Gate 2 - Group 15 - 2012

Revision as of 03:14, 26 October 2012

Introduction

The purpose of the second gate was to get an in depth understanding of the outer and inner subsystems involved in the circular saw. Determining how these subsystems did or did not interact with one another was also crucial. To accomplish this, a complete dissection of our product was done. Each step was recorded in detail for further analysis. This was be crucial because it will be used in the future for determining how the various connections are implemented and also how they directly/indirectly effect performance and arrangement within the product.

Project Management: Preliminary Project Review

Cause for Corrective Action

Overall, the work and management plans we developed during gate 1 have served us very well. While there have been a couple challenges and the process was not flawless, we have had a fair amount of success. At this point, we are on track to finish all of our requirements efficiently and on time. Considering all of the different factors that have played a role in our success so far, many are due to the plans we created ahead of time. Some of the key aspects that have worked for us are:

• Creation of an outline of dis-assembly steps based on what we expected to encounter in the circular saw.
• Knowledge of what tools (in general) would be needed ahead of time.
• Creation of a properly organized cataloging system.
• Emphasis on taking ample time to proceed with caution in order to prevent careless mistakes.
• Creation of clearly defined roles for each member to contribute.
• Taking advantage of the ability of the group members to work well together.

However, there have been some challenges that we have faced along the way as well. Since nobody was particularly familiar with the structure of a circular saw, it took a while to dis-assemble it properly. At each step in the process, we had to make sure that we carefully considered all of the possible outcomes due to our actions. While it took a little while, the extended usage of time ensured that no costly mistakes were made. Furthermore, some of the components were very difficult to remove and took a lot more time to do so properly. In fact, one of the components was left intact since it was force fit by a machine. The part’s removal had no real benefit and we did not have the proper tools to undo the strong bond in place.

Originally in gate 1, we had planned to make decisions based off of an evaluation of the difficulty it would take to remove a part and how its removal would affect the rest of the system. In the end, our original plans and guidelines proved to be very useful as we took apart our circular saw. While they were not extremely specific, their intention was to lay a foundation that would help us proceed with confidence. After the entire process, it seems that despite several challenges, we have managed to dissect our product successfully. Our management and work plans played a significant part in accomplishing our tasks and will continue to be for the remainder of the project.

Product Archaeology: Product Dissection

In order to dis-assemble the product, the following tools are needed;

• T20 Torx Screwdriver
• 13 mm Torque Wrench
• Allen Key Set
• Hammer
• Hands

Product Dissection Guide

Step #	Description	Tool Required	Photograph
1	Remove screw connecting lower guard lift lever to lower guard and then remove lever.	T20 Torx Screwdriver
2	Unscrew blade nut in the center of the saw and remove along with inner and outer washers.	Torque Wrench (13mm)
3	Remove screws joining housing to upper blade guard (requires stablization of saw to prevent rotation due to force).	T20 Torx Screwdriver
4	Remove screws from back of motor housing.	T20 Torx Screwdriver
5	Remove screws connecting upper blade guard to housing.	T20 Torx Screwdriver
6	Remove C-ring sheathed behind the guards using two Allen keys small enough to maneuver in the space available. Use one end of each wrench to push each end of the C-ring until it slides off (requires solid stabilization of the circular saw to prevent movement from a large applied force).	Allen Keys
7	Rotate lower blade guard and remove final screw connecting upper blade guard to the housing.	T20 Torx Screwdriver
8	Detach spring connected from the lower to upper blade shaft. Slide Lower blade guard and pinion shaft out of center of circular saw.	Hands
9	Remove the spring and pinion shaft connected to lower blade guard.	Hands
10	Pull armature out of upper blade guard.	Hands
11	Remove two screws attaching 120V field to housing.	T20 Torx Screwdriver
12	Press in both spring stops and pull out of motor housing.	Hands
13	Remove screws holding handle halves together.	T20 Torx Screwdriver
14	Separate trigger from handle half.	Hands
15	Slide 120V field out of motor housing.	Hands
16	Detach power supply wires from 120V field.	Hands
17	Pull bearing out of upper blade guard.	Hands
18	Remove wing nut from foot.	Hands
19	Remove rolling pin connecting upper blade guard to foot.	Hammer and Allen Key/Screwdriver

Figure 1. Step by step dissection guide

Total Dissection Time: 1 hour and 13 minutes

Catalog of Parts

Part #	Quantity	Part Name	Photograph	Part #	Quantity	Part Name	Component Photograph	Part #	Quantity	Part Name	Photograph
1	1	Motor Housing		2	1	Motor Housing (Back)		3	1	Outer Motor (120V Field)
4	1	Inner Motor (120 Armature)		5	1	Trigger		6	1	Power Connection Cable
7	1	Upper Blade Guard		8	1	Bearing		9	3	Short Screws
10	6	Medium Screws		11	4	Long Screws		12	1	Lower Blade Guard
13	1	Blade Nut		14	1	Inner & Outer Washers		15	1	Spring
16	1	Lower Guard Lift Lever		17	1	Wing Nut		18	1	Roller Pin
19	2	Spring Stops		20	1	Pinion Shaft		21	1	Handle
22	1	C-Ring
23	1	Saw Blade
24	1	Utility Wrench
25	1	Propeller		26	1	Foot

Figure 2. Complete list of parts with pictures

Product Dissection Challenges

Though the product dissection was successful, our group faced a number of challenges. One of our group members was absent during the dissection, but we were able to make up for that by designating a documenter, a photographer, and two people to work on the disassembly. Our plan worked well since most of the dissection steps did not require more than one or two people to work on the physical dissection; however there were a few steps that required everyone in the group to hold the product securely so that greater force could be applied during the removal of a part. In addition, splitting up the tasks of photographing and documenting ensured that these two steps were done simultaneously and overall increased the speed of the dissection process.

Another challenge faced during the dissection process was that our group initially went in with no plan for removing any of the parts. We tackled this issue by carefully considering which steps to take after removing each part and thought about how the removal of one part would affect our ability to remove another.

Lastly, the greatest challenge that our group faced was the attempt to remove the physically connected parts of the circular saw such as the rolling pin holding the upper blade guard and foot together. Since these parts were inserted using a machine and were physically connected with large amounts of friction, they required great amounts of force to remove and we were not able to completely disassemble them with the simple tools at our disposal.

Ease of Dis-assembly

The difficulty of each step can be approximated by taking into consideration the amount of time it takes, the precision required, and the sheer amount of force necessary. A slight increase in difficulty may also be added if it is easy to damage a part during that dissection step. Due to the varying nature of each consideration, a single component of great difficulty can make the step rate highly on the scale. Alternatively, multiple components with a medium rating can contribute to create an overall more difficult step. To accommodate this factor the overall difficulty will allow a range for most of the difficulty components. Minimum and maximum values will dictate some placement (shown in parenthesis), with the following formula taking over for overlapping possibilities.

- Note: this allows for a theoretical maximum overall difficulty of 6, but we have decided to regard it as a 5 for the sake of simplicity.

The overall difficulty is based on a 1-5 rating, with 1 being the easiest and 5 being the toughest. The difficulty components are also based on a 1-5 scale, except for the possibility of damage which is based on a 0-4 scale. During all steps the assumption will be made that the proper tool is used. If a different tool is used a step’s difficulty could increase exponentially or become nearly impossible to complete. A (T) next to the difficulty rating will signify that a tool is required for that step.

Figure 3. Difficulty rating scale based on the min/max constraints and formula provided

Figure 4. Actual difficulty rating of each step

Subsystem Connections

Connections of Subsystems

The subsystems of the circular saw were determined to be the following;

• Power Supply Cord & Motor
• Propeller & Exhaust Vents
• Foot
• Handle & Trigger
• Saw Blade & Pinion Shaft

Below are diagrams that relate the subsystems and their functions to one another.

Figure 5. Diagram of overall function of circular saw.

Figure 6. Diagram of subsystems in circular saw.

Analysis of Connections

Analysis of Arrangements