O. SPAI] et al.: APPLICATION VALIDITY OF THE TECHNOLOGICAL PROCEDURE FOR MAKING ...
77–81
APPLICATION VALIDITY OF THE TECHNOLOGICAL
PROCEDURE FOR MAKING SPIRAL DRILL-BIT GROOVES
OVREDNOTENJE UPORABNOSTI TEHNOLO[KEGA POSTOPKA
IZDELAVE SPIRALNIH SVEDROV
Obrad Spai}
1*
, Milan Vuk~evi}
2
, Budimirka Marinovi}
1
, Aleksandra Koprivica
1
,
Janko Jovanovi}
2
1
University of East Sarajevo, Faculty of Production and Management Trebinje, Stepe Stepanovi}a bb, Trebinje 89101, Bosnia and Herzegovina
2
University of Montenegro, Faculty of Mechanical Engineering, Podgorica 81000, Montenegro
Prejem rokopisa – received: 2020-05-07; sprejem za objavo – accepted for publication: 2020-09-17
doi:10.17222/mit.2020.071
The current world trends and the global market require production organizations to increase the quality while reducing the costs
of their products. In most cases, traditional production technologies of spiral drill bits (SD) cannot meet these expectations, as
they most often fulfil only one of the set requirements. Thus, the cost of a SD produced with the rolling technology is low, but
its quality is also much lower than that of the drills produced with the grinding technology whose cost is also much higher. The
grooves of the SDs produced with our new technological method have advantages over the grooves produced with the rolling
technology or grinding technology, and the savings in the material and grinding wheel are higher compared to the SDs produced
with the grinding technology. This paper presents an analysis of the application of this new technological process for producing
SD grooves.
Keywords: drilling, grinding, rolling, new technologies
Trenutni svetovni trendi na globalnem trgu zahtevajo od proizvodnih podjetij stalno izbolj{evanje kakovosti njihovih izdelkov
ob isto~asnem zmanj{evanju stro{kov. V ve~ini primerov tradicionalne tehnologije proizvodnje oz. izdelave spiralnih svedrov
(SD) ne morejo izpolnjevati teh zahtev in lahko pogosto izpolnijo le enega od zahtevanih pogojev. Stro{ki izdelave spiralnih
svedrov, izdelanih s tehnologijo valjanja so ni`ji in tudi njihova kvaliteta je slab{a od tistih, ki so izdelani s precej dra`jo
tehnologijo bru{enja. Izdelava trna in brazd na spiralnih svedrih z novim tehnolo{kim postopkom omogo~a zmanj{anje porabe
materiala v primerjavi z obstoje~ima tehnologijama izdelave z valjanjem in bru{enjem. V pri~ujo~em ~lanku avtorji opisujejo,
analizirajo in ocenjujejo nov tehnolo{ki postopek izdelave spiralnih svedrov.
Klju~ne besede: rezkanje, bru{enje, valjanje, nove tehnologije
1 INTRODUCTION
One of the most commonly used cutting tools is a
spiral drill bit (SD), which can be manufactured using
technologies such as: forging, milling, grinding, rolling
and extrusion.
1–3
The geometry of SDs is more complex
than the geometry of other cutting tools, so it takes a lot
of time, engineering knowledge and research to construct
and manufacture them.
4
Therefore, the researchers in this field tried, based on
the appropriate input parameters, to develop software so-
lutions for an automatic generation of 3D models. Thus,
in 2006, Vijayaraghavan
5
developed a tool in SolidWorks
2003 for an automatic generation of 3D models of SDs,
based on the production parameters. In the production of
conventional SDs with two spiral grooves, the two basic
operations are the fabrication of the spiral groove and
grinding the front surface, which defines the geometric
parameters of a SD. Parameters such as the top angle and
core thickness imply the functions of a SD. In 2012, J.
Jovanovi} et al.
6
developed software for a profile genera-
tion of SD-groove tools depending on the nominal diam-
eter of the SD, core diameter, angle of rise and top angle,
provided that the main cutting edge is a straight line and
the width values of the key and groove are in a ratio of
1:1.
Production technologies of SDs do not satisfy the cri-
teria of quality and costs equally. So, for example, the
rolling technology results in material savings and better
strength properties.
1
This means that the cost is lower,
but the quality is also much lower than that of the drill
bits made with the grinding technology, whose cost is
much higher.
When analyzing grinding and rolling, from the aspect
of their advantages and disadvantages, we decided to de-
sign a new technological process for producing the
groove of a SD, based on the advantages of these two
technologies.
This new technological process involves a combina-
tion of the rolling technology as the initial operation, and
the grinding technology as the finishing operation. With
the groove thus produced, the SD retains all the advan-
tages of the rolling technology (good mechanical proper-
ties due to the continuous flow of material fibers, consid-
erable material savings and reduced main fabrication
time) and grinding technology (greatly improved geo-
Materiali in tehnologije / Materials and technology 55 (2021) 1, 77–81 77
UDK 620.1:620.162:621.95 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 55(1)77(2021)
*Corresponding author's e-mail:
obradspaic59@gmail.com, obrad.spaic@fpm.ues.rs.ba (Obrad Spai})

metric accuracy and quality of the machined surface and
reduced cutting resistance).
This paper analyzes the justification for the applica-
tion of the new technological process for the production
of SD grooves in relation to rolling and grinding as the
most commonly used technologies for producing SD
grooves so far.
2 TECHNOLOGIES FOR PRODUCING
SD GROOVES
SD-producing technologies are named after the
method of making grooves: forging, milling, grinding
and extrusion.
1,6–11
2.1 Grinding technology
The first steps in the production of the spiral groove
on a drill bit by grinding were made in 1931 on drill bits
with small diameters (up to Ø3.0 mm), but the technol-
ogy began to be applied in the regular production of tools
only in the late 1950s.
The development of deep grinding (full grinding or
single grinding) made it possible to produce spiral
grooves on larger drill bits, see Figure 1.
The main advantages of producing the spiral groove
on a drill bit with the grinding technology are signifi-
cantly improved surface quality and accuracy of shapes
and dimensions.
2.2 Rolling technology
The rolling process of SD manufacturing, illustrated
in Figure 2, was introduced into industrial production in
the 1960s and had a lot of advantages in the serial and
mass production. The productivity of the SD production
by rolling increased by 15–20 times in comparison to the
milling technology, while the material saving went up to
30 %. Namely, with this technology, there is no loss of
material in the formation of grooves because it is trans-
formed into the drill bit during the rolling process.
The advantages of producing the spiral groove of a
drill bit with the rolling technology are increased mate-
rial savings, good mechanical properties of the drill due
to the continuous flow of fibers of the material and the
deviation of the groove-profile dimensions.
3 ANALYSIS OF THE SD-GROOVE
PRODUCTION WITH THE GRINDING AND
ROLLING TECHNOLOGIES
An economic analysis of the production of SD
grooves with the rolling and grinding technologies was
carried out, considering two aspects:
• saving the basic material and
• grinding-wheel savings.
The analysis was carried out on DIN 338 drill bits
with nominal diameters of (Ø12, Ø15 and Ø20) mm,
made of high-speed steel (EN standard HS 6-5-2, DIN
S 6-5-2, W. Nr. 1.3343), which is most commonly used
for the production of SDs. A higher carbon content af-
fects the formation of carbides.
12
In accordance with the SD producer’s technological
charts, the dimensions and weights of the raw parts for
the SD nominal diameters of Ø12, Ø15 and Ø20 mm,
used for rolling and grinding are shown in Table 1.
Table 1: Dimensions and weights of raw parts for SD rolling and
grinding
Nominal diameter of the SD (mm) Ø12 Ø15 Ø20
Total length of the SD (mm) 151 169 205
Length of the handle (mm) 49 54 64
Dimensions of the
raw part
Nominal di-
ameter (mm)
12.3 15.3 20.3
Length (mm)
Rolling 104 114 143
Grinding 151 169 205
Weight of the raw
part (g/piece)
Rolling 100.84 171.03 377.67
Grinding 146.41 253.54 541.41
Difference in
weight
(g) 45.57 82.51 163.74
(%) 31.12 32.54 30.24
From the data presented in Table 1, it can be con-
cluded that the material savings in the production of SD
grooves by rolling are significant, amounting to about
30 %. The conducted analysis confirms the economic
justification for designing a new technological process
for the production of SD grooves.
4 ANALYSIS OF THE NEW TECHNOLOGICAL
PROCEDURE OF PRODUCING SD GROOVES
With the new technological process, rolling is per-
formed as the pre-operation with a grinding additive, fol-
lowed by heat treatment and a grinding operation as the
finishing operation.
O. SPAI] et al.: APPLICATION VALIDITY OF THE TECHNOLOGICAL PROCEDURE FOR MAKING ...
78 Materiali in tehnologije / Materials and technology 55 (2021) 1, 77–81
Figure 2: Production of SD by rolling
Figure 1: Production of SD grooves by grinding

The rolling process allows us to achieve good me-
chanical properties due to the continuity of the fiber
flow, considerable material savings and reduced fabrica-
tion time, while the grinding process ensures that the SD
exhibits, in addition to the aforementioned characteris-
tics, features such as significantly improved dimensional
accuracy and surface quality.
It is important to note that the combination of techno-
logical processes caused, in addition to the material sav-
ings and due to a small grinding additive, significant sav-
ings in the consumption of the grinding wheel, compared
to the grinding technology.
The economic analysis of the new technological pro-
cess for producing SD grooves was also carried out on
SD DIN 338 with nominal diameters of Ø12, Ø15 and
Ø20 mm, made of the HS 6-5-2 high-speed steel, with
respect to material and grinding-wheel savings.
4.1 Economic analysis of the new technological pro-
cess for producing SD grooves with respect to mate-
rial savings
SDs are produced with the new technology from a
raw part with the same nominal diameter as with the pre-
viously analyzed technologies, Table 1.
However, since the new technological process of pro-
ducing SD grooves includes a rolling operation with a
grinding additive (A
2
), Figure 3, a smaller volume of the
material is extruded from the spiral grooves into the
body of the SD.
As the length of the formed spiral part of the ex-
truded material is smaller, the length of the raw part must
be longer than the length of the groove raw part of the
SD made by rolling by length x.InFigure 3, the groove
surface in the cross-section of the SD after the rolling
operation is denoted by A
1
and after the grinding opera-
tion by A
1
+ A
2
. The difference between the length of the
raw part used for the new method of producing SD
grooves and the length of the groove raw part of the SD
made by rolling, that is, the length of the SD body made
from the volume of the grinding additive can be obtained
from the equality of the volume of the grinding extension
and the volume of the SD body formed with the grinding
additive:
V
ga
= V
ba
(1),
where
V
ga
– the volume of the grinding additive and
V
ba
– the volume of the SD body made with the grinding
additive.
Acknowledging that:
V
ga
= A
2
· l
s
and V
ba
= A
t
· x (2),
where
A
2
– the surface of the cross-section of the grinding ad-
ditive,
l
s
– the length of the raw part where groove rolling is
performed,
A
t
= A – A
1
– the surface of the cross-section of the SD
body,
A – the surface of the cross-section of the raw part and
A
1
– the surface of the cross-section of 2 grooves with
the grinding additive,
x – the length of the SD body made with the grinding
additive.
Thus, we obtain:
x
V
A
Al
AA
==
⋅
−
ga
t
s 2
1
(3)
The cross-sectional surface of the grinding additive
A
2
and the cross-sectional surface of the grooves for roll-
ing A
1
were determined with respect to the nominal di-
ameter of the SD, the core diameter and the angle of rise
of the spiral, provided that the groove: key ratio is 1:1.
For the grinding procedure, the diameter and core thick-
ness were set according to the SD producer’s technology
charts, and the rolling operation was expected to provide
a grinding additive of 0.5 mm for SD Ø12, 0.55 mm for
SD Ø15 and 0.75 mm for SD Ø20 mm. For both opera-
tions, an angle of rise of 27
+/–2
of the grooves was
adopted. According to A. K. Dell et al.
13
and L. F. Xavier
et al.
14
, the best geometry of a SD depends on the prop-
erty of the drilling material, and for the drilling of steel
and cast iron, they propose an angle of rise of 24–32°.
O. SPAI] et al.: APPLICATION VALIDITY OF THE TECHNOLOGICAL PROCEDURE FOR MAKING ...
Materiali in tehnologije / Materials and technology 55 (2021) 1, 77–81 79
Figure 3: Cross-section surfaces of the SD
Table 2: Dimensions of the SD groove according to the new technological procedure
Nominal diameter
of SD
Rolling operation Grinding operation
Core diameter Core thickening
Angle of rise of
spiral
Core diameter Core thickening
Angle of rise of
spiral
Ø12 3.0 0.96–1.20
27
+/–2
°
2.0 0.96–1.20
27
+/–2
° Ø15 3.4 1.20–1.50 2.38 1.20–1.50
Ø20 4.0 1.40–1.75 3.0 1.40–1.75

The data for the SD nominal diameters of (Ø12, Ø15 and
Ø20) mm are shown in Table 2.
Based on the dimensions of the SD groove, Table 2,
provided that the groove and the key width were in a ra-
tio of 1:1, and after the sharpening operation at a top an-
gle of 118°, the cutting edge was a straight line, generat-
ing a geometric model of a SD in the AutoCAD
application program. The surface of the grinding additive
A
2
and the SD groove surface were measured in the SD
cross-section for rolling and grinding. The obtained val-
ues are shown in Table 3.
Table 3: Dimensions of the SD groove for rolling and grinding
Nominal
diameter
D (mm)
Rolling oper-
ation
Grinding operation
Groove sur-
face
A1
(mm
2
)
Groove sur-
face
A1
+A
2
(mm
2
)
Surface of grinding
additive
A
2
(mm
2
)
Ø12 45.26 55.94 10.68
Ø15 73.24 88.05 14.81
Ø20 130.72 157.78 27.06
The difference in the length of the raw part of the SD
grooves made with the new technological process with
respect to the rolling technology is the length of the SD
body made from the grinding additive x for the SDs with
the nominal diameters of (Ø12, Ø15 and Ø20) mm, as
shown in Table 4.
Table 4: Calculation of the difference in the length of the raw part
Nominal diameter of SD Ø12 Ø15 Ø20
Length of the raw part at which
the grooves are rolled l
s
(mm)
55 60 79
Cross-sectional surface of the
grinding additive A
2
(mm
2
)
10.68 14.81 27.06
Cross-section of the raw part A
(mm
2
)
113.04 176.63 314.00
Cross-sectional surface of 2
grooves A
1
(mm
2
)
45.26 73.24 130.72
Difference in the raw-part length
x (mm)
8.67 8.60 11.66
The difference in the length of the raw part used for
making SD grooves with the new technological proce-
dure compared to the SD grooves made with the rolling
process and the length of the raw part for making SD
grooves with the rolling process represents the length of
the raw part for making SD grooves with the new tech-
nological process. Calculated in that way, the dimensions
of the raw parts for the production of SDs with nominal
diameters of (Ø12, Ø15 and Ø20) mm are shown in Ta-
ble 5.
Table 5: Dimensions of the raw part and savings of the material for
the production of SDs with the new technological process
Nominal di-
ameter of
SD
Length of the raw part (mm)
Material
savings
New tech-
nological
process
Grinding
process
(kg) (8 %)
Ø12 113 151 35.43 25
Ø15 123 169 66.36 27
Ø20 155 205 126.97 24
4.2 Economic analysis of the new technological pro-
cess of producing SD grooves with respect to grind-
ing-wheel savings
By making SD grooves with the new technological
process, in comparison to making SD grooves with the
grinding technology, in addition to material savings, a
saving in the grinding wheel is achieved, which is pro-
portional to the amount of the material removed during
the grinding operation. Figure 3 shows the cross-sec-
tional surfaces of the SD grooves made with the grinding
technology (A
1
+A
2
) as well as the cross-sectional sur-
face of the grinding additive, removed after the rolling
within the new technological process for making SD
grooves.
A comparative analysis of the volume of the material
removed during the formation of grooves with the SD
grinding technology and the new technological proce-
dure is given in Table 6.
5 CONCLUSION
The new SD-groove production technology is a com-
bination of two processes: rolling and grinding. The roll-
ing process is performed with a grinding additive. This
additive is removed during the grinding process. SDs
with grooves produced with this method retain all the ad-
vantages of the grooves produced by rolling and the
O. SPAI] et al.: APPLICATION VALIDITY OF THE TECHNOLOGICAL PROCEDURE FOR MAKING ...
80 Materiali in tehnologije / Materials and technology 55 (2021) 1, 77–81
Table 6: Comparative analysis of the volume of the material taken off when making grooves with the SD grinding technology and the new techno-
logical process
Nominal
diameter
Grinding operation New operation
Difference in
the volume
of the cutting
material
l
1·A1 (mm
3
)
Relative
savings
(%)
Surface of
the groove
A
1
+A
2
(mm
2
)
Length of
the spiral
l
1
(mm)
Volume of
the cutting
material
l
1·(A1+A2)
(mm
3
)
Surface of
the grinding
additive
A
2
(mm
2
)
Length of
the spiral
l
1
(mm)
Volume of
the cutting
material
l
1
·A
2
(mm
3
)
Ø12 55.94 102 5705.88 10.68 102 1089.36 4616.52 80.91
Ø15 88.05 115 10127.75 14.81 115 1703.15 8424.60 83.18
Ø20 157.78 141 22246.98 27.06 141 3815.46 18431.52 82.85

grooves produced by grinding while, at the same time,
eliminating their disadvantages.
In addition, the conducted economic analysis showed
that this technological process allows us to achieve mate-
rial savings of 24–27 % and grinding-wheel savings of
82–83 %.
Acknowledgment
This paper is the result of a scientific research project
"Making of grooves of spiral drills using a combination
of rolling and grinding processes", funded by the Minis-
try of Science and Technology Development, Higher Ed-
ucation and Information Society of the Republic of
Srpska.
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Materiali in tehnologije / Materials and technology 55 (2021) 1, 77–81 81