Gate 3 - Group 15 - 2012
The purpose of the third gate was to complete detailed analyses of the different parts of the circular saw. The analyses examined the functions of each part of the circular saw and how they were manufactured. In addition, the analyses covered an in dept investigation of the most essential parts of the tool and explained the reasons for their designs. Upon completion of the study, an engineering analysis of the saw blade was conducted and numerous suggestions for design revisions were made for the circular saw on a component level.
Project Management: Coordination Review
Cause for Corrective Action
The only challenge that our group has faced during this gate was that everyone had been on a very busy schedule while studying for exams in all of our courses while trying to complete this gate, however we have worked around this by putting enough work into each part every day so that they could be completed by our predetermined due date without having to do all of the work for them at once. The next challenge that our group will face will be managing the work for gate 4 while everyone is home during the fall recess. Since the next gate will be due the following week after we return, we will need to divide up all of the work and set a predetermined due date ahead of time so that group members can work on their parts at home.
Product Archaeology: Product Evaluation
Figure 1. Table of Components
Component Complexity Scale
Based on the three main factors constituting the manufacturing of a component (Function, Form, and Manufacturing Method), we can create the following chart for the use in assigning complexity ratings to different parts of the circular saw.
For a more accurate complexity rating, the components were broken down into seven smaller subcategories. Function was split into two separate parts, number of functions and motion of part. Form was broken down into aesthetic quality, finish level of product, and complexity of geometry. The manufacturing method portion was sectioned into difficulty of process and the number of processes needed.
All seven of these components are ranked individually on a scale from 1-3. These “points” are then used on the complexity conversion chart to get the corresponding level of complexity. The first tiers of the complexity rating chart consist of a two point gap, the fourth tier has a three point, and the fifth tier a six point. This was done due to the similar nature of many of the circular saw parts and the design of the table outlining the complexity points. If an even distribution of points was done, then the majority of parts would have ended up in the same tier when they shouldn't have. This is because it is very difficult for even a complex component to contain all seven levels of difficulty on a high scale. This method of distribution allows for a more accurate level of final difficulty appraisal. The two-step process also helps to get a more accurate final complexity rating. It has the added benefit of being more detailed, and although there are more parts, each part has a more intuitive description. This allows the rating system to actually work faster than a fewer component, but more complex rating style.
|Complexity Points||# of Primary Functions||Motion of Part||Aesthetic Quality Needed||Finish Level of Product||Complexity of Geometry||Difficulty of Manufacturing Process||# of Processes Needed|
|1||1||Does not move||None/Minimal||None/Minimal||Low||Low||1-2|
Figure 2.1 Complexity Point Chart
|Complexity Rating||# of Complexity Points Required|
Figure 2.2. Component Complexity Rating Chart
- Component Function
Although they are some of the cheaper internal parts of the circular saw, they are still arguably one of the most important. These carbon brushes are an important intermediate flow channel that helps to transmit electrical energy from stationary wires to a rotating motor shaft. Without this part the motor could not function, and thus the circular saw would be worthless (along with most other modern motors, alternators and generators). They also provide some friction, but that is a necessity to make a proper connection and to transmit the energy. In an ideal case the friction would be eliminated if possible to increase performance. This component operates in a harsh environmental and is constantly being submitted to frictional forces caused by the rotation of the motor. This will be evaluated and explained more in depth in the materials section.
- Component Form
The general shape of the component is that of a rectangle. One rectangular hole is cut on the front horizontal face, and two smaller ones are cut on the back horizontal face. Another smaller, but movable rectangle extrudes from the primary one. It has a slight indented curve to the front face to hug the shaft and groves. The back end of the rectangle opens up and widens to form a base, but is covered by a thin copper plate. This copper plate is in connection with a copper roller pin extruding from the front horizontal face of the main rectangle. If the base was removed the brush would be both horizontally symmetrical in the YZ and XY plane, but it would not have axial or vertical symmetry. To and from all of the extreme points, the carbon brush measures 13/8” x 1” x 5/8” and weighs approximately ¼ of an ounce.
This component is shaped this way due to economical and functional concerns. The rectangular main body helps to provide rigidity, along with being able to contain the internal spring. The rectangular shape is also easy to work with, shape and modify into its final form. The long and thin copper plate helps to maximize surface area, and thus increase potential contact points while minimizing cost. The graphite rectangle’s curve and groves help to ensure a better connection with the rotating shaft.
The carbon brush is comprised of four different material types. The plastic casing was chosen because of its rigidity and ease of manufacture. However the primary reason for its use is due to its low cost. This allows the savings to be passed onto the consumer, allowing for a cheaper product. The copper is used for the primary transfer of electrical energy through this component. Copper was chosen due to its relatively low cost and conductive properties. Copper was shaped into the base plate and a roller pin to provide contact with stationary wires. A string of bundled copper wire also runs through the spring inside of the plastic casing. This wire transfers the electrical energy from the copper plate to the graphite brush at the end. The brush’s material was carefully chosen to help mitigate slippage with the motor shaft while still transferring electrical energy. Friction was also intended to be minimal. Graphite is a conductor, but it has the added quality of being “soft” which allows it to slowly wear away. This is not ideal, but necessary for the function of the part since it provides a smoother connection. Steel was chosen for the spring since it is economical and also easily worked with. The spring provides a force to the graphite brush which keeps it in contact with the shaft as it slowly wears away, allowing it to be used even as its size shrinks.
As stated above manufacture processes were not the main concern in the selection of these materials. The main driving factor was the dire for low cost, but still dependable and functional components (thus an economical factor). Globally all of these materials are widely available allowing the product to be manufactured in a multitude of different locations promoting versatility in the production process.
This component has virtually no aesthetic properties; it is purely for functional reasons. Proof of this is the fact that it is not visible to the consumer unless the product is completely stripped apart. The plastic parts of the component are black, with the graphite being grey and the copper bronze. The black finish was chosen primarily for cost reasons, while the grey and bronze colors are the inherent colors of the materials being used. The plastic has a smooth/glossy finish, but this is due to the manufacturing process and not so much for a functional reason. The graphite however does have a rough characteristic to it, and this is to provide clean contact with the motor shaft.
- Manufacturing Methods
Different manufacturing processes were used for the different materials. The central plastic casing was injection molded. This is evident due to the ejector pin marks at the top of the component. A minor deformation can also be seen on the product which was probably due to an uneven filling of the mold. The copper portion, being primarily flat, was stamped out. The small tubular portion was rolled to acquire its designated shape. The steel springs were first drawn out into a wire like substance and finally spun into its final shape. Minimal evidence of the last two methods exists because they are partially hidden by the plastic casing. The nature of both processes also leaves little evidence behind as well. The material choices did have some impact on the processes chosen. Injection molding is a common, fast, and cost effective method of plastic parts of low to high complexity. The plastic casing fits this profile perfectly. However the copper plate and steel spring’s material choice had little impact on their manufacture processes. Their overall shape and desired functions had much more of an impact. All of these processes were chosen for a few different reasons. First, their relatively low cost contributes to the desire to be economical, helping to pass the savings on to potential customers and the manufacturer alike. The ease of these processes also allows this product to be made universally on a global scale. This allows for more variety and flexibility in the manufacture process and where it is ultimately done. Furthermore injection molding wastes little material making it an excellent choice to reduce the company’s net environmental impact.
- Figure 3. Manufacturing Method Evidence for Carbon Brushes
- Complexity Rating
Using the chart (Figure 2.1) defined earlier in this report we will now analyze the complexity of this part. The carbon brush only has one primary function, transferring electricity from the stationary wires to the moving shaft (1). Motion within the part does happen due to the spring and external forces caused by the rotating shaft. However this motion is constrained (2). This is an internal part and not seen by the user, its aesthetic quality needed is minimal (1). The finish level of the product is also minimal due to the nature of the part (1). The carbon brush does have a moderately complex geometry however due to the various holes, gaps and shapes comprising it (2). The difficulty of the manufacture processes average to have a moderate difficulty (2). The number of processes needed for the completion of this part is over five, due to all of the different materials (3). Summing all of the complexity points we get the number 12, which gives this part a complexity of 3 using the conversion chart (Figure 2.2).
- Component Function
The saw blade is an integral component of the circular saw. It is also the only real part of the saw that can be interchanged freely to allow more versatility. The saw blade is the primary cutting agent of the circular saw and thus has a lot to do with the performance of the entire product. A poorly made blade is not only inefficient, but also dangerous to use. The circular saw blade takes rotational energy from the motor and uses its inertia to cut through solid objects. Friction and material forces counteract the applied rotational energy gained through electromagnetic conversion. The saw blade is “open” (not protected) so it has direct contact with the environment. However since it is a corded (and not battery operated) the product will primarily be used indoors where environmental concerns are limited. The circular saw’s working environment can range from a relatively clean garage to dusty factory. The garage is the more likely scenario since this is a relatively low end product and designed for the average consumer.
- Component Form
The overall shape of the circular saw is that of a circle; however teeth are cut into the edges. It has axial, horizontal and vertical symmetry (since it is a circle). The product does have three dimensions, but its primary characteristics are present in a two dimensional configuration. The blades shape is due to the attempt to maximize cutting efficiency, while still providing a durable and resilient product. If the blade was too thick its cutting efficiency would be decreased and it would waste material while cutting. However if the blade is too thin it would wear out quicker and also be more prone to damage. This particular blade has a diameter of 7 ¼” and a width of slightly under ¼”. The total weight of the blade is slightly over one pound.
Circular saw blades are primarily made of steel. Steel was chosen due to its cost to strength ratio. It is also widely available and easier to work with than some other metals. The strength of steel is also a big advantage since it will have to endure a wide range of rotational and counteractive resistive forces. Most saw blades also have carbide tips added to them to increase performance and longevity. The tip material was chosen due to its material properties. For its cost ratio and availability it helps to prolong the life of the saw and enhance performance more than most other available materials. As stated above the material choices were largely driven for economic purposes. However both materials are also widely available on a global scale. This allows them to be manufactured in different locations with ease. Also by prolonging the overall life of the blade through the use of carbide tips the net waste of the product is reduced. The blades are able to last much longer, thus lowering the disposal rate and ultimately how many blades end up in a landfill or that need to be recycled. This decreases the impact on the environment significantly. On a societal front, the steel also helps to ensure a high level of safety and functionality to the consumer.
The aesthetic properties of the saw are of a limited and secondary nature. The smoothness and fine surface finish of the blade helps to increase performance; however it does give the blade a more professional and reliable look. A blade with a rough finish would give off the appearance of being unreliable and potentially dangerous, so some aesthetic appeal can came into play. Additionally component is mostly grey, but that is only because that is the color of ordinary steel.
- Manufacturing Methods
Circular saw blades are initially cut out of a sheet of steel, a laser is usually used here. This gives the saw its general appearance, including its teeth. The blades are then fed into rollers that press groves onto both sides. These act as tension rings that help to decrease vibration within the blade and to increase its durability. Without these groves the blade would not cut straight. The blade is then fed into a different type of roller that forces the disk into a completely flat shape. This helps to eliminate any abnormalities present in the original sheet metal. A grinding wheel then polishes the blade giving it a smoother finish, enhancing its look and reducing the friction it will face while in use. The disks are then baked in an industrial oven to increase their hardness. Once the steel portion of the blade is finished carbide tips are applied to each of the saw’s teeth. The carbide tips are first cut, their precision is confirmed with a laser, and finally they are brazed onto the actual saw blade. Evidence of these processes is limited due to the lack of characteristic left by these methods. However we can take this lack of evidence as a form of proof itself. For example laser cutting will not leave any ejector or riser marks. The only real visible evidence of any manufacture method is the heat/fusion marks left by the brazing process. These processes are not catered to the materials selected for the circular saw blades. In fact it is arguably the opposite. Steel was chosen due to its cost, availability, and ease of alteration. Having a material that is easy to work with makes the manufacture process much easier. The shape of the saw blade was a decisive factor in the processes selected however. The simplistic, circular and ultimately thin profile makes it the perfect component to be laser cut out of sheet metal. It is albeit wasteful on material, but it ensures a durable final product free of most impurities and weaknesses due even flows and/or cooling. Ultimately this boils down to economic and societal concerns. This method of manufacture ensures a safe product for its users, but is still relatively cheap allowing for a low cost final product that can still net the manufacturer a sales profit. An added benefit is that steel and carbide are relatively common materials allowing them to be manufactured globally with ease.
- Figure 4. Manufacturing Evidence for Saw Blade
- Complexity Rating
Using the chart (Figure 2.1) defined earlier in this report we will now analyze the complexity of this part. The saw blade only has one primary function, which is the cutting of material (1). Motion does occur, however it is constrained and occurs only about an axis (2). The aesthetic quality of the saw blade is minimal (1), however its finish level is high to ensure an efficient product (3). The complexity of the geometry itself is low being a simple two dimension shape (1), but the difficulty of the manufacture processes are of a moderate level (2). The two types of rolling, laser cutting, heat tempering and soldering validates my assessment of that assumption. This ties into the number of processes needed, which as we see is over five (3). Summing all of the complexity points we get a net score of 13, and thus a level 4 on the complexity scale.
- Component Function
The main function of the trigger is to act as the main interface between the user and the circular saw. The trigger senses the input from the user, and then uses that input to determine if the saw should activate or remain off. This is a relatively basic trigger and it only has two essential positions, on or off. No variable levels of speed or achievable with this trigger. However that is by design. During circular saw cutting applications maximum speed is usually preferred as it allows for smoother and quicker cuts. Having a variable sensing trigger could complicate the users experience and potentially become a safety hazard. The cost of the circular saw would also increase. There are some genuine, but limited applications of having a variable sensing trigger on a circular saw. However the raw economical costs coupled with the risks to user safety make a basic trigger the better option. Half of the trigger is exposed, while the other half is protected by the handle. This means that the trigger is susceptible to outside conditions. Being a corded product though, the primary use of this circular saw will be indoors. Its working conditions can range widely from a relatively clean home, to a dusty factory. Since this is a lower end product it will tend to see much more household use than industrial use.
- Component Form
The main shape of the trigger itself is that of a black rectangle. The center of the trigger is moderately concave, with its slope asymmetrically distributed to the top and bottom portions. This helps to produce an ergonomic effect that reduces fatigue and wear on the user’s finger during prolonged operation. Attached to the main trigger is a black rectangle that houses the vital electrical components of the trigger. This mechanism is hidden when the circular saw is fully assembled however. Symmetry is limited, but it can be argued that horizontal symmetry does exist in the YZ plane. This component is three dimensional by design, since it would fairly difficult to fit electrical components inside of a two or one dimensional object. Not to mention that it would be rather uncomfortable to use a two dimensional trigger. This component is measured at roughly 2” x ½” x 1.5” from extreme end to extreme end. It also weighs roughly 3 ounces.
This component is entirely compromised from plastic (except for the internal circuits). Plastic was chosen since this module will not be experiencing any extreme forces, so a more durable material is not needed. Plastic is also very cheap compared to most materials. It is also easy to work with and can be conformed into a variety of shapes with minimal effort along with coming in a range of colors. Plastic is also more comfortable when it make contact with human skin than some other materials, like steel for example. Multiple contributing factors can be seen to come into play for these decisions. The dark black color contrasts with the red handle and helps to attract the user’s eye to the trigger. This helps to make it more universally accessible on a global scale. The selection of plastic was due to its low cost, along with the notable reasons mentioned above. These all contribute to plastics economic reasons for selection. Also environmentally the plastic components can be melted down and recycled with relative ease.
Aesthetically the triggers functions are limited. However the same attributes that make it aesthetically pleasing also make it a better designed product. The concave shape of the trigger along with its smooth finish lets a potential buyer know that they can use the product for long periods of time with low finger fatigue/discomfort. The black color contrasting against the red handle also lets a potential buyer/user easily see the trigger component. This is important across language barriers and makes the trigger more universal.
- Manufacturing Methods
Injection molding was used to create the trigger system. A four step process was used during the manufacture of the trigger however since the trigger is integrally composed of four separate parts. The main body is comprised of two hollow shells that are held together by a tamper resistant screw. The actual trigger and top push switch were molded separately as well. They were fitted together to complete their form. Evidence of this process can be seen through ejector marks on the head and body of the shell. The shape and material of the part can also help in the determination of the process used. Injection molding was selected because it is a viable and economical method of production of both simple and complex plastic parts. It is also accomplished with relative ease and can thus be completed easily in different regions around the world. However the main driving factor is its economic properties, allowing for a cheaper product to be sold. Injection molding is also easy on the environment since little material is wasted during the process.
- Figure 5. Manufacturing Method Evidence for Trigger
- Complexity Rating
Using the chart (Figure 2.1) defined earlier in this report we will now analyze the complexity of this part. The trigger has two primary functions, to sense user input and to act as a switch/gate for the electrical energy entering it (2). The part does move, however it is heavily restrained and limited (2). The aesthetic quality is minimal, yet still necessary. However most of the product is hidden within the blade so a minimal rating is justified (1). The finish level of the product must ensure a comfortable grip for the user, netting it a moderate desired finish level (2). The complexity of geometry is moderate also due to the various curves and extrusions present on the component (2). The manufacture process consists primarily of injection molding, a relatively simple process for plastic components (1). The sheer number of manufacture processes for the shell of this component is four, due to the split molding of the two sides, the trigger itself and the top piece (2). Summing all of the complexity points we get a net score of 12, and thus a complexity rating of 3.
Central Power Cable
- Component Function
The primary function of the central power cable is to deliver electrical energy from a power source to the saw’s motor. However the power cable first passes electricity through the trigger before it reaches its final destination. This cable preforms only a single main function, however secondary functions such as safety (due to the insulation properties of the casing) are also present. This component functions in the open and is not protected by auxiliary materials except for its own. Since this is a corded saw its outdoor use would be minimal and most of its work will be done indoors. Also being a lower end product it will primarily be used by home owners, and thus operate inside of the typical home most frequently.
- Component Form
The general shape of the central power cable is that of a long cylindrical tube/cylinder with an approximate radius of 2/8” and overall length of 5’. However that generic shape changes on both ends. One end enlarges into the power plug, with the various groves and rounded surfaces common on most commercial cables. It is much more rectangular in shape than the main cable. Its rough dimensions at its extreme points are roughly 6.9/8” x 6.1/8” x 1”. The two prongs sticking out of it are 7/16” about, a universal standard that ensures the correct fit into the outlet. The opposite end that is connected to the actual circular saw has less of an extreme change in shape. Its circumference slowly grows for about two and a half inches before rounding off at its largest diameter of 5/8”. It then splits into two much smaller cables; however these are different components that will not be discussed in this section. The majority of the cable is symmetrical about the axis, excluding the power plug. However the entire cable is symmetrical if cut perfectly horizontally or along the central line looking down at the product. This products shape/profile is primarily in one dimension, since it is only used/carries energy in one plane (simplified case). This shape is due to a few reasons. First of all the cable shell needs to be large enough to not only carry the internal wiring, but thick enough to provide insulation (for safety) and protection (for the delicate internal wires). The length needs to be long enough to allow the user a big enough range of motion to perform various tasks, but not too long where it becomes a burden or difficult to transport. The full cable weighs a little less than two pounds.
The cable is made (for the most part) entirely from rubber. Manufacturing processes had nothing to do with this decision since very few economical options exist for an insulated, cheap, and flexible material. Two main material properties exist to make a good cable, flexibility and to be an insulator. Global factors influencing its design is the desire to for it to be durable and useable (to a practical degree) in a wide variety of climates. Rubber is also widely available in most areas. Although this circular saw is not intended to be used in the rain, the rubber coating would provide some protection to the internal wires. Economically the cheap cost of rubber makes it a prime candidate for use on a power cable. Its low cost keeps the overall price of the saw lower, allowing the manufacturer the ability to pass on the savings to the customer.
This component does not have a purpose on a pure aesthetic viewpoint. However a nicer looking/finished product drives more sales because it looks more reliable, functional and professional. The color of the cable is a dark black. This helps the cable to blend in, or at the very least be unobtrusive visually. Bright colors would be disruptive and unwanted even if they are more easily seen thus helping to prevent tripping. The surface finish of the product is very smooth and almost glossy. This is for both aesthetic and functional purposes. As stated above the smoothness attributes to the esthetic appeal which helps to promote a better quality product. On a functional level the finish helps to mitigate potential snags, and it is also easier to handle.
- Manufacturing Methods
The method of manufacturing for this component was injection molding. Evidence can be seen on both the power plug and the connection base where parting lines are both visible. Injection molding is a great way to mass produce rubber products economically and with relative ease. The shape is also a contributing factor, especially for both end pieces. However since the shape is so basic it had little weight on the overall decision for its manufacture. Various other factors came into play during the decision to choose the process however. Injection molding (on an economical and environmental standpoint) wastes little material, making it both cost effective and better for the environmental. Also the relative ease of the process makes it a viable option in manufacture plants around the globe.
- Figure 6. Manufacturing Method Evidence for Central Power Cable
- Complexity Rating
Using the chart (Figure 2.1) defined earlier in this report we will now analyze the complexity of this part. This cable does preform two functions, the assisted transportation of electricity and the insulation of the wires; however only one is a primary function (1). This part does not have any inherent movement associated with it (1). The aesthetic quality of this component is also minimal. It must have some appealing qualities, but its function is actually to blend in (1). The finish level is also minimal, with enough of a finish level coming from the injection molding process (1). The actual difficulty of manufacture is also low due to the simple geometry and injection molding (1). It does however require a three step injection molding process comprising of the central wire, body and head (2). This results in a net complexity point score of 8, and thus a complexity rating of 1.
• The main function of the Handle is to give the operator the ability to efficiently handle the circular saw while in use. In addition, it also houses the trigger mechanism and related wiring to power the rotation of the saw blade. • One flow associated with this component is the chain reaction used to turn on the circular saw; due to the pull of the trigger. • Environmentally, the handle has to deal with whatever conditions it is placed in since it is on the exterior. This could mean hot/cold temperatures or any forces that are placed upon it. One such example could be the constant contact and friction with the users hand while in use.
• There is no basic shape that the handle can justly be compared to. Overall, its general shape is defined by several curves and splines. • Since this part is technically one half of the handle, this means it is symmetric to the other half. Both pieces join together to form the whole handle apparatus. • The component is primarily three dimensional. • While there are no general dimensions we can associate with this part and a shape, it would be able to fit in an approximately 20 x 19 x 5 (centimeter) box. • Thanks to its curved form, the handle is ergonomically designed to provide a comfortable grip for the user’s hand. Furthermore, the interior has plenty of ribbing to ensure stability and strength. • Weight: 3.1 ounces • Material: ABS Plastic • The piece was probably made from ABS Plastic due to its strength and very low weight. Using this material ensures that it won’t break and prevents the addition of any unnecessary weight. • No specific material property is needed for the handle to function. It could be made of numerous materials it just so happens that ABS Plastic is the most efficient. • Global Factor: ABS Plastic is a commonly used plastic in industry throughout the world. • Societal Factor: safe to use thanks to its significant strength providing plenty of support to handle the immense forces when cutting. • Economic Factor: much cheaper than other suitable materials such as steel. • Environmental Factor: ABS Plastic is recyclable like many other plastics. Also does not contain the hazardous compound Bisphenol A. • Aesthetic Purpose: its vivid red color serves to clearly show the user where they can safely grab the circular saw with no risk of injury. In addition, it has a textured surface where the hand contacts the handle to prevent slipping and promote a strong grip. The rest of the surface has a glossy smooth finish.
• Injection Molding: process of forcing molten (ABS) plastic into a mold that can be reused and letting it cool down to get a finished product. • Evidence: small riser mark on grip area of the handle. Plastic components are most commonly produced using the method of injection molding. • Material choice definitely affected this decision since injection molding is a very common procedure when dealing with plastics. • Since it has a complex shape, the ability to reuse a single mold to form the same part cuts down time and costs. • Global Factor: Injection molding is very common in modern industry. • Societal Factor: molds can be reused so production can keep up with demand. • Economic: reusable molds drive down the production cost and make the product cheaper when it comes to the market. • Environmental: once again the reusable molds prove to be useful considering they prevent having to make new molds and thereby wasting material.
Lower Blade Guard
• For the lower blade guard, its job to protect the user from the possibility of a serious injury is extremely important. Although the circular saw could technically be used without it, there is no doubt that it serves an important purpose and has prevented untold amounts of devastating accidents. • The flows associated with this component are purely mechanical. As the user begins to push the circular saw through the cutting material, the lower blade guard rotates up into the cavity of the upper blade guard. It will continuously push up into the upper blade guard to reveal as little of the blade as possible (to protect the user) while still allowing the circular saw to cut as efficiently as possible. • During the operation of the circular saw, the lower blade guard will be exposed to fragments flying at high velocity and heat energy. Therefore, it must be able to withstand a considerable amount of wear and tear since it is so close to the actual blade itself; as well as the cutting surface.
• The general shape of the lower blade guard is a half circle. However, it does have a small cavity for the blade to fit into and a protrusion on the top with a screw thread for attachment. On its back is an array of 10 rib like extrusions on the surface for support. • While there is no true symmetry overall for the entire lower blade guard, the ribbing on the back surface is symmetric. • The piece is close to being two dimensional if it wasn’t for the cavity where the blade goes; making it a three dimensional piece. • Overall size is defined by the diameter of the half circle; which is approximately 20 cm. The depth is around 1.6 cm for the main body and 4.2 cm when including the other extrusions. • The half circle shape of the lower blade guard is concentric to the blade so that it can pass through while spinning without coming into contact. Since it is a half circle, it can reveal up to half of the blade at one time or even less as a safety precaution. • Weight: 13.9 ounces • Material: Steel • Steel is the perfect material to be used for the lower blade guard. It is a very strong material and relatively light weight considering how strong it really is. There is no doubt that steel is needed not only to withstand the wear and tear from use, but also to protect the user. • Global Factor: Steel is readily available around the world because it is used so often in all aspects of industry. • Societal Factor: without an extremely strong material being used for the blade guard, the saw might still be able to hurt the user if an accident occurred. Since the main function of the lower blade guard is to protect the user, it makes sense that steel would be used to fully protect them. • Economic Factor: Steel has become much cheaper over the years thanks to its widespread use. Furthermore, since it is such a strong material, less of it is needed in order to guarantee protection from the saw blade. Therefore driving costs down even further. • Environmental Factor: Over time most materials will degrade and lose their ability to allow a component to function. Luckily, steel is extremely resistant to the outside forces imposed upon it and truly has the ability to last a lifetime. This means it won’t need to be replaced very often and the product won’t be continuously wasted. However, when it is no longer needed, the steel component can be melted down and eventually recycled. • Aesthetic Properties: The lower blade guard is a standard silver color and has no real need to have overwhelmingly pleasing aesthetic properties. Although, it does have a glossy finish which does make it more appealing than if it wasn’t finished. On the other hand, there are shallow engravings on the outer edge in the shape of an arrow. These serve as a guide for the user to understand the direction of rotation of the blade guard. As a guideline to instruct the user how to properly replace the blade, there is an instructional sticker on the inside of the lower blade guard.
• Die Casting: the steel was melted down into liquid form and then poured into a die in the form of the lower blade guard. After it has cooled down and hardened, the lower blade guard is finished for aesthetic purposes and then the final product is ready. The die is also made of steel and can be reused. • Evidence: die casting is typically used for steel parts that aren’t extremely complicated. There is also a small riser mark on the back of the blade guard. • As usual, the choice of material influenced the decision to create the lower blade guard from die casting. Steel is one of the most common used metals in die casting and has a good level of fluidity to fit the mold. However, the shape impacted the decision more so due to the lack of great complexity. The manufacturer could achieve plenty of precision using a die cast and they still get to reuse the mold as well. • Global/Societal Factor: reusable molds allow for large scale replication to meet up with the demand of the market. Keeps production moving at a fast pace while still providing high quality products that are safe to use. • Economic Factor: having a reusable mold is a huge factor because it greatly drives down the cost to produce each blade guard. • Environmental Factor: the die can be used multiple times which decreases the amount of waste produced. Even if the die were to be decommissioned from the workplace, it can be recycled since it is made of steel anyway.
• The motor housing unit’s main function is self-explanatory since it is primarily used to house the motor that propels the saw blade. It is a rigid structure designed to contain and protect the important mechanisms within. • Another general purpose it has is to connect the handle to the body of the rest of the circular saw. It also is vented to allow air flow in order to dissipate some of the heat being generated. • Flows associated with this part are all contained within the interior. While the only flow the actual motor housing goes through is transfer of heat energy; the motor inside goes through more complex flows. • The motor housing unit is on the exterior of the circular saw and thus has to be resilient when facing anything in the environment it is left it. Aside from this, it also has to be able to withstand a considerable amount of heat due to the energy produced from the motor while it is running.
• Overall the motor housing looks like a large hollow cylinder with a couple features that branch off. For example, there are three extrusions at the base for screws to connect the unit to the circular saw. As well as the array at the top of the motor housing that tapers off and allows the exhaust cover to be fastened. • Aside from some minor differences in the orientation, the motor housing is very close to being symmetric. The array at the top (for the exhaust cover) was clearly designed with symmetry in mind. Furthermore, the screw extrusions at the base form an equilateral triangle with one another. • This piece is three dimensional and the basic cylindrical shape has a base diameter of 10 cm and a height of 11.8 cm. The screw extrusions have a diameter of 1 cm and the array at the top is an additional 3.2 cm high. • The shape of the motor housing unit is designed to contain the motor while taking up as little space as possible. Also, it will help heat flow out of the chamber into the environment. • Weight: 7.0 ounces • Material: Thermodynamic/ABS Plastic • The piece was probably made from Thermodynamic/ABS Plastic due to its strength and very low weight. Using this material ensures that it won’t break and prevents the addition of any unnecessary weight. In addition, this piece needs to have a high tolerance for heat since it is housing the motor. • This Thermodynamic Plastic was chosen due to its property to withstand high temperatures that would be produced from the motor. • Global Factor: Thermodynamic/ABS Plastic is a commonly used plastic in industry throughout the world. • Societal Factor: safe to use thanks to its significant strength providing plenty of support to handle the immense forces when cutting. • Economic Factor: Not too expensive to the point where it would drive up the cost for the entire circular saw. • Environmental Factor: Thermodynamic plastic is recyclable like many other plastics. Also does not contain the hazardous compound Bisphenol A. • Aesthetic Properties: the motor housing is a vivid hue of red with a basic finish, not like the smoother glossy finish on the handle. Other than the fact that it is used to complement the red color of the handle, there is no real purpose. It may also be used to signify a safe area to grab the circular saw without risk of injury. This would make sense because the cylindrical shape would make it a good spot for the user to place their other hand; thereby providing further support while working.
• Injection Molding: process of forcing molten (Thermodynamic/ABS) plastic into a mold that can be reused and letting it cool to get a finished product. • Evidence: riser mark seen on the array at the top of the cylindrical shape. • Material choice definitely affected this decision since injection molding is a very common procedure when dealing with plastics. • Since it has a complex shape, the ability to reuse a single mold to form the same part cuts down time and costs. • Global Factor: Injection molding is very common in modern industry. • Societal Factor: molds can be reused so production can keep up with demand. • Economic: reusable molds drive down the production cost and make the product cheaper when it comes to the market. • Environmental: once again the reusable molds prove to be useful considering they prevent having to make new molds and thereby wasting material.
Analysis for Part #8
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Solid Modeled Assembly
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Component and Assembly Models
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An engineer might need to determine the torque needed to be supplied by the circular saw’s motor in order to accelerate the saw blade to its maximum angular velocity. In order to do this, they would need to create a mathematical model that relates the maximum angular velocity and the torque needed to achieve it. In addition, the engineer would need to know an approximate amount of time in which they would like the saw to accelerate to a full speed in.
- Figure 7. Diagram of relations between saw blade, pinion shaft, and motor.
In this model, the following assumptions are made; the saw is modeled as a solid disk, parts to not degrade or deform over time, all power supplied to the motor is used to generate torque, no energy loss due to heat or friction, components are not subjected to any other forces, saw will be accelerating without making contact with material being cut, any form of air resistance against saw blade during acceleration is negligible, gears and pinion shaft do not slip, and the time needed to accelerate the blade has already been predetermined by the engineer.
- Figure 8. Governing Equations in Engineering Analysis
- Figure 9. Calculation of Torque in Engineering Analysis
Dimensions are consistent with what is asked, no mathematical errors.
The torque required as a result of using the equation derived in the previous part of the analysis assumes that no energy is lost due to friction, heat, or any external forces. If these were included in another analysis, then the actual amount of torque needed would be higher in order to make up for these losses in energy. In addition, it is also assumed that the materials are ideal and will not be deformed by forces acting upon them. With this in consideration, stronger materials would need to be used for higher amounts of torque to decrease the chances of the part failing during the saw’s usage. In addition, further analysis will be needed to determine the torque necessary to cut different types of materials since this analysis only deals with the acceleration of the blade without it actually cutting anything. Based on the variables in this derived equation, it is apparent that the motor will need to produce more torque for a blade with a larger diameter or larger mass. In addition, more torque will be necessary in order to accelerate the blade in a smaller period of time. Another interesting observation is that that the ratio of the radius of the shaft of the motor to the radius of the pinion shaft makes a large difference in the torque required. If the pinion has a larger radius than the motor shaft, then less torque will need to be provided (which is expected based on the relationship of torque and gear ratio). This information can be useful for an engineer if they wish to determine what sizes of shafts will be necessary inside of the machine, especially with spacial constraints on inside of the saw itself. It will also be useful in designing a saw blade to fit within a certain sized set of blade guards.
- The first component revision considered for the circular saw is exchanging the plastic material and style of grip on the already existing model for a more ergonomic rubber grip. A construction worker or person working in their garage on a warm day will most likely have sweat form on their hands and a smooth plastic surface is not a very good type of interface for them to work with. This can become a serious safety hazard to the user and those around them because in the event that they lose control, the saw could slip from their grasp while the blade is still in motion. By changing the handle to a rubber grip, the safety of the product would increase greatly for the average user because it would provide them with a surface of greater friction to work with. A more ergonomic shape would also make the product more comfortable to work with over extended periods of time and would also increase the safety of the tool because it would allow the user to have a more intuitive grasp and better control of the saw. In addition, ability of the user to control the saw accurately would also increase by allowing the user to have a steadier grip on the tool, thus making it easier for them to guide it. The process of manufacturing the grip wouldn't be very expensive because it would most likely be made using injection molding. This is economically beneficial during manufacturing because the molds used to create the grip could be re-used over again and the grips could be produced very quickly. The grip would cost more to produce and take extra time to put onto the circular saw, but this change would greatly benefit the safety of the users. In addition, this added safety feature would also make the saw look like a more attractive option to consumers because of its added safety precaution.
- Figure 10. Handle Revision Suggestion 
- Another revision on the component level is changing the types of screws that secure some of the parts of the circular saw. For example, the current model uses Torx screws to hold the handle halves together. The average person usually keeps Phillips or slot screw drivers in their tool set, but not necessarily a Torx head screw driver. One might argue that this is done purposefully so that the average user doesn't tamper with the circular saw and impact its overall safety; however there are basic repairs that may be performed by separating the handle halves. For example, a person with knowledge of basic soldering would be able to repair the wires connecting the trigger to the 120V field in the event that they become severed over a long period of use. It would be difficult for the user to remove the screws if they don’t possess a Torx screwdriver head, but changing it to a Phillips head would allow them to have easy access to that component for repairs. This could also help the user save money because they could fix the inside of the saw by themselves instead of having to take it in to have repairs done. The screws on the blade guards and components of the saw that are essential to safety involving the blade should not be removed because tampering with any of those parts could seriously increase the risk of the user hurting themselves in the event that they re-assemble the tool incorrectly and attempt to use it again.
- Figure 11. Torx Screw Revision Suggestion
- Another component to make changes to is the exhaust cover on the back of the motor housing. The current model features two screws that insert directly into the front of the exhaust cover and into the interior of the casing. In addition, the Skilsaw logo is molded into the plastic grill running across the cover. Both of these features can hinder air flow and can allow material to get caught in them. If this were to happen, then the user would have to unscrew the exhaust cover and then manually empty the contents out by themselves. A possible redesign of the exhaust cover would feature screws that are inserted along or directly into the side of the motor housing so that they don’t inhibit the flow out of the grill. In addition, the molded logo would be removed and instead it would be placed somewhere plainly visible on the side of the motor housing. This revision would increase the safety of the circular saw by ensuring that there is no blockage in the exhaust and can help increase performance by increasing the area in which hot hair may flow out of the motor housing. Blockage would be detrimental to the circular saw because it would lower the rate at which heat is removed from the motor and could even start an electrical fire if the material in the blockage reaches too high of a temperature. Economically, it may be more expensive to place the screws somewhere else and have the logo applied in a different area instead of having it placed directly onto the tool during manufacturing, however the increase in safety would be worth the redesign. The spacing between the horizontal plastic pieces in the exhaust cover would remain at the same distance because increasing it any more might result in the user accidentally inserting foreign objects into the motor housing and potentially damaging moving parts. In addition, it could be a safety hazard if the user accidentally gets anything connected to them caught inside of the tool while it is in motion.
- Figure 12. Exhaust Cover Revision Suggestion
 Handle Design Revision:
 ESA Manufacturing Process Characteristics:
 How It's Made - Circular Sawblades:
 Manufacturing Processes: