Group 26 - Craftsman 1/2 in Impact Wrench - Gate 2

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Contents

Introduction

Gate one prepared us for the dissection process required for gate two. In gate two, we will show a thorough step by step procedure of the dissection of our impact wrench including the tools necessary for the dissection. The tools will be shown through a picture and labeled. The difficulty of each step will also be noted. The reader will also learn the subsystems and about their functions. The dissection process will be explained in a step by step procedure with a difficulty scale from one to three. The difference between each number will be explained as well including an estimate of how long the step took. The dissection process took a total of thirteen steps for us. Next to each step, a clear picture will also be displayed so that the reader can better understand the specific step. Along with the picture and description, the tool/tools we needed for that specific step will be written as well.

Cause for Corrective Action

The work management plan that we had set up in gate one did not work as well as we thought it would. Mostly in part because the plan was very vague and we did not set up designated meeting dates and times to bring the group together. Now we are going back an revising our previous plan and assigning specific days of the week for group meetings so we can get our selves on a consistent schedule that will work for the whole group and help us get our project done in a timely manner so we are never cramping work in at the last minute. Once we have this new management plan we expect to be able to be much more efficient in our productivity in completing the assigned sections. Also before it was not very clear to everyone what was expected to write up and submit for the wiki page. We now plan to make very specific goals and objectives for each person for every gate so there is no question as to what is asked of each of us. This will also be improved through us setting up designated times each week when we are going to meet up as a group. Even if it is just for half an hour to make sure that each group member knows what is expected from him that week. As far as communication we have been doing pretty good in that everyone is responding to the group texts that are being sent out making it an easy and reliable way for the group to contact each other in a timely manner. One way that we plan on improving our communication is to send out group emails incase someone’s phone has a problem. With sending out emails we will have a place where everyone can check to make sure they are up to date with what is going on each week. Overall the main thing that we are going to focus on to avoid future problems in to make sure we are spreading our work out and not leaving anything to the last minute (the weekend before). Leaving a few days to just look over the gates and make revisions. When taking a look at our wrench we did not expect to run into many set backs when dissecting because of the basic nature of a pneumatic impact wrench. Turns out that just has we expected the dissection process was not very difficult at all, it was almost all just unscrewing a few screws and the inner pieces just fell apart once the outer casing was removed. This is always a plus because when it comes to putting the wrench back together it should not be much of a challenge.

Dissection Process

completely disassembled product
Tools required (from left to right) Allen Key Set, Torx Head Screwdriver, Socket Wrench, Philips Head Screwdriver, and Flathead Screwdriver
Description of Difficulty for Dissection Procedures
Level of Difficulty Requirements
1 Requires no tools and the disassembly can be performed in a matter of seconds
2 Needed a tool to unscrew any fasteners, bolts, clips or use for leverage to remove mechanical parts. Took no more than 1 min to disassemble
3 Required some thought process for what tools to use for disassembly but took no longer than 5 min to resolve,
Dissection Procedure
Step Level of Difficulty Tools Needed Description of Process
1 2 Torx head key

A torx head key was used to take off four long screws on back plate of impact wrench. These four bolts are the essential components that hold together the entire impact gun. The bolts are long enough to go from the rear end cap, pass though the impact housing and thread into the hammer case. Each one has a washer, rubber gasket and blue Locktite for assembly purpose.

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2 2 Flat head screwdriver

The front the end plate and hammer case where removed using a flat head screw driver insert between a small existing gap and twist off. Both have red rubber gaskets to keep the entire impact housing air tight during operation. This also keeps any small dust particles from entering the internal components resulting in a decreased tool life.

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3 1 Hand

The Hammer cage was removed from the hammer case simply by hand. This part contains the cam, hammer dog and hammer pin. This unit transmits a rapid succession of impulses to the anvil which aids in the process of removing hardware easily and tightening to a torque specification. (Impulse system)

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4 1 Hand

The anvil was taken out from the rear of the hammer case. This part transmits both rotational energy and impulse force to the desired attached socket.

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5 1 Hand

From the back side of the housing assembly, the rear end plate and rotor assembly were removed by hand. The rotor spins on a bearing pressed into the rear endplate. This is where compressed air is transmitted into rotational energy (Pneumatic system)

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6 1 Hand

Once the rotor assembly was removed, 6 rotor blades were extracted from the rotor. Rotor is off centered in the rotor cylinder. When air flows through the rear endplate, at extremely high pressure these blades slide out from the grooved rotor slot and make an tight seal spin the unit

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7 2 Flat head screw driver

The rotor cylinder was extracted from the impact housing assembly using a flat head screw driver. There is a dowel pic on each side that hold the front and rear endplates in place. On the bottom of the rotor cylinder are two exhaust ports where air is exited from the pneumatic system down through the tool handle.

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8 1 Hand

The front end plate was pushed out from the front side of the impact housing. There is a balling bearing pressed into this part allowing the rotor spin freely. Two groves are milled into the metal that allows air to pass between blades causing a rotational motion.

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9 3 2.5mm Allen key

A small allen key was used to push a dowel pin out of the impact housing. This held the trigger and trigger spring in place. This trigger system enables the user engage or disengage tool operation. (Trigger System)

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10 2 Allen key

A 1/16” Allen key was used to remove a screw connecting the reverse switch onto the reverse valve. The direction of the trigger switch regulates magnitude of compressed air and direction of air flow entering the rotor cylinder. This enables the user to choose a forward or reverse direction of rotation and amount torque applied. (Regulatory System)

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11 3 3/4” socket & 3/8” drive

A 3/4” socket was attached to a 3/8” socket wrench to unscrew the bottom inlet bushing. Once this was removed the valve spring can be extracted from the impact trigger housing. A quick connect air fitting attaches to the inlet bushing supplying the impact gun with pressurized air from a compressor.

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12 2 Flathead screwdriver

The throttle valve can detach from the valve spring by using a flat head screw driver to twist In between the two parts. The throttle valve is connected to the trigger system. When the trigger is pressed in it pushes the throttle valve and spring down to allow air into the rotator system. When released the spring pushes the valve closed to stop air flow.

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13 1 Hand

The Exhaust deflector sound balls were removed from the bottom trigger handle. This is where exhaust air exits the impact gun. The sounds balls disrupt and muffle the exhaust air making tool more quite during operation.

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Ease of disassembly

The entire product can easily be disassembled in a matter of minutes and requires very few basic household tools to complete all of the processes. Because dissecting the wrench required such a minimal amount of effort and thought, it can be assumed the the product was meant to be taken apart by the consumer. Evidence of this is shown by how the back plate is held in place by screws rather than having a more permanent seal.

Subsystems

The Craftsman ½” impact gun is comprised of five mechanical operating systems which converts compressed gas into mechanical energy to operate. This includes the pneumatic air supply, trigger valve system, rotating assembly, impact system and air supply regulation system. These components interact in a precise and complex order. Each system is composed of numerous parts with extremely close tolerances to carry out the impact guns functionality. Pneumatic Air Supply


The Craftsman Impact gun operates of a pneumatic air supply system which uses pressurized gas to drive mechanical motion. Pneumatic systems are widely used in our society especially in industrial sectors. This is mainly because there is an unlimited supply of air in the atmosphere to produce compressed gas and transmit energy. Pneumatic tools are extremely durable and very reliable when maintained properly. Set aside from that, there are no risk factors for overloading or over heating components. There are two ways the impact gun can be attached to an air compressor, either hard piped or through an air hose. Hard piped air systems are mainly used in mechanical and industrial shops where multiple pneumatic tools need to operate. These systems consist of a large air supply, stop valve, filter, regulator and lubricator. A hard piped air supply has greater tool performance because the gas is filtered, lubricated and maintained at constant pressure. For small home owner applications an air compressor needs to be purchased to satisfy the impact guns 5.2 SCFM consumption at 90PSI. It is also recommended that a 3/8 inch ID hose no longer than 25ft be used because it will cause a pressure drop impeding on tool performance. The impact gun is connected to an air supply hose via a quick connect coupler located on the handle. Once the compressor is turned on, air is charged to the trigger system. The user can now engage and limit the amount of air entering the impact wrench.

Trigger System

The trigger system allows the user to control the amount of pressurized air entering the impact gun. This system is not like an on/off switch. Air flow can be regulated based on the desired output. The trigger system is composed of a trigger, trigger spring, throttle valve and throttle spring. When the operator starts to squeeze the trigger, it pushes down on the throttle valve enabling pressurized air to enter. When it is released, the trigger and throttle spring close the valve to suspend air flow. The main energy sources through this system is considered to be potential mass air flow at the throttle valve and user input to allow tool operation. When the impact wrench is connected to an air compressor air is charged into the handle. Energy is expended by the user to compress the trigger, enabling air to move on through the regulator system and into the rotational system. Pressurized air is the impact wrenches main source of energy to convert into a mechanical output force. These connections were implemented and designed by global, economic and societal factors. The impact wrench was designed to operate off compressed air which is obtained through an electrical power source. Its intended market of distribution is in well developed countries having the correct power sources to offer. The trigger and handle were designed to use in both left and right hand. This a societal design factor enabling society choose which hand is most comfortable to hold the impact wrench in. Another factor that was considered during development was the cost for manufacturing. Parts contained within the trigger system are simple a lack complexity. Therefore its cheap to manufacture and develop lowering over retail cost. This is considered an economical factor craftsman considered during product system development.

Regulator/Control System

Once the trigger system is engaged, air is fed through a throttle valve to the power regulator and control system. The power regulator is an adjustable switch located on the rear of the impact gun. The switch is connected to the regulator valve which can be positioned left or right. When the regulator is in the right hand position, air flows into the cylinder enabling a clockwise rotation of the rotary wheel and anvil. This angular motion will tighten bolts. When the regulator is in the left hand position, air flows into the cylinder enabling a counter-clockwise rotation of the rotary wheel and anvil. This angular motion will loosen bolts. The further you position the switch and regulator in each direction more torque will be achieved. The main source of energy passing through the regulator system is mass air flow and user input. As air is fed through the throttle valve contained in the trigger system, the regulator acts as a buffer or boundary. When positioned, one of two channel is blocked off to force air into the other. The direction is dependent on which way the user orientates the regulator switch. User input can also be another energy system associated with this system. Output direction and magnitude are two variables that can be altered within the system. the systems placement in the impact wrench is essential in providing a feature to change direction of angular force. Once air passes by the directional valve it enters the rotational assembly, the next system contained within the tool. Craftsman designed the regulator assembly with multiple factors in mind. On the switch, F and R letters are indented on the encasement which explain what oriented position provides a forward or reverse tool operation. This identifies that intended global distribution is in the United States which use this familiar notation. International parts may be developed with different indentations for society to comprehend.

Rotating Assembly:

Once the power regulator is pressurized, air is fed into the rotor cylinder. This is where compressed gas gets converted to mechanical rotational energy. The rotating assembly consists of a rotor cylinder, rotary wheel, 6 rotor blades, and front/rear plate. When this system is assembled the rotary wheel sits off centered from the cylinder. It is closer to the top than bottom. Each rotor blade can move in and out of a slot to constantly touch the inner cylinder wall surface. This allows the outer surface blade edge to continuously seal the cylinder walls during this off centered rotation. When pressurized air passes into the cylinder via regulator system, mass flow energy passes between the sealed rotor blades, spins the rotor wheel and is expelled through the exhaust port. The rotor wheel then translates this rotational energy to the anvil by a spline connection. placement of the rotational is vital for the tool to operate correctly. Compressed air is converted to rotational energy that drives the hammer system. it placement in the impact wrench is essential for transmitting the proper form of energy. This system is much more complex than the regulator and trigger system. Multiple parts are involved with converting mechanical pressurized air to rotational energy. for Example, the rotor wheel shaft rests on two ball bearings to minimize any potential frictional forces for maximum efficiency. This also decreases heat transfer between multiple internal parts. This system is designed to operate at an extremely high free speed of 7400rpm. Craftsman must design this system to withstand the large forces each part experienced. 5.2 CFM of air at 90 psi is converted to 400ft-lbs within the assembly. Craftsman engineered this product for homeowners and automobile enthusiasts that do not have the need for professional high durability power tools. It can be said the price represents quality. the rotational system is designed to withstand normal forces experienced within a residential environment. Whether its tightening on lug nuts car wheel or lagging bolts on a newly purchased wooden jungle gym. these engineering decisions are based off societal factors explained above. Over engineering a part can also affect multiple economic factors as well. Stronger materials needed for manufacturing or expensive production methods have a direct impact on power tool retail price. Since the impact wrench is considered a standard version with a low cost, its design is not as efficient, durable and powerful as professional models.

Impact/Anvil System

The impact/anvil system is located after the rotational assembly system. This system only uses rotational mechanical force, not pressured gas and energy to operate. It’s to be noted that this system only engages when there is a resulting force on the impact gun. If the gun is held in the air freely with no load, it will spin at a very high RPM. The impact system only works when a bolt needs to torqued down or taken off. This quick succession of force is prominent in removing stubborn hardware without breakage or failure. As pressurized gas spins the rotary wheel connected to an anvil. When there is a load force on the gun, a hammer dog hits the anvil causing a very quick impulse force. This force translates through the anvil to the desired part to be loosened or tightened. The main from of energy translating into this system is angular force from the rotary shaft. Therefore it is essential that its placement exists after the rotational assembly to generate angular force. All interactions between parts mechanical in nature. close tolerances exits between these internal components for this impact action to occur. When a load is externally applied the anvil shaft, a cam is locked into the anvil causing a sharp impulse force and is released. This subsequent action occurs once every to revolutions to aid in tightening or loosening bolts. Factors that contributed to Craftsman engineering and development are mostly economical. the hammer system is designed off specific force constraints and safety factors. The assembly must not be over or under engineered to preform its specific duty. Material composition, complexity, and manufacturing process are all economic factors contributing to overall retail price. The hammer and rotational systems are two assemblies that contribute most to production cost due to their interactions, part complexity and material cost.

Functional Model

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Subsystem placement