Group 38 - Ryobi Angle Grinder

Latest revision as of 22:27, 9 December 2007

Ryobi Angle Grinder

Executive Summary

Our project was to reverse engineer a Ryobi Angle Grinder. The objective of the project was to understand why and how the components were manufactured, designed, and assembled. During the disassembly and reassembly, we learned how an electric motor works, how power is converted to perform work, and how that work is translated through gears and shafts to provide the product with its purpose, a spinning disk. The grinder is used to grind, sand, buff, and cut assorted materials. It is useful on metal especially. However, it can be used on wood, plastics, and concrete. The angle grinder is an important tool in construction, automotive repair, metalworking, and rescue. Angle grinders are very simple power tools and are used in both commercial and private projects.

The grinder has many features, including a removable handle, rotating guard, a wheel-changing wrench, and a lock-on switch. The handle screws into either side for easy use by left-handed and right-handed users. The guard serves as protection from sparks and shrapnel. The guard can be removed for easier access to smaller areas. The grinder can be fitted with several different kinds of disks, including diamond-edged wheels, abrasive disks, and buffing and sanding pads. To switch the wheel, the grinder comes with a convenient wrench built into the handle. Though users may never switch the kinds of wheels they use, wheels wear down and the wrench is commonly used to replace them with a fresh wheel. There is a lock-on switch for ease and comfort during long period use.

Although the angle grinder is a very handy tool, our group had several recommendations for improvements that Ryobi could have made. Some of our recommendations at the product level included a light, a cordless option, and a relocation of the trigger for more comfortable use.

Introduction

Group Members

• John Sisti - Introduction; After Disassembly; Assembly
• Jennifer Blersch - Executive Summary; After Assembly; General Editing
• Alex Poniatowski - Disassembly; After Disassembly; CAD Drawings
• Thomas Ryan - Disassembly; After Disassembly; Assembly; Presentation
• David Welch - Assembly; After Assembly
• Brian Literman - Pre-disassembly; Assembly; PowerPoint; Presentation; Executive Summary

The Ryobi Angle Grinder, Model Number AG402, comes packaged with the grinder, a side handle, a wrench for changing the grinding wheel, directions and safety precautions, and a grinding wheel. Our grinding wheel was removed for safety. The standard grinding wheel measures 4-1/2". The angle grinder weighs four pounds. The grinder has a 10 foot long cord which sends 120V AC from an outlet to power the motor. The motor operates at 60 Hz and 4.4 Amps. The motor and wheel spin at the same rate, up to 11,000 RPM. The arbor threads that hold the grinding wheel on are 5/8" x 11" UNC.

Before Disassembly

The purpose of the angle grinder is to grind down, cut, sand, polish, and buff. It works on a range of materials, including plastics, concrete, and wood, but mostly metal. The grinding wheel tends to clog with material when used with plastics or rubbers because the heat created can melt the object. The grinder takes electrical energy and transfers it to mechanical energy via an electric motor. It is an AC motor, as the specification sheet showed, so there should be no conversion between AC and DC. The power from the cord, when activated by the switch, goes to the electric motor, polarizing the stator and the rotor. The poles of the stator resist the poles of the rotor, enabling a constant spin. This motion is then translated through gears and eventually through to the grinding wheel. To keep the angle grinder from spinning out of control when it is turned on and contacted with a material, mechanical energy from the operator's hands needs to be applied to the system for steady, accurate use. One or two hands can be used with the assistance of the side handle..

The brand new angle grinder worked as expected. The arbor spins as it should, most likely at 11000 RPM. It was louder than an electric motor should be. This high volume was the first improvement to the grinder that we noted. Any noise made by a process, such as changing an electric current into mechanical energy via an electric motor, is a loss of energy. By reducing the noise of the motor and gears, the grinder could be more powerful while using the same amount of electricity. Also, lowering the volume would greatly reduce the strain on the user's ears.

Initially, the group guessed that there would be around 100 parts and nearly 15 different materials used.

Disassembly Procedure

After Disassembly

Exploded View

Part Number	Name	Manufacturing Process	Material	Picture	Reasoning	Improvements
1	Casing	Injection Molding	ABS Plastic
2	Handle	Injection Molding	ABS Plastic
3	Wrench	Machined	Stainless Steel
4	Square Nut	Machined	Stainless Steel
5	Guard	Machined	Iron
6	Screw (4)	Machined	Stainless Steel
7	Washer (4)	Machined	Stainless Steel
8	Spacer (4)	Machined	Stainless Steel
9	Bevel Gear	Machined	Steel
10	Gear Washer (2)	Machined	Steel
11	Head Piece	Cast/Forged	Steel
12	Rotor/Armature	Forged/Welded	Steel
13	Spacer	Injection Molding	ABS Plastic
14	Screw (2)	Machined	Stainless Steel
15	Cord Cover	Injection	Rubber
16	Short Screw	Machined	Stainless Steel
17	Clamp	Forged	Stainless Steel
18	Power Switch	Injection Molding	ABS Plastic
19	Screw	Machined	Stainless Steel
20	Brush Holder (2)	Forged	Brass
21	Brush (2)	Machined	Carbon
22	Brush Wire (2)	Drawn/Coated	Copper
23	Clips (4)	Forged	Stainless Steel
24	Brace	Forged	Stainless Steel
25	Stator	Forged/Welded	Steel
26	Wires (4)	Drawn/Coated	Copper
27	Bearing Cover	Injection	Rubber
28	Collar	Injection Molded	ABS Plastic
29	Arbor Head	Machined	Steel
30	Bottom Disk	Machined	Steel
31	Top Disk	Machined	Steel

Assembly

After Assembly

Now that we have taken apart the product, we've been able to understand its full mechanical workings. The product takes 120 volts of electricity from an outlet as its primary power source. The electricity travels through the power cord and through the power switch when activated. The electricity polarizes the stator and rotor, spinning the rotor. This is where the electrical energy is transformed into mechanical energy. The armature, which is attached to the rotor, translates the rotational motion through the head gear. The bevel gear in the arbor changes the rotational axis of the head gear 90 degrees. The bevel gear spins the arbor which is where the disk is attached causing a useful rotation for the angle grinder to operate.

After disassembly, the angle grinder ran the same as before disassembly.

Analysis could be used at various steps in the design/ production of the product. During the initial design processes, mathematical models could be made in order to model power usage ( electrical work) for the amount of mechanical work that is desired by the initial requirements of the product. Market analysis could be conducted prior to design in order to develop a range of parameters set by the consumer market itself ( i.e.- average weights, sizes, strengths of similar products and components). Physical models could be used in order to show contours, dimensions, and even weight.

Once the design is underway, working prototypes could be tested in a variety of ways. Stress analysis could be conducted to determine if the housing of the product will be able to withstand a rigorous environment (including extreme temperatures) and drops from elevated heights(impact strength). Analysis on moving components of the product could be conducted in order to determine fatigue life of components and materials, as well as the longevity of the actual motor.

The closer the product advances to mass production/distribution the more precise the analysis and modeling should be. This means rough analysis when determining something like the overall weight the angle grinder can have, and very precise analysis when trying to find the optimum rotational speed for angle grinders as well as the motor/gear reduction in order to produce it.

The assembly process for the Ryobi angle grinder was almost a mirror image to the disassembly process. All of the components went to together in the reverse order of the other process. The only difference in the use of tools for assembly when compared to disassembly was the need for some kind of guide( used screwdriver shaft) for getting the wiring back into the casing during assembly. This was actually the only difficult part of the entire project.

The angle grinder went back together exactly as it was given to us... fully assembled, no extra parts. The grinder is in perfect working condition. <embed src="http://www.youtube.com/v/cRwbUPjdSEE&rel=1" type="application/x-shockwave-flash" wmode="transparent" width="425" height="355"></embed>

Assembly/Disassembly of the Arbor Head and Bevel Gear section of the Angle Grinder

References

http://www.ryobitools.com/products