Oops, although thinner than a human hair, 0.02mm compared to 0.05mm, tolerance is still worlds apart. In the ultra-precise domain of high-tech engineering, how could things have gone so wrong? There are reasons.

Splitting hairs in millimeters

Terry Gou’s robot army of smartphone assemblers just got orders to retreat back to the R&D lab for refinements: seems that the robots are caught in a tolerance bind.

Apple (NASDAQ: APPL) won’t let any of Foxconn’ Foxbots near its iPhone 6 assembly lines because they lack the 0.02mm working tolerance specified by Apple as necessary to put together the iPhone 6.

Remember that 0.02mm is thinner than a human hair.

For Foxconn (Hon Hai), that’s a major defeat. A reversal of fortune that may be exacerbated by the fact that other OEMs, most notably Samsung and Motorola, may also reject these mechanical workers for their Smartphone product assemblies.

Seems inconceivable that Foxconn could have gotten it all so wrong, especially since it is Apple’s major partner in the phone assembly business and an insider with trusted past performance.

Gou had hoped to put 10,000 nimble-fingered Foxbots on his production lines, joining the 1.2 million human workers in his factories across China. That 10,000 would have begun the onslaught to eventually deploying 1 million Foxbots in those plants.

Delays have plagued Foxconn’s million-robot army since it was first announced in 2011. That year, Gou claimed that his company already had 10,000 robots deployed. That number was due to swell to 300,000 in 2012, then balloon up to 1 million by 2014.

This first batch of 10,000 not making the cut means that Foxconn will have to scramble around to hire tens of thousands more humans, which is the exact opposite direction that the company wished to travel. Currently, Foxconn has recruiters at train stations signing up new workers as first-timers embark after long trips from their home villages to the city.

Impressive as a 0.05mm tolerance is for robot assemblers, the Foxbots are still not precise enough for Apple’s iPhone 6 requirement of 0.02mm.

Haste makes waste

Ryan Whitwam, reporting for ExtremeTech, said: “Most robots don’t have the manual dexterity required to drop tiny components into devices on an industrial scale. The technology required to make this work exists, but you’d have to design entirely new industrial robots to make it happen.”

Two crucial oversights in Foxconn’s development of the robots may have been that the iPhone 6 is markedly different from previous Apple Smartphones.

Apple’s iPhone 6 — both standard and “phablet” variant –boasts a completely revamped design with a thinner chassis and next-gen A8 SoC (system-on-a-chip technology) that is a 2 billion-transistor, 20nm powerhouse.

Despite almost doubling the transistor count, the die size is startlingly 13 percent smaller. Such rearchitected design changes up the ante on precision assembly.

Also, “Foxconn was looking to save money fast,” said ExtremeTech, “so it used automotive robots as the basis of the Foxbot design.”

Concurring with that view, is MacRumors‘ Kelly Hodgkins: “The lineage of the robots, which were adapted from the car manufacturing industry. The larger, clunky robots are not designed with the flexibility necessary for the assembly of Apple’s thin and complex devices.”

“Foxconn reportedly is working on the second-generation Foxbot, but the technology still may need additional years of refinement before it can make a meaningful contribution to the assembly process,” she said.

ExtremeTech added that Gou’s team is “reportedly redesigning the robotic arms in hopes a more precise version will get Apple’s seal of approval. That could take several years of research, but the resulting robots could have much greater finesse. There?s even talk of abandoning the automotive robot frame and instead designing something more like a human arm with multiple fingers.”

So what was so much at stake that haste may have sunk the ship? “Each Foxbot can complete an average of 30,000 devices per year, meaning a release of 10,000 would theoretically yield 300 million iPhones if completely tasked to that production line,” the site said.

Also, at a cost of $20,000 to $25,000 each — which is cheap for an industrial robot — the robots (pay once and use forever) could also represent a substantial savings for Foxconn’s payroll and housing costs. The company currently employs over 1 million workers at its various factories across China.

Removing workers 10,000 at a time would offer up substantial savings. Miscalculations, missteps in design and haste, however, caused the Foxbot army to about face and march for home.