Latest revision as of 12:12, 10 December 2007

Ryobi Corner Cat Finish Sander

Executive Summary

The purpose of our project was to analyze the function and design of a Ryobi Corner Cat Finish Sander. We started by analyzing the sander from the user's standpoint. After briefly sanding a piece of wood, we concluded that the product functioned well and the ergonomic design fit well into the palm of our hands.

We then disassembled the entire product and noted the quantity, material and shape of each component and its purpose as it pertains to the overall function of the sander. Looking at these pieces in detail allowed us to see how each piece was designed for a specific function. After deciding on the function of each piece, we were able to re-evaluate the shape and material in order to improve the pieces' function and/or to reduce cost. Ideas for improvements, including ways in which parts could be combined or eliminated, were also brainstormed. In the following report, you will see pictures of each of these parts and Auto CAD drawings of key components.

Following the disassembly, we attempted to reassemble the product. This process proved much more difficult than the disassembly. Yet, after fumbling some pieces around, the product had been returned to its original condition. We tested it again to make sure it worked, and it did. Towards the end of our report we included a description of how the product works now that we have dissected the entire sander. We decided on a list of the features that we liked and ones that we didn't like. We also suggested some changes in the design of the product that would either fix the things we didn't like or aid in the cost of manufacturing and assembly of the sander. Overall, we thought Ryobi did a good job designing the Corner Cat.

Introduction

The Ryobi Corner Cat Finish Sander is used for light, detailed sanding. It runs on 120V AC power at a speed of 12,500 orbits per minute. It features an ergonomic comfort grip, a dust bag, an iron-shaped pad design, and Velcro for easy attaching/removing sandpaper and other pads. The small, compact design and uniquely shaped pad allows the Corner Cat to reach tight spaces that larger sanders may not be able to reach.

Specifications

Motor: 120V, AC only, 1.2 Amp

Orbits Per Minute: 12,500 (no load speed)

Orbit Diameter: 1/16"

Pad Size: 3 3/4" x 5 1/2"

Cord Length: 10 ft.

Weight: 2.5 lbs.

Greg Cummings: oral presentation

Anthony Wasch: oral presentation

Rick Hills: written presentation

Jeff Ackerman: written presentation

Jonathan Loebel: CAD drawings

(All members contributed to the assembly and disassembly process)

Power Point file: Presentation

Before Disassembly

• The purpose of the Ryobi Corner Cat was fairly obvious; it is used to sand and polish wood and other surfaces. Similar to other small power tools, we assumed the Corner Cat converted electrical AC power from an outelet into mechanical energy using a motor.
• After operating the product for a while, we concluded that it functioned well. The sander vibrated rapidly and sounded much like a vaccum. We assumed the vibration was due to a rotating weight much like the ones in cell phones or gaming controllers. The combination of the vacuum-like sound and the dustbag meant that there was also a suction component involved within the sander.
• We estimated that the sander contained 37 components all made of either plastic, rubber, aluminum, copper, canvas or Velcro.

Disassembly Procedure

Disassembly time: about 30 minutes

Step #	Process	Tool Used	Difficulty	Image
1	Removed top (3 screws)	Phillips Head Screwdriver / Hands	Easy
2	Unscrewed 2 inside screws	Phillips Head Screwdriver	Easy
3	Unscrewed casing (4 screws)	Phillips Head Screwdriver	Easy	Video of Step 3
4	Unscrewed 2 screws near the top	Phillips Head Screwdriver	Easy
5	Removed bottom plate (5 small screws)	Phillips Head Screwdriver / Hands	Easy
6	Removed fan housing (4 small screws)	Phillips Head Screwdriver / Hands	Easy
7	Unscrewed 3rd tier of bottom screws (2)	Phillips Head Screwdriver	Easy
8	Removed half of the casing	Hands	Easy	Video of step 8
9	Removed interior supports	Hands	Easy
10	Removed motor from casing	Hands	Easy	Video of step 9

After Disassembly

Part Table

Part #	Part Name	Quantity	Material	Function	Reason for Shape	Manufacturing Process	Image
1	Top Screws	3	Steel for durability	Fasten top	Threaded for fastening	Machined
2	Inside Top Screws	4	Steel	Fasten casing	Threaded for fastening	Machined
3	Side Panel Screws	4	Steel	Fasten sides together	Threaded for fastening	Machined
4	Bottom Screws	5	Steel	Fasten bottom	Threaded for fastening	Machined
5	Inside Bottom Screws	4	Steel	Fasten casing	Threaded for fastening	Machined
6	Third Tier Bottom Screws	2	Steel	Fasten casing	Threaded for fastening	Machined
7	Casing	2	ABS Plastic for light weight, low cost, ergonomics	Holds all components together, allows for air flow	To protect components, aesthetics, air flow to dust bag and cooling	Injection-Molded
8	Top	1	Rubber for grip, ergonomics, dampening vibration	Facilitates grip, reduces vibration transfered to user, allows for one-handed use	Curved and ribbed on sides for grip	Injection-Molded
9	Dust Bag	1	Canvas and ABS Plastic for dust collection, durability	Collecting dust during sanding operation	Space for collecting dust	Injection-Molded (ABS Plastic) and Manufactured (Canvas)
10	Bottom Cover	1	ABS Plastic	Protecting Velcro pad while not in use and doubles as a sandpaper punch to maintain sandpaper shape	Fits iron-shaped Velcro pad and punches sandpaper for extended use	Injection-Molded
11	Velcro Pad	1	Velcro Sheet for easy fastening	Fastening included sandpaper/scrubbing pads for sanding/polishing using Velcro	Iron-shaped for flat sanding on wide back and fine sanding on tip and Velcro surface to easily affix sandpaper/scrubbing pads	Manufactured
12	Bottom Plate	1	ABS Plastic	Attaching Velcro pad, allow fan to suck dust through pad to dust collector, transmit mechanical vibration to Velcro pad and sandpaper	Holes to allow dust to travel through, fits form of case while allowing for vibration, fits iron-shaped Velcro pad, and has a slot for shaft to transmit vibration from the motor	Injection-Molded
13	Fan Housing	1	ABS Plastic	Funneling dust pumped up by fan to dust collector, separating components, and providing support for structure	Fits case to support it and has a large hole to allow dust to travel through	Injection-Molded
14	Plastic Supports	2	ABS Plastic	Fastening the Bottom Piece to the case during operation	Plastic supports fit tightly, strongly affixing the Bottom Plate to the case, and are good at absorbing vibration with their rib-like structure	Injection-Molded
15	On/Off Switch	1	ABS Plastic	Click the switch connected to the cord inside, which closes the circuit and sends AC power to the motor	Fits into side within finger reach for one-handed use	Injection-Molded
16	Cord	1	Copper and Plastic for conductivity, insulation	Transmits AC electric power to motor and when the switch is closed	Copper wires are insulated by plastic and the long length (10 ft) allows for use further from outlet	Manufactured
17	Stator	1	Cast Iron, Copper, Plastic	Coils supplied with AC current produce a rotating magnetic field causing the rotor to rotate	Surrounds the rotor to create a rotating magnetic field around it	Die-Cast, Manufactured
18	Rotor	1	Cast Iron, Steel, Copper, Plastic	The rotor is attached to a slightly offset and weighted output shaft that is given torque by the rotating magnetic field. This creates non-symmetrical motion which causes the bottom plate and Velcro pad to vibrate at high speeds; the fan at the bottom sucks dust through the holes in the Velcro pad, bottom plate, and fan housing to the dust bag and helps cool the motor by circulating air flow	Slightly offset and weighted on one side of the fan to produce asymmetrical rotation and create vibration; fan shape	Die-Cast, Manufactured	First video of Rotor, Second video of Rotor

Accessories

Type	Quantity	Recommended Use	Image
Heavy-Duty Scrubbing Pad	1	Paint and rust removal
Light Scrubbing Pad	1	Light scrubbing and cleaning
Polishing Pad	1	Polishing
60-Grit Sanding Sheet	2	Coarse sanding
120-Grit Sanding Sheet	3	Light sanding
240-Grit Sanding Sheet	2	Finish sanding

CAD Drawings

CAD drawings were made in Solid Works

View	Image	Native File
Rotor (Isometric)
Rotor (Isometric 2)
Rotor (Side)
Rotor (Top)
Rotor (Bottom)
Rotor (Exploded)		Media:finalassembly.sldasm, Media:finalassembly2.sldasm
Rotor with Stator (Isometric)		Media:finalassemblyiso.sldasm
Rotor with Stator (Isometric 2)		Media:finalassemblyiso2.sldasm
Rotor with Stator (Side)		Media:finalassemblyside.sldasm

How the Components Are Assembled

The rotor is placed inside the stator; both components are inserted precisely into the casing.

Assembly

Assembly time: about 2 hours due to alignment issues

After Assembly

How it Works

Turning the switch "On" completes an electric circuit and allows AC current to flow through the power cord to the AC motor from a 120V AC outlet. This current travels through the twisted copper coils of the stator (see parts list), creating a rotating magnetic field. A torque is then applied to the rotor (inside the stator) due to its magnetic attraction to this rotating magnetic field. Due to the shaft being slightly offset and weighted, it oscillates slightly as it rotates with the rotor. This oscillation is what causes the rapid vibration in the bottom plate of the sander. A fan is also located at the bottom of the shaft which creates air flow through the bottom plate to the dust bag as it spins rapidly (hence a cleaner working area). The air flow also circulates through the casing and acts as engine coolant for the motor. The no-load speed of the rotor is 12,500 orbits per minute (OPM), which is very fast. The orbit diameter is 1/16 in. The OPM of the rotor is a measure of how many oscillations per minute the rotor has. The higher the OPM, the faster the sanding pad moves slightly back and forth, creating more abrasive sanding action.

Possible Analyses for Testing/Designing

The white, plastic supports in the case could be analyzed for stress forces such as sheer and compression. Estimates could be used for this stress analysis, especially considering data (such as the modulus of elasticity for plastic) is readily available. The fan could be tested for the amount of air circulation it generates at certain speeds. Basic estimates and models could be used to analyze the air speed of similar devices, which can then be compared to the specifications of the sander. More specific calculations may be required to design the amount of current flow through the motor and how this current affects the speed of the motor.

Reflection on Disassembly/Assembly

The assembly process was essentially the reverse of the disassembly process. However, it was more complicated and time consuming because it was difficult to align the stator properly in the case and fit all the wiring in a place that wouldn't obstruct the rotation of the motor. The same tools were used (Phillips Head Screwdriver and hands) and we were able to reassemble the entire product to its initial working state.

Overall Design

Pros

• Compact size

• Lightweight

• Inexpensive
  • $30 at Home Depot

• Ergonomic rubber grip

• Sawdust collector

• Versatile
  • Left/Right hand usability
  • One-Handed usability

• Simplicity
  • Only 18 components, 36 parts

• Multi-Use functionality due to iron-shape of base
  • Tip for precision, wide back for covering more surface (Video of sander in action: Sanding)

• Extra pads included
  • See Accessories section

• Bottom cover sandpaper punch
  • Allows for dust collection

• Similarity of Parts with other Ryobi Products
  • Easy, cheap replacement of parts and streamlined manufacturing for Ryobi products

Cons

• Variance of Screws

• Small Sawdust Bag

• Flimsy Wire Connection on Toggle Switch

• Difficult to align stator and wires in the casing

• Warning label on power cord in Spanish and French

Suggested Design Changes & Recommendations

• Use only one type of screw
  • Although they were all Phillips Head screws, money could saved at the manufacturing level by using only one type of screw

Make the bottom piece and Velcro pad one piece

• Combine the bottom plate and Velcro pad into one component
  • This could further lower cost at the manufacturing level

• Include a larger sawdust bag
  • Bag would have to be emptied often during extended use

• Strengthen the wire connection on toggle switch
  • Improve the fit on the wire’s connector

• Provide better cues for aligning the stator and wires in the case
  • Include a diagram in the manual or clearly mark the inside of the case

• Have warning labels on power cord in English

• Include variable speed functionality
  • This would be a useful feature to have for advanced users to adjust the sander for certain applications, but would increase the cost and is a function probably best left for more expensive sanders to fulfill

• Make cordless
  • This would be a useful feature to have for all users, but would significantly increase the cost and is a function probably best left for more expensive sanders to fulfill

Conclusion

Overall, we felt that the Ryobi Corner Cat Finish Sander was extremely well-designed. Every aspect of the product (small, simple, inexpensive, and 'easy to use') allows it to perform exactly according to its purpose. Due to this great correlation between form and function, it is a great tool for both the handy-man working around the house and the full-time contractor.

References

http://en.wikipedia.org/wiki/Electric_motor#Components

• How an AC electric motor works

http://home.howstuffworks.com/sander.htm

• Information on different types of sanders

http://www.ryobitools.com/products

• Specifications

http://www.homedepot.com/

• Price, further specifications