Group 13 - Skil Circular Saw

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Skil Saw

Contents

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:

ACMotor.gif[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.

Circular Saw Process.jpg

Part List

Assembly277.png

Item # Quantity Designation Material Manufacturing Process Picture
1 1 Housing Polysufone(plastic) Injection Moulding
Field within Housing.JPG
2 1 Field (120V) Copper,steel,phenolics (plastic) drawing,stamping,I.M. respectively
PA150257.JPG
3 1 Armature (120V) copper, steel, phenolics (plastic) drawing, stamping, I.M.,Turning
Armature.JPG
4 1 On/Off Switch Polysufone(plastic) compression moulding
277Switch.JPG
5 1 Main Connection Cable Copper,steel, poss. pvc (plastic) drawing,stamping,extrusion
Maincord5.JPG
8 1 Nameplate plastic (thin flexible) sheet forming
Part9-277g808.JPG
9 1 Reference Plate steel stamping, bending
Ref Plate.JPG
14 1 Bearing Sleeve Bearing Bronze Pressed (oil-impregnated)
19 8 Self-Tapping Screw Hardened steel Machining
19screws.JPG
20 1 Reference Plate plastic (thin flexible) sheet forming
Nameplate277G13-08.JPG
22 2 Plain Washer steel stamped
Washer3.jpg
23 1 Washer steel stamped
Washer4.jpg
24 1 Protective Cover Aluminum Cast
Protective Cover.JPG
26 1 Bearing Flange steel turned
Bearing Flange.JPG
27 4 Screw steel Machining
Bearing Screws (27).JPG
28 2 Supporting Disk carbon steel turned
Supporting Disc.JPG
29 1 Housing Cover polysulfone (plastic) Injection Moulding
Housing Cover.jpg
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
Back of Guard Plate.JPG
33 1 Spring steel Rolling
Close-up of Spring Connection.JPG
34 1 Lever Plastic compression moulding
G13lever.JPG
36 1 Retaining Ring Hardened steel turned, bending, quenching
Retaining Ring.JPG
39 6 Headless Screw steel Machined
Headless Screw.JPG
40 1 Casing Foot Galvanized steel stamped,bending
Casing Foot and Box Wrench.JPG
41 1 Round Head Bolt steel Machining
Round head bolt.JPG
42 1 Wing Nut steel Machine Milled & Tapped
Wing Nut.JPG
43 1 Roller Pin steel Rolling
Rolling Pin.JPG
48 1 Guide Piece polysulfone injection moulding
49 1 Stop polyurethane Transfer moulding
Stop, Spacer Bolt and Socket Head Screw.JPG
50 1 Spacer Bolt soft carbon steel Machining
Stop, Spacer Bolt and Socket Head Screw.JPG
51 1 Socket Head Screw steel turning, milling, drilling, tapping
Stop, Spacer Bolt and Socket Head Screw.JPG
52 1 HEXAGON SCREW steel turning, milling, thread rolling.
Hexagon Screw.JPG
66 1 SINTERED-METAL BUSHING steel machined,bending
67 1 REFERENCE PLATE steel stamped
Reference Plate.JPG
651 1 BOX WRENCH steel stamping, bending, drilling
Box Wrench.JPG
810 1 CARBON-BRUSH SET Carbon pressed powder
825 1 Pinion Shaft steel Machined (lathe)
Pinion Shaft.JPG
837 1 SET OF HANDLES Polysulfones (plastic) compression moulding
Set of Handles.jpg
846 1 LEVER Polysulfones (plastic) compression moulding
Handle and Fastener.JPG

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
Bearing Flange.JPG
Transmission.jpg
28 2 Supporting Disk carbon steel turned
Supporting Disc.JPG
Supporting Disk.jpg
52 1 HEXAGON SCREW steel turning, milling, thread rolling.
Hexagon Screw.JPG
Hexagon Screw.jpg
825 1 Pinion Shaft steel Machined (lathe)
Pinion Shaft.JPG
Pinion Shaft.jpg

Link to .zip CAD Files: File: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