Group 37 - Black and Decker Jig Saw
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.
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
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.
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.
After inspection of the saw we assumed there to be approximately 30 parts.
We assumed there to be approximately 5 different types of materials used in the product. These included:
|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|
|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||Injection molded||Hold and protect components|
|3||Front Casing||1||ABS Plastic||Injection 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||Injection molded, extruded and assembled||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, Injection 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||Injection molded case, extruded wire and spring||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||Injection molded||Protects user from blade|
|21||Air duct||1||Plastic||Injection molded||Deflects air to blade in order to blow shavings away|
|22||Internal plastic screw gear||1||Plastic||Injection 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||Injection 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
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.
- 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.
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.
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:
- Drop test to test the strength of the casing
- Endurance test to test out the durability of the motor and the brushes
- 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