Team Member: Daniel Massimini


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Electronics Wear

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Reverse Engineering a Sunglass Case

To begin, several commercial sunglass cases were purchased. The cases chosen are a representation of many of the commercially available styles, shapes, sizes and construction for this hard style case.

The first step was to separate the liner from the hard outer shell. The liner was made from thin plastic and had a smooth outer face and soft inner surface where the glasses will contact. The case was made from tempered steel and held together by a miniature piano hinge.

Upon dissembling the three sunglass cases, it was evident that they all had the same style of construction and possibly shared a similar style of manufacturing. The shells appear to be stamped from tempered steel or the hardness may have been a result of work hardening during stamping.

Measuring the wall thickness of the case showed that the case material was approximately 30 gauge which corresponds to a thickness of 0.0120". Other gauge thicknesses were ruled out as 29 gauge is 0.0135" and 31 gauge is 0.0105." This thinness of material further supports the steel being heat treated in some fashion to increase its strength, as untreated steel this thin is fairly flexible.

A close up of the hinge identifies two important aspects of the design. (1) How the hinge was attached to the steel shell halves and (2) the spring mechanism to hold the shells closed, but also limit the total angular excursion.  The hinge was mechanically fastened to the shell with folded tabs of the outer shell through the hinge to form a compression joint.  The springs are C-shaped and attach to cutouts in the hinge, the spring constant determine the force required to open the case.

The sunglass case from the backside shows the tabs of the shell folded over to the inside of the case where it mechanically fastens the hinge firmly in place.


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