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Mechanical Engineering
Design of a Small-Scale FDM 3D Printer
A Final Report
Submitted byRobert Embury
May 9, 2017
Submitted toDr. Richard Mindek
Dr. Said Dini
WESTERN NEW ENGLAND UNIVERSITY1215 Wilbraham Road
Springfield, Massachusetts
Mechanical Engineering
ME 440 Senior Design Projects
May 9, 2017
Design of a Small-Scale FDM 3D Printer
A Final Report
Submitted By
Robert Embury
Submitted to
Dr. Richard MindekDr. Said Dini
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ABSTRACT
The object of this project was to design and build a small-scale FDM 3D printer for use
in educational demonstrations by the College of Engineering at Western New England
University. The goal of the project was to create a printer which would be small enough to be
carried easily by a single person into a classroom. To achieve this, the printer design was
restricted to fit inside of a 12” cube and to weigh less than 15lbs. In addition, the frame needed to
be robust enough to maintain a dimensional accuracy of 0.005” on any parts created, without the
need for recalibration after being moved.
Using SolidWorks’ Finite Element Analysis, backed by hand calculations, a design was
created for a 3D printer, which fit the above criteria. Issues in the design were addressed as
needed during the building phase of the project and final empirical observations allowed for fine
tuning of the machine. The results of this process yielded a printer which fits inside of a 12”
cube, weighs 10.9lbs, holds a horizontal dimensional accuracy of ± 0.002” and a vertical
accuracy of 0.0031” and does not require recalibration after being moved.
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TABLE OF CONTENTS
Abstract………………………………………………………………………………….……….3
Table of Contents…………………………………………………………………………….….4
Introduction…………………………………………………………………………….…….….5
Constraints…………………………………………………………………………….……..….6
Printer Design and Theory of Operation……………………………………………….…..….6
Theory and Analytical Effort………………………………...……………………………..….15
Experimental Procedure…………………………………..………………………….……..
….29
Results and Discussion……………………...…………………………………………...…..….41
Conclusion………………………………………………………………………...……..…..….44
Recommendations for Future Work………………………………………...……………..….45
Bibliography…………………………………………………………………..……………..….46
Appendix A – Marlin Firmware Configuration……………………………………..………..47
Appendix B – Simplify 3D Settings………………………………………………….…..…….54
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INTRODUCTION
The College of Engineering (CoE) at Western New England University does not
currently have a small-scale 3D printer which can be brought into the classroom for
demonstration purposes. While the CoE owns several benchtop models, they are too large and
heavy to be easily moved by a single person. In addition, these printers were not designed to be
moved around without being recalibrated. 3D printing and additive manufacturing are becoming
more and more prevalent in industry with an increasing number of companies looking for 3D
printing experience on résumés. According to Wanted Analytics [1], a global analytics firm, there
was an 1,834% increase from 2011 to 2015 in engineering job postings in which 3D printing
experience was required. Furthermore, Wanted Analytics also found that “35% of all ads posted
online for engineering jobs” in September of 2015 “prioritized 3D printing and additive
manufacturing as the most sought-after skill.” [1] By designing and building a small-scale printer,
Western New England University can increase exposure for its students to 3D printing
technology and give them a competitive advantage over students at other schools.
With tech giants such as Boeing, Pratt and Whitney, Google and others all pouring
money into 3D printing research, it is becoming increasingly important for students to have a
working understanding of the technology. In 2015, Pratt and Whitney invested $9 million in its
new Additive Manufacturing Innovation Center. [2] Research is currently being done on both
metal powder 3D printing as well as continuous strand nylon reinforced printing. Direct Metal
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Laser Sintering, DMLS, uses lasers to essentially weld powered metals together one layer at a
time. While the DMLS process is different from standard FDM printing, a background in 3D
printing technology would prove to be a significant advantage when learning DMLS. Likewise,
the research in continuous strand nylon reinforced printing has shown some very promising
results. This type of printing is nearly identical to standard FDM printing with the only change
being a continuous strand of nylon, Kevlar, or carbon fiber, which is placed into the center of the
flow of melted plastic leaving the nozzle of the print head. One Cambridge, MA based company
has found that parts created using this technology have exceeded the strength to weight ratio of
6061 aluminum. [3]
CONSTRAINTS
There were four major constraints which guided the design of this project. The printer’s
overall size could not exceed 12” x 12” x 12”. The printer could not weigh more than 15lbs. The
printer must be able to hold a dimensional accuracy of 0.005” on any parts it creates, and the
printer will not require any recalibration after being moved.
PRINTER DESIGN AND THEORY OF OPERATION
Fused Deposition Modeling 3D printing, FDM, is a small subset of additive manufacturing in
which thermoplastic filaments are extruded into layers which are then built upon each other to
create solid 3D models. By stacking these layers on top of one another hundreds or thousands of
times, very intricate and complex models can begin to take shape. Each of these layers starts out
as an outline, known as the perimeter. The user can select the number of passes the nozzle must
make along the perimeter before starting the infill. A typical number used is 2 perimeters. This
means that an FDM 3D printed part has a thin wall which is two times the thickness of the
extruded bead of plastic leaving the nozzle. After the perimeters are completed, the printer
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begins laying down the infill; a semi-solid scaffold like structure which allows 3D printed parts
to be strong yet light. While there are dozens of types of infill, the two most common are linear
grids and honeycomb. An example the entire FDM 3D printing process can be seen below in
Figure 1.
The 3D printing process begins with a 3D solid model. This model is imported into software
known as the “slicer” which takes the solid model and converts it into a series of triangles. Each
triangle represents a point of travel for the print head to reach during a print. The slicer also
controls key settings for the printer such as print speeds, layer resolution and extrusion
temperature. The slicer then saves these movements and printer parameters into a *.gcode file
which can be fed into the printer’s microcontroller where it is then processed and converted to
electrical signals to control the stepper motors of the printer.
Several of the key components of an FDM 3D printer can be seen in Figure 2 which shows
the basic design of the FDM printer used for this project. FDM printing offers several advantages
over traditional subtractive manufacturing like machining. The cost of using 3D printing in
industry for prototyping is significantly less than traditional manufacturing techniques. It also
allows for complex shapes to be created with relative ease, some of which would be impossible
to create using traditional manufacturing techniques.
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Figure 1 - Fused Deposition Modeling Example [4]
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Figure 2 - Key 3D Printer Components
To achieve motion on all 3 axes, the printer’s bed moves front to back while the
significantly lighter print head moves left to right and up and down. Reducing the motion of the
heavier bed to a single axis allows the printer’s frame to be less bulky and resistant to deflection,
thus making the design less complex and more lightweight. Printers with beds that do not move
along the vertical axis are known as Cartesian Style printers. Figures 3, 4 and 5 below
demonstrate how each axis of motion is achieved using this design.
Motion Limit Switch (End Stop)
Nema 17 Stepper Motor
Inductive Proximity Sensor
Print Bed
Print Head
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Figure 3 - X Axis (Left/Right Movement of Print Head)
Figure 4 - Y Axis (Front/Back Movement of Print Bed)
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Figure 5 - Z Axis (Vertical Movement of X Axis Assembly)
Stepper motors are used to drive motion along each of the three axes. They can move in
discrete steps by energizing their internal coils in sequence. Because of this, stepper motors offer
the positional accuracy and holding toque required to produce accurate 3D prints. These motors
come in two distinct types, unipolar and bipolar. For this design, two phase bipolar stepper
motors were used since they offer higher holding torque than their unipolar counterparts, since
unipolar stepper motors can only energize half of the available coils at a time. Stepper motors
come in several standardized sizes. The motors used in this project are Nema 17 stepper motors,
which offer a balance between size/weight and available torque.
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The type of component used to transmit power along the X and Y axes varied from the Z
axis. On the X and Y axes, GT2 6mm timing belts were chosen. Per the manufacturer’s
specification, these belts are able to hold their positioning within 0.0005”. [5][6] They are
extremely lightweight and can be used to transmit rapid motion. For the Z axis, a lead screw was
chosen. Since the Z-axis moves very little, the ability to accurately hold position and to move in
small increments were the key criteria. With this in mind, a single-start, 8mm lead screw was
chosen. One full rotation of the screw results in 8mm (0.31496”) of movement. Combined with
1.8̊ stepper motors and 1/16 microstepping motor drivers the theoretical minimum distance that
the lead screw can travel is 0.00157”.
A key feature of the printer’s design is the use of Open Builds V-Slot extruded rails and
Delrin wheels. By using the V-Slot rails, it was possible to combine the structural portion of the
frame’s design with the frame’s ability to accurately translate linear motion. The Open Build’s
V-Slot rail has a small channel cut into each face of the extrusion, which allows for a Delrin
wheel to roll smoothly along the channel. An example of this can be seen below in Figure 6. By
including an accurate way to translate linear motion into the extrusions, it eliminated the need for
use of secondary hardware such as linear rails or smooth rods, which would add unnecessary
weight to the printer.
Figure 6 - Open Builds V-Slot Extruded Rail and Delrin Wheel
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In order to accurately control the stepper motors, specialized stepper motor drivers are
required. The stepper motor drivers used in this project were Texas Instruments DRV8825,
which consist of two H-bridge drivers and a microstepping indexer. [7] The H-bridge drivers allow
for voltage to be applied in either direction across a circuit, which allows the stepper motors to
run both forwards and backwards. Two H bridges are needed in order to drive the two phases of
the bipolar stepper motors. The microstepping indexer allows for partial turns of the stepper
motor. In the case of 3D printing, a driver capable of 1/16 to 1/128 microsteps is typical. Each
driver can be configured to use a varying number of microsteps from a full step down to the
maximum supported microstep for that driver based upon different combinations of jumper pins
used in the microcontroller. The DRV8825 stepper drives support up to 1/32 microstepping and
thus 1/32 microstepping was used for the printer.
The microcontroller is the brain of the printer. It reads in *.gcode commands from a 3D
model and converts them to meaningful signals for the stepper drivers. It controls all aspects of
the printer such as position, velocity and extruder speed. They are also used to control the
temperature of the heated nozzle and/or a heated build plate. The most common controller
combination used in 3D printers is the Arduino MEGA 2560 and the RAMPS 1.4 shown in
Figure 7. The Arduino MEGA 2560 is a small, yet powerful, 8-bit controller with a 16 MHz
processor. Its processor is fast enough to control a Cartesian style printer using a single extruder.
In order to interface the stepper motor drivers, thermistors and other printer components a
RAMPS 1.4 backpack board is often used. The RepRap Arduino MEGA Pololu Shield Version
1.4 is an open source interface board, which is both inexpensive and very well documented. It
supports 5 total stepper motor drivers drawing up to 2.5A each, two heated nozzles (hot ends),
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and a headed bed, as well as several other auxiliary ports for additional equipment, such as
inductive probes used for uneven bed compensation (auto bed leveling).
Figure 7 - RAMPS 1.4 Wiring Diagram
The “hot end” used to melt and extrude plastic that was selected for this project was the
1.75mm E3D V6 Hot End. This hot end has the highest throughput rate of any readily available
hot end currently on the market at 10mm3/s. A higher throughput translates into faster printing
speeds and, in turn, shortened print times. It also has a large range of interchangeable nozzles
with varying orifice sizes ranging from 0.1mm up to 0.6mm. The orifice size chosen for this
design was 0.5mm, which comes standard with the E3D V6. E3D recommends that the vertical
layer resolution used in a model be limited by the size of the nozzle orifice. The minimum layer
height is recommended to be 20% of the nozzle orifice or 0.08mm while the maximum layer
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resolution is recommended to be 80% or 0.32mm. [8] Using the 0.5mm nozzle gives the printer a
theoretical vertical tolerance of 0.0032”.
While there are several different open source codes available to run the microcontroller,
the most developed is the Marlin firmware package. Marlin firmware is the result of a global
effort to produce an open source software package for the first in-home desktop 3D printers,
which started in 2011 under the RepRap project. The firmware is ultimately what is responsible
for making the printer work by controlling every aspect of the electronics. As part of the
firmware package, which is coded in the Arduino environment in C++, there are two
configuration files available for modification, Configuration.h and ADV_Configuration.h. These
two files store all the variables required to build a 3D printer from scratch, including minimum
and maximum movement speeds, PID feedback loops for consistent and even heating of both the
nozzle and bed of the printer, and print head travel limits. These files also include variables used
to enable automatic bed leveling when using an inductive proximity sensor.
Automatic bed leveling is an essential piece of this project. In order to eliminate the need
to recalibrate the printer after being carried into a classroom, an inductive probe is used in the
design. The inductive probe replaces the mechanical limit switch in the vertical axis. By placing
the probe close to the tip of the nozzle, it is possible to create a plane of best fit by probing the
bed in several locations. This information is fed into the firmware where it modifies the *.gcode
to account for any uneven areas of the print surface. It can also be used to correct the print if the
bed is not perfectly perpendicular to the print head. When enabled, automatic bed leveling will
constantly adjust the vertical height of the print head in order to compensate for any unevenness
in the print bed. The result is a much more dimensionally accurate part as well as significantly
better adhesion between the print bed and the first layer of the print.
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THEORY AND ANALYTICAL EFFORT
Throughout this project, numerous equations were used to determine many of the key
aspects of the printer such as the deflection of the X-Axis extrusion when treated as a simple
cantilever beam, the power requirements of the printer, and the torque requirements for the Z
axis stepper motor to raise and lower the print head.
In the design phase of the project several major design decisions needed to be made in
order to choose the best parts to complete the printer within the constraints of the project. The
first was to find the minimum required torque for the Z-axis stepper motor, which is used to raise
and lower the print head. The equation used to determine the required torque can be seen below
in Equation 1. To find the estimated load on the motor, SolidWorks’ Mass Property feature was
used which can be seen below in Figure 8. The mass of the entire X-Axis assembly was
estimated to be 754.17 grams. This weight was found assuming 100% solid 3D printed parts and
a solid steel block of equal dimensions for the stepper motor, resulting in a much higher than
actual estimate. Using a single-start, 8mm lead screw the minimum torque required to raise the
print head was 49.29 oz.-in. In order to ensure that the stepper motor had ample holding torque, a
Nema 17, 84 oz.-in. stepper motor was selected to move each axis of the printer.
T r=f∗dm
2(l−π∗f ¿dm
π ¿dm−F∗l)
Eq. 1
Where:
T r=Torque required ¿ raise load ,N−mm.
f=Frictioncoeffcient
dm=Pitchdiameter , mm
l=LeadF=Load , grams
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Figure 8 - X-Axis Total Weight Estimate
In order to maintain a 0.005” tolerance, the deflection of the X-Axis need to be
calculated. Due to the complex geometry of the Open Builds V-Slot Extruded Rail, a simplified
model was used for hand calculations to later be verified by SolidWorks Finite Element
Analysis. The area moment of inertia for the V-Slot rail was obtained from SolidWorks and was
determined to be 4.816 cm4. Using Equation 2 below, the dimensions of a square beam with the
same area moment of inertia was found which confirmed the SolidWorks value.
I=b∗h3
12
Eq. 2
Where:
I=Areamoment of inertia , cm4
b=Base , cm
h=Height , cm
To calculate the deflection of the print head, the X-Axis extrusion was treated as a simple
cantilever beam with one fixed end and a load on the other. The equation for the deflection of
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such a beam can be seen below in Equation 3. While the actual weight of the print head was
approximately 0.4 lbs, the mass used in the calculations was 10 lbs. in order to ensure that the
maximum deflection was within the design criteria and to account for added deflections during
axis acceleration. Using an area moment of inertia of 11.571 in4, 8.5 in. beam length and a
Young’s Modulus of 10,000 KSI for 6061 Aluminum, the maximum deflection was calculated to
be 0.00177”.
δmax=P∗l3
3∗E∗I
Eq. 3
Where:
δmax=Maximumdeflectionat end of beam,∈.
P=Load , lbf .
l=Length of beam,∈¿
E=Modulus of Elasticity , PSI
I=Areamoment of inertia ,¿4
Calibration of the printer also required calculations in order to determine the number of
microsteps that each axis needed to turn in order to move 1 millimeter. The equation to
determine this is a simple ratio, which can be seen below in Equation 4. This calibration needed
to be done for all 3 axes, as well as for the extruder.
Snew=Sold (lexla
)
Eq. 4
Where:
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Snew=New steps per mm
Sold=Old steps per mm.
lex=Lengthmoved expected
la=Length moved actual
In addition to the above equations, some basic power calculations were required to
determine the minimum power supply requirements for the printer. Equation 5 was used for each
of the electrical components of the printer. These values were summed together to get the
minimum required power for the design. Motor efficiencies were not considered for this
calculation.
P=I∗V
Eq. 5
Where:
P=Power ,Watts
I=Current , Amperes
V=Voltage ,Volts
The electrical components present in the design consisted of the following: a 40W
heating element for the print head, a 12V, 0.1A, 50mm radial blower fan for part cooling, a 12V,
0.08A, 30mm fan to cool the heat sink on the hot end, an Arduino MEGA 2560 microcontroller
running at 12V drawing 2A, a RAMPS 1.4 stepper motor driver at 12V drawing 10A, a RepRap
LCD screen, which runs at 5V drawing 0.1A peak and four 84 oz.-in. Nema 17 stepper motors,
which draw 2.0A at peak load and run off 2.8V. Using Equation 5 above, it was determined that
the minimum required power was 211.48W. With this in mind, a 12V, 300W power supply was
chosen for the project.
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Finite Element Analysis was also used to determine the deflection of the X-Axis V-Slot
aluminum extrusion as well as the maximum stress in some of the 3D printed parts used in the
design. During the analysis of the X-Axis aluminum extrusion a load of 10lbs. was applied to the
end of the extrusion to account of any acceleration the printer would undergo while in use. The
actual weight of the print carriage is approximately 0.4lbs. Figure 9 below demonstrates the
setup of the FEA model in SolidWorks.
Figure 9 - X-Axis Extrusion Displacement FEA Results
A convergence study was done on this setup to determine the optimal mesh size. A convergence
plot can be seen below in Figure 10 and a table of the mesh sized used can be seen in Table 1. A
mesh size of 0.4” with 25 elements around all circles and radii was found to be optimal for this
model.
Fully Fixed
10lbs Load
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Figure 10 - X-Axis Extrusion Convergence Plot
Table 1 - X- Extrusion Convergence Values
Mesh Size (in) Mesh Size (mm) Max Stress (psi) Max Deflection (in)0.4 10.16 1117 0.0019480.2 5.08 1245 0.0019490.1 2.54 1259 0.001952
0.05 1.27 1261 0.0019560.025 0.635 1255 0.001954
Load: 10lb
The maximum calculated deflection that the X-Axis extrusion was found to be 0.001948”. Using
Equation 3, the maximum deflection of the extrusion was found to be 0.00177”, leaving a %
error between the two values of 9.13%.
FEA was also used to determine the maximum stress in the X-Axis Extrusion. Using the
same setup as shown above in Figure 9, the maximum stress in the part was found to be 1261.43
PSI with the mesh size converging at 0.005” with 25 elements around all circles and radii. Figure
11 below shows these results. The yield stress of the 6061 aluminum used is 40,000 PSI, so
failure in yielding is not likely to occur. Fatigue failure was not analyzed.
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Figure 11 - X-Axis Extrusion Maximum Stress
Two of the 3D printed parts used in the design were also analyzed using Finite Element
Analysis. The X-Axis Stepper Motor Plate had to different sets of analyses performed in order to
determine stress concentrations around varying hole locations on the part.
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Figure 12 below shows the first setup for the X-Axis Stepper Motor Plate in which the plate is
fixed at the three V-Slot wheel holes and a torque of 85 in-lb. is applied to the front face. This
torque was used to simulate the loading which occurs from the print head being extended to the
farthest point on the X-Axis extrusion with a 10lbs. load used for the print head.
Figure 12 - X-Axis Stepper Motor Plate Setup #1 - Fixed V-Slot Wheel Holes
A convergence study was performed on the results of several different mesh sizes to find
optimal mesh size for the model. These can be found below in Figure 13 and Table 2.
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Figure 13 - X-Axis Stepper Motor Plate Stress Convergence - V-Slot Holes Fixed Stress Analysis
Table 2 - X-Axis Stepper Motor Plate Convergence - V-Slot Holes Fixed Stress Analysis
Mesh Size (in) Mesh Size (mm) Max Stress (psi) % Change Stress0.25 6.35 1501 -0.2 5.08 1318 -13.88%0.1 2.54 1449 9.04%
0.05 1.27 1483 2.29%0.025 0.635 1499 1.07%
Load: 10lb - 25 Elements per Hole
The mesh converged at a value of 1318 PSI using a mesh size of 0.2”. The yield strength of
PETG, the material used to 3D print the part, is 8000 PSI. The maximum stress from this loading
is located along the inside edge of the forward-most V-Slot wheel hole. This stress concentration
is highlighted in red in Figure 14 below.
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Figure 14 - X-Axis Stepper Motor Plate - V-Slot Holes Fixed Stress Analysis
The second setup for the X-Axis Stepper Motor Plate analysis can be seen below in
Figure 15. In this setup, the loading was again simulated using a torque about the front face of
the plate of 85 in-lb. The plate was fully fixed at the four screw holes located in the center of the
place, which are used to affix the plate to the X-Axis extrusion.
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Figure 15 - X-Axis Stepper Motor Plate Setup #2 - Fixed V-Slot Wheel Holes
A convergence study was performed on the results of several different mesh sizes to find optimal
mesh size for the model. These can be found below in Figure 16 and Table 3.
Figure 16 - X-Axis Stepper Motor Plate Stress Convergence - Extrusion Holes Fixed Stress Analysis
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Table 3 - X-Axis Stepper Motor Plate Convergence - Extrusion Holes Fixed Stress Analysis
Mesh Size (in) Mesh Size (mm) Max Stress (psi) % Change Stress0.25 6.35 1205 -0.2 5.08 1189 -1.35%0.1 2.54 1182 -0.59%
0.05 1.27 1197 1.25%0.025 0.635 1199 0.17%
Load: 10lb - 25 Elements per Hole
The mesh converged at a value of 1182 PSI using a mesh size of 0.1”. The maximum stress from
this loading again occurred along the inside edge of the forward-most V-Slot wheel hole. This
stress concentration is highlighted in red in Figure 17 below.
Figure 17 - X-Axis Stepper Motor Plate - Extrusion Holes Fixed Stress Analysis
The second 3D printed part which was analyzed using Finite Element Analysis was the Z-Axis
Rod Coupling Plate. This plate is responsible for attaching the entire X-Axis assembly to the
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threaded rod. This plate was analyzed using two different setups. The first setup fixed the brass
nut hole while applying two separate torques on the side and back face of the plate. The two
torques combined to simulate a 10lbs. load on the farthest end of the X-Axis extrusion. An
example of the setup for this analysis can be seen below in Figure 18.
Figure 18 - Z-Axis Rod Coupling Plate - Brass Nut Fixed
A convergence study was performed on the results of several different mesh sizes to find optimal
mesh size for the model. These can be found below in Figure 19 and Table 4.
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Figure 19 - Z-Axis Rod Coupling Plate - Brass Nut Hole Fixed Convergence
Table 4 - Z-Axis Rod Coupling Plate - Brass Nut Hole Fixed Convergence
Mesh Size (in) Mesh Size (mm) Max Stress (psi)0.25 6.35 35400.2 5.08 3883
0.15 3.81 40010.125 3.175 3874
0.1 2.54 38680.05 1.27 4138
Load: 10lb - 25 Elements per Hole
The mesh converged at a value of 3874 PSI using a mesh size of 0.125”. The maximum stress
from this loading occurred along the inside edge of the brass nut hole. This was the largest stress
found for any of the 3D printed parts evaluated. This stress concentration is highlighted in red in
Figure 20 below.
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Figure 20 - Z-Axis Rod Coupling Plate – Brass Nut Hole Fixed
The second case analyzed for the Z-Axis plate was using the same torques as in the first
case and fixing the plate by the three V-Slot wheel holes. Again, a mesh convergence study was
done to determine the optimal mesh size for the model. The study can be found below in Figure
21 and Table 5 below. The mesh converged at a size of 0.1”, and a stress of 859 PSI.
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Figure 21 - Z-Axis Rod Coupling Plate - V-Slot Wheel Holes Fixed Convergence
Table 5- Z-Axis Rod Coupling Plate - V-Slot Wheel Holes Fixed Convergence
Mesh Size (in) Mesh Size (mm) Max Stress (psi)0.25 6.35 679.70.2 5.08 774.90.1 2.54 858.6
0.05 1.27 798.2
Load: 10lb - 25 Elements per Hole
EXPERIMENTAL PROCEDURE
All the 3D printed parts used in this project were made using Polyethylene Terephthalate
(Glycol Modified) which is a light yet rigid thermoplastic commonly used in FDM 3D printers.
Due to the nature of the 3D printed parts, the typical material properties of PETG was not
accurate to use. This is because the parts created for this project were not completely solid.
Instead, each of the parts consisted of a 1.2mm thick wall filled with an internal grid structure,
which allows the parts to retain most of their mechanical strength while significantly reducing
their weight. An example of this internal grid structure can be seen below in Figure 22 and the
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settings used to produce the parts can be found in Table 6 below. The parts used to complete this
project were printed with 70% infill.
Figure 22 - FDM 3D Printing Infill Comparison - Linear Grid [9]
Table 6 - Printer Settings for Printed Components
Extruder Temp. C 240Bed Temp. C 80
Layer Width, mm 0.6# of Perimeters 2
Wall Thickness, mm 1.2Infill % 70
Layer Height, mm 0.3Print Speed, mm/s 80
Once the parts were 3D printed, assembly of the printer began, using the SolidWork’s
model as a guide. During the assembly phase of the project several unexpected issues arose
which needed to be addressed. One persistent issue that arose often during the assembly process
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was that the dimensions on some of the 3D printed parts was too tight, meaning that some of the
dimensions needed to be slightly modified.
One example of this issue arising can be seen below in Figure 23. In this instance, Delrin
wheel axle holes on the Bed Plate, which is responsible for interfacing 3 V-Slot wheels with the
aluminum build plate, were spaced too far apart. This meant that the V-Slot wheels were not able
to be seated tightly against the channels in the aluminum rail. This led to unwanted play in the
build plate. To resolve this issue, one of the holes in the Bed Plate was elongated into a slot and
an M3 screw was added to the assembly, which allows for the positioning of the V-Slot wheel to
be adjusted as needed. This simple change dramatically reduced the play in the build plate
which, in turn, helped to bring the printer’s Y-Axis tolerance down.
Figure 23 - Z-Axis Bed Plate Design Modification
Another issue which arose during the assembly of the printer was that the X-Axis Stepper Plate
could not be secured to the X-Axis extrusion after tightening the front V-Slot wheel into
position. To resolve this issue, four small holes were added to the Z-Axis Rod Coupling Plate
which allows for a screw driver to pass through the plate to tighten the X-Axis Stepper Motor
Plate to the X-Axis Extrusion. A picture of this can be seen below in Figure 24.
Original Design Modified Design
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Figure 24 - Screw Access Holes Added to Z-Axis Rod Coupling Plate
In order to adapt the standard Marlin firmware to the printer, extensive modification was
required. The original files were downloaded from the project’s website. [10] The most current
version was used as the base firmware for this project which was Marlin 1.1.0-RC8. A snippet of
the firmware code can be found in Appendix A and the full firmware file can be found on the
Design Files CD included with this project under the folder “Marlin-RC”.
All of the modifications done to the firmware are located within the “Configuration.h”
and “Adv_Configuration.h” classes. The first section of code modified was to control the
microstepping of the stepper motors. In order to produce accurate parts, the number of
microsteps sent to each stepper motor needed to be calibrated so that the printer moved the
expected distance each time. To start, the RepRap calculator [11] was used to get a rough idea of
the microsteps per millimeter for each axis.
X-Axis Stepper Plate
Z-Axis Rod Coupling Plate
X-Axis Extrusion
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Both the X and Y axes use GT2 timing belts for their motion system. Each belt has a
tooth pitch of 2mm and the pulley on each stepper motor has 8 teeth. Using this information, a
rough estimate was calculated for the microsteps that the X and Y axes required to move 1
millimeter. For the X and Y axes the starting steps per millimeter value came to 200. These
calculations can be seen below in Figure 25.
Figure 25 - X/Y Axis Initial Microstepping Calculation
Likewise, a rough estimate for the Z-Axis steps per millimeter was also calculated. In this case, a
single start, 8mm lead screw was entered into the calculator. The Z-Axis steps per millimeter
was estimated to be 3200. This calculation can be seen below in Figure 26.
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Figure 26 - Z-Axis Initial Microstepping Calculation
Once the rough microstep count for each axis was input into the firmware, calibration of
the extruder began. Like the stepper motors on the X, Y and Z axes, the extruder stepper motor
needed to be calibrated so that the printer would extrude the correct amount of filament during
the printing process. This was done by telling the extruder stepper motor to extrude 10mm of
filament using the console menu in the slicer program. During the first test, the extruder out
pushed 26.53mm of filament. This can be seen below in Figure 27. Next, using Equation 4, a
new value for the extruder microsteps per millimeter was calculated. After this was completed,
the printer was set to extrude another 10mm of filament. This time 10.00mm of filament was
extruded, meaning that the extruder was properly calibrated. This can be seen below in Figure
28.
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Figure 27 - Uncalibrated Extruder - 10mm Test
Figure 28 - Calibrated Extruder - 10mm Test
The next step was to test the accuracy of these estimated values. To do this, a simple cube
was used. The nominal dimensions of the cube can be seen below in Figure 29.
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Figure 29 - Nominal Dimensions of Test Cube [12]
Using Equation 4, each of the 3 axes was calibrated so that the dimensions of the cube
were as accurate as possible. The estimated microstepping brought the dimensions of the cube to
within 0.008”, however after calibration the printer was able to achieve a dimensional accuracy
of 0.002”, which is well within the 0.005” tolerance goal of the project. The tabulated results of
the calibration tests can be seen below in Table 7.
Table 7 - Pre and Post Calibration Cube Dimensions
Printer X (mm) Y (mm) Z (mm) X (in) X Difference(in) Y (in) Y Difference(in) Z (in) Z Difference(in)Nominal Size 20.00 20.00 20.00 0.787 N/A 0.787 N/A 0.787 N/AUncalibrated 19.86 19.80 20.18 0.782 0.006 0.780 0.008 0.794 -0.007
Calibrated 19.96 19.98 20.01 0.786 0.002 0.787 0.001 0.788 0.000
WNEU Printer
Before further printing could take place, a starting *.gcode script was written to enable
the printer’s autoleveling feature, as well as to prime the nozzle with filament before a print. This
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script can be seen below in Figure 30. The command, M502, is used to reset the printer’s on-
board memory. This is needed to reset any previous data from the auto leveling sequence which
could cause issues with the printer. The G28 command on the second line moves both the X and
Y axes to their home positions. G0Y35 moves the Y axis forward 35mm in order for the print
bed to be moved directly under the nozzle. The G28 command is then used a second time to
home the Z-Axis. The G29 command is responsible for beginning the auto leveling sequence.
This command works by moving the print head to 9 locations on the print bed in a grid pattern.
At each point the nozzle is lowered down onto the bed until the inductive probe is triggered.
Since the probe triggers at the same distance from the aluminum print bed each time, the
firmware is able to plot out all 9 points to create a plane of best fit. The plane that is created from
this process is then used to adjust the positioning of the first layer of each print. If the print bed is
uneven or is not leveled the Z-Axis will raise or lower accordingly in order to keep the print head
at a constant distance from the print bed throughout the print. The final three lines of code in the
script move the print head to the front left corner of the print bed and purge 15mm of material
through the nozzle in order to prime the nozzle for extrusion. This ensures that plastic is ready to
flow through the nozzle immediately during the printing process.
Figure 30 - Starting G-Code
Once the printer was fully calibrated to produce dimensionally accurate parts, the printer
profile needed to be calibrated. Using the slicer program “Simplify 3D” many of the printer
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parameters, such as extruder temperature, print speed and layer resolution, needed to be adjusted
in order to for the printer to produce visually appealing parts without any artifacts, stringing, or
other defects. The test piece used to fine-tune the printer’s settings was a small boat found on the
open source file sharing website “Thingiverse”. This boat, titled “3D Benchy” was designed
specifically to test several key aspects of a printer’s performance such as its ability to produce
smooth curves. [13] It also demonstrates a printer’s ability to produce multiple small features
without having any additional material “stringing” between them. A picture of the first part to be
printed by the printer can be seen below in Figure 31 with many of the issues highlighted in red.
Figure 31 - Test Print #1 - "3D Benchy"
Stringing Gaps in top layer
Layers Misaligned “Z-Banding”
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The most obvious defect in this first print was the stringing. The excess material is produced
when the print head jumps from feature to feature over open air. In a fully tuned printer, the
material in the nozzle is retracted the proper amount so that no material oozes from the nozzle
while the print head is moved. The default retraction distance for the E3D Hot End is 1.4mm. To
remove any stringing from the print, the retraction distance, the distance the material is pulled
from the nozzle tip back into the hot end, was increased to 2.0mm.
The next defect in the print were the gaps in the top layer of the part. This can occur for
several reasons, however after reviewing the printer’s settings it was determined that the cause of
this issue was an improper nozzle orifice value in the slicer program. The slicer was expecting a
0.6mm nozzle orifice while the actual nozzle orifice was 0.4mm. Because of this discrepancy,
the extruded lines of plastic were smaller than the slicer expected. To resolve this issue the
nozzle diameter was updated in the slicer.
The final issue present in the test piece were the misaligned layers on the print. This issue
occurs when the print head vibrates too much during a print, causing the layers to misalign and
cause “Z-banding” in the print. The solution to this issue is one of print speed. Of the numerous
print speed settings that can be adjusted in Simplify 3D, the value responsible for correcting this
issue was the “Outer Perimeter Speed”. This value controls the print head’s speed while printing
the outer most perimeter wall, which is directly responsible for the observable print quality. The
default print speed was 60mm/s. To reduce the Z-banding in the print the outer perimeter speed
was reduced to 30mm/s.
The final test for the printer was to show that the printer could maintain a 0.005”
tolerance after being carried around, while also requiring no recalibration. To test this, the printer
was unplugged and the filament was removed. Then the printer was carried by the handle for
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1,000 feet before being set down and plugged back in. Once the filament was reloaded into the
extruder, another 20mm test cube was printed. The results from this test were recorded and can
be found in the Results and Discussion section of this report in Table 8. Two other off-the-shelf
printers were also used to compare the dimensional accuracy of this printer. These results can
also be found in Table 8.
The first printer that was used to compare results was a Prusa Research i3, which has
been the top selling desktop printer for under $1000 for the last 2 years. [14] An image of this
printer can be seen below in Figure 32. The second printer used in testing was a MakerBot
Replicator 5th Gen. This is the exact model of printer that the College of Engineering at WNEU
currently uses to rapid prototype many of the parts used in design projects throughout the
engineering curriculum. An image of this printer can be seen in Figure 33 below.
Figure 32 - Prusa Research i3
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Figure 33 - MakerBot Replicator 5th Gen.
RESULTS AND DISCUSSION
After the printer was fully calibrated to produce dimensionally accurate parts, and the
slicer settings were fine tuned for the printer, several complex parts were created in order to
verify the printer accuracy. The full list of settings used for this printer can be seen in Appendix
B. Figure 34 below shows the fully calibrated “3D Benchy” test print next to the original piece.
The three major issues present in the original piece were eliminated through careful tuning of the
printer’s settings.
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Figure 34 - Original Print vs. Fully Calibrated Print
After verifying that the print was optimally setup, the next test was performed. During
this test, the printer was carried for 1,000 feet. The results were recorded below in Table 8.
Table 8 - 3D Printer Dimensional Accuracy Comparison
Printer X (mm) Y (mm) Z (mm) X (in) X Difference(in) Y (in) Y Difference(in) Z (in) Z Difference(in)Cube Nominal Size 20.00 20.00 20.00 0.787 N/A 0.787 N/A 0.787 N/A
Prusa i3 20.00 20.07 19.93 0.787 0.000 0.790 -0.003 0.785 0.003MakerBot Replicator 20.16 20.16 20.19 0.794 -0.006 0.794 -0.006 0.795 -0.007
WNEU Printer - Before Moving 19.96 19.98 20.01 0.786 0.002 0.787 0.001 0.788 0.000WNEU Printer - After Carried for 1000ft 19.96 19.98 20.01 0.786 0.002 0.787 0.001 0.788 0.000
20mm Cube Tolerance Test
As the results in Table 8 clearly show, the dimensional accuracy of the WNEU printer
built in this project do not change, even after moving the printer 1000 feet. The inductive probe
and auto leveling also ensured that the printer did not require any further calibration after moving
the printer.
The final method used to evaluate the quality of the 3D printer was to print several
models of varying complexity to test different aspects of printer performance. The first of these
prints was a nut and bolt assembly. This assembly was used to gauge the printer’s ability to
create parts, which need to fit together snugly. The nut and bolt were printed with a vertical layer
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resolution of 150 microns (0.0059”) in order to reduce any roughness which could cause the
prints to bind while threading them together. Figure 35 below shows the results of this test. The
nut and bolt thread together effortlessly and there are no visible defects in either print.
Figure 35 - 150 Micron Nut and Bolt Set
The next print used to gauge the printer’s quality was a file from the website “3D Hubs”. The
files, titled “Marvin”, is a small figurine, which has many intricate features and was designed to
test key aspects of a printer such as its ability to produce smooth curves as well as produce clean
“overhangs”. An overhang is any area of a print where material must travel over open air to
bridge two points. The eyes on this model have a 0.5” overhang to test this feature. As seen
below in Figure 36, the model produced shows no discernible defects. The overhanging areas in
the eyes of the model show no dropping or sagging and the curves of the model appear smooth.
This model was printed using the printer’s finest vertical resolution of 80 microns (0.0031”).
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Figure 36 - 3D Hubs Marvin - Fine Detail Test
CONCLUSION
The printer produced during this design project was a resounding success satisfying all
four of the design constraints. The printer’s final dimensions are 12” x 12” x 12” and it weighs
10.9lbs. The dimensional accuracy of the parts that it can produce is within the 0.005” tolerance,
which was set as a design constraint. Because of the successful use of the inductive proximity
sensor and Marlin’s auto leveling algorithm, the printer also requires no recalibration, even after
being moved over a long distance. The 1/32 microstepping DRV8825 stepper drivers provide
enough resolution to accurately create smooth, curved surfaces, and the 50mm radial blower part
cooling fan provides sufficient cooling for the printer, allowing it to produce crisp overhanging
features. The 0.5mmm nozzle is small enough for the printer to accurately replicate threads
which can glide past one another with little friction. The WNEU Printer has a maximum build
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volume of 90mm x 130mm x 100mm (3.54” x 5.11” x 3.94”). The printer has a dimensional
accuracy of 0.002” in the X/Y plane and 0.0031” along the vertical axis. The maximum tested
printing speed is 50mm/s. This translates to a throughput of 6mm3/s.
RECOMMENDATIONS FOR FUTURE WORK
While the WNEU printer was successful in meeting all of the original project goals, there are
some areas in which the printer can be improved. Currently, the printer is only able to print using
materials with a low glass transition temperature such as Polylactide (PLA). This is because the
build plate is not heated. By adding a heated build plate, dozens of addition materials will be able
to be used, including several engineering grade materials such as ABS and Polycarbonate.
Another aspect of the printer which can be improved is the wiring. Currently there is no
shielding to cover the wires leaving the hot end to connect to the microcontroller. While a goal of
the project was to create a printer that was as open as possible, these wires do not need to be
exposed to demonstrate the functionality of the technology and thus should be covered and
further cleaned up to increase the printer’s longevity and enhance the printer’s overall look. One
final improvement that could be made would be to machine all the plastic parts out of aluminum.
While the 3D printed PETG parts are certainly strong enough to resist most of the forces on the
printer, it is currently unknown how durable the parts will remain over time. There is no readily
available fatigue or failure analysis of PETG when used in 3D printed parts. Since the printer
weighs just 10.9lbs., it would be possible to machine these parts from aluminum and keep the
printer under an overall weight of 15lbs.
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BIBLIOGRAPHY
[1] "3D Printing Skills: Now Highly Coveted Among Tech Jobs | AIM for Brilliance Blog." AIM Careerlink. N.p., 16 Sept. 2014. Web. 02 Nov. 2016. [2] "Additive Manufacturing Innovation Center" Pratt & Whitney to Deliver First Entry Into Service Engine Parts Using Additive Manufacturing. Pratt and Whitney, 1 Apr. 2015. Web. 02 Nov. 2016.
[3] "Print Plastic as Strong as Metal." Markforged. MarkForged, n.d. Web. 02 Nov. 2016. [4] "What Is FDM?" 3D Hubs. N.p., n.d. Web. 29 Apr. 2017.
[5] SDP/SI. "HANDBOOK OF TIMING BELTS AND PULLEYS." SpringerReference (n.d.): n. pag. GT2 Timing Belt Accuracy. SDP/SI. Web. 27 Jan. 2017.
[6] "GT2 Belting - Open Ended." Inventables. SDP/SI, n.d. Web. 01 Feb. 2017.
[7] "DRV8825 (ACTIVE)." DRV8825 2.5A Bipolar Stepper Motor Driver with On-Chip 1/32 Microstepping Indexer (Step/Dir Ctrl) | TI.com. Texas Instruments, n.d. Web. 27 Apr. 2017.
[8] "Nozzles." E3D Online. E3D, n.d. Web. 1 May 2017.
[9] Infill Comparison. Digital image. N.p., n.d. Web. 4 May 2017.
[10] "Marlin Firmware - Official Site." Marlin 3D Printer Firmware. N.p., n.d. Web. 19 Apr. 2017.
[11] "RepRap Calculator." Prusa Printers. Prusa Research, n.d. Web. 3 Apr. 2017.
[12] IDig3Dprinting. "XYZ 20mm Calibration Cube by IDig3Dprinting." Thingiverse. Thingiverse, 19 Jan. 2016. Web. 19 Apr. 2017.
[13] Creative Tools. "3D Benchy by CreativeTools" Thingiverse. Thingiverse, 9 Apr. 2015. Web. 19 Apr. 2017.
[14] "3D Printing Trends 2017." 3D Hubs. N.p., n.d. Web. 05 May 2017.
[15] 3D Hubs. "3D Hubs Marvin – Key Chain" Thingiverse. Thingiverse, 30 Dec. 2013. Web. 19 Apr. 2017.
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Appendix A – Marlin Firmware Configuration
See project CD for complete Marlin Firmware File – “Marlin-RC”
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Appendix B – Simplify 3D SettingsSee project CD for complete .FFF import file “WNEU Printer”
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