Cutting Fluids‘ Everything flows and nothing_5 pptx

Figure 211. Some typical, but extreme skin disorders – attributed to exposure to cutting uids. [Courtesy of Castrol Industrial].
Cutting Fluids 
Many  other  skin  conditions  can  occur  and  their 
causes can  emanate from a number of MWF sources 
–  going  beyond  the  current  scope  and  objectives  of 
this chapter. Although through the application of bar
-
rier and conditioning creams, together with clean and 
suitable protective clothing, coupled to good washing 
facilities,  these  factors  will  inevitably  lessen  the  pos
-
sibility of allergic reactions and skin disorders.
Tumours and Cancerous Effects
However,  less  well  known  than  the  allergic  and  skin 
condition  previously  mentioned,  are  the  other  more 
serious debilitating health eects on the machine tool 
personnel  exposed  to  MWF’s.  Industrial  experience 
suggests that continuous and long exposure to certain 
mineral oils can give rise to skin thickening, known as 
keratosis, whereby ‘warty-elevations’ (i.e. see Fig. 211b) 
can slowly develop over a period of some years. Hence, 
these warts will either: remain as they are; disappear; 
or in the worse case scenario, become malignant. 
A  considerable  volume  of  research  in  both  the 
chemical  and  biological  elds  has  been  undertaken, 
in  particular,  into  the  eects  of  mineral  oils  in  cut
-
ting uids and their aect on worker’s health. Mineral 
oils may contain  carcinogens  – chemical  compounds 
which  are  active  in  causing  cancer,  with  currently,  a 
number  of  these  compounds  having  been  identied. 

ey occur in the main, as polycyclic aromatic hydro-
carbons and, when present in modern rened mineral 
oils exist in extremely small proportions – making their 
‘positive’  chemical  identication  exceedingly  dicult 
to  dene.  Oil  renement  by  acid  treatment  has  now 
been  replaced  by  more  modern  rening  techniques, 
including solvent-rened treatment and hydrogenera
-
tion  –  greatly  reducing  the  undesirable  proportions 
of  aromatic  compounds  (i.e.  these  latter  compounds 
being  potential  carcinogens)
33
.  Moreover,  chemical 
coolants  were  originally  based  on  diethanolamine 
and  sodium  nitrate,  which  for  some  time  have  been 
suspected  of  forming  ethanolnitrosamine  –  another 
suspected  carcinogen.  In  order  to  remove  this  pos
-
sible carcinogen, in 1984, cutting uid manufacturers 
removed the nitrates from their formulations. Finally, 
33  ‘N-nitrosamines’ ,  and its chemical  compounds  are a signi-
cant  danger  to  worker’s  health  and,  the  American  Environ-
mental  Protection  Agency  (EPA),  stated  in  a  report  of their 
ndings in 1974, that: ‘As a family of carcinogens, the nitrosa-
mines have no equal.’
if  one  considers  permissible  exposure  levels  (PEL’s) 
from nitrosamine sources. en, it has been stated that 
smoking twenty (untipped) cigarettes per  day will de-
liver 
0.8 micrograms of various nitrosamines which al-

most 
equates to eating a kilogram of fatty bacon per day 
(i.e.  6  microgrames),  thus,  when  undertaking  these 
 seriously  debilitating  smoking/eating  toxicity  habits 
over a signicant period of time, they would consider
-
ably increase the risk of cancer.
Cutting Fluid Mists
Mists resulting from  machining  operations  and  their 
subsequent collection resulting from the application of 
cutting uids, are usually given a low priority by most 
manufacturers when compiling a list of potential capi
-
tal items for the workshop. To press this point still fur
-
ther, many companies would much sooner purchase a 
new  machine  tool,  than  install  a  special-purpose  air 
cleaner.  In  the  automotive  industries  interest  in  the 
level  of  air  quality  has  some  degree  of  importance, 
while elsewhere in smaller production workshops it is 
somewhat  of  a  hit-or-miss  aair.  Given  the  potential 
worker  health  risks  involved  today,  with  high-speed 
machining  (HSM)  coupled  to  increased  tooling  cut
-
ting  data  and  higher-pressure  coolant  supplies  (i.e. 
see  Fig.  195 – top),  possibly  the  greatest  threat  posed 
to a worker is from atomised mists (i.e. sub-
µm size) 
within  the  local  atmosphere.  Many  companies  that 
incorporate mist collection ltering, will only remove 

particles of >4 
µm in size, leaving the critical sub-µm 
particles still present in the atmosphere. 
e earliest chemical interventions to reduce mist
-
ing  were  high-molecular-weight  polymer  additives, 
that act to stabilise MWF’s and thus suppress mist for
-
mation.  With  conventional  petroleum-based  uids, 
polyisobutylene  has  been  the  preferred  anti-mist  ad
-
ditive.  While,  for  aqueous-based  cutting uids,  poly
-
ethylene  oxide  (PEO)  has  been  utilised.  Due  to  the 
susceptibility  of  PEO’s  to  shear  degradation,  repeti
-
tive additions of the PEO polymer are needed to main
-
tain  mist  reduction.  Today,  a  newer  class  of  shear-
stable  polymers has  been developed  to overcome  the 
shear degradation  as  indicated  by PEO’s. ese latest 
polymer  products  have  been  derived  from  complex: 
2-acrylamido-2methlypropane  sulphonic acid  mono
-
mers,  hence,  providing  longer-term  performance  in 
continuously  recirculating  aqueous-based  MWF  sys
-
tems. 
So, very high concentration cutting uid mists will 
over  a  short  period  of  time  cause:  ‘smarting’  of  the 

eyes; irritation of exposed skin; result in slight irrita
-
 Chapter 
tion  of  the  mouth  and  throat;  by  inhalation,  will  ir-
ritate the lungs; by ingestion, of the stomach – it may 
promote  nausea;  and  aect  other  internal  organs. 
If  exposed to  toxic  mists  over a  long period  of  time, 
this could cause  lasting damage  to both external and 
internal  bodily-parts,  with  at  the  extreme  condition, 
promoting the growth of malignant tumours. In order 
to restrict misting and minimise operator health risks, 
then  special-purpose  ltering  systems  have  been  de
-
veloped, which will be briey reviewed below.
e  conventional  mist-collection  technology, 
such as:  lters;  rotating  drums;  or  cyclones;  will  col
-
lect  particles  of  >1 µm  in  diameter,  but  cannot  cope 
with smaller sub-µm particles. Further, it has been re
-
ported  that  brous  lters  once  they  are  wet,  lose  ef
-
ciency over time – see Fig. 212. erefore, the opti
-
mum manner of removing sub-µm mists are by tting 
one of the following: 
High-eciency Particulate Air l-
ters (HEPA); 
Electrostatic Precipitators (ESP’s);  or  Fi-
bre-bed systems. Probably the two best systems for re-

moval of sub-µm mist particles are the HEPA and ESP 
systems. Each one has its disadvantages, with HEPA l
-
ters being expensive and become clogged, thereby los
-
ing eciency. So, when disposable lter replacements 
are  needed  this  hidden  replacements  cost,  will  result 
in both costly maintenance and disposal. While, ESP’s 
need  frequent  maintenance  and  cleaning,  thus  rep
-
resenting a  continuous  on-going  cost  burden. Mean
-
while, Fibre-bed systems oer high eciency in mist 
collection,  but  with  ease  of  maintenance,  although 
they are larger requiring more electrical power to op
-
erate them. 
Vegetable Oil-Based MWF’s
Driven  by  the  health  and  safety  concerns  of  both 
workers and manufacturers alike,  vegetable oil-based 
MWF’s have been developed, to substitute for the same 
machining operations as either the mineral-, or petro
-
leum-based  uids,  currently  undertake.  It  has  been 
reported  that  compared  with  mineral  oil-based  cut
-
ting uids, the alternative vegetable-based MWF’s, en
-
hance cutting performance by extending tool life while 
improving  machined  surface  texture,  with  the  addi

-
tional  benet  of  being  an  environmentally-friendly 
MWF.  In  particular, 
Soybean oils have  shown  con-
siderable  promise  as  a  practical  alternative  to  ‘tradi
-
tional’ MWF’s, where they have improved component 
surface  texture  and  reduced  tool  chatter.  One  of  the 
principle  reasons  for  these  surface  texture  and  ma
-
chining improvements, is that the vegetable oil-based 
MWF’s have enhanced lubricity, coupled with a slight 
‘polar-charge’  –  which  acts  to  attract  the  vegetable 
oil  molecules to  the  metallic  surface being  tenacious 
enough  to  resist  any  subsequent  wipe-o.  e  oppo
-
site is true for a mineral-based oil, where there is no 
molecular  charge,  so  oers  little  improvement  in  lu
-
bricity. 
Mineral-based  MWF’s  are  just  straight  hydrocar
-
bon,  while  their  vegetable  oil  counterparts  contain 
oxygen,  which  is  tenaciously-attracted  to  the  sterile 
elevated temperature of the recently-machined work
-
piece’s  metallic  surface,  thus  it  bonds  more  strongly 
–  acting  as  a result as  a  better  lubricant. Yet  another 
performance  benet  of  utilising  vegetable-based  oils 
over their mineral-based equivalents, is that they have 

a  higher  ‘ash-point’
34
,  which  reduces  both  the  ten-
dency for smoke formation and re-risk. Yet another 
reason  for  selecting  a vegetable-based  MWF  over  its 
mineral-based counterpart, is that it has a high natural 
viscosity
35
.  Hence,  as  the  machining  temperature 
increases, the viscosity of the vegetable oil drops more
slowly than for that of a mineral oil. Conversely, as the 
temperature 
falls, the vegetable oil remains more uid 
than its counterpart mineral oil. us, facilitating more 
ecient and quicker drainage from both the swarf and 
workpiece.  e  high 
viscosity index
36
  of  vegetable  oil 
ensures that it provides more lubricity-stability, across 
the operating temperature range being found during a 
range of machining operations. High viscosity allows 
vegetable  oils  to  be  used  as  a  slideway  lubricant  and 
for gear lubrication in gearboxes, acting as a so-called: 
‘multi-functional uid’ (i.e. see Section 8.9). 
Along with  the above stated  benets,  there is  also 
a down-side to vegetable-based uid applications, the 
limitations  are  that  they  lack  sucient  oxidative  sta
-
34  ‘Flash-point’ of oils, is the instantaneous ignition of the oil at 

a specic temperature, without  the aid  of a  ame. So, in  the 
case of a Soybean oil it has a ash-point of 232°C, while a typi-
cal mineral oil has a ash-point of just 113°C. 
35  ‘Viscosity’ , can be dened* as: ‘e resistance of a uid to shear
force.’  erefore,  the  shear  force  per  unit  area  is  a  constant 
times the velocity gradient, with the constant being the coef-
cient  of  viscosity.  SI  units  are:  Newton-seconds  per  square 
metre  (Ns  m
–2
),  denoted  by  the  Greek  symbol:  ‘µ’.  [Source: 
Carvill, 1999]
  *While  another  denition  for  a  uid’s viscosity  is:  ‘e bulk
property of a uid, semi-uid, or semi-solid substance that
causes it to resist ow.’ [Kalpakjian, 1984]
36  ‘Viscosity index’ ,  can  be  dened  as:  ‘A measure of a uid’s
change of viscosity with temperature: the higher the index, the
smaller the relative change in viscosity.’ [Kalpakjian, 1984]
Cutting Fluids 
bility  for  many  machining  applications.  us,  a  low 
oxidative stability means that the oil will oxidise quite 
quickly  during  use,  becoming thick  as  it polymerises 
to a plastic-like consistency. Once the oil has become 
too thick, or even too thin for that matter, the cutting 
tool’s edge(s) will quickly wear-out. Vegetable oils be
-
come oxidised and as a result, will chemically change, 
along  with  their  viscosity  and  lubricating  abilities. 
ere is some concern among users of vegetable-based 
cutting uids, that this oil reacts with the environment 
(i.e.  oxygen  and  metals),  thus breaking-down,  which 

is not the case for petroleum-based products. Both of 
these  uid  products  oxidise  with  heat,  but  vegetable 
oils are more susceptible to oxidation. While another 
Figure 212. At the lter some droplets and volatiles are re-
moved from the atmosphere, but the remainder pass through
and are re-entrained. Other particulates are ‘indenitely’ re-
tained, but with time reduce lter eciency. Optimum lters
. maximise droplet removal, while minimising evaporation and
re-entrainment – at a reasonable pressure-drop. [Source: Raynor
P. & Leith, D. – Univ. of North Carolina, 2003]
 Chapter 
drawback to utilising vegetable-based oils, are its lack 
of 
hydrolytic stability
37
.  Typically,  when  making  an 
emulsion; obviously oil and water are present; so if ox
-
ygen and some form of alkaline component is at hand, 
it may cause certain ester linkages within the vegetable 
oil  to  break  down.  ese  broken-down  components 
act in a dierent manner to that of the original vegeta
-
ble oil, thereby aecting its cutting uid performance. 
Conversely, mineral-based cutting oils are resistant to 
hydrolytic reactions. Vegetable oils can support micro
-
bial growth more readily than the equivalent mineral-
based cutting uids. Although this vegetable oil’s bio
-

degradability is ideal for subsequent waste treatment, 
conversely,  when  this  product  is  ‘festering’  in  a  ma
-
chine’s sump, it becomes both smelly and sour, via its 
bactericide and fungicide reactions. Finally, for many 
companies, probably the biggest limitation in changing 
over to vegetable-based products in machining opera
-
tions is its purchase cost. For example, canola oil, can 
cost up to 300% more than its equivalent petroleum-
based product and to compound the nancial problem 
still further, costly ingredients are necessary to control 
oxidation and enhance its biological stability – consid
-
erably adding to the nished product’s cost.
8.12 Fluid Machining
Strategies: Dry;
Near-Dry; or Wet
So  far,  this  chapter  has  been  principally  concerned 
with all aspects of ood/wet coolant applications to the 
overall machining process. Several other complemen
-
tary  cutting  strategies  can be adopted,  these  include: 
dry;  near-dry; together with  wet machining;  thus,  in 
the following sections a discussion of these important 
issues and concerns will be briey mentioned.
37  ‘Hydrolytic stability’:  ester  molecules consist  jointly  of con-
densed  fatty  acids  and  alcohols;  so  the  vegetable  oils  will 
 naturally  exist  as  esters  –  oen  termed  ‘triglycerides’ ,  these 
being a condensation of fatty acid, plus glycerine. Under the 

right conditions, the triglyceride can split and revert back to a 
fatty acid and glycerine, which acts dierently from that of the 
original ester.  In the  case  of mineral-based oils,  they  do  not
contain these ester linkages and as such, will not break down, 
nor ‘hydrolise’.
.. Wet- and Dry-Machining –
the Issues and Concerns
In  the  past  twenty-ve  years  the  cost  of  cutting  u-
ids  has  risen  from  just  3%  of  the  overall  cost  of  the 
machining  process,  to  that  of  >15%  of  a  production 
shop’s cost. Cutting uids and especially ones that are 
oil-based products have become something of a liabil
-
ity of late, this is due in the main, to many countries 
‘Environmental Protection Agencies’ , strictly regulat
-
ing their ensuing disposal – at the end of their natural 
life. In many countries ‘spent’ cutting uids have been 
re-classied  as  either  ‘toxic-’ ,  or  ‘hazardous-waste’ , 
moreover, if they have been found to have machined 
certain  alloyed  and  exotic  material  workpieces,  they 
are  under  even  harsher  disposal  regulations.  Due  to 
the increasing popularity today of high-speed machin
-
ing (HSM) – more will be said on this subject in the 
following chapter – coupled to increased cutting data 
and the application of coolants via high-pressure sys
-
tems,  these  factors  have  signicantly  contributed  to 
the  creation  of  air-borne  mists  within  the  workshop 

environment  (i.e.  see  Fig.  212).  Such  coolant  mists 
now  have  even  stricter  permissible  exposure  levels 
(PEL’s) imposed in the working environment, to regu
-
late  and  control  these  air-borne  particulates,  thereby 
minimising  workers  health  risks.  us,  the  cost  of: 
uid maintenance; record-keeping; with strict compli
-
ance to current and proposed regulations, have rapidly 
increased  the  overall price  of  cutting  uids. In many 
manufacturing  companies  involved  in  a  signicant 
amount  of  machining  operations,  they  are  consider
-
ing the strategy of cutting dry, to overcome the cutting 
uid-based  costs  and  disposal  concerns  during  and 
 aer their subsequent usage. 
For many companies involved in signicant work
-
piece  machining  operations,  they  are  unsure  if  they 
could cut all their components ‘dry’. Furthermore, they 
are under the impression that to achieve higher cutting 
data  and  ‘hard-part’  machining,  then  cutting  uids 
are  essential in  achieving  these objectives. Moreover, 
many  companies  also  believe  that  the  cost  of  chang
-
ing from a ‘wet-’ to ‘dry-machining’ operations would 
be prohibitively high. Neither of these impressions are 
true. So, by machining ‘dry’ it can be considered as a 
standard  operational  procedure  for  most  metal-cut
-

ting operations, including: turning, drilling and mill
-
ing  operations  (i.e  see  Figs.  39,  49  and  168a,  respec
-
tively). Moreover, it is not only possible to ‘hard-part’: 
turn (Fig.  15) and bore (Fig. 65b); or mill (Fig. 172); 
etc.;  but  these  can now  be  classied  as  highly-prot
-
able ‘dry-machining’ activities. 
Cutting Fluids 
Probably  the  chief  obstacle  to  dry-machining  ac-
ceptance,  is  that  conventional  wisdom  dictates  that 
MWF’s are vital in attaining acceptable machined n
-
ishes and will considerably extend the tooling’s life. In 
many  circumstances  these  are  valid  points,  but  with 
some  of  the  advanced  cemented  carbide  grades  and 
high-technology  coatings,  such  tooling  can  be  oper
-
ated  at  higher  cutting  data  than  was  previously  the 
case and, cope with their elevated machining tempera
-
tures. In fact,  if 
interrupted cutting  occurs, the  hotter 
the 
cutting zone becomes, the more unsuitable will be 
the 
application of a cutting uid – as the thermal shock
38

becomes greater with a ‘wet-machining’ strategy.
Present  tool  coating technologies  are  vital to  dry-
machining applications, as they both control the tem
-
perature  uctuations,  while  restricting  heat  transfer 
from  the  cutting  vicinity  to  the  insert,  or  tool.  Mul
-
tiple  coatings  act  as  a  heat  barrier  because  they  of
-
fer  a lower  thermal  conductivity  to  that  of  the  tool’s 
substrate  and  the  workpiece  material.  us,  coated 
inserts/tooling absorb less heat and as a result, can tol
-
erate  higher  cutting temperatures,  allowing  more  ag
-
gressive cutting data, whilst not debilitating the tool’s 
life. Coating thickness is also important, as the  thin
-
ner the overall coatings, the better they can withstand 
temperature  uctuations,  that  might  otherwise  arise, 
if thicker coatings were utilised. e main reason for 
this improved thermal shock performance of thinner, 
rather than thicker tool coatings, is that a thinner coat 
is less likely to incur the same stresses, hence, they are 
less susceptible to cracking as a result. So, by running 
thin coatings in ‘dry-machining’ operations, normally 
extends tool edge life by up to 40%, over thicker coat
-
ings
39

. 
38  ‘ermal shock/fatigue’ ,  the  cyclical  nature  of  both  rapid 
heating followed by immediate cooling – in for example face-
milling  (i.e  see  Fig.  213 – top),  or  when  interrupted  turning 
(e.g. when eccentric turning, or OD/ID machining with either 
splines  and  keyways  present),  promotes  potential  tool  edge 
fracturing – resulting from the cyclic thermal stresses and in-
creased temperature gradients,  being  exacerbated by  the  ap-
plication of a cutting uid.
39  ‘in coats-v-thick coats’ , the former coating oers longer life 
than the latter coating process. Today, it is normal to utilise the 
coating  process  of:  physical vapour deposition (PVD)  as  this 
type of coating is thinner and will adhere/bond more strongly, 
than  the  alternative  chemical vapour deposition  process.  For 
example, a TiAlN PVD coated insert/tool can have a hardness 
of 3,500 Hv, withstanding cutting temperatures up to 800°C.
‘Dry-machining’ – some Factors for Consideration
•
  Adopting a ‘dry machining’ strategy will only make 
sense, if 
all the cutting processes in the part’s manu-
facture can be performed 
without coolant,
•
  Only  by  utilising  specialised  cutting  tool  geome-
tries, can ‘dry-machining’ be possible and eective,
•
  Tooling typically having special hard multi-layered, 
or 
diamond-like coatings,  etc., to  isolate heat and 

create 
minimal thermal conduction across the tool/
chip interface,
•
  Employing  cutting  tool  materials  producing sharp
edge geometries – to reduce heat,
•
  For drilling operations, utilise ‘so-glide’ coatings – 
for 
lubrication, with the necessary and appropriate 
ecient chip transportation geometries,
•
  Speedy and ecient removal of  both chips and as-
sociated 
steam – by suction – are important factors 
in ‘dry-machining’ ,
•
  Utilise  new machining  concepts,  plus  the  latest 
fully-enclosed machine tools – whenever possible,
•
  Employ faster, rather than slower cutting data, to al-
low the majority of heat to be conned to the evacu-
ated chips.
.. Near-Dry Machining
e strategy of ‘near-dry’ machining is not a new con-
cept, it has been in existence for more than 50 years. 
However,  this  machining  and  lubricating  approach 
is  still  not  a  universal  practice,  which  is  surprising 
when one considers the real benets that accrue from 
the practice over  its ‘wet-machining’  counterpart.  As 

its name implies, in ‘near-dry’ machining little lubri
-
cant is used – normally vegetable-based oils, meaning 
that  both cutting  uid treatment  and its disposal are 
eliminated. Further, instigating a ‘near-dry’ machining 
strategy means that there are fewer worker health risks 
from resultant mists, which might otherwise create: re
-
NB  From  a  metallurgical/materials  science  viewpoint,  the: 
TiAlN – PVD tool coating can attribute its superior mechani-
cal/physical  properties  to  an  amorphous  aluminium-oxide 
lm that forms at the tool/chip interface, as some of the alu-
minium of the coating surface oxidises at these elevated ma-
chining temperatures. While, even more exotic multiple-type 
diamond-like coatings can be applied and their like, which of-
fer even greater cutting performance – in certain machining 
circumstances, when applied to the tool’s cutting edge(s).
 Chapter 
spiratory problems: skin irritations; etc. e ‘near-dry’ 
cutting approach can be exploited across a wide range 
of either ferrous, or non-ferrous workpiece metals. 
Most machine tools are equipped with the capabi-
lity of supplying ood coolant to the cutting process, 
together with ‘through-coolant’ tooling systems, mean
-
ing that the cost to recongure for that of a ‘near-dry’ 
technology  is  not  prohibitive.  Assuming  the  worse-
case  scenario  of  requiring  a  through-coolant  tool
-
ing  system,  then  probably  just  over  $5,000  at  today’s 

prices  should  prove  sucient  capital  to  complete  the 
task.  Some  re-tooling  to  complement  the  ‘near-dry’ 
machining  production  techniques  may  be  necessary, 
allowing the precise application of lubricant to the cut
-
ting edge(s). Further, the user must consider a method 
for ecient chip removal from the cutting area. Usu
-
ally,  with  external  ‘near-dry’  cutting  operations,  the 
lubricant  is  transported  within  the  media  of  a  com
-
pressed air application, via the correct-sized aperture 
nozzle – pointed toward the cutting zone. Control of 
the volume of lubricant delivery to the tool and work
-
piece area is critical, with the common misconception 
being  that 
more  lubricant  is  better!  e  optimum  ar-
rangement for ‘near-dry’ lubricant application, is when 
the 
minimum of over-spray and resultant misting does 
not occur. 
With  external  ‘near-dry’  operations,  dispensing 
systems usually consists of reservoir metering pumps 
and valves, being mounted on the machine tool’s exte
-
rior – at some convenient location. While the nozzles 
are  strategically-mounted  so  that  they  can  easily  be 
directly aimed at the tool’s cutting edge(s). Normally, 
the  nozzles  are  a  manufactured  from  either  copper, 

or  plastic  and  ‘snap-together’  –  being  much  smaller 
in  size  than  their  ‘wet-machining’  counterparts.  For 
internal  machining  operations,  having  tooling  with 
‘through-the-nose’  delivery,  the  lubricant  is  mixed 
with  compressed  air  prior  to  delivery  to  the  cutting 
zone.  e  admixing  of  compressed  air  and  lubricant 
keeps the lubricant in suspension, with these oil par
-
ticles being  broken-down  into  minute  particles  prior 
to  being  fed  into  the  compressed  air  jet  stream  – on 
their way to the tooling.
For  ‘conventional’  ood  coolant  delivery  the  sys
-
tems, the coolant channels are lled with cutting uid, 
which  inevitably  nds  its  way  to  the  cutting  zone.  If 
however,  in  a  ‘near-dry’  machining  conguration,  a 
heavy  mist of lubricating oil oats through  the com
-
pressed  air,  attempting  to  negotiate  all  of  the  twists 
and turns on its way to the cutting zone, this may pres
-
ent  a  potential  lubrication  clogging/starvation  prob
-
lem. Hence, for a successful ‘near-dry’ delivery system, 
the  lubricant  channels  need  to  be  smooth  and  even, 
with direct ows from the coolant pump to the cutting 
zone. 
A  basic  misapprehension  by  some  machine  tool 
designers and manufacturers, is that copious volumes 
of ood coolant are necessary to remove large quanti

-
ties  of  swarf.  In  fact,  just  the  opposite  can  occur,  as 
wet chips will not only pack tightly together but have 
a  surface  tension property  to  them,  tending to  make 
them  adhere  to  machine  tool  surfaces  (i.e.  see  Foot
-
note 29, 
‘Lang’s chip-packing ratio’ in Chapter 2). is 
is not generally the case for ‘near-dry’ lubrication, as 
the chips here, have a thin layer of non-oxidising lu
-
bricant  surrounding  them  and  with  their  evacuation 
velocity  –  aer  being  machined,  coupled  to  gravita
-
tional  eects,  means that they  will  fall to the bottom 
of the swarf tray, or into the chip conveyor. It is good 
working practice to use the external air-only supply’s 
blow-o nozzles to clear away chips form the cutting 
area
40
, however, it is not recommended to use the oil/
mist to achieve  chip clearance, as it will simply  blow 
the  lubricant  straight  past  the  cutting  edge(s),  while 
probably  creating  an  unwanted  oil-misting  problem. 
It is possible to incorporate both ‘wet-’ and ‘near-dry’ 
lubrication  systems  onto  the  same  machine  tool.  It 
has been reported that for external/internal work the 
change-over  from one system  say, from  ‘wet-’ , to the 
other – ‘near-dry’ , takes about 3 minutes to complete. 
For  ‘near-dry’  machining  to  be  successful,  it  de

-
pends upon various factors, including: workpiece ma
-
terial to be machined; tool geometry and its coating(s); 
speeds  and  feeds  selected;  plus  other  important  fac
-
tors. If applied correctly, ‘near-dry’ machining has sig
-
nicant direct and indirect benets to the machining 
process as a whole. 
Economics of: ‘Dry-’; ‘Near-Dry’;
and ‘ Wet-Machining’.
For  any  tool  and  workpiece  lubrication  strategy  to 
operate  eectively,  a range  of  cost  factors  need  to be 
considered,  regardless  of  the  method  of  machining 
40  ‘Chilled compressed air’ , has been successfully utilised in the 
past  for  not  only  removing  chips  from  the  cutting  vicinity, 
but on certain materials, the continuous application of chilled 
compressed  air  acts  simply  as  a  form  of ‘basic  lubricant’  for 
the cutting process in hand. 
Cutting Fluids 
undertaken. In Fig. 213, a table has been constructed 
to  show  the  relative  merits  of  the  three  machining 
strategies  previously  discussed,  namely:  ‘dry-’;  ‘near-
dry’; or ‘wet-machining’. e cost component for each 
of these lubrication  strategies has been  broken down 
into its relevant parts, with some of them not being ap
-
plicable to every lubrication application. If one ignores 
the  individual  cumulative  factor  in  the  overall  cost 

and simply looks at the ‘bottom-line’ , namely, the total 
relative costs for each process, then a clear message is 
being  given here! Explicitly,  that ‘wet-machining’-  in 
certain  cases,  when  compared  to  ‘dry-machining’  is 
Figure 213. Indicates the comparative costs for utilising either: ‘dry-’, ‘near-dry-’ or ‘wet-machining’ strategies.
 Chapter 
>330% more expensive overall, this being a good rea-
son  to  look  carefully  at  employing  ‘dry-machining’ 
techniques – when applicable!
In  Appendix  14,  a  MWF  ‘trouble-shooting  guide’ 
has been included, to help establish the relative causes 
and  remedies  for  certain  uid-related  problems  –  as 
they arise.
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 Chapter 