When Liu Li first produced that smooth stream of iron filings, her excitement didn't last long. Once she stopped cutting and turned off the lathe, the roar of the machines in the workshop returned, bringing her back to reality—Master Wang was already there with calipers, measuring the cylindrical surface he had just turned.
"Forty-one millimeters and seven marks." After announcing the numbers, Master Wang handed over the calipers, his tone flat. "The blueprint requires forty millimeters, zero marks at the top and negative twenty marks at the bottom. Your machine is too big."
Liu Li gripped the calipers and measured again. The graduations on the vernier were clearly visible, and her initial excitement vanished instantly. It wasn't just a little off; it was completely substandard. Before, filing cubes had honed her hand precision; now, dealing with a lathe meant she had to precisely engrave the dimensions from the blueprints onto the rotating metal machine—much more difficult.
"When working on a lathe, dimensions are everything." Master Wang tapped the workpiece. "Feel is important, but in the end, the measuring tools have the final say. Keep practicing."
As the new bar stock was loaded onto the lathe, Liu Li took a deep breath, recalling the feeling from before, and slowly turned the feed handwheel. This time, she deliberately slowed down the speed and reduced the feed rate, but the measurement was still too high—40 millimeters and 30 marks. The third time, she almost held her breath, her hands barely daring to tremble, but she was still five marks short, failing to reach the acceptable range.
The sense of frustration accumulated like the pile of iron filings beside him. Even though his skills were getting better and better, and the iron filings were still smooth, why were the dimensions always just a little off? Master Wang didn't say anything, just stood there watching, occasionally picking up a scrap piece, touching it a couple of times, and then putting it down again. That silence was more stressful than anything he could say.
During lunch break, Liu Li stared blankly at her lunchbox. Zhang Shulan nudged her with her elbow: "What's wrong? Having trouble learning to use the lathe? I saw you working on it quite happily this morning, with long bits of metal flying everywhere."
"It's easy to produce metal filings from a machine, but it's hard to get the dimensions right." Liu Li poked at the potatoes in her lunchbox. "It's always just a little off; it's like my hands don't obey me."
“It’s always like this at the beginning!” Zhang Shulan waved her hand. “We’re really unpredictable when it comes to sand casting. Every batch comes out looking like something else. You should learn from Master Wang. He’s strict, but you’ll get better with time.”
Liu Li knew it was meant as comfort, but she also understood that Master Wang's strictness was an obstacle she had to overcome. She continued practicing that afternoon and discovered that there were too many pitfalls affecting the dimensions: the tool would dull with use, and even a slight wear on the tip would cause the dimensions to deviate; the iron would expand when heated during machining and shrink when cooled; even the barely perceptible jerking when cranking the handwheel could leave marks on the workpiece, affecting measurements.
She was battling an invisible adversary, lurking in tool wear, cutting heat, and machine tool clearances—an adversary she couldn't defend against. For several days, a small pile of scrap bars accumulated. There was progress—from being dozens of marks out of tolerance to managing to stay within ten marks—but she just couldn't consistently stay within the acceptable range of negative ten to negative twenty marks. Seeing hope, yet unable to reach the finish line—that feeling was the most agonizing.
Sun Peng would deliberately walk past her workstation, glancing at the pile of scrap materials. He didn't say anything harsh, but his eyes were sharp as needles, clearly waiting to see her stumble and see how this person who "could talk to technicians about technology" couldn't withstand the real skills.
That afternoon, Liu Li turned the machine to exactly 40 millimeters, just hitting the upper limit. It was acceptable for the edge trimming, but far from a "good job." Frustrated, she turned off the machine. Master Wang finally came over, and without looking at the workpiece, he picked up her notebook and flipped through it—it was filled with notes on the rotation speed, feed rate, tool status, final dimensions, and any problems found.
"What did you see?" Master Wang asked.
Liu Li pointed to the notebook: "Master, the newly sharpened knife is accurate at first, but it becomes dull after a few turns, and the size is larger; also, with the same feed scale, the force in the hand is different when turning the first and the second, and the size is also slightly different."
Master Wang closed the book, a hint of approval finally appearing in his eyes: "It wasn't a waste of time." He walked to the lathe and pointed to the feed box, "A machine tool isn't a ruler; it has gaps and can deform. A cutting tool isn't a diamond drill; it can wear out. Turning iron isn't like planing wood; it generates heat and makes the workpiece 'grow'."
He picked up a lathe tool and pointed to the invisible arc at the tip: "That's called the tool tip arc. The amount you feed by cranking the handwheel doesn't equal the amount you cut less workpiece; you have to convert it. If the depth of cut is too deep, the machine will 'yield,' and you won't actually cut as much as you think; if the tool tip is dull, the position will shift back, and what looks like ten micrometers of cutting might only have cut eight micrometers..."
Liu Li immediately understood! Before, she was only staring at the handwheel and the scale, forgetting that the entire turning process is dynamic and not simply a matter of "following the diagram".
"So feel is important," Master Wang summarized, "but feel must be built on understanding the principles. You need to know how the speed, feed, and depth of cut affect each other, when to sharpen the tool, and when to adjust the dimensions. That's the true skill of a lathe operator."
He picked up the workpiece that had passed the edge-grinding test and weighed it in his hand: "You guessed right this time. We'll change jobs tomorrow, keep the tolerance within ten marks, and keep practicing."
The tolerance was ten millimeters! The requirements were twice as strict! Liu Li's relaxed energy was renewed, but the previous confusion was gone from her eyes, replaced by a competitive drive—she had finally gotten the hang of it.
As she was packing up her tools to leave work, she caught a glimpse of Sun Peng whispering with the warehouse keeper by the tool cabinet. The two of them even glanced in her direction. Liu Li's heart skipped a beat: Sun Peng hadn't caused any trouble these past few days, but he was already acting strangely. Now that he was hanging out with the tool keeper, who knew what kind of mischief he was up to.
She knew that getting to the perfect size was difficult, but preventing people from sabotaging her behind her back was probably even harder. Mastering the lathe was destined to be a bumpy road.
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