Group 33 - Skil Circular Saw
Contents |
Team Members
Sehwan Jun : Group Manager Responsibilities include a central contact for the group as well as scheduling and work assignments.
Brian Mitrowitz : Publication Manager Responsibilities include taking of pictures and video and editing information to be viewed on the Wiki page.
Jane Pattison :Technical Writer Responsibilities include the writing of technical papers related to the product.
Yukie Furukawa : Organization Expert Responsibilities include the organization of parts and paperwork.
Tomoaki Furukawa : Dissection Expert Responsibilities include the disassemble and measuring of parts of the Skilsaw.
Preliminary Appraisal
We are dissecting a Skil saw model 5400 circular saw. Its primary use it cutting relatively thin wood such as sheets of plywood or boards up to its maximum cut depth of 2-1/2 in. With a suitable blade it can also be used to cut other materials such as plastic, veneer, and metal. This model is primarily targeted at non-professional users.
The saw uses a small motor to convert electricity from a standard wall outlet into mechanical energy to drive a shaft on which the saw blade is mounted. It is not currently working; we think either the switch is broken or the carbon brushes in the motor are missing. Most of the visible outer parts of the saw are plastic, including the handles, housing, and the covering of the power cord. The guards are aluminum. The base plate and blade mount are steel. It also has a rubber stop that keeps the rotating guard from turning too far when it's released. Internally, the motor and power cord contain copper, and the motor uses carbon brushes.
This is not a very complex product; it uses a common mechanism (the electric motor) to perform a single task (running a saw blade). It doesn’t have a lot of settings or alternative functions. According to the manufacturer’s parts list, it has 57 components, which includes all of the fasteners and the individual parts of the motor. None of these components are complicated.
Under normal use, this product does not require regular maintenance; under unusually heavy use it might be necessary to replace the brushes in the motor occasionally. It is solidly constructed, and unlikely to need frequent repairs.
There are a large number of very similar hand-held saws on the market. This model runs from about $25 to $60, which is at the bottom end of the price range. It has a definite advantage in cost; some of the alternatives cost over $200. All of them have similar safety features. The engine used in this product has a good weight-to-power ratio, but is noisy and inefficient. The more expensive alternatives are frequently packaged with extra blades (this one is sold with a single blade suitable for wood), or have extra capabilities for cutting other materials. There are several cordless alternatives, which have the advantages that they can be used without easy access to an outlet, and the user can't trip over the cord, but they are also considerably more expensive, and are heavier due to the added weight of the battery.
Product Dissection
Dissection Notes
The following are the steps we went through to disassemble the saw. This device is not intended to be taken apart as thoroughly as we did; under normal use only the ½ in bolt and the rings that hold the saw blade in place would be taken off. That being said, it was not exceptionally difficult to disassemble; there are only a couple tricky parts, which are noted below. In the course of taking it apart, we discovered that one of the wires leading from the power switch to the motor has been disconnected from the switch; this is probably why the saw doesn't currently work, although there may also be other problems that we didn't find. We used T20 and T27 screwdrivers, a ½ in socket wrench, and a flat head screwdriver in the process. There are only three types of screw used; 2 in (long), 1 in (medium) and ½ in (short). Torx screws are commonly used in automated assembly plants because they resist cam-out better than Phillips screws. The limited number of fasteners simplifies the manufacturing process. We were forced to deviate from our original plan in several places. First, the base plate is attached by a pin, which we were not able to remove. In addition, we discovered that the guards can't be separated from the handles until the small handle connecting the base plate and the curved slot that controls the depth of cut is removed. Each step is rated with a difficulty of 1 to 5, 1 indicating a very simple step, no more complicated than removing some screws, and 5 indicating a very complex step that required several tries or more than one pair of hands. Most of the steps are at the low end of the scale.
Dissection Procedure
1. Remove wing nut and carriage bolt holding the base plate in place; this lets the base plate move out of the way of accessing the blade mount assembly. Difficulty 1
2. Remove rubber stop; this allows the rotating guard to move freely and gives access to several screws behind the guard. The stop can easily be removed by hand. Difficulty 1
3. Remove the bolt, washers, and rings that hold the blade in place, using a ½ in socket wrench. Difficulty 1
4. Remove spring attached to the rotating guard by unhooking it from the fixed guard and pulling it back through the hole in the rotating guard. This allows the guard to move in a full circle, and stops it from springing back into place when released, which makes it easier to access the screws holding the guard assembly onto the housing covering the motor. Difficulty 3
5. Access and remove the screws holding the fixed guard onto the housing. There will be 4 long and 3 short screws. At this point, it is possible to pull the housing an inch or so away from the guard assembly, but it can't be removed completely yet. Difficulty 2
6. Remove the plastic handle from the rotating guard; it is attached by 1 small screw. Difficulty 1
7. Remove the two medium screws holding the back of the housing over the motor and take off the backplate. Difficulty 1
8. Remove the 6 medium screws holding the handle pieces together, and separate the two parts of the handle. The step requires a screwdriver with a long, straight shank since two of the screws are set in deep holes; a screwdriver with interchangeable bits will not work because the collar is too wide to fit. Difficulty 2
9. Remove the red handle in the curved slot that controls the depth of cut. This is the last fasteners holding the guard assembly and the housing together; once this is removed, the guard assembly and the shaft that the blade mounts on can be separated from the motor. The handle is held on by a snap ring around the nut, which can be removed with a flat head screwdriver. This is a more complicated step than most of the others because the guards and shaft need to be held in place while the handle is removed. Difficulty 5
10. Lift the housing off the motor. This will separate the housing, stator, and baseplate from the rotor, shaft, and guards. Difficulty 4
11. Once the guards, shaft, and rotor have been separated from the housing and stator, the rotating and fixed guards can be taken apart, and the gear and shaft that the blade mounts on can be separated from the rotor. Difficulty 2
12. Remove the two long screws holding the stator in place, and remove the carbon brushes. Difficulty 3
13. Pull the stator out of the housing. It will not separate completely from the housing due to the power cord, which runs through a hole in the housing and connects to the stator. Difficulty 2
14. Remove the ends of the power cord from the contacts on the stator, completely separating the power cord and housing from the stator. Remove the bronze bearing from the end of the motor housing.
15. Remove snap ring; pull spindle out of rotating guard
