpiece’s volume,
as follows: ‘It is the [workpiece] size in which the work envelope
is smaller than 490 cm
3
’. (Source: Destefani, 2005)
68 ‘Meso-scale machining’*, this term has been coined and has
been dened as: ‘Millimetre-sized parts, with micron-sized fea-
tures’. For example, minute component features that can have
micron-sized tolerances (<1 µm). Recently in the USA, these
‘meso-machining technologies’ have included both micro-
milling and -turning, with in the former case, utilising micro-
end mills of ≈φ20 µm, while in the latter case, using micro-
turning tools of 10 µm in width. Hence, these technologies can
machine part features in the 25 µm range.(Source: Kennedy,

2006)
*e term: ‘meso-’ meaning: ‘middle’ , or ‘intermediate’.
(Source: Concise Oxford Dictionary)
NB In this case, the so-called ‘meso-machining operations’ ,
refer to machining in between the:nano- and micro-machin-
ing ranges.
centre-height – the ‘ideal positioning’. erefore,
the tool can be set marginally higher than ‘true’ cen-
tre-height, which increases the angular clearance –
relative to the hole, thereby allowing a freer cutting
condition. Further, if any potential vibrations occur
the micro-tool is both deected downward toward
the centre and (radially) slightly out-of-cut, some-
what reducing this ‘grabbing tendency’.
•
Choosing the right speed and feed – when the bore
is <φ6 mm, then ‘standard’ speeds and feeds cannot
be used. For example, when boring say, a φ1 mm
hole, one would expect to utilise a cutting speed of
perhaps ≈140 m min
–1
, which equates to a spindle
speed of ≈44,600 rev min
–1
– which is totally un-
realistic for most types of turning machine tool. If
any vibration occurred, then the micro-boring tool
would be immediately destroyed. So pragmatically,
if we limit the spindle speed to 6,000 rev min
–1

,
which would signicantly drop the cutting speed to
≈19 m min
–1
, we would also need to complemen-
tarily reduce the micro-boring insert’s pressure by
reducing the D
OC
to <0.1 mm which – to minimise
tool deection and potential breakage. Feedrates
for ‘macro-boring operations’ , are normally dic
-
tated by the ‘close-relationship’ between its tool
nose radius and the bored-hole surface texture re-
quirements. Conversely, for micro-boring these are
not the controlling factors anymore. Here, minimi-
sation of cutting forces is vitally important by se-
lecting a feedrate that should not exceed 0.125 mm
rev
–1
– which automatically overcomes any micro-
bored surface texture issues,
•
Ensuring adequate chip evacuation – is a real dif-
culty with such small bored holes, as little in the
way of unlled volumetric capacity exists with the
micro-boring tool situated inside the hole. So, with
the micro-boring tool inside the hole – accounting
for 60% of the available volumetric space, how can
the chips escape? By utilising a ‘through-insert-

coolant’ micro-boring insert (Fig 255c and d) with
the coolant under pressure, it can reach the cutting
edge. is coolant aids in both forcing and ush-
ing chips out of the bore’s mouth, which minimises
any of these work-hardened chips, creating a chip-
packing tendency in the bore, with the potential of
causing tool breakage,
•
Providing adequate tool stability and location –
these are important factors for micro-boring tooling.
Micro-boring inserts and their respective toolhold-
ers are designed for quick, simple and repeatable
 Chapter 
setups, with some tooling manufacturers design-
ing the tooling assembly to avoid inserts twisting
in-cut. ese design innovations range from: in-
sert-clamping ats; inserts having angle-ground
back-ends; to that of ‘teardrop-shaped inserts’ (i.e
see Fig. 255d) – this latter type rmly ‘wedging’ the
insert as it attempts twist – under the torque and
bending moments while boring.
If these micro-tooling factors are adhered to, then the
problems that are likely to be encountered when mi-
cro-machining are signicantly reduced, which means
that any form of micro-machining activities can be
achieved – with due diligence. So that a considerable
amount of micro-machining can be undertaken, ma-
chine tool companies have been developing a range of
specialised machines to cater for this market. Hence,
with the expansion of micro-machining activities this

being a somewhat ‘growth industry’
69
, let us briey
consider these specialised micro-machine tools and
the technical challenges they had to overcome in order
to cope with such minute cutters and invariably minis-
cule workpiece volumetric dimensions.
.. Micro-Machine Tools
CNC machine tools designed to machine parts, or
moulds that have small dimensional size, typically
with a linear dimension of ≤ 10 mm, or having detailed
part features of ≤ 0.1 mm, require some signicant ac-
curate and precision enhancements, if they are to cope
with the micro-machining demands of late. A typical
micro-machining machine tool will be mentioned,
‘high-lighting’ some of its important design features,
so that one can gain an insight into the careful at-
tention to detailing necessary for minute component
manufacturing.
One such machine tool produced by the Japanese
company Makino (not shown), has a ‘footprint’ of
≈ 1.8 m × 2.4 m, with a signicant weight of ≈
5 tonnes,
with a worktable size of ≈ 300mm × 200 mm, having
three axis travel of: 200 mm in X-axis; 150 mm in Y-
69 As a ‘total aside and not related to the main topic’ and, for you
‘acionados’ of English language – isn’t this above statement
(i.e. in italics), the basis for a: ‘double’ – oxymoron?
** Oxymoron: expression with contradictory words – e.g.
‘Wise fool’ or, ‘Legal murder’.

axis; and 150 mm in Z-axis. Obviously for such minute
micropart features to be machined, the positional ac-
curacy and repeatability of the slideways are of crucial
importance, as such, the machine’s positional accuracy
is ± 0.3 µm, with a repeatability of ± 0.2 µm. is ma-
chine features unique workholding equipment, such
as a direct-chucking spindle, which has been designed
to eliminate the toolholder-induced variables, en-
abling miniature components to be produced, such as:
medical instruments; semi-conductor devices; optical
products; etc.
A major factor with any micro-machining machine
tool like the one mentioned above, is its machining
environment and more specically, its ‘thermal condi-
tions’
70
. As the minute part’s temperature changes along
with that of the machine’s spindle – during machining,
any dimensional modications on say, a ‘macro-scaled
part’ could normally be considered as negligible, but
on micro-sized workpieces, these linear variations be-
come signicant dimensional issues. In order to vir-
tually eliminate spindle growth the machine tool has
to be designed for a stable environment, when one is
attempting to hold ‘micrometre-accuracies’. Machine
tool features necessary in reducing this spindle/ma-
chine expansion, include, an automatic spindle lu-
bricant temperature controller – to reduce spindle
growth, coupled with the machine’s granite base – as
granite has only 10 to 20% of the thermal conductivity

70 ‘ermal conditions and eects’ , in particular will aect either
the machine tool’s linear expansion/contraction – depending
upon whether there is a temperature rise, or fall, respectively.
Simplistically and in this instance, ignoring any uncertainty
factors, then , ‘Coecient of thermal expansion’ which is nor-
mally denoted by the symbol ‘α’ , can be dened as: ‘A measure
of the change in length of a material subjected to a change in
temperature’. us:

α =
Change in length
L

(�T)
=
strain
(�T)
=
є
(�T)

Where: L
o
= original length (mm), ∆T = change in temperature
(°C). Or, this thermal expansion equation can be alternatively
written, as follows: ∆L = (L) (Cα) (∆T) Where: ∆L = change
in length – by thermal expansion (mm), L = original length
(mm), Cα = coecient of thermal expansion, ∆T = change in
temperature (°C).
NB e uncertainty contributions here, may be combined, in

the following manner: u
d
= √(u
0
)
2
+ (u
c
)
2 
Where: u
d
= ‘design-
stage’ uncertainty, u
0 
= interpolation uncertainty, u
c 
= instru-
ment/equipment uncertainty. (Source: Figliola and Beasley et
al., 2000)
Machining and Monitoring Strategies 
of an equivalent cast iron structure, thus structurally-
minimising the eects of ambient temperature changes.
Moreover, for any form of extremely critical and preci-
sion miniature part manufacture, the entire machine
tool can be situated in a ‘thermal chamber’ , this in ef-
fect acts as a ‘controlled-temperature environment’.
Micro-tools of for example, φ50 µm – as has already
be mentioned, are almost impossible to see, let alone
attempting to set them to length. In order to facilitate

this minute tool setting operation – to sub-µm accu-
racy, the machine tool company developed a hybrid
automatic tool-length measuring system. is system
of tool length measurement is achieved by combining
a static low-pressure contact sensor in conjunction
with non-contacting sensing
71
, this being performed
while the tool is rotating at speed. Together, these two
sensing techniques permit sub-µm tool positioning
accuracy, during machining operations.
Obtaining the most advantageous micro-machine
tool for a particular type of minute ‘workpiece group’ ,
should be taken by considering the part’s features – in-
cluding its geometric conguration, together with the
level of accuracy and precision required and whether
these parts are produced as ‘one-os’ (i.e. as custom-
ised-specials), or in various batch sizes.
.. Nano-Machining
and Machine Tools
When attempting to machine components to toler-
ances of nanometric dimensions, the actual problems
considerably exacerbate, even when compared to that
of machining in the sub-micrometre range. Usually,
conventional cutting edges that have been honed, can-
not hope to cope with miniscule D
OC
conditions, as
the edge is just simply not sharp enough and will tend
71 ‘Non-contacting tool sensing’ , is ahieved as follows: while

the spindle is rotating the tool’s tip position is measured via a
non-contact electro-magnetic sensor. is tool measurement
takes into account the thermal displacement of the tip, caused
by its rotation. us, the system’s contolller merges these two
measurements.
NB e tool’s length measurement operation occurs by mea-
suring the spindle growth and waiting until it stabilises – within
specic user-dened limits, such as for example, within2 µm.
Once the spindle is ‘stable’ , it can machine the workpiece at
the desired level of accuracy and precision.
to ‘plough’ , instead of cut. In order to machine such
components, oen on either very ductile workpiece
materials, or glasses, monolithic diamond tooling is
invariably utilised with the tool orientated so avoiding
its natural fracture planes. It is normal practice when
machining components to a few billionth parts of a
metre (i.e. 1 nm = 10
–9
m), that a wide range of ‘pro-
cess, environmental and machine tool inuences’ are
acknowledged and then subsequently minimised. In
fact, the Japanese Professor Nakazawa (1994) consid-
ered the machine tool’s inuences when machining at
high precision and, stated they could be broken down
into the three following requirements, mentioning
that the:
1. Machine tool’s built-in reference must not vary,
2. Machine tool’s must follow this kinematic reference
at its highest precision,
3. Machine’s movement must be accurately trans

-
ferred to the workpiece.
Moreover, Nakazawa presented a useful table of the ma-
jor factors that disturb the relative tool-to-workpiece po-
sitions in ‘forced machining’ , as presented in Table 17.
In fact these ‘requirements’ are usually adequate
for the level of machining into the sub-micrometre
range, but once one proceeds to ‘ultra-high precision
machining’ operations within the nano-range, then
many other factors contribute to the overall success
of the cutting process (Fig. 256). As previously men-
Table 17. Factors that disturb relative tool-to-workpiece cut-
ting positions
Factors: Internal/
External:
Conditions:
Heat source Internal Machining energy at machining
point motor, ball leadscrew, bea-
ring, guide, hydraulics
External Convection (air conditioning)
Radiation (lighting, body heat)
Vibrations Internal Vibrations created by the ma-
chining mechanism motor, ball
leadscrew, joints, bearings, guides
External Other machines, moving vehicles,
people
Dust Internal Matter from the workpiece, or tool
External Dust in surrounding air, particles
in cuting uid
[Source: Nakazawa, 1994]

.
 Chapter 
Figure 256. The error sources from the processes; environment and machine tool; on workpiece accuracy. [Source: Breuck-
mann & Langenbeck, 1989]
.
Machining and Monitoring Strategies 
tioned, ultra-precision machining does not usually en-
tail machining very diminutive components, but it is
normally concerned with holding exceptionally tight
tolerances on macro-sized parts (Fig. 257b). In fact, a
diamond turning machine tool that can manufacture
components to nano-tolerances is depicted in Fig.
257a. is ultra-precision CNC lathe is considered to
be the most accurate and precise machine of its type
currently available. erefore, it is worth discussing
the machine and its environment, as its installation
and operation encapsulates all of the error sources
shown in Fig. 256.
Nano-Machine Tool and its Facilities
In Fig. 257a, is shown a very expensive and highly
sophisticated machine tool, it was delivered to the
Atomic Weapons Establishment (Aldermaston, UK)
from the manufacturers Craneld Precision Engi-
neering (UK). Its intended purpose was to machine
Perspex optics and large thin-walled aspheric shells
having form errors of <5 µm, together with wafer-thin
laser targets having micro-machined features, but held
to tolerances of ± 10 nm, by single-crystal (monolithic)
diamond tools – these diamond cutting edges being
orientated along their correct crystallographic plane,

allowing turned surface texture values (Ra) of <1 nm
to be achieved.
If an ultra-precision machine tool is required to
work at nanometric resolution, then if it needs to be
located within a manufacturing plant, the machine
tool must have a special-purpose facility designed,
constructed and built to exceptionally-stringent
and specied requirements. Prior to discussing this
facility, it is worth describing some features of this a
machine tool, so that one can comprehend the signi-
cant technical problems that had to be overcome, in
order for it to achieve a ‘true’ nano-machining capabil-
ity.
e machine tool was constructed on a polymer
concrete base, that consisted of 8 tonnes of synthetic
granite, giving the desirable properties of: excellent
thermal stability; high stiness; plus good vibration
damping characteristics. Strangely for a diamond
turning machine, the headstock was equipped with a
hybrid hydraulic/air spindle rather than an air-bear-
ing design, because this spindle’s specially-designed
construction enabled an increased load-carrying ca-
pacity (57 kg), coupled to superior stiness. Spindle
speed range was from: 200 to 5,000 rev min
–1
. ree-
axes were tted, two linear axes – running on fully-
constrained hydrostatic dovetail bearings with linear
motor drives and one rotational axis. ese axes kine-
matics were: X-axis (520 mm); Z-axis (220 mm); B-

axis (360°) – as illustrated in Fig. 256-middle le. A la-
ser-positioning system was tted to the axes, having a
resolution of 1.25 nano-metres, incorporating a wave-
length tracker, to compensate for any environmental
changes to the air: temperature; pressure; humidity;
hydrocarbon content; etc. e CNC controller utilised
a high resolution (1 nm) fast feed-forward operation,
thereby reducing servo-following errors, combined
with real-time axis compensation together with a
two-dimensional error compensation capability – for
straightness and orthogonality.
Tool-setting errors on the monolithic diamond
tooling, were minimised by a unique probe and optical
setting technique (Fig. 256 – middle-right), reducing
form errors, when utilising the rotational B-axis for
spherical/aspherical turned component geometry
72
.
e nanocentre machine tool, was housed in a tem-
perature-controlled environmental enclosure, consist-
ing of the temperature being held at: 20°C ± 0.5°C, en
-
closed within 100 mm thick high density polyurethane
foam panelling – providing high thermal resistance,
with an air-tight seal. e positive-pressure air-supply
unit was situated outside – in an adjoining plant room,
ducted into the enclosure by dra-free ducts, with ten
platinum resistance temperature probes (i.e. resolu-
tion 0.001°C) strategically situated within the volume
space, continually monitoring the enclosure’s temper-

ature. Lighting from the uorescent lights had their
chokes removed from the enclosure, thereby reducing
the localised air temperature ‘stratication eects’ by
72 ‘Form errors’ , the principal causes of form error when spheri-
cal/aspherical diamond turning components, can be sum-
marised in the following manner:
Conical error – due to spindle misalignment,
Chevron and Ogive errors* – due to rst-order tool wear
and centring errors,Waviness error – resulting from sub-
strate vibration and tool prole error,
Astigmatism – created by the component xturing arrange-
ments and material stiness.
*Chevron error occurs when turning a convex spherical formed
component – due to the tool ‘over-shooting’ , while, an Ogive
error results from the tool stopping short – this latter error
creating an ‘ogival arch eect’ , with both these prole errors
being due to an incorrect tool centre height setup.(Sources:
Myler and Page, 1988; Wheeler, 2001)
–
–
–
 Chapter 
Figure 257. Nanometric machining to ultra-precise dimensional and surface texture characteristics. [Source:
Lamb & Gull, 1999]
.
Machining and Monitoring Strategies 
over 1°C. e hydraulic and electronic cabinets were
temperature – controlled to ± 1°C. e
‘refractive index
of the air’ had to be corrected – based upon a modi-

cation to the Edlen (1966) equation, as the laser path
positional monitoring system would otherwise be af-
fected, with a correction factor being entered into the
CNC controller.
e ‘T-shaped base’ of the Nanocentre was sup-
ported on three pneumatic mounts that were ‘tuned’ to
eliminate oor-borne vibrations of ≥ 2.5 Hz. Two types
of vibrational sources occur, namely forced- and self-
excited, with the forced vibrations originating from
external sources – through the foundations, while the
self-excited vibrations normally being the result of in-
ternal sources. A ‘oor vibration audit’ on the vibra-
tional inuences was conducted, to establish whether
the overall enclosure was suciently vibration absor-
bent. e oor vibration spectra gave typical vibra-
tional readings of 1 nm (rms) at frequencies of 25 Hz,
during the tests, with the external air compressors
emitting a oor borne 25 Hz frequency component,
which had to be subsequently nullied. Further testing
procedures were undertaken, including ‘modal analy-
sis’ and ‘thermal imaging’ of the machine’s structure,
together with a full calibration of the machine tool’s
kinematics.
Once all of these tests and various others had been
completed and compensated for, then a machining
testing program could then be undertaken. A typi-
cal test piece is illustrated in Fig. 257b, where an al-
uminium 6061-T6 part was heat treated and then
stabilised, of φ250 mm copper-plated (200 µm depth
coating) part. ese testpieces were faced-o with a

monolithic diamond tool – taking very shallow D
OC
’s
of just a few micrometres, producing for example, a
face-turned surface texture averaging ≈ 2.8 nm
Ra.
Later, proling tests were also conducted, prior to -
nal operational acceptance by AWE, from the machine
tool builder.
Prior to completing this summation of the just
some of the rigorous testing procedures carried out to
ensure that the Nanocentre machine tool could oper-
ate within the nanometric range of ultra-high machin-
ing operation, it is worth making an unusual point
concerning human intervention at this exacting-level
of machining. It was found that when several person-
nel were within the machine tool enclosure while
machining took place, then the thermal output from
these people, inuenced the part’s dimensional size
– without actually contacting the machine, by simply
acting as a heat-emitting source
73
. Moreover, it was
also found that when diamond-turning
74
by facing-o
a very ductile testpiece similar to that depicted in Fig.
257b, when these people were in conversation during
the nanometric cutting of the part, their ‘voice signa-
tures’ – in the form of air-borne vibrations were ‘ma-

chined’ into the surface – in a similar manner to that of
an acrylic recording of a record in the past! erefore,
in order to ensure that both the human thermal eects
and the vibrational perturbations (i.e. by air-borne vi-
brations – talking), the personnel had to be removed
while any ultra-precision machining operations were
in progress.
Ultra-precision machining at these nano-metric
levels of operation, severely stretches today’s levels
of technological challenges for: machine tools, me-
trology, plant and equipment, as we approach that of
atomic-levels of precisional uncertainties
75
. It is not
just the case of purchasing an extremely accurate and
73 ‘Human body – as a heat source’. e average body – in a
‘sedentary state’ , will emit ≈100 W of heat. So, here in this
case, when there are two people present in the machine tool
enclosure, they will radiate ≈200 W of heat – inuencing
the machine’s and hence, the workpiece’s thermal expansion
– when machining at nanometric levels of accuracy and preci-
sion. (Internet source: Burruss, R.A.P., Virtual People, 2005)
74 ‘Monolithic diamond’ , has some of the following characteris-
tics: hardness of ≈8,000 Hv; Density (ρ) of 3,515 kg m
–3
; com-
pressive strength of 7,000 MPa; and a Young’s modulus (E) of
930 GPa.(Source: Cardarelli et al., 2000)
75 ‘Atomic radius’ , for example, for some typical elements, ranges
from that of: carbon, having an atomic radius of ≈0.071 nm

(i.e. its atomic ≈φ0.142 nm)*, iron’s atomic radius is ≈0.124 nm
(i.e. ≈φ0.248 nm, or ≈¼ nm)*, Aluminium’s atomic radius is
≈0.143 nm (i.e ≈φ0.286 nm, or >¼ nm), Cesium’s atomic radius
is ≈0.265 nm (i.e ≈φ0.530 nm, or >½ nm).(Source: Callister, Jr.
et al., 2003)*Slight digression here, may help explain why these
atomic radii are important, when certain elements are alloyed
together, such as iron and carbon, these being the main con-
stituents of plain carbon steel.When an allotropic change oc-
curs to the iron’s atomic lattice structure (i.e. BCC→FCC @
≈910°C), then the carbon being somewhat smaller, can t into
these (now) larger interstitial sites – voids – within the FCC
iron lattice – distorting the adjacent iron atoms. Upon rapid
cooling (e.g. by water quenching), some of the carbon is
‘trapped’ and severely distorts the structure as it attempts to
transform back to the original BCC form. Hence, this dis-
torted structure of iron-carbon – termed martensite, is both
a very hard, but brittle structure, requiring tempering: if it is
to act as a hardened and tempered workpiece material. is is
the basis (i.e. somewhat simplied), behind this iron-carbon
heat-treatment process.
 Chapter 