The news that Master Wang was going to teach Liu Li how to repair equipment spread throughout the workshop within two days. The veteran workers huddled together and whispered, "Is Old Wang going to pass on his most secret skills?" Some were skeptical, saying, "A young girl like her is already quite capable of lifting a wrench, let alone repairing a grinding machine?"

Master Wang ignored the gossip. The next day, as soon as he arrived at work, he took Liu Li to the machine at the very back of the workshop, which was covered with a dust cloth—an old M131W universal cylindrical grinder that had been out of service for almost half a month due to frequent precision problems.

"Do you know why we chose this one?" Master Wang lifted the dust cover, revealing the rusty exterior of the grinding machine. "This thing is the most precious and delicate one in the workshop. Once you figure it out, all the other machines are a piece of cake."

Liu Li stared at the complex structure of the grinding machine, feeling both nervous and expectant. Compared to a lathe, the parts of a grinding machine are finer, and the requirements are more stringent—the spindle must rotate steadily, and the grinding wheel must travel straight; even the slightest deviation is unacceptable.

Master Wang's teaching method remained the same, straightforward. He handed over an instruction manual thicker than a brick, along with a set of gleaming repair tools: "Let's take it apart first."

"Take it apart...?" Liu Li gripped the wrench, a little apprehensive—this grinding machine was worth a lot of money, what if she couldn't put it back together after taking it apart?

"Don't dare?" Master Wang raised an eyebrow.

Liu Li gritted her teeth, took the tools, and said, "I dare!"

Disassembling the machine was much more difficult than she had imagined. Some screws were so rusted that they couldn't be tightened at all; some small parts were hidden in nooks and crannies, and could easily be lost if she wasn't careful. Master Wang didn't lend a hand, but just watched from the side. Only when she really got stuck would he give her a suggestion: "Soak it in kerosene for a while before tightening it" and "Use a dial indicator to check the runout before disassembling the spindle and write it down."

Liu Li has small hands, which usually makes it inconvenient to change tools on a lathe. But now it has become an advantage – she can easily unscrew small screws hidden deep inside by sticking her fingers into narrow gaps.

By the end of the first day, the grinding machine's spindle box was completely disassembled, with parts filling the entire workbench. Liu Li labeled each part in the order it was disassembled, and her notebook was filled with sketches, clearly remembering which screw was where and which gear meshed with which part.

"Come again tomorrow." Master Wang glanced at her workbench, offered no further comment, and simply said one sentence.

In the days that followed, Liu Li was extremely busy—she spun parts during the day to ensure production targets were met; and she spent her evenings by the grinding machine, disassembling parts, studying blueprints, and taking notes. Sometimes when Fu Jingchen came over after get off work, he would find her with her hands covered in grease, hunched over blueprints, the tea in the enamel mug in front of her long since gone cold.

"Do you need any help?" Fu Jingchen handed over a clean cotton gauze.

Liu Li shook her head, her eyes still fixed on the blueprints: "My master said that you have to do it yourself to remember it well."

On the fifth day of disassembly, the entire grinder was finally reduced to a pile of parts. Looking at the parts scattered all over the floor, Liu Li felt a sense of relief—during the disassembly process, she gradually figured out the use of each part, and the dry principles in the books suddenly came alive.

Next came assembly, which was much more difficult than disassembly. Master Wang was right: "If you break something during disassembly, you can replace it, but if you assemble it incorrectly, all the precision will be lost." Liu Li didn't dare to slack off. When installing the bearing sleeve, she followed the master's instructions and heated the kerosene to 80 degrees Celsius so that it fit perfectly. When adjusting the gear clearance, she used a feeler gauge to measure it little by little until the clearance was exactly 0.02 millimeters.

The most difficult part was adjusting the spindle. She squatted in front of the grinder, repeatedly adjusting the tightness of the front and rear bearings. Every time the dial indicator needle wobbled, her heart clenched. For two whole afternoons, she finally breathed a sigh of relief when the needle's wobbling was controlled within 0.005 millimeters.

"Alright." Master Wang leaned over to take a look, and a smile finally appeared on his lips.

When Liu Li connected the power and tested the machine, her palms were sweaty. After pressing the switch, the grinding machine emitted a steady "humming" sound, the grinding wheel rotated steadily and evenly, and the pointers on the instrument panel were all within the normal range.

"You've graduated," Master Wang said, patting her on the shoulder.

Liu Li's joy didn't last long. During debugging, she discovered something was wrong with the grinder's hydraulic system—the oil temperature would rise after running for a while, causing the grinding wheel to move slower and reducing accuracy. Pointing to the hydraulic schematic diagram, she asked Master Wang, "Master, isn't there a design flaw in this part?"

Master Wang glanced at the blueprints and said in a flat tone, "It's an old problem; everyone in the factory knows about it."

"Maybe if we modify the oil system, it will be better," Liu Li said softly.

Master Wang gave her a deep look: "The idea is good, but now is not the time."

Liu Li knew in her heart that saying there was a problem with the equipment design in the workshop was no small matter. But the thought had already taken root in her mind.

To her even greater surprise, the next morning, Master Wang handed her a set of keys—keys to the workshop equipment toolbox. "From now on, you'll be doing the workshop equipment maintenance with me."

The bunch of keys felt heavy. Liu Li held them in her hand, knowing that it represented her master's trust and, more importantly, his responsibility.

A few days later, Fu Jingchen brought another message: "The factory has taken on a batch of export work, and there are a few parts with extremely high precision requirements that the existing machines cannot handle." He pointed to the spindle sleeve on the drawing, "Look, the inner hole precision needs to be 0.005 millimeters, and it has to be mirror-finished. The current grinding machines simply cannot achieve that."

Liu Li's heart skipped a beat as she remembered the grinding machine that had just been repaired and the unresolved hydraulic problem.

Perhaps this is an opportunity. But she knows that modifying tooling is easy, but modifying equipment is difficult—this time, she will face a problem far more complex than that of the ball joint device.