Group 3 - Skil Circular Saw

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Contents

Executive Summary

The task of our group is to reverse engineer a Circular Saw manufactured by Skil. To begin this process, we first analyzed how the saw performs its task, more specifically, how the energy is transferred from electrical energy from the wall, to the mechanical energy used to cut the material. After this, we then began to disassemble the saw, documenting the whole procedure and taking note of each component as it was removed. After the saw was completely broken down to the level of our ability, each of the components were distributed to team members and individually analyzed, to determine the process they were manufactured by, why that process was chosen, and the purpose of each part. This required each member to have a thorough understanding of manufacturing processes and the overall operation of the saw. After the in-depth analysis was performed, the saw was reassembled. Although all the components were put together in their respective places, the saw would not run again due to a faulty component that will have to be replaced. The Skil circular saw is a complex piece of machinery that can only be truly understood once it has been taken apart.

Group Members

  • Michael Mercurio – Wiki-Master, Communication Liaison
    • Handle development of Wiki page.
    • Main point of contact for group.
    • Engineering analysis.
  • John McGreevy – Solid Modeling Expert, Wiki Development
    • Handle solid modeling of components.
    • Assist Wiki development.
    • Dissection/reassembly lead.
  • Adonis Pimienta-Penalver – Solid Modeling Expert, Work Outline
    • Handle solid modeling of components.
    • Dissection/reassembly aide.
    • Engineering analysis.
  • Ian Michaliszyn – Technical Expert
    • Supervise dissection/reassembly practices.
    • Dissection/reassembly aide.
    • Engineering analysis.


Request for Proposal

Gate #1 of the reverse engineering projected is designated as the Request for Proposal. This gate is designed to help the group become familiar with Skil Saw, designate group roles, and outline a time frame for completion of future gates. The gate was amassed by the following components.

Work Proposal


It is our group's main goal to reverse engineer our product, the Skil® Circular Saw Model#: 5400 in the most efficient way. To do this we have set out the following goals:

  1. Coming together: The members of our party will outline goals and deadlines to meet in order to stay in track with the project. A separation of tasks will be carried out, which will provide each member with perspective on what is expected of him throughout the course of the semester. Also, our group has converged on a singular communication portal, via e-mail in this case, in order to keep everyone updated on each other's work. A wiki page will also be utilized to keep track of our progress and to communicate our work with our professors and ourselves in a neat, organized manner.
  2. Initial assessment: A preliminary research will be carried out, in order to gain valuable information about our product. This will help us better understand the functions and characteristics of our product that will be useful for future tasks in this project. We will also carry out an initial visual assessment of the product, to indentify the best ways to disassemble it and become familiar with its physical characteristics.
  3. Disassembly: This will consist of carefully taking the product apart into single functional units. All four members of this group expect to take part in this activity; which will give us all familiarity with the object, which will serve as a reference for future steps in this project. With the four of us working on the product disassembly, it is expected that this would take no longer than 3 hours. The most challenging aspect of the disassembly part of this project could be that our group may not have the proper tools to take it apart. This can be resolved by performing more in depth research of our part, in order to find out the specific requirements to meet for a successful disassembly. However, our party believes that taking this particular product apart will be rather simple, since the tools to do so are readily available. While taking the product apart, we will also keep a detailed record using hand-drawn pictures and notes to record the position of each singular part with respect to the rest of the product. The tools required to carry out the dissection are summarized in Table 3.1.1.
  4. Component analysis: It is this party's goal to achieve familiarity with the characteristics, functions and position of each of the functional units of the product at hand; in order to achieve this we will write a list or summary of the components of the assembly, model and assemble each component of the product in a solid modeling software, and finally propose changes in the product design that will serve as alternative to its assembly.
  5. Reassembly: Following the notes and steps outlined in the disassembly process, our group will come together to reassemble the object to its initial configuration. The tools used to achieve this will be the same tools used for when we took the saw apart. After reassembly, we will assess the products functionality and therefore our own ability to understand it.
  6. Presentation: Our party will come together with the knowledge we have gained throughout the semester to assess our work on this product. We will give an oral presentation outlining the details of our work, our shortcomings and our successes. It is in our interest to create a dynamic, well organized presentation in order to better convey our results to our audience.

Our group is comprised of capable students, who are committed to delivering a proper, satisfactory final presentation of our project by the deadline. Among the four of us, there are two who can do solid-modeling work in two different modeling programs. We also count with a student willing and capable to manage the wiki page of our project and update it in a timely and organized manner. We are all enthusiastic that this project can be done in a proper way without putting too much strain on one particular member of the group. Despite our willingness to work, one of the shortcomings we may experience is related to communication and scheduling: the members of this party are not all sophomores, and have very different class schedules; this may me prejudicial to our group dynamic, since we may not be able to always meet together to share our work with each other. However, we are optimistic this possible setback will not influence our drive to finish our work with quality and in a timely manner.

TOOLS OBTAINED AT:
Torx Bit Set Provided by Michael Mercurio
Standard Adjustable Wrench Provided in Dissection Lab
Phillips Head Screw Driver Provided in Dissection Lab
Pliers Provided in Dissection Lab
Allen Wrench Set Provided in Dissection Lab

Table 3.1.1 - Tool Summary

Management Proposal


Our Management proposal can be viewed here

Initial Product Assessment


The intended use of the Skil Circular Saw is to make accurate cuts into a given material. The saw could be used in either a professional or home setting. However, the saw’s features, size, and power rating warrant basic projects mainly characterized by wooden/light metal construction. While there is only one function of the saw, there are a few variances on that function. The saw provides a depth adjustment control, to vary the depth of the cut to the desired dimension, and an angle adjuster, to vary the angle at which a cut will be made.

The saw works by the user disengaging the trigger lock, and simultaneously pressing the trigger. There is a cover over the blade, which retracts during cutting due to the force of the material pushing on the cover itself. The saw blade spins by converting electrical energy into mechanical energy. The electrical energy is converted into mechanical energy by an electric motor located in the housing, which draws its power from a 120 volt wall socket.

The product does work well. When plugged in, the safety on the handle prevents the trigger from accidentally being pulled and starting the saw. The motor runs well, at speed, and does not make any grinding noises. However, there is no blade, so there is no way of telling if that part of the saw is in working order.

This product is complex compared to a tool such as a screwdriver or a hand saw, because there are moving parts. However, it is nowhere near as complex as some tools such as a mill or a lathe, because those tools use much more power, have many more moving parts, and require more skill to operate. There are about 7 major components, the plastic handle/motor cover, an AC motor, the shaft to the saw, the saw itself, the saw shield, the foot which it what goes on the surface being cut, and the power cord. All the components are fairly simple, with the exception being the motor. The motor is complex because it converts the electrical energy into mechanical energy, while providing 2.3 Horsepower.

There are several materials used in the product. The two most evident are plastic, for the handle and motor cover, while the rest that is visible is either stainless or galvanized steel. The parts that are not visible are the drive shaft and the motor. The drive shaft is most likely some stronger alloy of steel. The motor must have copper, because it is an electric motor, along with a magnet (most likely steel), and possibly aluminum too, along with a non-conductive material to hold it together.

The group as a whole would have been very happy to use the Skil Saw. It contains not only ergonomic features that make it comfortable to use, but also has many safety features that prevent injuries in case the user loses control of the saw.

The main handle is shaped to allow the saw to be firmly gripped, with the trigger placed in a way that enables it to be easily pressed by the index finger. There is also an auxiliary handle that makes it easier for the user control the direction of the saw, as well as helping resist kickback forces if the saw binds in the material being cut. The product also contains a bevel and a line guide that let the user perform accurate cuts at various angles with ease. These features make the saw very comfortable to use as well as allowing for more control and precision compared to hand saws that lack these components

This product is not overly complex but there are still a few key components that need to be regularly maintained. The most obvious are the various switch levers and ventilation openings, which must be kept free of foreign material. The blade must also be cleaned of wood pitch to allow for easy cutting and replaced when it becomes dull. Other components like the carbon brushes and commutator also experience wear after many hours of use and should be replaced when necessary. If the bearings begin to become noisy when under excessive load it is important to replace them in order to prevent overheating or motor failure. Unlike cleaning the saw and replacing the blade every so often, critical components like the carbon brushes, commutator, and bearings are somewhat more difficult to replace. If these components require servicing, it should be done by someone who has the proper training and tools.

An alternative product that is designed to perform the same task would be a worm drive circular saw. The Skil Saw is an inline Saw in which the motor housing sits perpendicular to the blade. The motor drives a shaft, which in turn turns the blade. In comparison, a worm drive saw has the motor housing positioned parallel to the blade. The motor then uses gears to increase the torque transferred to the blade. A worm drive saw can cost anywhere between $60-$150 more then an inline saw due to its increased complexity. It has the advantage of being able to cut through much denser and thicker wood with smoother cuts. Cutting the same wood with an inline saw would require much more effort as well as time. The only disadvantages of a worm gear saw are the increase in price as well as the increase in size and weight. A worm gear saw also requires more maintenance since the gears must be regularly re-lubricated.

Preliminary Project Review

Causes for Corrective Action


  1. Introduction: This small assessment of the progress of our group will consist of a few subsections: The “Coming Together” section explains the actions that our group has taken to stay in contact with each other and deliver every task with quality and on time. The rest of the subsections deal with the specific requirements we have overcome up until this point in the project.
  2. Coming together: Our group has stayed on track to successfully complete this project; therefore, no corrective action is needed to achieve timely completion. As members of an engineering work group, each one of us understands that there are certain responsibilities that each must carry in order to put together a high-quality outcome in a timely manner. This is the main reason why our party has succeeded in abiding by the plan we set forth in the previous gate delivery. According to our plan in the work and management proposal, the integrants of this party is aware of the goals and deadlines that we have to meet as a group, and the individual requirements each one of us is expected to meet in order to complete this project in a timely manner. Our group has designated a specific communication mechanism to interact with each other and announce updates about the progress of our work, which has been done via e-mail and our designated wiki page; this strategy has also worked in our favor because it creates team spirit and provides everyone with confidence to be able to point out any errors or suggest a different course of action to tackle a specific problem. Our team values the input that any of its members may contribute, therefore we have emphasized in integrating everyone every time a task needs to be completed; no matter how small the problem at hand is, we try to give everyone a task to complete and a way to get involved. Group meetings occur every after-class session on Mondays. The meetings start by gathering the group members in the lecture hall and then we proceed to move to a more adequate location depending on the magnitude of the current task. During the meetings, the member of the party discuss on the specifics to reach the completion of the project in a timely manner, and set smaller deadlines to turn each member’s individual work in to the wiki page manager.
  3. Initial assessment: A preliminary research work has been completed in the subject of our specific product. This has provided with a wider view of the functions, materials, purposes, alternatives and background of our product. This small preliminary work proved to be very important at the time of disassembly, since it helped the members of the disassembly team to know what to expect during the performance of their task.
  4. Disassembly: The disassembly section of our work was in great part helped by the enthusiasm and ability of the member of our team. It was carried out in a very short time, using the tools that we set out to obtain, listed in the previous report. The disassembly team carefully took apart the saw, taking not of the position of each part and examining the placement of them in order to understand which function it carries into the entire assembly. There were a few short comings during the disassembly. Several parts on the saw seemed to have been altered to fit back into place during the process of the prior reassembly. Most notably was the pin attaching the motor housing to the saw footing (this is part #43 on the explosion below). This seemed to be hammered into place, and thus preventing future removal.

Product Dissection Plan


Explosion of Skil Circular Saw provided by manufacturer with part numbers for reference.
Tools Required:
T20 & T30 Torx bit
Pliers
Provided blade wrench (#651)


Difficulty is defined by the following scale (1-5) where:

1 - Determining the approach and performing the action require little to no thought, and uses basic or no tools.

5 - Takes several minutes to develop a procedure to perform the action, the action takes some time, and complex tools may be required.


Procedure:
Step # Description Difficulty
1 Remove Wing nut (#42) on side to allow foot (#40) to rotate 1
2 20 bit torque nut on 8 bolts (#19) to remove plastic cover (#29) around motor 2
3 Remove Plastic components #837 and #29 2
4 Remove trigger assembly (#4) from plastic component (#837) 1
5 Use provided Blade Wrench (#651) to remove bolt (#52) that retains blade along with 2 washers (#28) 2
6 T20 Torx bit on 7 bolts (#27) to separate blade cover (#24 & #32) 3
7 T30 Torx bit on final bolt (#51) to remove blade cover stopper (#49) 1
8 Unhook blade guard spring (#33) from housing (#24) 1
9 Loosen depth switch (#846) to allow easy access to other components 1
10 Remove snap ring from depth switch 4
11 Slide off depth switch 1
12 Unscrew depth switch nut by hand 1
13 Separate safety cover (#32) from protective cover (#24) 1
14 Remove electric motor armature (#3) from housing (#1) 1
15 Use pliers to remove additional motor components (motor brushes) (#810) 2
16 T20 Torx bit to remove outer section of electric motor field (#2) from motor housing (#1) 1
17 Remove trigger wires (#30 & #31) from field (#2) 5
18 Remove trigger wires (#30 & #31) from housing (#1) by sliding them out of holes they are threaded through 1
19 Remove gear (#825) from protective cover (#24) 1

Overall, the product is designed with most parts to be taken apart easily, while a few parts are a bit more difficult to take apart. The easier parts in this product to remove include separating the major components from each other, such as the blade housing from the foot and motor assembly. The plastic components were also designed to be taken apart simply. The harder parts to remove were the motor components. The reasoning behind this is interchangeable parts. The parts that are cheaper and more likely to wear or break, such as the plastic, are easier to replace, while the components that are less likely to break, or parts that if broken, it would be easier and more cost effective to buy an entire new product, such as the electric motor. If the motor breaks, the cost to replace one would justify buying an entirely new saw in this case.

The primary fasteners used in the saw are Torx screws. While other screw heads, such as Phillips heads, are designed to slip or cam out to prevent over-tightening, Torx heads are designed to prevent the screwdriver from slipping and to ensure a tight fit. The blade was held in with a special nut that can only be removed with the provided tool built into the foot. This makes it easy to swap different blades while on the job, as the wrench required is a part of the saw and is hard to misplace or lose. The final type of fastener is a quick release lever, which when switched up, loosens its hold on a component allowing it to side. This is used to adjust the depth and angle of the saw blade quickly and without any tools.

Coordination Review

Component Summary

Procedure:
Part # (Shown in diagram above) and Name Reason for Materials Used Forces Applied Manufacturing Process Reason for Shape of Part Functional or Cosmetic Complexity Photo
1 (Housing) Black Plastic because it is cheap, can be easily molded into any shape and it is not subjected to high forces. The force of the screws holding the components together. (Approx. less than a pound) Plastic injected into a mold which then cools and solidifies in shape. Part is shaped the way it is so it can protect the electric motor, as well as provide a location for other components to connect to. Functional and Cosmetic: Protects the motor, but also has an aesthetic look and appeal to the operator. Fairly complex as the mold must be precise because many different components are connected to it that have to be lined up accurately relative to one another. Part 1
2 (Field Magnet) The coiled wire is made from copper because of its good electrical conductivity and ductility. The core is made from ferrite because it easily allows magnetic fields to flow through it and confines and guides them in a specific direction. These components are all held in place by polystyrene because of its light weight and good electrical insulation properties. The forces applied by the two screws that keep the field magnet secured to the housing. (Approx. less than a pound) The polystyrene frame is injected and molded into shape. The copper wire is made either by drawing it through a die or pulling it through a draw plate. It is then coiled around the frame. The ferrite core is made by pressing and sintering ferrite dust into thin plates that are then laminated to reduce eddy currents. The plates are made to be magnetically oriented in a specific way and stacked together to produce a core of desired shape and thickness. The coiled wire and ferrite core are all shaped and oriented in a way that will cause the magnetic fields created to apply force to the armature and make it rotate with a certain amount of torque. Functional: Directs magnetic fields in such a way that causes the armature to rotate and in turn power the blade. Very complex since the coil most have a certain number of wires in it and shaped in a specific way. The ferrite core must also have a specific magnetic orientation, shape, and size. The frame has to be designed in a way that will orient the coil and ferrite core the correct way in order to properly direct the magnetic fields that are created. Part 2
4 (Trigger) Plastic because it is cheap, can be easily molded into any shape and it is not subjected to high forces. Also the copper wires for the electricity, and a return spring for the trigger. The force of the finger pulling back on it. (Approx. less than a pound) Plastic injected into a mold which then cools and solidifies in shape. Part is shaped the way it is so it can be easily engaged by the user, while also preventing the saw from accidentally starting. Functional: The part must start the motor only when the operator desires it, and not accidentally. This is done by forcing the user to toggle a safety switch before the trigger will engage the motor. Fairly complex as the mold must be precise so the switch does not stick yet must not be too easily engaged. Part 4
19 (Screw) Steel, because it is strong enough to hold parts securely, and cheap enough to keep prices low. The force required to keep the two plastic components together. (Approx. less than a pound) Steel extruded, threaded on a lathe, and having the head forged. Part has a Torx and a flathead socket to allow it to be removed easily. Functional: Keeps the plastic components together to allow for comfortable use by the operator. Fairly simple as it is just a screw with a specified length. Part 19
27 (Screw) Steel, because it is strong enough to hold parts securely, and cheap enough to keep prices low. The force required to keep the rigid blade cover to the plastic cover. (Approx. less than a pound) Steel extruded, threaded on a lathe, and having the head forged. Part has Torx head to prevent slipping while being tightened and threads to keep it in place. Functional: Keeps the blade cover and the plastic cover together to protect the user from chips being cut by the saw and from accidentally cutting himself on the blade. Fairly simple as it is just a screw with a specified length. Part 27
33 (Spring) Steel because it is a reliable material to make springs out of. The weight of the moving blade cover. (Approx. less than a pound) Metal wire drawn out and wrapped around into spring shape. Part is shaped the way it is because it is the most effective spring shape for the situation. Functional: Returns the blade cover to 'safe' position to protect operator. Fairly simple as it is just a basic spring. Part 33
39 (Screw) Steel, because it is strong enough to hold parts securely, and cheap enough to keep prices low. The force required to affix metal components to the plastic cover. (Approx. less than a pound) Steel extruded, threaded on a lathe, and having the head forged. Part has Torx head to prevent slipping while being tightened and threads to keep it in place. Functional: Keeps the stationary motor components affixed to the plastic cover. Also used to keep the blade cover and the plastic cover together to protect the user from chips being cut by the saw and from accidentally cutting himself on the blade. Fairly simple as it is just a screw with a specified length. Part 39
40 (Casing Foot) Galvanized steel because it is cheap, rust resistant, and sturdy. The weight of the entire saw is placed on the foot (Approx. a few pounds) Sheet metal stamped out and bent into shape. Markings are engraved so that the user can line up the saw relative to a reference to make an accurate cut. Part is bent the way it is so it can steady the saw as it cuts so it can cut accurately. Functional: Provides guidance to the operator. Fairly complex as the markings must be accurate and the connections to the other components must also be accurate. Part 40
41 (Round Head Bolt) Steel, because it is strong enough to keep the positioning wing nut securely, and cheap enough to keep prices low. The force required to keep the two components together to keep the blade angle constant. (Approx. less than a pound) Steel extruded, threaded on a lathe, and having the head forged. Part has a round head to prevent interference with other components and threaded to screw in. Functional: Keeps the angle between the blade and the material being cut constant. Fairly simple as it is just a bolt in a specific shape. Part 41
42 (Wing Nut) Steel, because it is strong enough to keep the positioning components secure, and cheap enough to keep prices low. The force required to keep the two components together to keep the blade angle constant. (Approx. less than a pound) Forged steel, stamped into shape. Part has a tapped hole to work with the screw and has wings so it can be manipulated by hand to provide a sufficient torque. Functional: Keeps the angle between the blade and the material being cut constant. Fairly simple as it is just a wing nut. Part 42
49 (Rubber Stop) Rubber, because it is soft and will stop the blade cover when it closes all the way without damaging it. The force of the blade cover as it closes (Approx. less than a pound) Rubber injected and molded into shape. Part is shaped in a cylinder for ease of manufacturing and allows it to stop the moving blade cover effectively. Functional: Stops blade cover motion while protecting it. Fairly simple as it is simply a rubber cylinder. Part 49
51 (Rubber Stop Screw) Steel, because it is strong enough to restrain the rubber stop, and cheap enough to keep prices low. The force of the blade cover as it closes (Approx. less than a pound) Steel extruded, threaded and having the head forged. Part has Torx head to prevent slipping while being tightened and threads to keep it in place. Functional: Supports what stops blade cover motion while protecting it. Fairly simple as it is just a screw in a specific shape. Part 51
52 (Blade Screw) Steel, because it is strong enough to keep the blade fastened securely, and cheap enough to keep prices low. The force required to keep the blade tight (Approx. a few pounds) Steel extruded, threaded and having the head forged. Part has hex head to match up with blade wrench and threaded to screw in. Functional: Stops blade from coming loose. Fairly simple as it is just a screw in a specific shape. Part 52
651 (Blade Wrench) Galvanized steel because it is cheap, rust resistant, and sturdy. A Torque is applied in order to tighten or loosen the blade nut. (Approx. a few ft lb) Sheet metal stamped out and bent into shape. Part is bent the way it is so it can easily manipulate the blade nut and is comfortable to hold in a human hand. Functional: Used in process to swap different blades to cut different objects. Not very complex. Part 651
810 (Carbon Brush Set) Black plastic because it is cheap, can be easily molded into any shape and it is not subjected to high forces. The spring is made of steel. The contact patch is copper. There is also a carbon insulator between the spring and the contact patch The force of the contact patch being held against the motor. (Approx. less than a pound) Plastic injected into a mold which then cools and solidifies in shape. The steel is drawn out and spun into the shape of the spring. The contact patch is stamped out and forget from a sheet. The carbon block is cut into shape from a sheet of carbon. Part is shaped the way it is to keep the contact patch in contact with the motor. Functional: A necessary component of the electric motor. Very complex because if it is not lined up perfectly, the motor will not run at all. Part 810
837 (Set of Handles) ABS, because it is lightweight, has good electrical insulation properties, and is much more sturdy and impact resistance than a comparable plastic such as polystyrene. The force exerted by the screws that keep the 2 pieces together. (Approx. less than a pound), the weight of the saw (Approx a few pounds), as well as the force applied by the user's hands when gripping the handle. (Approx. a few pounds) ABS is injected and molded into shape The part is shaped in such a way that allow a person's hands to comfortably grip it. The trigger that powers the saw is also positioned so that it can be pressed by the index finger while the handle is being gripped. Functional: Is used to allow the user to grip the saw firmly for precise cutting and control over kickback forces. Somewhat complex since it is very intricately shaped so it can be gripped easily as well as securely mounted to the saw. It also has a housing inside it for the trigger and bracing that gives it rigidity since it is mostly hollow. Part 837
24 (Blade Housing) Aluminum - Easy to shape. Light weight. Durable enough for intended use. Forces applied to shape the housing must be large enough to overcome internal resistance provided by aluminum. Cast used to create extrusions on back. Casting is preferred for large scale production. Shaping done to create necessary shape to house the blade, cover the upper half of the blade, and provide access to the blade for maintenance and replacement. Cutting/drilling preformed to create dust exit, ventilation behind blade, and tap holes for screws. Component shape is governed by the shape/size of saw blade. Cuts on outside of blade housing are purely cosmetic. Housing is shaped to protect user from injury, and provide enough clearance between the spinning blade and the housing. Dust exist is cut such that during cutting, the sawdust will exit the housing to the side and therefore, will not expel towards the operator. Establishing a scale of 1 -5; 1 corresponding to a component with no moving parts and possessing a very simple shape, and 5 corresponding to a component with multiple moving parts that interact with each other, and possessing a very complex shape, the blade housing would attain a value of 2.5 due to its lack of additional component integration and it’s precise required shape. Housing1 Housing2
32 (Blade Guard) Aluminum - Easy to shape. Light weight. Durable enough for intended use. Forces applied to shape the housing must be large enough to overcome internal resistance provided by aluminum. Cast used to create extrusions on back. Casting is preferred for large scale production. Shaping done to create necessary shape to house the blade, cover the upper half of the blade, and provide access to the blade for maintenance and replacement. Cutting/drilling preformed to create dust exit, ventilation behind blade, and tap holes for screws. Component shape is governed by the shape/size of saw blade. Cuts on outside of blade guard are purely cosmetic. Guard is designed to prevent injury by covering the bottom half of the blade. The blade guard retracts as the user moves the saw through the material, while covering any remaining accessible blade area. Several holes are added for functionality such has spring attachment. Establishing a scale of 1 -5; 1 corresponding to a component with no moving parts and possessing a very simple shape, and 5 corresponding to a component with multiple moving parts that interact with each other, and possessing a very complex shape, the blade guard would attain a value of 2.5 due to its lack of additional component integration and it’s precise required shape. Guard1 Guard2
26 (Bearing Assembly) Aluminum - Easy to shape. Light weight. Durable enough for intended use. No external forces applied as component is purely manufactured by casting. Manufactured by casting. Outer cylindrical shell and inner cylindrical shell cast separately. Lubrication applied to reduce friction and increase longevity. Cylindrical shape necessary to house shaft assembly. Component is purely functional. Due to the location of the component, no cosmetic manufacturing need be done. Assembly manufactured purely to satisfy the functional requirement. Establishing a scale of 1 -5; 1 corresponding to a component with no moving parts and possessing a very simple shape, and 5 corresponding to a component with multiple moving parts that interact with each other, and possessing a very complex shape, the bearing would attain a value of 3.5 due to the integration of the ball bearings, and the precision required during manufacturing. Bearing1 Bearing2
3 (Motor) Shaft, stator and fan are made of Steel, because it is strong enough to serve as a secure shaft, and cheap enough to keep prices low. Wires are made of copper, a cheap and efficient material to conduct electricity. Significant torque is applied to the shaft from the magnetic field created by the stators. The shaft is able to convert this magnetic field force into shaft work in the order of 2.3 HP. It is possible that there are also shearing forces from the bearings and the connections at the front end of the shaft. The shaft was cut down on a lathe and the star shape on the front end is forged, The wires are drawn through wire drawing. The fan was stamped out of sheet metal and bent into the desired place. The part is made the way it is because it is the most efficient way to transmit torque from the magnetic field forces created by the stators. Functional: The shaft and stator work together to convert magnetic field forces into shaft work to rotate the blade. The copper coil serves to provide this magnetic field and the fan cools the housing to prevent overheating from long service times. Very complex since the coil must have a certain number of wires in it and shaped in a specific way. The placement of the stator and the fan as well as their dimensions are important to the proper functioning of the device. Part 3
825(Pinion Shaft) Steel, because it is strong enough to hold parts securely, and cheap enough to keep prices low. The force required to keep the forge and extrude the shaft. Steel extruded, threaded on a lathe, and having both ends cut and head forged. Part has a Torx and a flathead socket to allow it to be removed easily. Functional: Holds the blade onto place. Simple as it is basically a shaft with an end made as a gear to receive the blade torque. Part 825
28 (Supporting Disc) Steel - Strong, durable and reliable. No external forces applied as component is purely manufactured by casting. Manufactured by casting. Outer cylindrical shell and inner cylindrical shell cast separately. Lubrication applied to reduce friction and increase longevity. Its shape is necessary to hold the pinion shaft in place. Component is purely functional. Even though the component is in the exterior of the device, it is manufactured purely to fulfill its functional need. Establishing a scale of 1 -5; 1 corresponding to a component with no moving parts and possessing a very simple shape, and 5 corresponding to a component with multiple moving parts that interact with each other, and possessing a very complex shape, the bearing would attain a value of 2 due to the simple design and the straight-forward functional requirement it possesses. Part 28
29 (Housing Cover) ABS, because it is lightweight, has good electrical insulation properties, and is much more sturdy and impact resistance than a comparable plastic such as polystyrene. The force applied by the user's hands when gripping the device to occasionally disassemble it. (Approx. a few pounds) ABS is injected and molded into shape The part is shaped in such a way that allows a person to not be hurt by the edges and protect the user from the motor. It also serves to maintain debris out of the housing. Functional: Is used to protect the inside of the housing and the motor from debris, and to prevent the user's fingers from getting hurt. Somewhat complex since it is very intricately shaped, in a scale of 1 to 5, it would place at a value of 1.5. Part 29
34 (Lever) Plastic because it is cheap, can be easily molded into any shape and it is not subjected to high forces. Also the copper wires for the electricity, and a return spring for the trigger. The force of the finger pulling back on it. (Approx. less than a pound) Plastic injected into a mold which then cools and solidifies in shape. Part is shaped the way it is so it can be easily engaged by the user, while also preventing the saw from accidentally starting. Functional: The part serves as lever for the user to lift the guard in order to perform maintenance duties. Fairly complex as the mold must be precise so the switch does not stick yet must not be too easily engaged. It also has an aesthetic factor to its shape, as it will be frequently used by the customer Part 34
14 (Bearing Sleeve) Phosphoric Bronze as it is considerably less brittle than steel and iron, it only oxidizes superficially and it provides good protection and structure to the motor assembly. There are torques applied onto it during the functioning of the device, however these may be very small. This part is phosphoric bronze cast and then bored to achieve the proper tolerance fit. The part is shaped as it is to stabilize the motor assembly with respect to the blade and the rest of the device. Functional: The part is purely functional as it is made the way it is to stabilize the device motor. The part is not very complex (1 in a 1 to 5 scale), since it is simply used to fulfill stabilization purposed. Part 14

Design Revisions

One possible revision would be to add a setting for the of torque output of the motor. This would be beneficial to the end-user because not all materials require as high of a torque or velocity as other materials. With a lower motor output, less energy would be required by the saw, thus decreasing the electrical power used, saving money for the user.

Another possible revision would be to added a rubberized section to the portion of the handle that is held by the hands. This would give the user a better grip when handling the saw which would result in better control as well as beneficial for overall safety.

Performing maintenance regularly on power tools is crucial in order to maximize the performance and lengthen the service life of the tool. Without the proper accessibility in order to perform maintenances or clean-ups, the tool can become defective and lose in service life. One of the design revisions we propose for this device is to enlarge the plastic clamps that hold the housing cover (item 29) to the device, the reason why we suggest this is because the clamps are very thin and may break easily during maintenance or clean up. Since this part serves as cover for the motor, it may accumulate significant dust during the use of the machine; thus, having a sturdy, durable clamp to attach the housing cover back into the device is crucial to maintain safety and durability of the part.

Also, a laser sight could be added to the saw, displaying the path that the saw will take, giving the user instant feedback about how accurately the saw is aligned. This will lead to more accurate cuts and a decrease in time required to make each cut.

Solid Modeled Assembly

Your group should provide solid models of 3-5 individual components using the CAD package of your choice. Briefly explain your choice of components and CAD package. Provide an assembly that shows the components being assembled in sequence. Publish these results to your group’s wiki.

In order to complete the solid modeling requirement of phase 3, our group has divided the modeling responsibilities between two members.

One of the solid models made is for the wrench used to swap cutting blades that was included with the saw. A model was created for this because the dimensions must be precise for it to fit in the location designed for it in the foot and to perform its job accurately, and it has many fine and intricate details.

CAD image of Wrench

Another model was created for the foot of the saw. This part is important because it is what the operator relies on to make a quick and accurate cut through the material. It also supports the weight of the saw on top of the material while still allowing a hole for the blade to cut.

CAD image of Foot

Models were also created for the inside of the motor. These include the steel rotor, the armature, the shaft and the bearing sleeve. For reasons of complexity, the copper wiring that is coiled inside the armature and around the shaft was omitted from the CAD models.

An animation of the rendered motor assembly

The modeling of this assembly is a complex process; obtaining dimensions and placements becomes difficult because of the intricacy of the part. Because of this reason and the importance that the motor bears in the functioning of the circular saw, we have chosen to create models for them.

The solid modeling software in which the parts were simulated were Pro/Engineer Wildfire 4.0 and SolidWorks 2009/2010; these programs’ versatility and rendering capabilities, combined with our familiarity with the programs were the main factors at the time leading to this choice of reliable software which could ensure accuracy, and realistic rendering.

We have also created separate solid models of the pinion shaft and the supporting disc that connect the motor shaft to the saw-blade.

Compressed folder of all the CAD files

Engineering Analysis

  • Diagram:

Diagram

  • Assumptions:
    • Saw blade is moving at a constant rate of rotation (5400 RPM)
    • Power supplied is constant and uninterrupted (2.3 HP)
    • Diameter of saw blade is 18.415 cm
    • Neglect friction
    • Force of wood on saw blade is equal to 4200 N
    • Frequency of rotation is constant at 60 Hz.
  • Governing Equations:

Governing Equations

  • Calculations:

Calculations

  • Solution Check:
    • This is a very reasonable amount of torque considering the rotational speed of the saw blade, and the force of the wood on the saw blade.
  • Discussion:
    • The amount of torque computed is the minimum amount that must be provided by the blade nut/bolt. The assumptions that were made were used to analyze a very strong piece of wood being cut by the saw, which would be operating at full output. Friction between the saw blade and bolt could be neglected because in comparison to the other forces acting on the blade, the friction would be small and therefore, the torque created would be negligible.

Product Reassembly Plan

Our group met to complete the reassembly process on Monday the 7th of December. Each member was tasked with the partial reassembly of a section of the device. Once we were all finished with our individual parts, we proceeded to put them all together; naturally, some parts had to be left to be assembled individually. The final assembly process went as planned, with the entire event spanning about 40 minutes. During the later stages of the process, we identified a connection issue with the carbon brushes. We tried to the best of our effort to obtain a proper connection for the severed wires and the carbon piece; the machine was tested several times to no avail. Upon closer inspection of the issue, our group understood that obtaining a proper connection between the wires and the carbon block was beyond our abilities.

Unfortunately, the saw does not work like it did when we received it at the beginning of the semester. We have determined that the problem is that for the carbon brushes, there is a torn wire that should be embedded into the carbon block, and it is beyond our ability to repair. We attempted to affix the wire to the carbon with electrical tape, however that proved to be futile. A way to correct this would be to order part # 810 from Skil Tools, which you can do through their catalog, and to replace the broken components.

The disassembly and reassembly processes were very similar. To reassemble the saw, pliers were not required because the components easily pushed into place, thus they did not pliers to remove. We used the disassembly process as a guideline to follow in reverse order, which was very useful to us and cut down on the time required and lowered our frustration. We were able to put the saw back together completely, even though the one set of components were broken, they still did not prevent themselves from fitting into their proper locations.

We would recommend to make the wires on the carbon brush set stronger, because they were broken when we took apart the saw, whether it was due to method we took it apart, or due to some malfunction while running the saw, as it was sparking very bright when we ran it at the beginning of the semester, so it may have already been severed and was just jumping the gap. We also recommend that the wires leading from the trigger to the motor be longer, because during the reassembly process, it was fairly difficult to slide the stater all the way to the back of the plastic housing.

Tools Required:
T20 & T30 Torx bit
Provided blade wrench (#651)


Difficulty is defined by the following scale (1-5) where:

1 - Determining the approach and performing the action require little to no thought, and uses basic or no tools.

3 - Part may be reluctant to be reinserted or may require a specific procedure to be reinserted.

5 - Takes several minutes to develop a procedure to perform the action, the action takes some time, and complex tools may be required. The procedure to reattach the part may not be intuitive, or at times, frustrating.


Note: Numbers in procedure correspond to part numbers on the schematic above in the Product Dissection Plan section.

Procedure:
Step # Description Difficulty
1 Insert gear (#825) into protective cover (#24) 1
2 Thread trigger wires (#30 & #31) through hole in housing (#1) and attach to back of the field 5
3 T20 Torx bit to attach outer section of electric motor field (#2) to motor housing (#1) using long screws (#39) 1
4 Attach motor brushes (#810) to the field through the back of the housing 3
5 Insert electric motor armature (#3) into the shaft in the back of the housing (#1) 2
6 Reattach the safety cover (#32) and the protective cover (#24) by sliding slots into each other 1
7 Screw back on depth switch nut by hand and slide on the depth switch (#846) and affix in place with snap ring 1
8 Reattach blade guard spring (#33) to protective cover, making sure the hook on the spring is secure around the notch(#24) 1
9 T30 Torx bit on final bolt (#51) to reattach blade cover stopper (#49) 1
10 T20 Torx bit on 7 bolts (#27) to attach blade covers together (#24 & #32) 3
11 Use provided Blade Wrench (#651) to screw in bolt (#52) that retains blade along with 2 washers (#28) 2
12 Insert trigger assembly (#4) into plastic handle components (#837) 1
13 Reattach plastic handle components (#837) to the housing (#1) 2
14 20 bit torque nut on 8 bolts (#19) to attach plastic cover (#29) to rear of the housing (#1) 2
15 Reattach wing nut (#42) on side to prevent foot (#40) from rotating 1