TURNING TO COATINGS
Tool coatings increase lubricity,
handle the heat, all to protect thesubstrate—p28

ISO 9001 AND ERP:A UNITED APPROACH
Work process documentation
is a good starting point for
both certification and software
selection—p32

ONTARIO’S CENTENNIAL COLLEGE
TRANSFORMS STUDENTS INTOSKILLED WORKERS
Mechanical engineering programs
use hands-on product development
approach to add a measure ofexcellence—p36

AEROSPACE SECTOR REPORT:A JETSTREAM OF TRENDS
5-axis machining, additive
manufacturing are necessary
for highly complex aerospace
work—p44

FEBRUARY 201741467014

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DEEP-HOLE DRILLINGREQUIRES KNOWLEDGE,
SPECIALIZED TOOLING, AND
THE CORRECT MACHINE

1/26/17 10:06 AM

Deep-hole drilling machines, such as thosemanufactured by Cheto, are one option for creating
deep, straight, round holes. Photo courtesy of Elliott
Matsuura Canada.

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GOINGDEEP
Deep-hole drilling requires
knowledge, specialized tooling,
and the correct machine
BY JOE THOMPSON
Editor’s Note: This article is based on ChetoCorp. Chief Technology Officer Sergio
Andre’s presentation at the International
Manufacturing Technology Show (IMTS),
Sept. 12-17, 2016, Chicago.

In drilling it’s all about the hole and, more
specifically, the parameters of the hole.
Straightness, cylindricity, and concentricity all need to be accurately maintained tocreate a high-quality hole. These factors also
are affected by drift, runout, and circularrunout which compromise hole quality.
Round holes are the easiest type of hole toproduce, and can be created using any number of methods, the most popular of which is
obviously drilling. Creating square, ovular,
or other complicated shapes, can be accomplished by using milling and EDM processes.
Inclined holes, through holes, and blindholes all create problems that must be solvedby the tool being used and with the correct
cutting parameters. All of this needs to becorrect to get the hole you want to the depth
you want.
And, the deeper the hole, the more difficult
creating it becomes.
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WHAT IS DEEP-HOLE DRILLING?
Deep-hole drilling typically is described asholemaking to length-to-diameter ratios thatare higher than 10xD.
It is a process that can be used with several
types of materials, including ferrous andnonferrous.
Producing a deep hole with a good finish,accurate diameter, and straightness control
is the goal of deep-hole drilling. Hole quality
is key to the development of high-quality
products.
The aerospace, automotive, oil and gas,hydraulics, maritime, medical, and mouldmaking industries all require deep-hole
drilling. Sometimes specialty tools need tobe employed to help ensure hole quality (seeFigure 1).

HoleDepth

Required Tool

5xD

Regular twist drill

10xD

High-performance twist drill with
coolant through the tool

20xD

Special deep-hole drilling tool with
coolant through the tool

100xD

Deep-hole drilling tool on machine
dedicated to deep-hole drilling

200xD

Deep-hole drilling tool on highperformance drilling machine

400xD

Special tool needed

Figure 1

DRILLING PROCESSES
Following are three common ways to drill
holes, and the process you select depends on
the type of part being produced and the typeof hole being drilled.
1. Tool rotation and stationary part. Thistype of drilling typically is used on nonsymmetrical parts or on round parts that
require out-of-centre drilling. In this case,cutting speed is determined by tool rotation speed. It must be noted that the occurrence of drift can be higher than with otherprocesses.
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2. Part rotation and stationary tool. This
type of drilling is commonly used for roundparts with deep, centred holes. Cutting
speed is determined by tool diameter plus
part rotation. Drift in this type of drilling isless compared to the tool rotation method.
3. Tool rotation and contrary part rotation. Drilling when both the tool and thepart are rotating is a method used for roundparts that need deep, centred holes. Cutting
speed is determined by tool diameter plus
the tool rotation plus part rotation. Drift inthis method is lower compared to the othertwo processes.

UNDERSTANDING DRIFT
The deeper a hole gets, the more chance
there is for the drill to drift, especially if
the tool encounters intersections with otherholes or part features. The amount of drift
varies depending on the type of drilling
operation being performed. Tool rotation (X),part rotation (Y), and tool rotation and contrary part rotation (Z) all produce different
drift (see Figure 2).
In all cases, the chance for drifting is
reduced if a pilot hole is used. According toCheto Corp. Chief Technology Officer Sergio
Andre, the angular alignment of the pilot
hole is key, and care must be taken when apilot hole meets an intersection.
Feed rate and other cutting parameters
also affect drift and, of course, different
materials require different parameters.

TOOLS AND SYSTEMS
Less than 70 years ago, the meaning of deephole drilling was automatically connected togundrilling. There simply weren’t any othermethods. Today, with advances in mechanical technology, more methods are available
that enable deep-hole drilling. The threemost common are the gundrill, single tube
system (STS), and ejector system.

GUNDRILL
As its name implies, the gundrill initially
was developed to drill gun tubes. It is amachine dedicated to creating long, straightholes with relatively small diameters, and it
can be used on several types of material.
The tools for this machine typically incorporate a single -edged head and V-shaped
flute. The drill body is slightly thinner thannormal to allow the chips and coolant toexit. Today some gundrills have a carbide
head and some use indexable inserts.
Coolant is fed through the coolant hole in
the tool from the spindle to the edge of thetool. A gundrill also can be used in a conventional drilling centre machine, but it
requires high coolant pressure.
It is possible to create small holes (thosewith diameters between 0.5 and 3 mm) witha gundrill given the appropriate tool andsetup. Hole diameters between 3 and 50 mm
are the normal range for gundrilling, butholes of 50 to 75 mm also are possible, butgundrilling in this range is less productive
than hole production on an STS machine.
When you use a gundrill with indexable
inserts, feeds 40 per cent higher than witha traditional gundrill can be achieved.
Combined with the quick replacement ofinserts and reduced storage needs, a gundrill with inserts can reduce setup time,production time, and overhead. However, theinitial cost is higher.

Figure 2—The data in the chart is based on information from single-flute gundrill-makers at optimal conditions. Chart
courtesy of Cheto Corp.

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When you are drilling with a drill bush or
making a pilot hole, you must start penetration without rotation or at a slow rotation(less than 50 RPM). Then the coolant and thespindle can start working. A similar method
is used when the desired depth is reached.
The coolant should be turned off and thegundrill removed with the spindle stopped
or in slow rotation (less than 50 RPM).

COOLANT USAGE
The recommended coolant type for deephole drilling process with a gundrill is oil.
Viscosity should be around 8 to 10 mm 2/s at
40 degrees C for diameters between 0.5 and1.5 mm. Oil viscosity should be around 10
to 15 mm 2/s at 40 degrees C for diameters
greater than 1.5 mm.
It is possible to use emulsion, but the feedmust be reduced to 60 to 80 per cent of what
is possible when using oil. When using anemulsion, however, coolant pressure can be
reduced to 20 per cent. It is paramount thatpressure and flow are adequate to remove
chips efficiently.
Gundrill Advantages•Good surface finish produced

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DeepHolDrillingFeature_Feb17CM.indd 20•Better roundness compared to using a
twist drill•Suitable for holes with diameters as small
as 0.5 mm•Can be sharpened eight to 15 times
Gundrill Disadvantages•Lower productivity caused by low feed
•Difficulty sharpening long and smalldiameter gundrills•Requires high coolant pressure•Not efficient for diameters greater than 50mm

STS MACHINES
Single tube systems (STS) employ coolantthat is fed through the exterior of the tool.
Seals are needed to ensure coolant reaches
the cutting area and the tool’s edge has an
opening to extract coolant and chips fromthe head to the chip box.
This type of system can’t be used withsmall-diameter tools. Most tools for STS
machines have a minimum diameter ofaround 15 mm. However, it can be used tocreate holes up to 300 mm in diameter.
Because an STS machine has high productivity, it should be considered first for batchwww.canadianmetalworking.com

1/25/17 2:42 PMproduction. It can be run using higher feeds
than the gundrill, and the edge of the tool
can perform several different operations,including drilling, machining, polishing,and trepanning.
The same tool can be used with different inserts on the cutting edge to improve
productivity and increase the number ofoperations.
Some disadvantages come along with an
STS setup, however.
It takes a while to change out a tool andaligning the tools can be a complicated task.
Usually the tools used in these machines are
not sharpened, so they become more expensive to use.
It is critical that the chips are broken into
small enough pieces that there is no chipcongestion in the flute. It also is necessary
to use high coolant flow. This requires ahigh-capacity tank, coolant filtration, andhigh-pressure pumps.

coolant to the edge of the tool, and the interior tube allows for the exit of coolant andchips. These systems also are commonly
called double tube systems (DTS).
Ejector systems require even more coolant
pressure than STS machines. They also are
more prone to congestion caused by failure
to successfully expel chips.
Like the STS machines, ejector systems
have high levels of productivity. The same
tool also can use different kinds of inserts
on the cutting edge. With this system, however, it is not necessary to change the entire
tool; just the head can be changed.
A drawback of these machines is that theycannot be used for holes with diameters lessthan 20 mm. Also, proper chip creation andcoolant pressure are important so that thereturn tube does not get clogged.

EJECTOR SYSTEM

Cheto Corp. courtesy of Elliott Matsuura
Canada, 905-829-2211, www.elliottmachin
ery.com.

This type of system is like an STS, but thecoolant is fed differently because the flute
has two tubes. The external tube pumps

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Editor Joe Thompson can be reached atjthompson@canadianmetalworking.com.

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