Group 36 - Ryobi Contractor's Saw

Executive Summary

In this project, our group was tasked to disassemble, analyze, reassemble, and recommend our improvements for the Skilsaw Contractor’s Saw. Before we disassembled the saw, we knew that the saw changed AC power into mechanical energy but we weren’t sure exactly how. After we took it apart, we saw that the AC power is transfer through the brushes into the rotor which rotates caused by the magnetic field of the stator. As the rotor spins, it turns gears which rotate the blade at approximately 700 rpm after the 6:1 gear reduction for safety reasons. The disassembly and reassembly both took about an hour and was fairly simple with the exception of a few parts that needed extra care and effort to remove. The saw’s handle and housing for the motor were made of plastics; the upper and lower guards were made of aluminum; and the rest of the saw was made of steel and other metals.

Introduction

The Skil saw is a circular saw design for cutting wood or other materials. This hand-held saw is powered by electricity that is converted to mechanical power. The device features 2.3 HP with 4,600 RPM and with the 7 1/4 " 40 tooth blade it weights 13.9 lb. This Skil saw is mainly black and the guards are in gray color. The device contains some of the essentials such as the safety switch and a vent to prevent from dis-functioning.

Rita Groetz is the teal leader. She schedules the meetigs as well as dealing with the communictions. She is the photographer and deals with the written materials. She also edits the written materials as well.

Kevin Bush is the person who disassemble and assembles the product. He had knowledge of the materials and the step and educated us on how things work and how they were made. He also did part of the CAD designs.

David Pohl was the designer. He made the CAD drawings and created the video from the CAD drawings.

Kevin Ho was responsible for the written material of the project. Tagging the parts and describing materials was part of his role.

Tai Nguyen was also responsible for the written materials of the project. Also took notes in one meeting and as well as observation in another.

Before Disassembly Section

This circular saw is primarily used for cutting wood. It runs on an AC current, and contains a 2.3 hp motor at 4600 rpm, turning electrical energy into mechanical energy. At the beginning of the project, it was new, so the group assumed that its initial operation was correct. The saw is operated by engaging a safety switch, and then a power switch. It was very loud, and even without the torque of the blade, kicked back when it was initially operated. This demonstrated the physical power of the motor. The group estimated that the saw would contain about 40 components, and predicted that those components would be made of plastic, steel, aluminum and copper.

Disassembly Procedure

1. Took out Wrench with hands

2. Remove rubber stopper with T-30 torx bit

3. Remove lower guard lift with T-20 torx bit

4. Remove spring from lower guard with needle nose pliers

5. Removed blade-holding bolt and “washers” with 13mm socket

6. Removed spring ring with swiss army knife

7. Removed C-clip and depth adjustment lever with pliers and a 12mm wrench

8. Removed lower guard with hands

9. Removed 3 short screws with T-20 screw driver and bearing flange

10.Removed pinion shaft

11.Removed 4 long screws from upper gaurd with a T-20 torx screwdriver

12.Removed upper guard with hands

13.Removed armature with hands

14.Removed plain washer and 2 washers from the armature

15.Removed 6 screws to take handle apart with T-20 torx screwdriver

16.Pulled the handle off with hands

17.Removed 2 medium screws and pulled off housing cover with hands

18.Slid out motor brushes with needle nose pliers

19.Took apart brushes with hands

20.Removed 2 long screws from stator

The disassembly was relatively easy except for pulling off the C-Clip, which needed to be slowly worked out of its former position.

After Disassembly

Component List

Part #	Component Name	Number of Parts of This Type	Material(s)	Manufacturing Process	Image
1	Motor Housing	1	Plastic, Brass, Galvanized Steel	Injection Molded, Die Cast and Machined, Stamped
2	Stator	1	Plastic, Copper, Magnetic Alloy	Injection Molded, Extruded, Stamped and Soldered
3	Trigger and Safety Switch	1	Plastic, Aluminum	Injection Molded, Extruded and Machined
4	Power Cord	1	Copper, Plastic	Both Extruded
5	Upper Guard	1	Aluminum, Brass	Die Cast and Machined, Machined
6	Pinion Shaft	1	Steel	Extruded and Machined. Also dipped in an anti-corrosion coating.
7	Central Washer	2	Steel	Die Cast
8	Depth Adjustment Lever	1	Plastic	Injection Molded
9	Rubber Stopper	1	Rubber	Injection Molded and Vulcanized
10	Handle	2	Plastic	Injection Molded
11	Rotor	1	Steel, Copper, Plastic	Stamped, Extruded and Machined, Extruded, and Injection Molded
12	Vent Cover	1	Plastic	Injection Molded
13	Lower Guard	1	Aluminum	Die Cast
14	Carbon Brush	2	Plastic, Copper, Carbon, Brass	Injection Molded, Extruded, Machined, Stamped
15	Lower Guard Lift Lever	1	Plastic	Injection Molded
16	Long Screw	6	Steel	Extruded and Machined
17	Medium Screws	8	Steel	Extruded and Machined
18	Short Screws	4	Steel	Extruded and Machined
19	Central Bolt	1	Steel	Extruded and Machined
20	Long Spring	1	Steel	Extruded
21	O-Spring	1	Steel	Extruded
21	C-Clip	1	Steel	Stamped
22	Large Gauge Screw	1	Steel	Extruded and Machined
23	Wing Nut Bolt	1	Steel	Extruded and Machined
24	Wing Nut	1	Steel	Stamped
25	Wrench	1	Galvanized Steel	Stamped
26	Plain Washer	1	Aluminum	Stamped
27	Washer	1	Aluminum	Stamped
28	Bearing Flange	1	Steel	Machined
29	Depth Adjustment Nut	1	Steel	Machined

Design Changes

While the long, medium, and short screws all took the same size bit and had the same thread, the large screw took a different bit. This group suggests that the large screw be changed to accommodate the same size bit as the others.

Also, the carbon brushes are simply set into the saw and held in place by the vent. The group suggests that the brushes are fastened in place independently.

PUT CAD IN HERE!!!

Assembly

1. Placed rotor and motor back in housing cover.

2. screw in the two screw back in stator.

3. placed screw back in housing.

4. placed handle back together with wires back inside.

5. Placed screws back in with T-20 torx screw driver.

6. Placed plain washer and 2 washers to the armature.

7. Placed armature back on.

8. Placed upper guard back on by hands.

9. Placed 4 screws back on upper guard with a T-20 torx screw driver.

10. Place pinion shaft back on.

11. Placed 3 short screw with T-20 screw driver back on.

12. Place lower guard back on.

13. Placed C-clip and depth adjustment lever with pliers and a 12mm wrench back on.

14. Place spring back on by hand

15. Placed blade-holding bolt and washers with 13mm socket back on.

16. Placed spring from lower guard with tweezer (difficult)

17. Placed lower guard lift with T-20 torx bit

18. Placed rubber stopper with T-30 torx bit

19. Placed wrench by hands back on.

After Assembly

Reassembly

Upon reassembling the saw, the group successfully tested it. It ran almost exactly as it had before, but once the switch was disengaged, the motor continued to spin from its momentum. The group surmised that the broken copper wiring in the carbon brushes must have had something to do with the braking of the motor. This problem could be quite dangerous if the lower guard malfunctioned.

Design Problems/ Changes

The group discovered that there was a lot of plastic used in the saw's construction. We felt that there was not enough metal at pivotal load-bearing locations on the saw. Instead, we found plastic at these locations. The high power of the drill and the brittle nature of the plastic could lead to a dangerous malfunction, were some of the plastic supports to break. We suggest that high-load areas be reinforced with some sort of steel.

We also noticed that there were no ball bearings on the bushings. Instead, the bushings were heavily lubricated with grease. If the lubricant was burned away by regular use, there could be a large amount of friction created, efficiently "burning out" the motor. We suggest that to increase the longevity of the saw, ball bearings are added to the bushings.

References

Product Detail - 7 1/4" Skilsaw - Model #5400-01. (n.d.). Retrieved December 3, 2007, from http://www.skiltools.com/en/AllTools/Category/Product/default.htm?pid=5400-01&cid=192160