Group 37 - Black and Decker Jig Saw

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

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

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

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