Lathe-Type 3D Printer

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ALEXANDROS KENICH MATTHIEU BURNAND-GALPIN ERWAN ROLLAND YOUSSEF IBRAHIM

LATHE-TYPE 3D PRINTER

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I

Lathe Type 3D Printer DMT Team Supervis ing Team

LATHE-TYPE 3D

PRINTER

ME3 DMT FINAL REPORT

PEOPLE

DMT Team

Name Contact Number Email

ERWAN ROLLAND 07 906 478 467 [email protected] MATTHIEU

BURNAND-GALPIN 07 824 967 269 [email protected] ALEXANDROS

KENICH 07 857 781 592 [email protected]

YOUSSEF IBRAHIM 07 896 669 666 [email protected]

Supervising Team

Name Contact Number Email Room

DR SHAUN CROFTON 02 075 947 085 [email protected] 551 DR PAUL HOOPER 02 075 947 128 [email protected] 393 DR DANIEL PLANT 02 075 947 128 [email protected] 002

MATTHIEU

BURNAND

GALPIN

Head of Control

GROUP 27

VERSION 1.3

Checked: E.R, M.B, Y.I

04/06/2013

MATTHIEU

BURNAND

GALPIN

Head of Control and Structure

ALEX

KENICH

Head of Programming

YOUSSEF

IBRAHIM

Head of Mechanical Design

ERWAN

ROLLAND

Project Manager

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II

ABSTRACT

This final report documents the design, making and testing of a novel lathe-type 3D printer. The prototype produced makes use of Fused Deposition Modelling and presents a viable alternative to Cartesian 3D printers currently in use. Methods were developed to generate G-Code machine commands which are used to produce these parts. The main objectives of the project were met; parts can be printed with good accuracy and with minimal effort. Through efficient management and organisation, the project was completed on time and under budget at £527.

The additive lathe prototype is capable of printing parts exhibiting complex geometries exclusive to cylindrical 3D printers. Parts previously impossible to create using additive manufacturing such as springs and propellers can be made with ease. The infill and aspect of cylindrical components can be controlled more precisely than is possible on a conventional 3D printer, and filament can be interwoven to improve mechanical properties.

The project could be extended by adding supplementary features to the software used to control the printer. In particular, writing code for a custom slicing procedure could streamline the generation of G-Code starting from a solid model. The printer provides an excellent foundation for these innovations to be implemented.

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III

1 I. BACKGROUND

I.1 Introduction

Fused Deposition Modelling 3D printers have recently garnered significant attention due to simplifications in design, leading to cheaper and more widely available printers. However, some limitations are associated to this technology, and several attempts have been made to overcome these [1].

The aim of the project described in this report is exploring one such possibility. A 3D printer was developed that, unlike a standard printer operating in Cartesian co-ordinates, operates in cylindrical co-ordinates. This is analogous to a lathe where material is deposited on a rotating cylinder rather than cut away. Efforts were also made to investigate the advantages of using a cylindrical printer over its Cartesian counterpart, exploring aspects such as the facilitation of creating certain geometries and the ability to control the disposition of the filament used to produce a printed part.

The report begins by introducing the topic of additive manufacturing and reviewing current 3D printing technology. Following this background information, the project plan used to conduct this project is briefly introduced. The design is explained in depth by exploring initial concepts and detailed features present in the final design. The design decisions concerning software and electronics are also presented.

Manufacturing considerations and the assembly process are then outlined, followed by information relating to the assessment and testing of the finalised prototype and the parts it can produce. The project costing is then presented followed by a discussion of the project, including its main achievements and potential areas of improvement.

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2 I.2 Technology Review

Increased interest in additive manufacturing methods has been accompanied by a popularisation of 3D printers. The applications of these devices range from rapid prototyping to specialist applications in medicine or aeronautics. While 3D printers are often grouped as single technology, they often operate using a variety of methods, and utilise a myriad of materials [1].

One of the most prominent 3D printing techniques is known as Fused Deposition Modelling (FDM). This method uses use thermoplastics such as ABS, polycarbonate and PLA, and has gathered considerable interest, as it is conceptually simple and relatively cheap. Material is fed into a heated nozzle, and laid upon a print bed while melted. As the layers solidify, a solid object is formed.

The team decided to conduct a short literature review to understand the basics of 3D printing, and to identify some of the shortcomings which could be overcome with a cylindrical printer. Additionally, past attempts to design cylindrical 3D printers were reviewed in order for our project to build upon their limitations.

Much of the on-going development surrounding FDM printers is concentrated around the RepRap Project (Replicating Rapid Prototyping Machine). The main advantage of these machines is that they can be built with standard components, and extensively customised. For these reasons, RepRap-type printers provide a good framework in which innovative features can be implemented with minimal cost and effort.

These machines operate in Cartesian coordinates; the print head can move in the X and Z directions, while the printbed is free to move in the Y direction using stepper motors. A picture of a typical RepRap machine is shown in figure 3.

Heated Nozzle

Print bed

Deposited material

Figure 2: Diagram of Fused Deposition Modelling (FDM) [1]

Print head X Axis motor Z Axis motor Control electronics Printed Fixtures Print bed

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One of these limitations is the difficulty of producing parts with large overhangs. This can be remedied by using a second material as a support, which can be removed once the part is completed. However, this method is significantly more costly and more complex.

Similarly, traditional FDM printers are often unable to create curved shapes with high accuracy. The smoothness of a circular part is limited by the step size on the motors. One of the shapes difficult to make on a Cartesian 3D printer is shown in figure 4 below.

Cylindrical-type 3D Printers

One of the attempts made to further 3D printer technology is the additive lathe. Unlike a traditional lathe, the exact angular position of the cylindrical printbed can be controlled using a stepped motor. Material can be deposited on the rotating print bed using a print head which moves in the X direction.

The additive lathe was created mainly as a proof of concept, and demonstrates the possibility of using a rotating print bed in a 3D printer with cylindrical coordinates [2]. Its main drawback stems from the omission of vertical mobility. As such, the range of parts that can be created is severely

Figure 4: Complex shape in on a Cartesian print bed (left) and cylindrical print bed (right)

Figure 5: Sketches of shapes difficult to make on a Cartesian printer [2]

Extruder Assembly Rotating Print Bed Chuck X Rails Z Y X Large overhangs No overhangs Z X Θ

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Implementation of a vertical axis Integration of electronics Feature interchangeable printbeds Create more complex parts Show off interweaving Identify main limitations of concept Show overhangs can be avoided Show viability of overhangs made on this printer.

Additionally, although a chuck is included, the design of the transmission does not enable the rotating print bed to be swapped for one with a different shape or material. Finally, this prototype cannot make use of existing software, and relies on custom electronics with reduced functionality. Only very simple parts can be produced by this printer, making it difficult to assess the increase in quality which can be offered by cylindrical printers. Furthermore, the design offers no upgradability, which would be desirable in order for a variety of print beds and materials to be tested.

Some of the aspects related to cylindrical printing have recently been patented [3]. The patent gives a very general overview of the systems which could be involved in such a machine, but gives minor indications on how these features could be implemented. A diagram of this machine is presented in figure 6 below.

Conclusion

While there have been some attempts to create a cylindrical 3D printer, most have been experimental, and no complex parts have been printed. As a result, many of the features which seem to be made possible with cylindrical printing are still hypothetical. The priority of the project is to construct a prototype which demonstrates some of these novel features. Another significant challenge is to integrate electronics and software with the printer. The main shortcomings of past projects which must be resolved with the project are presented in figure 7 below.

Figure 6: Diagram of a cylindrical printer [3]

Electronics Printhead Deposited

material

Rotating bit

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5 I.3 Group contributions

The group benefitted from excellent team cohesion and maintained well-distributed responsibilities and work amongst team members. While all team members contributed to the overall design, problem solving and report writing, each team member focused on particular aspects of the project. ERWAN: PROJECT MANAGER

As project manager, Erwan coordinated the team’s efforts and scheduled meetings. He was a driving force in maintaining the team’s motivation high and ensured deadlines were met. Erwan played a pivotal role in the Electronics and Programming aspects of the project, as he was responsible for selecting and implementing hardware and software solutions for the printer. He was also in charge of modifying and tweaking the printer’s firmware to adapt it to cylindrical coordinates. As project manager, Erwan also held the responsibility for ensuring the quality of the reports. He was in charge of assembling the reports, unifying the formatting and final editing.

MATTHIEU: HEAD OF CONTROL AND STRUCTURE

As Head of Control, Matthieu worked on obtaining the best possible printing accuracy. To this effect, he was responsible for selecting the motors and designing the transmission while minimising backlash. He was also in charge of designing the print bed assembly and all the components that relate to it. He was also the main architect of the CAD model and ensured the overall design was coherent. As such, he played a vital role in the manufacturing process and ensured quality control. Matthieu was also in charge of the acrylic sheets, from purchase to the design. He conducted and evaluated the impact of the laser cutter on the Perspex sheet and updated the CAD file accordingly. Matthieu also played a significant role in programming; he developed and tested the MATLAB program. Finally, along with Erwan, he was responsible for editing and proofreading the reports. YOUSSEF: HEAD OF MECHANICAL DESIGN

In the design process, Youssef held responsibility for the design of the X and Z axis components. He adapted standard RepRap x and z axis components for cylindrical printing. He distinguished himself in the manufacturing and assembly process. He played a key role in manufacturing and used his technical abilities to fix problems during the assembly process. Once the printer was assembled, he contributed heavily to increasing the practicality and aesthetic appeal of the printer. Along with Matthieu, he was an important contributor to the CAD. Finally, he generated innovative ideas for the poster.

ALEX: HEAD OF ELECTRONICS AND PROGRAMMING

Alex played varied roles as part of the team. As head of electronics and programming, Alex contributed to the programming through his expert knowledge of C. Possessing clear artistic skills; he was in charge of visual representation and photography of the printer. His skills in scene setting and lighting ensured aesthetic and precise representations of the printer and test parts. Alex also brought forward his image processing skills to design the poster. He also made subtle modifications to the CAD file, and was the driving force behind the assembly drawing. Finally he kept track of the teams spending and budgeting.

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6 II. PROJECT PLANNING

One of the main aims of the project was to demonstrate the viability of the cylindrical 3D printer concept. As such, the team’s approach to the project was relatively unrestrained and free of commercial considerations. One limitation however was the project budget, which could not exceed £600. As a result of these criteria, the group prioritised innovation over cost-effectiveness, exploring different methods and perspectives towards the realisation of the end product.

II.1 Product Design Specification

Starting from the project brief, a Product Design Specification (PDS) was produced in order to identify the key requirements which our project would need to satisfy. Additionally, these objectives were quantified in order to provide a framework for the design process. The criteria outlined below are of varying importance to the success of the project and a weighting from 1 (low importance) to 6 (high importance) was assigned to each criterion.

Aspect Criteria Weight Objective Testing

Per

fo

rman

ce

Quality High precision

printing 4 <0.5mm Print a part with intricate details Homogeneous

deposition 5

Smooth and

even Print a part with smooth features Large printing

volume 3

At least 200x200x150

mm

Print a large part

Use mains power 6 220V

Standard Plug into socket No large

vibrations 3

<3mm

displacement Print while on a hard surface Easy STL to

G-Code translation 3

Less than

5min Record time to process STL

Reliability

Seldom breaks

down 3 - Focus Group Evaluation Long life 2 At least 10

hours Print for 10 hours without maintenance Can be used for

lengthy jobs 4 At least 20min

Print for at least 20 minutes continuously

Robustness

Must withstand

light loads 3 Up to 100N Place 10kg mass on printer Must resist

regular use 3

At least 10

parts Print 10 parts consecutively

Efficiency

Prints parts

quickly 3 0.1cm3/s

Print cylinder and perform simple calculations

Minimal number

of parts 1 Less than 50 Check with bill of materials

Safety

Low risk to user

Heat protection 4 Heat insulated Check temperature in vicinity of heater during operation

Electrical

Protection 5

Electrically

insulated Focus Group Evaluation Safe disposal 1 Relevant

Standards Focus Group Evaluation Use of safe

materials 1

Relevant

standards Focus Group Evaluation No sharp edges 2 - Focus Group Evaluation

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Aspect Criteria Weight Target Testing

Er

g

o

n

o

mi

c

s

Size and Weight Reasonably compact 1 Less than 500x500x500mm Measure Dimensions Moderate weight 1 Less than 20kg Weigh printer

Compact

add-ons and tools 2 User testing Focus Group Evaluation

Usability

Easy to set up 3 User testing Focus Group Evaluation Accessible

controls and features

4 Clear and concise Focus Group Evaluation Good visibility of

printing process 2 - Focus Group Evaluation Minimal effort to

operate 3 No physical strain Focus Group Evaluation Low noise 2 Less than 60dB Focus Group Evaluation

Easily serviceable

parts

3 Design Review Focus Group Evaluation

Maintenance Use cheap

processes 2

Within costing

budget Focus Group Evaluation

U

se

r

A

p

eal

Manufacturing Use FDM printer for parts 1 For standard

components Print parts from Cartesian printer Easy to

manufacture 2 Design Review Focus Group Evaluation Within budget 6 Less than £600 Calculate cost of project

Cost

Low operating

costs 1 Less than £10/kg Check cost of filament Features

interweaving 4 Prototype testing

Print cylindrical part with interweaving

Proof of Concept

Faster printing

of some shapes 3 20% Reduction Compare to Cartesian printer Accurate

G-Code and path 3

No construction errors

Compare accuracy of parts to Cartesian printer

Following the construction of the PDS, a Quality Function Deployment matrix (QFD) was produced in order to relate engineering requirements to the functions the printer would need to fulfil. This matrix was instrumental in establishing key features the printer would need to accommodate. Additionally, the relative importance of each function was used to determine which tasks would need to be prioritised. The result of this analysis was used to allocate the team’s time and resources.

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1 8 15 22 29 5 12 19 26 3 10 17 24 31 7 14 21 28 4 11 18 25 1 8 15 22 1 8 15 22 29 6 13 20 27 3 10 17

DMT project selection Form a group and choose a project All Initial research and

understanding Background reading on 3D printers All Project plan report Writing of the project plan report E & Y

Progress report Writing of the progress report A & M Poster design Brainstorming for poster ideas and poster

design A

Log book Keeping track of new ideas and progress in a

log book E

Final report Drafting, writing and editing of the final report E & M Seminar preparation Preparing for the presentation of the project Y In-depth understanding of

software

Understanding CAM software, G-code,

Arduino… A & E Software selection Selecting open source and intercompatible

software E

Adapting the software to cylindrical coordinates

Modifying the CAM and slicer softwares to allow for cylindrical printing A Analysis and corrections Simulation of G-code and verification of its

good functioning A Understanding the

requirements

Understanding what components are necessary to ensure control of the actuators M Selecting adapted

components

Selecting the relevant chipboards and servos all while minimisimg cost E General ideas Design concepts and general arrangement of

the printer M

Finalising design Finalising the design of the printer M & Y 3D modelling of the printer Solidworks modelling of the printer with all the

standard parts Y Determining parts to buy From part requirements and assembly choose

parts to purchase All Purchasing of parts Passing orders to purchase the parts, allowing

plenty of time for reception A Receiving of parts Reception and quality testing of parts M Manufacture of parts using

the existing RepRap

From the CAD model, print parts for the building of the cylindrical printer M Manufacture of other parts Manufacture of other parts required for the

printer Y

Assembly Mechanical assembly of the printer and linking it to the electronics E Testing Testing of quality of assembly, response to

command M

Calibrating Calibrating printer parameters to optimise printing speed A Modifying From built device, make modifications to parts

to optimise printing E Printing an object Printing test specimens to prove that the

printer is functioning correctly Y

P u rc h as in g M e ch an ic al May P la n n in g October

Section Name Description Team June

Key Milestones T e st in g P ro gr am m in g C o n tr o l

Completed task: Incomplete task:

November December January Febuary March

M an u fa ct u ri n g April Christmas Holidays Project plan

report Progressreport

Final report, log book and poster

presentation hand in

Seminar

Easter Holidays Exams

Design

Review Seminar Review

II.2 Gantt chart

The time allocations for tasks and milestones in the project are illustrated in a Gantt chart. This chart was updated at various stages to reflect modifications in the project. In order to ensure that each task was completed within the allocated time frame, individual team members were assigned responsibility for specific tasks. Their role was also to ensure the task was delivered on time. Peer review sessions were also marked on the chart to ensure that all deliverables could be checked before their deadline. The most recent Gantt chart (21/04/2013) is shown in table 3 below.

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Figure 8: Total Quality Management criteria [4]

Cross-functional Product Design Supervisor Involvment Strategic Planning Process Management Information and Feedback Supplier quality management Comitted Leadership Team Involvement

II.3 Quality Management

To ensure the quality of the project and to guarantee the planning was respected, the group adopted the Total Quality Management (TQM) philosophy of management. This process revolves around eight main points adapted to this project. These are shown in figure 8 below.

These eight points were central to the elaboration of the quality tables, inspired by Deming’s Plan-Do-Check-Act (PDCA) cycle. Team members were given responsibility for the completion of different stages of each task. The outcome was then checked by a different member to ensure quality and to avoid errors. The quality tables constructed for this purpose are shown in the project plan report [4].

Meetings with all group members present were scheduled three times a week. This was done to ensure that everyone was up to date with the status of the project, and to enable external input to be incorporated in tasks conducted individually. During these sessions running roughly two hours, team members were able to work on their tasks together. This was an effective way to ensure consistent quality and good communication between group members.

These gatherings were supplemented with weekly supervisor meetings. These sessions brought to light any issues with the design, and enabled the team to check whether the direction and scope of the project were consistent with expectations. Suggestions from the supervising team to amend the design were implemented by the appropriate members delegated in the quality plan. A timetable of a typical week is shown in figure 9 below.

Figure 9: Typical Weekly DMT timetable

Finally, two formal peer-reviews were planned to assess the quality of the final design and seminar. These were conducted with two fellow students from other DMT groups. This provided an external perspective and additional ideas for dealing with shortcomings in the design and constructive criticism for the presentation of the seminar.

Monday Tuesday Wednesday Thrursday Friday

A fte rn o o n M o rn in g Supervisor Meeting DMT

Project Work Session 2: Check

task progress Session 1: Set

tasks for week

Session 3: Results and feedback Lectures and study

Lectures and study

DMT Project Work DMT

Project Work Session 2: Check

task progress Session 1: Set

tasks for week

Session 3: Results and feedback Lectures and study

Lectures and study Lectures and study

DMT Project Work

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10 III. DESIGN PROCESS

A large amount of time was voluntarily dedicated to the design process, in order to ensure the final design fulfilled or exceeded engineering requirements. The first section of this chapter shows the elaboration of conceptual designs, culminating in the finalised design of the printer. Subsequent sections showcase the main features of the printer, as well as key design decisions. A more complete explanation of the design choices is explored in the Progress Report [5]. Finally, an assembly drawing of the printer is presented along with the bill of materials.

III.1 Design Evolution

Initial designs were drafted informally during the first weeks of the project. Team members’ contributions were unhindered; to ensure all design possibilities were equally considered. A list of advantages and disadvantages was compiled for each concept in order to distinguish them, and to ensure subsequent iterations would build upon their failings.

III.1.1 FIRST CONCEPT

This design is inspired by the RepRap Mendel printer, which allows for most components to be acquired easily. The X and Z axes are similar to the Mendel, while the Y axis is modified to support a cylindrical print bed operating on a pulley system. Using a bevel gear transmission, a flat print bed can be added on removable rails to allow for Cartesian printing.

III.1.2 SECOND CONCEPT

Deviating from RepRap models, this design was elongated to make more room for the cylindrical print bed. The print head would only move in the X direction while the print bed would be made to rotate and move in the Y direction. This design could also be made to accept a flat print bed.

Large print bed and printing volume

Perspex sheets on edges improve stability

Z Axis not included The print bed is only

supported at one end (risk of deflection)

Enables Cartesian and cylindrical printing

Structure could lack stability Original Mendel dimensions leave little space for a cylindrical print bed

Figure 10: Sketch and Evaluation of the First Concept [5]

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III.1.3 THIRD CONCEPT

This design involved fixing the cylindrical print bed to a movable support, allowing for the whole print bed to move in the Y-axis using a threaded rod linear drive system. The print head is fixed on vertical supports and moves up and down in the Z-axis as well as laterally in the X-axis. This idea was based around exploring the choice of which axes can be fixed.

III.1.4 FINAL CONCEPT

Combining the best features from the initial ideas, this finalised concept was produced. The whole assembly is housed between two end plates and rests on a base. The print head is mounted on a carriage and allowed to move up and down on the Z axis and laterally onthe X-axis. The print bed is fixed in the centre of the assembly, and can be interchanged with several different sized print beds. A support is added on the non-driven end of the print bed to prevent any sagging or axial deflection during printing.

The idea for a Cartesian flat print bed was abandoned as it was deemed unnecessarily complex, and deviated from the original direction of the project. While promising, 4 axis designs were abandoned as they were too complex to be incorporated effectively in a timely manner.

Printhead can move both in X and Z directions

Print bed supported on both sides Hot end and sharp edges are in the open (safety hazard)

Cartesian printing is not included Print head support lacks lateral stiffness

Figure 13: Sketch of the Final Concept [5]

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III.1.5 FINAL DESIGN

Starting from the final concept, a detailed design was drafted over a period of 10 weeks. In order to streamline this process, design tasks were divided into four sections; structural, control, mechanical and electronics & programming. These tasks were conducted in tandem to ensure the design was coherent, and fit requirements. The figure below shows the main features of the printer, and indicates in which section of the report they are explained in more detail.

Vertical axis clamps (III.4): These clamps are used to hold the vertical rails. They

are printed parts from a conventional FDM printer.

Perspex body (III.3): Perspex is the selected body

material because it is a cheap alternative to metal, more aesthetic and does not

compromise the structural integrity of the printer.

Print bed (III.4): The print bed is held in a chuck so

that it can rotate while printing. The print bed can

be changed by unloading the chuck and inserting any

cylinder with appropriate dimensions. The print bed is

covered in polyamide tape for adherence.

Power supply (III.6): The power pack supplies the power to the motors, the Arduino and the heating element. It is placed in a slot

under the print bed for proximity to the motors to

keep wiring neat and for safety of the operator. Vertical axis rails (III.4):

These steel rods are threaded which enables movement of the extruder

head in the vertical axis.

Fixtures (III.4): LM8UU linear bearings enable smooth vertical motion. This

allows for accurate displacement in the vertical

direction. Print head (III.4): The

extruder head deposits molten polymer onto the cylindrical bed in successive

layers to produce printed parts.

Pulley system (III.5): This system uses the appropriate

gears and belt to provide sufficient step-down in motor speed while also limiting any

backlash.

Arduino and RAMPS (III.6): These elements take the instructions provided by the user on the PC and convert them to motor instructions

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Figure 15: Main features of the Perspex Structure

III.3 Structural Design

The structure encompasses the components that support and locate the functional elements of the printer. This mainly comprises of the Perspex body panels, which were carefully designed. Indeed, as they are relatively brittle, they cannot be reworked or modified once sent to the laser cutter. This section explores the overall frame design, develops a more specific design rationale behind the motor plate and discusses fits and tolerances used in this structure.

III.3.1 BODY PANELS

The body panels provide both support and location for the printer’s components. This structure must also limit the vibration that can be caused by moving parts. Perspex is a material that meets these requirements. It can easily be manufactured with high tolerances using a laser cutter. This is important for precisely locating printer components as this process is highly accurate and repeatable.

Other options such as sheet metal and medium density fibre (MDF) were disregarded because they were either hard to manufacture or presented low durability. Perspex provides an elegant solution combining structural stiffness and ease of manufacture, while allowing good visibility during printing.

The structure is formed by six Perspex sheets, which form a pocket under the main printing area. This pocket was implemented in response to supervisor feedback in order to enhance the overall stability of the printer. Vibrations caused by moving parts are reduced further by using 10mm thick Perspex sheets. This pocket also acts as storage for electronic components and the power supply, with cooling provided by ventilation holes. These features are shown in figure 15.

Top plate Shear plate Holes for wires and cables Ventilation holes Base plate Slot for plastic

filament feed Z axis

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The plates are locked into place using a slotting system and fastened using bolts. A more detailed description of the fastening methods can be found in the next section. Clearance holes are cut to fix motors and other components.

Motor Plate: Design for Manufacture

The design of the motor plate is extremely important to the design, as it locates components essential to the alignment of the print bed and its transmission. Like the other body panels, this component was designed specifically to be laser cut. As such, nominal dimensions were adapted using data obtained by conducting tests on the laser cutter. These tests were necessary to achieve the tight tolerances necessary to locate critical components such as the motor and bearings. These precautions were crucial to obtain the printing precision accuracy set in the PDS.

Figure 16: Design of the motor support plate

The shape of the plate is designed to accommodate the supported parts while minimising the use of material. All exposed corners are filleted, in order to reduce stress concentrations and crack formation characteristic of acrylic sheets. This implementation was also deemed necessary from a safety perspective. Corners in contact with other components were left square to promote stability. III.3.2 FASTENING

Proper fastening is paramount to ensure a perfectly rigid structure, and is essential to the quality of printed parts. This is provided in part by slotting the panels together tightly, as shown in figure 17 overleaf.

Slot for the top plate boss

Slot for locating the

rotational axis motor

Slot for the shear plate

boss

Slot for the base plate Bearing housing hole Clearance hole for M4 bolt Filleted edges Bottom plate boss

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Additional fastening is provided by standard M4 bolts located fitted in clearance holes. Square cuts through the body panels enable nuts to be attached and tightened. The conjunction of these two methods the body panels are rigidly secured without imparting excessive bending stresses or sharp cracks in the Perspex. Bolts were preferred to self-tapping screws, which were dismissed due to the brittle nature of Perspex.

For further stability, adhesives are also used between the constituent panels due to Perspex’s compatibility with glue. This forms very strong bonds that eliminate any residual gaps between the panels.

III.3.3 FITS AND TOLERANCES

The connecting slots between the Perspex sheets require tight dimensional accuracy and hence precise dimensions for the Perspex sheet are evaluated. The 10mm sheet is of actual thickness 9.51mm and of satisfactory uniformity (±0.04mm).

Slots between acrylic sheets are designed to have transition fits. This type of fit ensures minimal movement between the parts whilst allowing for the plates to be assembled manually. The transition fits are made such that the nominal sizes of both mating parts are equal. The width of cut of the laser cutting machine is used to compensate the parts before the cut. This ensures the resulting parts are of the required dimension.

The cut by the laser also generates a taper; the cut surface is not perpendicular to the sheet. This is incorporated into the design by orientating the parts during manufacturing to facilitate the assembly of the slotted parts.

Figure 18: Perspex fastening method Figure 17: Body panels slotting system

Square hole containing

nut Bolt

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16 III.4 Control and Transmission

Control and transmission components are key in ensuring high printing accuracy. Motors and transmission methods are carefully selected to minimise backlash. In this section, the reasons behind the selection of the motors are explored in detail as well as an explanation of the transmission design. Finally, the design rationale of the print bed assembly is explained.

III.4.1.1 MOTOR SELECTION

The printer is operated using 5 stepper motors. One is used for the main rotational axis, another for the horizontal X axis, and two are required for the Z axis. Stepper motors are selected as they natively incorporate feedback and have high angular precision. Two different motors are used in the printer, their characteristics and the reasons they were selected are detailed below. The rotational axis has a separate NEMA 23, high accuracy motor.

The requirements for the rotational axis are unique to this printer axis, and precise calculations were necessary to specify the required motor characteristics. The maximum printing radius is 50mm and the required precision of the nozzle is of 0.2mm. From this, the required angular accuracy θ of the print bed is then:

Stepper motors generally come with step sizes of 1.8° or 0.9°, so a 0.9° step motor was selected to minimize gear reduction. This corresponds to a minimal gear reduction of ⁄ .

To ensure quick displacement of the print bed and the nozzle head, an arbitrary minimal angular acceleration of 100rad.s-2 was set. From this, the minimal motor torque M was calculated (with the mass moment of inertia Ig=0.005 kg.m-2, calculated from the chuck and print bed):

The Nanotec ST5709S1208-B (NEMA 23) fulfils these requirements and has a dynamic torque of 1.06N.m. This is higher than the required torque but can be useful to overcome friction in bearings as well as other factors that may increase the required moment [4].

The requirements for the other motors necessary in this project are identical to those in the Mendel RepRap printer. As such, the choice of X and Z axis motors is inspired by those of other RepRap printers. Therefore, FL42STH47-1206AC (NEMA 17) motors are selected. They are rated with an angular accuracy of 1.8° and a torque of 0.44N.m. A picture of the motors is presented in figure 19.

NEMA 17

NEMA 23

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Detailed calculations pertaining to motor selection are presented in Appendix A1.

III.4.1 TRANSMISSION DESIGN

The main transmission of the Y-axis is comprised of a pulley system using a timing belt. The main advantage of this setup over traditional gears is the minimisation of backlash. Indeed, any clearance between mating components would cause an error in the angular position of the print bed. The belt selected is specifically designed to contend with frequent changes of direction, which is particularly relevant for this application. The choice of using a belt also gave the team more flexibility during the design process, as the distance between the pinion and gear could be varied. A rendering of the Y-axis transmission is shown in figure 20 below.

The transmission is designed so that a minimum of 6 teeth are meshed at all times. This implementation is included in order to reduce backlash. The size and module of the transmission and pinion are balanced to satisfy the requirement while limiting the inertial forces caused by large gears. As such, a 15 tooth pinion and a 60 tooth pulley with a module of 3mm were chosen, resulting in a reduction factor of 4. Detailed calculations for the length of the belt are shown in Appendix A1.

III.4.2 PRINT BED ASSEMBLY

The print bed assembly is constituted of multiple components, which together fulfil the requirements set by the PDS. The components of the print bed assembly are matched to the engineering requirements of the printer in figure 21 below.

Figure 20: Belt and pulley arrangement for transmission between the motor and print bed

Pinion Pulley Timing Belt NEMA23 Motor

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The print bed was effectively designed as two separate parts; the bearing housing and the mobile support, shown in figure 22. The former connects the print bed to the transmission, while the latter provides location and support at the other end.

Figure 22: Bearing Housing Assembly (left) and Mobile Support (right)

Bearing Housing

The power from the motor is transmitted through a belt to a pulley as shown in figure 22. To obtain high precision printing, the shaft’s only degree of freedom is rotation. As thermal expansion was identified to be negligible, axial displacement of the shaft was restricted in both directions using a step in the shaft and a bolt and washer. Torque is transmitted from the pulley to the shaft from the pulley using a square key. This solution was preferred to a grub screw, which would be less reliable at relatively high torques.

The shaft is mounted on radial ball bearings enclosed in a bearing housing. This bearing housing guarantees both bearings are aligned. This is crucial to ensure precise rotation of the print bed, as inaccuracies in the bearing alignment are amplified by the length of the print bed. The bearing housing is designed to be manufactured in one session on the same lathe to ensure the bearing bores at both ends are concentric. This arrangement is shown in figure 23 below.

Bearing Housing Assembly Mobile Support Assembly

Figure 23: Section view of rotational axis transmission

Chuck Pulley Shaft Bearing housing Bearing housing support Flange Perspex Bolt

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The bearing housing is supported by the Perspex sheet on one side and by a special support which also axially locates the housing. The bearings are axially located by a specially printed flange as well as steps in the bearing housing. Finally, the chuck is fastened to the shaft using a thread and a bolt. Another option considered was to use a Morse taper and collar to secure the chuck. However, using a thread and bolt provides a more compact solution, as the morse taper is long and heavy. Additionally, the Morse taper requires a relatively strong axial force, typically present in lathes.

Mobile support assembly

The chuck is fixed onto the shaft with a thread and a bolt which fits inside the chuck. This reduces the movement of the chuck and prevents it from rotating on the shaft thread. At its other end, the print bed is supported by the live centre in the mobile support. The printer is designed to accommodate print beds with a maximum diameter of 100mm. To ensure all print beds can be fitted, these all incorporate a 15mm boss at the end held by the chuck.

The print bed is supported at one end by a live centre placed on a mobile support. The purpose of the live support is to limit the deflection of the print bed without hindering the rotation of the print bed. The mobile support the live centre is placed on is free to slide axially, which enables print beds of different lengths to be used with the printer.

In order to obtain perfect alignment of the live centre with the chuck holding the print bed, the deflection of the guide rails is kept to a minimum. This is achieved by using 8mm thick steel rods, and by reducing the weight of the mobile support with a large hole. These implementations lead to a maximum deflection of 0.25mm in the worst case scenario. Detailed calculations for the deflection of the rails are shown in Appendix A1.

Adjustable screws Slide Rails Live Centre Print Bed

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20 III.5 Mechanical Design

III.5.1 PRINT HEAD CARRIAGE

Movement of the print head in the horizontal and vertical directions is achieved through the print head carriage. The carriage is controlled with 3 stepper motors; two for the Z direction and one for the X direction. The mounts and fixtures employed are all designed to be 3D printed, which is necessary to create complex shapes in a minimal time frame.

Two stepper motors performing exactly the same movements are required for the Z axis to ensure the carriage remains level. Alternatively, a belt system could have been used, but this can easily introduce levelling issues due to backlash and frictional losses.

The Z axis stepper motors employ a worm gear system where the carriage mounts ride onto two threaded shafts connected to the stepper motors via rigid shaft couplers. Rotation of the motors translates into linear vertical motion of the carriage through nuts fitted inside the mounts. To add rigidity and locational restraint, two guide rails are clamped to the end Perspex plates. Linear bearings are pressed into the carriage end fixtures. The bearings ride onto the vertical guide rails, contributing to the levelling the assembly.

X axis control is achieved through a stepper motor mounted onto one of the carriage end fixtures. A belt and pulley system translates the rotation of the motor into linear lateral movement of the print head. The belt runs from on fixture to the other, looping around the stepper pulley at one end and bearings at the other. This belt is clamped onto the print head mid length.

End Fixture X-axis Motor Z-Rail Linear Bearings Belt Clamps Pulley Bearings Belt Print Head Assembly Z axis nuts

Figure 25: Print Head Assembly

Figure 26: Print Head Carriage

Threaded Rod Carriage End Fixtures Z-axis Motors

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Extruder

Stepper Motor

Mounting plate

Double bevel gear system

Hobbed Bolt Filament

Filament inlet

III.5.2 PRINT HEAD ASSEMBLY

The print head consists of and extruder and a hot end (nozzle) assembly. The extruder employs an additional stepper motor that, via a double bevel gear system, pulls in filament from the spool into the nozzle. The double bevel gears are necessary to reduce backlash, which would lead to uneven extrusion of the printing material. A spring and bearing system applies tangential force onto the incoming filament against a hobbed bolt. The hobbed bolt is rotated by the stepper motor, pulling in or reversing the filament through the use of sharp teeth cut into the bolt.

The filament is forced into the hot end where it melts on contact with the heated brass nozzle. The nozzle is heated by a resistive heater, and temperature control is achieved through feedback from a thermistor fixed into a recess in the nozzle. The nozzle is threaded onto a PEEK (Poly-ether-ether-ketone) polymer hollow shaft through which the filament passes before melting in the nozzle. A PTFE (poly-tetra-floro-ethene) tube fixed inside the PEEK shaft acts as a filament guide as it can withstand the heat without melting and provides a sleek, no stick surface.

PEEK Mount

Brass Nozzle PTFE Sleeve

Figure 27: Extruder Features

Figure 28: Hot End Assembly

Spring pressure system

Wade Extruder Hot end Gripping Teeth Hobbed Bolt

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Figure 29: PLA Spool mount

Printing starts when the nozzle reaches the required temperature and filament flow is controlled by the extruder stepper motor. In addition to forcing the filament into the nozzle for extrusion, the extruder assembly can also reverse and pull the filament back, preventing the polymer melt from dripping while the print head rapidly moves from one position to the other.

III.4.4 PRINT MATERIAL SELECTION

Selecting an appropriate printing material is an important decision as it has an influence on certain components of the printer such as the print head, extruder gears and the print bed. While the design can be used with a variety of print materials, one was prioritised for the sake of the design. The first consideration for material selection is the availability of the material in filament form. Only PLA and ABS are readily available and for a reasonable price. Table 4 draws a list of the pros and cons of both materials to determine the most adequate one for cylindrical printing. These are weighted and scored with a maximum weighted total of 1000.

Table 4: Criteria and importance for material selection

Criteria PLA ABS

Description Weight Description Score Description Score

Warping Resistance 8 High 50 Low 5

Cost of Material 2 Inexpensive 35 Inexpensive 35

Heat Settings Required 2 Lower; 160-220⁰C 25 Higher; 215-250⁰C 10 Extrusion Facility 4 High force required 15 Moderate force 25

Mechanical Properties 4 Mediocre 15 Superior 30

Weighted Total 640‰ Weighted Total 350‰

Table 4 stresses the importance of the material stability at different temperatures. Choosing ABS would require a heated print bed, adding complexity to the project. Printing an ABS part on a cold bed would result in significant warping and the possibility of the printed object falling off the print bed during the printing process. From this analysis PLA is chosen as the printing material thanks to its limited warping and lower glass transition temperature. The printer is designed to accommodate for PLA, however ABS can still be used if necessary by tweaking the slicing software parameters. The PLA filament is wound around an overhung spool mounted onto a simple bearing system to ensure continuous, unhindered delivery of the filament. The filament is then guided via adhesive clamps attached to the Perspex frame, through a slot cut into the top plate and into the extruder assembly.

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Slicing Software Printer Interface

Micro-controller Circuit Board

Alternatives

.STL file _{.GCode File} _Commands

Signal Printer Commands Corresponding Modifications Main Components Edit slicing code for cylindrical coordinates Manually modify Gcode to adapt to geometry Rewrite firmware to adapt to cylindrical coordinates Calibrate motor drivers and thermistors Slic3r (Pearl) Pronterface, Reoplicator G (Interchangeable) Sanguinolu (Intergrated) RAMPS (Marlin, Sprinter) Arduino Mega, Duo or Uno (C) Skeinforge (Python)

III.5 Electronics and Programming

Unlike the mechanical and structural design, much of the electronics and software aspects of the project are constructed using pre-existing solutions. On top of this, several modifications are implemented to tailor the equipment to the specifics of the project. The flowchart below presents the key tasks and deliverables that must be fulfilled by the electronics and software. Alternatives considered during the design process are also presented, and accompanied with requirements and modifications unique to our project. This is presented in figure 30.

The hardware and software can be divided into 3 main sections; PC software, printer hardware, and printer firmware. These aspects are presented below, along with key design decisions.

III.5.1 PC SOFTWARE

The first task fulfilled by the PC software is the conversion of an .STL file to G-Code which can be sent and processed by the printer firmware. While a variety of software packages can fulfil this role, an additional objective of the project is to explore the feasibility of a custom slicing procedure to enable printing in cylindrical coordinates. In order to fulfil these two objectives, the printer uses two different software; Skeinforge and Slic3r. An interaction matrix was used to highlight the differences between these two programs, while showing the uses best adapted to each one.

Table 5: Software Selection Matrix

Criteria Skeinforge Slic3r

Description Weight Description Score Description Score

Programming

Language 5 Python 35 Perl 50

Options 3 Exhaustive 45 Basic 25

Support 2 User Forum 30 User+Developer Forum 40

Access 3 Files on Github 30 Open Source File 40

Weighted Total 700‰ Weighted Total 730‰

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As demonstrated, Skeinforge presents more flexibility due to the variety of built in options. Conversely, Slic3r offers much less functionality, but has a simple coding structure which can be edited more easily. For these reasons, Skeinforge was primarily used to generate G-Code, while Slic3r was also used to explore the possibility of implementing a cylindrical slicing procedure by editing the program’s source code. The main functionalities of Slic3r are presented in figure 31.

A separate program is used to send the G-Code file created by the slicing program directly to the printer. This is achieved using Printrun (Pronterface). Unlike its alternatives, Printrun is not constructed with a particular model of 3D Printer in mind, meaning that many more settings are left to the user. A key feature is that G-Code files sent to the printer can be overridden at any time simply by typing G-Code commands into the user interface. A variety of common G-Code commands were gathered to enable small mistakes to be corrected and without stopping the printer to re-upload a new G-Code file. A screenshot of the Printrun interface is presented figure 32.

Figure 32: Printrun interface and settings

GCode can be sent manually to the printer Printhead trajectory can be visualised beforehand Estimation of print duration

Figure 31: Slic3r user interface and settings

Multiple parts can processed at once Print settings are easily stored and managed Orientati on errors can be quickly spotted in the preview

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III.5.2 HARDWARE SELECTION

The main role fulfilled by the hardware on the printer is to receive and interpret G-Code commands to control the motors and heating element using feedback from the endstops and thermistors. These tasks are fulfilled by combining an Arduino Mega microcontroller to a RAMPS module (RepRap Mega Pololu Shield). The Arduino is used to relay commands from the PC to the RAMPS. The RAMPS is fitted with stepper motor drivers and connected to a power source in order to control the printer. This setup is shown in figure 33 below.

The RAMPS is fitted to a 12V 360W power supply to power to stepper motor drivers and heating element. Although our calculations showed that the RAMPS would draw no more than 13A at peak operation, and that a 240W source would have been sufficient, higher capacity was selected to ensure fans and additional motors could be added if necessary in the future. In particular, the possibility of adding a small blow heater was considered as an alternative to the heated print beds in traditional 3D printers.

One of the specificities of our design compared to Cartesian 3D printers is that the range in the Y direction (print bed rotation) is virtually unlimited. In some components, the print bed is rotated continuously during the entire printing job. For this reason, the Y axis motor is typically active for extensive amounts of time. In order to prevent the stepper motors from overheating due to this phenomenon, these were fitted with straight-fin heat sinks using thermal tape, as shown in figure 34 below. Stepper motor drivers USB connection to Arduino Power Supply to RAMPS

Figure 33: Arduino and RAMPS setup

Straight-fin heat sink Straight-fin heat sink Current can be adjusted with a screw

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The setup outlined above was chosen over a Sanguinolu, a cheaper all-in-one alternative designed specifically for 3D printers. However, the Sanguinolu can only hold 4 stepper motor drivers. Given that one of these drivers must be used to control the extruder motor, and that two motors are needed for the Z-Axis, this limitation rules out the possibility of creating a 4-axis machine. Although a 4-axis machine was not strictly necessary given the design specifications, the Sanguinolu offered fewer options for overall upgradability and flexibility. Furthermore, although buying a Sanguinolu could save us £20, the cost of the Arduino and RAMPS was well within our costing plan, and would present a more versatile basis for potential upgrades in the future.

III.5.3 WIRING AND SETUP

A schematic of the RAMPS wiring to the printer components is presented in figure 35 below. Although the endstop for the Y axis (rotation of the print bed) is not needed for location purposes, leaving it out would have caused several conflicts in the Arduino firmware.

III.5.4 PRINTER FIRMWARE

The firmware used to control the printer is stored on the Arduino and written in C. The main role of this firmware is to interpret G-Code commands to control the motors and heating elements while incorporating feedback from thermistors and endstops. This role is fulfilled by the open-source firmware Marlin, which is used with many traditional 3D printers.

Unlike some firmware developed specifically for commercial 3D printers, a large amount of settings used by Marlin can be changed by editing the firmware code. Given that one of the main challenges associated to this project is to adapt Cartesian coordinated into cylindrical ones, this aspect of the firmware is fundamental.

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The Marlin software was chosen over the firmware used by the other 3D printer in the Polymer Processing lab, Sprinter. Although Sprinter has many of the advantages associated to Marlin outlined above, some underlying settings in its coding give printed parts a different aspect.

The choice to use Marlin was done by printing two identical parts using both firmware. These parts are shown in figure 36 below.

As shown above, parts printed with Marlin have a superior surface finish compared to parts printed with the Sprinter firmware. Additionally, the irregular surface of the latter was identified as a source of embrittlement, and an overall lower quality. Given the similar format between the two firmware codes, a separate version of Sprinter was kept up to date with the latest settings as a backup. III.5.5 SOFTWARE MODIFICATION

One of the objectives set by the team at the start at the project was to explore the possibility of writing a custom slicing procedure for cylindrical coordinates. While this implementation was not required for the purpose of the project, it would prove essential for the cylindrical printer to be used on a regular basis. A diagram comparing traditional (Cartesian) and cylindrical slicing is shown in figure 37 [6].

The preferred method to achieve this goal was to edit Slic3r source code to accommodate cylindrical coordinates. The first task undertaken to this effect was to divide the source code into main functional blocks, in order to identify which portions of the code would need to be edited or revised.

Figure 37: Comparison of Cartesian and Cylindrical Slicing [6]

Printed with Sprinter:

uneven surface

Figure 36: Identical parts printed with Sprinter (left) and Marlin (right)

Printed with Marlin: smooth surface

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The Slic3r program accesses the Slic3r.pm module in order to carry out the main functions delivered by the program. These “main” modules are the ones which slice the solid model into a physical trajectory. Additionally, post-processing modules are used to create the G-Code, while incorporating user settings such as filament width and extruders speed. Finally, test files are used for development purposes to assess the performance of these modules on an individual basis. A simplified layout of the Slic3r source constructed for this purpose is shown in figure 38 below.

The sections of the code requiring modification form a large proportion of the main modules, and to a lesser extent, some of the post-processing modules. These are outlined in orange in figure 38 above. In particular, the elements determining the geometry and extrusion path would require most attention.

A modified slicing procedure was outlined conceptually. This procedure was inspired by literature on Cartesian slicing, as well as a variety of papers on novel slicing methods. The method is based on iteration: each layer is processed separately, and “flattened out” onto a Cartesian plane. Once the polygons for this layer have been constructed, the extrusion path is computed, and projected onto a surface of radius R. This operation is repeated for each successive layer as the projection radius is increased, in order to form a cylindrical shape.

This method is only valid since the solid model is deconstructed into relatively thin layers (less than δ=1mm). One key consideration is that as R is incremented, the total printing surface is increased by a factor 2πδ, and the amount of material deposited must be varied accordingly.

The main advantage of this approach is that it can make use of many of the existing features in available slicing programs, since most operations are carried out in a Cartesian plane. A simplified flowchart of this procedure is presented in figure 39 overleaf.

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Upon inspection of the source code, many of the new functions which need to be implemented necessitate the modification of several subroutines forming part of the Slic3r program. One of these subroutines is presented in figure 40 below.

This particular subroutine participates to the elaboration of a polygon map. The Slic3r program is constructed in a way in which all programs are interdependent, and changes made to one section of the code must be adapted to all its linked routines. The changes needed to use cylindrical coordinates are fundamental in nature, and our examination of the code revealed that their implementation would require more modification than could be achieved through tweaking.

In light of these observations, the custom slicing procedure drafted cannot be easily included into the existing code. While this would be possible in theory, a more efficient approach would be to rewrite a program from scratch. This time investment would allow creating a program specifically for this purpose. Alternatively, software used for CNC lathes could be used as a more adapted starting point. However, the source code for these programs is not openly available.

As a result, for the purpose of this project, cylindrical parts are constructed by constructing extrusion paths using alternative methods, rather than by using a cylindrical slicing procedure. These methods are outlined in section V.2.

Figure 40: Excerpt of Perl Code for one of the Slic3r Subroutines from Geometry. Figure 39: Cylindrical Coordinates Slicing procedure (REF)

Variables are set as part of the subroutine Routines are linked together

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30 IV. MANUFACTURING AND ASSEMBLY

While a substantial amount of the parts were purchased, unique components such as the Perspex plates and those relating to the print bed assembly were manufactured. This section gives an account of how the parts used in the printer were manufactured. Explanations relating to the assembly and calibration of the printer are also presented.

IV.1 Perspex Structure

One of the key parts to be manufactured was the Perspex structure. As they provide both support and location for many of the printer’s components, the Perspex sheets required high precision manufacturing. The Perspex sheets fit together using slots with tightly toleranced transition fits. LASER CUTTING TESTS

One concern was that the width of the laser in the laser cutting machine would increase the actual size of cut and increase clearances. To evaluate the laser width, three test samples were cut and measured. The data and calculations related to these tests are presented in Appendix A1.

The first test was carried out on a Perspex sheet of thickness 6mm. The aim of this test was to evaluate how repeatable the laser cutter was and to get an idea of the surface finish that could be achieved. The width of the laser cutter was determined by comparing the actual dimension of the cuts to the one set in the solid model. The cutting accuracy was determined to be 0.27mm. A second test was carried out, this time on the sheet used for the printer. Two test parts that slot into each other were made in order to test the transition fit. The test yielded a laser width of 0.43mm which was different from the previous results. This was attributed to the fact that a new Perspex sheet with slightly different material properties and thickness was used.

Following these tests, the laser cutter broke down and the lens was replaced. Due to the high tolerances required for the transition fit, a final test was undertaken to evaluate the impact of this change. This time a simple slot and fit were made. The fit was tight and worked correctly. However, the laser width now changed to 0.28mm. This was the value that was retained for the final design and is compensated for on the solid model that was sent for manufacture. All test parts confirmed the need for compensating however the cutter was very repeatable (±0.03mm). The test parts also displayed the evidence of a tap of around 0.05mm throughout the 10mm thick Perspex. The final parts were cut in order to use this tap to facilitate manual assembly.

PERSPEX SHEET LAYOUT

Given the high price of the Perspex sheets, an optimal layout was determined to minimise the

Figure 41: Laser Cutter Test Part 1

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amount of Perspex necessary to print all the parts. Additional space was added to enable parts to be recut if any errors were made. This resulted in the purchasing of a 1000×750x10mm sheet.

IV.2 Printed Parts

The required printed parts were initially to be purchased as they are usually sold in sets. However access to the 3D printers on campus provided the added design flexibility of printing custom parts tailored to the cylindrical printer. Shown below are some of the .STL files used to print the required parts.

Another aspect to consider was the material from which the parts could be made. PLA and ABS plastics are the most widely used polymers as they are ideally suited for 3D printing. ABS, having slightly better mechanical properties than PLA, is preferable for parts subjected to high stresses. Due to limited access to ABS printing filament, the only option of obtaining highly stressed parts was through purchasing. The parts that were not easily available for purchasing online were made using a printer provided by the Imperial College Robotics Society (ICRS). All remaining parts were printed using PLA with the printer in the Polymer Processing Laboratory (PPL) in the Mechanical Engineering Department. Figure 43 below shows a summary of how the printed parts were obtained and from which polymer they were printed.

Figure 43: Origin of 3D printed parts

Printed Part Material Acquisition

Carriage ABS Printed by ICRS

Z-Clamp ABS Printed by ICRS

Z-Clamp (Short) ABS Printed by ICRS

Clamp Top ABS Printed by ICRS

Endstop Mount ABS Printed by ICRS

Bearing Flange PLA Printed in PPL

Guide Rail Washer PLA Printed in PPL

X-Belt Clamp ABS Printed by ICRS

X-Belt Guide ABS Printed by ICRS

X-Belt Tensioner PLA Printed in PPL

X-Carriage Mount ABS Printed by ICRS

X-Carriage Mount (Motor) ABS Printed by ICRS

Extruder Assembly PLA Purchased Online

Lathe-Type 3D Printer