1. I graduated with high honours from the University of Toronto with a
Bachelor of Applied Science in Mechanical Engineering. I have a
keen interest in problem solving, especially with regard to the design
of creative and innovative solutions to real world problems. There is
seldom greater satisfaction than witnessing design work come to
fruition. The following depicts my preferred design work.
DAVE WAKNIN
Engineering Portfolio
408—2200 Ward Street
Montreal QC H4M 2R1
Canada
1-514-833-2091
dave.waknin@mail.utoronto.ca
DAVE WAKNIN

2. Table of Contents
Multidisciplinary Projects
1.1 Table Tennis Serving Machine (Demo Video Here)...............................................3
1.2 3D Printer: Filament Feeder 1.....................................................................................4
1.3 3D Printer: Filament Feeder 2.....................................................................................5
International Project
2.1 Scaffold Bracing Device...............................................................................................6
Finite Element Analysis Projects
3.1 Wrench Design .............................................................................................................7
3.2 Truss Support ...............................................................................................................8
3.3 Tensile Member............................................................................................................9
Additional Designs
4.1 Pressure Test Canister Redesign..............................................................................10
4.2 Redesign of a Can Opener’s Spur Gears.................................................................10
4.3 Design of an Electric Pencil Sharpener Gear Train ...............................................10
Letters of Recommendation
5.1 Dr. Peter Weiss ...........................................................................................................11
5.2 Dr. Mathew Mackay ..................................................................................................12
N.B. Table of Contents is hyperlinked (clickable) to the corresponding pages.

3. 3
Multidisciplinary: Table Tennis Serving Machine
Design Features
 For mechanical and coding simplicity, the barrel rotates only about the vertical axis
 The maximum velocity and feed rate were set to match the typical human reaction time
for competitive gameplay
 The fixed height and vertical angle of the barrel have been set, based on kinematics, to
achieve the maximum velocity distribution for diverse gameplay situations
 Firing mechanism is composed of two independently rotating wheels directly driven by
DC motors for consistent launch velocity while avoiding unintended spin on the ball
 Barrel and firing mechanism rest on a lazy Susan and are rotated by a servo motor
 Hopper is independently supported to minimize the polar moment of inertia of the
firing mechanism and is set directly above the axis of rotation of the barrel to remain
inline while it rotates
 The hopper possesses an agitator, powered by a DC motor, to maintain constant
feeding
 A cam mechanism is utilized to feed and push (low pressure angle) a single ball into the
barrel per rotation and is powered by a stepper motor for controllable feeding rates
Conclusion and Final Notes
In order to view an initial demonstration video of the machine in action,
please click here. After the initial testing and demonstration, improvements
were to be made. However, due to financial and time constraints, the design
modifications were simply stated in the final report.
Context and Project Requirements
The problem statement of this term project (winter 2015) was to design any
embedded system that required the use of a microcontroller. My responsibili-
ties involved the mechanical design; that is, the firing, aiming, feeding and
loading mechanisms. I also established the required motor specifications and
helped in motor selection. Lastly, I was charged with machining and assembly.
Approach
Design a simple and reliable, yet competitive, machine with only a single axis
of rotation, but that can later be adapted to a more complex two-axis design
with minimal modifications.

4. 4
Multidisciplinary: 3D Printer - Filament Feeder 1
Design Features
 The filament is fed into the extruder via a drive gear; the gear
possesses striations to increase feeding force and minimize filament
slippage
 A stepper motor allows for accurate and controllable movements
 The drive gear is directly driven by the motor for simplicity
 A bearing, supported by a pivoting arm, forces the filament against
the drive gear for accurate feeding while minimizing friction
 Interference fit between the filament and drive gear is adjustable via
springs and bolts supporting the bearing’s pivoting arm
 The pivoting arm has a hole to guide the filament into a polyether
ether ketone (PEEK) thermal break between the cold-end and hot-end
 Feeder is composed of aluminum for its ease of machining and high
heat transfer abilities to avoid premature melting
 An aluminum heat sink is used to increase heat conduction away from
the filament, thus further avoiding premature melting
 A fan is added to the heat sink for more effective cooling
 A Pico hot-end is used for fast, accurate and reliable deposition
Conclusion and Final Notes
All discussed components are designed from scratch apart from the
drive gear, motor, heat sink, fan and hot-end. A second filament feeder
design for the same project is depicted in the following page.
Context and Project Requirements
Within a term project (winter 2014), the task was to design a
filament 3D printer for use by hobbyists. As part of my
responsibilities, I was charged with the extruder design,
specifically the feeding mechanism. The main requirements
involved high speed and accuracy as well as low cost and low
energy consumption.
Approach 1
Design a simple, yet high performing, extruder feeding
mechanism with the minimal amount of components to
minimize size, weight and cost while increasing reliability.

5. 5
Multidisciplinary: 3D Printer - Filament Feeder 2
Design Features
 Bowden principle decreases inertia, momentum and vibration of extruder
 A stepper motor allows for accurate and controllable movements
 Unlike a typical drive gear, a screw-drive has all of its teeth in contact with the filament at once,
creating a larger force and minimizing potential slip
 The screw has threads removed in two sections so that it can be properly supported within the
housing; it rests on two bearings to minimize energy loss via friction and to avoid heat buildup
 Feeder is composed of aluminum for its high heat transfer abilities to avoid premature melting
as well as due to its corrosion resistance to avoid impurity deposition on the filament
 Two aluminum heat sinks are used in order to cover the entire back area of the feeder, thus
maximizing the contact area and increasing heat conduction to further avoid premature melting
 Fans are added to the heat sinks for cooling via forced convection
 Interference fit between the filament and screw is adjustable via the springs on the outer bolts
 Filament tube is composed of PTFE for low friction and high thermal resistance
 A Pico hot-end is used for fast, accurate and reliable deposition
Conclusion and Final Notes
All discussed components are designed from scratch apart from the motor, heat
sinks, fans and hot-end. In addition, in retrospect, only four bolts and springs
would be necessary as opposed to the eight used in this design. The fans are also
excessive and the heat sinks would be sufficient. Lastly, the Bowden extruder
(feeder 2) was selected for the final proposal, as opposed to the previous
extruder (feeder 1).
Approach 2
Design a feeding mechanism for a Bowden-
type extruder to minimize size and weight,
while modifying it to alleviate some of the
disadvantages possessed by this type of
extruder.

6. 6
International Project: Scaffold Bracing Device
Context and Project Requirements
As part of a final year project (fall 2014 - winter 2015), in collaboration with Peking
University as well as the National University of Singapore, a means of securing planks
and ladders to a scaffold was to be developed. The solution was to be a single design
that is reusable and does not pose safety concerns. Due to the high variability in
component dimensions, no state of the art solution was feasible. I was charged with
leading the design process for the University of Toronto’s candidate design. The main
concerns were repeatable and efficient use while being capable of withstanding the
working conditions.
Approach
 Validate the clients claim that no viable off-the-shelf solution exists
 Conduct brainstorming, blue sky thinking, functional decomposition, function-means
-tree, TRIZ and design methods to establish candidate designs; the decided upon
design was analogous to a cargo lash with a ratchet
 Determine optimum lashing pattern to minimize material use and installation time
 Explore different types of lashing devices such as wire ropes and webbing
 Evaluate different types of metals (plain steel, galvanized steel, stainless steel and
Monel) for wire rope designs, aramid fibers (Kevlar, Nomex, Technora, Vectran and
Twaron) for webbing designs and the possibility of other solutions (SparkGard,
Ponsa fire retardant coating and BioThane webbing)
 Determine most practical and efficient tightening mechanism (worm and wheel,
ratchet and pawl, turnbuckle, rack and pinion, over-center buckle)
 Determine best combination of lashing material, lashing device and tightening
mechanism
 Conduct economic and life cycle analyses to determine viability of final design
 Conduct appropriate tests (stress versus strain behavior, tension required to avoid
slippage, creep analysis, ease of installation, FEM simulations and heat tests) to
validate theoretical calculations, initial assumptions and design feasibility
Design Features
 Design is reusable and possesses a lower environmental impact than current system
 Relieves safety concerns possessed by currently used system
 Reduces installation time and therefore also reduces cost
 Design had insufficient creep resistance and temperature resistance
Conclusion and Final Notes
It was concluded by all participating universities that, based on the unique working
conditions at Sembawang Shipyard, the currently used wires are the optimal design for
securing the planks and ladders to the poles. As a final note, it was recommended to the
academic supervisor that the project be abandoned midway; however, due to its
educational purposes, the project had to be pursued.

7. 7
Finite Element Analysis: Wrench Design
Design Features
 Adopted a Warren Truss design to the wrench’s handle to efficiently reduce its weight
 At critical locations, struts were utilized; otherwise, material was completely removed
 Minimized stress concentrations by filleting all internal corners and avoiding geometric discontinuities
Conclusion and Final Notes
The mass of the wrench was decreased from 2.20 kg to 0.985 kg (55 %
reduction). In hindsight, a final vertex sizing should have been implemented at all
locations of relatively high stress to confirm that the weakest locations have not
changed.
Context and Project Requirements
As part of an individual Finite Element Analysis report (winter 2014), the goal
was to redesign a wrench in order to optimize its strength-to-weight ratio. The
mass of the wrench was to be minimized, without altering its periphery, while
also maintaining a safety factor of at least 2 against yielding when subjected to
a specified load.
Approach
 Study initial stresses and strategically remove mass from locations of low
stress
 Employ mesh convergence analysis at locations of highest stress via vertex
sizing in order to maintain simulation accuracy while reducing computation
time
 Avoided further mesh analyses by maintaining initial locations of highest
stress as weakest points throughout design process (without vertex sizing)
 Balance structural rigidity throughout specimen to allow for most uniform
distribution of elastic energy storage

8. 8
Finite Element Analysis: Truss Support
Design Features
 Aluminum was selected for its high specific modulus and titanium for its high specific strength
 Given the asymmetrical state of stress, circular rods were selected as they do not warp under torsional stresses and do
not possess stress concentrations (corners)
 Since the deflection constraint was more difficult to meet than the yield constraint, locations of higher stress are designed
with aluminum to limit deflection and locations of lower stress are designed with small amounts of titanium to minimize
mass
Context and Project Requirements
The objective of this Finite Element Analysis assignment was to design a
truss (stage support) as light as possible and stiff enough to resist a
maximum deflection of 1 inch, while supporting its own weight (B) and
a force of 500 lbf (C). The truss is pivot supported at its back-end (A). A
safety factor of at least 2 against yielding and deflection is required. The
structural design of the truss is restricted to that shown on the left. The
design parameters involve material and cross section selection; cost is
irrelevant.
Conclusion and Final Notes
Due to the large length to cross-sectional area ratio, the rods can be considered
slender; therefore, only axial stresses are relevant and the cross-sectional shape is
not. The final design possessed a safety factor of 2.4320, a total deformation of
0.99195 inch and a weight of 4.3157 lbm. This deformation was approximated
and validated via Castigilano’s second theorem. As a final note, since the rods are
thin and the truss is intended as a stage support (potential interaction with
fireworks), magnesium was not considered due to its high flammability.
Approach
 Initially simulate the entire structure with rods of the same cross section and
material for a consistent comparison of stresses and deflections
 Test hollow cross sections as they have larger moments of inertia per unit
weight and should diminish both bending stresses and deflections
 Survey available materials on ANSYS for highest specific modulus and
highest specific strength (importing materials was not allowed)
 Rods with high stress are designed with high specific modulus material and
rods with low stress are designed with high specific strength material
 Adjust radii of rods in groups based on stress level and iterate process to
meet constraints

9. 9
Finite Element Analysis: Tensile Member
Context and Project Requirements
The goal of this Finite Element Analysis report (winter 2014) was to design a tensile
member with the maximum strength-to-weight ratio. The initial component was a slab of
PMMA (shown on right). The constraints are as follows:
 A minimum of 0.25 inch of acrylic must remain between adjacent cutouts
 The loading holes must be a maximum of 1 inch from the loading edges
 The width and height through the center of the plate must remain 6 inch
Approach
 Optimize computation time by considering a 2D model, a quarter specimen (two planes
of symmetry) and a mesh convergence analysis
 Use vertex sizing to refine the mesh at critical locations to improve accuracy yet
minimize computation time
 Two potential methods to increase strength-to-weight ratio: designing internal cutouts
to distribute the stress or simply removing as much unstressed material as possible
 Since it is difficult to uniformly distribute stress within the member via cutouts, the
width of the structure was reduced to remove excess material
Design Features
 All edges and corners are filleted to eliminate stress concentrations
 The maximum distance from the hole to the loading edge (1 inch) was chosen to
maximize the amount of energy absorption prior to failure
 All unstressed material was removed to optimize the member’s strength-to-weight
ratio (the removal of the corners was accepted despite the first constraint)
 An oval cutout was placed along the stress chains to distribute stress along the
member while minimizing weight
 The dimensions of the oval have been changed and iterated to provide the highest
strength-to-weight ratio
Conclusion and Final Notes
Stress chains follow the path of least resistance and therefore do not distribute well as
they simply go around cutouts and maintain high stresses near boundaries. However,
internal cutouts can decrease weight while increasing structural elasticity thus decreasing
the stress on the loading holes by allowing the rest of the structure to absorb most of the
strain energy. The strength-to-weight ratio of the tensile specimen increased by a factor of
5.75 between the initial slab and the final design.

10. 10
Pressure Test Canister Redesign
Additional Designs
During my summer research internship at McGill University
(summer 2014), as a side project, I was tasked with
redesigning a test pressure system to achieve lower
pressures of 0.100 Torr. It was believed that a hi-vacuum
pump was needed. I had the flexibility of changing most of
the design and buy a new pump (2000 CAD budget). Before
buying a new pump, I decided to research the canister
(bottom-half section on left) which was much cheaper to
change. The assumption was that the current pump may be
able to achieve such pressures but the canister design is inhibiting it. Based on research and tests, I
determined that PVC is not suitable for low pressures since it outgases and does not form a good
vacuum seal to itself (PVC cement) or to metal fittings. The new canister was composed mostly of scrap metal collected
around the lab welded together; Teflon tape was used on fittings to eliminate leaks and the clearance present in the
collimator and piezoelectric pin holes were sealed via epoxy. The final design was to be made wholly of aluminum. The tested
design achieved a pressure of 0.070 Torr with less than 5 % of the allotted budget as a new pump was no longer needed.
As part of a group assignment (winter 2014), in which we dissected a can opener, I was
tasked with redesigning its gear train to produce 50 % more torque (original design is
depicted on left). The number of teeth on the larger gear was increased from 52 to 78. It
was also possible to reduce the number of teeth on the pinion, however this was not done
so as to avoid undercutting. Furthermore, it was
important to maintain the center-to-center
distance so as to comply with the housing dimensions. In order to do so, the
module of both gears had to be reduced. The tooth profile was also changed to a
stub tooth with a pressure angle of 20 degrees. This profile minimizes the size of
the pinion’s dedendum to maximize its strength while also avoiding a new shaft
design. To support the additional torque requirement, the thickness of the larger
gear was increased. The final design is shown on the right.
In this assignment, the task was to design the powertrain of an
electric mechanism and choose an accordingly sized motor.
The exploded view to the left is that of an electric pencil
sharpener. The design consists of a planetary gear train so as to
achieve an effective ratio of 9:1 while remaining compact. The
planet carrier is the output of the gear train and acts as the
sharpener via the conical loft at its center. The motor chosen
was a 75 W brushless DC motor; it is rated to have an output of
1620 rpm and a torque of about 0.442 Nm. With the effective
ratio of 9:1, the output would rotate at 180 rpm with a torque of about 4 N∙m, which is necessary to shear off excess wood
from a pencil. The motor has been modeled as a cylinder for simplicity reasons.
Redesign of a Can Opener’s Spur Gears
Design of an Electric Pencil Sharpener Gear Train

11. 11
Letter of Recommendation: Dr. Peter Weiss

12. 12
Letter of Recommendation: Dr. Matthew Mackay