Difference between revisions of "Group 37 - Black and Decker Jig Saw"

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Revision as of 01:38, 10 December 2007

Black and Decker Jig Saw.JPG


Contents

Executive Summary

The purpose of this project was to dissect the Black and Decker 4.5 Amp jigsaw and to identify the different processes of production and operation. This was accomplished through a dissection of the product and analyzing each part individually. These steps can be viewed in our Disassembly Procedure and After Disassembly sections. In total we have found 39 pieces to make up the saw, all with a great importance to proper functioning. The jig saw converted electrical energy to linear mechanical energy through a designated path. This process is explained in our Post Assembly Review section. There were no parts that could be left out of the product; however there are aspects that could be improved. These are discussed in our After Disassembly Assessment section.

Introduction

The Black and Decker 4.5 Amp jigsaw is a handheld power tool that is designed for light cutting through materials such as wood, plastic, and metal. Its small blade allows for cutting in tight spots and sharp corners.

Group members include:

  • Jonathan Mills
  • Michael DiGiovanni
  • Joshua Benson
  • Matt Bryden
  • Jason Bhatti
  • Dominic D'Costa


Before Disassembly Section

Purpose

The purpose of the product is to cut through wood, metal or plastic quickly and safely. The adjustable shoe plate allows for angled cuts and the jig saws compact design allows for easy maneuverability through sharp intricate cuts.

How it works

We assumed that an electric motor took in AC power to create rotational motion in a set of gears. Through an offset gear, rotational motion was converted to linear motion in order to drive the saw blade up and down.

Condition

The product worked great and had no evidence of prior use or disassembly. The input was AC power and the output was linear motion of the blade. It sounded like some type of electric motor was inside.

Parts

After inspection of the saw we assumed there to be approximately 30 parts.

Materials

We assumed there to be approximately 5 different types of materials used in the product. These included:

  • Plastic
  • Steel
  • Gel
  • Copper
  • Aluminum

Disassembly Procedure

Step # Process Tool Used Level of Difficulty Picture of step
1 Remove the Seven Philip screws from the rear casing with a medium size Phillips-head screw driver. Phillips-head screw driver medium
Step 1.jpg
2 Loosen external plate gear Hands easy
Step 2.jpg
3 Remove back casing of the jig saw to view internal components Hands easy
Step 3.jpg
4 Lift out blade guard, Gel Max grip and external plate gear Hands easy
Step 4.jpg
5 Remove shoe plate and unscrew internal gear from shoe plate bolt and air duct from shoe plate Hands easy
Step 5.jpg
6 Remove Phillips-head screw from the motor mount Phillips-head screw driver easy
Step 6.jpg
7 Remove two Phillips head screws from the power cord and remove the bracket Phillips-head screw driver easy
Step 7.jpg
8 Remove trigger lock from casing then pull the spring and the spacers from the inside of the trigger lock Hands medium
Step 8.jpg
9 Remove trigger from casing Hands easy
Step 9.jpg
10 Remove power cord, wires, motor and all gear components from the casing as one piece Hands medium
Step 10.jpg
11 Remove linear oscillator from motor assembly Hands easy
Step 12.jpg
12 Remove two Allen wrench screws from the linear oscillator to release the blade holder Allen wrench Hard
Step 11.jpg
13 Remove two steel guide supports and felt protection plate from the linear oscillator by sliding of the ends Hands easy
Step 13.jpg
14 Take the blade holder and remove the plastic lever, then remove two springs from blade holder Hands Hard
Step 14.jpg
15 Remove bushing from main steel gear Hands easy
Step 15.jpg
16 Remove gear from ¼ inch plate by pulling gently Hands easy
Step 16.jpg
17 Slide ¼ inch plate and the thin spacer from the motor mount Hands easy
Step 17.jpg
18 Slide armature out of Slater Hands easy
Step 18.jpg

After Disassembly

Part Table

Part # Part Name Quantity Material Manufacturing Process Purpose Picture 3D Drawing
1 Casing Screws 7 Steel Extruded and machined Hold casing together
Casing screws.jpg
2 Back Casing 1 ABS Plastic Injected molded Hold and protect components
Back casing.jpg
3 Front Casing 1 ABS Plastic Injected molded Hold and protect components as well as secure motor, cord and blades
Front casing.jpg
4 Power Cord 1 Plastic, copper wire and braded insulation Copper wire is extruded, twisted and then wrapped with insulation and plastic coating Supply AC power to the saw
Jig saw power cord.jpg
5 Trigger Switch Assembly 1 Plastic, Copper, Steel and aluminum Manufactured To Convert AC to DC power and send it to motor in variable amounts
Trigger switch assembly.jpg
6 Lead Wires 2 Plastic and copper Copper wire is extruded and coated with plastic insulation To supply motor with electrical current
Jig saw lead wires.jpg
7 Stator 1 Steal, plastic, copper, metal, paper Pressed, Injected molded, extruded, assembled Creates magnetic field in order to spin the armature
Jig saw stator.jpg
8 Armature 1 Steel, copper, plastic Pressed, extruded, machined, assembled Creates rotational motion
Black and Decker jig saw armature.jpg
9 Brushes 2 Plastic, carbon, copper Manufactured Change the polarity on the motor by rubbing against copper
Jig saw brushes.jpg
10 Thin spacer plate 1 Steel Stamped Reduces wear on larger metal plate
Thin spacer plate.jpg
11 1/4 inch metal spacer guide 1 Steel Casted and machined Guides gear movement
Quarter inch metal spacer guide.jpg
Quarter inch metal spacer guide CAD.jpg
12 Oscillating gear 1 Steel Machined Start of rotational motion to linear motion
Oscillating gear.jpg
Oscillating gear CAD.jpg
13 Bushing 1 Steel Machined Link between gear and linear oscillator
Bushing.jpg
14 Guide support 2 Steel Machined Guides and supports linear oscillator
Guide support.jpg
Guide support CAD.jpg
15 Felt piece 1 Felt Cut Dampen vibration and keep debris out of the saw
Jig saw felt piece.jpg
16 Linear oscillator 1 Steel Machined Oscillates vertically and holds the blade
Linear oscillator.jpg
Linear oscillator CAD.jpg
17 Blade holder/changer 1 Steel and copper Cast and stamped Hold cutting blade
Blade holder and changer.jpg
18 Blade holder spring 2 Steel Extruded and wound Supply pressure to blade to hold it in place
Blade holder spring.jpg
19 Lever 1 Plastic Injected molded Depress springs to allow for blade change
Lever.jpg
20 Blade guard 1 Plastic Injected molded Protects user from blade
Blade guard.jpg
21 Air duct 1 Plastic Injected molded Deflects air to blade in order to blow shavings away
Air duct.jpg
22 Internal plastic screw gear 1 Plastic Injected molded and machined threads Tightens and loosens shoe plate
Internal plastic screw gear.jpg
23 Shoe plate bolt 1 Steel Cast and machined Holds shoe plate in place
Shoe plate bolt.jpg
24 Saw blade guide 1 Steel Pressed and machined roller Guides and supports blade
Saw blade guide.jpg
25 Shoe Plate 1 Steel Pressed Keeps blade equidistant from cutting surface and supports saw
Shoe Plate.jpg
26 Air duct part 2 1 Plastic Injected molded Continues are deflection to blade for shaving removal
Air duct part 2.jpg
27 External thumb gear 1 Plastic Injection molded Provides user access to loosen or tighten shoe plate angle
External thumb gear.jpg
28 Trigger lock 1 Plastic Injection molded Locks trigger on
Trigger lock.jpg
29 Trigger lock spring 1 Steel Extruded and wound Keeps trigger lock in either on or off position
Trigger lock spring.jpg
30 Trigger lock spacer 2 Plastic Injection molded Catch casing in order to hold trigger lock centered
Trigger lock spacer.jpg
31 Gel Max grip 1 Plastic and Gel Filled and stamped Provide soft grip for users hand
Gel Max grip.jpg
32 Power cord screws 2 Steel Extruded and machined Secure power cord bracket to front casing
Power cord screws.jpg
33 Power cord bracket 1 Steel Stamped Hold down power cord
Power cord bracket.jpg
34 Power cord protector 1 Plastic Injection molded Protects power cord and keeps contaminates out of casing
Power cord protector.jpg
35 Fan 1 Plastic Injection molded Keeps motor cool and directs air through air duct
Jig saw fan.jpg
36 Motor mount 1 Steel Cast Holds motor down and connects gears
Motor mount.jpg
37 Extra blade holder 1 Plastic Injection Molded Holds extra blades for easy access
Extra blade holder.jpg
38 Allen head screws 2 Steel Extruded and machined Hold blade holder to linear oscillator
Allen head screws.jpg
39 Motor mount screw 1 Steel Extruded and machined Holds top of motor to front casing
Motor mount screw.jpg

After Disassembly Assessment

Materials

During the design process of the Black and Decker jigsaw, after each component has been designed to its working shape it must be analyzed so the proper material can be selected to create each part. Things that must be put into consideration are the various types of stresses and forces that are to be applied to each part. For the jigsaw there are five different materials that compose the entire powertool: ABS plastic, steel, copper, carbon, and the gel.

  • ABS plastic is used in parts such as the casing, shoe plate gears, and air ducts 1 and 2. This material was chosen for these parts because they experience little wear, high speeds, or forces. This material is also cost effective and ideal for the mass production of parts as the Black and Decker makes a large quantity of jigsaws each year. Everyone of these parts are injection molded which is a quick method of production.
  • Steel is used in components such as the gears, shoeplate, linear ocilator, and the 1/4" plate. This material was chosen because its level of hardness allows for a long lifespan of the product as all of these components experience a great deal of wear and tensions. The gears are constantly spinning at a high rpm and constantly rub against each other. If made out of a soft material the internal parts would last only a fraction of the time.
  • Copper was used in any part that needed to carry an electrical current such as the wires, coils in the stator and armature, and springs in the brushes. While being slightly costly copper has a very high conductivity and allows the electrical components to function properly.
  • Carbon was used in the brushes to pass current to the armature and alternate the polarity in the motor. This is what allows the motor to turn.
  • The "Gelmax" grip was made with gel to cushion the operators hand when the jigsaw is in use. This gel is ideal for this part because it freezes at very low temperatures which allows for the use of the saw outdoors during all seasons.



Improvements/Design Changes


  • 1/4” plate has extra holes that are not needed. Machining could be cut down by eliminating these.


  • The gear has holes that are not needed which can be eliminated and cut down on production costs.


  • A stop could be incorporated into the casing so the armature is more easily placed into the correct spot into the stator. This would make the assembly easier and reduce the chance of rubbing in the motor.


  • Wires that connect the stator to the brushes could be shortened so they don’t have to be wrapped around the brushes. This would make assembly easier and cut down on the cost of the product.


  • In the jigsaw there are two different length screws, both with the same thread. If there was one size screw to fasten all parts, the assembly would be easier and the cost would be cut down.


  • Although all of the parts are necessary in the operation of the saw, two pieces of the assembly that could be combined are the air duct 1 and air duct 2 as this piece constantly falls apart upon reassembly. There is no need to separate these components as they would be stronger as one and not give the hassle when assembling the saw.


Gear Assembly

The components in the gear assembly fit together very easily and compiled completely by hand. The quarter inch plate acts as a spacer and a holder for the gears which slide into the alotted slots. These slots allow the gears to rotate freely in the given space. On the right side of the gear is an offset post that a bushing slides onto. This bushing is what sits in the linear oscillator and reduces friction while in operation. The linear oscillator is next slid onto the bushing and the guide supports are slid tho the ends of the oscillator. These are what holds the oscillator in place and protects the casing from wear.


Assembly1.jpg
Assembly2.jpg
Assembly3.jpg
Exploded1.jpg
Exploded2.jpg
Exploded3.jpg
Assembly1.jpg

Assembly Procedure Table

Step # Process Tool Used Level of Difficult
1 Slide armature into Slater Hands easy
2 Slide thin spacer and then the 1/4 inch plate onto the motor mount Hands easy
3 Put steel gear back on to gear box by sliding the shaft into the motor mount make sure the gears line up Hands medium
4 Place the bushing back onto the gear Hands easy
5 Place the springs and the lever back onto the Blade holder Hands medium
6 Put the guide supports and felt protector plate back onto the oscillator Hands easy
7 Slide the blade holder onto to the linear oscillator and put in two Allen wrench screws to hold in place Hands and Allen wrench hard
8 Place linear oscillator onto the steel gear Hands medium
9 Carefully place the power cord motor and gear components back into the casing, realign motor to the grooves and motor mount to designated grooves to assure exact fit Hands hard
10 Push the brushes back into designated brackets and align wires to the grooves in the casing Hands hard
11 Assemble trigger lock and slide trigger lock and trigger into casing Hands medium
12 Place bracket for power cord into place and hold it in with two Phillips-head screws Phillips-head screw driver easy
13 Put Phillips-head screw into motor mount Phillips-head screw driver easy
14 Place the blade guide and bolt through shoe plate and attach internal gear screw to the bolt Hands medium
15 Place shoe plate assemble into casing Hands hard
16 Place external gear screw, Gel Max grip, blade guard back into the casing Hands easy
17 Take the two casings and put them together Hands medium
18 Insert 7 Phillips-head screws into the casing Phillips-head screw driver easy

Post Assembly Review

  • After it was reassembled the jig saw still functioned and sounded the same as it did when we had first gotten it and tested it out and it sounded and looked like it was functioning like nothing ever happened to it. It didn't show any signs of failure or overheating or binding of the gears.


  • The jig saw functions by converted AC power which is brought into the jig saw via the power cord to DC power. The power travels to the switch which is located in the handle of the jigsaw. The switch regulates the amount of electricity that travels to the motor which provides the variable speeds. The electricity travels to the motor and the motor creates a magnetic field from the current traveling through the copper coils. The magnetic field is located between the Slater and the Armature which creates the Armature to spin causing rotational energy. The rotational energy spins the gear which is connected to the linear oscillator which converts the energy into linear energy. The linear energy moves the blade in a linear motion resulting in a cutting action.


  • Some analysis procedures that could be performed to test the product would be:
  1. Drop test to test the strength of the casing
  2. Endurance test to test out the durability of the motor and the brushes
  3. Test by cutting through different materials with different hardness to test motor's power


  • The disassembly and the assembly of the Black & Decker jigsaw were for the most part on the easy side for difficulty. The disassembly steps mirrored the assembly steps, every part came out just as easy as they went back in. The only steps that were really difficult would be getting the motor and the motor bracket to line up into their grooves

References

http://en.wikipedia.org/wiki/Armature

http://www.blackanddecker.com/ProductGuide

http://electronics.howstuffworks.com/motor1.htm