Group 34 - Black and Decker Reciprocating Saw

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Handisaw

Contents

Executive Summary

The Black and Decker Reciprocating Hand Saw was our group’s assigned product. Before the disassembly process, the group members made some assumptions of the product such as the amount of parts that we thought was in the saw. After that we took apart the product, making sure to notice and record the steps in order for easy reassembly, whilst taking pictures. Further along in the project, our group took all the separate parts, named them, and made many observations about them such as dimensions, color, materials used, and their total number in the saw. We also made educated guesses as to the manufacturing processes used by the company to make all the components, and other general comments. Then some of us generated three dimensional AutoCAD drawings for visual purposes. At this point, since we as a group had a good idea of what the purpose of all the components was, there came a few design improvements that could have been made to the product. After reassembling the saw and recording the steps once again, the hands on part of the project was over; therefore, all of us reviewed the whole process, retested the product, and thought up some basic models for it.

Introduction

Our product was a Black & Decker reciprocating saw. According to the Black & Decker website, the saw can cut almost anything, anytime, anywhere including thin metal, up to 1" wood, plastic, and drywall. The saw also has a tool-free blade exchange which provides quick and easy blade changes. The saw has cordless operation for quick and convenient cutting. It is lightweight and compact for easy access to tight areas. It is also capable of making up to 200 cuts of 1/2" oak dowels. Group 34 is made up of members Philip Strojny(group leader), Ed Papaj, Steve Mangone, and Patrick Lynah. Our group as a whole was a part of the disassembly and reassembly process of our product. We documented the process for disassembly and reassembly very carefully. We took photos and video of our process. After the disassembly and reassembly processes, Ed and Patrick drew up some CAD drawings of the main components of the reciprocating saw. Philip and Steve made the in-class presentation and Philip presented it in class. Everyone in our group was then responsible for different parts of our Ciber-U report.

How It Works

Group 34 and destroyed car 018 copy.jpg

Our saw works by converting electrical power into mechanical power in the form of the blade moving. The saw has 5 main components. The user will pull the lock down and pull the trigger for the saw to be operating and the blade to be moving. What has when the user pulls down on the lock and pulls the trigger is it acts as a switch allowing electrical power to go from the battery to the electric motor. The electric motor then takes the electrical power and converts it into mechanical motion. The mechanical motion the motor creates is an output shaft that spins. The shaft is connected to a transmission which through gear reduction rotates at a lesser speed than the output shaft of the motor. This gear reduction is needed because the output shaft of the motor spins faster than that of the optimal blade speed. Now a worm gear component is connected to the output of the transmission. This worm gear is what then changes the spinning motion from the transmission into the sliding or sawing motion of the blade. The shaft of the gear spins and on the shaft of the worm gear component is a unique orbital track. The shaft that holds the actual saw blade is then connected to the track of the worm gear component so then when the shaft of the worm gear component spins the saw blade translates horizontally creating the desired sawing motion.

Here is a closer look at the worm gear component:

100 1686.JPG

Worm gear operation










Pre-disassembly

The assumptions that where made before the disassembly was that the saw moves back and forth on a linear path which is powered by an electrical motor. We did not know how this specific motion was achieved but it was soon figured out through the dissection of the product. Also the group assumed that electrical energy was transformed into mechanical energy in a specific manner which was soon learned. How the product operated was quite simple. The operator would pull down the safety trigger then would pull the actual trigger which then engaged the reciprocating saw. A sound was created by the operation on the saw and it resembled a pulsating sound. The estimated amount of parts where 50 to 100 parts which where presumed to be four possible types of materials such as metal, ABS plastic, rubber, and metal composites.


Disassembly

Disassembly Charger

1.) Three Phillips head screws removed from wall mounted battery charger for product

  • Tool: Phillips head screw driver
  • • Easy

2.) -Removed the flat bottom cover from the wall mounted battery charger

  • No tool needed
  • • Easy

3) -Removed the curved cover section from wall mounted battery charger

  • Tool: Flat head screw driver (need to gently pry away cover from wall attachment area)
  • • Medium difficulty

4) -Removed the circuit board contained within the battery charger which transferred the electrical energy from the power source (wall outlet) to the product.

  • No tool needed
  • • Easy
Group 34 and destroyed car 015.jpg
Group 34 and destroyed car 018.jpg
100 1686.JPG
100 1690.JPG
100 1390.JPG
100 1389.JPG
100 1684.JPG

Disassembly of Black and Decker Reciprocating Saw

1) Nine Phillips head screws from product where removed form product

  • Tool: Phillips head screw driver
  • • Easy

2) Product cover was removed

  • No tool needed
  • • Easy

3) Trigger, the safety switch and springs removed

  • No tool needed
  • • Easy

4) Springs where then removed from trigger and safety switch (grand total of 2 springs)

  • No tool needed
  • • Easy

5) Removed the saw safety guard from product cover

  • No tool need
  • • Easy

6) Removed motor assembly from electric trigger, battery, and charger plug-in.

  • No tool needed
  • • Easy

7) Electric trigger and charger plug-in was disconnected from lithium ion battery pack

  • Needle nose pliers
  • • Medium difficulty

8) Four Phillips head screws where removed from transmission and worm gear cover

  • Phillips head screw driver
  • • easy

9) Cover of the worm gear removed

  • No tool needed
  • • Easy

10) Saw blade attachment and attachment arm which connects with worm gear removed

  • No tool needed
  • • Easy

11) Two 2.5mm Allen head bolts from attachment arm which holds blade attachment device securely in place removed

  • 2.5mm hex key
  • • Easy

12) Other half of worm gear cover removed

  • No tool needed
  • • Easy

13) Worm gear assembly that changes circular motion into linear motion

  • No tool needed
  • • Easy

14) Worm gear disassembly (11 parts)

  1. T shaped spacer that aids in holding assembly in transmission and worm gear housing
  2. Washer removed
  3. Very small ball bearing removed
  4. Washer removed
  5. Actual worm gear removed
  6. Removed a holding pin fro worm gear
  7. Washer small ball bearing
  8. Washer
  9. T shaped spacer that aids in holding assembly in transmission and worm gear housing
  10. A cylindrical bar is left that all the above parts slide onto
  • No tool needed
  • • Medium difficult (slippery due to grease)

15) Transmission

  1. disassembly(9 parts)
  2. Transmission part that is attached to cylindrical bar and three small gears removed
  3. Three equidistant small gears that attached to transmission part and very small gear streamlined into electrical motor

removed

  1. Removed large washer
  2. Two Phillips head screws removed from transmission housing
  3. Transmission Housing that held above parts together detached from electrical motor
  4. Transmission assembly is now removed from electrical motor
  • Philips head screw driver
  • • Medium difficulty (slippery due to grease)

16) Due to all previous disassembly steps the electric motor is left alone and cannot be disassembled due to an impossible re-assembly


After disassembly

Reciprocating Saw Parts Table
Part Number Name Quantity Purpose Manufacturing Process Material Picture
1 Left outer product housing 1 Holds internal parts in place Injection molding ABS plastic
1(ABC).JPG
2 Right outer product housing 1 Holds internal parts in place Injecting molding ABS plastic
2(ABC).JPG
3 Cutting blade safety guard 1 Partial protection from blade Metal-casting Metal alloy
3(ABC).JPG
4 Charger 1 Transfers energy from wall to charging apparatus Injection molding, human assembly, extrusion ABS plastic
4(ABC).JPG
5 Wall mounted charging apparatus 1 Holds product in place will charging on wall Injection molding ABS plastic
5(ABC).JPG
6 Back plate of wall mounted charger 1 Holds guts of wall mounted charging apparatus Injection molding ABS plastic
6(ABC).JPG
7 Cover plate of wall mounted charger 1 Holds product in place and transfers energy to battery Injection molding ABS plastic
7(ABC).JPG
8 Wall mounted charging guts 1 Has light to tell consumer that product is charging Human assembly, injection molding, extrusion ABS plastic, copper
8(ABC).JPG
9 Worm gear assembly housing screws 4 Holds worm gear assembly in place Machining Metal alloy
9(ABC).JPG
10 Outer housing screws 9 Firmly holds outer product covers together Machining Metal alloy
1010.JPG
11 Transmission gear 3 Makes electric motor speed slower Metal-casting Metal alloy
1111.JPG
12 Electric motor 1 Produces power for product to perform correctly Injection molding, metal-casting, human assembly ABS plastic, metal alloy
1212.JPG
13 Transmission part 1 Holds gears in place transfer reduced power to worm gear shaft Metal-casting Metal alloy
1313.JPG
14 Inner transmission washer 1 Provides barrier for gears and reduces friction for transmission housing Injection molding ABS plastic
1414.JPG
15 Transmission housing 1 Holds entire transmission system in place Injection molding ABS plastic
1515.JPG
16 Left Worm gear housing 1 Holds worm gear system in place Injection molding ABS plastic
1616.JPG
17 Right worm gear housing 1 Holds worm gear system in place Injection molding ABS plastic
1717.JPG
18 Cutting blade armature 1 Helps transfer circular motion into linear motion to produce reciprocating motion Metal-casting, machining Metal alloy
1818.JPG
19 Cutting blade holding bracket 1 Firmly holds blade in place Metal-casting, machining Metal alloy
1919.JPG
20 Trigger spring 1 Helps trigger go to off position when not in use Forming Aluminum
2020.JPG
21 Safety trigger spring 1 Returns safety trigger to original place when not in use Forming Aluminum
2121.JPG
22 Product battery pack 1 Provides power for electric motor Human assembly Battery materials
2222.JPG
23 Operating trigger 1 When pressed, product will operate Injection molding ABS plastic
2323.JPG
24 Safety trigger 1 When pressed allows operating trigger to engage for product use Injection molding ABS plastic
2424.JPG
25 Battery, trigger, connecting wires 1 Transfers power to electric motor when trigger is pressed Injection molding, extrusion, human assembly ABS plastic, copper
2525.JPG
26 Specialized worm gear 1 Allows for circular motion to become linear motion Injection molding ABS plastic
2626.JPG
27 Worm gear shaft pin 1 Holds worm gear in place Extrusion Metal alloy
2727.JPG
28 Worm gear ball bearing 2 Allows a free moving surface between worm gear and worm gear shaft mounts Extrusion, human assembly Metal alloy
2828.JPG
29 Worm gear washer 4 Provides protection/barrier for worm shaft mounts and worm gear Extrusion Metal alloy
2929.JPG
30 Worm gear shaft mounting bracket 2 Holds worm gear shaft in place within worm gear housing bracket Metal-casting Metal alloy
3030.JPG
31 Worm gear shaft 1 Holds worm gear assembly in place and transfer power from electric motor/transmission system to worm gear Metal-casting Metal alloy
31(31).JPG


Assembly

1) Transmission (difficult)

a) Large washer placed in transmission housing

b) Place the geared side of the electrical motor into the closed end of the transmission housing through the whole in the center

c) Place the three small gears in the transmission housing making sure the mesh with the electric motor gear

d) Tighten the motor to the transmission housing using a Phillips head screw driver to tighten the two screws

e) Fit the transmission part into the three gears, this becomes quite time consuming and frustrating especially with the grease


2) Worm Gear (easy)

a) Spacer placed onto cylindrical shaft with the cylindrical portion facing inward towards the shaft

b) Place washer on shaft

c) Place the small ball bearing on shaft

d) Place washer on shaft

e) Place holding pin in worm gear

f) Slide worm gear on shaft

g) Place washer on shaft

h) Place ball small ball bearing on shaft

i) Place washer on shaft

j) Place spacer on shaft again with the cylindrical portion facing inward towards the shaft


3) Attachment Arm (easy)

a) Use 2.5 mm hex key to attach the saw blade holder to attachment arm using 2.5 mm allen head bolts


4) Transmission/Worm Gear assembly Housing (easy)

a) Place the worm gear assembly shaft into back of transmission part, place the end with the stopper into the transmission part

b) Fit one side of the housing into the transmission housing allowing the worm gear assembly to sit in housing

c) Place attachment arm above worm gear assembly fitting the two cylindrical guides around the groove in the worm gear allowing for movement

d) Fit the other side of the housing on

e) Using a Phillips head screw driver secure it using the 4 small Phillips head screws


5) Place Parts into Product Cover (easy)

a) Place the completed transmission into the top of the casing where the flanges in the shape on the transmission is making sure the saw blade holder will be sitting outside of the saw when the other cover is placed on

b) Connect the electric trigger to the battery pack

c) Connect battery pack to electric motor

d) Place batter pack into the bottom of the cover in its designated spot where the flanges are, placing the electric trigger in its spot next to the trigger housing

e) Place the safety switch in the switch housing on the top attaching the one end of the spring to the cylindrical part of the cover and the other end to the switch

f) Place the trigger in the trigger housing ensuring the spring is place as shown and that the electronic trigger is placed as shown

g) Place the saw guard on the front

h) Fit the other side of the cover on

i) Secure it using a Phillips screw driver and nine screws.

After Assembly

After our assembly of the product, the product worked the same as it did before we disassembled. The assembly process is the reverse of the disassembly process. The same tools were used to both disassemble and reassemble the product. An Analysis of our product could be done to figure out the power output of the saw. Another analysis that could be done would be to see how much stress the saw blade can undergo before breaking.

CAD Drawings

Transmission Gear (there were three of these inside of the housing part)
1111.JPG

This gear is one of three that fit together on the transmission part shown, and went inside the housing.

Transmission Housing
1515.JPG

The housing that holds the shaft with the specialized worm gear.

Transmission Part
1313.JPG
100 1723.JPG

Keeps the three transmission gears together.

Worm Gear

This is the specialized worm gear that changes the spinning motion of the transmission into the translational motion of the saw blade

Recommendations

Although the Black and Decker reciprocating saw has proven to be remarkably effective there are still improvements that could be made upon it. The first issue has to do with the ergonomics of the product. The rubber handle is not terribly uncomfortable, however after long use may not feel as comfortable. The handle could have a gel grip such as the ones used for wrist supports on keyboards but to a lesser degree.


The saw is relatively small and this allows for it to fit into small spaces, however if a rotating head was placed on the saw then it could be used to get into tighter spaces or cut at an awkward angle. Some models of
A freely rotating head already on use on another reciprocating saw.
reciprocating saws already use this technology and with great effectiveness. A proven method to accomplish this freely moving head is to have an elbow joint for up and down movement then after the elbow to have the head rotate 360 degrees.


The Black and Decker Handisaw uses a six volt battery and provides a respectable battery life. Although the battery life is good, it can be made better with a Lithium-ion battery. The Lithium-ion battery has one of the best energy to weight ratio, which is very important for a cordless electronic of any type. It also has one of the slowest charge losses when not being used. However there is a downside to Lithium-ion and its durability. While it may be slightly less durably then a nickel battery it would be housed inside the casing shielding it from forces such as dropping and normal stress from use.


The most disappointing aspect of the Black and Decker Handisaw is the charging apparatus. It may seem like a good idea to have a wall mounted charger but rather it forces the user to mount the charger someplace and always charge it from there. The wall-charger is a great option to have but it must also have the option of just plugging it into the wall. The wall charger is impractical if the Handisaw is brought to a worksite. The saw should be packaged with the wall-charger as well as a cord to plug into the wall. Also when it hangs on the wall-charger it can easily be knock off the charger and if it has the blade attached can be very hazardous. A small clamp or clip can be placed on the wall-charger to prevent accidental dropping.