Group 20 - Black and Decker Jigsaw Final Report

From GICL Wiki
Jump to: navigation, search
Figure 1: Black and Decker Jigsaw JS510G Click for larger view

This team dissected the Black and Decker Jigsaw, JS510G. It is designed to be an economical saw for a hobbyist or home construction worker at the price point of $30. Over the course of the semester, the team dissected the saw to further their understanding of the components and design decisions. The first step was to observe all possible features of the jigsaw without using tools outside of those required for normal usage in order to come to preliminary conclusions. The next step in the process was to carefully disassemble the product to get an in depth view of the inner workings. This enabled the team to draw conclusions of the individual components that make up the saw.

Before disassembling the jigsaw, the team drew several conclusions. First, the outer shell is a durable thick plastic that is shaped to protect the user from any dangerous spinning components in the interior. In addition, the distinct color choice, orange and black, has a significant purpose besides being purely aesthetic. The Black and Decker Company design all their products with the same colors to make a cohesive collection of products. Another observation that the team made was the power source. The jigsaw is a corded saw that uses electricity from an outlet in order to power the blade. There are both advantages and disadvantages to this decision. One advantage of a corded saw over a battery is that the outlet continuously provides electricity so the saw will never die in the middle of a project. Batteries always have to be charged ahead of time, and have the possibility of losing power, decreasing the effectiveness of the saw. A disadvantage of the cord is the limitation in the length. The user must be in close proximity with and outlet, which could hinder the ease of use. Another step the team took before disassembling the jigsaw was to create a conceptual model of the energy flow. (Figure 2). The primary function was found to be removing material. This function is then broken down into sub processes that include sensing the user input, controlling the motor, and finally transforming the electrical energy into translational energy.

Figure 2: Energy Flow Click for larger view

Once the team completed all the analysis possible, they disassembled the saw. A complete breakdown can be found in Gate 2. Once opened, it was found that all of the components are connected linearly; this compact placement allows the company to conserve materials. The trigger sends an electric signal that actuates the motor. The motor’s rotational energy is then transformed into translational energy of the blade motion due to the gear set up. The fan, located on the motor, serves the dual purpose of cooling the motor as well as blowing away any excess material such as sawdust as a result of using the saw. Some key components of this system include the field assembly and the shaft assembly. The field assembly as seen in Figure 3, creates a magnetic field in which the armature assembly spins. This component is made out of aluminum, the choice of material in this case is pivotal since aluminum is not magnetic and therefore will not impede on the function of the field assembly. This piece was machined, the evidence of which can be seen by the grooves where it was likely turned on a lathe to create the round shape.

Figure 3: Field Assembly, Click to View

The shaft assembly is also of importance. Figure 4 is a computer model of the piece and figure 5 is an exploded view, which depicts the order in which the parts were placed. This assembly is what houses the blade and is the final step in the energy flow. Here, the rational energy of the armature assembly is converted to translational energy due to the gear orientation. In addition, this assembly contains the blade guard which is a pivotal safety piece that blocks the user from moving parts. More in depth information about component functionality can be found in Gate 3.

Figure 4: CAD Assembly, click to view
Figure 5: Exploded view, click to view

While the Black and Decker Jigsaw is a very successful functional saw, there are some improvements and redesigns that can be made. First, the blade guard can be improved upon in order to increase user safety. The guard can be made to wrap around the blade leaving no are exposed. An additional advantage would be to prevent unwanted material from entering the blade area. To implement this, the company would need to redesign the outside shell to include a groove that the blade would lock into. This would require an initial investment of creating a cast, however, in mass production; this design would likely be acceptable.

Another design change would be the blade actuation. The trigger is located on the only handle of the blade. Should the user grab the saw by the handle if plugged into the wall, the blade would start creating an unsafe situation. This can be resolved by implementing a safety lock. The lock would have to slide forward before the user can actuate the blade. This can be seen in figure 6. Before the safety trigger can be produced, springs must be researched in order to find one with the appropriate spring constant and length. In addition, there should be a simulation that tests for the maximum force the trigger can withstand before snapping. This would then dictate the material used for the trigger. Finally, there must be research done to see what the ideal ergonomic design for the trigger is, that is comfortable for the average consumer.

Figure 6: Safety Trigger, click to view

In conclusion, the Black and Decker Jigsaw modes JS510G is a function saw for home constructors and hobbyists. Its strength is in its durability and ease of use. It’s components are arranged in a linear fashion to conserve space and materials, and all the materials are chosen to balance cost and durability. While there are many good things about the saw, there could be some things improved upon for safety reasons. Such changes include an enhanced blade guard and a safety trigger.