Weed whacker
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| Trigger Sleeve Screw || 7 || Secures trigger sleeve to upper shaft. || 0.1 || Steel || Heading and Thread Rolling || [[Image:weedwhacker_triggersleeve_screws1.JPG|200px]] | | Trigger Sleeve Screw || 7 || Secures trigger sleeve to upper shaft. || 0.1 || Steel || Heading and Thread Rolling || [[Image:weedwhacker_triggersleeve_screws1.JPG|200px]] | ||
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'''**'''Note: Some assemblies and parts were not disassembled in order to avoid destroying the parts. | '''**'''Note: Some assemblies and parts were not disassembled in order to avoid destroying the parts. |
Revision as of 22:22, 18 September 2008
Contents |
Executive Summary
For our Engineering Design II project, we have decided to dissect and improve the 2-Cycle Straight Shaft Trimmer made by Troy-Bilt. We intend to improve its user functionality, the manufacturing process, and also reduce the impact the life of this product has on the environment. We will disassemble this trimmer in order to take a close look at all of its parts. By performing DFMA, FMEA, and DFE, we will carefully document our findings, decisions, and conclusions in order for our client to clearly see the merits in the product we have reinvented.
Stakeholders
There are several stakeholders that will be affected by our changes to this product. They include:
The manufacturer
Fulltime/partime gardeners
Lawn owners
Raw material suppliers
Gardening/home improvement stores
Product Usage
Usage of a weed whacker is very straight forward. For situations and areas where a lawnmower would be difficult to use, the hand-held weed whacker becomes a tool of choice. The convenience of this gardening tool comes from its ability to quickly cut vegetation in hard to reach places without damaging structures that may surround it.
In order to power on the weed whacker, first make sure there is sufficient gas in the tank. Click the on/off switch to on. Intructions on how to start the motor are included on a sticker on the straight shaft, and are as follows:
For a cold engine:
1. Press bulb 10 times.
2. Move blue choke lever to "1".
3. Squeeze trigger and pull rope 5 times.
4. Move blue choke lever to "2".
5. Squeeze trigger and pull rope till engine starts. If it doesn't start, repeat steps 1-5.
6. Let engine run 15-30 seconds.
7. Move blue choke lever to "3".
For a warm engine:
1. Move blue choke lever to "2".
2. Squeeze trigger and pull rope till engine starts.
3. Move blue choke lever to "3".
Once the engine is running, it is a simple matter of pointing the spinning wire towards the vegetation you wish to cut. If you wish to lengthen the wire, tap the bottom of the weed whacker to the ground, and a pre-measured length of wire will be added on. To stop the motor, simply press and hold the off button.
System Functions
After starting the engine, the weed whacker is controlled by a single trigger. This trigger controls the fuel feed to the engine allowing the user to change the rotational speeds of the two-cycle engine.
The power of the engine is transferred to an axle contained in the upper shaft. The axle is held in the center of the shaft using spacers. The end of the upper axle is shaped to slip over the end of the lower axle. The two axles connect using a square cross section that allows the power from the upper axle to completely transfer to the lower axle. To compensate for the possibility of misalignment, the two axles are made to be flexible.
The lower shaft is held to the upper shaft using the shaft clamp. This shaft clamp is screwed directly into the upper shaft, and holds the lower shaft by the metal nub.
At the bottom of the lower shaft, there is a large metal housing. Within this housing, there are four bearings and a set of bevel gears. The lower axle attaches to the bevel gear in the same manner as the two axles. Two bearings are placed on each end to keep the bevel gears in contact. With the gears, the power transfers completely from the lower axle to the weed whacker head.
Attached to the weed whacker head, is a reel that contains a long piece of wire. The wire is fed through two small holes exposing approximately 5 inches of wire. While the head is rotating, the wires are used to cut weeds. Due to the high speeds of the wire, there is no need for sharp edges, as the impact from the wire alone is enough to cut through plants.