Group 23 - Ryobi Angle Grinder

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Ryobi Angle Grinder

Contents

Executive Summary

Group 23 was assigned a Ryobi Angle Grinder and worked throughout the semester to dissect and analyze the components that made this product work. This work was done in order to complete the five required project gates which were: Request for Proposal, Preliminary Project Review, Coordination Review, Critical Project Review, and Project Delivery. Included in this Wiki page are all the deliverables for each of the five project gates, albeit organized into simplified phases as such: Before Disassembly, During Disassembly, After Disassembly, and Reassembly. A considerable amount of time and thought went into this product dissection and overall group 23 is pleased with their results.


Before Disassembly

Request for Proposal

Work Proposal

Management Proposal

Group Member Roles

Initial Product Assessment


During Disassembly

During this disassembly plan it seemed appropriate to take notes and lots of pictures to identify exactly what happened in each step. This resulted in a total disassembly time of approximately one hour and twenty minutes.

Product Dissection Plan

The following steps will be rated by ease according to the following scale:

Scale of Ease

1) Easily removed by hand

2) Easily removed with a tool

3) Removed with some difficulty with a tool

4) Removed using a special tool or more than 1 person

5) Required special assistance to remove


Dissection Process

1) Removed handle.

Difficulty Rating: 1 
Tools used: Hand
Shown: Handle removed.


2) Removed the guard.

Difficulty Rating: 2 
Tools used: 10mm wrench/Number 1 Phillips head screwdriver
Shown: Removed Guard along with wrench and screwdriver used.


3) Removed four screws holding the clutch on and removed the clutch.

Difficulty Rating: 2 
Tools used: Number 1 Phillips head screwdriver/Hand
Shown: 4 screws removed from clutch.
Shown: Removed clutch.



4) Removed four screws holding the casing together.

Difficulty Rating: 2 
Tools used: Number 1 Phillips head screwdriver
Shown: Gear housing removed from plastic casing along with 4 screws and screwdriver used to remove them.


5) Removed motor from casing.

a. The first of the screws on the motor assembly was removed

Difficulty Rating: 2 
Tools used: Number 1 Phillips head screwdriver.
Shown: Top portion of motor assembly with small bevel gear and 2-hole washer secured by 2 screws.


b. The other screw was stripped and could not be removed using the screwdriver.

Difficulty Rating: 3 
Tools used: Pliers
Shown: Stripped screw.


c. Motor removed from casing.

Difficulty Rating: 1 
Tools used: Hand
Shown: Motor removed from plastic casing by only a small tug.


6) Removed screws to housing of electrical components.

Difficulty Rating: 2 
Tools used: Number 1 Phillips head screwdriver
Shown: Exposed wiring between upper and lower portion of plastic casing.


7) Removed the gear and washer from the plate on top of the motor.

Difficulty Rating: 1 
Tools used: By hand
Shown: Small bevel gear, the 2-hole washer, and 2 screws with washers each.
  • Important note - There is a keyway for the gear to attach onto the motor shaft, however, upon dissection there was either no key present or it was lost during dissection. Our group strongly believes that this key was lost before we were given the product, probably by the group that dissected this angle grinder last semester, after our searching for it turned up nothing.


The only fasteners used to hold this product together were screws. There were variations in length and thread count between the various screws, but all the screws head's were made to fit a number 1 Phillips head screwdriver. Screws were the only type of fastener used in the product because they are cheap, easy to tighten, and can hold up well against the vibrations from the motor and gears.


During the dissection of the product no special tools were required. The product was disassembled using only a person's hands, a number 1 Phillips head screwdriver, a 10mm wrench, and a pair of pliers.


Based upon the scale of ease from above and each of the difficulty ratings for each step, it seems that the product might be intended to be taken apart easily. Anybody that owns a number 1 Phillips head screwdriver could disassemble this angle grinder to the point of taking the motor out of the plastic casing. The stripped screw was rated the highest difficulty out of all of our steps and even that wasn't very hard to do if you had a pair of pliers. The thing I am curious about is why would a typical consumer have a need to disassemble this particular angle grinder in the first place? So it seems that because of the types of fasteners used to hold this product together (screws) that this angle grinder is, by default, easy to take apart.

Causes for corrective action

So far, our work and management plans for our group have been highly successful. This is due to the fact that all group members were aware of when meetings were and was expected of them to accomplish for each meeting. Also, all group members were present for every scheduled meeting. We hope our management plans will continue to be accurate for the next gate of the project, however, potential problems could arise in both the solid modeling of the product, which could turn out to be more challenging than expected, and more tasks are required for the next gate. Proper time management will be crucial.


After Disassembly

After the completion of the disassembly, we were left with all the individual components that were unable to be disassembled any further. Time was taken to make observations of each component regarding the materials they were made out of, how they were produced, their function, and other details that must be taken into account in order for a thorough analysis to be completed. Computer modeling was used to provide helpful visualizations of some essential components in the product. Hypothetical design revisions to the original product along with creating unique analysis problems for the product are both important steps engineers must follow in order to fully understand the product being analyzed.

Component Summary

Complexity Scale:

1. A solid, smooth part with or without simple holes.

2. A solid non smooth and/or threaded part with or without holes of varying depth.

3. A solid part with very precise bevels, with or without holes of varying depth.

4. A solid part with complex extrusions and threaded holes of varying depth.

5. A permanent assembly multiple smaller precise parts.


Plastic Casing

Q1.jpg

Function: Houses and protects all of the parts necessary to run the tool.

Material: Plastic

Manufacturing Process: Injection Molding

Cosmetic or Functional: Both

Complexity: 1

Number: 1

Discussion: The plastic casing is a particular shape because it needs to snuggly fit all the other components to protect them from breaking. Plastic was selected because it is inexpensive to manufacture per part and is durable enough for the use of the product. Injection molding allows for the housing to be blue and nicer to look at (making the part also cosmetic). Any force applied to the housing would come from the part being dropped, and as this could be incredibly varied, it is difficult to estimate the magnitude.


Motor

Q2.jpg

Function: Produces mechanical energy which powers the angle grinder.

Material: Aluminum, Copper, Plastic, Steel

Manufacturing Process: Sand Casted, Drawn and Spun, Injection Molding, Turned and Milled

Cosmetic or Functional: Functional

Complexity: 5

Number: 1

Discussion: The motor is made from several materials. The shaft is turned steel and is meant to provide torque provided by magnetic forces to the bevel gear. The plastic fan on the end pulls air through the motor to cool it and is thus made to be the shape of an impellor. It is made of plastic because it can easily be made to its unique shape by injection molding, is inexpensive to mass produce, and light. The forces it experiences are from torque from the shaft and aerodynamic drag from the blades. The copper wire is wound around the shaft to maximize the number of loops and magnetic field strength. It is manufactured by being drawn, and is coated with a casing to prevent short circuiting. Copper was chosen because it is highly conductive, easily drawn and relatively inexpensive for its small application. Around the edge of the copper wire are a number of small plates that hold the wire in place. The plates are very small and wedged between each other to reduce electron eddy currents that could cause heating and warping of the part. Notches are also taken off of the plates in order to help balance the motor for a smooth rotation under use. These plates were likely stamped and then turned to allow for an odd unique shape with a smooth and circular outside edge. They are likely the shape they are to allow for easy shaving in order to balance the motor while still allowing for a uniform magnetic field distribution.


Accessory Wheel Mount

Q3.jpg

Function: Acts as a base for a grinding wheel to be attached, and well as a base for the bevel gear.

Material: Steel, Plastic

Manufacturing Process: Turned and Milled, Injection Molding

Cosmetic or Functional: Functional

Complexity: 4

Number: 1

Discussion: The accessory wheel mount is the particular shape it is so that it can fit on the gear casing, allowing for the two components to fit together. Plastic was used for this part of the accessory wheel mount to keep the gear shaft in place with a light-weight component. The only forces on this part would be the forces from the bolt canceling out the face of the shaft pushing on the inside bearing structure. This part is injection molded so to allow a cheap, plastic design to be used for the component. The steel mount for the accessory wheel is the shape it is to allow a different accessory wheel to easily and quickly be replaced. This is accomplished with a threaded shaft and a compression block that holds the grinding wheel to the shaft without worry of unscrewing. The threaded shaft is also threaded in a manner opposing the rotation of the shaft so the compression block will not become unthreaded. The shaft was mainly turned to allow for a circular and precise part. The holes in the compression block were likely milled out.


Handle

Q4.jpg

Function: Provides stability when operating the tool.

Material: Plastic

Manufacturing Process: Injection Molded

Cosmetic or Functional: Both

Complexity: 2

Number: 1

Discussion: The handle has a shape that is specifically designed for a hand to comfortably and effectively grasp. It is also adjustable for left and right hand users. Plastic was selected because it is inexpensive to manufacture per part and is durable enough for the use of the product. Injection molding was selected because it is a good process to use with plastic and because it allows the component to be a nice color.


Bevel Gear

Q5.jpg

Function: To spin the accessory wheel mount.

Material: Steel

Manufacturing Process: Turned and Milled

Cosmetic or Functional: Functional

Complexity: 3

Number: 1

Discussion: The shape is significant because it is made to fit onto and spin the accessory wheel mount. Steel was selected because it is strong, corrosion resistant, and highly durable. The manufacturing processes of turning and milling were selected because they allow for high precision when creating the gear teeth. Forces applied to the bevel gear include torque transferred from the other accessory wheel mount and resistance from the grind wheel (friction).


Motor Holder

Q6.jpg

Function: To stabilize and protect the motor inside the housing.

Material: Plastic

Manufacturing Process: Injection Molded

Cosmetic or Functional: Functional

Complexity: 1

Number: 1

Discussion: The shape was selected because it fits perfectly in the housing and stabilizes the motor. Plastic was selected because it is inexpensive to manufacture per part and is durable enough for the use of the product. Injection molding was selected because it is a good process to use with plastic and because it allows the component to be a nice color. No forces are applied to the part.


Gear Box

Q7.jpg

Function: Provides a protective housing for the gears to keep them aligned.

Material: Aluminum

Manufacturing Process: Sand Casted

Cosmetic or Functional: Functional

Complexity: 3

Number: 1

Discussion: The shape is somewhat hollowed out in order to fit the gears inside of it, and it connects to the housing at a ninety degree angle. Aluminum was selected because it is less expensive and not as heavy as steel, but still durable enough for the intended use. Sand casting was selected because it allows for a fair amount of detail and is economical for large runs. No forces are applied to this component.


Accessory Wheel Guard

Q8.jpg

Function: Protect the user from flying debris.

Material: Aluminum

Manufacturing Process: Sand Casted

Cosmetic or Functional: Functional

Complexity: 2

Number: 1

Discussion: The shape was selected so that it fits on the accessory wheel mount and provides adequate protection from debris. It is also adjustable for left or right hand users. Aluminum was selected because it is less expensive and not as heavy as steel, but still durable enough for the intended use. Sand casting was selected because it allows for a fair amount of detail and is economical for large runs.


Small Bevel Gear

Q9.jpg

Function: Transfers and changes direction of mechanical energy from one gear to the other.

Material: Steel

Manufacturing Process: Turned and Milled

Cosmetic or Functional: Functional

Complexity: 3

Number: 1

Discussion: The shape is significant because it is made to fit onto and spin the larger bevel gear. Steel was selected because it is strong, corrosion resistant, and highly durable. The manufacturing processes of turning and milling were selected because they allow for high precision when creating the gear teeth. Forces applied to the small bevel gear include torque transferred from the motor and resistance from the larger bevel gear.


Lock Washer

Q10.jpg

Material: Steel

Manufacturing Process: Stamped

Cosmetic or Functional: Functional

Complexity: 1

Number: 5


Washer

Q11.jpg

Material: Steel

Manufacturing Process: Stamped

Cosmetic or Functional: Functional

Complexity: 1

Number: 3


Plastic Screw – 3.5mm x 25mm

Q12.jpg

Material: Steel

Manufacturing Process: Turned and Milled

Cosmetic or Functional: Functional

Complexity: 2

Number: 4


Plastic Screw – 3.5mm x 10mm

Q13.jpg

Material: Steel

Manufacturing Process: Turned and Milled

Cosmetic or Functional: Functional

Complexity: 2

Number: 2


Machine Screw – 3.5mm x 19mm

Q14.jpg

Material: Steel

Manufacturing Process: Turned and Milled

Cosmetic or Functional: Functional

Complexity: 2

Number: 4


Machine Screw – 3.5mm x 10mm

Q15.jpg

Material: Steel

Manufacturing Process: Turned and Milled

Cosmetic or Functional: Functional

Complexity: 2

Number: 2


Plastic Screw – 3.5mm x 16mm

Q16.jpg

Material: Steel

Manufacturing Process: Turned and Milled

Cosmetic or Functional: Functional

Complexity: 2

Number: 1


Key

Q17.jpg

Material: Steel

Manufacturing Process: Milled

Cosmetic or Functional: Functional

Complexity: 1

Number: 1


Two-Hole Washer

Q18.jpg

Material: Steel

Manufacturing Process: Stamped

Cosmetic or Functional: Functional

Complexity: 1

Number: 1


Three-Hole Washer

Q19.jpg

Material: Steel

Manufacturing Process: Stamped

Cosmetic or Functional: Functional

Complexity: 1

Number: 1


Design Revisions

1. Guard Revision:

Normally, according to the manufacture the only part of the angle grinder that needs to be replaced due to normal wear and tear is the guard. It is recommended by the company to replace after extended use. Our group proposes that the guard should be made out of a lightweight plastic as opposed to aluminum. This would make the part both lighter and less expensive to produce. Because it is less expensive even if the new guard was not as durable as the previous guard the difference in cost would make up for it being replaced earlier. This would be a worthwhile chance because plastics are much cheaper and easier to produce than aluminum parts.

Pros:
      *Cheaper and easier to produce
      *Cheaper to replace
      *Lighter
Cons:
      *More likely to break
      *Plastic is worse for the environment than aluminum 

2. Power supply revision:

We propose that we could replace the power source, currently supplied by AC current, with a rechargeable battery and recharger. This would be taking existing technology and applying it to our product to make it more appealing to the consumer. It would make it more portable because it would not be inhibited by the cord, it would also allow it to be used in areas where there is not outlets available. However, this change would increase the price because it would add parts and make it more difficult to manufacture. The casing would also need to be redesigned to house the battery.

Pros:
      *Increased mobility
      *Increased consumer appeal
      *Battery is compatible with other tools
Cons:
      *Decreased voltage
      *Possible failure of battery due to user error


3. Gear revision:

We thought it would be a good idea to look at how the grind wheel is spun and see if we could change the speed at which it spun. This would make it a more effective cutting and grinding tool. In order to achieve this, we would redesign the bevel gear so it has a smaller radius. This would change the gear ratio and cause it to spin faster. The bevel gear is the part that drives the grind wheel so it would increase the speed of the grind wheel. This would make the angle grinder able to cut more efficiently and the consumer would be able to use the grinder to cut stronger materials.

Pros: 
      *Increased grind wheel speed
Cons:
      *Decreased torque


Solid Modeled Assembly

Displays how teeth of small bevel gear and large bevel mesh together.
Upper view of the gear housing.
Exploded view of the gear housing.


The bevel gear, small bevel gear, key, and the upper portion of the motor component were chosen to be modeled in Solid Works because they are very crucial components that allow the angle grinder to function. The motor component was unable to be disassembled any further than what is shown in the Component Summary section, but through basic visualization of the component we were able to model the motor shaft and the motor shaft bearing as they would look if they could be removed from the motor component. The motor shaft was important to model because it delivers torque to the small bevel gear, which then provides torque to the larger bevel gear to allow the spinning of an accessory wheel. Without any of these parts, the line of power becomes incomplete and no torque gets transferred to the output shaft and the accessory wheel will not spin then. The motor bearing was modeled because it provide crucial support and proper rotation of the motor shaft.

We elected to use Solid Works to solid model our gear assembly. We chose this because one of our group members was proficient in Solid Works from previous classes. He also had it on his computer so he was able to access it very easily and complete the assignment on time with little trouble.


Engineering Analysis

How it is Helpful

Engineering Analysis is a process that can be incredibly useful in both the design and testing stages of a product. When a product is being designed, one should consider various ways in which the product will fail, the circumstances in which the failure would occur, and how to prevent the failure if it is unacceptable. For example, through engineering analysis, one can approximate how much force an angle grinder should be able to withstand without breaking. Once this is established, this approximation can be tested during the testing stages of the product to ensure it holds up.

Problem Statement:

A customer will be dissatisfied if an angle grinder breaks when dropped. In order for the customer to be happy, what is the maximum force the angle grinder casing should withstand before it breaks?


Diagram:

MAEdiagram.jpg

Assumptions:

The maximum height the angle grinder would be dropped from would be 2.4 m. (This would be if a person were 7 ft tall and holding the angle grinder above them.)

The angle grinder will land on its casing.

The angle grinder experiences no spin during the fall.

The surface the angle grinder lands on is hard.

The mass of the angle grinder is 2.041 kg.

Gravity is 9.8 m/s2


Governing Equations:

F=ma


Calculations:

F=ma

F=(2.041 kg)(9.8 m/s2)

F=20.0 N


Solution Check:

This solution appears to be quite reasonable; an angle grinder should be able to hold up against a force equivalent to about 20 apples (1N is approximately the weight of one apple) without breaking. That amount of force isn’t unheard of and would very likely be applied if the grinder were dropped.


Discuss and Interpret:

For this calculation, we figured out the maximum force the angle grinder would need to withstand in order to ensure that a customer would not be dissatisfied if it broke. To do this, we found the mass of the angle grinder to be 2.041 kg, and when it was multiplied by the acceleration due to gravity, the force applied to the angle grinder came to 20.0 N. This means the angle grinder should be able to withstand 20.0 N without breaking. Several assumptions were made to arrive at this calculation. For example, an angle grinder is probably not a power tool one would carry onto a ladder; therefore it seems reasonable to assume it wouldn’t be dropped from a distance above about eight feet. This would be if a person was about seven feet tall and was raising the angle grinder above them to use it. Other assumptions were made regarding the drop of the angle grinder, mostly in order to make the calculation simpler. If the tool were really dropped, it is likely it would spin or turn during the fall, and it may not land directly on its casing. Any of these factors would impact the force applied to the angle grinder, and possibly make it greater than 20.0 N. If this is the case, and the angle grinder can only deal with a force of 20.0 N then it is likely the tool will break. While this calculation is very basic, it is still reasonable that an angle grinder should be able to withstand an applied force of 20.0 N without breaking.


Reassembly

Reassembly of the angle grinder seemed a bit easier than the disassembly of it probably due to each group members growing familiarity with all the components and how they all mesh and fit together. Only one additional task deviated from the reversed disassembly plan which was to hold back two metal brushings which were preventing the motor from sliding back into the plastic casing, other than that the reassembly was the same as the disassembly but in reverse. When we were done we all sighed a sigh of relief when we flipped the switch and found that the angle grinder still ran just like it did before we disassembled it.

Product Reassembly Plan

The following steps will be rated by ease according to the following scale:

Scale of Ease

1) Easily removed by hand

2) Easily removed with a tool

3) Removed with some difficulty with a tool

4) Removed using a special tool or more than 1 person

5) Required special assistance to remove

Step by Step Process

Step 1) In order to get the motor into the housing we needed to hold the metal brushes back to free up the space to slide the motor back into the housing. This step required two people, one to hold the brushings back and another to slide the motor in. Difficulty rating: 3

Shown (top to bottom): Small bevel gear, Motor, Motor holder, Housing

Step 2) Slid plastic housing over metal housing. Difficulty rating: 1

Shown: Plastic housing over Metal housing

Step 3) Screwed screw into plastic housing. Difficulty rating: 2

Shown: Plastic casing, Screwdriver

Step 4) Placed metal plate over the gear shaft and screwed 2 screws securing the plate. Difficulty rating: 2

Shown: Motor in casing, 2 screws, Metal plate, Screwdriver

Step 5) Put the gear assembly onto the motor assembly and attached them with 4 screws. Difficulty rating: 2

Shown: Gear assembly attached to motor assembly, 3 of 4 screws (4th is behind Gear assembly)

Step 6) Put the bevel gear assembly into the gear assembly casing, secured it with 4 screws. Difficulty rating: 2

Shown: Bevel Gear Assembly, 4 screws, Motor inside housing, Screwdriver

Step 7) Attached the guard with a screw. Difficulty rating: 2

Shown: Guard attached to accessory wheel mount assembly

Step 8) Screwed handle onto the assembly. Difficulty rating: 1

Shown: Handle attached to Housing

Analysis

  • After reassembly, the product ran as well as it did when we initially tested it. The gears spin as they are supposed to, and as well as they did before disassembly. However, we cannot confirm whether the angle grinder can successfully grind because we did not receive an accessory grind wheel. (We never had an accessory grind wheel so we are unable to confirm whether or not the angle grinder could ever successfully grind.)
  • During the reassembly, no additional tools were required. The only tools necessary were those originally used in the disassembly (pliers, wrench, screwdriver, hand). The only difference between disassembly and reassembly was the difficulty encountered when putting the motor back into the housing; the brushes needed to be held open in order for the motor to go back in place. We were also able to reassemble the entire product. We had no odd parts or screws left over.
  • We believe the design of this angle grinder as a whole is satisfactory. While we suggested a few design revisions on the component level (shown above in Section 4.2), there are no additional design recommendations to be made to the angle grinder. The product successfully does the job it was designed to perform.


Conclusion

Our group worked successfully together to be able to complete the assignment in a timely fashion and to our satisfaction. Through our cooperation, teamwork, and dedication, we were not only able to successfully dissect and analyze the product, but put the product back together and in working order. We were also able to successfully study the individual components of our product and perform engineering analysis on it. We believe this project was useful in learning more about what engineers do, and will help us as we further our careers in engineering.

References

http://www.ryobitools.com

http://www.homedepot.com