Group 3 - Skil Circular Saw
- 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.
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:
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
|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
Group meetings will take place immediately following class on Mondays. The group will commence in the lecture hall and move to an appropriate area depending on the task at hand. Group meetings will focus on completing portions of tasks, and adjusting the completion timeline accordingly. All group members will put forth equal contributions to any/all reports necessary for the duration of the project.
The following is an estimation of when tasks/sub-tasks will begin, and the amount of time each task will take. This allows the group to meet project deadlines, while providing a sensible duration. The dates projected allow for reasonable adjustments when applicable.
|Tasks||Sub-Tasks||Start Date||Duration (Days)|
|Request for Proposal||Initial Product Assessment||10/5/09||3|
|Preliminary Project Review||Product Dissection Plan||10/9/09||4|
|Causes for Corrective Action||10/16/09||11|
|Coordination Review||Component Summary||10/29/09||8|
|Solid Modeled Assembly||11/8/09||10|
|Critical Project Review||Product Re-assembly Plan||11/21/09||8|
|Submit Final Report||12/11/09||N/A|
Table 3.2.2 - Timeline Estimates
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
- 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.
- 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.
- 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.
- 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
|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.
5 - Takes several minutes to develop a procedure to perform the action, the action takes some time, and complex tools may be required.
|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.
|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|
|2 (Field Magnet)|
|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.|
|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.|
|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.|
|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.|
|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.|
|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.|
|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.|
|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.|
|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.|
|56 (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.|
|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.|
|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.||ABS is injected and molded into shape||Functional: Is used to allow the user to grip the saw firmly for precise cutting and control over kickback forces.|
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.
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.
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.
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.
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.