Group 32 - Chainsaw

Revision as of 03:15, 16 December 2009

Group info

Group Members

Cam Borowiec - Project Leader

Andrew Koonce - Wiki Expert

Scott Chown - Communications Liason

Matt Lang - Solid Modeling Expert

Gagan Reddy - Dissection Leader

Group Member Pros/Cons

Gate 1: Request for a Proposal

Gate 1 can be found here.

This Includes our work proposal, management proposal, Gantt Chart, and Initial Product Assessment.

Gate 2: Preliminary Project Review

Gate 2 can be found here.

This includes any causes for corrective action, an analysis of the disassembly, and a step by step process of the disassembly.

Gate 3: Coordination Review

Gate 3 can be found here.

This includes a component summary, some suggested design revisions, solid modeling of a main system, and an analysis of engine seizure.

Component Summary

Part	Material	Reason the Material Was Used	Manufacturing Process	Reason for the Shape of the Part	Quantity	Function	Forces Applied	Complexity	Photo
Main Casing	Aluminum Alloy	Aluminum is a light and cheap material and the alloy used is very durable	Molded and then tapping was used to create threaded holes	The part contours the hidden components while minimizing the total size of the chainsaw.	2 parts	It houses all of the rest of the components.	The casing will endure any forces from dropping or misuse. Also, it supports the chainsaw's weight in the user's hands.	1
Clutch Cover	Aluminum Alloy	Aluminum is a light and cheap material and the alloy used is very durable	Molded and then tapping was used to create threaded holes	The part contours the hidden components while minimizing the total size of the chainsaw.	1	It covers and protects the clutch.	There should only be the force of the screws holding the cover on. However, the cover may endure forces from dropping or misuse.	1
Fly Wheel Cover	Aluminum Alloy	Aluminum is a light and cheap material and the alloy used is very durable	Molded and then tapping was used to create threaded holes	The part contours the hidden components while minimizing the total size of the chainsaw.	1	It covers and protects the flywheel, and it also houses the starter unit which is a pull cord on a spring.	There should only be the force of the screws holding the case on. However, the cover may endure forces from dropping or misuse.	1
Bottom Cover	Aluminum Alloy	Aluminum is a light and cheap material and the alloy used is very durable	Molded	The part contours the hidden components while minimizing the total size of the chainsaw.	1	It covers bottom of chainsaw.	There should only be the force of the screws holding the case on. However, the cover may endure forces from dropping or misuse.	1
Intake Cover	Plastic	Plastic is lightweight and the case should not undergo any strong forces.	Molded	The square shape maximizes the cross-sectional area available to the filter to allow for the largest intake volume.	1	It covers intake and protects the filter from large debris.	There should only be the force of the screws holding the case on. However, the cover may endure forces from dropping or misuse.	1
Fuel Lines	Rubber	Rubber is safe to use with oil and gasoline without contamination, and it can be easily moved to fit in many places.	Molded	A hose is the simplest method of transporting fluids and lightweight.	3	It carries fuel from the tank to the intake and the cylinder. Also it carries excess gas out of the system.	The only forces acting on the fuel lines are negligible.	1
Pull Cord	Plastic handle and rope connected to a steel spring and plastic cover and plastic gear	The materials were selected to reduce weight	The handle was molded. The rope was wound, then knotted at one end and connected to handle. The plastic cover and gear wear also molded. The spring was extruded and bended.	The handle was made to fit in an average hand comfortably, while the other parts were shaped to perform their assigned tasks. The rope and spring are standard shapes, and the gears were made to allow the cord to engage the flywheel.	1	The pull cord and assembly, start the rotation of the crankshaft and allow the chainsaw to start running.	The forces applied are the external pull from the user, and the counter-torque from the flywheel, when it is engaged.	3
Bar	Iron	Iron is a very strong material, and this part undergoes the main force of the chainsaw.	Pressed	The shape holds the chain in tension.	1	It holds the chain in place, and transfers the driving force from the user to the wood.	This part undergoes the largest force, when the chainsaw is pushed into the wood.	1
Cylinder	Aluminum Alloy	The alloy used was chosen to reduce weight but still be strong enough to withstand the forces of general use.	Molded and then milled	The cylindrical bore is the common shape for an engine to have for the chemical reaction to occur. There are two notches at the bottom of the cylinder to allow the oil and fuel to move in and out of the crankcase. The outside has spaces to allow air cooling of the cylinder during operation.	1	It houses the piston, and it is the location of the main source of energy, which is combustion.	The cylinder undergoes a continuous change in forces as the chainsaw is used. The forces result from the expansion, heating, and compression of gases inside of it.	1
Spark Plug	copper, ceramic, and plastic	The copper is used to transfer the electric charge. The ceramic and plastic are used as insulators to prevent any shorting within the spark plug.	Molded, then threaded with a die	Spark plugs are always the same shape, to reduce size and allow the movement of charge easily.	1	It provides a spark for the combustion.	The spark plug should only undergo the force from the gases.	2
Handle & Grip	Steel and Rubber	The steel handle is very stiff and sturdy preventing any damage that may occur from the misuse of the chainsaw. The rubber grip reduces vibrations in the handle and makes it more comfortable to hold.	Molded and bent	The large handle allows for a wide variety of hand positions and gives you a sturdy grip.	1	It allows the chainsaw to be held and manuevered accurately and comfortably.	The handle undergoes all of the forces the user applies to the chainsaw and the weight of the chainsaw acting on it.	1
Exhuast	Steel and Aluminum	Steel is used on the exterior of the exhaust to withstand any misuse and damage. Aluminum is used in the interior parts of the exhaust to save weight, and to absorb the vibrations from the engine.	Molded	The exhaust is shaped to maximize the noise reduction from the engine while still not getting in the way of the user. Also, the gases are directed away from the user off to the side to prevent inhalation or burns.	3 pieces, 1 unit	It directs exhuast fumes out of the cylinder into the air and also muffles sound of the engine.	There should only be the force of the screws holding the exhaust on. However, the exhaust cover may endure forces from dropping or misuse.	1
Heat Shield	Aluminum	Aluminum is a lightweight material that can deflect a decent amount of heat.	Bent and Pressed	The heat shield contours the cylinder around the edges facing the user. This causes the heat to be deflected away from the user.	1	It guards the operator from the heat coming off of the cylinder	The only force exerted on this part is the compression force holding it in place.	1
Air Filter	Foam and Plastic	The foam is porous, allowing air to flow and dirt particles to be blocked.	Not Machined	The shape maximizes surface area to allow for a larger amount of filtering.	1	It filters the air and protects the intake from taking in debris.	The only force on the filter is the flow of air entering the chainsaw.	1
Flywheel	Aluminum and Magnet	The magnet is necessary to trigger the magneto. The heavy aluminum creates a high rotational inertia keeping the crankshaft moving.	Molded	The fins on the flywheel allow air to be drawn in, cooling the system. The cylindrical shape has a radial symmetry, which is necessary for high rpms.	1	It keeps the crankshaft spinning and triggers the magneto.	There is a torque applied to the flywheel from the crankshaft, and from the pull cord gear.	1
Magneto	Iron, copper and rubber	Iron is necessary because it is highly affected by a magnetic field. The rubber insulates the signal and the copper transfers the signal with a low resistance.	Milled	The iron has two curved parts that match the curve and location of the magnets on the flywheel. The rubber casing and hosing is shaped to transfer the signal to the spark plug.	1	It send signal from the flywheel to the spark plug.	There is a magnetic force exerted on the magneto from the flywheel.	3
Ignition switch/cables	aluminum and copper wire	The aluminum is lightweight, and the copper has a low resistance for transferring current.	Lathed	The switch is small, but still large enough to easily be used.	1	It allows the engine to start.	There is a force exerted on the switch whenever the chainsaw is turned on or off.	2
Battery and cables	Alkaline Battery and copper wire	N/A	N/A	The battery is a cylinder to maximize capacitance.	1	It is the energy source for the electrical system.	N/A	2
Fuel and oil caps	Plastic	Plastic is lightweight and fuel safe. Also it is easily molded.	Molded	The cap provides a large enough surface for the user to easily remove, and the thread holds the caps in tight.	2	They help contain the contents of fluids in the tanks.	There is a torque applied by the user to remove and attach the caps.	1
Spring loaded timing mechanism	plastic and aluminum	The aluminum is flexible allowing pressure to be provided to the cam and pin. The plastic is lightweight.	Molded and Bent	N/A	1	It controls the timing of the spark plug.	There is a force on the aluminum strip that holds it against the pin. A force is exerted against the plastic piece from the cam.	2
Trigger and connecting wire	plastic and aluminum	The materials are used to reduce weight.	Molded and Bent	Plastic can be easily molded. The metal is a stock aluminum rod bent into the desired shape.	1	It converts user input into mechanical system.		1
Piston ring	Steel	Steel has a higher boiling point then the aluminum parts around it, resulting in less expansion from heat. Also steel is a stronger material than aluminum.	Pressed	The ring has a gap to allow it to be slightly stretched and compressed to fit on the piston.	1	It seals the wall of the cylinder to the piston and creates a ring of oil around the piston for lubrication.	The force from the expanding gases and friction from the cylinder are acting on the piston ring. Also, the piston ring moves along with the piston causing a transfer in forces between them.	1
Timing mechanism cover	Plastic	The plastic is lightweight and flexible.	Molded	The cover is shaped to reduce the space it takes up, while fully covering the parts below.	1	It prevents damage to timing mechanism.	N/A	2
Timing mechanism switch	Aluminum		Pressed		1	It completes the circuit with the battery.		2
Fuel ratio adjuster	Rubber and Iron				1	It Regulates fuel to air mixture.		2	N/A
Air intake lock	Steel		Pressed		1	It locks the air intake cover over the intake.		1
Choke switch	Plastic		Molded		1	It triggers the choke in the intake.		1
Intake	Aluminum, Plastic and Rubber Gaskets		Die Cast		1	It regulates the air intake and mixes the air with the fuel.		5
Piston	Aluminum Alloy	Aluminum is lightweight, machined with a low coefficient of friction.	Die Cast	The piston contours the cylinder with a slot cut into it for the piston ring. The shape is designed to minimize weight while maintaining strength.	1	It transfers the pressure force from the expanding gases to the connecting rod.	The forces from combustion and expanding gas are acted on the piston. Also, the crankshaft exerts an initial force on the piston when the chainsaw is first started.	1
Connecting Rod	Aluminum Alloy	A high strength aluminum alloy was used, because it is easily machined, and has a high tensile strength.	Pressed	A single piece connecting rod was used to reduce weight, and there is no need for it to be disassembled many times.	1	It transfers the mechanical force from the piston to the crankshaft.	Forces are transferred between the piston and the crankshaft via the connecting rod.	1	N/A
Crankshaft	Iron	Iron is used to endure the high stress, and to transfer high torque to the clutch.	Die Cast and cut in a lathe	a three part crankshaft was used because they are stronger and easier to machine.	1	It transfers rotational motion between the clutch, flywheel, and piston.	High torque is transferred between the flywheel, piston and clutch.	2
Clutch	Iron	Steel is very strong and the weight is needed to balance the flywheel.	Die Cast	Since the clutch is constantly rotating, it must be round. Also, the two springs cause the clutch to engage/disengage at a certain rotational velocity.	1	It engages and disengages the gear connected to the bar at different rpm speeds.	A torque is applied from the crankshaft to engage/disengage the clutch.	3
Bolts	Steel	Steel is a common material used for Bolts.	Molded and extruded through a die		40 (The different sizes are listed below)	They hold the parts together.	A torque is applied to attach/remove the bolt.	1
Nuts	Steel	Steel is a common material used for nuts.	Molded and tapped	Steel is strong, and a common material for nuts.	11 (The different sizes are listed below)	They help the bolts attach to the parts.	A torque is applied to attach/remove the nuts.	1

The complexity scale is rated as listed below.

• 1 = One or two parts that easily fit together
• 2 = Three to seven parts that require some knowledge to assemble
• 3 = Seven to twelve parts that require accuracy, and full knowledge of the products use, to assemble.
• 4 = More than twelve parts that require full knowledge of the mechanical system.
• 5 = It has many parts that require machines and careful examination to assemble.

Design Revisions

The design of the chainsaw is relatively obsolete because of its age. With it being 29 years old, there have been many advances in technology that we have today that could make the chainsaw significantly better.

• One of these new design methods would be to put 2 piston rings around the piston head instead of the single one that is on our chainsaw now. This is not a very technologically advanced design but, it is very cheap to do and will help the consumer greatly. This ensures that if the primary piston ring breaks or wears down and releases the seal to the cylinder wall, there is a back up that will keep the chainsaw working properly without the need of emergency repair.

• Another simple add on to the chainsaw would be a temperature gauge that reads the heat inside the cylinder. This is a simple way of making the consumer aware of lack of oil in the gas/oil mixture which is needed for the piston to work properly. This would be a much more expensive addition than the piston ring but it could save the chainsaw from complete uselessness. If a user knew that the chainsaw was becoming over heated, he could let it cool before the engine seized or fix the ratio of oil and gas.

• One thing that is common with chainsaws today, which would be a great improvement on the chainsaw we have is an external fuel tank made of plastic. This tank would be cheaper to produce than its aluminum counterpart in our chainsaw. The disadvantages of the aluminum fuel tank is that the aluminum is heavier than the plastic the external tank would be made out of and that the fuel tank could have a larger volume if it was placed outside the body of the chainsaw instead of being crammed into the body. This would greatly benefit the consumer while also benefitting the company. The company would save a great amount of money switching from aluminum or an aluminum alloy to a cheaply mass produced plastic tank while the customer enjoys a lighter and longer lasting, in terms of refueling, chainsaw.

Solid Model Assembly

We chose Autodesk Inventor 2010 for our solid modeling program. We did this because our solid modeling expert has been working with this program for 5 years, and he would not have to learn another programs' mechanics. We chose to model the piston assembly because it provides the main power for our system to work.

A video of our assembly can be found here

The part and assembly files can be downloaded by clicking -> Media:Chainsaw.zip

Also, a free 30-day trial of Autodesk Inventor can be downloaded here

Engineering Analysis

Problem Statement:

What is the frictional force needed for a 2-stroke engine to cease?

Diagram:

Assumptions:

• Friction is constant around the entire cylinder
• Coefficient of friction between the piston and cylinder is .03
• The normal force at cease is 110N
• Temperature is constant
• Piston and cylinder made of Aluminum

General Equations:

Ff =u*N

Calculations:

Ff = .03*110N= 3.3N

Solution Check:

The values for the coefficient of friction and the normal force were obtained from VTT research notes on the friction inside of a 2-stroke engine. This helps to confirm that the force I obtained is close to the actual force.

Gate 4: Critical Design Review

Reassembly Process

The Difficulty Scale is rated accordingly:

• 1 = No tool required
• 2 = One tool required with little force required
• 3 = One tool required with a large force or accuracy required
• 4 = Multiple or specialized tools required with little force required
• 5 = Multiple or specialized tools required with a large force or accuracy required

Final Assessment

Does your product run the same as it did before you disassembled it?

The product still does not work. The pull start still gets jammed and slowly recoils, and the engine needs replacement parts in order to be repaired. Also, there is a hole in the crankcase preventing the chainsaw from ever working.

What were the differences between the disassembly and the reassembly processes?

During reassembly the same tools were used, however there is more detailed work required to make the chainsaw work. This includes a miniscule distance between the magneto and the flywheel, The timing of the spark plug must be accurately positioned, and the carberator must be tuned according to the manual. Overall we were able to reassembly the chainsaw with no problems.