Group 20 - Black and Decker Jig Saw-Gate 2
We are still working diligently on our project and part of our initial plan has worked very well and other parts have not gone as planned. We have followed our plan to meet every Monday after class in the Capen café. This part of the plan has worked very well due to everyone’s schedule allowing this time to work. This is the time when we can all meet as a group without missing anyone. In our work proposal from gate one we stated “To disassemble, the team will collectively meet twice a week in the lab. We will make every effort to all attend so that information and knowledge are not lost in communication.” There have been some problems with this part of our initial proposal, every member of our group has a very busy schedule and we are all doing our best to coordinate meeting times but there have been meetings were all members could not be present. We have also not been able to meet the said two days a week in the lab. We have found that we had all of the tools necessary to disassemble our product outside of the lab, so we did not follow the plan exactly. Also we did not follow the plan to bag and catalog all of the parts during the disassembling process. Due to the time that we have had to work together we were able to disassemble our product, indentify the pieces, photograph the process and also reassembly our product, so there was no need to bag and tag the pieces.
We have addressed the issue of not being able to meet all together by taking many pictures and going over the dissection process with whoever could not be at the meeting. For the same issue that may occur in the future we have been considering and will be discussing setting up a different meeting time on top of our Monday meeting so that we would have at least two meetings every week that everyone would be able to attend.
Difficulty Scale Key
To quantify the difficulty of each disassembly step, several factors must be taken into consideration. These factors include:
- Tools required to complete step
- Time required to complete step
- Complexity (number of part interactions)
Each step’s difficulty can be described numerically on a scale ranging from 1 to 5. A difficulty of 1 indicates that the three factors mentioned above are minimal. A difficulty of 5 indicates that the part to be reassembled required tools, was time consuming, had multiple interactions, or was some combination of these. Due to the nature of the various assemblies involved, there were instances where several parts had to be assembled simultaneously. In this case, each part will be assigned a difficulty as well as the overall difficulty of the assembly. The overall difficulty of the specific assembly will be noted with an asterisk.
|Step||Description||Part||Tools Required|| Level
|1||Turning the actuator and gear assembly unscrewed the locking screw, which released the blade support and shoe assembly. These Parts were meant to be disassembled. The actuator/gear assembly is labeled with instructions for removal.||Locking screw and shoe assembly||No tools needed||2 3*||None|
|2||The removal of all 7 screws holding the plastic housing together.
This part was meant to be taken apart. Screws are a non-permanent method of attachment and the heads were Phillips. This part was meant to be taken apart. Screws are a non-permanent method of attachment and the heads were Phillips.
|Screws||Phillips head screwdriver||2||None
|3||Removal of the plastic housing||Plastic outer housing||No tools needed||1||None|
|4||Removal of the actuator/gear assembly and the blade guard
These parts were not attached to the drill and were likely intended to be removed at some point for cleaning, maintenance, etc.
|Actuator/gear assembly, Blade guard||No tools||1|
|5||We then removed the shaft assembly. The shaft assembly was also not attached to the other members in any way and was likely intended to be removed. The individual pieces of the assembly are held together by screws. The disassembly of the shaft assembly would be difficult but not impossible if there was a need to replace a part.||Shaft assembly||No tools needed||1|
|6||We took out the rest of the assembly out of the housing. All pieces were not fastened in any way and are easily replaceable in case of part failure.||Everything else that was in the housing, everything was connected||No tools needed||2 4*||None|
|7||Removal of the gear assembly that rotates the shaft assembly||Gear assembly||No tools needed||1|
|8||Removal of the counterweight||Counterweight||No tools needed||1|
|9||Removal of the thrust plate||Thrust plate||No tools needed||1||None|
|10||We removed the armature assembly from the field assembly. While it is easily separable, if there was a failure in the motor, it is unlikely only one piece would be replaced rather than the whole motor. It is possible that the pieces
Were intended to come apart to easily remove debris that may enter the housing.
|Armature and Field assembly||No tools needed||1|
|11||We then removed the Brush boxes. The brush boxes are attached to the motor, so if the motor is meant to come out, the brush boxes are also meant to come out.||Brush boxes||No tools needed||2|
|12||We removed the switch assembly from the trigger assembly. There is very little that can go wrong with these parts so it is unlikely they were meant to be disassembled.||Switch assembly/Trigger assembly||No tools needed||2||None|
|13||Removal of the trigger conductor. This is part of the switch which is not meant to be disassembled.||Trigger conductor||No tools needed||2||None
|14||We pried open the switch box to take out the chip and look inside the switch assembly. This part was very difficult to disassemble. The plastic clips were positioned so it is very easy to connect them but very difficult to remove them.||Switch Box||Flathead screw driver and razor blade||4|
Table 2-1: Disassembly Table
Sub System Analysis
The process of removing the material is broken down into a few subsystems. When the user pulls the trigger the saw detects the trigger being pulled, measures the pressure on the switch, and produces the right amount of energy. The electrical energy generated is then converted to rotational mechanical energy as it turns the motor. That rotational mechanical energy is then converted into translational mechanical energy when it oscillates the shaft assembly.
All subsystems are connected linearly except the air flow that cools the motor and the final energy input to push the saw in a given direction. The electricity enters through the cord and is connected to the trigger. Once the trigger is pulled the electricity travels down to the motor. The motor turns a fan consisting of many blades that pulls air through the back of the jigsaw (below the cord). In doing so, the air travels across the motor, cooling it. The air is then pushed down to the jigsaw’s blade area where we assume it is used to blow sawdust away. The excess air is discharged though the sides. The motor also turns the gear assembly. The gear assembly is directly connected to the shaft assembly; this connection is the transition from rotational to translational motion. This translational motion combined with the input of human energy to guide the saw finishes the process and removes the material.
The components are placed in a line toward the blade holder. They are positioned that way so the parts take up as little space as possible. The safety guard and blade can not touch each other. The better the connection between the subsystems, the better the jigsaw performs. That way the energy lost can be minimized.
Depending on what country you are in, you might need a different plug. This means slightly different models will have to be manufactured. This will increase the production cost.This jigsaw is relatively cheap therefore the economic concern is to balance the quality of the part with the cost. The handle design is pretty ergonomic and the guard helps with safety. This makes it more comfortable for the operator to use.
The better the connection between the subsystems, the better the jigsaw performs. That way the energy lost can be minimized. The cord enters the casing through the rear of the saw. It then connects to the motor which turns the gears. The gears then connect to the shaft assembly causing it to move in a cutting motion. The blade is held by the shaft assembly. It then cuts the material with the assistance of the guide. The blade guard also covers the blade to protect the operator.