Cupertino, CA 桰t's not easy being beautiful. Like a beauty queen with a blemish, the Power Mac G4 Cube from Apple has drawn some catty comments from a few users who contend that the computer's acrylic enclosure tends to develop unattractive cracks.
Maybe Apple had it coming. After all, the company's fervent descriptions of the Cube's beauty, while arguably true, just about dare people to look for flaws. Now a few sharp-eyed observers think they've found them, and their disappointed Internet postings describe the appearance of small cracks in the Cube's surface. Thoughts about Apple's just deserts aside, though, these alleged defects raise a more important question for the plastics engineer. Are the cracks real?
Probably not. Apple makes a strong case that the untrained consumer's eye can easily mistake the normally visible traces of the molding process for stress cracks. "They're not cracks at all, they're mold lines," insists Linda McNulty, director of Apple's desktop products. Indeed, the design of the two-piece enclosure does make the mold, or weld, lines just about impossible to hide through design practice.
The main housing component, which defines the 8-inch Cube's shape and surrounds the Cube's sheet-metal enclosed core, is crystal clear. Acrylic's optical clarity helps create the impression that the core floats above your desktop, but clear plastics tend to reveal their weld lines more readily than colored or painted materials. Also, the Cube is meant to be viewed from all angles, preventing Apple's engineers from hiding the weld line in back of or beneath the housing.
The second enclosure component posed its own weld-line problems. This ribbed white vent panel, which forms the Cube's top, features five different openings for screws and computer hardware. Each of these results in more weld lines and no out-of-the way place to hide them, according to McNulty.
Weld lines may be inevitable in many plastic parts, but McNulty reports that plenty engineering effort went into minimizing their visual impact. She says some of the mold lines were incorporated into the design. "We intentionally lined up the mold lines with the centers of the screws," she says. Apple also tried to lessen the lines by molding the 9-mm thick acrylic walls at high injection pressures (20,000 psi). Finally the company experimented with several different gate locations during a tooling development process that took 12 months.