Group 20 - Black and Decker Drill

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Black & Decker DR202B Screw Gun

Complete.jpg

Contents

Executive Summary

A screw gun is an alternate tool that performs the same function as a screw driver. Once receiving the screw gun before disassembling it, we made some predictions and assumptions on how it works. In addition we estimated how many components were in the gun and what materials were most likely used. To understand how the screw gun functions we disassembled the screw gun and explored its insides to find out how it operates. We disassembled and analyzed each component individually, jotting down notes and discussing, why it was made the way it was, what is unnecessary, and how to improve on the design. By reason we were able to figure out how the gun transformed the energy from the wall into mechanical energy. We also determined what each component’s purpose was and what material it was made out of. When drawing up what components in the gun we also discussed what material they were going to be made up of.

Following disassembly we photographed each component and the processes that were taken to disassemble the screw gun. Subsequently we reassembled the screw gun confirming that it was still operational. We proceeded by recording some observations. We recorded how many of each component were in the screw gun with its purpose and what material it was made out of and how it was made. In addition we explained why each component used was made the way it was. We also discussed what improvements could be made with explanations why it would improve the product either on the functionality side, manufacturing, or ergonomic. Later we constructed a 3-D CAD diagram of the components in the screw gun in order to further understand why each component was used and how the product operates.

We concluded the project by drawing up a report that included everything we have done in the project. The report clearly describes how the product works in detail, along with what each part’s purpose of the screw gun was.

Introduction

The Black & Decker DR202B Screw gun is design for quick fastening and unfastening screws. It is the new age of screw drivers. We disassembled the screw gun to further understand the minds of its creators and what improvements we can make to it.

Jordan- Class presentation, wrote how it works and the design changes. He is also the group leader.

Tim- Wrote disassembly, reassembly, disassembly/reassembly discussion and made disassembly video.

Jim- Made tool parts list, worked on Wiki and organized it.

Greg- Wrote intro and executive summary, took pictures and wrote references.

Abhishek- Made CAD drawing, worked on Wiki, and researched the manufacturing processes and the materials used.

Before Disassembly

Purpose

  • The screwgun is used for drilling and driving. Its uses include screwing, unscrewing and drilling holes.
  • It is plugged into an electrical outlet which powers the turning of the driver.
  • It uses electrical power from the outlet that is transfered to mechanical power.

Operation

  • The product is brand new, so it runs well.
  • It makes a motor like sound that is quite loud for such a small object.
  • Air is blown out of the side of the drill in order to cool it.
  • The tip of the chuck rotates very rapidly.

Components

We estimated the components within the screwgun based on what it would take to convert the electrical power to mechanical power and the known functions of the product.

  • There has to be something to convert the electical power to mechanical power
  • The locking mechanism has to cut the power.
  • A mechanism to keep the screwgun drilling without holding in the trigger.
  • A mechanism to switch the drill from forward to reverse.
  • A component which allows the speed of the bit to vary as pressure on the trigger varies.

Types of Material

  • Plastics
  • Copper
  • Iron
  • Rubber

Disassembly Procedure

Step # Procedure Tool Used Ease (Scale of 1-10, 10 being easiest) Image
1 Remove all screws from the outer casing Phillips Head Screwdriver 9
Complete.jpg
2 Remove one half of the outer casing Hands 10
IMG 2578.jpg
3 Remove the two screws holding the metal piece that holds down the wires Phillips Head Screwdriver 9
IMG 2591.jpg
4 Remove the metal piece holding the wires down Hands 10
IMG 2533.jpg
5 Remove the rotational changer from the electromagnetic field Hands 9
IMG 2531.jpg
6 Remove the bit holder from the outer casing Hands 10
IMG 2528.jpg
7 Remove the other half of the outer casing Hands 7
Outside.jpg
8 Pull apart the chuck from the gears Hands 9
IMG 2564.jpg
9 Pull the other set of gears apart from the gasket Hands 9
IMG 2589.jpg
10 Unscrew the screws holding the field together Phillips Head Screwdriver 7
IMG 2538.jpg
11 Remove the inner coil from the field Hands 6 Coils.jpg


<embed src="http://www.youtube.com/v/AXCB9-dORfQ&rel=1" type="application/x-shockwave-flash" wmode="transparent" width="425" height="355"></embed>

After Disassembly

Part Table

Part # Part Name Function # Of This Type Material and Reason for Choice of Material Reason for Part's Shape Manufacturing Process Image Part # (where applicable)
1 Screw Hold material in place. 11 Steel
Strength and Durability
Torx heads allow for more efficient manufacturing. They are easily aligned and the screwdriver does not turn out. Machined
IMG 2591.jpg
2 Top Shell Provide housing for internal components 1 ABS Plastic
Lightweight, Durable
Protection of inner parts and to hold them in place Injection Molding
IMG 2578.jpg
200522-47
3 Bottom Shell Provide housing for internal components 1 ABS Plastic
Lightweight, Durable
Protection of inner parts and to hold them in place Injection Molding
Outside.jpg
200522-47
4 Rubberized Grips Provide grip for user 2 Rubber
Ergonomic Comfort and Grip
Follows same shape as shell, placed in areas of user contact Injection Molding
IMG 2575.jpg
5 Rear Plate Ventilation and holds level 1 ABS Plastic
Lightweight, Durable, Non-Conductive
Fits between top and bottom shells and holds the level in place. Injection Molding
IMG 2529.jpg
6 Level Allows user to accurately align gun in a perpendicular position relative to the surface 1 Plastic & Mineral Oil
Mineral Oil's viscosity is ideal for the level
Has two gauges, so one level can be used in both vertical and horizontal drilling positions Injection Molding
IMG 2529.jpg
5 612596
7 Accessory Bit Holder Provides a place to store an extra bit. 1 Rubber
Soft enough to allow the bit to be removed and inserted easily, yet hard enough to securely hold the bit
Shaped to take up the least amount of room yet still be able to house the bit and allow user to remove. Injection Molding
IMG 2528.jpg
8 Accessory bit Driving phillips and flat head screws. 1 Steel
Strength and Durability
Combines both Phillips and Flat Head bit types in one tool. Machined
IMG 2527.jpg
9 Power Cord Transports AC power from outlet to drill. 1 Plastic
Flexible & Non Conductive

Copper
Conductivity
Long cylindrical shape to enclose the wire while remaining flexible. Moderate length to not always be in the way but in some situations an extension cord would be needed. Extruded
IMG 2571.jpg
10 Main Plug Supplies power. 1 Plastic & Copper
Insulation
Conductivity
A two prong plug is used because there is no need to ground the gun due to the plastic outer shell. Allows gun to be used in all outlets and extension cords. Injection Molding & Sheet Metal Forming
IMG 2572.jpg
11 Strain Relief Provides flexibility of cord without strain on wires. 1 Rubber
Flexibility
A large strain relief piece is used in order to protect the internal wiring and power cord. Injection Molding
IMG 2579.jpg
12 Chuck Holds the bit securely in place. 1 ABS Plastic & Steel
While the plastic is lightweight, it is not strong enough to hold the bit under high torque, therefore steel is used for the core.
Although not as strong, a keyless chuck is much more convenient than a keyed chuck. The user does not need to worry about losing the check key. Injection Molding, Die Cast & Machined
IMG 2564.jpg
20050530-3-1
13 Anti-Theft Strip Prevent theft of the product. 1 Plastic & Metal
Easily detected by store security system.
An industry standard part. Great way to prevent a loss of money to company and store. Small and compact to not waste space inside gun. Injection Molding & Sheet Metal Forming
IMG 2593.jpg
14 Wire Clamp Keeps wires in place to prevent strain on them and keep them out of the way. 1 Metal
Strength
The clamp is curved to provide extra holding force and room for the wires. Machined
IMG 2533.jpg
15 Trigger/Inverter Determines speed of drill by amount of user input. 1 ABS Plastic, Steel & Silicon
The plastic serves to insulate the user from the current inside. The spring and computer chip within the inverter control the amount of energy that goes to the motor by how much the trigger is pressed.
Ergonomically conforms to the user's fingers, providing a better grip. Injection Molding
IMG 2582.jpg
611719-01
16 Internal Wiring Carries current. 1 Copper & Plastic Insulation The wiring is compact and flexible enough to fit in small crevices with and around other parts in the gun yet still transport power efficiently. Extruded
IMG 2585.jpg
17 Direction Switch Allows for easy change in the direction of rotational motion. 1 ABS Plastic
Lightweight, Non-Conductive, Strong
It has a ball on one end which connects into the motor, allowing it to change the direction. Injection Molding
IMG 2531.jpg
18 Motor
See Motor/Gearbox Part Table below
Provides the rotational motion of the gun. 1 Copper, Plastics, Steel The motor takes DC power from the inverter and uses it to create a magnetic field which creates rotational torque and rotates the screw gun rotor. Extruded, Die Cast & Machined
IMG 2538.jpg
19 Motor Shaft It is surrounded by the Rotor and is extended past the motor to spin the fan and the gearbox. The first gear of the gearbox is part of the Motor Shaft. 1 Steel
Strong
The end of the shaft is machined in order to mesh with the first gear of the gearbox. Machined
IMG 2561small.jpg
20 Fan Cool internal components of gun. 1 ABS Plastic
Lightweight, Strong
Attached to the motor shaft in order to use its rotation to blow heat out of the gun through vents in the outer shell. Injection Molding
IMG 2561small.jpg
21 Commutator Charges the coils in the rotor. 1 Copper
Conductive
It has notches so only one coil will receive electricity at a time from the brushes. Extruded, Forming, Die Cast
IMG 2540small.jpg
22 Rotor Creates a magnetic field when energized from the commutator, it is the only part in the motor that rotates. 1 Copper
Conductive
Cylindrical so it can rotate about its central axis. Extruded, Forming
Conductive
IMG 2538.jpg
23 Stator Creates an electric field when electricity is ran through it. 1 Copper, Plastic & Steel
Conductive
Cylindrical so it can rotate about its central axis. Injection Molding, Die cast & Forming
IMG 2538.jpg
051705-XP 385849-00
24 Brushes Contact points for commutator, completes circuit. 2 Carbon (Graphite)
Conducts as well as withstands rotating forces while staying stationary.
They are small enough to only touch one part of the commutator at a time, but thick enough to carry current. Extruded
IMG 2562.JPG
25 Coil Springs Applies force on brushes in order to make contact with commutator. 2 Metal
Strength
Functionality, provides force necessary. Extruded, Sheet Metal Forming
IMG 2562.JPG
26 Retaining Clip Secures components to motor shaft. 2 Steel
Strength
Provides holding power in a compact, space saving design. Sheet Metal Forming
IMG 2538.jpg
27 End Cap
See Motor/Gearbox Part Table below
Immobilizes the motor shaft. 1 Iron
Very Sturdy
Allows the motor shaft to be locked in place. Die Cast
IMG 2562.JPG
28 Gearbox
See Motor/Gearbox Part Table below
Converts the high speed/low torque output of the motor to a lower speed/high torque which is preferred. 1 Steel
Strength
Creates gear reduction Die Cast & Machined
IMG 2589.jpg
29 Gasket
See Motor/Gearbox Part Table below
Stabilizes inner workings of drill, secures shaft to the gearbox. 1 Stainless Steel
Strength
Fits into the outer shell well. Die Cast
IMG 2544small.jpg
30 Gear 2 and 3
See Motor/Gearbox Part Table below
Gets rotated by the gear on the end of the Motor shaft and then rotates gear 4. 1 Stainless Steel
Strength
Notches are used to force rotation. Die Cast
IMG 2543small.jpg
31 Gear 4
See Motor/Gearbox Part Table below
Gets rotated by gears 2 and 3 and is directly connected to the Chuck. 1 Stainless Steel
Strength
Notches are used to force rotation. Die Cast
IMG 2568small.jpg
32 Washer 1
See Motor/Gearbox Part Table below
Separates the chuck from the Motor Shaft while not preventing rotation. 1 Stainless Steel
Strength
Fits around the Motor Shaft. Die Cast
IMG 2545small.jpg
33 Washer 2
See Motor/Gearbox Part Table below
Separates the chuck from the Motor Shaft while not preventing rotation. 1 Stainless Steel
Strength
Fits around the Motor Shaft. Die Cast
IMG 2545small.jpg

Motor/Gearbox Part Table

Part No. Part Name CAD 3-D CAD 2-D
18 Motor
Motor1.jpg
No 2-D
29 Gasket
Gearplate1.jpg
No 2-D
30 Gears 2 and 3
Gear 1.jpg
No 2-D
31 Gear 4
Topgear.jpg
No 2-D
27 Endcap
End bracket1.jpg
End bracket2.jpg
26 Retaining Clip
Retaining clip1.jpg
Retaining clip2.jpg
32 Washer 1
Washer1.jpg
Washer2.jpg
33 Washer 2
Bushing1.jpg
Bushing2.jpg
20 Chuck
Top part 11.jpg
No 2-D

Component Improvements

On a component level of the screw gun, it is very efficiently made. There are no unnecessary parts to the screw gun; however, there is a lot of space that inefficiently used inside the gun. There is empty space throughout the screw gun, however this should not be changed because it serves an ergonomic purpose for stability and grip. There are wires that could be shortened in order to fit into the shell better because the hardest part of the reassembly was trying to get the wires all inside so that the shell would close. If the gears were housed in some compartment all together so that they could come in and out as one piece, instead of four different gears, it would make the assembly much more efficient as well.

Assembly Procedure

Step # Procedure Tool Used Ease (Scale of 1-10, 10 being easiest) Image
1 Assemble the gears into the gasket and attach them to the chuck Hands 8
IMG 2589.jpg
2 Place the rotor in the field and screw the two screws into the field Hands, Phillips Head Screwdriver 6
IMG 2538.jpg
3 Attach the gasket to the fan and rotor, being sure the rotor doesn't switch directions Hands 5
IMG 2535.JPG
4 Place the field, fan, gears and chuck into the outer casing Hands 6
DRILL.jpg
5 Place the rotational changer into the field and the outer casing Hands 10
IMG 2531.jpg
6 Place the wires and trigger into the outer casing, being sure the wires are pressed down and out of the way of the casing Hands 8
IMG 2582.jpg
7 Screw the wire holder into place Phillips Head Screwdriver 8
IMG 2533.jpg
8 Push the wire down through the bottom of the drill Hands 9
IMG 2579.jpg
9 Place the drill bit holder into the casing Hands 10
IMG 2528.jpg
10 Place the bubble level into the casing Hands 10
IMG 2529.jpg
11 Screw the casing together, being sure not to pinch the wires Phillips Head Screwdriver 8
Complete.jpg

After Assembly

Design Changes

The Black & Decker screw gun was a very well designed product, however there are a few changes that could be made to the design that would improve the final product. While operating the screw gun, there was excessive noise, which could be easily dampened by insulating the motor of the screw gun. Another improvement of the operation of the screw gun would be to increase the length of the attached cord to facilitate use without a separate extension cord. An option that could be added to the screw gun is an exterior battery pack, so that the screw gun can be used far away from an electrical outlet, along with saving the consumer the hassle and money of buying an additional screw gun to get this feature. The size of the chuck also presented a possible problem because it is significantly larger than the screws it uses, which does not allow it to screw or drill into corners. If the chuck was manufactured thinner, it would greatly increase the ergonomics of the gun, as well as save materials. A small LED could be attached to the tip of the gun to allow drilling at night, as well as in dark corners.

How it Works

A screw gun is a device that takes electrical power and transfers it to rotational power. The Black & Decker DR202B screw gun is a corded gun that first transfers ‘AC’ power to ‘DC’ power through an Inverter. The Inverter is located inside the trigger mechanism of the gun, which consists of a computer chip and a spring that varies the amount of energy that goes to the motor by how much the trigger is pressed. The Inverter is necessary because the motor of the screw gun is an Induction Motor, which only works with DC power.

The motor has two parts to it, an outside hollow cylinder, and an inside cylinder that surrounds the rotor. The outside cylinder is called the stator which consists of two copper coils that when energized create a North pole on top of the motor and a south pole on the bottom. The inner cylinder is called the rotor and consists of 12 different coils wrapped lengthwise along the rotor. There are two brushes that carry the current and polarize only one coil at a time in such a way that there is a torque produced. As the rotor begins to rotate the brushes do not rotate and thus change which coil is polarized so that the torque is continuous. There is also a forward and reverse feature to the screw gun which restricts the rotation in one direction.

The next component down the shaft of the screw gun is a series of 4 gears. The gears are different sizes and perform gear reduction, which slows the output rotation, while increasing the torque output. The gears lead to the chuck, which holds the bit in place. The chuck works by using screw threads to transfer rotational work to translational work.

After the screw gun was assembled it operates the same as it did before. We were careful to disassemble anything that we would not be able to put back together, such as the chuck, which would have required cutting it open with a saw.

Disassembly/Reassembly Discussion

When the drill was disassembled, it was very simple to remove all of the parts inside the casing. After unscrewing the clamp holding down the wires, the entire drill came out of the casing. Then, it was just a matter of sliding the gears apart, and sliding the gasket off of the motor shaft. The difficult part was taking the chuck apart. In order to do this, we had to put the bottom of the chuck in a vice, clamp the top of it, and take a torque-set screwdriver and unscrew the screw that was holding it together. But in order to take the chuck apart further we would have had to saw the chuck apart, and because the drill needed to be in one piece when we handed it in, we stopped there.

The reassembly process was a little more tedious. First, the gears were slid back together and placed on the gasket and the chuck. Then, the gasket was slid back onto the motor shaft. When drill parts were back together, we placed them into the casing and tried to put the casing together. But, because the commutator was pushed in, the drill didn't go into the casing correctly and prevented the casing from closing completely. After we pulled the commutator back out, the casing when on properly and we were able to screw it back together.

Analysis

It would be very easy to test the power output of the screw gun. It would first be necessary to determine the revolutions per minute directly out of the motor. As it passes through the gear reduction, there are two small gears which turn many times in order to rotate the two large gears once. If the number of notches on the large gears are counted and divided by the number of notches on the small gears, the number calculated will be the factor that the output speed decreases by after it goes through the gears. The torque output can be found using a torque wrench. These are the major output quantities that would be used in testing the product. The input quantities would only be the electrical power that it consumes, which would give an efficiency of the screw gun as a whole.

The engineering model that would be required would be fairly simple; the only equation needed would be that the efficiency equals the power output divided by the electrical power input. Both these number can be found through experiment with a great deal of accuracy. There would really be no way of estimating these power quantities because there is nothing to base the estimations off of. The model would therefore need to be very precise.

References

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