Study on Accuracy Parameters of parts for a 3D Printed Mechanical Clock

3D Printing Final Term Report May 18th
2015
1 Denny G., Dipen P., Milind S., Samket D.
3D Printed Clock (Study of Accuracy)
Introduction:
The purpose of this project is to understand and learn about 3D printing technology. A 3D
printing process can print almost anything which is being manufactured with the use of
conventional manufacturing technology. A 3D printer is calibrated with parametric default
setting which is able to successfully print every part, but has a low possibility of successfully
printing every part accurately. Due to the variation in complexity from part to part, changing the
parametric values for every part would play a significant role in printing the part accurately. To
validate this theory, we are going to print a mechanical gear.
Objective:
Our objective is to study the parametric factors affecting the accuracy of a mechanical gear
through a 3D printing process.
Conclusions from Literature Review:
From the literature survey we came to a better understanding of 3D processes, types of 3D
printer, materials, clock mechanism and the intricate parts required.
The accuracy of these intricate parts is of importance because it directly implies conformance to
time units in minute hand, second hand and hour hand. The articles gave us an overview of how
factors would affect a print quality. Here, ‘factors’ mean printer settings, material properties and
orientation of the part on the build plate.
Fused Deposition Modeling for 3D printing:
There are several types of 3D printers. The main differences between the types of printers are in
the way layers are deposited to create parts and in the materials that are used. For our project
work, we have used FDM printing technology. In FDM, plastic filaments are extruded through a
hot extrusion nozzle onto the build table. After an entire layer of material is added to the object,
the printer lowers the build table and then adds the next layer. In this technology, the filament in
introduced into the extruder, from the top. The filament enters the extruder with the help of
rollers, stabilising the filament for unidirectional penetration. The nozzle at the bottom of the
extruder extrudes the melted filament on the build plate. The extruded material is laid on the
previous layer so that the two layers join together on cooling, to form a shape. Thus a 3D object
is formed.
Material Properties:
Makerbot ABS filament is the one of the recommended and most consistent filament designed
for the Makerbot Replicator 2X Desktop 3D printer. ABS plastic is considered strong, flexible
(compared to PLA), machinability, higher temperature resistance, and is often a preferred plastic
for engineers for mechanical applications in mind. The ABS filaments (Fig. 1) that we have used
for DOE test print parts (red in colour) are sourced from and produced by Makerbot Industries.
But we have also printed other test parts with ABS filaments which are sourced from and
produced by BuMatusa & Filament.com. The filament has a diameter of 1.75 mm which is
compatible with the Makerbot Replicator 2X (Fig. 2).

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Fig. 1: Filaments Fig. 2: Makerbot Replicator 2X
Methods:
I. Converting your CAD file to .stl format:
To create a part using Additive Manufacturing the following steps need to be followed.
a. Create a 3D model:
A 3D model of an object can be created on any 3D modelling software such as CAD
software (the most popular category of software, for e.g. SolidWorks) (Fig. 3), freeform
modelling tool software (for e.g. Maya) and sculpting tool software (for e.g. 123D
Sculpt), etc.
b. Save the 3D model as .stl extension file:
The 3D model when completed must be saved as, with the filename having an extension
.stl (For e.g. gear.stl)
Fig. 3: A CAD model of the gear on Solid works

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II. Setting up the .stl file into Makerbot Readable format with a set of predefined parameters:
a. Setting up the Part:
The .stl file is imported into the Makerbot Desktop software (Fig. 4) which slices the 3D
model. Before the Makerbot Desktop slices a part, the user needs to specify the Position
(Fig. 5), Dimension (Fig. 6) and Orientation (Fig. 7) of the Part to be printed.
Fig. 4: Makerbot Desktop Interface
Fig. 5: Part Position Settings Fig. 6: Part Dimension Settings
Fig. 7: Part Orientation Settings Fig. 8: Changing Part View

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As for our part, the gear, we would position the gear on the platform at the center of the build
plate. We would not change any dimensions of the gear as it fits within the build plate. The
gear’s central axis is positioned vertically, to print in z direction.
b. Printer Settings for the Part:
With a wide selection of printing parameters we can select the desired print quality. As
shown in Fig. 9, we have selected High Profile (Default profile) for printing. The
software automatically calculates the input values to be optimal, for all the parameters
which would affect the quality of the part such as Resolution, Quality, Temperature,
Speed, etc.
Fig. 9: Print Settings for the gear
c. Slicing the .stl file:
We now slice the model, by clicking on ‘Exporting print file’ and following the steps to
save it in .x3g extension (for e.g. gear.x3g) as shown in Fig. 10, Fig. 11, Fig. 12 and Fig.
13. By slicing the 3D model, the software generates a G-code for the Makerbot 3D
printer. Slicing divides a model into printable layers and plots the toolpaths to fill them
in. This code is used by the Makerbot 3D printer to follow a path towards printing a part
successfully.

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Fig. 10: Export Print File Fig. 11: Printing Details of the Print file
Fig. 12: Save the Print file on SD card Fig. 13: Converting the file to .x3g format
We have now converted our part into a Makerbot Compatible format. Now we would set up our
Makerbot Replicator 2X, for the part to be printed.
III. Setting up the Makerbot:
a. Tape the build plate: It is important to tape the build plate with a smooth platform tape so
that the part does not rip off from its position.
b. Level the Build plate: To level the build plate, follow the instructions given on the
display of the Makerbot. It is important to level the build plate so that every printed layer
is parallel to the build plate.
c. Check the Filament spool: It is important to check the filament spool before starting the
print. If the filament is tangled, the part will not be printed.
d. Check the Performance of the Extruder: The filament should be rolled in by the extruder
rollers from the top so that it would extrude the filament from the bottom nozzle onto the
build plate. The extruder should be checked for any filament pieces stuck between the
roller and the nozzle, by loading and unloading the filament as instructed in the Utilities
Menu.
e. Keep the printing chamber isolated: As shown in Fig. 2, it is important to keep the inner
chamber isolated/covered or else the part would not print to be accurate due to warping.
After checking all the above printer conditions, we can now insert the SD card to print our
desired part, i.e. gear.x3g

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Test Printing Parts:
We have referred to different types of 3D Clock Designs from open source websites such as
www.grabcad.com & www.thingiverse.com for test printing a range of sizes of gears. We
convert the .stl file into .x3g format using the default available profile ‘High Profile ABS’ in
Makerbot Desktop (Fig. 9). We test printed two parts, Fig. 14 a clock shaft and Fig. 15 a spur
gear.
Fig. 14: Two different results Fig. 15: The tooth profile on the left hand side is in good
when we printed a small shaft shape than the tooth profile on the right hand
and a large shaft. side.
Design Of Experiment (DOE):
A process is accurate (unbiased) if its average result is on target. The amount by which the
average result is away from a set target is a measure of the process inaccuracy or bias. In most
cases it is possible to compensate for process inaccuracies.
Design of Experiments (DOE) is a powerful tool that can be used in a variety of experimental
situations. DOE allows for multiple input factors to be manipulated determining their effect on a
desired output (response). By manipulating multiple inputs at the same time, DOE can identify
important interactions that may be missed when experimenting with one factor at a time. All
possible combinations can be investigated (full factorial) and a design matrix made or only a
portion of the possible combinations (fractional factorial). Fractional factorials will not be
discussed here.
Why use DOE?
We use DOE when more than one input factor is suspected of influencing an output. For
example, it may be desirable in our case to understand the effect of temperature and orientation
on build/fit accuracy.
When you are doing a 3D print of a model there are multiple parameters that you have control of
and these parameters of the printing process can affect things like quality, durability and speed of
the printing process. So you should know what and how to change in order to get a stronger
model or a faster print or actually a useable print if you are having trouble printing a 3D model.

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We take three factor combinations in three different axes using the 2 factorial DOE method.
Some of the factors that may affect the accuracy of the part are, Orientation, Layer Thickness,
Infill Density, No. of shells, Temperature of the build plate, Temperature of the Extruder, Speed
of the extrusion, speed of travel of the extruder across the build plate, raft & support.
We studied the factors to find 3 most important factors affecting the part accuracy. Therefore in
Table 1, we have described the three factors which we have considered for DOE.
Layer Height is the main parameter that affects print quality as it sets the thickness of each layer
that is being printed. The lower the number, the thinner each layer is, the better quality you get of
your 3D prints.
Infill is a value usually represented in percentage that shows how much a solid model should be
filled in with material when printed. Normally, unless you want maximum strength, you would
not need to go for maximum fill of a 3D model, especially if you also want to save on material
costs, model weight and want to get the print faster.
Number of Shells (Outline/Perimeter Shells) is a value that sets the number of outlines printed
on each layer of your object, the more shells the stronger the printed object is, so setting a higher
number of essentially shells make the printed part with denser outside walls
Table 1
Table 2
Test Prints:
As shown in Fig. 16, Fig. 17, and Fig. 18 we have printed 24 such parts. These 24 parts have
been defined with the Parameters in Table 2. These test parts would be measured for its
accuracy.

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Fig. 16: 8 Test parts printed in Z – orientation Fig. 17: Test part printed in Y - orientation
to the central axis of the gear geometry. to the central axis of the gear geometry.
Fig. 18: Test printed parts in Z - Y – X Orientation respectively
For this project, a Vernier caliper (Fig. 19) and an Optical Comparator/Projector (Fig. 20) were
used.

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Fig. 19: Vernier Caliper Fig. 20: Optical Comparator
Five parameters of the gear was selected which includes Addendum Circle Diameter, Dedendum
Circle Diameter, Pitch Circle Diameter, Face Width and Tooth Thickness. One set of
measurement of these parameters using a Vernier caliper as shown in Tables 3 - 5. Parts printed
in Z-orientation (E1-E8), Y-orientation (E9-E16) and X-orientation (E17 – E24) was measured
with the caliper.

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Table 3: Measurement of 3D printed gear using Vernier Caliper

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The optical comparator used for the project is a Starrett HB 350. It is a simple bench mounted
unit with a horizontal lens axis and a single mirror optical system. In order to measure the
component parts, the optical projector is connected to a Quadra-Chek 200. The Quadra-Chek 200
system is an advanced readout system for performing 2, 3 and 4 axis measurements at very high
levels for precision and accuracy.
Parts of the mechanical clock were measured with the optical comparator. The measurements are
shown in Table 6. Only parts printed in Z-orientation (E1-E8) were measured as they had better
part quality and less obstruction, from support structures, in viewing the images.

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Table 6: Measurement of 3D printed gear using Optical Comparator
Fig.21: Measurement of gear Face Width using Fig.22: Measurement of Addendum,
Optical Comparator Dedendum, PCD and Tooth Thickness
The parts are positioned on the bench where a shadow image of the part is projected on the
screen. The parts are adjusted accordingly so that the reference points can be clearly made on the
screen. Measurements are taken by rotating the spindles in the x direction and y direction. The
Quadra-Chek 200 comparator measures the distance from reference points to the end points. For
the project, 8 gear parts were measured, out of which the addendum circle diameter (ACD),
Dedendum circle diameter (DCD), pitch circle diameter, face width and tooth thickness were
examined. 5 sets of reading for each part was done to compare the dimensional accuracy. The
optical comparator provides a closer look up on the gear teeth and provides better dimensional
accuracy than a Vernier caliper.

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Analyzing the Measured Parameters:
From the Optical Comparator Measurement Table 6, we would calculate the error value by
referring the True Value of the gear part.
Addendum CD Dedendum CD PCD Face Width Tooth Thickness
2.856 inches 2.670 inches 2.750 inches 0.025 inches 0.05 inches
Table 7: True Values of the part from the CAD file depicted in Fig. 3.
for the part with least error in its geometrical dimensions.
A MATLAB code has been developed to find the root mean square value of each parameter of
the gear. The MATLAB code has been attached in APPENDIX – I.
The Results are displayed in Table 8 as below:
Table 8: Root Mean Square Values
Results:
1. Tables 3, 4, 5 & 6 are the results of our experiment with different combination of
parameters.
2. We compared the values of Vernier calliper and Optical comparator. We have
considered the Measurement Values of Optical Comparator in for Calculating least
error.
3. RMS method is used to find optimal parameter using MATLAB. It points us in the
direction of specimen E7 to have the least error print quality(300 micron layer
thickness, 10% infill density, 3shells)
4. These parameters can be used to print similar gear components with great accuracy
and appealing surface finish.
References:
1. www.grabcad.com
2. www.thingiverse.com
3. http://3dprintingforbeginners.com/software-tools/
4. http://makezine.com/magazine/guide-to-3d-printing-2014/know-your-slicing-and-
controlsoftware-for-3d-printers/
5. D. Dimitrov W. van Wijck K. Schreve N. de Beer, (2006),"Investigating the achievable accuracy of three
dimensional printing",Rapid Prototyping Journal, Vol. 12 Iss 1 pp. 42 – 52.

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Gantt chart:

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APPENDIX – I
Root Mean Square MATLAB program
%% Z-orientation%%
clc
clear all
Validation_Addendum = [ 2.856;2.856;2.856;2.856;2.856];
Validation_Dedendum = [2.683;2.683;2.683;2.683;2.683];
Validation_PCD = [2.7695;2.7695;2.7695;2.7695;2.7695];
Validation_Facewidth = [0.225;0.225;0.225;0.225;0.225];
Validation_Tooththickness = [0.05;0.05;0.05;0.05;0.05];
e1=[2.845 2.813 2.847 2.858 2.854;
2.690 2.671 2.727 2.698 2.692;
2.760 2.742 2.778 2.769 2.777;
0.235 0.236 0.228 0.232 0.233;
0.054 0.049 0.047 0.047 0.048];
E1=e1'
e2=[2.839 2.831 2.820 2.820 2.834;
2.670 2.662 2.660 2.651 2.672;
2.745 2.746 2.734 2.735 2.750;
0.229 0.232 0.234 0.223 0.230;
0.063 0.054 0.050 0.049 0.048];
E2=e2'
e3=[2.839 2.826 2.834 2.842 2.842;
2.676 2.663 2.662 2.673 2.671;
2.756 2.744 2.739 2.741 2.7456;
0.230 0.227 0.217 0.214 0.226;
0.055 0.055 0.0540 0.055 0.059];
E3=e3'
e4=[2.846 2.828 2.844 2.845 2.846;
2.676 2.668 2.674 2.681 2.672;
2.749 2.748 2.7354 2.759 2.756;
0.226 0.231 0.226 0.218 0.226;
0.054 0.052 0.059 0.050 0.069];
E4=e4'
e5=[2.831 2.828 2.830 2.832 2.830;
2.657 2.665 2.672 2.671 2.671;
2.737 2.746 2.751 2.747 2.741;
0.235 0.230 0.216 0.222 0.231;
0.059 0.062 0.055 0.067 0.062];
E5=e5'
e6=[2.847 2.838 2.841 2.866 2.866;
2.691 2.681 2.674 2.6706 2.683;
2.767 2.759 2.747 2.771 2.759;
0.209 0.212 0.224 0.217 0.219;
0.061 0.077 0.065 0.065 0.070];
E6=e6'
e7=[2.836 2.826 2.856 2.854 2.860;
2.678 2.685 2.688 2.6702 2.691;
2.754 2.755 2.765 2.774 2.755;
0.2320 0.2230 0.233 0.230 0.233;

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0.060 0.058 0.059 0.059 0.059];
E7=e7'
e8=[2.816 2.826 2.817 2.816 2.815;
2.656 2.662 2.655 2.640 2.638;
2.725 2.744 2.730 2.726 2.720;
0.230 0.231 0.232 0.231 0.232;
0.052 0.063 0.048 0.059 0.058];
E8=e8'
Addendum_rms1 = sqrt((sum((Validation_Addendum-E1(:,1)).^2))/5)
Dedendum_rms1 = sqrt((sum((Validation_Dedendum-E1(:,2)).^2))/5)
PCD_rms1 = sqrt((sum((Validation_PCD-E1(:,3)).^2))/5)
Facewidth_rms1 = sqrt((sum((Validation_Facewidth-E1(:,4)).^2))/5)
Tooththickness_rms1 = sqrt((sum((Validation_Tooththickness-
E1(:,5)).^2))/5)
E2(:,5)).^2))/5)
E3(:,5)).^2))/5)
E4(:,5)).^2))/5)
E5(:,5)).^2))/5)

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E6(:,5)).^2))/5)
E7(:,5)).^2))/5)
E8(:,5)).^2))/5)
fprintf ('n');
fprintf (' Part Number t Addendum Cir Dia t Dedendum Cir Dia tt Pitch
Cir Dia tt Face Width tt Tooth Thickness n');
fprintf ('n');
fprintf ('ttE1tt')
fprintf ('t%.8fttt',Addendum_rms1)
fprintf ('t%.8fttt',Dedendum_rms1)
fprintf ('t%.8ftt',PCD_rms1)
fprintf (' %.8ftt',Facewidth_rms1)
fprintf ('t%.8ft', Tooththickness_rms1)
fprintf ('n');
fprintf ('ttE2tt')
fprintf ('n');
fprintf ('ttE3tt')
fprintf ('n');
fprintf ('ttE4tt')
fprintf ('n');
fprintf ('ttE5tt')
fprintf ('n');
fprintf ('ttE6tt')

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fprintf ('n');
fprintf ('ttE7tt')
fprintf ('n');
fprintf ('ttE8tt')
fprintf ('n');

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