Gate 2 - Group 15 - 2012

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Contents

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.

The next set of challenges that our group will face will be in gate 3. The next gate covers a very large amount of material and is due right around when there is a large block of exams for all of our classes. In order to work around this issue, we will need to plan accordingly so that we can do all of the work for the gate while still leaving time to attend for other classes. This will be critical due to the size of the next gate assignment and the amount of detail that needs to be put into it.

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 # Difficulty Level Description Tool Required Photograph
1 1 Remove screw connecting lower guard lift lever to lower guard and then remove lever. T20 Torx Screwdriver Group15F2012lowguardlift.jpeg
2 2 Unscrew blade nut in the center of the saw and remove along with inner and outer washers. Torque Wrench (13mm) Group15F2012step2.jpeg
3 3 Remove screws joining housing to upper blade guard (requires stablization of saw to prevent rotation due to force). T20 Torx Screwdriver Group15F2012step13.jpeg
4 1 Remove screws from back of motor housing. T20 Torx Screwdriver Group15F2012step4.jpeg
5 1 Remove screws connecting upper blade guard to housing. T20 Torx Screwdriver Group15F2012step5.jpeg
6 4 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 Group15F2012step6.jpeg
7 2 Rotate lower blade guard and remove final screw connecting upper blade guard to the housing. T20 Torx Screwdriver Group15F2012step7.jpeg
8 2 Detach spring connected from the lower to upper blade shaft. Slide Lower blade guard and pinion shaft out of center of circular saw. Hands Group15F2012nophoto.jpeg
9 1 Remove the spring and pinion shaft connected to lower blade guard. Hands Group15F2012step9.jpeg
10 4 Pull armature out of upper blade guard. Hands Group15F2012step10.jpeg
11 2 Remove two screws attaching 120V field to housing. T20 Torx Screwdriver Group15F2012step11.jpeg
12 5 Press in both spring stops and pull out of motor housing. Hands Group15F2012step12.jpeg
13 2 Remove screws holding handle halves together. T20 Torx Screwdriver Group15F2012nophoto.jpeg
141 Separate trigger from handle half. Hands Group15F2012step14.jpeg
15 1 Slide 120V field out of motor housing. Hands Group15F2012nophoto.jpeg
16 1 Detach power supply wires from 120V field. Hands Group15F2012nophoto.jpeg
17 2 Pull bearing out of upper blade guard. Hands Group15F2012nophoto.jpeg
18 2 Remove wing nut from foot. Hands Group15F2012nophoto.jpeg
19 5 Remove rolling pin connecting upper blade guard to foot. Hammer and Allen Key/Screwdriver Group15F2012step19.jpeg

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 Group15F2012housingF.jpeg 2 1 Motor Housing (Back) Group15F2012housingB.jpeg 3 1 Outer Motor (120V Field) Group15F2012outmot.jpeg
4 1 Inner Motor (120 Armature) Group15F2012innermot.jpeg 5 1 Trigger Group15F2012trigger.jpeg 6 1 Power Connection Cable Group15F2012powercon.jpeg
7 1 Upper Blade Guard Group15F2012upbladeg.jpeg 8 1 Bearing Group15F2012bearing.jpeg 9 3 Short Torx Screws Group15F2012shsc.jpeg
10 6 Medium Torx Screws Group15F2012medsc.jpeg 11 4 Long Torx Screws Group15F2012longsc.jpeg 12 1 Lower Blade Guard Group15F2012lowbladeg.jpeg
13 1 Blade Nut Group15F2012bladenut.jpeg 14 1 Inner & Outer Washers Group15F2012wash.jpeg 15 1 Spring Group15F2012spring.jpeg
16 1 Lower Guard Lift Lever Group15F2012lowguardlift.jpeg 17 1 Wing Nut Group15F2012wingnut.jpeg 18 1 Roller Pin Group15F2012rollpin.jpeg
19 2 Spring Stops Group15F2012springstop.jpeg 20 1 Pinion Shaft Group15F2012pinion.jpeg 21 1 Handle Group15F2012handle.jpeg
22 1 C-Ring Group15F2012cring.jpeg
23 1 Saw Blade Group15F2012sawblad.jpeg
24 1 Utility Wrench Group15F2012utilwre.jpeg
25 1 Propeller Group15F2012prop.jpeg 26 1 Foot Group15F2012foot.jpeg

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 Disassembly\'\'\'

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.

Group15F2012overalldiff.jpg


- 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.

Group15F2012diffr.jpeg

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

Group15F2012diffstep.jpg

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

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

Group15F2012subsystems1.jpg

Figure 5. Diagram of overall function of circular saw.

Group15F2012subsystems2.jpg

Figure 6. Diagram of subsystems in circular saw.

Analysis of Connections

The subsystems are connected in the way that they are in order for the machine to work in the most functional way possible. The handle and trigger are connected to the motor physically so that current may pass through the power cord from an external source and into the motor when the trigger is pressed in by the user. The propeller is connected to the 120V armature so that it may use the rotational energy provided by the motor. It uses this energy to blow out any debris that may accumulate while the saw is cutting and may also cool the inside of the motor housing down by removing thermal energy through the exhaust vents. The blade is also physically connected to the motor via the pinion shaft and bearing so that the rotational energy supplied by the motor may be used to spin it and cut materials. Lastly, the foot is connected to the base of the circular saw so that it may offer it support and function as a stable surface for the user to guide their path upon.

  • Physical Connections
The physical connections are implemented primarily by using Torx head screws with the exception of the power chords and the pieces that rotate such as the propeller or bearing. The housing and handles are held together with Torx head screws and are not very difficult to remove, which suggests that they are intended to be taken apart in the event that repairs need to be made inside of them. The power cords are connected to the motor via metal loops, which are easily slid off of the points where they make contact with the motor. This suggests that the connection is designed to be removable so that the wires may be removed or replaced if they become damaged. On the other hand, components such as the bearing and propeller are connected to the circular saw using a force fit and have large amounts of friction holding them in place, which suggests that they are not meant to be disassembled because it could affect the performance or safety of the machine.
  • Signal Connections
The signal connections include the trigger and motor which are connected by the main power cords. When the trigger is pressed down, the electricity is allowed to flow from the trigger and enter the motor where it may then be converted into mechanical energy. The signal is driven by human action because the trigger needs to be pressed down in order for the signal to occur. The trigger allows for the operator to control when the electricity flows to the motor and thus serves as a point for the user to provide a signal for the product.
  • Mass Connections
Mass is transferred within the circular saw via the upper blade guard and exhaust ports. When material is cut, the waste material travels along the upper blade guard and exits the other end where it is sprayed onto the floor or surrounding area. Any waste material that finds its way to the motor housing is expelled by the propeller, which spins and creates an air current to carry dust along until it exits the exhaust ports. The mass flowing within the product is primarily waste material and eventually leaves the system so that it does not interfere with any of the components.
  • Energy Connections
The primary flow of energy in the circular saw is the flow of electricity. The electricity travels from an outlet usually found within the operating environment and travels through the main power cords until it reaches the trigger. Upon signalling, the trigger will allow the electricity to flow to the motor. Once the electricity reaches the motor, it is converted to mechanical energy which is used to ultimately rotate the saw blade. Other forms of energy include thermal and acoustic energy. Thermal energy is associated with the blade from the friction occurring when materials are cut. This thermal energy is dissipated into the surroundings after the material, waste, and saw blade cool down. Thermal energy also flows from the active inner parts of the circular saw, where it is then dissipated through the exhaust ports in the back of the motor housing. Lastly, acoustic energy is associated with the sound of the saw blade cutting material and is immediately dissipated to the operating environment.

Performance and GSEE Factors

Performance influences the connection types found in the circular saw because the parts that are designed to make contact with or experience forces from the material being cut are connected with force fits that are very difficult to remove. If these components become loosened, then they could vibrate and cause the system to not function as efficiently as it was intended to. In addition; if spinning parts become loose, then they could also pose a serious safety hazard to the user. The components connected with screws or loops are parts are designed that way that they are easily removed in the event that repairs need to be made inside of the circular saw.

The designs of the types of connections made in the circular saw are primarily influenced by economical, global, societal, and environmental factors.

  • Economic
The economic concerns were material cost and the method of obtaining the materials to construct the components and their connections. For example, metal screws are easy to manufacture, may be mass produced, are extremely common in places such as hardware stores, and are relatively cheap. In addition, they serve as good ways to keep components physically connected, which makes them an affordable option when considering the cost of constructing the product.
  • Global
The global factors are concerned with the area in which the circular saw is sold. If components in the saw degrade, then they must be located within a region where new ones are easily found and may be replaced. If not, the connections within the circular saw will be interrupted and the product will be potentially rendered useless. In addition, the location of the typical customer would be in a garage or construction zone. Since these areas are not subjected to extreme climates, the connections within the saw do not need to be manufactured with the same strength as say, the connections within a piece of aerospace equipment which are often subjected to extremely high or low temperatures.
  • Societal
The societal concerns have to do with the safety based on the way that the connections are established. The force fits indicate that a very secure method of holding the rotating components was necessary in order to keep them from becoming detached and harming the user. In addition, torx screws require a screwdriver with a type of head that isn\'t typically owned by the average person. This is evidence that the tool is not meant to be taken apart due to safety reasons.
  • Environmental
The environmental factors have to do with the end of the product’s life. Broken components and circular saws that have been rendered useless need to be disposed somewhere, so the parts may have been designed such that they may be re-used or will contribute the smallest amount of waste possible.

Analysis of Arrangements

Each subsystem is placed in a way such that it may optimally interact with the other subsystems that it is intended to. The trigger and handle are arranged with the power cords and are placed in direct connection with the motor so that there is a straight path for current to flow through. The cords are arranged simplistically and may be easily removed if the handle is disassembled. The propeller is purposefully placed on the 120V armature so that it may directly use the rotational motion supplied by the motor. In addition, the saw blade is arranged such that it receives the desired amount of torque from the pinion shaft, which is turned by the motor. This is designed as such so that the blade still utilizes the rotational motion of the motor, but achieves a desired speed through the use of the pinion shaft. The foot is placed directly under the circular saw such that it may function to support the entire device and serve as a stable surface to guide the saw upon while cutting material.

Though the subsystems may be arranged closely to one another, they are placed in a way such that the order in which they function allows the device to perform its function. For example, the motor, propeller, and blade are arranged so that they take full advantage of the rotation of the motor, but they are not intended to directly interact with the foot because they serve entirely different purposes. The foot serves as a support and base to move the circular saw in a straight path while the motor, propeller, and blade use rotational motion to accomplish their tasks.