Link: Design Revisions

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By means of applied, cautious analysis on the product level subsequent to product dissection, as is characteristic of a reverse engineering undertaking, group 29 had evolved an intimate familiarity with the Homelite® VersaTool™. In particular, the technicians of the group sought, and achieved, to gain robust insights into the product's manufactured configuration, functionality, and in broad terms, conceivably practical reforms to its design.

Weighing the quantitative outcome of analyzing the likelihood of the conditions necessary for the product's failure, which receives a detailed probe in the following subsection, Engineering Analysis, and the qualitative approach to surveying the efficiency and cost-effectiveness of the product's design, there arises occasion for several recommendations on the issue concerning design revisions.

In brief, after subjecting the dissected product to analytical rigor, three modifications materialized as both practical and technically feasible, no less cost-effective either. Namely, the recommendations, which primarily involve external aspects of the line trimmer in question, are revealed below. For the sake of concise exposition as prelude to the revisions, they are roundly introduced as the following:

  1. Replacement of comparatively uncommon Torx screws with the more prevalent alternative, the Hex-head screw, manufactured with comparable diameter and direction of threading; thereby, the revision enhances the serviceability of the product, benefiting both the consumer (predominantly targeted as the typical homeowner) and the manufacturer.

  2. Secondly, a more elaborate revision than the former, it involves reconfiguring the assembly, or more generally, the conception, of the fastening device integrated in the line spool; in effect, as an external application and of minimal intricacy in design, the proposed contrivance proves functional, durable, and of reliable manufacture pursuant to specifications in agreement with existing dimensions of the line spool.

  3. Still a third, but less technical than the second, design revision addresses the "grass deflection shield"; constituted from steel, the mount is unnecessarily bulky and weighty, effectively a power drain on the line trimmer's engine. Whereas the steel-constituted shield imposes considerable weight on the machinery of the line trimmer, such a lighter, but sufficiently reinforced, material as a dense form of plastic can suffice for the purpose the shield serves.

With the foregoing introduced and digested, the noted design revisions receive further elaboration on their respective technical particulars in the content below.

Design Revisions

1. Fasteners

The Homelite® VersaTool™ Line Trimmer contains approximately 45 fasteners in its complete assembly, give or take about 5. Approximately 37, or 82%, of these fasteners are “Torx screws.” Torx screws serve well for using a driver that will not slip out of the fastener head with relative ease, whereas a screw driver would. As an additional reason behind the utility of the Torx screw, the manufacturer of the product devises something considered a” torque-limiting driver,” which allows the fastener to reach a certain needed torque without overcoming or breaking the fastener. However, the Torx driver, especially the limiting-torque driver, can prove to be an uncommon tool for the product’s target audience, namely, the average homeowner.

To use a fastener that requires an uncommon tool in an abundance of 82% of all the fasteners used in the product seems unfit, and more than likely inconvenient, for the consumer. Indeed, the product’s design does not render it conducive to disassembly at the hands of the typical homeowner; however, the curious or mechanically inclined proprietor will at some point, sooner or later, require physical disassembly of the product to whatever degree, whether it is a do-it-yourself effort or otherwise. Therefore, accounting for consumer autonomy in terms of freely modifying or adjusting the product’s components with the intention of maintaining the machine in proper functioning order, this revision is an imperative design concern to addressed by the manufacturer, particularly when this could affect the customer's decision to purchase the product.


The plan for the Homelite® line trimmer is to remove many of these Torx screws and replace them with regular Hex-head screws. The Hex-head is more common than the Torx variety, and the tool for removing and replacing these fasteners are very common as well. The limiting-torque driver therefore proves altogether unnecessary, and if needed by any chance, it is manufactured for Hex-head screws. Additionally, after supplanting the 35 or so Torx screws with the suggested Hex-head screws, there remain fasteners that are difficult to access using a wrench or socket; these could remain as the original Torx screws, or be replaced by the Hex head variety, considering nut drivers are just as common as Torx drivers.

The central focus of this revision is to satisfy the product’s target consumer base with fasteners that are, in general, common in households of the typical homeowner(s). Further, the revision sacrifices no other aspect of the product, and its functionality, weight, and cost would remain relatively unchanged. The revision is strictly to capture the target audience’s attention, and allow, in a way, for easier, and perhaps more convenient, maintenance.

2. Line Spool

The Homelite® line trimmer under analysis has a detachable line spool, which enables the user to replenish the cutting line comparatively easily. However, the line spool is somewhat difficult to remove from the line trimmer; the revision here, therefore, would allow the user to detach the line spool very easily. To remove the line spool currently (as explained in the Product Dissection Plan of the Preliminary Project Review, Step 18) one needs to use a holding pin and insert it into two aligning holes situated above the line spool, and then unscrew the line spool via some type of pliers. This requires the use of two tools and tedious focus for the holding pin.


Although this demands a description involving expression that proves invariably elusive, the attempt to articulate herein the conceived amendment to the product’s design will yield fruit nonetheless, to whatever extent. The overall idea is to allow the line spool to be removed quickly, without the intervention of any tools. To achieve this, many features that are directly connected to the line spool will necessitate replacement.

  • First, the gear shaft that directly drives the line spool must be manufactured in a manner vastly different from that involved in its original manufacture. It must be given a hollow center, and then threaded to fit a 3/8 of an inch (3/8 ”) screw.

  • Subsequently, the exterior needs to be geared all the way, and the external threads obviously removed. Allowing 1/4 of an inch (1/4 ”) space of solid metal between the inner threads and the outer gear, and 1/8 of an inch (1/8 ”) tooth size of the gear, make the total diameter of this new shaft 1–1/8 inches.

  • Next, the line spool itself has to be changed. Instead of its center being threaded, it must now be geared to the size of the new geared shaft. The line spool now simply slides onto the shaft. Finally, we must now introduce a new component for this revision to work. The component is a washer, but not an ordinary metal washer. It is made out of dense plastic/rubber material, essentially from that which the line spool is comprised. This washer will be at least 1/2 of an inch (1/2 ”) thick, with a 3/8 of an inch (3/8 ”) hole through its center, and will also contain a cut-out section in its top. This section will be a counter-bored hole ¼ of an inch (1/4 ”) down, and then shaped into the exact dimensions of the head of the (3/8 ”) Hex-head screw to be used.

  • The screw is then inserted in the hole, and its head should sit in tightly with the washer's counter-bored cut-out. The screw and washer assembly is then brought to the bottom of the line spool shaft assembly. The screw is then fastened into the hollow-threaded shaft, using the washer to turn it since the Hex-head fits snugly with the washer’s counter-bored cut-out. The revision is complete after the fastener is tightened as tightly as possible with only the human hand applied as manual input.

  • The line spool will now spin due to the geared center, and it will not slide off due to the washer and screw. To remove the line spool one must simply unscrew the fastener by turning the washer by hand. This will remove the washer, allowing the line spool to simply slide off its geared shaft.

While definitely helping to arrest the attention of the target audience, this revision also negatively affects the product in other respects. The cost will increase, for instance, due to the new and more complicated manufacturing process, along with the addition of a new component. Still, this revision will pay for itself, in a sense, as the market seeks a mechanically efficient, but cost-effective, product that is easier to use.

3. Grass Deflection Shield

Like most line trimmers, the Homelite®, UT 15151 VersaTool™, is equipped with a grass deflection shield. It is constituted from some metallic substance, presumably steel of a grade that had been determined by the manufacturer to be cost-effective. Indeed, this material is expensive and heavy. Although durable and highly effective at withstanding the forces from stray particulate matter, other materials could suffice at similar capacity and strength as that associated with steel.


The approach for this revision is simple: to change the material used for the grass deflection shield. Myriad other, similar products do not use metal; instead, they usually have mounted a shield, or a near cousin of this, that consists of a dense plastic substance. The revision is to do just that: to change the material of the grass deflection guard to a dense plastic similar to what constitutes the line spool. In so doing, the manufacturer conceivably economizes on the material cost, curtails other manufacturing-related expenses, and perhaps even increases earnings from sales.

While plastic is a petroleum-derived substance, and therefore will vary in value, either appreciating or depreciating, with respect to the indexed price of crude oil, the physical attributes and properties of plastic augment its appeal as the material with which to supplant steel for the grass deflection shield. The material, even after being molded, for example, will cost less than the steel substance used originally in the design of the shield. Further, by implementing this revision the Homelite® VersaTool™ will weigh less than its former self, allowing facile maneuvering with the product for the typical homeowner. Nothing mechanical or functional is compromised by this revision, for it does not affect anything besides the material of the grass deflection guard, not components vital to the operation of the product. And the guard will also work just as effectively as the metallic one, because it does not experience forces beyond the capacity and resilience of the dense plastic.

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Reverse Engineering Team Project: Homelite® VersaTool™ Line Trimmer (Group 29)