Direct 3D Printing of a hand splint using Reverse Engineering

Abstract

The present work is focused on the direct manufacturing of a hand splint using free-open access software and a low-cost three-dimensional printer (3DP). The hand digital model was created using panoramic photos by a common mobile phone camera. The photos were used as input to the "3DF-Zephyr" free software for creating the hand surface model. Then, the hand surface model was transferred into the "Autodesk fusion 360" free software and the surface model of the hand splint was generated and modified according to the design requirements. Sequentially, both hand and hand splint were translated to Stereolithography (STL) files and transferred to open access "MakerBot" 3D printing software in order to prepare the G-codes for 3D printing. A low cost 3D printer was used for building the models while Polylactic acid (PLA) was the material of the customized 3D physical models.

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IOP Conference Series: Materials Science and Engineering
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Direct 3D Printing of a hand splint using Reverse Engineering
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IManEE 2020
IOP Conf. Series: Materials Science and Engineering 1037 (2021) 012019
IOP Publishing
doi:10.1088/1757-899X/1037/1/012019
1
Direct 3D Printing of a hand splint using Reverse Engineering
J Kechagias1, K Kitsakis1, A Zacharias1, K Theocharis1, K-E Aslani1,4, M
Petousis2, N A Fountas3 and N M Vaxevadnidis3*
1University of Thessaly, General Department, Larissa, Gaiopolis, GR 41500, Greece.
2Hellenic Mediterranean University, Mechanical Engineering Department,
Estavromenos, GR 71410, Heraklion, Crete, Greece.
3School of Pedagogical and Technological Education (ASPETE), Department of
Mechanical Engineering Educators, Amarousion, GR 15122, Greece.
4University of West Attica, Department of Mechanical Engineering, Aigaleo, GR 122
44, Greece.
*Corresponding author’s e-mail: vaxev@aspete.gr
Abstract. The present work is focused on the direct manufacturing of a hand splint using free-
open access software and a low-cost three-dimensional printer (3DP). The hand digital model
was created using panoramic photos by a common mobile phone camera. The photos were used
as input to the “3DF-Zephyr” free software for creating the hand surface model. Then, the hand
surface model was transferred into the “Autodesk fusion 360” free software and the surface
model of the hand splint was generated and modified according to the design requirements.
Sequentially, both hand and hand splint were translated to Stereolithography (STL) files and
transferred to open access “MakerBot” 3D printing software in order to prepare the G-codes for
3D printing. A low cost 3D printer was used for building the models while Polylactic acid (PLA)
was the material of the customized 3D physical models.
Keywords: 3D printing; reverse engineering; open software; hand splint
1. Introduction
3D printing and especially Fused Deposition Modelling (FDM) is one of the most widespread Additive
Manufacturing processes for customized plastic parts directly from digital data [1]. Nowadays, FDM is
known as Fused Filament Fabrication (FFF) and becomes more available to small firms or home users
due to the low cost of the materials and the equipment used [2].
Reverse engineering refers to techniques that create CAD models from physical parts (damaged or
broken) by data digitization method (MRI, CMM, photos etc.) [3]. These models are transferred into
special CAD/CAM programs in order to create codes (similar to G-Codes) [4]. Finally, they are usually
remanufactured with the use of 3D printing. Every 3D printing process comprises three stages: pre-
processing of the STL-file, actual building and, post-processing of the prototype [5].

IManEE 2020
IOP Conf. Series: Materials Science and Engineering 1037 (2021) 012019
IOP Publishing
doi:10.1088/1757-899X/1037/1/012019
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One of the most widespread 3D printing processes is Fused Filament Fabrication (FFF) [6]. This method
generally uses polymers [7], while a large number of process parameters affect the final printed parts
quality [4, 8].
In this project, direct manufacturing of a hand splint using free-open access software and an FFF 3D
printer was attempted. A variety of studies related to 3D printing for fast production of customized three-
dimensional-printed hand splints were found [9-11]. In our project, low cost 3D printing parts using free
software is the main concept, as well as the evaluation of the proposed procedure as a sustainable choice.
First, a hand digital model was created using panoramic photos of a common mobile phone camera.
Then, the photos were used as input to the '3DF-Zephyr' free software for creating the hand surface
model. After that, the hand surface model was transferred into 'Autodesk fusion 360' free software and
the surface model of the hand splint was generated and modified according to the design requirements.
Sequentially, both hand and hand splint, were saved as Stereolithography (STL) files and transferred to
the open access 'MakerBot print' 3D printing software in order to prepare the g-codes for 3D printing.
An FFF printer was used for models’ building. PLA was the printing material of the customized 3D
physical models.
2. Materials and methods
2.1. Photogrammetry software
The program used to scan the hand was ‘3DF Zephyr’, which, although originally downloaded to the
lite version, had to be upgraded to its Professional version. The upgrade was valid for one month. The
tool used to photograph the hand was a common mobile phone. Another program that was proposed was
the Autodesk Recap photo. The scanning process had to be repeated several times to achieve the desired
result.
2.2. 3D design of the Splint
The scanned hand was inserted into the Autodesk fusion 360 software. Some other software tools such
as Rhinoceros 5 or Meshmixer could have done the same process, too. Before the splint was designed,
the triangles of the STL mesh file had to be lowered, to make the hand smoother on the 3D printer (Fig.
1).
Figure 1. Hand 3D model taken using 3DF Zephyr.

IManEE 2020
IOP Conf. Series: Materials Science and Engineering 1037 (2021) 012019
IOP Publishing
doi:10.1088/1757-899X/1037/1/012019
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Figure 2. Hand splint 3D model.
Initially, a tube was designed which was moved around the hand and using the ‘edit form’ command it
came close enough to the curves of the hand. The command used to create the tube is:
sculpt/create/cylinder. The next command utilized was “thicken” to give the required thickness.
Then, after the splint took the shape of the hand, its buttons were designed, which are circular in the
form of a groove, so that they can be closed using a washer. In order to facilitate the installation and the
removal of the washer, recesses were designed that allow the placement of the finger (Fig. 2). The
dimensions of the buttons are: Splint length: 13.78 cm; Splint thickness: ≈ 5mm; Button diameter: 20mm
(outer) - 15mm (inner); Slot thickness: 5mm; Slot depth: 3.5mm; Diameter for finger on the clasp
(Depth: 3mm, Tolerance: ± 0.3mm, the lowest point in oval shape).
The number of buttons designed is four. Their location was chosen based on the ease of splitting, the
splint was into two parts, which was then performed. Next, the object was divided into two parts. To do
this, a line was drawn with a sketch that passes through the centres of all four buttons, and with the use
of the “extrude” command, the line was drawn, so that it could pass through the object to be split.
Finally, for the separation of the object, the “split body” command was utilized, in which the designed
line was selected, and the object that will be divided into two parts was used.
Afterwards, holes were drilled to ventilate the human limb and to save material. In order to open the
holes, it was necessary to decide the suitable pattern. It was decided to design holes in the formation, of
the part, with triangular and oval shape. For the formation of the holes, each hole was designed
separately. After the design was made, the hole was moved near the splint, placed at the appropriate
height and angle and with the use of the “extrude” command the opening was made. In order for the
splint to have a smoother surface at the points where the holes were opened, the fillet command was
used. All fillet commands were made with a radius of one millimetre (1 mm).
Figure 3. Hand splint 3D model.
2.3. STL files preparation
The next step was the STL files preparation.
First the hand was divided in two parts to facilitate the printing but also to fit the hand in the printer
working volume. Then, part of the fingers was removed as this saved material and time, in addition they
do not significantly affect the work, so with that in mind they were removed.
After that, separation follows: the first part consists of the point where the fingers were cut and about
8.1 cm to the right, and the second was the part that remained.

IManEE 2020
IOP Conf. Series: Materials Science and Engineering 1037 (2021) 012019
IOP Publishing
doi:10.1088/1757-899X/1037/1/012019
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After cutting, each section needed to be exported in a file format suitable for the 3d printer software
(STL files). The program used for this was ‘meshmixer’, a software that will specify the format for
exporting the file. With the same way hand-splint split into two parts with the same commands used for
the hand and then exported to ‘meshmixer’. Prior to printing, the “sculpt” command was executed via
‘meshmixer’ to make the surface of the splint smoother in areas where many pixels appear.
2.4. Hand and hand splint printing
MakerBot Print was used for orientation and layer build style settings (Fig. 4). Wanhao Duplicator 4X
FFF 3D Printer was used for printing the STL files (Figs. 5, 6, 7). The printer prepared with the following
settings: Extruder temperature: 220° C; Platform temperature: 90° C; Travel speed: 150mm/s; Minimum
layer duration: 5.0 s; Device settings: Low. Material used was PLA.
Figure 4. Hand and hand splint preparation for printing.

IManEE 2020
IOP Conf. Series: Materials Science and Engineering 1037 (2021) 012019
IOP Publishing
doi:10.1088/1757-899X/1037/1/012019
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Figure 5. Hand physical models.
Figure 6. Hand splint physical models.
Figure 7. Assembly of hand and hand splint.

IManEE 2020
IOP Conf. Series: Materials Science and Engineering 1037 (2021) 012019
IOP Publishing
doi:10.1088/1757-899X/1037/1/012019
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3. Results and discussion
The printing process of the hand and the hand splint was time consuming and, in some cases, required
some corrections and reprinting from the beginning. The hand takes about four (4) hours for each part
with the resolution setting at low. The difficulty encountered in this case was related to the extraction of
the material by the extruders. During material delivery, as the extracellular material was moved, the
material that was injected was carried away and detached from the printer base. This problem, in the
end, was overcome by using hairspray, on the paper tapes that were already on the base of the printer as
well as by increasing the base temperature so as not to entice the material with the movement of the
extruder.
After the hand was 3D printed in two parts, it was then required to scrape the piece with a spatula, from
the wrist to the fingers at the point of the thumb so that the piece would be smoother and the splint would
fit better. After sanding the piece, the two parts were glued together with benzine glue so that the hand
3D printing process could be completed.
As for the 3D printing of the splint, the time it took was about four (4) hours for each piece. The
difficulties in this case are related to the stability of the 3D print since there are holes in the splint. In
order to overcome these difficulties, the parameter of the auxiliary material was selected during the
processing of the 3D print settings in order to make the printing more robust. Moreover, during the 3D
printing process, it was required to use the lacquer, so that the material does not come off the base. When
the 3D printing of the two parts of the splint was completed, the auxiliary material was removed using
the spatula, which was also used for smoothing in order to have the desired result.
4. Conclusions
In this project a hand splint and the hand prototype were 3D printed using FFF 3D printing technology
and photogrammetry software. All software used in this project are open (free). Material used for 3d
printings was the PLA biocompatible material. The procedure takes a lot of work to select the
appropriate software for the manipulation of the panoramic photos (scanning data) and to translate them
to STL 3D digital hand geometric model. Hand splint produced using appropriate software tools that
produce CAD data from digital data (photogrammetry data). Finally, STL preparation for 3d printing
and 3d printer settings are very important in order to have good quality physical models. Optimization
of the process parameters is proposed as future work in order to have even better results.
Acknowledgements
The authors wish to thank the Special Account for Research of ASPETE for supporting this work
through the funding program “Strengthening research of ASPETE faculty members”.
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