Group 13 - Skil Circular Saw

Latest revision as of 18:44, 17 March 2009

Skil Saw

Executive Summary

This project is a documentation of the disassembly and basic analysis of a Skill Saw brand circular saw model 54HD. Our team disassembled, analyzed, documented, modeled, and reassembled this circular saw, gaining insights into its design and construction. Each individual part was looked at for a purpose and manufacturing technique used in the construction of the material. Though this analysis, we were able to learn about the products function as well as come up with some potential design and manufacturing improvements. This product was working when obtained, and was working correctly upon reassembly. The following information contains a detailed summary of the work completed by our team during the fall 2008 semester.

Introduction

Group Members

• Nick Day

Worked on PowerPoint Editing

Wrote Assembly & Disassembly Paragraphs on the Wiki

Helped Post Process Pictures

Disassembly/Reassembly

• Dan DiNardo

Filled out parts list

Identified materials and construction methods

Disassembly/Reassembly

• Ian Duncan

Picture labeling/uploading during Disassembly/Assembly

PowerPoint Editing

Disassembly/Reassembly

Wikipedia Page

• Dan Pastuf

Presentation

Principle for Wikipedia Page

CAD Drawing

• Jonathan Resnick

Presentation

Disassembly/Reassembly

Predisassembly Analysis

The Skil Circular Saw Model 54HD is a electrical hardware tool which is used to cut various materials depending on the blade chosen. The principle material this tool is meant to cut is wood. It works by converting electrical power from a standard wall outlet to mechanical energy through electromagnetic forces. At this point in the dissection, we believed that the unit was a direct shaft saw which means it is attach directly to the spinning motor shaft to the blade. Upon plugging this product in and turning it on, the unit appears to be in perfect working order, minus the blade (which it was explained was for safety/liability reasons by the Lab). The unit seems to be in brand new shape. When turned on, the system appears to make a whirring noise, at a steady level. Also, the estimations of parts at this point was in the range of 100 to 150 pieces, including all of the various nuts, bolts, rubber gaskets, and screws, as well as the main components. We anticipated at this point that there were around seven to ten different materials, although the main components were Rubber, Copper, Plastic, and Aluminum materials.

Disassembly

The first stage of disassembly of our Circular Saw consisted of removing the skid plate that was attached to the bottom of the unit. This was the only component that gave us any difficulty, as the pin that held the skid plate to the mounting bracket, made of rolled steel, was a tight fit, and had to be forcefully removed. All other parts required only unscrewing or unbolting the part in order to remove. We then removed the Blade Guard and the pieces that held it in place, such as the guard tension spring, a rubber stop, and other various clips and screws. Then the Blade Housing was removed, which exposed the Main Motor and Housing. There are three components to this section, the Housing, the Armature and the Final Drive Gear. This basically works like an electromagnet, where a copper coil(armature) spins within the main blade housing, creating alternating polarities. We also took apart the handle, which was very easily dissected. This helped our group to understand how the integrated variable resistor trigger system worked. Below is the chronological order of the disassemble process:

Tools used

• T20 torx screwdriver
• Phillips head screwdriver
• Standard Pliers
• Allen wrench
• Standard Carpenter Hammer

Order Breakdown

1) Disassemble Skid Plate

a. Adjusting wing nut in front

i. Screws off readily

b. Remove Cutting depth adjustment lever (red plastic lever)

i. Remove c clip and nut (easily removed)

c. Remove pin that holds front mounting bracket to skid plate.

i. We carefully hammered it out using an Allen wrench consisting of a similar diameter and we used a wood hammer. (not too difficult)

2) Blade Guard

a. Remove blade guard tension spring

b. Remove blade guard rubber stop (torque screw)

c. Remove blade guard flipper handle (torque screw)

d. Use flat head to remove retainer clip which holds the blade guard secure to the shaft.

i. We first tried removing the nut on the end of the shaft but that did not work, then realized that there was a retainer clip.

3) Blade Housing

a. Remove main blade housing

b. Remove retainer screws for housing

c. Remove blade shield

i. All of this was fairly straight forward and easy.

ii. A brush from the motor fell out when we did this.

4) Main Motor & shaft Housing

a. Remove 3 torque screws around gearbox.

b. Remove 4 torque screws securing blade housing to main housing

i. (easy, all screws were torque size T20)

c. Separate main housing from blade housing

i. Other brush from the motor fell out when we did this.

d. 3 main components –

i. Housing

ii. Armature (has thrust washer) fins – copper

iii. Final drive gear

5) Handle

a. Remove handle screws (6 - T20)

b. Separates horizontally into 2 halves.

How it Works

The design works by applying an electric current to an electromagnetic motor. The motor is connected to a gear reduction system that is then fitted to the blade via a friction clamp. Upon pulling on the switch, current is allowed to flow though the system and start the blade. The Switch itself is a variable resistor, so that the harder you pull, the more power is applied to the system. After the power begins to flow to the electrical motor, magnetic and electrical fields begin to interact to start the armature in a curricular motion. A diagram of this follows:

[1]

The turning armature is in contact with a gear reduction piece, which allows the motor to be reduced to a speed conducive to the spinning blade. The gear reduction piece has on the other end two supporting disks, which are locked into place around the cutting blade with the hexagon screw in order to lock the blade into place.

To cut materials, forward motion is applied by the user which allows the blade access to materials to be cut.

Part List

Item #	Quantity	Designation	Material	Manufacturing Process	Picture
1	1	Housing	Polysufone(plastic)	Injection Moulding
2	1	Field (120V)	Copper,steel,phenolics (plastic)	drawing,stamping,I.M. respectively
3	1	Armature (120V)	copper, steel, phenolics (plastic)	drawing, stamping, I.M.,Turning
4	1	On/Off Switch	Polysufone(plastic)	compression moulding
5	1	Main Connection Cable	Copper,steel, poss. pvc (plastic)	drawing,stamping,extrusion
8	1	Nameplate	plastic (thin flexible)	sheet forming
9	1	Reference Plate	steel	stamping, bending
14	1	Bearing Sleeve	Bearing Bronze	Pressed (oil-impregnated)	File:Citationneeded.JPG 160px
19	8	Self-Tapping Screw	Hardened steel	Machining
20	1	Reference Plate	plastic (thin flexible)	sheet forming
22	2	Plain Washer	steel	stamped
23	1	Washer	steel	stamped
24	1	Protective Cover	Aluminum	Cast
26	1	Bearing Flange	steel	turned
27	4	Screw	steel	Machining
28	2	Supporting Disk	carbon steel	turned
29	1	Housing Cover	polysulfone (plastic)	Injection Moulding
30	1	Connecting Cable (385 mm)	copper, polypropylene or pvc	drawing, extrusion moulding
31	1	Connecting Cable	Polypropylene or pvc	extrusion moulding
32	1	Guard Plate	Cast Aluminum	Casting
33	1	Spring	steel	Rolling
34	1	Lever	Plastic	compression moulding
36	1	Retaining Ring	Hardened steel	turned, bending, quenching
39	6	Headless Screw	steel	Machined
40	1	Casing Foot	Galvanized steel	stamped,bending
41	1	Round Head Bolt	steel	Machining
42	1	Wing Nut	steel	Machine Milled & Tapped
43	1	Roller Pin	steel	Rolling
48	1	Guide Piece	polysulfone	injection moulding
49	1	Stop	polyurethane	Transfer moulding
50	1	Spacer Bolt	soft carbon steel	Machining
51	1	Socket Head Screw	steel	turning, milling, drilling, tapping
52	1	HEXAGON SCREW	steel	turning, milling, thread rolling.
66	1	SINTERED-METAL BUSHING	steel	machined,bending
67	1	REFERENCE PLATE	steel	stamped
651	1	BOX WRENCH	steel	stamping, bending, drilling
810	1	CARBON-BRUSH SET	Carbon	pressed powder
825	1	Pinion Shaft	steel	Machined (lathe)
837	1	SET OF HANDLES	Polysulfones (plastic)	compression moulding
846	1	LEVER	Polysulfones (plastic)	compression moulding

Key Component Analysis

Why is the component made of its material:

1) Housing - Has to be durable to resist impacts, easily formed into its complex shape, and cheap.

2) Field - Must be an electrical conductor, resist melting from operating temperatures, and use a non- conductive material for wire windings.

3) Armature - Has to conduct electricity, use an electrical insulator for wire windings, and be capable of effectively transfering torques.

4) Main Cable - Needs to be flexible, electrically conductive, and electrical conductors have to be insulated against the outside environment.

5) Bearing Sleeve - Must support main motor shaft while protecting against friction.

6) Protective Cover - Must be rigid, formed easily and cheap so that it contours the blade, and provide support to the adjoining components such as the motor housing.

7) Guard Plate - similar to the protective cover, this component must also be rigid for protection against the blade. Aluminum alloy also aids in weight reduction.

8) Casing foot - Steel can be thin and still provide good strength and it is produced inexpensively.

9) Final drive gears - Steel has higher strength and reliability than other materials such as aluminum and bronze.

C.A.D. Images / Files

The following parts have been modeled into a 3D program:

Item #	Quantity	Designation	Material	Manufacturing Process	Picture	CAD
26	1	Bearing Flange	steel	turned
28	2	Supporting Disk	carbon steel	turned
52	1	HEXAGON SCREW	steel	turning, milling, thread rolling.
825	1	Pinion Shaft	steel	Machined (lathe)

Link to .zip CAD Files: Skill_Saw.zip

Re-Assembly

Our groups re-assembly process was essentially the disassembly in reverse. We began with the Trigger/handle component and worked our way back, using our prior knowledge and the cataloged pictures to correctly complete the project. We then reconstructed the Main Blade housing, the main component of the tool. The main change that our group made was reconnecting the skid plate before the blade guard, which did not alter its usage by any means, it just slightly increased the level of difficulty of reattaching the blade guard with the skid plate already in place. This error in the "timeline" did not cause any problems in our groups effort, and was reletively miniscule, so it could be said that our re-assembly and disassembly were a "mirror image" of one another. Here is the chronological of the reassembly process:

Tools used

• T20 torx screwdriver
• Phillips head screwdriver
• Pliers
• Allen wrench

Order Breakdown

1) Trigger/handle assembly

a. Use T-20 torque screw driver to tighten all screws around handle

b. Insert armature brushes that fell out during disassembly

i. Hard to place correctly

c. Insert motor armature into housing

i. The motor runs while the armature is simply sitting in the housing

ii. (we tried, we’re retarded)

iii. Place washer on armature

d. Screw on back plate of motor housing using T-20 screws

2) Main Blade Housing

a. Insert main blade housing onto armature and slide down until its flush with motor housing

b. Screw on the T-20 torque screws which attach motor housing to blade housing.

c. Insert final drive into slot

d. Screw to blade housing (3 T-20 screws)

3) Skid Plate

a. Bang out pin which holds plate to motor housing

b. Slide plate into place

c. Hammer pin back into housing to secure skid plate

i. Difficult to hammer in

ii. Took a while to accomplish

d. Insert wrench into skid plate

e. Screw on cutting depth adjusting lever

i. Insert skid plate height adjustment guide bar

ii. Insert nut

iii. Tighten it so its adjustable

iv. Place adjustment height locking lever so its positioned upward about 45 degrees from level and push it down to lock.

v. Insert lever retaining clip

f. Adjust angle of cutting plane

g. Insert wing nut and bolt and screw on loosely.

4) Blade Guard

a. Screwed on red blade guard adjusting lever

b. Slide onto axle

i. Adjust height of skid plate to fit guard on

c. Slide securing clip onto axle to hold together

d. Hook blade guard spring to both mounts

e. Screw blade guard stopper to main blade housing (T-27)

After Assembly

When our group received the saw, it was in working order. We were able to successfully disassemble and reassemble the product with all of the components still in working order. This product was relatively easy to dissect and understand. It uses a simple electromagnetic motor to successfully complete it desired use. Nothing was broken on our model and all of the pieces interacted as they were designed to by the Skil company. This project helped to further our group members knowledge of how these motors, and products in which they are incorporated, are intended to work and how all of their internal components interact.

Design Improvements

Ergonomics

• Formed rubber grip handle for improved control and quality feel
• Use of helical gears to help improve noise reduction
• Nylon fan for reduction of moment of inertia of armature
• Built in LED light for illumination of cutting surface
• Laser light to for improvement sight of movement
• Ball bearings for motor shaft for increased performance and reliability
• Reverse curve in guard plate to direct wood chips down and away from operator
• Multiple languages on some of the molded material
• Use earth friendly materials such as recyclable material for easier disposal

Performance

• Larger armature for increased torque output
• Lengthened armature shaft with carrier bearing to prevent lateral motion of armature
• Cam operated tensioner (locking mechanism) for quicker angle cut adjustment
• Make usable in a vacuum

Manufacturing

• Change final drive locking mechanism for easy loosening or tightening of the blade bolt
• Replace the spring loaded pin with a small bolt for handle mounting
• Use of connection clips instead of soldered wire connections for easy removal of power supply cord

References

1. http://www.ibiblio.org/kuphaldt/socratic/doc/topical.html
2. http://www.physclips.unsw.edu.au/jw/electricmotors.html