Group 15 - Black and Decker Drill

Executive Summary

Our group was chosen to dissect, examine, and reassemble a Black and Decker Power Drill.

Before assembly, our group discussed the possible mechanical and/or electrical components in the drill and hypothesized their functions. After all the guessing, our group started to disassemble the drill.

The disassembling process was both educational and exciting for our group. We took each component out of the drill and examined it to try to have a clearer explanation of its purpose and function. A detailed list of these components can be found in the Disassembly Procedure section. After we took out each individual component, we inspected its shape, material, etc.

Further examination of each of the components and background research led to the conclusion of their functions. Pictures and CAD Drawings of each part and its function are located in the After Disassembly section. After we received all of the information we needed, we assembled the drill and found it to be in working order.

During the assembling of the drill, it was extremely challenging for everything to fit correctly. The steps that we took to assemble the drill are located in the Reassembly Procedure section.

After we disassembled, examined, and assembled the drill, we all now have a complete understanding of how the power drill operates. A full conclusion of our project is located in the After Assembly section.

Introduction

Our product for this project is a Black & Decker DR202B 3/8” Variable Speed Reversible Drill and Driver. The objective of this project is for our group to get a better understanding of the thought process that went into the manufacturing of this product. Moreover, on the basis of our analysis we aim to make suggestions which would better this product.

Our group consists of five members and all tasks for our report were distributed as follows:

• Jonathan Barsa: Introduction and Executive Summary.
• Lauryn Brown: Disassembly Procedure and Parts List.
• Douglas Byrne (Group Leader): Pre Disassembly, Parts List and CAD Drawings.
• Holly Czechowski: Reassembly Procedure, Post Assembly Discussion and Class Presentation.
• Rohan Thadani: Introduction and Executive Summary.

For the Disassembly of the product we worked together and input from all the group members was considered and discussed for the Analysis and Suggestions part of our report.

Pre Disassembly Analysis

Basic Description

The Black & Decker DR202B 3/8” Variable Speed Reversible Drill and Driver is designed to accept various bit sizes in order to drill holes and drive screws through a number of different materials. Attachments can be bought to use the drill as a mixer for cement and other compounds. It takes electrical energy supplied by an electrical outlet, and converts it to rotational energy using the motor. The rotational energy is then transferred through a set of gears to provide greater torque to the bit.

Product Operation

The drill has a two pronged polarized plug and operates on standard 120 VAC and draws 5 A. It uses a keyless chuck to hold the bit in place. There is a direction reversal switch and a trigger that can be depressed at different levels to operate at different speeds. The trigger can be locked in the fully depressed position. When activated, the motor turns the shaft, turning the fan, gears and bit. The product was in proper working condition before disassembly.

Part List

1. Cord
2. Strain Relief
3. Plug
4. Housing (2 pieces)
5. Level
6. Trigger
7. Trigger lock
8. Direction Switch
9. Motor
10. Shaft
11. Fan
12. Gears
13. Chuck
14. Bit
15. Screws (9+)

Materials

1. Plastic (Various Types)
2. Rubber
3. Metal
   1. Copper wire
   2. Shaft
4. Permanent Magnet
5. Liquid in Level

Disassembly Procedure

Step No.	Step Description	Relative Difficulty (Easy) 1 ↔ 10 (Difficult)	Tool(s) Required	Image
1	Remove Chuck The shorter end of an Allen Key is inserted into the chuck, and the hammer is used to turn the chuck in a counterclockwise direction (With respect to the front of the drill). Once loosened, the chuck can be removed by hand.	5 Requires a great deal of force to be applied, although this is by design.	≥¼ Inch Allen Key Hammer
2	Remove 9 Screws Screws are easily removed with a Phillips Head screw driver.	2 No real difficulty in removing the screws but doing so was rather tedious. Would be nearly impossible to do without proper tools.	#15 Torx Screwdriver
3	Remove Top Shell Once the 9 screws are out the top shell can be easily lifted off with your hands.	1	none
4	Bubble Level and Drill Bit attachment Both attachments are located on the top of the drill and fit in between the two sides of the casing.	1	none
5	2 screws holding the cable clamp in place Easily removed with screwdriver.	1	#15 Torx Screwdriver
6	Cable Clamp Lifts off after screws are removed.	2	none	After Removal
7	Trigger Lifts right out after the cable clamp is removed.	1	none
8	Directional Switch Found under the motor. Slightly difficult to remove due to its position in the casing.	3 Fits tightly into place, needed to be pried out.	none
9	Gearbox When directional switch is removed this component lifts out of the casing without the aid of any tools. However, some pressure is needed to condense the part in order for it to be lifted out. Sort of like a spring.	3 Some difficulty removing this component, due to the tight fit.	none
10	Motor and Fan Motor and fan slide away from the rest of the assembly and are removed last.	1	none
11	Separate Stator and Rotor The springs holding the brushes in place are removed and the brushes slid out of the way. The two pieces then can be separated.	5 The springs are small and are under a relatively large force. Care must also be taken to prevent damage to the carbon brushes.	Pliers or a Small Screwdriver to remove the springs.	Here the Rotor and both springs have been removed.

After Disassembly

Part Table

Part No.	Part Name and Function	# Of This Type	Material and Reason for Choice of Material	Reason for Part's Shape	Manufacturing Process	Image
1	Screw Hold material in place.	11	Metal Strength and Durability	Torx heads make manufacturing more efficient. They are easily aligned like Phillips head screws, but unlike Phillips heads, the screwdriver does not turn out.	Machined
2	Top Shell Protect Inside Pieces (Motor and Gear Assembly)	1	Plastic Lightweight, Non-Conductive, Strong	Designed to accommodate parts inside and for ease of use.	Injection Molding
3	Bottom Shell Protect Inside Pieces (Motor and Gear Assembly)	1	Plastic Lightweight, Non-Conductive, Strong	Designed to accommodate parts inside and for ease of use.	Injection Molding
4	Rubberized Grips Place to hold drill.	2 pieces	Rubber Ergonomic Comfort and Easy Grip	Fits around plastic shell.	Injection Molding
5	Rear Plate Ventilation and holds Bubble Level	1	Plastic Lightweight & Non-Conductive	Fits between Top and Bottom Shells and holds the Bubble Level in place.	Injection Molding
6	Bubble Level Make sure drilling/driving occurs perpendicularly to the surface.	1	Plastic & Mineral Oil The Plastic is Transparent & Mineral Oil will not break down or react with the plastic	Has two gauges, so one level can be used for both vertical and horizontal leveling.	Injection Molding
7	Accessory Bit Holder Easy access to extra bit.	1	Rubber Soft enough to allow the bit to be removed and inserted easily, yet hard enough to retain the bit	Shaped to take up the least amount of room yet still be able to house the bit.	Injection Molding
8	Accessory (Screw driving) Bit For use when driving screws.	1	Metal Strength and Durability	Combines both Phillips and Flat Head bit types in one tool.	Machined
9	Power Cord Transports power to drill.	1	Plastic Flexible & Non Conductive Copper Good Resistance/Cost ratio	Long cylindrical shape to enclose the wire but remain flexible. Small enough to not be cumbersome.	Extruded
10	Main Plug Supplies power.	1	Plastic & Copper	The plastic shell does not need to be grounded, allowing a two prong plug to be used. A two prong plug can fit in more outlets than a three prong plug.	Injection Molding & Sheet Metal Forming
11	Strain Relief Provides flexibility of cord without strain on wires.	1	Rubber Flexibility	A rather large strain relief piece is used here. The tool may be lowered from a height (e.g. from a ladder) by its cord so the strain reliever and cable clamp must be able to support this weight.	Injection Molding
12	Wire/Cable Clamp Keeps wires in place to prevent strain on them.	1	Metal Strength	The Clamp is curved to provide extra holding force.	Die Cast
13	Anti-Theft Strip Reduce theft of the product.	1	Plastic & Metal Readily detected by store security system.	An industry standard part. There are multiple types available, this being one of the smaller ones.	Injection Molding & Sheet Metal Forming
14	Trigger Determines speed of drill.	1	Plastic & Metal The plastic serves to insulate the user from the current inside.	The shape conforms to the user's fingers, providing a better grip.	Injection Molding
15	Internal Wiring	1	Copper & Plastic Insulation	The wiring is compact enough to fit in small crevices within the drill yet still transport power efficiently.	Extruded
16	Direction Switch Allows for easy change in the direction of rotational motion.	1	Plastic Lightweight, Non-Conductive, Strong	Its length is used for leverage and it has a grommet on one end so it can be attached to the motor.	Injection Molding
17	Motor Shaft See also: Motor Parts Table Gearbox Parts Table	1	Metal Good Torsional Strength	Easily attached to gears to transfer rotational energy.	Machined
18	Motor See Motor Parts Table	1	Various	A universal motor can run on either AC or DC current. Therefore, one motor can be used in both the corded and cordless lines. A universal motor, unlike other AC motor types, can run faster than the cycle rate of the power supplied.	Various
19	Shaft Alignment Alignment of Components	1	Metal	This shape is the easiest way to connect all of the components. It is also easy to manufacture.	Die Cast
20	Fan Cool down system, reduce heat loss and increase lifespan of parts.	1	Plastic Lightweight, reducing wasted power	Increases the output "wind force" of the fan.	Injection Molding
21	Gearbox See Gearbox Parts Table	1	Various	The gearbox converts the rotation supplied by the motor from High Speed/Low Torque to Lower Speed/ High Torque. Torque is more important than speed in this application, especially when drilling into hard materials.	Various
22	Chuck Holds the bit securely in place.	1	Plastic & Metal The plastic is Lightweight & Non-Conductive, protecting the user. The plastic is not strong enough to hold the bit under high stress, therefore metal is used for the core.	While not always as strong as a keyed chuck, a keyless chuck is much more convenient than a keyed chuck. On a consumer level model like this one, a keyless chuck is sufficient.	Injection Molding & Die Cast & Machined

Motor Parts

A basic motor parts diagram

Part No.	Part Name	# Of This Type	Material	Manufacturing Process	Image
17	Motor Shaft	1	Metal	Machined
18A	Commutator	1	Metal (Copper)	Machined & Sheet Metal Forming
18B	Rotor	1	Copper Wire & Metal Core	Wire is wound around the Die Cast Core
18C	Brushes	2	Carbon	Machined
18D	Brush Holders	1	Metal	Sheet Metal Forming
18E	Stator Coils	1	Copper Wire	Copper Wire is wound around the Core
18F	Stator Core	1	Metal	Die Cast

Gearbox Parts

CAD Model zipped packages include .bmp and .png images, Autodesk Inventor .ipt files, .igs, .stl and .stp files. See the image captions for links to the Zip packages for individual parts.

The package for the overall assembly includes .bmp and .png images, Autodesk Inventor .ipa and .ipn files, .igs, .sat and .stp files. The .ipa and .ipn files are dependent on the .ipt files. All the .ipt, .ipa and .ipn files can also be found in a single separate package.

Overall Assembly: Group15 Gearbox Assembly.zip
Package of all .ipt, .ipa and .ipn files: Group15 Inventor Files.zip
Explosion Animation: Group15 Gearbox Explosion.wmv

Part No.	Part Name	Material	Manufacturing Process	Image	CAD Model
17	Motor Shaft	Metal	Machined		Cad Model
21A	Plate A	Metal	Die Cast		Cad Model
21B	Motor Shaft Bearing	Metal	Die Cast		Cad Model
21C	Shaft 1	Metal	Extruded		Cad Model
21D	Metal Spacer	Metal	Machined		Cad Model
21E	Gear A	Metal	Machined		Cad Model
21F	Gear B	Metal	Machined		Cad Model
21G	Shaft 2	Metal	Machined		Cad Model
21H	Gear C	Metal	Machined		Cad Model
21I	Rubber Spacer	Rubber	Injection Molding		Cad Model
21J	Plate B	Metal	Die Cast		Cad Model
21K	Fabric Spacer	Fabric	Large sheets of fabric are layered and machine cut to form different sized spacers.		Cad Model

Design Changes on a Component Level

The rear plate could easily be incorporated into either of the shell halves. In the current design, the level would be located at the joint between the two halves of the shell. However, this issue could be designed around with relative ease. The level also needs a different method of retention. It currently fits loosely into a slot and can be rotated along its horizontal axis, rendering it rather inaccurate. Some sort of adhesive or mechanical fastener could be used.

Reassembly Procedure

Step No.	Step Description	Relative Difficulty (Easy) 1 ↔ 10 (Difficult)	Tool(s) Required
1	Put together Stator and Rotor Replace the springs and put the brushes back in place. Stator and Rotor will slide together.	5 Springs were somewhat difficult to replace. Took around 15 minutes. Very hard not to scrape the carbon brushes.	Pliers or a Small Screwdriver
2	Motor and Fan Motor and fan slide back into the shell quite easily if assembled properly. The brushes slip off the commutator easily.	3	none
3	Gearbox This was a little more difficult to get back into the casing. The assembly will not fit into the shell if it is not properly aligned. The brushes easily slip off the commutator and when not in place, the assembly will not fit into place. It is difficult to reposition the brushes without causing damage.	6 Difficult to attain realignment. Time consuming, took > 20 minutes.	none
4	Directional Switch The end pops right into the circular hole on the motor. A little more difficult to get the other end back in place because of visual restrictions.	3 Must be exactly centered in the plastic groves which was difficult.	none
5	Trigger Easily replaced, aligning the trigger lock with its corresponding hole.	1	none
6	Wire/Cable Clamp Put wire underneath the clamp and then replace the clamp.	1	none
7	2 Screws holding the wire/cable clamp in place Easily replaced with screwdriver.	1	#15 Torx Screwdriver
8	Bubble Level and Drill Bit attachment Slide attachments back into respective spots on casing.	1	none
9	Top Shell Make sure everything is aligned, press down. Be careful not to bump the directional switch.	2	none
10	Replace 9 Screws Screws can be reinserted. The order does not matter because they are all the same.	2 Time consuming more than anything else. Some force applied.	#15 Torx Screwdriver
11	Replace Chuck Replace chuck by hand and use Allen key to tighten.	4 Must make it very tight.	≥¼ Inch Allen Key

After Assembly

How It Works

The drill works mostly by converting electrical energy to mechanical energy. It is run by an AC motor. This is known because it is powered from an outlet. If it were DC it would be powered by a battery or a generator that runs off of DC power. After taking apart the drill, it was decided that the major components of the drill are the stator, commutator, rotor, and gear system.

Specifically, power from the electrical outlet travels through the cord and goes into the stator. There are windings in the stator and windings in the rotor that create a magnetic field. The power then goes from the winding in the stator to the commutator, which is basically just a set of copper bars attached to the rotor. The commutator is there to control the direction of the current. So the power in the commutator then travels to the windings in the rotor and an electromotive force is produced that acts opposite to the current. This force is what turns the rotor. Now the torque created from the rotor is transferred to a set of gears. The gears are used to amplify the torque from the rotor and in effect drive the drill bit.

One more important aspect is that there is a fan between the motor and gears used to cool down the system and provide a default load, preventing the motor from spinning too fast and damaging itself. The fan is also needed for efficiency purposes and most likely to extend the lifespan of the components. Keeping components cool and avoiding any over heating can extend the life of the product.

Disassembly/Reassembly Discussion

The disassembly and reassembly procedures were actually done twice. The first time the drill was taken apart, the actual motor was not disassembled into its separate parts. The reassembly for this was still a little bit difficult. It was a challenge to get the motor and gears back in the right spot, most likely due to a lack of experience in working with the components and the fact that the pieces were in there fairly tightly. However, once they were back together, the drill was plugged in and it worked fine. The second time the drill was disassembled, the motor was taken apart further to show its component parts, i.e. the commutator, stator, brushes, and armature. When reassembling the drill this time, the parts went together with more ease, but when plugged in it had a very bad burning smell. The burning smell probably came from some small shavings of the carbon brushes, left over in the drill casing from the reassembly process. The same sets of tools were used for the disassembly and reassembly procedures. The processes were almost reverses of each other except for the time factor. It took considerably longer to reassemble the product than to take it apart, i.e. one minute for disassembly and ten minutes for reassembly. In all, the product was completely reassembled, but it is suggested that it be used with extra caution.

Types of Analysis

A strength of materials test is suggested for the plastic casing. It would test to see if the casing could withstand a drop from a certain height without breaking/cracking. An actual drill could be used to serve as the model in this test. Another type of analysis would be an efficiency/size/shape analysis on the motor. People want the most power for their money, so increasing the efficiency would be ideal. The fan is crucial in terms of efficiency because it removes the excess heat from the system. For example, when you have a 100HP motor that is 90% efficient it means that 90HP is actually doing the work and 10HP is being lost to heat. The fan could reduce the amount being lost to heat, therefore increasing the efficiency. Perhaps the fan in the drill could be a different size/shape in order for it to remove the heat more effectively. In this case a precise model probably should be used. The fan is also important because cooling down the components could also extend the life of the product. Moreover ergonomic analysis also plays a crucial role in the manufacturing of this product. The drill is insured to be light weight and has a fairly good grip to give the consumer proper handle on the tool.

Recommended Design Changes

One recommended change would be to have a longer cord to the drill. A longer cord could get rid of the need for extension cords, however it could also start to get in the way for smaller jobs if the cord is too long. The cost of a longer cord also comes in to play here. In this case, a customer survey with a promotional coupon might result in the preferred cord length. A customer survey could also be used to see whether or not they use the level on the end and its' efficiency. In an evaluation of the drill, the level was found to be somewhat useless and a waste of money. Also, a keyless chuck could be convenient to the user, but a lot of times the bit can be adjusted tighter when you have a key. In this case a force analysis could be done to see how tight one really needs the bit to be to drill/drive into certain materials or perform certain tasks. That would determine whether a keyless chuck would be sufficient for most uses of the drill. It might be the case that a keyless chuck is fine for drilling through certain thicknesses or materials, but once a certain thickness is surpassed or a different material is used, a chuck with a key might be necessary. Also, during the analysis it was found that it would be advantageous to the consumer if the trigger could be locked into intermediate speeds and not only on its maximum speed. This decision may increase the cost of production but would improve overall customer satisfaction with the product. Yet another suggestion is to vary the color of the product. Black and Decker equipment is primarily orange and black. However, from a marketing stand point, these colors may represent to the customer a standard duty tool. A heavy duty drill could be created in a different color combination, say silver and black or all black. This would indicate to the consumer the variation in Black and Decker products. It will also provide an easier visual separation between standard duty and heavy duty equipment. This could increase sales for Black and Decker because it would signify a wider variation in their product line. Diversifying your product can lead to a broader consumer audience thus improving sales.

References

Armature (electrical engineering). (2006, October 13). In Wikipedia, The Free Encyclopedia. Retrieved 22:02, November 14, 2006, from http://en.wikipedia.org/w/index.php?title=Armature_%28electrical_engineering%29&oldid=81309367

Black & Decker. (2003). Instruction Manual for Models DR201, DR202, DR211, DR220, DR403, DR501 and DR601. Towson, MD: Author.

Commutator (electric). (2006, September 18). In Wikipedia, The Free Encyclopedia. Retrieved 22:01, November 14, 2006, from http://en.wikipedia.org/w/index.php?title=Commutator_%28electric%29&oldid=76368620