Gate 4 - Group 4

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Contents

Gate 4: Product Explanation

Purpose

Nearing the end of our course project, the next step in our product-analyzing process is the reassembly of our drill. We documented each step as we put the product back together, and presented the steps in a way such that anybody could follow its directions to reassemble the drill. Afterwards we were able to make a few detailed conclusions about our product, including a discussion about a major mechanism found inside, and recommendations for design revisions at a system level.

Project Management: Critical Project Review

Cause for Corrective Action

Our goup management has not been confronted with any new, unexpected problems, in addition to those mentioned in previous gates. We have concluded how extremely difficult it is for all four members to meet together outside of class time, due to personal schedules, yet we have still succeeded in combining our efforts to complete project work. While keeping in close contact via email and text messaging, we have found it most beneficial to evenly distribute the work amongst the group members, by collectively determining who is best suited to complete certain tasks. While each member has had their schedules filled with other homework, exams, and working several days a week, careful planning and time management has proven beneficial for the completetion of gates thus far.

Product Archaeology: Reassembly

Exploded view.JPG


Difficulty Scale
Difficulty Level: Required tools and time:
1 No tools, takes a short amount of time, quite intuitive.
2 No tools, takes a decent amount of time, less intuitive.
3 Requires a tool, takes a short amount of time, quite intuitive.
4 Requires a tool, takes a decent amount of time, less intuitive.
Step # Descriptive Action Tool Used (If Any) Difficulty Image Guide
1 Slide field into field casing until front of field is flush with screw holes on inside of field casing. Hand 1
Step 1 Field g4.JPG
2 Use a T10 screwdriver to fasten 2 T10 screws on inside of field casing. T10 Screwdriver 3
Step 2 Field Screw g4.JPG
3 Insert 2 plugs into baffle. Hand 1
Step 3 rubber g4.JPG
4 Insert baffle in field casing with plugs facing towards the field. A substantial amount of force is required to snap the baffle into place. The baffle will be flush with the field casing when properly in place. Hand 2
Step 4 baffle g4.JPG
5 Insert armature through field until attached gearbox is flush with field casing. A substantial amount of force is required to push armature through field due to the magnetic attraction between the two. Hand 2
Step 5 Armature g4.JPG
Step 5 Armature 2 g4.jpg
6 Place ball bearing on end of gear shaft. This can be done by hand, pliers in photo were used only to help show bearing. Hand 1
Step 6 bearing g4.JPG
7 Insert the gear shaft into the gearbox, bearing side first. Twist the gear to allow it to mesh together with the drive shaft. Hand 2
Step 7 gear g4.JPG
8 Strech the o ring around the outside of the gearbox. Hand 1
Step 8 oring g4.JPG
9 Insert selector switch into top of gearbox. Hand 1
Step 9 selector g4.JPG
10 Slide chuck assembly over gearbox. Twist the chuck to allow for gears to mesh together. Be careful not to damage or move the o ring while sliding chuck assembly on. Hand 2
Step 10 chuck g4.JPG
Step 10 chuck 2 g4.jpg
11 Use a T20 screwdriver to fasten 2 T20 screws on side of chuck assembly. T20 Screwdriver 3
Step 11 2 t20 g4.JPG
12 Use a T20 screwdriver to fasten a T20 screw on bottom of chuck assembly. T20 Screwdriver 3
Step 11 g4.JPG
13 Snap + and - bursh assemblies into place on back side of field casing near exposed armature. Hand 2
Step 12 brush g4.JPG
14 Use a T20 screwdriver to fasten a T20 screw on (+) white brush assembly. T20 Screwdriver 3
Step 13 white brush g4.JPG
15 Use a T20 screwdriver to fasten a T20 screw on (-) black brush assembly. T20 Screwdriver 3
Step 14 black brush g4.JPG
16 Connect wire from (+) white brush assembly to tab 7 on trigger assembly. Hand 1
Step 15 + brush g4.JPG
17 Connect wire from (-) black brush assembly to tab 6 on trigger assembly. Hand 1
Step 16 - brush g4.JPG
18 Connect red wire from field to tab 4 on trigger assembly. Hand 1
Step 17 red g4.JPG
19 Connect black wire from field to tab 3 on trigger assembly. Hand 1
Step 18 black g4.JPG
20 Snap trigger assembly into opening on field casing. Hand 2
Step 19 Trigger g4.JPG
Step 19 Trigger 2 g4.jpg
21 Snap handle cover onto back side of field casing. Be careful that wires under handle cover are not pinched. Hand 2
Step 20 handle casing g4.JPG
22 Use a T20 screwdriver to fasten 3 T20 screws on handle cover. T20 Screwdriver 3
Step 21 3 t20 g4.JPG
23 Slide lag bolt through anchor until threads are exposed on opposite side. Hand 1
Step 22 lag bolt g4.JPG
24 Twist handle clockwise onto lag bolt to fasten handle to anchor. Hand 1
Step 23 handle g4.JPG
25 Slide anchor of handle assembly over chuck assembly. Hand 1
Step 24 anchor g4.JPG
26 Twist handle to tighten anchor onto chuch assembly. Hand 1
Step 25 twist g4.JPG
27 Slide chuck key through 2 holes on key holder. Hand 1
Step 26 key g4.JPG
28 Wrap keyholder around powercord. Hand 1
Step 27 power cord g4.JPG
Step 28 complete g4.JPG

Product Archaeology: Mechanisms

The gear system found inside our product is an important mechanism that plays a major role in the function of this drill. Its purpose is to transfer the rotational energy of the motor to the rotational energy of the chuck/bit, by changing the RPM. The motor produces the correct amount of power required for the drill, but the rotational speed needs to be changed to acquire the correct amount of torque. In Gate 3 we completed an analysis on the design of this gear train, which helped give us a better understanding of its functionality and purpose.

Assembly Drawings
n = number of teeth on gear

As the motor transfers electrical energy into mechanical energy, it rotates the armature at a very high RPM (near 30,000), much too fast for the chuck/drill bit to turn. Therefore, the use of a simple gear system is required to "step down" the input (armature) speed to the output (drill bit) speed. The typical drill bit speed of a hammerdrill ranges from 1100 to 3000 RPM, so the designers had to calculate the gear sizes required to accurately step down the motor speed to this range of output speeds.

This gear system works by changing the rotational speed from the armature, to a shaft, then to the output chuck. They are connected in order by meshing gears that contain different numbers of teeth. Going from a gear with a low number of teeth to a gear with a high number of teeth will decrease or "step down" the RPM's, because one full rotation of the first gear will result in only a fraction of a rotation in the second (dependent on the teeth ratio). The opposite is true for two gears that go from a high number of teeth to a lower number. In our case, the armature gives an input speed of approximately 30,000 RPM and has a gear with 5 teeth on it. This gear meshes with a gear of 31 teeth. With such a large gear tooth ratio, the rotational speed is stepped down to around 5,000 RPM. On the same shaft holding gear #2 is also a third gear, which roates at the same RPM despite having a different number of teeth. Therefore, we can mesh this third gear with a fourth gear (which is directly connected to the chuck assembly), giving a final step down to our output speed. Listed below are two equations required for the design of this mechanism:

  • (w2)/(w1) = (n1)/(n2)

Where: "w" = the rotational speed in RPM and "n" = the number of teeth on the gear

  • Overall Gear Ratio = (Output Rate)/(Input Rate)

(The above equations were cited from http://www.efunda.com/designstandards/gears/gears_compound_train.cfm)

Product Archaeology: Design Revisions

Inclusion of a Rechargeable Battery / Removal of a Corded Power Supply

An ordinary drill battery pack
  • For the first design revision, we suggest that the DeWalt Hammerdrill be updated with a rechargeable battery for a power supply instead of the current corded system. Overall this exchange in power supply would allow for the hammerdrill to be used in areas where an outlet may be absent or too far away for the cord to reach. It would remove the hassle of having to hook up an extension cord as well as allow for the use of the hammerdrill in areas such as in new housing where electricity may not be readily available yet. In terms of the new housing areas, the hammerdrill could then be opened in a new market of construction as well as household projects with no redesign required. If the hammerdrill is to be sold on a global market as well, a battery powered device would remove the aspect of having to design different power cords since many different countries have diverse wall sockets compared to the U.S. Another reason for the change is that corded drills can often be dangerous in some areas due to a dangling cord. A cordless drill is much easier to maneuver and ideal for quick jobs. The only downfall to the battery exchange is that charging is required, and cordless drills usually cannot provide as much torque since the voltage is supplied through a small battery pack. Although with this particular hammerdrill, it is not extremely powerful so a battery inclusion would not change its torque output much. In terms of end-life of the product, the battery would need to be properly disposed of. The hammerdrill itself may increase in price slightly since extra batteries may need to be purchased, but if the consumer wants a convenient, maneuverable hammerdrill, a battery powered drill would be best. Since this particular hammerdrill is meant for household use, which usually pertains to quick fix up jobs, a redesign of a battery powered device is intuitive.
  • Summarized GSEE Factors (from above):
    • Global – No redesign for the power cord’s socket input, if sold in different countries.
    • Societal – More convenient, and maneuverable for quick jobs and areas without wall sockets and electricity. It is also less dangerous since a cord is not dangling around close to the work area.
    • Economical – Slight increase in cost if more batteries must be purchased for the device, but a production cost would decrease in terms of redesign of the power cord if sold in globally. New markets could be opened and the device could be sold to consumers other than for household use such as construction since they may need a device where a corded power supply in unavailable.
    • Environmental – The new redesign would require a properly disposed battery at end-life.

Inclusion of a high/low gear setting

Example gear switch
  • For the second design revision, we suggest that the DeWalt Hammerdrill be equipped with a high and low gear setting. This would be in place of the current single gear setting. Adding this setting to the drill makes the drill more useful. Having a high gear setting comes in handy for high speed drilling applications. On the contrary, having a low gear setting is useful for situations requiring the high amounts of torque.If this design revision was implemented, it would open up a new market for the drill. Currently, without the advanced features such as having a gear switch, the hammer drill is aimed for home use. If it were given a high/low gear setting, it would be more marketable for construction work as well as serious household applications. With the inclusion of a high/low gear, the overall price of the hammer drill may increase somewhat due to the need to include a different gearbox and a switch assembly. However, it may be a requirement of the consumer to include a high/low gear for the job they need to do. Having a high/low gear in the hammer drill makes the drill much more useful in that the user can choose which gear best fits the job at hand.
  • Summarized GSEE Factors (from above):
    • Societal- Drill becomes more useful because it can be used in high speed or high torque scenarios.
    • Economical- Price of drill will increase due to cost of gears and switch assembly.

Inclusion of a variable clutch

Example drill with variable clutch dial
  • For the third design revision, our group suggests that the DeWalt Hammerdrill be equipped with a variable clutch.This would be in place of the existing system without a variable clutch. This change would make the hammer drill more useful overall for many reasons. The clutch would be located just behind the chuck inside the drills casing. A predetermined level of resistance is set by the user. Most high end drills include over 20 different preset resistances. When this resistance is met by the drill, the clutch disengages the drive shaft thus stopping the chuck from spinning. When this happens, the drill will make a clicking sound. This is a result of the motor still spinning but the chuck is not. Having an adjustable clutch on a hammer drill is very useful. It gives the user much more control over the drill. It also prevents the drill from stripping out or over driving screws. Having an adjustable clutch would not limit the power of the hammer drill because a setting would be included that would provide full power to the bit. Having an adjustable chuck would open up the hammer drill to more marketable for construction workers or serious household projects. With the addition of an adjustable clutch to the hammer drill, the price is likely to increase due to the manufacturing and assembly costs of the new parts. However, for users requiring an adjustable clutch, the price wouldn't be an issue.
  • Summarized GSEE Factors (from above):
    • Societal – An adjustable clutch makes the hammer drill safer and easier to use. No more stripping out or over driving screws.
    • Economical – Slight increase in price due to cost of new parts and assembly is not an issue for consumers requiring an adjustable clutch as a feature.