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Drilling, Reaming and Grinding
Introduction
Grinding, drillingand reaming are some of the oldestand most fundamental manufacturing
processes still used in modern times. They are, in essence, extremelysimple material removal
processes that use many small cutting surfaces as opposed to a single cutting surface. This
report is a description of these processes and summary of their most common variants and
applications. It will also cover the limitsof accuracy, efficiency,size, shape and materials that
these processes can be used on.
Drilling
Process and Variants
Drilling is the “use of a rotating multi-pointdrill to cut a round hole into a work piece” (Tooling U
SME, 2013). The process begins with a centre hole being made on the work piece.The centre
hole is a small indent on the surface of the work piece that marks the spot to be drilled.It is
used to stabilise the drill bit as it enters the material and reduces the feed force required. The
centre hole is made using a centre punch, spot drilling,spot facing or forging a mark into place.
For manual operations, an upright drill press, radial drill press or hand drill is commonly used.
For automated operations, Computer Numeric Control (CNC) Machines are used. Using an
upright drill press, the drill is moved in and out of the material to remove swarf and prevent the
apparatus from jamming.
Restrictions on Shape and Size/Material Compatibility
The most common drill bit is the Jobbers, or “Twist” drill bit. A diagram of this drill bit is shown
below. There are two important features that define the size of the drill bit; the diameter of the
bit and the flute length. The flute length is between 9 to 14 times the diameter of the drill bit.
They are important as the flute length determineshow deep can the bit drill into a material and
the diameter determinesthe size of the hole.
Figure 1: Jobbers Drill Bit (Schey, 2000)
A drill bit can be made in any size to order. However, the BS 328 definesmetric drill bit sizes
from 0.2mm to 25.0mm in diameter and the ANSI B94.11M-1979 definessizesfrom 1/64th inch
to 1 inch in 1/64th increments. These standards are important as they allow standard gauges to
be stocked and sold easily.Drill bits are not just limitedto circular shapes. Instead there are a
whole host of differentbits, used to drill different types of holes or through differentmaterials.
Some examples are the gun drill bit, the Forstner drill bit, the spade drill bit and the indexable
insert drill bit. Technically, we can apply drillingon any material we want. But usually, this
process is used for major construction materials; metals, woods and cements.

Group 13 Drilling, Reaming and Grinding
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Accuracy and Repeatability
In terms of accuracy and repeatability there are two important tolerances to note: locational
tolerance and size tolerance. Locational tolerance measures how far the centre of the drill bit
deviates from the ideal centre. This depends on the type of drillingapparatus used. Computer
Numerical Control (CNC) machines have much better tolerances compared to manual
operations due to its high precision. The table overleaf shows that as the diameter of the drilled
hole increases, the size tolerances increase as well.The size tolerance also increases as the
drillingdepth increases. This is because at greater depths, the drill bit tends to drift due to
vibrations (Schey, 2000).
Surface Detail
Surface roughness is definedas the quality of finishof a material or workpiece after the
manufacturing process applied to it. There is a direct relation betweenthe surface quality of a
drilledhole and parameters like cutting speed, the feedrate of the drill and whether a lubricant,
or “cutting fluid” is used or not. Surface roughness increases proportionally with the feed rate.
In order to increase the efficiencyin manufacturing, it is necessary to remove high quantities of
chips. The increasing demands for greater productivity at manufacturing facilitiesresults in the
need for high feedrates. As cutting temperatures and feed rates increase, tool life decreases
and surface finishworsens (Dhar, Ahmed, & and Islam, 2007). Increasing the cutting speed
improves the surface finishby decreasing the magnitude of the cutting forces, this improves the
surface quality of the drilledholes.The poorest surface roughness is achieved using “dry”
drillingprocesses that do not use a cutting fluid.Less roughness occurs when cutting fluid is
used because cutting fluidsreduce contact between the bit and the material.
Production Economics
In the production economics of drilling the first factor that will influence efficiencyis the
material of the work piece. Some materials are very hard so we drill bits that are made of
stronger material are required, these are often more expensive.In addition to that, more energy
and time is used to drill which leads to inefficiency.Secondly,the depth and diameter has an
influence as well.Usually, we will use the ratio of depth and diameter to describe a hole.The
larger the ratio is, the more difficultit is to drill because it is very hard for some chips to get out
from the hole which will damage the work piece and drill bit. The process requires low tooling
costs and for manual operations, can be operated by an unskilledoperator. This process
produces a lot of swarf (debris) which is wastage of precious material.
Reaming
Process and Variants:
Reaming is a manufacturing process whereby a previouslymade hole is enlarged and finishedto
accurate dimensions. It is performed predominantly on metal using a rotary cutting tool called a
reamer, either by hand or using a machine such as a lathe or CNC machine. Drilling and other
hole forming processes often leave poor surface finishesand are therefore not suited to
manufactured products that require extremelytight tolerances (Wikipedia, 2013). Through
reaming, a holes surface finish can be smoothed and tolerances tightened,enabling more
precise manufacturing. This is especiallyrelevant as the need to manufacture to tight
tolerances and increased precision has increased with the introduction of CAD (computer aided

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Figure 2:Diagramshowing a commonreaming operation
(http://www.custompartnet.com/wu/hole-making)
Figure 3:Picture ofa square shankhandreamer
(http://www.engineeringsupplies.co.uk/29mm-square-shank-
hand-reamer-p-3793.html)
design) and CAM (computer aided manufacture), which allows extremely detailedparts to be
designed.
The process of reaming has similarities to that of drilling,in that a tool (a reamer) is rotated and
inserted into a workpiece, removing material; it is important to remove these chips of material
quickly as they can end up getting ground back against the reamed surface, degrading the
surface finish.The difference in the process is that reaming can only be performed on an
existinghole; you cannot start a hole with a reamer as it has a flat end rather than a cutting
edge. A reamer usually has 4 to 8 flutes compared to 2 to 3 for a drill bit, and also has a much
larger pitch than a drill bit. However similar they may look, reamers are markedly differentto
drill bits and actually have more in common with grinding, both being finishingprocesses.
There are many different types of reamers for a wide range of applications. Some of the more
common variants are: straight reamers, which are the most common and simplest form of
reamers. Their only function is to improve the surface finishon the inside of drilledholes.
Machine reamers have a short taper, as the reamer can be accurately pre aligned. These are
used in machines such as lathes and many CNC machines. Hand Reamers have a longer taper
than a machine reamer to make it easier to start the process by hand power. Tapered reamers
are used to finish tapered holes. These are common in the aircraft industry where a taper pin is
used as a self-tighteningdevice to join two pieces of material together (such as two wing
sections in a glider). Combination reamers have a specificshape to ream multiple internal
diameters in a workpiece using only one tool. These are only used for complex parts in industry
to reduce the number of turret operations (Wikipedia,2013).
As well as these differenttypes of reamers, there are a number of flute styles that are used in
industry; straight flute reamers (with a pitch of 90⁰) are used for a wide variety of applications.
In blind-hole applications, the chips produced are not drawn out naturally and so non-chip
forming materials such as bronze and cast iron are preferred. In through-hole applications,
where a hole has beenmade through a piece of material, chips will be forced out through the
other side of the hole when coolant is used. Right hand spiral reamers are the most common
spiral flute reamer. They are designed to pull chips and coolant out of the hole and so are ideal
for blind-hole applications where the hole is not made through the entire piece of material. Left
hand spiral reamers are only used in through-hole applications as the spiral means that chips
and coolant are forced in front of the reamer. In a blind-hole the chips would gather at the
bottom of the hole and prevent the reamer from attaining its target depth (Tools-n-Gizmos,
2007).

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Reamers are usually made of two materials; HSS (High Speed Steel), a tool steel with
approximately a 0.7% Carbon content, and Tungsten Carbide. Tungsten Carbide tools are usually
harder than HSS, a 9-9.5 on the Mohs scale compared to 7.5-8 for HSS. HSS can be strengthened
by adding 5% to 8% of cobalt. This also increases the wear resistance.
The advantages of tungsten carbide are that it can withstand much higher temperatures than
standard high speed steel tools. This allowsfor higher cutting speeds to be utilized. Under
similar applications, a tungsten carbide tool has a cutting speed between4 to 12 times faster
than high speed steel (thisof course depends on the operation and type of material being
machined). The productivity of machining is proportional to cutting speed and so increases with
the use of tungsten carbide. A major disadvantage of Tungsten Carbide is that it is very brittle
and can shatter under lateral stresses, which takes away from the advantage of a longer tool life
for Tungsten reamers (Tools-n-Gizmos,2007). However, for high performance applications where
CNC machinery is used to reduce any errors resultingin lateral stress it is ideal.
Any material that already contains a hole can be reamed, but for most applications, this is
limitedto common construction and manufacturing materials such as metal, wood and cement.
Reamers, like drill bits, are standardised by the BS 328 and ANSI B94.11M-1979 standards, and,
while usually cylindrical, can have other profiles,such as conical reamers.
For some hard materials, only a tungsten carbide tool can be used. This is because other tools
would wear away too quickly, such as when machining stainlesssteel in a large quantity
production. Because of its hardness, tungsten carbide tools also maintain a sharp edge and so
maintain a better finishon parts. A disadvantage of this being that when a carbide tool
eventuallyneeds to be sharpened super-abrasive grinding is needed(such as a synthetic
diamond grinding wheel).
Reaming is usually done to a fairlytight tolerance. Since it is a material removal process, reamed
holes can only be larger or equal in size to the reamer itself.The use of lubrication has a
significant effect on the accuracy of a reaming process, lubricated, or “wet” reaming has a
tolerance of approximately +0.025mm, whereas “dry” reaming has a tolerance of +0.030mm.
Since “dry” reaming can seriously damage a reamer, “wet” reaming is much more repeatable
than “dry” reaming and hence cutting fluidis normally used (Wikipedia,2013)
Surface Detail
Reaming is a finishingprocess, closelyrelated to grinding as well as drilling. The reaming process
removes a small amount of material (typically5% of the amount of a similar sized drill bit) and
leaves a very smooth surface. Typical surface finishesof reamed holes are in the region of 0.8-
3.2 µm, compared to 1.6-6.3 µm for drilled holes (Booker, 2013)
Tungsten carbide reamers can stay sharp for up to 10 times longer than their HSS counterpart
(http://www.firearmsid.com/feature%20articles/rifledbarrelmanuf/barrelmanufacture.htm
12/12/13). This makes it more efficientfor long production runs because using HSS, production
would need to be stopped more often to change and sharpen the tool. Another result of
minimal wear to tungsten carbide cutting edges is the consistent quality of hole size and surface
finishproduced by these tools. HSS can produce a good finishat the start of its life but this

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declinesmuch more rapidly than that of carbide. The efficiencyof any reaming process closely
depends on the material of the workpiece, type of reamer used and the local application. For
example a small company reaming a relativelysoft material in small production runs will find
HSS to be more cost efficient.This is because a good tool life can be achieved when machining
softer materials and free cutting steelsso the outright cost of the tool will affect the production
economics more than any long-term benefitsof carbide. Whereas a large production run using
hard materials will find tungsten carbide to be more efficient.
A fact worth taking into consideration for the economics of reaming is there is a noticeable
difference between the price of a high speed steel reamer and a tungsten carbide reamer. For
example,a HSS 4mm straight shank reamer costs £15 and a Tungsten Carbide version costs £40.
(Cromwell Industries, 2013)
Grinding
Process and Variants
Grinding is a manufacturing process whereby an object is rubbed with an abrasive material,
usually to change its shape of surface roughness. Grinding is usually used as a final finishing
process, but is also used as a manufacturing process in itself;for instance, it is used to shape
glass into lenses (Malkin/Guo, 2008). In modern grinding, this abrasive is usually a grinding
wheel,or a specialist grinding tool shaped for a specific use; available shapes include cups,
cones and spheres (Norton Industrial, 2013). Grinding wheelsand other grinding tools are
composed of grains of a hard abrasive material held together by a flexible bondingagent such as
resin or rubber, the grains and bonding agent are mixed and compressed at high pressure into
appropriately shaped moulds and then baked in industrial ovens at slowly increasing
temperatures; resulting in a hard, rocklike substance (How It’s Made, 2004). Wheels can be
manufactured for specificpurposes and are classifiedby factors such as porosity, grain material
and grain fineness.
The most common abrasive materials are silicon carbides and aluminium oxides,superabrasive
grinding wheels are composed of synthetic diamond or CBN (Cubic Boron Nitride),and are used
to grind harder or more brittle materials than conventional abrasive wheels.Each abrasive grain
is a microscopic cutting tool which remove a small amount of material from the object, and
therefore the grains make up a single cutting surface across the surface of the wheel,they wear
down the asperities of the workpiece, resulting in a smoother surface finish (Malkin/Guo, 2013).
The excess material is removed as dust and debris, which is washed away by “grinding fluids”,
which are sprayed on the object during the grinding process. Due to the heat and friction
grinding produces, “straight” mineral based and “soluble” water based oils are used as
combined lubricants and cooling fluids (Malkin/Guo, 2008). Grinding blunts the abrasive grains
and changes the shape of the wheel,meaning the wheel needs to be “dressed”, breaking away
the outer layer of the wheel with a tool known as a “wheel dresser”, until the wheel surface is
clean and sharp (listoftools.com, 2013)
Some of the more common variants of grinding are: straight surface grinding, where the face of
a grinding wheel is pressed against the surface being grinded, the grinding wheel is rotated
about a drive dog or centre driver, and the workpiece is supported by either a vacuum or
magnetic chuck on a reciprocating table (Wikipedia, 2013). Cylindrical grinding is used to grind
curved surfaces, internal cylindrical grinding is used to grind the inside of the curved surface,
external cylindrical grinding is used to grind the outside of the curved surface (Malkin/Guo,
2008). Creep feed grinding is a grinding process used to remove large amounts of material

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quickly using deep cuts with the wheel as the material is fed in slowly (wikipedia.org, 2013).
Centreless grinding is used to grind cylindrical objects by rotating them betweena grinding
roller and a regulating roller while supporting the object with a blade (Malkin/Guo, 2008).
Finally,electrochemical grinding is a newer process that can only be used on hard metals, in
electrochemical grinding the grinding wheel is a metallic disc studded with abrasives, and the
lubricant is replaced with an electrolyte solution. The object being ground is positivelycharged,
and the wheel is negativelycharged; a redox reaction occurs and the surface of the object is
oxidised.This oxide is weaker than the metal and requires less force to remove, this means the
wheel needs to exert lesspressure and spin at a lower speed,this results in smoother, truer
surfaces than traditional mechanical grinding, since the wheel does not exert forces of sufficient
magnitude to cause significant elastic deformation in the material (Wikipedia, 2013).
Figure 4: Diagram ofgrinding machines in operation, thefreedictionary.com/The Great Soviet Dictionary (2013/1979)
When a piece is grinded the wheel or tool is spun about its axis and either held against the
object, or the object is held against the cutting surface of the wheel (Malkin/Guo, 2008).
Grinding machines range from small, handheld tools for delicate precision work, to large
industrial machines used for heavy duty grinding in steel mills,this, combined with the variety of
available wheel geometries and configurations means that there are nearly limitless variants
and applications of grinding, and the sizes and shapes it can produce.
Grinding as a process is compatible with almost every material. In fact, grinding is the only way
to machine materials like glass, which are too brittle for other machining processes. There are
some limits however; for instance, synthetic diamond wheelscannot be used to grind steels,
because the heat produced by grinding, and the carbon the diamond is composed of, causes the
steel to undergo “graphitisation”, a process whereby the steel decays into a brittle iron/graphite
mixture (Foulds/Viswanathan, 2001). As such CBN is used exclusivelyfor ferrous metals. Despite
this, everything from sewing machine components, to drill bits, to blocks of stone can be
grinded.

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Figure 5: Handheld grinding tools, arabianOilandGas.com (2009) Figure 6: Reciprocating surface grinding machine, mechlook.com (2009)
Elastic deformations and deflections caused by grinding forces are the main source of inaccuracy
in grinding (Malkin/Guo, 2008). Despite them, however, grinding is a very accurate, if inefficient
and wasteful, process. For common use, the tolerance of grinding is between 2.5-25 µm, but
this varies depending on the size of the workpiece, the greater the dimensions of the workpiece,
the greater the tolerance of the grinding process (Booker, 2013). The accuracy of the grinding
process also varies depending on the grinding process used, e.g. the typical tolerance for surface
grinding is ±5 µm, whereas the typical tolerance for cylindrical grinding is ±13 µm (Wikipedia,
2013). Grinding has become more accurate and repeatable with the advent of AC (Adaptive
Control), wherein the workpiece and grinding process itself is computer monitored in real time
and, since the process is also computer controlled, can be adapted to compensate for any
deflectionsin the piece that may cause inaccuracies (Malkin/Guo, 2008).
Surface Detail
As well as being very accurate, grinding is also the only process that can produce the necessary
surface finishesfor applications such as precision bearings (Malkin/Guo, 2008). Surface
roughness ranges between 0.1-1.6 µm for common use, lower on average than many
manufacturing processes such as casting and forging (Booker, 2013). In recent years grinding has
become more efficient;firstly, as other manufacturing processes become more accurate and
produce products that require less finishing, meaning less grinding is necessary, and less
material is wasted; secondly, with computer optimisation, a computer program can calculate an
optimum grinding process from the parameters of the process, and computer control ensures
the piece is ground to the optimum surface finish (Malkin/Guo, 2008).
There is a complex equation for determiningthe total cost of grinding an object which shows
that the majority of the individual costs vary depending on the speed of the wheel.
Figure 7: Equation showing the total cost per piece of a grinding process, IITK (2013)

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Therefore, there is an optimum speed for each grinding process to minimise costs; this speed
must be calculated for each individual grinding process, (IITK, 2013).
Conclusion
Drilling,reaming and grinding are all processes that removes a small amount of material using
multiple cutting surfaces to change the shape or surface finishof a workpiece. However, while
drillingand reaming are focussed on holes, grinding is used on whole outer surfaces of
manufactured parts. They also all use tool piecesthat spin about an axis.All three processes
have relativelylow tolerances that increase with the dimensions of the workpiece, but are all
wasteful and inefficientprocesses. Similarly,all three processes are made more efficient
through the use of computer control and lubricants. While all three processes are technically
compatible with a wide range of materials, and have no limiton size and shape, for all practical
purposes grinding is the most versatile.
References
 Arabian Oil and Gas Staff,http://www.arabianoilandgas.com/article-5291-safety-tools-releases-new-
range/#.UotTRSpNwqs (Safety Tools releases new range(, Arabian Oil and Gas,19 April 2009
 Bawa H.S., ManufacturingProcesses –I, Tata McGraw-Hill,(2006)
 Dhar, N., Ahmed, M., & and Islam,S.(2007). An experimental investigation on effect of minimum
quantitylubrication in machiningAISI 1040 steel.International Journal of MachineTools & Manufacture
Vol 47.
 Dr Julian Booker, “DESIGN AND MANUFACTUREV 1- Engineering DrawingHandout”, University of Bristol,
2013
 http://en.wikipedia.org/wiki/Drilling (12/11/13)
 http://en.wikipedia.org/wiki/Grinding_(abrasive_cutting) (2/11/13)
 http://en.wikipedia.org/wiki/Reamer (2/11/13)
 http://www.firearmsid.com/feature%20articles/rifledbarrelmanuf/barrelmanufacture.htm (12/12/13)
 Engineers Edge LLC. (1 November, 2013).Engineers Edge LLC. Retrieved from Engineers Edge LLC Drill
Tolerances:http://www.engineersedge.com/manufacturing/drill-mechanical-tolerances.htm
 Foulds/Viswanathan,“Journal of MaterialsEngineeringand Performance, Volume 10 Issue4”, Springer
Science+Business Media,August 2001
 http://encyclopedia2.thefreedictionary.com/Grinding+Machine,thefreedictionary.com (The Great Soviet
Dictionary),2013 (1979)
 http://home.iitk.ac.in/~jrkumar/ME%20361/Grinding%20and%20Economics%20of%20Machining%20Ope
ration.pdf,“Grinding and Economics of MachiningOperation”,Indian Instituteof Technology Kanpur,
publishingdateunknown, accessed online2013
 http://www.listoftools.com/grinding_operations/truing_and_dressing_the_wheel.html , 2013
 http://www.nortonindustrial.com/, 2013
 http://www.tools-n-gizmos.com/info/Reamer_Basics.html (Reamer Basics),Tools-N-Gizmos.com,2013
 http://www.youtube.com/watch?v=ggMi0Ym6fnM, “How It’s Made: GrindingWheels”, Science Channel,
2004
 https://www.cromwell.co.uk/index.php?search_all=reamer&search.x=0&search.y=0&p=advancedsearch&
q=0 (Search Products:Reamers), Cromwell Industries,2013
 Schey, J. A. (2000).Introduction to ManufacturingProcesses.In J. A. Schey, Introduction to Manufacturing
Processes (pp. 674-676).McGraw-Hill Higher Education.
 Stephen Malkin/ChangshengGuo, “GrindingTechnology- Theory and Applicationsof Machiningwith
Abrasives”,Industrial Press Inc.,2008
 ToolingU SME. (1st December, 2013).ToolingU SME. Retrieved from
http://www.toolingu.com/definition-200110-12893-drilling.html
 Vishnu,http://www.mechlook.com/types-of-grinding-machines/ (Types of GrindingMachines),
mechlook.com, 21 August 2009

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