The process of molding plastic car parts inevitably leaves behind some faint work lines. To achieve the stunning finish of a Century bumper, one master plastics polisher smooths these markings down to thousandths of a millimeter.
A world of “knack and intuition” that eludes automation
So, what makes the polishing process technically difficult? As with many craft skills, this “knack and intuition” world is difficult to quantify, and Yamanaka says the only way to master a feel for it is through hands-on experience.
When polishing, for example, you want to run the sandpaper as flat as possible across the part. But the part’s edges have more give and fit more closely to the paper, so you tend to take off more than expected. To get around that, I imagine that I’m polishing a level plane in midair.
As the work proceeds, parts also heat up from friction, and you might get what looks like eraser shavings coming off bit by bit. You need to track each of these unpredictable elements with your eyes and hands as you work, constantly judging the angle and force with which to apply the sandpaper. That’s what makes automation so difficult.
For Yamanaka, even more challenging than the polishing process was the task of assessing how much work the parting lines needed to reach Century-level quality.
It’s not like we had decided in advance that the PLs would be polished down to 0.002 mm. Time and again, we repeated the process of examining the finish after painting and, if the quality wasn’t up to scratch, cut the polished area to check the cross-section under a microscope. Eventually, we arrived at 0.002 mm.
For a time, I became unable to judge how much polishing was needed in this process objectively, and it took me longer than necessary to establish my method. That’s something I want to learn from and improve on for the next project.
As a craftsperson, Yamanaka is still not fully satisfied with the current quality and wants to keep pushing himself to aim higher. He also hopes to apply his skills to training future generations. As a master of plastics polishing, he will no doubt continue to play a role in the “inheritance and evolution” of Century carmaking.