IRJET- Project Didactic of a Mini CNC Milling Machine

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 05 Issue: 11 | Nov 2018 www.irjet.net p-ISSN: 2395-0072
© 2018, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 323
Project Didactic of a Mini CNC Milling Machine
José L. Hernández C.1, Mariela Hernández V.2, Juan Alberto Villegas G.3, Ericka Sánchez V.4,
Omar Ezael Ramírez V.5, Jesús Salvador Montiel S.6
1,2,3,4,5,6 Industrial Maintenance Engineering, Technological Tlaxcala University, El Carmen Xalpatlahuaya,
Huamantla, Tlaxcala 90500, Mexico.
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Abstract - The present investigation shows the results of
the construction of a prototype CNC milling machine
(Control Numeric Computer). The milling cutter is
controlled by a CNC Shield card and an Arduino card. The
axes work with stepper motors. The CNC is designed to work
with wood, copper and iron plates; it has the option to work
with plotter. Copper tracks can be recorded for electronic
circuits.
The results show the correct operation at different
programmed speeds. The programming of the milling
machine is simple, it allows its application in small
workshops, and this research has a great opportunity of
application at a higher level so that students develop their
design skills and can improve it.
Currently there are different types of milling machines that
cover up to six axes of work with a design that constantly
improves day by day, the advantages of this type of
machinery make the machining centers be present in
virtually all manufacturing processes, from the most
advanced even the most modern to more traditional sectors.
The control of the CNC milling machine is carried out
through the universal G-code intermediary to establish
communication with the Arduino card and the CNC
protection card that will be responsible for sending the
instructions that the motors must accomplish. For its
implementation, machining tests were performed, which
showed a statistically satisfactory performance.
Key Words: Stepper motors, Universal-G-Code-Sender
program, CNC Shield card, Arduino card, Manufacturing,
1. INTRODUCTION
The C language performs the drilling operation using
computerized machines (CNC), which have a great
capacity of automatic reception of the given instructions,
by means of software, to manufacture work pieces or
moulds by means of complex movements given. It is very
important to know the meaning of milling, which is an
indispensable tool or tool machine for the realization of
machining by removing chips from a piece by the
movement of a rotating tool of different cutting edges
called milling. [1]
The investigations carried out on the implementation of
the CNC in motion machines have established in general
terms the main tools and commands necessary for the
optimal operation of any CNC machine prototype. For the
benefit of the student community, the prototype of a great
contribution was implemented for the students of the
industrial maintenance career, who begin to know the way
of working of the control languages. [3].
Among the tools we can find: linear cutters, rotation
cutters, work pieces and other components. The
components of the structure of the tool are described by
the Cartesian coordinates system specified by the original
point (established point of origin) and three other points
selected from the three axes perpendicular to each other.
[4] These three points are different from the origin of the
machine's coordinate system. On the other hand, the
commands used by a CNC system are usually G codes,
which contain incremental or absolute positioning data for
each axis. [2], [6].
Manipulating this type of machinery is very easy because,
knowing the programming language, it allows to design
models in two dimensions, like electrical circuits that can
be used in different types of future projects, since it will
facilitate the recording of the necessary tracks and get the
plates. [7] [10]
Since its development in 1980, additive manufacturing has
become a powerful facet of manufacturing. [8] that is
defined by the American Society for Testing and Materials
(ASTM) as "the process of grouping material to create
objects from 3D data models". The evolution of the
concept in the first decade of the 21st century has made
available a large number of processes and materials in the
manufacturing industry. [3]
1.1 Computer numerical control
The first numerical remote-control machines were built
in the 40s and 50s by engineer John T. Parsons. These
initial servomechanisms developed rapidly with analog
and digital equipment. The cheapening and miniaturization
of the processors has generalized the digital electronics in
all the types of tools, which gave rise to the denomination
of numerical control by computer or numerical computer
control (CNC), to differentiate them from the machines that
did not have a computer. The principle of common
operation of all applications of the numerical control is the
control of the relative position of a tool or processing
element with respect to the object to be processed. [7]. The
application of the numerical control covers a great variety
of processes; the applications are divided into two
categories: applications with machine tools and
applications without machine tools. [7]
The numerical control is a form of programmable
automation in which the processing equipment is
controlled by numbers, letters and other symbols. These
numbers, letters and symbols are coded in an appropriate

format to define a program of instructions to develop a
specific task. When the task in question changes, the
instructional program changes. [7].
This system has revolutionized the industry due to the
cheapening of the microprocessors and the simplification
of the programming of the CNC machines. The numerical
control by computer (or more commonly known as CNC) is
a system that allows to control at all times the position of a
physical element. Normally a tool, which is mounted on a
machine.
This is achieved through a program and a set of
aggregate orders. With both, it can control the position
coordinates of a point (the tool that works with the
product) with respect to an origin (the position of the
machine).
The ability to change the program makes the numerical
control appropriate for low or medium production
volumes, since it is easier to write new programs than to
make changes in the processing equipment.
The research helped the elaboration of the project,
which provides knowledge for the students of the
Technological University of Tlaxcala, who could design and
elaborate printed circuit boards.
2. Universal G-code Sender communication with
prototype
Once the G-Code files have been created, a program is
needed to analyze them and issue the commands to the
Shield CNC card. A good open source that works well with
Shield CNC (and all GRLB hardware) is Universal G-Code-
Sender.
It must vectorize the images or designs intended to
make and post-process them to the G code, which is what
the machine reads. The theory of stepper motors is simple,
when the processing card sends a pulse to the motor
controller, it advances one step. This technique is very
popular in robotic machines because it lets us know how
many pulses, it has sent and how much the machine will
advance.
What you need is to move from a pulsed language to
something simpler to explain, such as the coordinates of
the motors.
The standard way to communicate with a machine of
this type is through the use of the G-Code language. Which
is a simple text system with the movements of the machine
and what it gets with the G-Code language. It is a text file
with all the movements of the machine.
The Inkscape program allows to determine the path by
stroke of the selected figures and by means of the complete
G-Code platform that is used to interact with advanced CNC
controllers such as GRBL.
Universal G-Code-Sender is a standalone Java
application that includes all external dependencies, which
means that, if you have the Java Runtime Environment
configuration, UGS provides the rest and we will manage
the process in the team.
Figure 1 shows a block the communication process
between the PC software and the G-Code-Sender which
interacts with the prototype mentioned in this article.
Fig -1: Process Flow Diagram
3. Prototype structure and drawing in
SolidWorks.
3.1. How the CNC is assembled
The project consists of three axes manufactured in a
wooden base of plywood of thickness 18 mm, with stepper
motors NEMA17, for each axis has a screw of endless
double entry, two steely axes that give support of 8 mm,
four linear bearings, a bed placed on the Y axis where the
process will take place, fasteners, a tower that supports the
x axis, has a support box in the mill that moves the z axis to
raise and descend.
Each of the axes and the bed are correctly calibrated so
that they can move easily without generating friction, thus
preventing overheating of the motors and avoiding driver
faults.
To begin the construction of the prototype, the
measurements were defined based on the realization of the
drawing in SolidWorks first, these measurements are
shown in the following table.
FlatCAM
Universal
G-Code-
Sender
Arduino
Card and
Shield CNC
Card.
Sprint Layout

Table -1: Measures for mechanical construction
Measures of the axes
No. of
pieces
Length Width Thicknes
s
X
axis
2 nylamid
plates
300 mm 70 mm 18 mm
Shaft
support
200mm 100 mm 18 mm
Y
axis
4 wood
plates
300 mm 70 mm 18 mm
1 milling
bed
200 mm 200 mm 18 mm
Z
axis
2 wood
plates
100 mm
100 mm 18mm
Bottom
base
100 mm
75 mm 18 mm
3.2. Construction of the X axis
In the base that will support the X axis, two steel shafts
are installed and the screw with four linear bearings of 8
mm. The linear bearings will be located 40mm from the
center with a separation of one side of 18mm and the other
of 24mm.
The stepper motor is installed and fixed in the columns,
the couplings and the bearing are located on the support
opposite side, observing that it is correctly adjusted and
leveled to avoid deviations in the milling.
The structure is fixed together with the base of the X
axis. The control interface is preloaded in a data acquisition
card of the Arduino family, specifically the UNO model, in
which the GRBL program is loaded, with the shield and the
driver for handling the engines. The Universal G-Code-
Sender program will be the one we will use for
programming.
This system is shown completely assembled in Figure 2.
Fig -2: X axis
3.3. Construction of the Y axis
In this axis, two holes are made through which the two
pitch shafts of 8 mm diameter are drilled and in the central
part to place the motor step by step, the motor will move
the Y axis. The holes are 3 mm diameter and the hole of the
arrow of the motor has a diameter of 22 mm, these
dimensions allow the movement of the flexible coupling, at
the other end there is a bearing that serves as a guide.
The adjustment of the motor plays a very important
role, due to the types of displacements that it makes for the
cuts. The bearing must be correctly adjusted, since it will
support the screw of the Y-axis, we must observe that the
screw must turn without problems, as well as the nut of the
bushing that moves the bed.
The wooden bed is square with measures of 101 mm
per side, the axes are 90 mm from the center to a height of
62 mm. The bed will be placed on 8 mm steel shafts, since
each one has two linear bearings, which will help us to give
support, stability and easy sliding to carry out the
development of the program we want to send.
This system is shown completely assembled in Figure 3.
Fig -3: Y axis
3.4. Construction of the Z axis
The Z axis consists of a top and a bottom lid, the base
that will support the milling tool. In the upper section, the
lid is drilled in the center of 10cm, we make hole holders
for the motor where the 8 mm axes go, the length of each
axis is 20cm.
The tool holder is thickness of 15 mm and width of 100
mm. The lower base is thickness of 18 mm, width of 100
mm and depth of 75 mm. The tool holder must be correctly
centered.
The linear bearings are the ones that support the two 8
mm axes and all these fits into the base that supports the
milling tool. In the upper base the flexible coupling and the
stepper motor are placed. In the lower base the bearing is
placed. This system is shown completely assembled in
figure 4.
Y axis
X axis

Fig -4: Z axis
4. Prototype control
The control is done with the Arduino UNO card and the
Shield CNC, the latter has the A4988 drivers, to increase the
current and voltage of the stepper motors.
The designs of the circuits are carried out in programs
such as Sprint Layout 6 or Easy EDA in which we can
design the tracks for the circuits that are intended to be
made, the difference is that the latter is worked for free, but
with internet to save circuits. Once the G-Code files have
been created, a program is needed to analyze them and
issue the commands to the Shield CNC card. This system is
shown completely assembled in figure 5.
Fig -5: Location of the control card
4.1. Setting the A4988 drivers
The voltage of each complete bridge is given by a
current control circuit, pulse width modulation (also
known as PWM, pulse-width modulation) of fixed
disconnection time that limits the load current to a value
wanted. Initially, outputs with field effect transistors or
FET (Field Electric Transistor) from the source and current
are activated diagonally and current flows through the
motor winding and the current sensing resistor RSx.
When the voltage across RSx is equal to the digital
output voltage to analogue converter (DAC), the current
sense comparator resets the PWM latch. Then, the latch
deactivates the appropriate origin controller and initiates a
fixed time reduction mode. [5]. The data with which they
are recommended work this type of controllers is shown in
table 2.
Table -2: Characteristics of the A4988 driver
Characteristics of the A4988 driver
Minimum voltage
3 V
Maximum voltage
5.5 V
Maximum current per
phase
2 A
Continuous current per
phase
1 A
Minimum voltage
operation
5 V
Maximum voltage
operation
35 V
The maximum value of the current limitation is
established by the selection of RSx and the voltage on the
Reference Voltage (Vref) pin. [5]
The transconductance function is approximated by the
maximum value of the current limitation, ITripMAX (A),
which is established by:
The values of the SMD resistors and the drivers is 0.2
Ohm (R200). Applying the formula of the datasheet of the
drivers A4899
Imax = Vref / (8xRs) (1)
Vref = 1.5 x (8x0.2) = 2.4 V (2)
Vref = 2.4 V (3)
To this data it is necessary to apply the 70% that gives
1.68V.
The problem is with the voltage values that are
measured when the potentiometer of the controllers is
turned. The minimum that was achieved is 4.2 V and the
maximum is 7 V.
5. Results.
The physical structure was improved to have better
accuracy in the engraving and thus make the circuits more
accurate.
Z axis

We show the development of a circuit that gives the
pulses of a led with an integrated circuit 555. We will
develop step by step the explanation of the load and the
program, how the tracks were designed and they became a
C language for the engines to carry out the process
The software for the realization of printed circuit
boards (PCB) is easy, fast and useful. The logical and
understandable structure of Sprint-Layout is very easy to
learn. The logical and understandable structure of Sprint-
Layout is very easy to learn.
Tracing of tracks is achieved by verifying their
dimensions. In the same edition of the tracks the elements
of the circuit were placed to obtain the precise
measurements.
Fig -6: Sprint-Layout program circuit.
At the end of the design, the tracks are vectorized in the
FlatCAM program that allows you to take your designs to a
CNC router. It is open source, written in Python and runs
smoothly on most platforms. In this program we will
generate the cutting path that the prototype will carry out.
Fig -7: Circuit in the FlatCAM program
Later, the files will be sent to the Universal G-Code-
Sender to load them, these files will be divided into three
parts, the first will be the tracks for the components, the
second will mark the positions of the holes to be made and
finally a frame will be made that will cut the plate section.
Fig -8: Displaying tracks in G-Code-Sender
Fig -9: G- Viewing perforations in G-Code-Sender
The code is loaded into the machine, which executes all
previously performed routes. The figure represents the
displacement on the X axis, the figure on the Y axis and the
figure on the Z axis. Therefore, the working plane is three-
dimensional.
Fig -10: Process in the prototype

Fig -11: Electronic circuit terminated
6. CONCLUSIONS
The present project of the CNC contains many advantages,
especially the control system, that is what makes it more
important. With regard to the time it takes to generate a
model, the process of cutting by a CNC is much shorter
than doing it by hand, besides not requiring labor, only
one operator for the machine.
The control system has a very efficient communication
with the computer software that sends the code. The
mechanical system has a functionality for the movements
in the programmed cutting axis. The mechanical control
system and the software work together, resulting in a
prototype useful for slabs in soft materials and high
precision.
The control system also comprises the power stage for the
motors. In the same way the system includes the Software
that contains the G code and will send it to the
microcontroller of the control system.
In the elaboration of this project we understood how to
calibrate each one of the bases of each axis, since this
influences the elaboration of the tracks. We understood
how to make the interface of the machine with the
software, manipulate this system is not of such complexity.
The set of these systems results in the roughing of
materials such as acrylic and wood. It allows us to record
the tracks of the circuits previously made in the program.
It is proposed as a posterior investigation the adaptation
of a plastic injection system that allows the realization of
3D figures.
REFERENCES
[1] Alonso, D., Gil, J. y Martínez, F. (2015). Prototipo de
máquina fresadora CNC para circuitos impresos.
Revista Tekhnê,12(1), 23-38
[2] Antonín Max et al. “Enhancement of teaching design of
CNC milling machines”, 2015
[3] Alonso Rodriguez, Jose Antonio. Sistemas de prototipo
rápido, Universidad Politecnica de Valencia. 2002
[4] Benhabib, Beno. Manufacturing: Design, Production,
Automation, and Integration New York: Marcel
Dekker, 2003
[5] C. Guillen, A. Duque, D. Buelvas, K. Grau & C. Ochoa,
“Revisión de sistemas de fresado CNC para la
elaboración de placas de circuitos impresos PCB”,
Investigación y Desarrollo en TIC, vol. 7, no. 2, pp. 61-
66, 2016.
[6] DMOS Microstepping Driver with Translator And
Overcurrent Protection “Driver A4988”, Allegro Micro
Systems.
[7] Groover, M. P. (2007). Fundamentos de manufactura
moderna. México: McGRAW HILL/INTERAMERICANA
EDITORES.
[8] INC, A. E. M. (2008). Sm series stepper motors
[Manual de software informático].
[9] J. J, Montes & M. Martín. “Control manual para CNC”.
Bachelor’s thesis, Universidad de Valladolid, España,
2013.
[10] M. Riquelme. “Diseño y fabricación de una fresadora
CNC de 3 ejes para el mecanizado de PCB con
plataformas de desarrollo abiertas”. Bachelor’s thesis,
Universidad Politécnica de Cartagena, Colombia, 2014.
[11] M. Cifuentes & J. S. Jaramillo. “Diseño de un sistema de
manufactura automático para circuitos impresos”.
Bachelor’s thesis. Facultad de Ingeniería y Tecnología.
Universidad Tecnológica de Pereira, Colombia, 2015.
[12] Salas, R., Pérez, J., y Ramírez, J. (2007). Técnicas de
diseño, desarrollo y montaje de circuitos impresos.
Universidad de los Andes. Venezuela.
BIOGRAPHIES
José Luis H. Corona Candidate for a
PhD from the Autonomous University
of Tlaxcala, Research Professor in the
area of Industrial Maintenance,
Desirable Profile before the PROMEP,
responsible for the CA of Industrial
Maintenance at the Technological
University of Tlaxcala.
Mariela Hernandez Vásquez
“Student of Industrial maintenance
engineering. T.S.U. In industrial
maintenance by the Technological
University of Tlaxcala. “
Juan Alberto Villegas Gomez
Ericka Sanchez Vazquez “Student of
Industrial maintenance engineering.
T.S.U. In industrial maintenance by
the Technological University of
Tlaxcala. “

Omar Ezael Ramírez Vera “Student
of Industrial maintenance
Jesús Salvador Montiel Soto
University of Tlaxcala. “ “

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