After her conversation with Fu Jingchen in the cafeteria, Liu Li's idea about the "grinding machine problem" finally came to fruition—it was no longer just wild speculation; she had a concrete direction and was just waiting to verify it with the blueprints.

Fu Jingchen was quite efficient. The next evening, just after he got off work, he stopped Liu Li at the workshop entrance. He was holding an old kraft paper file bag, the opening of which was tightly tied with thin hemp rope. When he saw Liu Li, he looked around before pulling her to the corner of the wall and lowering his voice: "I found the thing, but... there are too many people around here, it's not convenient to look at it."

Liu Lixin's heart jumped, and she quickly nodded: "Then where to?"

“There are hardly any people in the reading room of the factory building at night, and there are large tables where you can spread out blueprints,” Fu Jingchen said.

The two didn't walk together, but kept a few steps apart, slowly making their way towards the factory. Early autumn days are short, and the streetlights were already on, casting long, dim shadows. Liu Li clutched the hem of her clothes, her heart filled with both nervousness and anticipation—those blueprints were the key to solving the grinding machine problem; whether they succeeded depended on them.

The reading room was at the very back of the factory building. Old Zhang, who was on duty at the door, was dozing off at the table. Hearing the noise, he raised his eyes, saw that it was Fu Jingchen, and waved his hand: "Go in, and remember to lock the door."

Fu Jingchen turned on the green-shaded desk lamp, its warm light spilling onto the red lacquered tabletop. He carefully untied the hemp rope from the file folder and pulled out a stack of blueprints. As soon as he spread them out, a strong smell of old ink wafted over. The blue-and-white drawings were covered with densely packed gears and shafts, the lines as thin as hair, along with a bunch of crooked German characters that made one dizzy just looking at them.

“These are just a few pictures, partial diagrams of the grinding machine's transmission system, not the complete set. Many of the annotations are still in German.” Fu Jingchen sighed, and took out a well-worn German-Chinese mechanical dictionary and a notebook with a kraft paper cover from his bag. “I learned some German in college, but I still have to look up the professional terms. I’ll take it one step at a time.”

The two immediately got to work. Fu Jingchen was in charge of looking up German words in the dictionary. He circled "Zahnrad" and wrote "gear" next to it after looking it up; when he came across "Achse", he marked it as "shaft"; when he turned to "Spiel", he suddenly stopped, his eyes lighting up: "This is 'clearance'! Meshing clearance!"

Liu Li leaned closer to take a look, and next to that marking on the drawing, Fu Jingchen had written "0.02-0.04 millimeters." She gasped, "So small? Just a few millimeters of space?"

“The clearance of high-speed transmission gears must be this precise.” Fu Jingchen pointed to two meshing helical gears on the drawing. “Look at this set, it should be transmitting the power of the motor to the lead screw of the worktable. The speed must be high. If the clearance changes, it will definitely vibrate when it rotates.”

Liu Li stared at the blueprints, slowly sketching out the three-dimensional shape in her mind—the two gears were tightly meshed, but if thermal expansion and contraction reduced the gap, or if the shaft was slightly misaligned, wouldn't it vibrate when rotating fast? This was exactly what she had guessed before!

Time flew by, and it was already pitch black outside. Inside the reading room, the only sounds were the rustling of dictionary pages and the occasional whispers of the two men. Old Zhang came in to refill the hot water, and seeing that the two men were still engrossed in their drawings, he didn't disturb them and quietly left.

However, there were also many difficulties—many German abbreviations could not be found, such as "Lager" followed by "K", and the two of them guessed for a long time before realizing that it might be "bearing housing"; there were also some tolerance symbols that looked strange and were not found in the dictionary, so they could only guess based on the context of the drawings.

"Look at this coupling, it seems to be able to compensate for slight misalignment?" Liu Li pointed to a strange structure on the drawing. "If the shaft moves a little, can it adjust it?"

Fu Jingchen leaned over and looked at it for a while, then flipped through the dictionary for a bit: "It might be... but the note next to it says that the preload should be adjusted after the equipment is heated up. If it is adjusted incorrectly when it is cold, it may go astray when it is heated up."

No sooner had he finished speaking than Fu Jingchen suddenly slammed his hand on the table, startling Liu Li. He pointed to an enlarged diagram in the corner of the blueprint, his voice low but excited: "I understand this part! It says that when installing this high-speed gear shaft, thermal deformation must be considered, and a lock nut is used to adjust the preload to compensate. If the preload is too loose, the shaft may shift, and the gear meshing will be misaligned!"

Liu Li suddenly stood up, almost knocking over her chair: "That's it! It must be because the preload was too loose, the shaft shifted a bit, and the gears didn't mesh properly, that's why it vibrates when it turns!"

Both of them forgot their fatigue and spent a long time studying the blueprints. Liu Li even drew the transmission route on the white paper and marked the places where problems might occur; Fu Jingchen copied down the key German annotations and translated them into Chinese.

Then Old Zhang came in again, holding an enamel mug: "Kids, it's almost eleven o'clock, the reading room needs to be locked, let's do it tomorrow."

The two of them then realized what had happened; their arms and legs were stiff, and their eyes were blurry. Fu Jingchen carefully folded the blueprints and put them back in the file folder, while Liu Li collected the white paper covered in writing and stuffed it into her pocket like a treasure.

Stepping out of the factory building, a gust of night wind made them both shiver. The factory area was quiet, save for the distant sound of patrolling footsteps.

"Today wasn't a wasted trip; at least we found out where the problem lies," Liu Li said, rubbing her hands together, her voice filled with excitement.

"Yes, but we still need to find a way to prove it, and we need to have an adjustment plan, otherwise the factory may not let us move," Fu Jingchen said.

“I know,” Liu Li looked up at the dark machining workshop, “We need to make a measurement plan first, then think about what tools to use for adjustment, and take it one step at a time.”

Fu Jingchen looked into her bright eyes and smiled: "Okay, I'll do it with you."

The two parted ways at the intersection. Liu Li walked towards her dormitory, clutching the few sheets of paper covered in writing in her hand, feeling quite at ease. Although there were still many parts of the blueprints she didn't understand, at least she had found the key—like finding a glimmer of light in the darkness. Now, all she had to do was walk in the direction of that light.