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Client Comments on Report

We received your report. Your summary suggests that you have identified changes in the screws, shafts, axles, and plastic parts for improvement, but what changes specifically? Please spell out the main findings in the summary.

• There are many different screws, however we only found the need for 2 different types. We found no purpose for using different thread lengths. Three of the different types of screws are only used once, and they are all similar sizes.

Detailed comments:

• Great list of stakeholder needs, but you seem to be missing a few such as easy to clean, easy to maintain, inexpensive to operate, etc. For such an awkward product, aren't shipping and storage important?
  • Yes, we overlooked the packaging of the product, as that is an important aspect in its LCA as well as its marketability.

• Nice observation that the product need not only be safe, reliable and easy to use, but must also appear as such.
  • Thanks.

• Your description of system functions bring up questions - how does the trigger control fuel feed to the engine? Where are the spacers to which you refer? How does the reel feed additional wire? Pictures or figures would be a great help in understanding the way these mechanisms function.
  • The trigger pulls a wire that directly connects to the fuel feed. The more it is pulled the more fuel is allowed to enter the engine.
  • The spacers are glued inside the shafts in order for the axle to stay centered.
  • The reel can be pushed in to temporarily unlock the upper head from the lower head, and whilst in operation friction and inertia turn the lower head to allow more wire, and centrifugal force make the wire extend from the head.

• Please include a picture or drawing of the assembly with parts from the BOM labeled. What are your findings from the BOM?

• What holds the two axles together?
  • The axles are not held together in any locking fashion. The square cross section mating is the only thing that allows the axles to transfer power. The shafts however are held together using a simple button on the shaft (using a piece of sheet metal as a spring) aligning with a hole on the shaft clamp. The upper shaft is directly screwed into the shaft clamp.

• Where and how are the bearings mounted? Your assembly picture may help show this.
  • The bearings are held in place by the bevel gear housing. The cast iron is shaped to fit them.

• Is part 14 a subassembly or a single part?
  • Part 14 is a single piece of injection molded plastic.

• Where are the spacers in your BOM?
  • Not there.

• What are your FMEA findings and conclusions?
  • We found that the biggest problems with this particular design are the bevel gears and the handle. The bevel gears are under a lot of stresses, such as fatigue and friction, and are also an essential part of the working mechanism. The handle is not secured properly, and can cause the user harm when it fails to function.

• Your DFMA mentions five different kinds of screws - where are they shown?
  • Three of them are shown, one was unable to be removed, and the fifth was neglected.

• Your DFE is not clear - you include two tables but do not explain what you are doing. Please explain.
  • The first table shows the list of sectors that are used to produce weed whackers. From this you can estimate the sector that has the most impact on the environment.
  • The second table shows that the main source of GHGs and pollution are caused from the usage of the product rather than the production.

• Your mechanical analysis is not clear. Please be more explicit in explaining your model. How is the moment of inertia calculated at the 45 degree angle? Is the number you calculate good or bad? Please define all symbols and describe where your equations come from - your equations are difficult to follow. Is your scenario of 1 foot movement within 1 second reasonable? Why is the hand distance 10 inches? Is 19 lbs good or bad? How should we interpret your results?

We look forward to seeing your market research and new ideas in the next report.

Client comments on the Mechanical Analysis

The mechanical analysis focuses on the weight balance of the weed whacker, which is important to the users. Here are few comments about the analysis:

• Apparently several assumptions have been made for your weight balance analysis. Please list them in an organized way.
  • To simplify the the system, we assumed that all parts were homogeneous density. We then simplified the inertia calculations by making all the parts point masses.

• The weed whacker is designed to be used at an inclined angle. Thus the free body-diagram should be analyzed at that assumed angle, not in horizontal.

• Please revise the free-body diagram and indicate the meaning of each location, for example, engine, whacker disc and user’s hand-holding locations, etc. From the current diagram, it is difficult for reader to identify these locations.

• The calculation for the impulse is not clear. Please include a simple diagram for better explaining the concept. Also, please define the notations used in the equations, including theta and alpha.