62: Chapter 62 Basic Skills

When visiting the Engineering Training Center for the second time, Jiang Lin changed into a pair of black anti-smashing shoes.

The toe caps were very hard, feeling a bit heavier than sneakers when walking, and the sound of his feet hitting the ground was also heavy.

Teacher Guo Jianye was already waiting by the registration desk.

Today, he was still wearing a dark blue work uniform, his work badge pressed over his pocket, holding a black signature pen in his hand.

Seeing Jiang Lin walk in, his first glance was still at the shoes.

"The shoes are fine."

Teacher Guo Jianye said.

Jiang Lin nodded: "Teacher Guo."

"Register."

Jiang Lin wrote his name, affiliation, and purpose of visit in the visitor registration log.

Affiliation: Jiangcheng No. 7 High School.

Purpose: Auditing basic manual training and low-risk operations.

Teacher Guo Jianye took a glance, picked up his pen, and added two characters after low-risk operations.

[Limited to Benchwork]

The handwriting pierced the back of the paper, carrying an unquestionable tone.

Jiang Lin had no objections.

Teacher Guo Jianye closed the registration log.

"Let's make it clear today, passing the safety test doesn't mean you can work casually. Today, you are only allowed to do basic benchwork: scribing, center punching, hand sawing, filing, deburring, measuring, and recording. Drilling machines, grinders, lathes, and milling machines are strictly off-limits."

"Understood."

"If you encounter any abnormalities, stop, call me, and do not continue on your own judgment."

"Understood."

Teacher Guo Jianye stared at him for two seconds, seemingly wanting to find a trace of impatience on his face.

None.

There was nothing at all.

Jiang Lin was as calm as an annealed steel ingot; its internal stresses had long been cleared out, leaving only pure stability.

Only then did Teacher Guo Jianye turn around: "Follow me into the benchwork area."

The benchwork area was on the east side of the Engineering Training Center, near a row of huge glass windows.

The morning sunlight shone through the uncleaned glass, casting beams of light into the air, where countless tiny metal dust particles tumbled within the light beams.

A row of cast-iron workbench tables was fixed to the ground, with a green bench vise on each table.

By the wall was a whole row of green tool cabinets, with Arabic numeral numbers pasted on the cabinet doors.

Placed by the window was an inspection surface plate, next to which were a scribing platform, several sets of V-blocks, vernier calipers, height gauges, and several boxes of files arranged by number with varying degrees of wear.

Beside them, a young teaching assistant in grey clothes was leaning against the edge of the table, lowering his head to swipe his phone, and the sound effects of game card drawing faintly came from the screen.

Teacher Guo Jianye walked over.

The young teaching assistant, who was only a second-year graduate student and had been conscripted by his advisor to be on duty at the center, hurriedly shoved his phone into his pocket and straightened up: "Teacher Guo."

Teacher Guo Jianye nodded in response, pulled an A4 sheet of paper from the nearby document rack, and handed it to Jiang Lin.

On it was today's training record sheet.

Jiang Lin took it and lowered his head to scan it.

The header was the name and date, below were the operation steps, on the right were the measurement data, and on the far right was a long column of signature confirmation boxes.

This form was simpler than any record in the Wasteland.

But it had something that the Wasteland did not have.

The chain of responsibility: who operates, who confirms, who allows entry into the next step.

Teacher Guo Jianye pointed at the form, his tone serious: "Every step you take today must be written down. Whatever you measure is what it is; don't find it troublesome, and don't make up data for me."

"Okay."

Jiang Lin placed the record sheet in a clean area of the workstation.

"Benchwork isn't just about being fast with your hands. If you are fast without records, no one can figure out what went wrong when a problem occurs, and that's just working blindly."

As he spoke, Teacher Guo Jianye pulled open the iron door of the material cabinet and retrieved a flat piece of low-carbon steel with a dull surface from inside.

"For the first piece, make a rectangular test piece to practice your hands first."

He slammed that piece of flat steel onto the table with a clatter.

"Material Q235, length one hundred and twenty millimeters, width thirty millimeters, thickness eight millimeters."

Teacher Guo Jianye's finger tapped on the steel plate, "You are required to saw off an eighty-millimeter section, then file it down to eighty, with a tolerance of plus or minus zero point one millimeter. The two long sides should be as parallel as possible, deburr the four corners, and finally write the measurement records on it."

This task was as basic as basic could get.

Every year when new students entered the Engineering Training Center, during the practical training class of the first week, they all did similar things.

Saw straight, file flat, deburr, measure dimensions.

For ordinary engineering undergraduates, holding a file for the first time, being able to control the dimensions within plus or minus zero point one millimeters and not filing it into a slope was already considered heaven's blessing plus a serious attitude.

The teaching assistant yawned nearby.

He thought they were going to make some high-tech, cutting-edge drone parts today, but it was just this?

Sawing an iron block?

This chore was so boring it could make someone fall asleep.

Jiang Lin's expression didn't change at all; he picked up the flat steel and looked at the surface of the material against the natural light outside the window.

This was a typical hot-rolled stock.

The edges had a bit of black scale, and the original end face was cut slightly crookedly, which should have been cut by a grinding wheel cutting machine.

There were slight rolling marks on the sides.

Q235, the most common low-carbon steel, commonly known as A3 steel.

Low carbon content, not high hardness, but good toughness.

This material felt slightly astringent to the touch, easy to saw, but hard to file.

If the file teeth were not clean, or if the pushing force was wrong, it was very easy for the teeth to stick, dragging ugly deep grooves across the surface.

"Can we begin?"

Jiang Lin asked.

Teacher Guo Jianye said: "Don't rush yet, state the procedure."

Jiang Lin put the flat steel back on the table.

"First inspect the jaws of the bench vise, confirming there are no iron filings and hard particles remaining. Use a relatively straight long side as a temporary reference, scribe an eighty-millimeter line, reserving the saw kerf and finishing allowance. For the center punch, start light and then heavy, confirm the point position before supplementing the punch."

"When clamping, make the saw cutting line as close to the jaws as possible to reduce vibration, but do not let the saw bow interfere with the bench vise when pressing down. After sawing, clean off the burrs, measure the allowance, and then divide into rough filing, fine filing, edge trimming, and chamfering. Before each measurement, the workpiece surface and the measuring jaws of the caliper must be cleaned."

He finished it in one breath, without a single stutter.

The teaching assistant listening nearby was stunned for a moment.

These words were memorized quite fluently; it was much smoother than those undergraduates who crammed memorization before final exams.

Teacher Guo Jianye was not so easily dismissed, and he followed up closely with an extremely fast speech rate: "Stance?"

"Left foot forward, right foot back, at a forty-five-degree angle with the bench. The center of gravity of the body falls on the left foot, the sawing direction avoids the center of the body to prevent broken saw blades from hurting people, and the falling material direction avoids the instep."

"What is used to clean chips?"

"A brush; it is strictly forbidden to wipe with hands, and strictly forbidden to blow with the mouth."

Teacher Guo Jianye's eyes narrowed into a slit, and he asked the last question: "At what dimension do you stop?"

"It depends on the requirements. For test pieces with plus or minus zero point one, do not chase zero. After approaching the target dimension, control the risk of over-cutting. Rather leave a two-silk allowance than ever file it to scrap."

Teacher Guo Jianye originally just asked routinely, wanting to suppress the young man's spirit.

Hearing the last sentence about not chasing zero, the pen that had been turning unconsciously in his hand suddenly stopped.

The bad habit that novices loved to commit most was an obsessive-compulsive attack, insisting on pegging the dimension at an absolute 80.00.

Often, that last file stroke went down with too much force, directly becoming 79.8, directly scrapping it.

Knowing not to chase zero and knowing the risk of over-cutting was not something that could just be seen from reading books.

Thoughts flashing past, Teacher Guo Jianye took half a step back, yielding the operating position: "Begin."

Jiang Lin stepped forward, did not directly pick up the material, but instead first picked up a bristle brush nearby and began to clean the bench vise.

This was not the symbolic sweeping that many students did to cope with inspections.

He carefully used the brush to clear away the tiny iron filings remaining in the cross patterns of the jaws, and then picked up a clean cotton cloth nearby to thoroughly wipe the jaws.

Then, he took off his gloves, and with the pads of his right index finger and thumb, gently wiped across every surface of the jaw edges through the cloth.

He was looking for invisible high points to the naked eye, or indentations and hard particles left by predecessors clamping hard objects.

After confirming it was completely smooth, he placed the flat steel on it.

His left hand held the workpiece, and his right hand rotated the bench vise handle.

First clamp lightly, try shaking the workpiece slightly, fine-tune the angle a bit to ensure the long side completely fits the jaws, and then clamp tightly.

For that final tightening motion, his wrist did not have any excess sudden burst of force.

Feeling that the force had reached the critical point, his wrist stopped steadily.

The clamping force at that moment stopped extremely accurately.

Teacher Guo Jianye stood at the rear side, his eyes narrowing slightly again.

This kind of thin flat steel tested clamping force the most.

Clamping too violently, the vise mesh patterns would directly press deep pits on the surface, and even cause microscopic bends inside that were invisible to the naked eye.

Clamping too lightly, when sawing later, it would make a sharp trilling sound in the jaws, and the saw blade could easily get stuck or even snap.

This point, many undergraduates could not do well even after he taught them three times and scolded them five times.

This thin-looking high school student, who hadn't been taught by anyone yet, seemed to already know the yield limit of this material deep in his bones.

Scribing phase.

Unlike ordinary people, Jiang Lin didn't just pick a random end face to start measuring.

He first took out a steel ruler, pressed it against the original end face of the material, looked at it against the light, and after confirming the end face was not flat, decisively shifted the reference to the longer rolled edge on the side.

His left hand pressed down the base of the vernier height gauge, his right hand adjusted the vernier, and locked it.

The scriber fell.

A thin, bright line was drawn across the steel surface, neither deep nor faint, formed in one go, without that kind of hesitating repetitive tracing.

Next was center punch positioning.

He picked up the small center punch and aimed at the scribed position.

His left hand pinched the middle section of the punch, with his little finger resting against the steel plate as a fulcrum.

His right hand picked up a small round-headed hammer.

"Ting."

The first strike was extremely light.

It just dotted a tiny indentation on the metal surface.

He lowered his head, lightly brushed across with his thumbnail, and confirmed that the point fell right in the exact center of the scribed line, without any deviation.

After confirming it was correct, he put the center punch back into that tiny indentation.

His wrist raised high.

"Clang!"

The second strike was decisive and slightly heavier.

A perfect inverted conical indentation appeared on the steel plate.

Teacher Guo Jianye finally put down the registration log he had been holding in his hand, and put his hands behind his back.

The teaching assistant nearby stopped looking at his phone too; he stepped closer by two steps and saw a bit of the knack.

When novices hit a center punch, they were most prone to making two fatal mistakes.

First, hitting heavily on the first hammer; once the point was crooked, that pit was so deep that even a file couldn't file it away, and it couldn't be saved at all.

Second, fearing to hit crookedly, tapping tremblingly, with a point as shallow as a mosquito bite; later when the drill bit went up, it would skid directly, and even the drill tip couldn't find a position.

Jiang Lin's these two strikes were smooth as flowing water.

This was simply not an action a student could make.

"Saw."

Teacher Guo Jianye said only one word.

Jiang Lin picked up the manual saw bow on the table.

He first flicked the saw blade with his thumb, listened to the sound of the tension, and glanced at the direction of the saw teeth.

The tooth tips faced forward; they weren't installed backward.

Only then did he start sawing.

The saw blade pressed on the allowance area about one millimeter outside the center punch line.

The angle was very small, probably only fifteen degrees.

For the very first three strokes, he applied almost no downward pressure.

The stroke was very short, moving only in the front third of the saw blade.

He was just establishing a solid saw path at the edge of the metal.

When the saw kerf reached a depth of two millimeters and was completely stable, Jiang Lin gradually leveled the saw bow and lengthened the stroke.

"Swish—Swish—Swish—"

The saw blade cut into the low-carbon steel.

In the entire workshop, instantly only this pure, boring yet extremely rhythmic sound remained.

The sound was very steady.

There was no tooth-skipping sound of the saw teeth suddenly getting stuck, no ugly screeching caused by frictional overheating or uneven force application, and even less of that common novice phenomenon where the saw bow swung sideways like a snake.

The teaching assistant watched nearby, becoming entranced.

Jiang Lin's movements were actually not fast, and could even be said to be unhurried.

However, every time he pushed, it was a complete full stroke.

The saw blade was pushed all the way from the front end to the rear end, and every single saw tooth was participating in cutting and exerting force.

As the saw bow advanced, his body's center of gravity moved slowly and evenly between his left and right feet.

His upper body maintained extreme stability, without that hurried nodding back and forth due to desperate exertion, and his wrists did not randomly twist to correct the deviated sawing route.

The whole movement looked so steady that it didn't look like he was sawing a hard steel plate.

Instead, it looked like he was following a void track only he could see, cutting away the excess metal bit by bit like cutting tofu.

The teaching assistant watched for a full half-minute, lowered his voice, leaned into Teacher Guo Jianye's ear and asked: "Teacher Guo, this kid has practiced, hasn't he? He has definitely practiced, right?"

Teacher Guo Jianye did not answer him.

The old teacher's somewhat turbid eyes were staring at that saw kerf like an eagle at this moment.

The saw kerf was extremely narrow, indicating that the saw blade was not twisted.

The saw kerf was extremely straight, indicating that the direction of force application had not the slightest deviation.

But what made Teacher Guo Jianye even more concerned was the key point when sawing reached two-thirds.

Many beginners, no matter how well they handled the earlier sawing, would reach the final stage, see the material about to drop, panic internally, and subconsciously increase the force in their hands to snap it off quickly.

The moment they applied extra force, their form would warp.

The saw blade would skew, and the metal at the exit would be brutally torn, leaving behind an ugly, oversized burr.

Then that severed piece would crash onto the workbench with a clatter, potentially even dropping onto their feet.

Even more dangerous was that due to the sudden loss of resistance, the operator's hand would lunge forward and smash against the vise.

But Jiang Lin did not.

He seemed to have anticipated the critical point of the metal's fracture long in advance.

With only the final two millimeters remaining, Jiang Lin actively shortened his stroke slightly, instantly easing the downward pressure.

He reached out his left hand, crossed over the vise, and caught the falling cutoff piece in an absolutely safe position.

At the same time, unknown to anyone, a small wooden pad was already clutched in his left palm, positioned right beneath the workpiece.

For the final few strokes, the saw blade drifted gently through the remaining cross-section almost entirely by its own weight.

"Click."

The cutoff piece landed steadily on the wooden pad.

The sound was exceptionally faint.

There was none of the terrifying clatter of metal hitting the ground, no savage tearing, and no unruly, jagged burrs.

Everything was under control.

Jiang Lin released the vise handle and removed the remaining portion of the workpiece.

He did not rush to show off his results.

He picked up a brush to clear away the iron filings from the end face, then picked up a vernier caliper to measure the post-sawing length.

The caliper's LCD screen flickered before settling on a number.

[ 80.27 mm ]

Seeing that number, Teacher Guo Jianye's gaze suddenly tightened.

This machining allowance was left with incredible precision.

For a manual test piece requiring an accuracy of plus or minus 0.1 millimeters, leaving a filing allowance of 0.2 to 0.3 millimeters after sawing was the ultimate sweet spot.

Leave an extra 0.5 millimeters?

That was just asking for trouble, forcing you to grind with a file for ages until your hands felt like they were going to fall off.

Leave less than 0.1 millimeters?

A single careless stroke of the file would cross the line, resulting in an immediate scrap.

80.27. This meant Jiang Lin only needed a couple of passes with a coarse file, followed by a light touch-up with a fine file, to complete the task to absolute perfection.

Jiang Lin recorded the data in his log sheet.

[ Post-sawing length: 80.27 mm ]

[ Saw kerf deflection: visually estimated less than 0.2 mm ]

[ Exit burrs: slight, repairable ]

After finishing, he placed the workpiece on the workbench.

Teacher Guo Jianye reached out his hand: "Let me take a look."

Jiang Lin handed it over.

Teacher Guo Jianye picked up the freshly cut piece of low-carbon steel, held it up to the light, and inspected the cross-section first.

A manual saw was not a surface grinder; it was impossible to produce a mirror-like finish that could reflect a person's reflection.

Yet on this cross-section, the tracks left by the saw teeth were evenly distributed and uniform in direction, resembling a fine, slanted sheet of rain.

There was not the slightest bit of chipping at the exit edge, and the deflection of the entire cross-section was so minimal that it didn't even need separate flattening.

This was using a manual saw—arguably the oldest and crudest tool in human industrial history—to forcefully produce results as stable and predictable as a CNC machine.

"Continue filing."

Teacher Guo Jianye placed the workpiece back onto the workbench, his tone carrying an unconscious hint of approval.

Jiang Lin turned around and drew a twelve-inch flat file from his tool kit.

This time, Teacher Guo Jianye walked directly around to Jiang Lin's side and back, fixing his eyes on Jiang Lin's shoulders, elbows, wrists, waist, and stance.

As the saying goes, laymen watch the spectacle, while experts watch the technique.

Anyone who truly understood benchwork would never judge a person's filing by looking at how many iron filings fell onto the bench or how shiny the workpiece was.

Instead, they looked at where the force originated.

The worst beginners relied entirely on wrist strength, resulting in a curved, arc-shaped surface that was high in the middle and low on both sides.

Those who knew a little better understood how to lock their wrists and push with their forearms.

Those who were even more proficient knew to use their shoulders to drive their forearms.

But truly ultimate, rock-stable filing looked just like what Jiang Lin was doing right now.

His stance formed a rock-solid triangle.

The moment the first file stroke was pushed out, Teacher Guo Jianye couldn't help but start nodding.

The file made contact with the steel surface.

A continuous rustling sound rang out as countless tiny, crisscrossing cutting edges bit into the material simultaneously and shaved away a uniform layer of metal.

Prolonged, low-pitched, and even.

When the file reached the end of its stroke, Jiang Lin's hands lifted slightly, applying zero pressure on the return trip to prevent wear on the file teeth.

Immediately following that, the second stroke fell.

Maintaining the exact same stance and translating from his waist and core, he seemed to have transformed into a low-speed, uniform human linear guide rail.

"Swish—"

The sound was completely indistinguishable from the first stroke.

The third stroke, the fourth stroke.

The force, angle, sound, and even the curl of the falling iron filings for every single stroke seemed cut from the exact same mold.

The teaching assistant stood nearby, his mouth parted slightly, completely forgetting to close it.

Having served as a teaching assistant at the Engineering Training Center for two years, he watched hundreds of engineering students file iron blocks every single year.

Most people's filing sounds resembled an ongoing argument with the metal.

Alternating between light and heavy, veering left and right, with the file occasionally jamming and emitting a desperate screech.

But Jiang Lin's rhythm sounded like a precision metronome.

Listening with eyes closed, it even carried a hypnotic sense of comfort.

After a dozen strokes, the tooth marks left by the sawing on the end face had been evenly shaved away, revealing a dull, matte metallic luster.

Jiang Lin halted his hands.

Cleared chips, wiped the caliper, and took measurements.

[ 80.14 mm ]

He put down the twelve-inch coarse file, refusing to push any further with it for sizing.

Coarse-toothed files removed material too aggressively; another couple of strokes would put him in the danger zone.

He switched to an eight-inch medium-fine flat file.

His grip changed.

His right hand held the handle, while his left hand no longer pressed down on the front end of the file, instead gently pinching it to serve purely as a guide.

After a few strokes, he measured again.

[ 80.07 mm ]

He switched to an even lighter pushing technique.

Relying solely on the subtle coordination of his wrist and forearm.

He measured.

[ 80.03 mm ]

Jiang Lin put down the vernier caliper, wrapped the workpiece in a cloth to wipe it clean, and stopped working.

Teacher Guo Jianye had been silently timing him the whole time and couldn't help asking, "You're still three microns away from 80. Not going to finish it?"

"The requirement is plus or minus 0.1, and the end face is basically flat now."

Jiang Lin looked at him, his tone completely flat, as if stating a law of Physics.

"If we keep chasing 80.00, even a tiny bit of extra force will increase the risk of over-cutting. If this piece had assembly requirements later to fit with other parts, we could redefine the datum and tolerances for an interference or clearance fit. But in this current isolated task, 80.03 is safer than 79.98. 79.98 is scrap, while 80.03 is a qualified product."

Teacher Guo Jianye couldn't help stepping forward, taking Jiang Lin's vernier caliper to measure the ends of the workpiece himself.

He locked the screw and checked the reading.

It was indeed 80.03 mm.

He loosened it, rotated it 180 degrees, and measured the long side on the opposite end.

80.04 mm.

The error was only a single micron.

This meant that the end face was not only accurate in length, but also virtually perpendicular to the original reference face.

Refusing to give up, Teacher Guo Jianye pulled a precision wide-base try square from the cabinet, placed it against the reference edge and the newly machined end face of the workpiece, and lifted it up to the window to check against the light.

The light leaking through was exceptionally faint—virtually a continuous dark line with no noticeable gaps.

This far surpassed the level of practical training for ordinary undergraduate students.

It was a standard that many young teaching assistants couldn't even achieve.

Teacher Guo Jianye put down the square, picked up the workpiece again, and examined its two long sides.

"In the task just now, I mentioned the parallelism of the two long sides, but I didn't require you to hit a specific tolerance figure," Teacher Guo Jianye asked probingly.

Jiang Lin nodded: "We can add it to the log sheet for measurement."

Teacher Guo Jianye glanced at him and suddenly asked: "In the absence of a dial indicator, how do you measure parallelism?"

"Use a vernier caliper," Jiang Lin replied instantly.

"Take three points along the length—front, middle, and back—measure the width at each point, and check the difference. But this method has limited accuracy and can only serve as a rough judgment because the caliper jaws have slight deformations. If you want higher accuracy, use a micrometer. To be even more rigorous, you should place the workpiece on a surface plate and use a dial indicator or micrometer to scan the edges."

"I didn't give you a micrometer here, nor a dial stand."

Teacher Guo Jianye slammed the workpiece down onto the bench with a heavy thud.

"Then I'll use the vernier caliper for an initial screening."

Jiang Lin took back the caliper, wiped clean the measuring jaws with his thumb, and measured three points along the long side.

Front section: 30.02 mm.

Middle section: 30.01 mm.

Rear section: 30.02 mm.

Seeing these figures, the teaching assistant couldn't hold back this time and blurted out: "Holy crap, was this stock already this exact width when it was rolled? How did you manage to keep it completely unchanged?"

Jiang Lin turned his head to look at him and patiently explained: "I didn't touch the file to the original edges; I only deburred the four corners and edges. Therefore, this parallelism isn't something I created—it belongs to the steel mill's rolling machine. This merely proves that during my clamping and operations, I didn't destroy its inherent original precision."

The teaching assistant froze, his face visibly turning red.

Teacher Guo Jianye let out an abrupt laugh nearby.

"Heh."

He really liked Jiang Lin's remark.

For people in technical fields, the most terrifying flaws were fishing for credit and vanity.

Those who truly knew their craft were never afraid to admit what wasn't their own doing.

Only those half-baked amateurs would take the precision inherently present in the material or provided by the machine tool and claim it as their own achievement to brag about.

"Deburr it," Teacher Guo Jianye said, putting away his smile.

Jiang Lin picked up a slender, fine file.

His movements became exceptionally light and deft.

Four edges, eight corners.

Instead of hacking away at the edges like many students trying to chase aesthetically pleasing rounded corners, he simply swept across them gently with the fine file at a forty-five-degree angle.

His motion was as light as a swallow skimming over water.

He removed only the dangerous burrs that could cut the skin, leaving behind subtle, touchable chamfers that completely preserved the original dimensions.

The final step.

Jiang Lin put down the file, meticulously cleaned the workbench with a brush, and swept all the iron filings into the collection box beneath the vise.

All tools were returned to their exact original positions and orientations.

The measured workpiece sat squarely beside the training log sheet.

When the entire process was complete, the cast-iron bench was so clean it gleamed, making it hard to imagine that someone had just finished performing cutting and grinding operations right there.

Teacher Guo Jianye glanced at the tidy bench, then looked at the piece of low-carbon steel, which resembled a small work of art.

"First piece, pass."

In the elderly teacher's voice, a rare trace of emotion surfaced.

The teaching assistant couldn't help muttering softly nearby: "Teacher Guo, how is this just a pass? Shouldn't it be a full score?"

Teacher Guo Jianye glared at him, his gaze stern.

The teaching assistant quickly shut his mouth and shrank his neck.

Without letting Jiang Lin rest, Teacher Guo Jianye turned around, opened the bottom drawer of the material cabinet, rummaged through it, and pulled out a thin piece of scrap metal.

It was an aluminum alloy plate.

"Second piece, with added requirements," Teacher Guo Jianye said, slapping the aluminum plate down onto the workbench with a sharp snap.

"Just now it was length and straightness; now, let's look at your hole-position logic. Suppose you need to drill a six-millimeter-diameter through-hole right in the dead center of this aluminum plate. The hole center should be twenty-five millimeters from each side. Walk me through your workflow."

Teacher Guo Jianye pressed both hands down on the workbench, staring straight at Jiang Lin.

Jiang Lin reached out and took the aluminum plate.

It felt exceptionally light in his hand.

The aluminum plate was about four millimeters thick, with some surface scratches and clear machine-shearing burrs along the edges.

Instead of immediately answering how he would drill it, his first step was to reach out for the fine-toothed flat file nearby.

Teacher Guo Jianye frowned: "I told you to lay out lines and drill, not to deburr."

"Burrs affect the fit of the straightedge, leading to inaccurate layout baselines. Plus, they cut your hands," Jiang Lin said, already using the file to rapidly shave away the surrounding burrs.

"More importantly, if we mount this on a drill press later for clamping, an aluminum plate with unclean edges and an uneven bottom will make the hold-down clamp unstable, making it prone to deflection."

Teacher Guo Jianye's brow smoothed out, and he didn't interrupt again.

Using a steel ruler, a try square, and a scriber, Jiang Lin quickly laid out the center crosshairs on the aluminum plate's surface.

This time, his movements were even lighter than they had been on the steel plate.

Because aluminum was so soft, pressing even slightly too hard with the scriber would cut a deep groove.

The intersection point was exceptionally fine—still perfectly formed in a single pass.

Center punch, positioning.

True to form, he gave a light tap to confirm first before striking a deeper indent with a heavier blow.

The punch mark landed squarely at the intersection of the two fine lines, with zero visible deviation to the naked eye.

"Good," Teacher Guo Jianye said, rapping on the table.

"Now, if I let you use the drill press, how would you clamp this plate?"

Jiang Lin glanced over the workbench.

He first placed a flat wooden backing board underneath, then picked up two adjacent step blocks and T-slot bolts, and simulated the clamping setup on the workbench.

"This kind of thin plate must absolutely not be drilled directly while holding it by hand."

Jiang Lin's tone turned extremely stern for the first time, as if blood had already appeared before his eyes.

"Why?" Teacher Guo Jianye asked knowingly.

"When the drill bit just enters the material, the cutting force is mainly downward, and a person will develop an illusion that 'I can hold it down.'

But the moment it is about to drill through, the chisel edge at the bottom loses resistance, and the flute on the outer edge of the drill bit will suddenly bite into the thin plate.

At this moment, the downward cutting force will instantly transform into a strong rotational component."

Jiang Lin drew a circle with his finger over the hole position on the aluminum plate and said,

"A four-millimeter-thick aluminum plate, once driven to spin, becomes a rotating flying knife with a speed of several hundred revolutions per minute, and a person's wrist will be instantly cut open."

Hearing this, the teaching assistant's scalp tingled, and he instinctively glanced at his own wrist.

Jiang Lin continued to fiddle with the clamp: "Therefore, it must be firmly fixed. The clamps should be placed on both sides of the hole position, and the distance must be moderate.

They cannot be too far from the hole, otherwise, the area near the hole will warp and deform when the drill bit presses down, nor can they be pressed on the path of the drill bit's retraction."

"Place a wooden board underneath as a sacrificial backing plate.

Receiving the exit of the drill bit can both protect the machine tool workbench and provide supporting force, greatly reducing the tearing burrs at the bottom exit."

"Before officially drilling a six-millimeter hole, I would first use a center drill or a three-millimeter short drill to pilot the hole.

Ordinary standard twist drills are too long and have poor rigidity, making them prone to deviation in soft aluminum."

This set of rhetoric can simply be called textbook-level safety and technological procedures.

Teacher Guo Jianye refused to give up and continued to up the ante: "What if there is no center drill on-site, only the six-millimeter drill bit you need to use?"

"Then minimize the extension length of the drill bit in the chuck to increase rigidity.

Set the feed rate to the minimum when starting to drill, scoop out a conical pit in the manner of micro-drilling, and continue only after confirming there is no deviation."

"What if there isn't even a drilling machine, and there is only a hand-held electric drill?" Teacher Guo Jianye was aggressive; this was already an extreme situation.

"If it is a hand-held electric drill, then it is not this set of procedures.

A hand-held electric drill cannot guarantee that the drill bit is absolutely vertical. If this is an important part, I would refuse to operate.

If it must be completed in the field, the fixture must be redesigned, such as using a thick steel plate with a standard hole as a drill bushing guide.

Otherwise, the hole position accuracy is uncontrollable, and the danger of lateral binding breaking the drill bit is extremely high."

Hearing this, the teaching assistant finally confirmed one thing in his heart.

Teacher Guo was not testing a student participating in basic training at all right now.

He was like facing an old master with equal experience, constantly changing variables to increase the difficulty, trying to squeeze out the very last bit of things from the other party's technical repository.

Yet Jiang Lin's answers were steady and secure.

There was no panic, and no wishful thinking.

It was as if he had already deduced accident contingency plans ten thousand times in his mind.

Teacher Guo Jianye took a deep breath, then slowly exhaled, and put away the scribed aluminum plate.

"Second item, pass."

Having said that, Teacher Guo Jianye seemed to have been stimulated with some long-lost interest today.

This time, he did not take common materials. He bent down and took out a yellowed small wooden box from the year-round locked drawer at the very bottom of the tool cabinet.

The wooden box opened.

Inside, lined with anti-rust paper, were three small-sized gray cast iron test blocks.

Each piece was only about fifty millimeters square, with a thickness of around ten millimeters.

The surface showed a grayish-black color, processed by an ordinary milling machine, and rows of clear circular-arc milling cutter marks were still left on it.

There was no obvious warping, but it certainly could not be called flat.

When Jiang Lin saw those three gray cast iron test blocks, there was finally a subtle flicker in his calm-as-an-ancient-well eyes.

His breathing also became slightly prolonged at this moment.

Teacher Guo Jianye keenly captured this change, the corners of his mouth curving into an arc: "It looks like you recognize this thing. Then let's see first whether you recognize what a true high point is."

Jiang Lin nodded.

Teacher Guo Jianye personally uncovered the covered ordinary inspection surface plate, wiped it carefully with a rag, and then took out a small tube of red lead powder and a bottle of engine oil from the cabinet, mixing out dark red red lead oil.

"You apply it." Teacher Guo Jianye pushed over the palette-like glass plate.

Jiang Lin took the coloring felt scraper.

If earlier during sawing and filing, he was like a merciless industrial machine, a stable slide rail,

then now, he seemed to have suddenly switched into an extremely meticulous, one might even say microscopic state.

The scraper dipped in a bit of red lead oil and pushed it apart on the edge of the cast iron inspection surface plate.

Thin.

Too thin.

That layer of red lead oil was pushed by him to the point of almost fading, leaving only an indistinct red shadow on the cast iron surface plate.

If one didn't look closely, they couldn't even tell there was pigment there.

The teaching assistant watched from the side in utter confusion, unable to help speaking out: "So thin, will it be able to print out points later? Dip a bit more."

Teacher Guo Jianye turned his head and glared fiercely at the teaching assistant, scaring him into swallowing the second half of his sentence.

Many fools think that the thicker the red lead is applied, the clearer the printed high points will be.

Yet they don't know that once the red lead is thick, what is printed on the workpiece is not the contact point at all, but the squeezed and flowing oil film.

You think it is a large piece of high point, but in fact, the middle is completely suspended; when you scrape down with a knife, the originally flat place is directly scraped into a deep pit.

Jiang Lin picked up the first test block with milling cutter marks and gently inverted it onto that extremely thin layer of red lead.

Both palms lay flat against the test block, utilizing only the metal's own dead weight, without applying any downward heavy pressure.

Then, his wrists exerted force, taking the test block to make a figure-eight translation on the surface plate with a stroke of no more than two centimeters.

Stop, lift, flip sides.

On the originally grayish-black bottom surface of Plate A, a few faint red spots appeared.

The red spots were mainly concentrated in the upper-left corner and lower-right corner, forming a diagonal contact.

Among them, the color in the upper-left corner was the heaviest, the exact center even revealing the true color of the metal, and there was a drag mark on the edge extremely like a comet's tail.

Jiang Lin cradled the test block in his hand and took only a glance.

"Single-corner hard point, accompanied by tiny rocking." Jiang Lin's voice was very soft. "The true highest point is not in the center of this large patch of red spots."

He pointed to those two tiny circular dots on the edge of the red spots that revealed the metal's true color.

"At these two compacted points, and that drag mark indicates that just now during translation, because this point was too high, it caused the test block to take it as an axis and undergo a rotation and slip invisible to the naked eye."

Teacher Guo Jianye's eyes suddenly burst with a flash of sharp light.

Without speaking, he directly turned around and groped out a flat-headed manual scraper wrapped with old cloth strips from the tool cart.

The cutting edge of this kind of scraper was made of cemented carbide, ground into an extremely tiny circular arc.

The scraper handle was polished smooth and glossy, not knowing how many years it had gone through.

Teacher Guo Jianye handed the scraper over.

"You can only scrape three strokes. Now tell me, where do you want to scrape?"

Jiang Lin took the scraper carrying the other's body temperature, gripped it in his hand, and weighed it.

"What is the target?" Jiang Lin asked in return.

This question was asked extremely well, extremely wonderfully.

Hearing that they could only scrape three strokes, many people's first reaction would be to wave the scraper and level the reddest area.

But scraping without a clear target is not reconditioning, but destroying the original surface support force.

Teacher Guo Jianye took a deep breath: "Make its contact points a bit more dispersed. Don't pursue flatness; just break the current support state."

"Understood."

Jiang Lin adjusted his stance, tightly gripping the back end of the scraper handle with his right hand, pressing it against the position of his right waist and hip bone, and holding the front section of the scraper with his left hand to apply downward pressure.

The scraper edge pressed against that upper-left corner compacted point that emitted white light.

"Chi."

The sound was short and crisp.

The first stroke was extremely short, with a travel of less than three millimeters.

As precisely as performing surgery, he only picked off a tiny peak, flicking up a sliver of iron filings thinner than a hair.

For the second stroke, the blade shifted and fell on the second-highest point in the lower-right corner on the diagonal side.

"Chi."

The third stroke.

The teaching assistant thought he would go scrape that patch of red spots.

But Jiang Lin's third stroke accurately fell on the very end of that comet drag mark.

"Chi."

The three strokes ended.

Jiang Lin withdrew the knife and stepped back.

The teaching assistant's face was full of confusion; he completely failed to understand what significance these three light-floating actions had.

The red spots were still there!

Teacher Guo Jianye understood.

Understood to the point that his breathing became somewhat heavy and thick.

The end of that drag mark was the equilibrium critical point where the contact state switched when the test block rocked.

Scraping there was equivalent to pulling out a wedge that made the seesaw tilt.

This was ten thousand times more brilliant than blindly scraping the center of the stressed red spots.

"Re-reveal the points," Teacher Guo Jianye commanded.

Jiang Lin picked up the rag and wiped the test block clean.

This time, Teacher Guo Jianye personally re-pushed a very thin layer of red lead on the surface plate.

The test block was put back on, gently pushed in a figure-eight, and flipped over.

This time, although the distribution of red spots on the bottom surface was still ugly, the pattern had completely changed.

The stubborn contact points originally concentrated in a single corner had dispersed.

The upper-left corner was no longer a patch of red, and the right side and lower-middle part miraculously gained a few faint light contact points.

In just three strokes, the mechanical support state was completely shattered and reorganized.

Teacher Guo Jianye stared at that test block for a very, very long time.

Then, without saying a word, he pushed the second and third pieces in front of Jiang Lin as well.

"The same three strokes."

This was the third time upping the ante.

The teaching assistant really felt scared this time.

He looked at Teacher Guo Jianye; Teacher Guo's current state was like he was bewitched.

This was no longer making a demonstration for a high school student; this looked like two peerless masters in a wuxia novel engaging in a closed-door magical duel deep in the mountains and forests.

Teacher Guo Jianye did not explain.

Jiang Lin did not ask either.

The problem with the second plate was completely different from the first plate.

After being placed on to reveal points, what appeared on the bottom surface was not isolated spots, but a strip-like red mark slanted from the upper-left to the lower-right.

Jiang Lin swept his gaze: "There is macroscopic distortion on the surface, not a single-point protrusion. Three strokes cannot level it; we can only adopt the truncation method to first break the continuous support of this highest band."

"Chi, chi, chi."

Three strokes went down.

It was like building three dams in the middle of a river.

Re-revealing points.

The strip-like red trace was indeed interrupted, two isolated contact areas appeared, and the trend of distortion was curbed.

The third plate.

Apply red lead, reveal points, flip sides.

This time, Jiang Lin held the third plate, staring at it for a full ten seconds without making a stroke.

"Why aren't you scraping?" Teacher Guo Jianye asked with a frown.

"This cannot be scraped." Jiang Lin raised his head.

"Why?"

"The distribution of the red spots has no stable and repetitive characteristics." Jiang Lin pointed virtually at those cluttered red spots with his finger. "There is a patch in the middle that is extremely red, but the edges carry blurred shadows. This does not conform to the mechanical normality of a milled surface. The greatest possibility is that the surface of the test block was not wiped clean and left oil stains, or a hard dust particle from the air was brought in during movement just now, causing the entire test block to be suspended."

Jiang Lin put down the scraper: "Encountering such fake points and directly cutting down is equivalent to forcibly scraping a non-existent high point into a real low pit. It must be cleaned and re-revealed."

Hearing this, Teacher Guo Jianye finally burst out with uncontainable radiance in his eyes.

Being able to accurately locate and cut down on the first two blocks showed that this young man's hands were extremely steady and his eyes were extremely piercing.

Resisting the urge to cut down in front of the messy red points on the third block showed that he had an extremely calm brain and absolute awe of variable control.

This is the true soul of a fitter!

"Go, get alcohol and dust-free cloth," Teacher Guo Jianye hurriedly ordered the teaching assistant.

The teaching assistant scrambled to fetch the cleaning supplies.

Jiang Lin meticulously cleaned the three plates and the surface plate all over again, re-applied red lead, and revealed the points once more.

This time, when the third plate was flipped over, that most prominent large red spot in the middle miraculously disappeared.

Replacing it were several uniform, true contact points along the edges.

The teaching assistant gasped a breath of cold air.

If that stroke had been scraped down just now, this plate would have truly been ruined.

Teacher Guo Jianye picked up that test block, turned around, and took it under the light to examine it back and forth for a long time.

Then, he slowly turned back around and carefully placed those three small cast iron test blocks back onto the tabletop in the order of one, two, and three.

He looked into Jiang Lin's eyes and said: "What you truly want to do is not this kind of playing house where you only scrape three strokes, right?"

Jiang Lin looked at him quietly without answering.

Teacher Guo Jianye pointed to those three pieces of gray cast iron: "You want to do the Three-Plate Grinding Method."

The teaching assistant nearby trembled all over upon hearing these four words.

"Three-Plate Grinding Method".

These four words were just a short page in mechanical engineering textbooks.

In the fitter teaching of the Engineering Training Center, they were merely an ancient myth casually mentioned when teachers taught the history of how humanity manufactured industrial mother machines with absolute flat planes.

Whitworth Three-Plate Grinding Method.

Without relying on any external benchmarks, relying solely on three uneven iron plates: A and B are ground together, B and C are ground together, and C and A are ground together.

Through this marvelous alternating cancellation, they ultimately manage to create something out of nothing, scraping out three flat surfaces.

To actually have students do this in a practical training class?

It is nearly impossible.

It is too slow, too tedious, and relies far too heavily on manual skill.

Furthermore, ninety-nine percent of students simply cannot understand the process of the red lead spots slowly evolving from one or two large patches at the very beginning into a sky full of stars.

They would only hack away randomly, ultimately scraping the three iron plates into three unsightly spherical surfaces.

"Yes." Jiang Lin met Teacher Guo Jianye's gaze without any evasion.

Teacher Guo Jianye stared at him for a moment, then suddenly turned around and took out a thick hardcover logbook from the deepest part of the cabinet.

Opening to a new page, he slapped it down on the desk.

"Very well."

The teaching assistant instinctively tried to stop him: "Teacher Guo, this isn't in the syllabus, and besides, it's too time-consuming."

Teacher Guo Jianye raised a hand to cut him off.

"These are not official surface plates." Teacher Guo Jianye pointed at the three test blocks. "Fifty-millimeter teaching samples, I'll give you one hour. Stop every fifteen minutes and let the assistant take pictures to record the distribution of the red lead spots."

Teacher Guo Jianye raised a single finger: "You are only allowed to use a manual scraper; no grinding wheels and no surface grinders are permitted. Today, I only care about your method and logic, not how many points per square inch you can ultimately scrape."

"Can you accept this?"

"Yes." Jiang Lin replied.

"There's one more rule: you must not get lost in it." Teacher Guo Jianye suddenly heightened his tone, as if issuing a precaution. "I've seen many veteran masters who, the moment they get a scraper, have eyes only for those red spots and forget even the passage of time. This is the Center, not your personal workshop. Every fifteen minutes, whenever I call to stop, you must stop immediately."

"Understood." Jiang Lin picked up a pen.

On the sides of the three test blocks, he carved respectively: [A] [B] [C]

Then, he wrote down a plan in the logbook.

[Objective: Mutual grinding of three small-sized cast iron test blocks, observing the macroscopic trend of contact points evolving from localized hard spots to a uniform distribution.]

[Limitations: The material of the teaching samples is uneven; they will not be used as official benchmarks.]

[Recording cycle: 15 minutes per session.]

Teacher Guo Jianye originally wanted to remind him of a few precautions.

But the engineering thinking revealed in those three lines of text made him swallow his words back down.

"Begin."

Jiang Lin began his true performance.

Step one: cleaning.

Jiang Lin first used a brush to thoroughly clean the workbench, then rinsed the inspection surface plate and test blocks with a large amount of alcohol, and finally dried them with non-woven fabric.

Mixing the red lead, making it extremely thin.

Round one.

A is coated with red lead, and B is pushed gently over it.

Jiang Lin's movement was very short.

Lifted, two dense red patches appeared on the bottom surface of plate B.

Jiang Lin did not rush to scrape; instead, he had B and C reveal their spots, followed by C and A.

After all three sets of red lead diagrams appeared, he picked up a 2B pencil and drew a simplified mechanical topology diagram on the record sheet.

[A-B: Double-corner hard points (concave-convex complementary)]

[B-C: Diagonal strip contact (twisted)]

[C-A: Unilateral high point (wedge-shaped)]

Teacher Guo Jianye stood to the side, looking at that schematic diagram, his breathing slowing by half a beat.

Many people doing the Three-Plate Grinding Method would scrape the moment they saw a red spot.

But Jiang Lin first established a three-dimensional error relationship model among these three plates.

It was as if he wasn't repairing a plate, but rather solving a complex three-body error equation in his brain.

Jiang Lin finally picked up the scraper.

The first cut landed on the edge of the hard point in the upper left corner of plate A.

"Ssssh."

The second cut landed at the end of the diagonal strip contact on plate B.

"Ssssh."

The third cut landed at the turning point of the unilateral high point on plate C.

"Ssssh."

He didn't crazily chase after the reddest areas like ordinary people would; instead, every single cut was like striking a vital acupuncture point, precisely severing the force-bearing nodes supporting the entire distorted structure.

Fifteen minutes passed extremely quickly.

"Stop."

Teacher Guo Jianye spoke right on schedule.

Jiang Lin's hand had just lifted. Hearing the voice, he didn't even finish swinging his blade; he hovered it directly in mid-air, then gently put the scraper down.

Absolute obedience to orders.

Teacher Guo Jianye nodded with satisfaction.

Truly difficult-to-manage masters are often not those who don't know how, but those who are too fanatical to stop.

The assistant hurriedly stepped forward to take pictures.

Re-revealing the spots.

The red spots on the three plates no longer crowded into the corners to form ugly large patches like they did at the beginning; instead, they began to fracture and spread toward the center.

Although it was far from flat, the trend of evolving toward a flat surface was correct.

The assistant wrote down in the logbook: [15 minutes: Hard points dispersed, contact area expanded from the corners to the center.]

Round two.

Jiang Lin's movements became even slower.

He began to consciously shorten the length of each cut.

The cutting edge of the scraper slid across the cast iron surface, no longer acting as a cutting plane, but rather severing the continuous support between those tiny high points.

A grinds B, B grinds C, C grinds A.

Repeating in a cycle.

At the twenty-seventh minute, a small episode occurred.

A bright spot suddenly appeared on plate B that was redder than everything around it.

The assistant thought Jiang Lin would definitely shovel it away with one cut.

But Jiang Lin stared at that red patch for two seconds, decisively put down his blade, wiped plate B clean again, applied a thin layer of red lead on plate A anew, and revealed the spots once more.

That vibrant red dot disappeared.

"A false particle point," Jiang Lin said without lifting his head, "cannot be scraped."

Teacher Guo Jianye glanced at the assistant, his eyes full of instruction: "This is what we call composure, write it down."

The assistant hurriedly wrote like flying: [27 minutes: Identified a false particle point, re-revealed after cleaning, no erroneous scraping. This is not just technique, but cultivation.]

Round three.

Jiang Lin's hand was so steady it was practically like a block of cast iron.

Scraping is completely different from the filing just now.

Filing is continuous, rhythmic physical labor.

Scraping involves short bursts of exertion, instantaneous judgment, immediate stopping, and judgment all over again.

It consumes mental energy to an extreme degree.

Every time he brought down his blade, it was like micro-carving.

Looking at the red spots, judging high and low.

Dropping the blade, retracting the blade, cleaning, revealing spots.

The sounds in the workshop became extremely light.

Only the occasional slight Ssssh sound from the scraper.

I don't know when it started, but outside the fitting area, two undergraduate students who were originally on duty in the lathe area also curiously wandered over.

They completely failed to understand what Jiang Lin was doing.

In their eyes, Jiang Lin was just holding a broken blade and rubbing it back and forth on three iron pieces.

But they could feel a strange atmosphere.

Teacher Guo Jianye, who usually always swore and looked down on everyone, stood straight with his hands clasped behind his back at this moment, looking like he didn't even dare to breathe heavily for fear of blowing away the dust on the surface plate.

The air in the entire fitting area seemed to have become solemn and sacred because of those three fifty-millimeter iron blocks.

Thirty minutes.

"Stop." Teacher Guo Jianye called to stop for the second time.

Jiang Lin stopped his blade and re-revealed the spots.

The moment the three test blocks were flipped over, the assistant's eyes went wide.

The red spots were completely shattered.

No longer those ugly large red patches.

On this tiny fifty-millimeter square surface, a dozen or so small, blurry red contact points were scattered like stars in the sky.

Although these points were not yet uniform, with fewer in the edge areas and slightly heavier in the center, they were still far from reaching the sky full of stars level of twenty-five points per square inch found on industrial machine tool guide rails.

However, these three pieces of iron already had the embryonic form of a datum plane.

They were no longer teaching scrap casually cut out by machines.

They had a soul.

"In the past dozen minutes or so, were you intentionally avoiding the central area when making your cuts?" Teacher Guo Jianye stared at the test blocks and asked uncertainly.

"It's not avoiding." Jiang Lin wiped a trace of sweat seeping from his forehead, "It's because of the temperature."

"Temperature?" The assistant was stunned.

Jiang Lin pointed at his own hand: "This size is too small, and the heat capacity is extremely low. Every time my palm gets close to it and presses down on it, human body heat is conducted to the cast iron. Localized heating in the central area will produce microscopic thermal expansion. If in the final stage I keep chasing after the red spots showing up in the center to scrape them, it's very easy to mistake the false high points produced by thermal expansion for real high points and scrape them off. Once the test blocks cool down, the middle will instead become a concave pit."

"We don't have the conditions of a constant-temperature room today, so we can't chase the extreme; we can only push from the edges, and each spot-revealing action must be extremely short."

Teacher Guo Jianye let out a long breath of turbid air trapped in his chest.

This sentence completely shattered the very last trace of doubt in his heart.

Understanding the impact of microscopic thermal expansion on contact points—how could this possibly be just a student?

This is a craftsman who has truly undergone rigorous tempering and understands the microscopic life of metal!

The last fifteen minutes.

Teacher Guo Jianye didn't interject a single word more.

Jiang Lin continued the cycle of A grinding B, B grinding C, and C grinding A.

The rhythm was so steady it made one's scalp tingle.

Until the forty-fifth minute.

Teacher Guo Jianye glanced at his watch: "Stop."

Jiang Lin put down the scraper and moved his slightly sore right wrist.

The assistant immediately rushed up to take pictures and record.

The final spot-revealing.

On the surfaces of the three test blocks, a relatively uniform and fine layer of red spots appeared.

Although limited by time, material, and temperature, there were still deficiencies at the edges, and some local unevenness in weight, and it wasn't perfect enough.

But it was enough.

Jiang Lin picked up a rag and wiped the red lead clean.

Then, he gently placed plate A onto plate B.

Without applying any pressure, he just pressed his fingers against the side of plate A and tried to push it flatly.

It didn't budge.

Between the two clean little pieces of cast iron, an extremely obvious sense of fit and resistance appeared.

The microscopic contact points interlocked with each other, and the extremely flat surfaces squeezed out the air in between, forming a weak vacuum negative pressure.

Seeing this scene, Teacher Guo Jianye couldn't help stepping forward.

He stretched out his calloused hand, pinched the upper plate A, and tried to lift it upward.

Plate B underneath was actually sucked along with it, leaving the ground slightly by one millimeter before dropping back onto the workbench with a smack.

That was the purest physical suction between two flat pieces of metal.

The workshop instantly became extremely quiet, and even the roaring sound of machine tools in the distance seemed to have vanished.

"Jiang Lin."

Teacher Guo Jianye called his name, his voice hoarse.

"According to undergraduate standards, I can't give you a score for this piece of work. Because the task is too low-level; it doesn't match your skill. However, I still can't let you directly operate the lathes and milling machines today—those are safety rules. Even if you were an immortal, you can't break the rules without going through the process."

"I understand." Jiang Lin nodded; he respected rules the most.

"But if we are only talking about the basic fitting skills of sawing, filing, scribing, center-punching, spot-revealing, and scraping."

Teacher Guo Jianye looked around at the bench vices, files, and measuring tools in the surroundings, and finally let his gaze fall back onto Jiang Lin, smiling self-deprecatingly.

"Here at the Engineering Training Center, I have nothing left to teach you. Perhaps the only thing I can tell you about is where the approval process is located in this building."

This sentence was the highest verdict given by a veteran practical training teacher who had worked half his life in the Engineering Training Center and touched countless pieces of steel, after witnessing a complete set of controlled operations that could be called art.

It was heavier than any score.

The assistant nearby looked at the thick training logbook, his pen tip suspended above the teacher's evaluation column, unable to fall for a long time.

He found that he didn't know what words to use to evaluate that complete set of actions just performed by this student.