Group 2 Gate 4

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Introduction

As the final part of the project, this section wraps the entire wiki together. It includes the product reassembly, as well as further analysis of the product. The product reassembly provides step by step instructions on how to put the chainsaw back together. The mechanism section explains how a mechanism provides motions and interactions within the chainsaw. The final section includes the design revisions on a system level that are believed to make the chainsaw more profitable and appealing the target audience.

Project Management

By this point in the project, all of the problems within the group have been settled. We had our problems, as discussed in previous sections, but they have been worked out and overcome. The only problem facing the project this time is Thanksgiving Break. It prevents the group for meeting for basically an entire week. To overcome this obstacle, each member of the group was assigned a small portion of the project that could be done on an individual basis before the break was over. Then, after everyone was back together we could do the final portion of the project, the product reassembly.

The plan to have individuals do a small portion of the project over Thanksgiving break works fairly well. Some of the members completed their assigned work, while others did not. The deadline was therefore pushed back to Wednesday before the gate was due. Everyone was able to complete their work by this time.

Since the presentation is due the same day that the gate is due, it was decided that the entire presentation would be completed and performed by one member. It was decided that that member would not have to do as much, if any work, on the wiki, since they would be busy with the presentation.

The reassembly was a bit more time consuming than previously believed. Because of this the group needed to spend more time putting the chainsaw back together. Some of the steps were very tricky and required a lot of time, but the rest of the assembly was fairly easy. During dissection, the group took very detailed notes so it was easy to follow the steps in reverse for reassembly.

Product Archeology

Tools Needed

• Flathead Screwdriver
• 7/16" Socket Wrench
• 5/16" Socket Wrench
• 1/2" Socket Wrench
• Long 5/8" Socket Wrench
• 5/32" Allen Key
• T20 Torx Head Screwdriver
• T15 Torx Head Screwdriver
• Needle Nose Pliers
• Pliers
• Vise

Difficulty Scale

The difficulty scale ranges in values between 1 and 5 with 1 being the easiest and 5 being the hardest. The scale is based on the number of tools used, the forced required to complete the step, time it takes to complete step, the number of hands/people needed, and difficulty of completing step. Some of the step difficulty may be more based on one factor than another.

• 1. The step requires no tools and is very easy to to accomplish. The time required and required coordination is minimal.
• 2. The step requires one tool at a time but is still fairly easy to accomplish. The time and required coordination is still minimal.
• 3. The step requires more than one tool or hand and is fairly time consuming. The component is accessible but the requires coordination.
• 4. The step requires more than one tool or hand and is moderately time consuming. It is hard to access the component but easy to accomplish the step once it is accessed.
• 5. The step requires more than one tool or hand and is very time consuming. requires intensive coordination and the component is not easily accessible.

Reassembly Steps

Table 1 shows a step by step reassembly of the chainsaw. It includes detailed descriptions of the instructions, tools required to complete each step, any notes that we have discovered during our reassembly, a difficulty scale, and a picture of any important or ambiguous part in the step. Following that is a quick description on how the chainsaw was originally assembled in the factory. The difficult scale is on a range from 1-5, 1 being the easiest and 5 being the hardest. The difficulty scale is based on the number of tools required to perform the step, the force needed to attach a component, the ease of accessing the component, and our personal experience from assembling the product.

Product Assembly By Steps
Step	Description/ Factory assembly methods	Tool Required	Difficulty of step (1-5)	Important/Ambiguous Part Locations
1	Screw in the black tuning screws labeled "hi" and "lo." Put on the black gasket. Then screw both cylindrical gates back on, being sure each gate is on the proper side. Also, screw the lever assembly (in red) back together. This metal assembly is very small and contains a pin, a lever and a spring. This simple bolted connection would be done with power tools.	Flathead Screwdriver	3	Lever system (in red) and various other carburetor parts
2	From the carburetor, screw in the four screws that have washers on them. Be sure to note the order in which the gaskets, plastic reservoirs, and metal pieces go. This is shown in the picture to the right. </br> This assembly was done carefully by hand being sure to assemble the pieces in the right order.	Flathead Screwdriver	2	Carburetor exploded view
3	Very carefully assemble the 20 roller pins around the outside of the crank shaft and screw in the two T15 Torx screws holding the rod to the crankshaft. Next, put the two big and two small spacers back on the crankshaft. This assembly is done with power tools using a special method to quickly put the cylinder bearings in place.	T15 Torx Screwdriver	5	Exploded view of rod assembly
4	Re-bolt the crankshaft by holding the crankshaft in a vise while securely screwing in the 7/16" nut on the brake side with a socket wrench. The nut is threaded the opposite way so turn it counter-clockwise to screw it in. Be sure to use a lot of force to get it secure. Re-bolt the other 1/2" nut from the other side of the crankshaft holding together the brake assembly and magnet head. The magnet will need to be hammered into place to ensure it remains secure. This process was done by power tools with a pressing machine to assemble the flywheel and tighten bolts that require force.	7/16" 1/2" Socket Wrench Vise	4	Exploded crankshaft and rod
5	Next connect the carburetor and alternator. From the alternator, connect the grounding wire and the on/off switch wire. From the carburetor, place the three plastic tubes in indicated slots and the gasket separating the carburetor and the combustion chamber. Use needle nose pliers to put the throttle cable back on by bending the wire to fit through the hole and cramp back on. Screw the 3 Torx head screws with a T20 Torx screwdriver. The bolted connections are done with power tools and the throttle cable was connected by hand with a precise needle nosed tool.	T20 Torx Screwdriver, Needle Nose Pliers	2	Three Torx head screws. (in red)
6	Put the piston/crankshaft assembly into the combustion chamber. Screw in the four flat head screws, highlighted in red, holding the casing of the crankshaft to the combustion chamber. This step was done with simple power tools.	Flathead Screwdriver	2	Four flat head screws (in red)
7	Replacing the trigger is a tricky step so it is broken into two steps. The trigger should be connected at the top of the wrap around casing by a spring. Use needle nose pliers to bend the spring back in. This spring is highlighted in gold in the image to the right. This spring was put in place with a special tool.	Needle Nose Pliers	3	Spring (in gold)
8	Replace the metal wire connecting the trigger and the throttle. The wire is highlighted in red in the picture to the right. Use needle nose pliers bend the cable back on. This step is especially difficult because bending the metal wire requires some force applied with the pliers. The wire is located in a tight space which also makes the process harder. The throttle cable was bent by a specific size pair of pliers.	Needle Nose Pliers	5	Throttle Cable (in red)
9	Replace the casing on the drivetrain as depicted in the image to the right. Screw in the three flathead screws holding the wrap around casing to the drivetrain system. The casing was assembled by hand and bolted together using power tools.	Flathead Screwdriver	3	Insert drivetrain system into case
10	Put the choke lever on and screw in the flathead screw that holds it in place. The screws are highlighted in red. The lever is a small black lever plastic piece on the left side near the red engine switch and shown in the picture. Also put the plastic handle back on by screwing in the two flathead screws with a screw driver. Next, put the spark plug wire back on and screw the spark plug on with a long 5/8" socket wrench. This needs to be a long socket so that it can reach the nut portion of the spark plug. A wrench of the same size can be used but it is harder to maneuver in this situation. This step was done with simple power tools.	Flathead Screwdriver, Long 5/8" Socket Wrench	2	Screw (in red) holding on choke
11	Next, attach the exhaust with two 5/32" Allen head screws. Next, attach the exhaust cover with the two 5/32" screws highlighted in red in the picture. This step was done with simple power tools.	5/32" Allen Key	2	Two screws (in red) holding on the exhaust cover plate.
12	To put the tanks back on, the tube that connects the tank to the carburetor must be connected as well as the tube that oils the chain. After that, simply slide the tank back into the closure until the tab shown in red snaps into place. After the tank is in place, put the black front housing on and screw in the screws in the top and bottom. The gas tank assembly was assembled by hand, spanning together the parts. The screws were added using power tools.	Table Cover 5/16" Socket Wrench Flathead Screwdriver Needle Hose Pliers	4	Tab (in red) located on the bottom of the case.
13	Next, put the starter housing back on. Screw in the four flathead screws. These screws are highlighted in red. Pull the starter cord back through the housing and tie it back on to the starter handle. Be sure to replace the filter that covers the air intake. The starter housing was bolted using power tools and the starter cord was tied by hand.	Flathead Screwdriver	2	Four flat head screws. (in red)
14	Put the blade, chain and aluminum handle back on. First, slide the blade on horizontally, allowing you to then put the chain on by wedging it around the blade and the drive wheel. Putting on the chain takes a little work but twisting the chain a little can help ease the step. To put the aluminum handle on, first put it in place then screw in the 5/16" bolt located on the top with a socket wrench and the flathead screw on the underside with a screwdriver. The parts were assembled by hand and bolted using power tools.	5/16" Socket Wrench Flathead Screwdriver	3
15	Turn the brake handle 180 degrees so that it can be put on. From the brake assembly, use pliers put on the pivot lever. This lodges the spring and the black lever. Then screw in the two flathead screws, highlighted in red, using a screwdriver. To put on the brake assembly, which is located on the chain side of the chainsaw, screw in the 7/16" nut and 7/16" bolt using a socket wrench. The last parts were assembled by hand and fasteners were bolted using power tools.	7/16" Socket Wrench, Flathead Screwdriver	3	Two screws, a nut and a bolt. (in red)

Table 1: Step by step assembly of chainsaw.

Mechanism

In the process of choosing which mechanism in our chainsaw to analyze, we decided to choose the piston, piston rod, crankshaft mechanism because, not only is it the most iconic mechanism that comes to mind, but it is also the most important mechanism in the whole chainsaw. It is located within the engine and creates all the power necessary for the entire chainsaw to work. Without this mechanism, there would be no power generated in the engine. Without the engine, there is no chainsaw. The proper name for this mechanism is called the "Crank-Slider" mechanism. It is an arrangement of mechanical parts designed to convert straight line motion into rotary motion, resulting in a reciprocating system of energy flow in the piston engine. The figure below is a general display of a basic crank-slider mechanism, and can provide assistance in explaining how this mechanism works.

Diagram

Crank-Slider Mechanism

Description

The darkly shaded part 1 is the combustion chamber of the engine which contains a cylinder. This frame is shown by its walls DE and FG, in which the piston, part 4, slides back and forth. The small circle at A represents the main crankshaft bearing (also located in part 1). The crankshaft is part 2, and it is shown as the straight member that extends from the main bearing at A to the crankpin bearing at B. The crankpin also connects to part 3 which is the connecting rod. The connecting rod is the straight member that extends from the crankpin bearing at B to the wristpin bearing at C. This wristpin bearing connects the connecting rod to the piston, part 4, which is shown as the beige colored rectangle inside the frame. These three bearings (the circles A, B, and C) allow its connected members to rotate, and move freely with respect to one another. The path of B is a circle of radius AB. When the crankpin bearing, B, is at point h, the piston head, part 4, will be in position H. When B is at point j, the piston head will then be in position J. In this gasoline engine, the head end of the cylinder (where the explosion of the gasoline-air mixture takes place) is at EG; the pressure produced by the explosion will push the piston from position H to position J. The return motion from J to H will require the rotational energy of a flywheel attached to the crankshaft and rotating about a bearing, colinear with bearing A.

Governing Equations for Design of Mechanism

EQ.1) Pressure = Force * Area

EQ.2) Area of circle = PI R^2

EQ.3) Torque = Force * Distance (perpendicular)

EQ.4) Power= Change in Work/ Change in Time

EQ.5) Distance = theta*radius

EQ.6) Friction Force= mu*Normal Force

Reference

While doing research about crank-sliders, we used the following links to help create the Mechanism part of this gate:

http://www.answers.com/topic/slider-crank-mechanism

http://www.britannica.com/EBchecked/topic/548729/slider-crank-mechanism

Image: http://engineering.myindialist.com/wp-content/uploads/2009/11/slidercrankmechanism.gif

Design Revisions

Change #1

Ease of Use

Reasons for Redesign

Chainsaws may not be the hardest product to use on the market, but in order to expand the target audience, it would be beneficial to have a simple to use chainsaw in order to convince a new group of people to buy the product. This chainsaw could become much easier to use with a few small changes including an electric starter, as well as placing clearly marked instructions on the product itself so that customers don't need to look through the manual to understand how to use the product for its most basic uses.

Design Considerations

Easier to use chainsaws would expand the number of people who could work in fields that require chainsaw use as it lowers the amount of knowledge needed. Making the product more intuitive would reduce the reputation that chainsaws are difficult to use or only for those who are "handy". This new chainsaw would be something that could be picked up and used by someone who has never used a chainsaw before without needing to read the manual.

With this more intuitive chainsaw in the hands of less experienced users, it is only proper to assume that users will have little experience maintaining them correctly. Therefore, when an issue arises, they will take their chainsaw straight to a mechanic to fix it. This will result in higher cost of ownership as well as a rise in demand for small appliance maintenance.

Effect on Target Audience and Price

With nothing but new features being added to the chainsaw, it would come at a higher cost. Not only would redesign be an obvious cost, but the additional features would only be additions to the everyday chainsaw. Therefore, cost of supplies would also come into play. When a product becomes more intuitive, it is able to be used by a larger target audience. However, those who currently know how to use modern chainsaws well will not prefer these more intuitive chainsaws as they will have a higher cost. This being said, it is safe to assume that the target audience of this new chainsaw will be new to the chainsaw market. People buying their first chainsaw will prefer this new type of chainsaw.

Change #2

Safety

Reason for Redesign

A chainsaw is a powerful cutting tool and if misused, it will easily sever limbs and severely wound people. A chainsaw could be made safer by giving it new features such as a safety switch, similar to what is found on guns, or a blade guard that is automatically moved out of the way when the trigger is pulled. One more way to make chainsaws safer would be to put an accelerometer in the blade that would detect kickback and deploy the guard when it is detected.

Design Considerations

According to the US consumer Product Safety Commission, there are approximately 100,000 chainsaw related injuries annually, most of which are due to kickback. With safety features in place to prevent these injuries, hospitals would have much less traffic. This would not only decrease the number of deaths due to chainsaw related incidents, but free up hospitals to prevent deaths due to other causes.

With more features being introduced to the chainsaw, it would have a higher likelihood to malfunction. With more malfunctions occurring, it is important to note that cost of ownership would increase. Users would be expected to spend more money per year on fixing this new chainsaw than they have in the past. As unfortunate as this is, it is worth the trade off, which is significantly fewer injuries per year.

Effect on Target Audience and Price

With only new features being added to the chainsaw, the price would necessarily increase, especially if there are electrical components being used in implementing safety devices. With a higher price as well as a higher cost of maintenance, this chainsaw would mostly only sell to people who are currently opposed to using chainsaws due to safety concerns. However, in an effort to prevent injuries, it is possible that over time government regulation will require the use of such safety standards in all chainsaws as long as they are available.

Change #3

Comfort

Reason for Redesign

In its current state, the chainsaw has a simple aluminum handle with no grip at all. Chainsaws are often very loud, shaky, and overall, unpleasant to use. With these flaws in mind, one could make the chainsaw more comfortable to use by putting in a rubber ergonomic handle which would reduce shake during use, as well as putting on a muffler in order to reduce noise pollution output.

Design Considerations

People who work for yard work companies would be using this device for several hours at a time. In its current state, this chainsaw would likely cause much discomfort and in some cases, medical damage due to extended exposure to vibrations up the users arm. It could also cause hearing damage if user is not using ear plugs.

Effect on Target Audience and Price

The shift in target audience would not be very significant since almost anyone who uses a chainsaw would prefer a more comfortable product. However, it would particularly target those who use chainsaws for many hours a day and do not want to have an uncomfortable work experience. This being said, the price tag of this chainsaw would be slightly higher than it would have been previously since there would be a necessary raise in cost of production given more supplies used.

Sources used in Design Revisions: US Consumer Product Safety Commission article- http://www.cpsc.gov/CPSCPUB/PREREL/prhtml80/80023.html