Development of a Plastic
ShredderRasmus Ekman
DIVISION OF PRODUCT DEVELOPMENT | DEPARTMENT OF DESIGN SCIENCES
FACULTY OF ENGINEERING LTH | LUND UNIVERSITY
2018

MASTER THESISDevelopment of a Plastic Shredder

Rasmus Ekman

Development of a Plastic Shredder
Copyright © 2018 Rasmus Ekman
Published by
Department of Design Sciences
Faculty of Engineering LTH, Lund University
P.O. Box 118, SE-221 00 Lund, Sweden

Subject: Machine Design for Engineers (MMK820)
Division: Product Development
Supervisor: Olaf Diegel
Examiner: Giorgos Nikoleris

Abstract

This report covers a project for the Division of Product Development at Lund
University to build and further develop a plastic shredder. It was based on opensource blueprints from the Precious Plastic machine series, a nonprofit project byDave Hakkens to reduce plastic waste. Its purpose is to shred common plastic waste
so that the shreds can be remelt to create new products by students in the subsequentmachines of the series. The main goals of the project were to build the shredder at
minimum cost and to develop an improved version after testing it. It was built using
in-house machines at the schools workshop and is powered by a gearmotor buildfrom parts found at a local junkyard. Minor modifications were made of the original
designs to improve handling and assembling of the machine. The gearmotor and its
electronics were also built on a separate platform to create a modularized unit thatis easily detached if desired to be used in other applications.
The shredder worked as intended but caused some difficulties during assembly. The
redesign addressed this issue aswell as increased the rate of cutting action bymodifying the knives and counterknives. Due to lack of time and restricted funds,
an actual version of this redesign was never built and tested.
Keywords: Product Development, Plastic, Waste, Shredder, Recycling

Sammanfattning

Den här rapporten behandlar ett projekt hos avdelningen för produktutveckling vid
Lunds Universitet för att bygga och vidareutveckla en flismaskin för plast. Den
baserade på open-source ritningar från Precious Plastics maskinserie, ett ideellt
projekt av Dave Hakkens för att reducera plastavfall. Dess syfte är att flisa vanligt
plastavfall så att flisorna kan smältas om för att skapa nya produkter av studenter ide följande maskinerna i serien. Projektets huvudmål var att bygga flismaskinen tillminimal kostnad och att utveckla en förbättrad version efter att ha testat den. Den
byggdes med hjälp av lokala maskiner i skolans verkstad och drivs av en växelmotor
som byggdes av delar som hittades hos en lokal skrothandlare. Mindre
modifikationer av originalritningarna gjordes för att förbättra hanteringen ochmonteringen av maskinen. Växelmotorn och dess elektronik byggdes även på enseparat plattform för att skapa en modulariserad enhet som är enkel att avskilja om
den önskas användas i andra syften.
Flismaskinen fungerade som tänkt men skapade vissa svårigheter undermonteringen. Den nya designen adresserade detta problemet såväl som ökade
skärfrekvensen genom att modifiera knivarna och motknivarna. I brist av tid och
begränsat kapital byggdes och testades aldrig en faktisk version av den nya
designen.
Nyckelord: Produktutveckling, Plast, Avfall, Flismaskin, ÅtervinningPreface

I would like to thank Professor Olaf Diegel for giving me the opportunity to do thisproject for the Division of Product Development and for the assistance he gave me
as supervisor of this project. Im also grateful to Johannes Ekdahl du Rietz andGiorgos Nikoleris for helping me with the electronic connections, in which I
realized I was hopelessly lost.
A special thank you is in order to all the instructors of the ID-A workshop at IKDC
who helped me untiringly. Whether I needed parts machined that I could not domyself or just someone to discuss technical difficulties with, they were there.

Lund, March 2018
Rasmus Ekman

Table of contents

Introduction ............................................................................................................. 1
1.1 Precious Plastic.............................................................................................. 1
1.2 Background ................................................................................................... 1
1.3 Aims and purpose .......................................................................................... 2
1.4 Scope ............................................................................................................. 2
1.5 Limitations..................................................................................................... 3
2 Method.................................................................................................................. 4
2.1 Project Plan.................................................................................................... 4
2.2 Pre-Study ....................................................................................................... 4
Provided Material ................................................................................... 4
Industrial Shredders ................................................................................ 4
2.3 Development Method for the Redesign ......................................................... 5
Gradual refinement of a new design ....................................................... 5
Building the new design ......................................................................... 5
Final Design............................................................................................ 5
3 Pre-study............................................................................................................... 6
3.1 Provided Material .......................................................................................... 6
Framework.............................................................................................. 7
Shredder Sub-part ................................................................................... 7
PSU......................................................................................................... 8
3.2 Industrial Shredders ....................................................................................... 8
Shafts ...................................................................................................... 9
Knives ..................................................................................................... 9
4 Building the Machine ......................................................................................... 12
4.1 PSU.............................................................................................................. 12

Worm Drive .......................................................................................... 13
Belt drive .............................................................................................. 17
Gear Reducer ........................................................................................ 19
PSU connection .................................................................................... 25
Paint and coating .................................................................................. 28
4.2 Shredder sub-part ........................................................................................ 30
Cutting the parts. .................................................................................. 30
Knife shaft ............................................................................................ 31
Knife configuration .............................................................................. 31
Assembling the SSP ............................................................................. 32
4.3 Framework................................................................................................... 33
4.4 PSU to SSP connection ............................................................................... 35
4.5 Hopper ......................................................................................................... 36
4.6 Electronics ................................................................................................... 37
4.7 Finishing ...................................................................................................... 37
5 Testing ................................................................................................................ 42
5.1 Different sieves............................................................................................ 42
5.2 Types of plastic waste ................................................................................. 45
5.3 Result of knife configuration ....................................................................... 46
6 Redesign ............................................................................................................. 47
6.1 Number of shafts ......................................................................................... 47
6.2 Knives.......................................................................................................... 47
6.3 Increasing the speed of the process ............................................................. 48
More cutting actions ............................................................................. 49
Housing ................................................................................................ 50
Bearing bolts......................................................................................... 52
Sieve ..................................................................................................... 53
Final design .......................................................................................... 54
Additional changes made to Hakkens design during building ............. 55
7 Discussion .......................................................................................................... 58

8 Conclusion .......................................................................................................... 61
References ............................................................................................................. 62
Appendix A Project Plan ....................................................................................... 64
Appendix B – Bill of Materials ............................................................................. 67
Appendix C - Power transmission per belt ............................................................ 68

Introduction

This first introductory chapter is meant to give an insight into the company fromwhich the basis of my master thesis stems, the goals of this project and thelimitations to how far the development process will be completed.

1.1 Precious Plastic
Precious Plastic is an open-source project that was started in 2013 by Dutch designerDave Hakkens [1]. The idea was to make a series of machines that were to decrease
the problem of plastic waste throughout the world by reshaping it into new products
on a local basis. Hakkens suggested that people all over the world could build theirown production line and pay the local citizens a small fee according to the weightof the raw material they bring to the workshop [2].
Version 1.0 was merely a proof of concept for his graduation project at Design
Academy in Eindhoven. More people got involved to help develop version 2.0 to
make them easier to build using basic materials that are available worldwide [1].
The blueprints and instructions were then shared freely at his website and he madea forum to form a community of machine developers that give feedback and help
each other with problems that may arise during the construction phase and as asource of inspiration for further uses. The machine that was built and developed inthis thesis is based on this version.

1.2 Background
The machine series was noticed by Olaf Diegel, Head of Division of ProductDevelopment at Lund University. He wanted students to build the machine series
for the benefit of the school so that other student could make simple products out ofrecycled plastic for other project courses. The series comprises a total of fourmachines: shredding, injection, compression and extrusion machines. The threelatter are dependent on the output of the shredder. They melt and reshape the plastic
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flakes that the shredder creates from the plastic waste. As this would be the firstmachine of the series to be built at the school, our top priority was therefore to build
a good and functioning shredder to have a foundation for other students to buildupon.

1.3 Aims and purpose
Hakkens was clear in his instructions that the Precious Plastic machines are not
perfect and so is under ongoing development by the community. Consequently,
problems were expected to arise during construction and testing since variations indimensions and tolerance will depend on the precision of the material supplier andmanufacturing methods. Since the blueprints only cover the actual shredder-part anda general framework, the actual setup would have to be modified to fit whatever
power supply unit (PSU) that was finally used.
To summarize, the main objectives of the project were to:






Build a functioning shredding machine for plastics waste.
Make an easily detachable modular PSU that can be used for other futureapplications.
Redevelop the shredder to improve performance, output quality, assembly
and/or user-friendliness, after testing of the machine.
If possible, rebuild the machine with the new improvements.
Minimize building cost.

1.4 Scope
The project ranged from the complete building and testing of the plastic shredder
provided by Hakkens to development of a new design of the shredder. Ultimately,
the goal was to build a physical and functioning version of the new design of theshredder.
No deeper analysis was made of the throughput of the machine in any of its versions
other than a cursory examination if the desired functionality is fulfilled.
To keep the costs to a minimum, the building of the machine was exclusively donein the schools workshop at IKDC, Lund.

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1.5 Limitations
The costs were not calculated as a considerable part of the machining was carriedout by the supervisors of the workshop when they were available. This was done
inbetween other work which made it difficult to assess the time spent on my project
and the corresponding costs. Besides, the majority of the costs were that of the PSU
and as such is highly dependent on what is available and varies greatly.
The project did not comprise any type of manual for the machine or protocols
regarding safety in operating or handling the machine. It is up to any user of themachine to use it responsibly and exercise caution on personal safety and integrityof the machine.
No CAD models were analyzed by FEM-based programs as the forces acting on theshredder would be too difficult to anticipate and model which would likely lead toirrelevant results.

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2 Method

The purpose of this chapter is to give insight into the methodology used during thecourse of the project. As it was of a more practical nature than most other mastertheses, the methodology that was found best suited turned out to be less theoreticaland strict than what might normally be the case.

2.1 Project Plan
The actual building of the machine involved several manufacturing steps that I
lacked practical experience with and so had to be done in part by the workshops
supervisors. The unregular accessibility of certain machines made it difficult to nail
down a precise project plan to follow. Consequently, at the start up of the project avery loose plan was made, see Appendix A, with expected milestones to aim
towards. This was intended to be amended as the project progressed.

2.2 Pre-Study
Provided Material
Before construction of the individual parts of the machine, it was decided that a
study of the provided blueprints and CAD-drawings would be undertaken. This
would give better understanding of how it was constructed and an oppotunity to
discover areas that could potentially cause problem during assembly. The Precious
Plastic forum, where other machine builders around the world post about theirprogress and problems that they encountered, would also be studied to this end.

Industrial Shredders
During construction phase of the provided original design, a study of current in-use
shredders designed for different purposes would be made to draw inspiration for thefollowing redesign of my own shredder.
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A study of the machine builds posted on the Precious Plastic forum by other people
could also give valuable insight into positives and negatives on the current design
and ideas for change.

2.3 Development Method for the Redesign
After a cursory study of the way these machines are built, it was realized that thedifferent possibilities of configuration are considerably limited. Therefore, it was
decided not to use the typical product development process taught by the school andformulated by Ulrich & Eppinger [3].

Gradual refinement of a new design
It was concluded that the most practical approach would be a very simple design
strategy. A few general construction ideas would be formulated and then evaluatedat that level. The ones that suited the projects particular situation and limitations
would then be refined further until a final version could be devised.

Building the new design
Ideally, there would be enough time to build the previously mentioned new designin actual scale and materials. Assuming that the original design would function
despite prospective flaws, the option to build this new version would largely comedown to a matter of cost. If built, the new design would be tested and compared tothe previously built version.

Final Design
If needed, a final design would be made to solve any resulting problems arising in
the previous testing. This last version were, however, not planned to be built due tothe aforementioned financial limitations. An illustration using a CAD model would
likely suffice to show any design changes at this stage.

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3 Pre-study

This chapter presents the result of the pre-study described in chapter 2.2.

3.1 Provided Material
The material provided by Precious Plastic to build the shredder can be found athttps://github.com/hakkens/precious-plastic-kit/archive/master.zip and containeverything needed to build any of the four machines, complemented by the
instruction videos on their homepage https://preciousplastic.com/en/videos/. See
Figure 3.1 for an overview of a shredder built by Precious Plastic.

Figure 3.1 A general view of the shredder as built by Precious Plastic.

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Framework
The first observation made while studying the material was that the framework
would have to be modified to fit whatever setup of PSU was to use. Furthermore,
the raised platform that is meant to support the shredder sub-part (SSP) would haveto be either very carefully measured to maintain axis alignment of the SSP shaft and
the PSU output shaft or another design should be used. Any misalignment would
cause unnecessary strain on the bearings. A, by such radial forces, gradual looseningof the bolts securing the positioning of the SSP shaft could, in a worst-case-scenario,
cause the knives to strike solidly into the counterknives, see Figure 3.2, and destroy
the machine.

Figure 3.2 SSP where knives (green) and counterknives (red) are marked.

Shredder Sub-part
The main issue seen in the SSP were the puzzle shaped connectors between the
different parts of the housing, as seen in Figure 3.3. Many of the parts that aresupposed to fit together tightly are designed with no gaps, i.e. a 10.0 mm wide malepart is designed to fit with a 10.0 mm wide female part.

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Figure 3.3 Two pieces with puzzle shaped connectors. Slits dependent on sheet metal thickness
marked by arrow.

The precision of the manufacturing method would greatly influence the outcome of
the fitting. Another influencing factor is the precision of the manufacturer of the
sheet metal as some fittings were dependent on this, i.e. the slits marked by a redarrow in Figure 3.3 where the width of the slits corresponds to the sheet thicknessof the connecting part.

PSU
As noted in the Bill of Materials from Precious Plastic, see Appendix B, thespecifications of the PSU call for a motor with a power of ~ 2 kW and an output
speed ~ 70 RPM. That would result in a torque of around 300 Nm at the output shaft.
Posts at the Precious Plastic forum told of builders that used other configurations
with less power and had mixed results. My conclusions were that 300 Nm is
probably more than what is actually necessary. I would, however, try to get as close
as I could to ensure that the machine does not clog and stop if I try to shred thicker
pieces of plastic.

3.2 Industrial Shredders
By investigating a multitude of different industrial shredders I realized that they allbuild on the same principle, with different configurations of two key aspects basedon the application of the machine.

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Shafts
The most basic disparity between the different designs is the number of knife shafts.
Most of the shredders studied were either single or double shafted but some heavyduty ones were even made with four. The obvious advantage of having several knife
shafts is of course that the number of cutting actions at any given time increases
with the number of shafts which increases the speed of the process. The majoradvantage with several shafts, however, seemed to be a noticable increase in its
ability to pull material through the machine. When comparing them to videos of
Hakken testing his machine, they appeard to have much less problems with thematerial to be shredded skipping on top of the knives.

Figure 3.4 Four shaft shredder

Knives
The second attribute that usually differs is the design of the knives themselves. Thisis highly dependent on the application they are to be used for. Heavy-duty shredding
such as cars, engine blocks, transmissions and other large metal pieces require theknives to be thicker and smaller, coupled with a slower speed to increase torque.
The number of teeth also affects the performance of the machine. More teeth meanfaster cutting; but it also increases the risk of the object to be shredded skipping on
top of the knives, as well as the risk of clogging the machine and thus forcing areverse of the spin direction. If the knives have too many teeth the machine may not
be able to shred tougher objects as more teeth will be engaged at any time.
Most machines use one of two tooth designs with minor variations. The first is in
the general shape of a hook where the cutting edges are square. The Precious Plastic
knives are based on this design, albeit a bit different than most other blades, see
Figure 3.5. Typically, the hook is made with a straight cutting edge and a straight orrounded supporting back, as seen in Figure 3.5. Hakkens used a curved cutting edge
9

instead. The other type uses triangularly shaped teeth and similarly shaped
counterknives, see Figure 3.6.

Figure 3.5 Left: shredder knives as designed by Precious Plastic. Right: Assorted industrial
shredder knives.

Figure 3.6 Triangular teeth and counterknives.

As seen in Figure 3.6 many high end shredding machines use easily replaceable
cutting edges to improve maintenance and longevity.
There are a few other variations typically adapted to the specific task they perform.
One such is a paper shredder. As the main purpose is not only to reduce it to smaller
pieces but also to destroy the information contained on it, the paper needs to be
reduced to small enough pieces that the text and images become unintelligible. As
the paper does not cause much resistance, these machines can be designed with alarger amount of blades that are much thinner. If shredding the papers into strips isenough, a simple dual-shaft design with completely round knives would suffice.
10

Should a finer shred be needed, the previously described hook-blades are analternative, see Figure 3.7.

Figure 3.7 Paper shredder with hook knives.

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4 Building the MachineThis chapter covers the entire building phase of the shredder by Precious Plastic
with some changes made to the design.

4.1 PSU
Based on the specifications and the load application it was decided that a geared
motor would be best suited for the task. Dave Hakkens uses an angular geared motorin his setup, as seen in Figure 4.1, that he found on a local junkyard, albeit with alower speed than the specified. Based on his instruction videos its speed wasapproximated to ~35 RPM.

Figure 4.1 Dave Hakkens angular geared motor.

12Worm Drive
The first plan was to buy a used motor and connect it to a new worm gear from
Liljenbergs AB, shown in Figure 4.2; they were reasonably priced and had highreduction ratios.

Figure 4.2 Worm gear from Liljenbergs AB.

A worm gear of similar type from Mekanex AB is supposed to handle max torquesof 1050 Nm [4]. The output shaft would then be connected to the knife shaft usinga jaw coupling, see Figure 4.3.

Figure 4.3 Jaw coupling.

These couplings are designed to be able to transfer large amounts of torque, as myapplication requires. The flexibility of the elastomer spider between the two claws
also allow a maximum misalignment of the two shafts of 0.9° [5]. This would makethe assembly a little bit easier. I found a motor, see Figure 4.4, at a local junkyard
with adequate power, see Figure 4.5, for 200 SEK.

13

Figure 4.4 Used motor from a local junkyard.

Figure 4.5 Rating plate of the motor.

It had previously been used as a pump so the pump housing had to be removed. A
lot of time was spent getting rid of the impeller that had rusted onto the motor,
without damaging the underlying shaft, see Figure 4.6. After connecting the motor
through a protective circuit breaker, see Figure 4.7, it ran without fault.
14

Figure 4.6 Motor after removing the pumphouse and part of the impeller.

Figure 4.7 Motor connected to a protective circuit breaker.

However, when Liljenbergs was called to place an order for the worm gear, the sales
representative informed that those were not dimensioned to handle such forces andthat worm gears are unsuited for this application. They work by using a screw15

shaped gear, called worm, to drive a larger gear, called worm gear, as can be seenin Figure 4.8. Ideally, the worm is made of hardened alloy steel and the worm gearof phosphor bronze [6].

Figure 4.8 The basic setup of a worm gear.

Besides offering a compact way to achieve high reductions ratios, this design works
as a kind of brake. The worm can drive the large wheel in both directions but theoutput shaft cannot drive the worm shaft. The sharp angles of the worm’s teeth
produce enough friction to lock the two gears together, resulting in the worm geartrying to shear off the teeth of the worm. This function does not affect my particularsituation though, as there is no risk of external forces driving the knife shaft.
However, since worm drive works entirely through a sliding frictional contact
between the gears, the system requires highly specified lubrication with highviscosity which makes it unsuited for this relatively simple machine [7]. According
to Liljenbergs it would instead be better to look for a coaxial gearmotor, as seen in
Figure 4.9.

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Figure 4.9 Coaxial gearmotor.

That turned out to be hard to find at low enough price. An offer for a new such from
Liljenbergs showed a total cost of 13950 SEK + 25% VAT and additional freight
cost, which would definitely be too much as the costs needed to be kept to aminimum. Most used gearmotors with a speed similar to the recommendation turned
out to have too low power output. Alternatively, a used gearmotor could be foundand then change the motor to the one already bought. Unfortunately, the motors
speed of 2820 RPM, as seen in Figure 4.5, is unusually high which forces a higher
reduction ratio of i:40 to reach 70 RPM on the output shaft. This turned out to be
hard to find in a strong enough design.

Belt drive
It was decided to instead use a V-belt drive transmission, also called friction drive,
see Figure 4.10 (left), as I could more or less easily modify the framework toaccommodate the system of pulleys and belts. Besides being a common andeconomic way of transmitting power, belt drive offers the significant advantages ofshock load dampening and not requiring lubrication [8]. It would also act as anadditional safeguard if plastic were to jam the machine or the knives would strikethe counterknives as the belts are free to slip if the resistance is too high. The
downside of the belts ability to slip is that its unsuited to applications that need highprecision of velocity ratio and timing, which fortunately, this machine does not. To
solve that problem, one could use ribbed belts, as shown in Figure 4.10 (right)
instead, as in the camshaft transmission of a car engine, see Figure 4.11.

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Figure 4.10 V-belt drive (left) and Ribbed belt drive (right).

Figure 4.11 Ribbed belt as a timing belt for the camshafts of a car engine.

To calculate the size and position of the pulleys, length of the belts and number ofbelts in the transmission a handbook on belt drives from Trelleborg AB was used.
The required high reduction rate means that if a small pulley with a diameter of 63
mm was used on the motor shaft, then the pulley on the knife shaft would have tobe 2.5 m in diameter. Obviously, this would not be practical. The solution would bea setup of several subsequent transmissions via separate shafts. As seen in Appendix
C the power that can be transmitted per belt is lower with decreasing speed anddiameter of the smallest pulley. This mean that the last step of the transmission isthe critical component. To avoid using very large pulleys, a balance would have to
be found between the size of the last reduction and the size of the smallest pulley.
As the availability of pulleys with more grooves than six is limited the first thing tocalculate was the smallest size possible of the knife shaft pulley and then dimension
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the remaining transmission from that. After numerous calculations with the
handbook, it was concluded that the most cost efficient way to achieve the required
reduction would be to use a reduction setup of i:4:3:3. However, to make sure thatthe right amount of tension was applied on each belt, either a springed tensioner, as
seen in Figure 4.12, would need to be used or the distance between the two passive
shafts with pulleys had to be adjustable.

Figure 4.12 Spring tensioner on a ribbed belt.

This made the construction relatively complex and quite costly. Before ordering theparts for the complete belt drive another search was made at the different markets
for used parts in hope of finding a gear reducer or a gearmotor with slower speed
and lower power.

Gear Reducer
Fortunately, deep in the junkyard, a complete coaxial gearmotor was found, see
Figure 4.13, that was not there the last time.

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Figure 4.13 Gearmotor as found on the junkyard.

Figure 4.14 Rating plate on the gearbox.

The motor did not have any plate that showed its speed or power, but the gearbox
just so happened to have almost exactly the right amount of reduction, as seen in
Figure 4.14. Its output shaft could not be turned but the flange connection to themotor was damaged, as seen in Figure 4.15, and the fan cover at the back wasbuckled. In hope that it was the motor that was damaged and not the gearbox, or thatany damage to the latter could be repaired, the gearmotor was bought for 250 SEK.
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It was taken apart in the workshop, see Figure 4.16, and luckily the gearbox worked
perfectly.

Figure 4.15 Damaged flange connection.

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Figure 4.16 Motor separated from gearbox.

It did, however, have a large pulley, see Figure 4.17, on the output shaft that was
fixed by rust from lying outdoors in the junkyard. Removing it turned out to be morecumbersome than expected. After several days of trying to disolve the rust aroundthe set screw and intense efforts to remove the set screw the easy way, see Figure
4.18, the best way to go forward seemed to be to drill out the screw and try to pull
off the pulley with a gear puller, as seen in Figure 4.19. Unfortunately, it would notbudge. Half a day with the angle grinder, gear puller and a wedge, however, did thetrick, see Figure 4.20.

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Figure 4.17 Pulley on the output shaft of the gearmotor.

Figure 4.18 Allen key twisted from trying to remove the set screw.

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Figure 4.19 Attempting to remove pulley with gear puller.

Figure 4.20 Successfully removing the pulley with an angle grinder.

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PSU connection
Next was the issue of connecting the motors output shaft to the now ready gearbox.
As seen in Figure 4.16, the helical gear at the end of the gearboxmotors shaft was
designed to fit with the gearbox. The first plan was to use as much of the
gearboxmotor as possible. It was disassembled and the shaft with the gear and flange
was kept intact. That way the gears relative position to the flange would remain
intact. As a result, only a connection between the motor and the gearboxmotors shaft
had to be made. Then a simple cover of the moving shafts would be made by waterjet
cutting two flanges that fit the gearbox and motor then weld them onto a steel pipe
large enough to accommodate the old rotor still on the shaft, see Figure 4.21.

Figure 4.21 First plan of PSU configuration.

The major problem with this setup is maintaining the correct alignment between the
two axes. A slight misalignment coupled with the high speed of the motor would
most likely cause severe vibrations throughout the construction. To reduce this issue
the rotor was cut from the shaft, see Figure 4.22, which allowed placement of the
motor right next to the flange of the gearbox, barring space for the connection, as
demonstrated in Figure 4.23.

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Figure 4.22 The gearboxmotors shaft after cutting off the rotor and removing the flange andhelical gear.

Figure 4.23 PSU configuration after removing the rotor with the remaining shaft connected to
the gearbox.

Instead of making a simple connector between the two shafts and securing it withset screws in both ends, as first intended, Jonny Nyman, instructor at the school’s
workshop, lathed an entire new shaft with the connector integrated, as seen in Figure
4.24. This reduction of a fitting between shaft and connection further decreased therisk of misalignment.

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Figure 4.24 CAD model of the lathed shaft with an intergrated connector.

Lastly, instead of welding the cut flanges with a pipe and risk improper mounting,a solid connection was lathed to fit between the motors and gearboxes flanges withintakes for the spigot and socket of the flanges. As the spigot and socket, see Figure
4.25, are designed to be concentric with the output and input shafts respectively, atight fitting would solve the issue of misalignment. The resulting flange connection
is shown in Figure 4.26.

Figure 4.25 Spigot (left) and socket (right) of the flanges marked by arrows.

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Figure 4.26 Lathed connection between motor and gearbox.

Paint and coating
Lastly the PSU needed a new finish. After thoroughly cleaning it, a gray primer wasapplied followed by a rich blue spraycolor, see Figure 4.27 and Figure 4.28.

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Figure 4.27 Motor prepared for primer and paint.

Figure 4.28 Motor after painting.

The complete PSU were then assembled and tested after refilling the gearbox withnew transmission oil. It functioned more or less perfectly. The finished PSU isshown in Figure 4.29.

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Figure 4.29 The finished PSU.

4.2 Shredder sub-partCutting the parts.
While finishing up the PSU work on the shredder sub-part was begun. As it turned
out, almost all the files provided by Precious Plastic for cutting the individual parts
had double lines that needed to be removed before they were sent to the waterjet
cutter. These so-called double lines are two lines that are drawn on top of eachother.
This would cause the waterjet program to want to engage each line twice fromdifferent directions,as seen in Figure 4.30, which would cut into the pieces that werebeing made.

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Figure 4.30 Double lines that cause double engaging points as seen on the rightmost line. The
object to be cut is a ring between the two lines. The blue lines represent the cutting path of thewaterjet cutter.

As anticipated in chapter 3.1.2 the fitting between most puzzle shaped connectors
were too tight and had to be considerably reduced at both thickness and width using
an angle grinder. The blueprints were not changed beforehand as the waterjet were
thought to follow the path of the lines in the blueprints; making the width of thewaterjet correspond to the gap between the connectors.

Knife shaft
As for the knife shaft, Jonny Nyman helped with the lathing of a hexagonal rod at
the ends of the shaft. This needed a high degree of accuracy to produce a tight fittingwith the bearings. He also helped with milling all hexagonal sides of the rod a small
fraction as the hexagonal holes in the cut knives were slightly too small to fit.

Knife configuration
Regarding the configuration of the knives it was decided to use a different setup
than Hakkens. Instead, each new knife was rotated “backward” a little until about
halfway where they would start rotating “forwards”. This created a V-shape as seenin Figure 4.31. The idea was that the flow of edges would somewhat “push” theremaining plastic shreds toward the center of the SSP to avoid having too muchmaterial rotating along the outer wall as there are only one cutting action per teethon the outer knives.
31

Figure 4.31 Knife configuration shaped like a V.

Assembling the SSP
The pieces were assembled according to Hakkens instruction videos and tightenedso that the knives ran smoothly. The finished SSP is shown in Figure 4.32.

Figure 4.32 The finished SSP.

32

4.3 Framework
The building of the framework was done in stages as the other parts of the machine
were completed. Firstly, since the PSU was to be detachable from the other parts, aseparate frame was welded, see Figure 4.33. This was then to be bolted to the main
frame, which was cut with angled ends to avoid open profiles at the corners whenwelded together. A simple shelf was made at the bottom for storage, e.g. containersof shredded plastic or raw material

Figure 4.33 Detachable frame for the PSU.

The original design called for the use of a platform of welded beams that the SSP
would rest on, see Figure 3.1. Due to lack of experience with welding it would most
likely not be perfectly aligned with the PSU. Instead, a modifiable solution was
opted for where the SSP was bolted onto a separate frame which was then mounted
on the main frame with four threaded bars. This allowed adjustment of the height of
the SSP platform and the rotation around two axes by adjusting the position of thenuts on the bars, as seen in Figure 4.34. Lastly, the bottom nuts were welded to themain framework after connecting the SSP to the PSU. The complete framwork with
SSP and PSU can be seen in Figure 4.35.

33

Figure 4.34 Adjustable framework solution for the SSP.

34

Figure 4.35 Complete framework with SSP an PSU.

4.4 PSU to SSP connection
The connector between the two shafts were lathed out of a solid block of steel. The
schools workshop lacked the equipment to make a keyway at the large end that
attaches to the output shaft of the PSU since the hole does not go all the way through.
However, one could be made at the SSP-end of the connector. The large end wereinstead fastened by two set screws burrowing into the keyway left in the PSU output
shaft from the previous key. The resulting connector is shown in Figure 4.36.

35

Figure 4.36 PSU to SSP connector.

4.5 Hopper
A crude hopper was made out of 1 mm sheet metal and welded together as seen in
Figure 4.37.

Figure 4.37 The hopper when mounted on the SSP.

36

4.6 Electronics
The basic electronic setup used to test the machine was a contactor and protective
circuit breaker combined with on and off buttons. For the final system, however, theability to run the shredder in both directions were needed in case the machine
clogged. It would also be necessary to add an emergency stop button in an accessible
position. The original plan was to place the box with the contactors more or less outof sight on the main frame, below the PSU. However, it was realized that removing
the PSU platform would require either disconnecting the motor from the circuit
breaker or make a limb on the platform that the box can be placed on. Such a limb
however would make it difficult to store the disconnected PSU as it would have to
be placed on a pallet or something similar. The most elegant solution seemed insteadto place it level with the platform and on the backside of the motor, as seen from theoperating side. To make the emergency button and spin direction switch accessible
but still attached to the PSU platform, the only logical position seemed to be at thecorner closest to the SSP on the operating side.

4.7 Finishing
To finish off the build the framework and hopper were sanded, primer was applied
then painted and finished with a clear coat. The complete machine is shown in
Figure 4.38-Figure 4.38.

37

Figure 4.38 Finished machine.

38

Figure 4.39 Finished Machine.

39

Figure 4.40 Finished Machine.

40

Figure 4.41 Finished machine, proudly presented by myself for scale.

41

5 Testing
5.1 Different sieves
The machine as designed by Hakkens uses a bent sieve made out of perforated
sheet metal as seen in Figure 5.1 that attaches to the SSP under the knives. This ismeant to keep the plastic inside the SSP till the shreds become small enough topass through the holes of the sieve. Modifing the number and sizes of the holeschanges the size of the shreds aswell as the processing time.

Figure 5.1 Sieve with a fine perforation.

As for the plastic that was shredded, plastic waste from the household was stored
to this end. Most of it was made out of either PP, PET, PS or HDPE.
Naturally, testing the machine started without a sieve to see what size of shreds it
would produce. As expected, the process was very quick and produced a wide
range of shred sizes, as can be seen in Figure 5.2, where household waste made of
PP were shredded. As the teeth of the knives are relatively long and there is little
chance of cross-cutting, the pieces tended to be in the shape of long strands whenshredding softer products with a lower material thickness, as compared to theseemingly random shapes seen in Figure 5.2. The wide spread of sizes makes it
unsuitable for remelting in subsequent machines.

42Figure 5.2 Different sizes when shredding without a sieve.

Not using a sieve turned out to be the prefered setup when shredding thin film of
LD-PE. The shape of film when scrunched up to a loose ball made sure that the
knives only cut small pieces at a time as they gradually pulled the plastic throughthe shredder. The film before and after shredding is shown in Figure 5.3.

Figure 5.3 LDPE-film before and after being shredded without a sieve.

The specifications did not state a recommended size of the perforation of the sieve
so at first the smaller of two available sizes in the workshop was used. It had ahole diameter of 3 mm with a spacing and row distance of 6 mm. The resulting
shreds turned out to be much finer compared to the un-sieved shreds. But the sieve
turned out to be too fine for practical use. Instead of falling through the mesh at areasonable rate, the majority of the shreds kept being swiveled around by the
knives without noticable cutting action. As the shredder was fed more plastic, thismass of shreds became large enough to cause substantial sideways movement of43

the SSP. Increasing the clamping force on the rubber cushions that were installed
between the SSP and its framework to reduce vibrations decreased this somewhat,
but this means that the bearings absorbed those forces instead. This problem was
attributed to two main issues. Firstly, the more obvious of the two, was that theperforation was simply too fine. The second was that the clearance between the
knives and the sieve was too large for the knives to help push the shreds throughthe sieve.
The other perforation available had a considerably larger perforation than the finerone. Its hole size was 10 mm with a spacing of 20 mm and the same holepositioning as the finer perforation, as can be seen in Figure 5.4.

Figure 5.4 Sieve with a larger perforation.

The process time was, as expected, good enough for practical application and only
had a minor buildup of material. The quality of the output, see Figure 5.5, turned
out to be fine enough when shredding a mixture of PP, PET and PS.

44

Figure 5.5 Output quality from a mixture of PP, PET and PS when using the sieve with larger
perforation.

5.2 Types of plastic waste
As this machine is meant to shred plastic waste, the different types of plastic thatwill be used in larger quantities is somewhat limited. Considering that the shredder
will be located at IKDC, a majority of the plastic waste will most likely be madeout of PET from plastic bottles and PP from assorted food containers. My
understanding from reading posts at the Precious Plastic forum was that many ofthe machines with a weaker PSU had problems with plastic bottles. These areusually designed with thicker plastic at the necks which made the machines stop
completely as the neck cloged the knives. The initial testing with softer PP waste
showed signs of wear on the knives through chipping of their leading edge, as seenin Figure 5.6. It was decided to test PET bottles lastly in case they would cause
any permanent damage. It turned out that worry was unfounded as no signs oftrouble were noticed from the machine, even when shredding particularly thickbottles.

45

Figure 5.6 Chipping of the teeth after testing the shredder.

5.3 Result of knife configuration
During testing with the fine sieve it was noticed that the flow of edges worked
better than anticipated as the vast majority of the buildup of material was pushed
towards the center of the shredder.

46

6 Redesign

Even at the early stages of testing it was realized that despite whatever flaws had
been found while building and testing the machine, it worked well enough not towarrant the cost and time it would take to build a new version of the SSP. The
updated version would have to be limited to a detailed CAD model.

6.1 Number of shafts
The first design choice was whether to continue using a single shaft, as Hakkens
did, or add a second shaft rotating counter to the first to reduce the problem ofskipping mentioned in Chapter 3.2.1. Any more than that would be superfluous to
the task that the shredder would be used for.
It was decided that the added complexity and cost of another shaft simply would not
be worth the advantages it provides. Having dual shafts would also mean that thesieve would be more complex as it would need to be made almost in the shape of a“w” as opposed to a half circle. It would also make the shredder considerably
bulkier. Large pieces of plastic would simply have to be cut into smaller pieces
beforehand or be handled differently.

6.2 Knives
Secondly, the teeth of the knives needed a remodeling. As the cutting edges are theones that work in conjunction with the counterknives of the housing, there were no
discernible reason why they should be designed the way Hakkens are. His knives
have a rounded leading face that ends in a very sharp point, as can be seen in Figure6.1. Making it that sharp also makes it weak, which is apparent from the jagged cutsseen on the knives after testing. The round face likely mean that the material will
also get pushed towards the middle of the teeth. The teeth have more cutting power
closer to the shaft, similar to a pair of scissors, so they were simply redesigned witha straight leading face instead, see Figure 6.2.

47

Figure 6.1 CAD view of Hakkes knives.

Figure 6.2 Redesigned knives with a straight leading face

6.3 Increasing the speed of the process
While Hakkens shredder may work adequately to what it is to be used for andproduce fine enough shreds, it may be improved upon to provide even finer shreds
at a reasonably rate. As mentioned in Chapter 5.1 using a finer sieve will provide
48

finer shreds, but the process will take too long if theres not enough cutting action.
The clearance between teeth and counterknives will also set a limit to how fine
shreds you can make. To increase the number of cutting motions, however, only two
options presented themselves: increase the speed and power of the PSU or increase
the number of teeth and/or counterknives.
During the testing of the shredder it was observed that the recommended 70 RPMof the motor may be a bit high. Some of the stronger waste products createdconsiderable forces when cut. Pieces could be thrown more than 2 meters away fromthe machine. Based on this, a slightly lower speed would be recommend; probably
closer to 50 RPM.
Using knives with two teeth on the infeed seemed appropriate though. Any morethan that would most likely make it more difficult to shred larger pieces.

More cutting actions
The conclusion was made that the infeed and outfeed needed to be separated toincrease the number of cutting actions. The first idea was to extend the shaft andgradually increase the number of teeth on the knives, as can be seen in Figure 6.3.
The eight-teethed knives at the end would significantly increase the number of
cutting motions. Hakkens design uses counterknives on only one side of themachine. In addition to more knives the idea was to improve upon this by providing
more counterknives per rotation after the infeed. One way to do that was to use
spacer disks with holes cut into them in a circular pattern around the shaft hole tofunction as counterknives, see Figure 6.4.

Figure 6.3 Extended shaft with increasing amount of teeth.

49Figure 6.4 Redesigned counterknife.

Housing
This would then be mounted inside a pipe, with an opening cut into one end forinfeed and another at the opposite end and side for outfeed, see Figure 6.5. Two
major issues were noticed with this design. The first was that the counterknives
would be very difficult to mount inside the pipe. Welding them on would be very
difficult if not impossible. Heating the pipe before inserting shaft and counterknives
could possibly hold them in place but maintaining their correct positions in regard
to the knives could prove even more difficult. It would also mean that you could notdisassemble the shredder without cutting the pipe open.

Figure 6.5 Conceptual image of knives mounted in a pipe where infeed and outfeed are marked
by arrows.

50

It was decided instead to integrate the housing with the counterknives by adding
outer spacers and ears to the counterknives where threaded bars would be used totighten the design, see Figure 6.6. The idea was to use the configuration of the knives
to push the shreds through the pipe-like design to the end with more teeth and theoutlet; alternatively while also tilting the shredder at a slight angle so that gravity
would help aswell.

Figure 6.6 Integrated housing with spacers and counterknives.

Finally, the middle step between infeed and outfeed that had four teeth per knife
was removed to make more room for the infeed. There were some problems during
testing with large pieces of waste skipping on the knives of Hakkens design due tothe infeed being too small. Modifying a spacer created the infeed, outfeed, endplates
and ears were added to attach a hopper, see Figure 6.7.

Figure 6.7 Extended infeed and modified housing.

51

Bearing bolts
As seen in Figure 6.8 the heads of the bolts that hold the bearings in Hakkens design
rests right where the outer knives rotate. There was some worry that the vibrationsof the machine might eventually loosen the bolts enough to put them into the pathof the knives, which would most likely destroy the machine. To avoid this, thebearings were mounted on an external bracket that would in turn be fastened to theouter endplate by the same threaded bars that held the rest together to maintainalignment. Furthermore, the hole sizes for the bolts were changed to match those of
the bearings since this caused a lot of trouble during assembly, see Figure 6.9.

Figure 6.8 Bearing bolts.

Figure 6.9 Exploded view of redesigned bearing assembly52SieveWhile the sieve in Hakkens shredder is fairly easy to remove and attach, it is slightly
more complex to fit while building it. Welding the perforated sheet to its supports
also splashed small beads of metal on the knives and knife spacers, see Figure 6.10.
These were difficult to remove and they ground against the housing andcounterknives.

Figure 6.10 Splashed beads of metal from welding the sieve to its supports.

To improve upon this, the idea was to design a sieve that you could somehow slide
into the machine without having to weld it to anything. By adding slits in thespacers, a sieve with bent ends should be able to be slide in and out with an end cap
to keep it in place, see Figure 6.11.

53

Figure 6.11 Exploded view of the redesigned mesh assembly.

Final design
This resulted in a new and final design shown in Figure 6.12-Figure 6.14.

Figure 6.12 Final redesign.

54

Figure 6.13 Final redesign - exploded view.

Figure 6.14 Final redesign - exploded view.

Additional changes made to Hakkens design during building
To make the machine more mobile the intended feet of the framework, see Figure
6.15, were changed to a pair of wheels in one end and rubber knobs in the other, see
Figure 6.16. It is still cumbersome to move but certainly a lot easier than the original
design.

55

Figure 6.15 Feet of the framework as designed by Hakkens.

Figure 6.16 Redesigned feet of the framework.

For obvious safety reasons, a hinged transparent lid to the hopper was added with asmall handle. This also prevents pieces from being thrown out of the machine. Also
for the sake of safety an emergency stop button was added which Hakkens design
did not have.
The very large collector that would stand at the shelf and reach up to the bottom of
the SSP as Hakkens designed and shown in Figure 3.1 seemed unnecessary. To
make it easier to handle, a simple rail to hold a smaller collector was opted for
instead, see Figure 6.17. This had the added benefit of leaving more free space atthe shelf.

56

Figure 6.17 Slide rail for a smaller collector.

57

7 Discussion

Early on it was realized that the total cost of 180 EUR projected in Appendix B
would probably not be enough and seemed unreasonably low. Through sheer luck a
motor and gearbox was found for a total of 450 SEK (~45 EUR) which was
surprisingly cheap, while the Bill of Materials estimates the cost to only 30 EUR.
Without that luck, the gearmotor or a motor with a different reduction would by far
have been the driving cost of the machine. The total cost of the machine would
therefore in most cases likely have been much higher than the projected.
Ideally it would have been preferable to play around with the configuration of theknives to see if a different setup might have worked better. Unfortunately, themargins were really small and the assembly was very difficult to get just right tomake it run smoothly. It was simply not worth the effort to take it all apart again
when it worked as well as it did.
During the planning phase a misstake was made in not checking that the holesizesof the shredders housing matched the holesizes of the bearings. The distance
between the bolt holes of the bearing house for the shaft diameter was the same as
the distance on the housing so it was assumed to be standardized. This caused a lotof trouble during assembly that would have been easily avoided had the holes of the
housing been modified in the drawing.
As previously mentioned the plan was to get as close to the 2 kW and 70 RPM PSU
recommendations as possible. Posts on the Precious Plastic forum told of someproblems when using weaker setups. In hindsight though, a significantly weakermotor would likely have sufficed, coupled with a slightly slower speed to retainsome of the torque. Plenty of weaker used gearmotors were found that might haveworked fine but was ignored. Had a complete PSU with the right specifications beenfound, that would have been perfect. But as it turned out, connecting the motor andgearbox took a lot more time than anticipated. Using a complete and ready motor
would have saved the roughly 7-8 weeks it took to design different setups of the
PSU and ultimately building the final PSU. Granted, a few other parts of the project
were worked on during this time. But as much of it was dependent on the PSU mostof the time was dedicated to completing it. Considering the low price for the motor
and gearbox a lot of money was saved compared to buying a new one or even a used
one with similar specifications. In the end, it was probably not worth the time spent
for the extra power gained and the money saved.

58

A considerable amount of time was also lost due to the fitting of all the different
pieces. Increasing the margins in the drawings could have solved this but it could
also have invited other troubles if they were made too large. As the schools
workshop had a waterjet cutter it was decided to cut all the pieces in-house using
this. Hakkens instructions however assume that a laser cutter is used which has amore precise cut. If the pieces had been ordered from an external company with a
new laser cutter the margins as designed might have been sufficient.
By only adding wheels in one end of the framework it was thought to be easy enoughto move around while also retaining some of the stability offered by stationary feet.
Due to the weight of the machine being positioned as high up as it is, it is still a bit
wobbly to move around. To anyone building a similar machine, it would berecommend to make the base a bit wider to improve stability. Wheels with brakes
should also be mounted instead of the now stationary end to make it even moremobile.
Regarding the holes making up the circularly patterned counter knives in theredesign, it is possible that it was a bit too eager in create more cutting action.
Without testing the design it is difficult to anticipate how it would behave, It is
possible that the holes were made too small and that those same spacers would act
more as a blockage in an actual live test. Unfortunately, the only way to get a
realistic idea of how it would work is by building and testing it.
A considerable advantage of the new design is that its very easy to modify to yourneeds. With a strong PSU, as was used in this project, it would not take any effort
at all to elongate it and create more space at both the inlet and outlet. If one did notwant to separate the inlet and outlet it would still be recommend to somehow
integrate the design of the new outlet and its sliding sieve with the inlet.
A thing to note is that all the plastic waste used during the testing was cleaned
beforehand and most of the labels were removed. Using dirty plastic was nevertested but as stainless steel was used for all the shredder parts, cleaning it should be
as simple as placing a plastic container under the shredder and pouring water withperhaps soap added over it while running the machine. The shreds would of course
also have to be cleaned before using them to create new products. Depending on thekind of dirt left on the waste however, it would likely cause problems with shreds
sticking to the machine instead of passing through the sieve.
One thing that could be improved upon for any future versions of the machine is thelid. It sorely needs a lid to keep plastic from jumping out of the machine, but to help
the shredding process the material often needs to be pushed towards the knives.
Integrating some kind of tool to force the plastic when it skips on top of the knives
with a sturdy lid would be a great improvement to its operation.
There are also likely numerous possible changes to be made when it comes to thesafety of the machine. One would be a microswitch mounted in the lid to stop themachine when opening it. This would however require a solution to the previously
59mentioned problem of plastic skipping on top of the knives as the lid needs to beopened to force down the plastic. Another solution might be to build a different kindof hopper where the feeding of the machine is made in a way that you cant get yourhands into the knives. There is also the safety concern of the open connection
between PSU and SSP. Some kind of casing should be made to protect the operator
from clothes and hair getting caught in it.

608 Conclusion

The goals of building a machine that can shred plastic waste into fine enough shreds
to be usable in future machines for producing new products were met. The PSU was
also made into a module by attaching it to a separate frame that fastened to themainframe by three bolts.
The final redesign provides an increase in the cutting action rate which, if working
as intended, should produce an increase in performance aswell as output. By
integrating the housing with the counterknives and spacers, the assembly was
greatly simplified through stacking of the knives, counterknives and different
spacers on the knife shaft and then tightening it with two threaded bars after adding
the endplates. The changing between different sieves to produce other quality ofoutput should also see a substantial improvement for user friendliness.
The material costs of building the machine was managed to be kept to a minimum,
though at a cost of greatly increased building time.
While unfortunately not being able to build the new design myself due to time andcost restraints, I am very proud of the results in both the machine that was built, thechanges made from Hakkens design of it and the new design that resulted from thetesting. The project has taught me a lot aswell as tested my abilities while still
fulfilling the requirements set on it at the outset.

61

References[1] About. (n.d.). Retrieved November 6, 2016 fromhttps://preciousplastic.com/en/about/[2] Etherinton, R. (October 21, 2013). Precious Plastic by Dave Hakkens.
Retrieved November 6, 2016 from http://www.dezeen.com/2013/10/21/preciousplastic-open-source-local-recycling-workshop-dave-hakkens/[3] Ulrich, K.T., Eppinger, S.D. (2012). Product Design and Development (5thed.). New York: McGraw-Hill.
[4] Snäckväxel – kvadratisk. (n.d.). Retrieved November 14 2016 fromhttp://www.mekanex.se/produkter/vaxlar/snackvaxlar/standard/[5] Klokopplingar. (n.d.) Retrieved November 14, 2016 fromhttp://www.mekanex.se/produkter/komponenter/axelkopplingar/klokopplingar/[6] Beardmore, R. (January 22, 2013). Worm Gears. Retrieved November 14,
2016 from http://www.roymech.co.uk/Useful_Tables/Drive/Worm_Gears.html[7] Black, A. (n.d.). The Ins and Outs of Worm Gears. Retrieved November 14,
2016 from http://www.machinerylubrication.com/Read/1080/worm-gears[8] Fox Maska, D. (April 1, 2008) V-belt selection it’s a veritable cinch.
Retrieved November 14, 2016 from http://machinedesign.com/archive/v-beltselection-its-veritable-cinch

FiguresFigure 3.1 A general view of the shredder as built by Precious Plastic.
https://github.com/hakkens/precious-plastic-kit/archive/master.zip
Figure 3.2 SSP where knives (green) and counterknives (red) are marked.
https://github.com/hakkens/precious-plastic-kit/archive/master.zip
Figure 3.3 Two pieces with puzzle shaped connectors. Slits dependent on sheet
metal thickness marked by arrow.
https://github.com/hakkens/precious-plastic-kit/archive/master.zip
Figure 3.4 Four shaft shredder.
http://www.stokkermill.com/wp-content/uploads/2015/05/quadrialbero.jpg
62Figure 3.5 Left: shredder knives as designed by Precious Plastic. Right: Assorted
industrial shredder knives.
Left: https://github.com/hakkens/precious-plastic-kit/archive/master.zip.
Right: http://3.imimg.com/data3/BG/YM/MY-7296216/shredder-cutters500x500.jpg
Figure 3.6 Triangular teeth and counterknives.
http://www.cmg-america.com/assets/images/loop-settori/single-shaft-shredders.jpg
Figure 3.7 Paper shredder with hook knives.
http://gsa.machine-solution.com/Shared/images/highsecuritypapershredders.jpg
Figure 4.1 Dave Hakkens angular geared motor.
https://github.com/hakkens/precious-plastic-kit/archive/master.zip
Figure 4.2 Worm gear from Liljenbergs AB.
http://www.liljenbergs.com/Images/products/snackvaxel_small.jpg
Figure 4.3 Jaw coupling.
Left: http://3.imimg.com/data3/NA/EE/MY-4199678/jaw-coupling-250x250.jpg.
Right:
http://www.abssac.co.uk/uploads/site/products/p_ye7di/img_CouplingKKa.jpg
Figure 4.8 The basic setup of a worm gear.
http://s.hswstatic.com/gif/gear-worm.jpg
Figure 4.9 Coaxial gearmotor.
http://www.busck.se/wp-content/uploads/ps-mi-t3a90s-4.png
Figure 4.10 V-belt drive (left) and Ribbed belt drive (right).
Left: http://www.monarchbearing.com/images/import/images/poly-v-beltdrives.jpg.
Right:
http://4.bp.blogspot.com/_fEJbY0LcQ2w/TI9mZwW7TKI/AAAAAAAAACM/zu_-LpyAsIc/s1600/fenner-v-belts.jpg
Figure 4.11 Ribbed belt as a timing belt for the camshafts of a car engine.
http://www.carscope.com/wp-content/uploads/2016/01/TimingBeltV6.jpg
Figure 6.15 Feet of the framework as designed by Hakkens.
https://github.com/hakkens/precious-plastic-kit/archive/master.zip

63Appendix A Project Plan

As can be seen in the following project plans they differ a lot. The first one shows
the original plan before starting the project. When made, I had no idea how longtime the different steps would take and tried to decide upon an ideal plan. The
second one shows approximately how long the different steps took and when they
were started. I was planning on building the machine from Hakkens in five weeks,
which in actuality took 9 weeks (excluding the finishing steps that were notnecessary to test the shredder). Although, as can be seen in the second plan, manyof these weeks were spent on the PSU. Had I found a ready gearbox early on I
could have spent all that time on the SSP and framework which would haveshortened their build time significantly. In the first plan I assumed that I would beworking on the report continuously throughout the project. I did not start on it until
about halfway through the project. In hindsight I should probably have started amonth earlier to give myself more time.

64

65

66

Appendix B – Bill of Materials

Bill of Materials as provided by Precious Plastic.

67

Appendix C - Power transmission
per belt

The following table shows the power transmitted per belt by speed and diameter ofthe smallest pulley for a profile SPZ belt from Trelleborg AB. Text of image inswedish.

68

69