Group 11 - Weed Eater Featherlite 20C - Gate 4

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Group 11 - Weed Eater Featherlite 20CGroup 11 - Weed Eater Featherlite 20C - Gate 4
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Figure 1: Fully assembled view of the product. }}
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Name of Artifact Featherlite 20C string trimmer
Manufacturer Weed Eater
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Group 11 - Weed Eater Featherlite 20C String Trimmer

Contents

Introduction

After disassembling the string trimmer and analyzing each of the components, the task of Gate 4 is the reassemble the product. Each step of the process is documented in a detailed fashion allowing someone not familiar with the product to be able to successfully reassemble it. Three design revisions pertaining to the system as a whole are described including their respective advantages, disadvantages, and their relevance to the four engineering factors.

Critical Project Review

Cause for Corrective Action

Since the due date for final gate is rapidly approaching so is the date for the final project submission. Thanksgiving provided the group members with a much needed break, but now it is the home stretch and time to jump back into the groove of completing the project. This point of the project is make or break. The group has to continue to work well together in order to ensure that the final product exemplifies our best work. Although the project has not always been smooth sailing, the group has addressed a large majority of the issues faced, which are outlined below.

Resolved Challenges

  • Managing Work For Gate 3: The week when Gate 3 was due was one of the busiest, if not the busiest, week of fall semester for every member of the group. This was because each person had at least three exams they needed to study for as well as homework for their other classes. Even with the long hours the group had to devote to studying and preparing for the various tests that week, they still found time to reschedule meetings in Capen library that made it easy to study prior to and after the meeting. Furthermore, the group scheduled time in advance to further examine the product and each individual component of it. Particularly with this gate, it was crucial that every member of the group contribute to the final submission of the gate in order to ensure that it got completed thoroughly and on time. The additional planning the group did for this gate was very helpful in the end in saving everyone time and effort.
  • Meetings: As the semester progressed, the weekly meetings that the group originally schedule in Gate 1 became inconvenient to the group members because of their increase in work load. The weekly meetings were held at different days and times each week based on the schedule of each member for that week. Since every member of the group is basically in the same classes, they had similar schedules making it easy to schedule times for meetings that could work for entire group. Depending on what needed to be accomplished during the meeting determined where that particular meeting was held enabling the group to get as much work done during that time as possible - it allowed the group to be as efficient as possible during that time.

Unresolved Challenges

  • Work Load Distribution: Evenly distributing the amount of work done by each group member for each gate continues to be a struggle for the group. Although one person is not stuck doing the entire project, certain members continue to doing the bulk of the necessary work. The uneven work load is mainly a result of the lengthy editing process, which comes as a result of different members having different levels of what they believe to be satisfactory work. Throughout the entire project, this has proved to be the biggest challenge and the most difficult one to resolve. The group has tried to resolve this issue by having the different members pitch in with editing, but the issue continues to exist because different group members have different standards for the quality of work that should be submitted. This leads to those particular members doing addition work to make the project better.
  • Project Presentation: With the presentation date already determined, the group has yet to decide who will be presenting. The meetings this week will not only focus on finishing Gate 4, but also on creating the PowerPoint presentation. It will be decided which group members will be presenting giving them ample time to prepare; this will also allow the members of the group who are not presenting to help those who are figure out exactly what to say and provide constructive criticism during practice presentations. Although the entire group will not be presenting, creating the presentation will be a group effort.

Product Archaeology

Reassembly Difficulty Scale

1 - Level 1 difficulty refers to a task that requires the minimal amount of work to complete. No tools are required to reassemble this part and can be done with a small amount of force. An example of this difficulty level is connecting the cutting shield to the bottom of the drive shaft housing. This only requires the person to tighten a wingnut needing little force to secure.

2 - Level 2 difficulty describes a task that requires the use of tools. Only a small amount of force is needed to complete the task. An example of this difficult level is attaching the spark plug to the cylinder. An adjustable wrench is needed, but a large amount of force is not needed to sufficiently tighten the part.

3 - Level 3 difficulty signifies a task that requires the use of tools, more than one step, and a considerable amount of force. An example of this is connecting the starter pulley assembly to the fan housing assembly. Winding the starter spring takes a long amount of time and requires an extensive amount of force in order for it to be wound into a small enough diameter. It often comes unwound before being able to secure it in place forcing the person to rewind it again.

Product Reassembly

The order of the steps taken to reassemble the string trimmer are thoroughly documented in Table 4-1. The tools needed, time required, difficultly, and a picture of the assembly are also shown in the table.

Table 4-1: Reassembly Process
Step Description Tools Required Time Required Photo Difficulty (1-3)
1 Rewind the starter spring to a diameter that is small enough to allow it to fit within the groove/indentation for it in the starter pulley kit. After fitting it in the starter pulley kit, put the metal cap on it and to secure it in place. Connect the starter pulley kit and the starter spring to the fan housing with the starter spring in the middle by tightening one size one flat head screw from the starter pulley kit through into the fan housing. This step took an extensive amount of time because winding the starter spring into such a tight spiral proved to be very difficult and required more than one try. After getting it rewound, it was still difficult to get it into its groove in the starter pulley kit without it coming unwound. Size one flat head screw, hands 15 minutes
Figure 4-1: Starter pulley connection
3
2 Attach the line limited to the bottom side of the cutting shield with a flat head screw. The line limiter has a hole for where the screw goes through it to connect it to the cutting shield, and a small projection that fits into a hole in the cutting shield allowing it to fit securely. Size one flat head screw, hands 1 minute
Figure 4-2: Line limiter
2
3 Attach the cutting shield to the drive shaft housing. This is done my tightening a wingnut on a square-head bolt to keep it tight and secure. Connected to the drive shaft housing is a flat rectangular piece of metal that wraps half way around it and then protrudes outward on both sides. One side has a hole in it that allows the bolt to go through it to attach to the cutting shield to the housing. The other side is connected to the shield b sliding into a gap in the shield. Hands 1 minute
Figure 4-3: Cutting shield attachment
1
4 Screw the hub onto the end of the driveshaft. The bottom end of the drive shaft is threaded and extends out of the drive shaft housing, and the hub has a metal cylinder going through the center of it that has internal threads allowing them to be connected. Hands 1 minute
Figure 4-4: The hub screwed onto the drive shaft
1
5 Place the compression spring around the smaller hole in the center of the hub. Put the retainer/clip inside the hole with the ends pointing outward locking the compression spring in place. Secure the retainer/clip to the hub by tightening a 5/32 inch hexagonal screw through the hole in the retainer/clip. Hands, H-5/32 Hexagonal Screwdriver 2 minutes
Figure 4-5: Assembly inside the cutting head
2
6 Connect the spool with line to the hub by simply pushing the spool onto the bottom of the hub. Hands 1 minute
Figure 4-6: The bottom of the cutting head
1
7 Slide the vertical grip down the drive shaft until it reaches the black plastic section overlaying the driveshaft housing. When it reaches this point and cannot go down any farther, secure it to the drive shaft housing by tightening a wingnut on a square-head bolt that extends through two holes in the vertical handle. Hands 2 minutes
Figure 4-7: Position of the vertical grip
1
8 Slide the fan housing over the top end of the drive shaft housing. The top of the drive shaft housing has two holes that extend through the diameter and overlap the two holes located on the bottom end of the fan housing. The fan housing is fixed in place by putting a 5/32 inch hexagonal screw through the four holes tightening a bolt onto the end H-5/32 hexagonal screwdriver, hands 2 minutes
Figure 4-8: Fan housing attachment
2
9 Slide the base of the piston into the cylinder so that the connecting rod assembly is pointing outward. Hands 1 minute
Figure 4-9: The position of the piston in the cylinder
1
10 Attach the cylinder with the piston to the crankcase on the side opposite that of the flywheel. Two holes in the cylinder line up with two holes in the crankcase where two 3/16 inch hexagonal screws are fed through and tightened. This is slightly difficult because the screws are located deep inside the cylinder making them hard to tighten. 3/16 Alan wrench, hands 3 minutes
Figure 4-10: The position of the cylinder attached to the crankcase
2
11 Attach the drive coupling to the crankshaft that is located inside the crankcase and extends out through the flywheel. The end of the crankshaft is threaded and the drive coupling has internal threads allowing it to be screwed on. Located between the drive coupling and the flywheel is a washer. The base of the drive coupling that connects to the flywheel has a hexagonal shape allowing it to be tightened easily with a wrench. Adjustable wrench, hands 2 minutes
Figure 4-11: The drive coupling attached the the flywheel with its hexagonal base
2
12 Screw the spark plug into the cylinder. The bottom side of the spark plug has thread and the cylinder has internal threads that allow for the spark plug to be attached. The bottom of the spark plug get tightened onto the cylinder so that the bottom is located inside the cylinder while the top of the spark plug remains outside of it. A portion of the spark plug has a hexagonal shape allowing it to be tightened with a wrench. Adjustable wrench, hands 2 minutes
Figure 4-12: The part of the spark plug located outside of the cylinder
2
13 Reassemble the carburetor kit, choke shutter, and choke plate mounting. The choke shutter should already be attached to the carburetor kit, but the choke plate mounting has to be connected to this assembly with four short silver Phillips head screws. The choke plate mounting has four small holes that correspond with four holes on the carburetor kit for the screw to be fastened. Size 1 Phillips head screwdriver, hands 3 minutes
Figure 4-13: The position of the parts with respect to each other
2
14 Put the cylinder gasket in the spaced allotted for it in the carburetor adapter and attach the carburetor adapter to the cylinder. Overlap the two holes in the carburetor adapter with with the two holes in the cylinder. Insert and tighten two T-20 torque screws to secure the two parts together. T-20 torque screwdriver, hands 1 minute
Figure 4-14: The placement of the carburetor adapter on the cylinder
2
15 Push the free end of the rubber casing of the throttle cable assembly into the hole for it in the carburetor adapter. The carburetor adapter has a small hole in it allowing the end of the rubber casing to be inserted with little force. Hands 1 minute
Figure 4-15: The throttle cable assembly in the hole in the carburetor adapter
1
16 Insert the end of the wire from the throttle cable assembly into the carburetor. The carburetor has a small hole that allows it to be slipped in and the end of the wire makes a 90 degree turn allowing only the end of the wire to be inserted into the hole and it to stay in place. Hands 1 minute
Figure 4-16: The placement of the wire in the carburetor
1
17 Attach the air box and carburetor to the carburetor adapter with two long 3/32 inch hexagonal screws. The carburetor is positioned so that choke shutter is pointed toward the air box and can be seen through the hole in the air box. The air box is positioned so that the screw enters through the inside and the three holes a on the upper side closer to the spark plug. H-3/32 hexagonal screwdriver, hands 3 minutes
Figure 4-17: The assembly of the air box and carburetor to the carburetor adapter
2
18 Place the green air box foam in the air box. Attach the air filter cover to the air box by hooking/snapping to bottom of it onto the the small bar of plastic at very bottom of the air box. The air filter cover is positioned so that the handle of the choke shutter is next to the label for the different choke "levels" Hands 1 minute
Figure 4-18: The position of the choke shutter with respect to the air filter cover
1
19 Attach the muffler kit to the cylinder on the side opposite to the air box. The two holes that extend through the muffler kit line up with two holes in the cylinder allowing two T-30 torque screws to be inserted and tightened. The gap created when putting the two halves together should be pointing left when inserting the screws. T-30 torque screwdriver, hands 3 minutes
Figure 4-19: Position of the muffler kit
2
20 Attach the ignition module to the crankcase with two long silver T-20 torque screws. Connect one side of the lead wire to the prong that extends out of the orange side of the ignition module. Insert the screw closest to the prong through the gold loop on the ground wire before inserting it into the ignition module. Attach the end of the rubber tube on the ignition module to the top of the spark plug. T-20 torque screwdriver, hands 4 minutes
Figure 4-20: The complete connection of the ignition module
3
21 Attach the two retainers (part 56) to the fan housing with two 4 mm hexagonal screws. The rounded side fits in the rounded groove made by the fan housing while the flat end extends over the starter pulley kit to further secure it. Size 4 hexagonal screwdriver, hands 2 minutes
Figure 4-21: The retainers helping secure the starter pulley kit
2
22 Load the engine assembly into the fan housing so that the air box is on the left and the muffler kit is on the right and secure it in place with four 5/32 inch hexagonal screws. The spark plug fits into a gap cut out from the fan housing. Feed the ground wire and lead wire through the rectangular hole in the fan housing allowing it to attach to the kill switch. Connect the ground wire to the side of the kill switch that reads hold and the lead wire to the other side of the kill switch. This proved to be difficult but getting the wires through the holes was a tricky task. H-3/32 hexagonal screwdriver, hands 4 minutes
Figure 4-22: The position of the engine assembly in the fan housing
3
23 Connect the cylindrical shaped part at the end of the throttle cable assembly to hole at the end of the trigger. Insert the small thin bar protruding from the bottom of the left throttle housing into the small hole toward the middle of the trigger. Attach the left and right throttle housing together over the very top of the drive housing to secure the throttle cable assembly and trigger in place. The throttle casings are connected by four 3/32 inch hexagonal screws that get inserted into the right throttle housing. H-3/32 hexagonal screws, hands 3 minutes
Figure 4-23: The throttle housing once connected
2
24 Attach the fuel tank to the crankcase on the side opposite of the cylinder with two T-20 torque screws. Connect the large fuel line to the part of the carburetor closer to the primer and connect the small fuel line to the lower part of the carburetor. T-20 torque screwdriver, hands 2 minutes
Figure 4-24: The fuel tank attachment
2
25 Attach the shroud to the outer casing with the fan housing with four T-20 torque screws. The shroud is positioned so that the gaps for the exhaust to escape are on the right side. T-20 torque screwdriver, hands 3 minutes
Figure 4-25: The position of the shroud connected to the fan housing
2

Original Assembly

The product was originally assembled in a factory via mass production. However, the steps taken to assemble the components are the same steps that the group took when reassembling the product. The same types of tools were used, but the order of the steps might have slight variation because some steps are interchangeable. For example, it does not matter at what point during the assembly the cutting head components are assembled - they can be assembled before or after the engine is assembled without having an impact on the finished product. When the group reassembled the product, hand tools were used, but when it was initially assembled to be sold automated machines and power tools were most likely used. The use of automated machines not only reduces the chance of error but makes the production consistent so all of the Weed Eater Featherlite 20C string trimmers are the same. Power tools were most likely used throughout the assembly because it makes the process a lot faster and the power tool itself generates the force needed to tighten the screws and fasteners rather than the person or machine doing the job. The steps taken to assemble the product are the same steps taken to disassemble the product except backwards. These steps might also be in a different order, but is not significant to the overall process taken.

Design Revision

Revision #1

Figure 4-26: Location of starter pulley assembly

The first alteration to the initial design of the product should be a change in the location of the starter pulley assembly to the back of the engine as shown in figure 4-26. The reason for this stems from the needs of both the operator during use, and anyone who would service the machine. The current location of the starter assembly is in front of the engine, closer to the drive shaft assembly. The flaws in design are due to poor user ergonomics when starting the machine. When starting, the operator is to place one hand around the handle, with a finger near the throttle lever for engagement once the machine begins ignition. The current location of the starter is only 8 inches away from the throttle. When the user is starting the machine, both hands are too close to each other, causing improper support of the unit when pulling the starter cable, as well as discomfort of the user. The other largest problem with the design is that if the starter is flawed, or needs repair, it is very difficult for the average person to access because the entire engine assembly has to be removed in order for the starter pulley kit to be reached. Therefore, the starter assembly should be moved to the rear of the engine, where all that is required for removal is the removal of three bolts. Although the average user will need not service the starter assembly, if an issue were to arise, the average user might be less apprehensive about fixing it themselves rather than bring the machine to a shop, or replacing the unit as a whole. Because of this, the lifespan, and cost effectivity of the machine has increased. As a result of the new location, the starter would sit at a different, less awkward angle, creating greater comfort for the operator. Making this design alteration would not have an impact on the consumer price because the the manufacturing processes are not being changed and the only part that would require alteration would be the rear plastic shroud - the current components are simply being rearranged. This design alteration would also have no impact on environmental factors or global factors.


Revision #2

Figure 4-27: Implementation of a clutching system

Another serious flaw with the current design of the product is the lack of a clutching system. A clutch would allow the engine to operate at low rotations per minute (idle) without the cutting head spinning. As shown in figure 4-27, once the engine operates at a high enough speed to cause the spring inside the clutch to stretch and expand the clutch to hook onto the component that rotates the drive shaft causing the cutting head to also rotate. This would be significantly safer when operating the machine when pets are potentially present, or when there is possibly gravel on the ground where it is started. With the implementation of a clutch, the head would not spin until the operator commands for it to do so. The weight of the clutching system is minimal when compared to the weight of the engine, addition of this unit will not offset the machine's balance. Since this improvement does not require a large amount of extra expenses for the manufacturing processes other than modifying the front shroud, implementing it into the current would not have a major impact on the consumer price. This alteration would reduce the amount of emissions released into the air because the prior to the cutting head rotating, the string trimmer will be running at the same low rpm, however there will be less strain on the engine, generating less power and using less gasoline. This also allows the gasoline to last longer and the user to fill up the fuel tank less often. Just like the other parts of a string trimmer, this component can also be produced globally allowing to be readily available anywhere where a string trimmer is needed.



Revision #3

Figure 4-28: Addition to the throttle system

One more part of the machine that needs alteration is the throttle system. In the current design there is no sort of safety lever in the throttle assembly. Consequently, the engine will increase speed whenever the throttle lever is touched, purposely or by accident. This can potentially be dangerous in an event where the machine is dropped or the throttle lever is accidentally nudged or pushed which would cause the engine to "rev" up, and the head to begin spinning at dangerous speeds. The implementation of a separate handle, as shown in figure 4-28, that needs to be squeezed first in order for the throttle to function makes the product more safe and would not greatly increase the overall price of the produce because the manufacturing required to produce it are minimal. Although it has negligible effect on environment factors, it can be globally produced allows it to be easily accessible for any company where string trimmers are manufactured and used.



References

http://www.protoolreviews.com/reviews/lawn-garden/stihl-fs-56-rc-e-trimmer/stihlFS56engine2.jpg

http://www.protoolreviews.com/reviews/lawn-garden/stihl-fs-56-rc-e-trimmer/stihlFS56throttle.jpg

http://www.plstudio.biz/product-feature-drawing/large/centrifugal-clutch.jpg