Group 16 - DeWalt 4 1/2 in Angle Grinder Gate 2

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Dewalt 4 1/2" Angle Grinder

Contents

Introduction

For this gate our group dissected our product and considered what its assembly revealed about the design factors that went into this product. Before we could do this, our group first had to analyze how our original plans outlined in Gate 1 had gone, and what changes needed to be made in order to make our group perform better. This group assessment is provided under the Project Management section below. We then proceeded to dissect our part, and have provided step-by-step instructions on how to do this. Under the Product Archaeology section we describe our scale of difficulty for disassembling each part and then provide the aforementioned step-by-step instructions, along with a rating of the difficulty of each step. Finally, under Connection of Subsystems our group documents the connections of the subsystems and considers the factors behind these design decisions.

Project Management

Summary

  • At the start of the first gate our group had gotten together and divided the work load amongst most of our group. Each individual that was present was given a task to perform so the work load was on every one (we thought). Michael Halloran was appointed our communication liaison and none of us had ever used wiki before. The other group members could not figure out the wiki so we sent email to the communication liaison to put it up on the wiki. He put all of our information together and posted it to our wiki, but Gate 1 was posted to our user page, not the main page, or a specific Gate 1 page.

Cause For Corrective Action

Potential problems

  • We didn't know how to use the wiki.
  • The communication in the group was limited to in class meetings and email.
  • The workload was unevenly distributed.

Proposed solutions

  • Our communication liaison went through wiki tutorials and attended office hours in order to learn how to use the wiki well.
  • He has showed the group the wiki basics so now we all can post at least basic text to our page.
  • The group as a whole had a meeting, and now understands the work needed to be done ahead of time so it could be proofread and reviewed.
  • We have discussed and redistributed the work load so that the communication liaison will have an appropriate amount of research and analysis given that he also has to form tables and upload images, which the rest of the group does not.

Product Archaeology

Difficulty Scale

In order to describe the difficulty of each step, we will use the categories outlined in Table 1. When assessing the difficulty of each step, it was important not just to assess the time a step took, but rather the aspects that would make the task challenging for the average user. We therefore considered the tools required for a task, the intuitiveness of the step, and any difficulties that may have arose from inaccessibility of a part or the amount of force that must be applied.


Difficulty Category Description Example
Easy This step involved minimal effort and either the use of no tools or a very simple one such as a screw driver. This step was completely intuitive, and simple to execute. Unscrewing a wing nut or a Phillips-head screw
Moderate This step required a little time and effort and involved more complex tools such as a wrench or pliers. This step may have required some thinking and observation of the components before it was clear what to do, and was somewhat challenging to execute. Removing electrical connections with pliers or unscrewing a screw that was partially blocked by other components
Difficult This step required inspection of several parts in order to determine how to do it. While it may have involved the same tools as a moderate step, it was a challenge to use them on the part that was to be removed, or a large amount of force may have been required. Executing these steps was very challenging and may have required multiple attempts or assistance from another person. Removing a bearing that is shrunk fit onto a shaft
Table 1: Categories of Difficulty for the Dissection Steps

Dissection Instructions

The instructions given in Table 2 are intended to provide a thorough and complete description of the dissection process such that an individual with no prior knowledge of the product could disassemble it in the same manner our group did. Pictures are provided for clarity and to specify which component of the product is being dealt with at any particular point.

  • Before beginning dissection, the following tools will be required:
    • Phillips-head Screwdriver
    • Torx Drivers: T-5, T-10, T-15
    • Needle-nose Pliers
    • Channellock Pliers
    • 3/8 in Crescent Wrench
Table 2: Step-by-Step Dissection
Step Tools Required Description Difficulty Image
1 None Twist the handle to unscrew it from the main components of the angle grinder. Then remove the clamp nut and back flange by similarly unscrewing them from the general assembly. Easy
Removable Parts.jpg
2 Phillips-Head screwdriver Use the screwdriver to remove the screw holding the two halves of the guard ring together, and then slide the guard off the general assembly. Easy
3 T-10 Torx Driver Use the Torx driver to remove the four screws attaching the gearbox to the main housing. Then pull the gearbox off and the attached drive shaft will come out with it. Moderate
Gearbox and Driveshaft Removal.jpg
4 T-15 Torx Driver Use the Torx driver to unscrew the four screws holding the housing together at the bottom (near plug) of the angle grinder. Separate the two halves and remove them. Easy
One Side Panel Removed
Both Side Panels
5 Phillips-Head Screwdriver Locate the red switch inside the now exposed interior, and use the screwdriver to loosen the clamps on the wires leading to the power cord. Now unscrew the two screws holding the power cord's plastic attachment in place, allowing you to pull the power cord out. Moderate
Power Cord to Brushes to Switch Assembly.jpg
6 Needle-nose Pliers Use the needle-nose pliers to grip the wire contacts between the red switch and the carbon brushes. These four contacts will slide right off. It is recommended a marker is used to note which wire went to which contact on the switch, so that it can be reassembled properly. Moderate
7 Needle-nose Pliers, T-5 Torx Driver Use the needle-nose pliers to grip the brush spring and pull back on it. You can now swing the brush out and release the spring. Repeat for the other side. Now use the Torx Driver to unscrew the screw holding the brush in place. The entire brush assembly can now be removed and taken apart by hand. Difficult
Spring-Brush Connection
Brush Components
8 T-5 Torx Driver Use the Torx driver to remove the four screws that hold the black fan baffle in place, and remove the fan baffle from the body. Easy
Fan Baffle.jpg
9 Needle-nose Pliers First, pull the switch off the switch bar until it snaps off. Then use the needle nose pliers to pull the switch bar out of its slot in the main housing. Moderate
Switch Contact and Switch Bar.jpg
10 None By banging the remaining housing on the work surface, the electromagnet will eventually be forced out. It is only held in place by a relatively loose press fit. Easy
Magnet in Casing.jpg
11 Channellock Pliers, 3/8 in Crescent Wrench Take the drive shaft-gearbox assembly and slide the drive shaft out the bottom of the gearbox. First unscrew the nut that is threaded on using the 3/8" crescent wrench. Remove the pinion by gripping it with the channellock pliers and pulling it off the drive shaft. The back ring retainer will then slide off. Next, remove the bearing by also gripping it with the channellock pliers and pulling it off the drive shaft. At this point it will help to have assistance, as the pinion and bearing are shrink fitted on, and will require a large amount of force to remove. Difficult
Drive Shaft Parts.jpg
12 T-10 Torx Driver Use the Torx driver to unscrew the screws holding the back of the of the gearbox in place, and then remove the back. Easy
Gear Box With Protective Panel Removed.jpg


Intent of Disassembly

  • Gaurd, Handle, and Axle nuts
-They are intended to be adjusted by the user. The gaurd can be removed or re positioned to accommodate various attachments. Axle nuts slip off.
  • Gearbox and Backplate
-Backplate removal is essential to routine maintenence (greasing) and inspection.
-The gearbox is not intended to be disassembled, the gear is shrink fitted onto the shaft. The component is sold as an entire unit because removing just the gear would dis-align the part and break the bearing.
  • Bottom of Plastic Housing
-This component makes access to routine maintenance sites quick and easy for the user.
  • Power cord Attachment
-Made so a replacement cord can be installed easily, a cord can also be changed to allow use in countries using 240v. In case of electrical fire this unit can be replaced easily as well.
  • Brushes Assembly (contacts)
-The brushes are a normal wear component in the grinder and must be replaced routinely throughout the tool lifetime. The ease of access is helpful in maintaining a working tool.
  • Fan Baffle
-This component can be removed for cleaning and for access to the coil.
  • Switch
-Can be removed with some intuition. Must be removable for replacement of broken switches. Its an inexpensive part that is critical to product operation.
  • Electromagnet (coil)
-Has an interference fit with the plastic housing, can be removed with little force.
-Can be removed for replacement of housing.
  • Gear and Bearing on main shaft
-Main shaft can be removed to access bearing and for inspection.
-Gear has a small nut holding it on. It can be replaced if damaged.
-Bearing requires a large amount of force to remove, and must be pressed on properly. This part can not be replaced easily without proper tools.
  • Plastic Housing
-Can be replaced if broken. Must disassemble entire tool. This is replaced only if severely damaged.

Challenges of Dissection

The dissection went very smoothly with the only significant challenge being the removal of the drive shaft bearing and the pinion. As mentioned in dissection, both of these parts were shrink fitted on, and removing them required more force than one person could apply with the channel-lock pliers. In order to remove these parts our group had to have one member hold the channel-lock pliers with both hands while another member grabbed the drive shaft and gradually slid the part off by pulling and wiggling the drive shaft. This step would be extremely difficult for a user to perform at home without any assistance.

Connections of Subsystems

The overall function of the DeWalt 4 1/2 in Angle Grinder is to grind materials by converting electrical energy into rotational mechanical energy. This occurs through a series of subsystems.

First Level of Subfunctions

AngleGrinderFunctionalModel001.jpg

Second Level of Subfunctions

AngleGrinderFunctionalModel002.jpg
AngleGrinderFunctionalModel003.jpg

How the Subsystems are Connected

Physically

To achieve the overall function, the subsystems must be physically connected. The power switch is connected to a plastic bar that slides back and forth and allows electricity into the electric motor. The electric motor is connected to the drive shaft. When the electric motor spins, the drive shaft rotates. The drive shaft then connects to the gearbox and to the gears inside. The rotation of the drive shaft causes the gears to turn. The gears are connected to the head, causing it to rotate and thus giving the operator the ability to grind materials.

Signals

For the angle grinder to run, the operator must send a signal to it. This is done using the power switch. The power switch can signal the angle grinder to turn on or shut off, depending on what the operator wants. The power switch is connected to a plastic bar that slides back and forth. When the operator turns the switch on, the bar slides sending a signal to allow electricity into the electric motor, thus activating the angle grinder. When the operator turns the switch off, the bar slides back into its original position sending a signal to stop sending electricity to the electric motor, thus deactivating the angle grinder.

Mass

There is no mass flowing through the angle grinder.

Energy

Electrical energy from an outlet enters the angle grinder through a cord. The electrical energy is then sent to the electric motor. The electric motor spins, converting the electrical energy into mechanical energy. The mechanical energy is then sent to the drive shaft where it becomes rotational mechanical energy. The drive shaft channels the rotational mechanical energy to the gear box and into the gears. The gears take this rotational mechanical energy to the head where it can be used to grind materials.

Why They are Connected

The subsystems must be connected in order for the angle grinder to work properly. The power switch is connected to the plastic bar in order for the on/off signal to be received. The power switch is not located at the bottom of the angle grinder where the electricity comes in so the plastic bar is used to send the on/off signal to the correct location. Once the signal is received, the electric motor can beginning converting electrical energy into mechanical energy. The drive shaft connects the electric motor to the gear box. The drive shaft must be connected to the electric motor to be able to rotate, allowing the rotational mechanical energy to be channeled to the gearbox and the gears. The gears must be connected to the drive shaft so they can turn, otherwise the gears won't do anything. The gears then take the rotational mechanical energy to the head, thus allowing the operator to grind materials.

Implementation of Connections

The connections between the different sub-systems of the angle grinder were each affected by GSEE factors. Even if a different design would achieve the same overall function, the angle grinder had to be designed to balance these concerns with overall performance and longevity. A summary of how the major connections were implemented along with the GSEE and performance factors for that implementation can be found in Table 3 below:

Table 3: Connection Implementations and Factors
Connection Implementation GSEE Factors* Performance Factors
Switch to Motor The switch uses a plastic bar to move an electrical switch, which in turn controls the flow of energy to the motor. Societal: This connection is not intuitive to replace because there are many wires and components that need to be in specific locations.

Economic: This connection involves fairly complicated parts, which may be expensive to manufacture.

Environmental: Because the components are so small, numerous, and consist of various materials, it may not be worthwhile to recycle the components at the end of life for the overall product.
The implementation of this connection gives the product greater reliability and durability than if the plastic switch were to directly move electrical contacts onto the motor (this would expose the switch to the motor's vibrations).
Power Cord to Motor The power cord runs two wires into the aforementioned electrical switch, which then runs two wires to the electromagnet and two wires to each brush. These brushes then deliver electricity to the motor armature (also known as the drive shaft.) Global: The power cord can easily be separated from the other electrical components, which allows easy replacement for use in countries with different electrical frequency.

Societal: These components are all easily accessible to allow the user to perform easy maintenance. Economic: This connection involves fairly complicated parts, which may be expensive to manufacture.

Environmental: Because the components are so small, numerous, and consist of various materials, it may not be worthwhile to recycle the components at the end of life for the overall product
The design of the armature and brushes allows the application of electricity to whatever wire loop is currently perpendicular to the magnetic field, thereby maximizing power output.
Drive Shaft to Gears The drive shaft and helical gear are connected by a pinion which is shrink fitted on. Economic:This connection is small but has very tight tolerances, which will probably make it fairly expensive to make. Environmental: Because the pinion is small and made of metal, it can be easily recycled at the end of the part's life The pinion is very good for performance as it enables the system to be rattled and dropped without losing the alignment of the gear grooves . A simple Bevel Gear would not be as robust (1800 Mechanical Movements)
Gears to Disc The rotational output of the gears is delivered to the grinding disc through a backing flange. This backing flange slides over the gears and is forced against the disc by the clamp nut. Global: This system is very intuitive to use and people from many parts of the world could figure it out for disc replacement.

Economic: The backing flange has very loose tolerances (it can turn about 10 degrees in either direction when put on properly) so it would be relatively cheap to manufacture.

Environmental: The backing flange is made entirely of metal, which would make it recyclable and reduce environmental impact.
This system of delivering power to the disc requires the use of the clamp nut, which partially obstructs the grinding disc in regular usage. With regards to power, there is minimal power loss from this system.

Note: *All factors may not apply to each connection

Reasons for Subsystem Arrangement

The subsystems are arranged in a way to have the system function properly, so the small angled grinder is intended to be smooth to get work done. Our above pictures show how different subsystems are assembled together to make this grinder.

  • The placement of the subsystems is reasonable in this small angled grinder. For instance:
    • The electric cord enters at the end, which is the energy source for the grinder. The placement of cord at the end is for the better starting input, as our final output is at grinder. Also, the power cord must lead directly into both the magnet and drive shaft.
    • The power switched is located at the top part (near the handle), this allows workers to power the machine on or off at the same time they are doing the work. (Without moving their hands from working position).
    • The drive shaft is, and must be placed within the motor, as it is the induced magnetic field along with the current through the drive shaft that allows the shaft to rotate.
    • The drive shaft leads to the gear box and grinder head, which is located a safe distance from the general housing so that the user will not be hurt by the grinder.

Subsystems that Cannot be Adjacent

  • The subsystems that cannot be adjacent would be grinder and motor. That is because; electric motor converts the electric energy to mechanical energy. Then the drive shaft must be connected in between electric motor and gear box in order to rotate the grinder. If this step did not happen and the grinder head was right on the motor, it wouldn’t make the 90 degree turn, which would remove much of the convenience of angle grinding.
  • The grinder head cannot be located near the control system (switch) because the operator would be in danger of being hit with debris when trying to turn the grinder off.

References

Title: 1800 Mechanical Movements, Devices and Appliances Author: Gardner D. Hiscox

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