Case Study: Product Development

From Concept to Production using CustomPartNet
With services including CAD modeling, design review, and rapid prototyping


Many users of CustomPartNet are not professional engineers, but rather students, inventors, or hobbyists that wish to design a new product. One such user, named Dick Gregg, found the CustomPartNet website and began reading the process overviews and design guidelines to learn how to properly design a part to be injection molded. However, like many amateur inventors, Dick lacked the technical expertise to implement what he had learned into creating professional CAD models and drawings. Such drawings would be needed for the prototyping and eventual production of his product. So, Dick decided to contact the staff at CustomPartNet for assistance.

The Product

Dick described his product, the "Bungee Block", as a "bungee cord tie-down device that utilizes a patent pending locking wheel system". The device was designed as a 3-piece assembly, through which a bungee cord would be fed, plus a separate cylindrical piece for the end of the cord. Dick wanted the Bungee Block to be available in 4 different sizes, to accommodate 1/8", 3/16", 1/4", and 3/8" diameter bungee cords. Therefore, a total of 16 separate components needed to be designed. Having some machining experience, Dick created a conceptual prototype from wood for each of the product sizes.

Wood prototype closeup     Wood prototypes demo     Wood prototypes wrapped
Wood prototypes of design concept for 1/8", 3/16", 1/4", and 3/8" Bungee Blocks

CAD Modeling

As mentioned above, Dick needed assistance in creating the CAD models and drawings to illustrate his design to manufacturers. With the use of some basic CAD software, he was able to model a rough version of his design to convey the concept and basic dimensions. From these drawings, CustomPartNet was asked to model all 16 components (4 for each of the 4 product sizes) plus the 4 assemblies of these components. Additionally, some features that Dick could not model, such as rounded corners and more complex surfaces, had to be added to the design. During the modeling process, minor corrections were also made to the dimensioning of the parts in case of a contradiction, omission, or error. After 48 hours, the CAD modeling work was completed and included the 3D models, 2D drawings, and rendered images for all parts and assemblies.

Design concept CAD model (Block A)     Design concept CAD model (Block B)     Design concept CAD model (Wheel)
CAD models of design concept (3 components for 1/4" Bungee Block)

Initial design CAD model (Block A)     Initial design CAD model (Block B)     Initial design CAD model (Wheel)     Initial design CAD model (Cylinder)     Initial design CAD model (Assembly)
CustomPartNet CAD models of initial design (4 components and assembly of 1/4" Bungee Block)

Design Review and Redesign

With the CAD modeling of the initial design complete, Dick began to investigate the manufacturability and cost of his product. He decided that the Bungee Block should be made from a durable plastic and wanted an initial run of 1000 products that could easily be scaled up to high volume production. From reading the CustomPartNet process overviews, Dick determined that the product should be injection molded and would require a redesign using proper DFM (Design for Manufacturing) design rules. He decided to ask CustomPartNet to perform a design review of all 16 parts and complete the CAD redesign, implementing all approved changes.

The initial stage of the design review was to propose possible design alternatives. Before addressing the design issues to improve manufacturability and part quality, CustomPartNet offered suggestions that may improve other areas. For example, two design concepts were modeled to demonstrate a new method of assembly and a slimmer exterior. Ultimately, Dick preferred to remain closer to his original concept.

Design Alternative 1     Design Alternative 2
Possible design alternatives

The design review process continued with making any changes that would improve the manufacturability, assembly, cost, and end-use of the product. The primary source of much of the redesign was the presence of thick material sections on many of the parts. Wall thickness that is too great and non-uniform will not only increase the time and cost of the injection molding process, but is likely to cause several part defects. In order to reduce the wall thickness of each part and make it more uniform throughout, the press-fit assembly features and wheel axle features had to be redesigned. The new press-fit assembly was designed to also ensure a more secure fit and the new wheel axle design allowed for a simpler and less expensive mold. Following these substantial changes, more minor alternations were made including the addition of rounded corners, draft angles, and ribs for structural support. Updated CAD models, drawings, and images were then created.

Redesign CAD model (Block A)     Redesign CAD model (Block B)     Redesign CAD model (Wheel)     Redesign CAD model (Cylinder)     Redesign CAD model (Assembly)
CustomPartNet CAD models of redesign (4 components and assembly of 1/4" Bungee Block)


After reviewing the redesigned parts, Dick was pleased with all of the changes but wanted to see how this new design would look and feel once manufactured. After all, the only design he had held and tested was his early conceptual model made from wood. CustomPartNet recommended the quick fabrication of a few prototypes using FDM (Fused Deposition Modeling), a rapid prototyping technology that build parts directly from the CAD models. These prototypes would allow Dick a quick and inexpensive way to test the form and fit of the components. Any desired changes to the design could be quickly implemented and new prototypes fabricated.

The first round of prototypes were fabricated and shipped to Dick in a matter of days. He was then able to not only see and feel his invention, but actually attach the bungee cords and test the functionality. The redesigned Bungee Blocks were a success. An added benefit of the prototypes was that Dick was able to identify a few areas for improvement that could only be noticed by handling a physical model of the product. At his request, CustomPartNet made some modifications to the design and created new CAD models and drawings. The changes included the following:

  • Slight increase in wall thickness for a more solid feel
  • Increase in diameter of assembly pins for added strength
  • Adjustment of wheel position for easier movement of the bungee cords
  • Decrease in clearances of the wheel axle to reduce wobbling

The new prototypes solved the remaining issues and Dick was now ready to proceed with the injection molding of his product.

FDM prototype closeup (Front)     FDM prototype closeup (Top)     FDM prototypes
FDM prototypes of final design for 1/8", 3/16", 1/4", and 3/8" Bungee Blocks

Final Product

CustomPartNet recently spoke to Dick to follow up on the development of the Bungee Block. He informed us that following the successful modeling and prototyping of the parts, he found a supplier to manufacture the parts through injection molding. The Bungee Block turned out exactly as he had hoped and will soon be available in stores.

Final product
Injection molded final product

"The configuration of the device is exactly as you drew it . . . The new units work perfectly."
- Dick Gregg