49: Chapter 49 Unstable Machine

On the evening of the second day, Jiang Lin sawed out a cut that was relatively close to a straight line for the first time.

Or rather, relatively close to a straight line.

At least to the naked eye, it finally had a bit of industrial geometric dignity, no longer a one-sided slaughter of the material.

That piece of flat steel was clamped in the vise, and looking at the cut from above, it no longer had that incredible arc of yesterday.

Of course, the burrs on both sides of the kerf were still heavy, and the end face was rough.

Therefore, he did not rush to be happy.

After the try square was placed against it, the lower left corner steadily touched the metal first, but the upper right corner was tilted up, leaving an obvious gap.

This meant that in the second half of the sawing process, his hand or the posture of the hacksaw frame had shifted, causing the cutting surface not to be a perfect vertical plane.

He picked up the feeler gauge again, pulled out the 0.10 mm blade first, and tentatively tried to insert it into that light gap.

Without any resistance, the blade slid right in.

He then pulled out the 0.15 mm blade, probed inward, felt a slight frictional force, but with a little effort, it still went in.

Next was 0.20 mm.

This time, the front end of the blade got stuck just as it touched the edge of the gap and could not go in.

0.15 could go in, 0.20 could not go in, so the actual clearance might be 0.16, or it might be 0.19.

This could only be considered a very rough estimate.

But this rough estimate was already enough to explain the problem.

It was cut crookedly.

But after all, it was better than yesterday.

Now this piece at least required taking out the tools in his hand to inspect, evaluating with the light gap and measuring with the feeler gauge, just to know how many millimeters it was crooked.

This was progress.

Very small.

So small that if it were placed in the Real World, Professor Lu Zhixing would probably just hold a thermos cup, stand aside and glance at it, and then say in that calm tone: "It's still early, keep practicing."

Jiang Lin released the crank of the vise, took down the flat steel, and gently rubbed the edge with the pad of his thumb.

The pad of his thumb was immediately scratched with a pale mark by those sharp burrs.

He rubbed his thumb against his rough trouser legs, took the piece of flat steel, and walked to the other side of the workbench.

He picked up a red marker and wrote a row of serial numbers on the relatively flat side of the material.

[Sawing Sample 002]

Then he followed up with a record in the logbook next to him.

[Unqualified, but the deviation direction is clear, recordable, and traceable.]

Starting from this evening of this day, Jiang Lin established a rule in his work habits.

He divided all the failed scrap into two categories.

One was pure waste with no analytical value at all.

It was thrown directly into the large scrap box in the corner of the stone house.

For example, the short pieces left behind when the saw blade suddenly broke due to uneven force, or the material whose entire end face was torn apart in vibration due to loose vise clamping.

Those things could only prove that his brain was offline at the time and his operation had serious errors. Other than wasting a section of steel, they could not provide him with any information about microscopic movement errors.

The other kind was the failed sample he was holding in his hand, which could expose specific problems and let him know where he started to go wrong.

In the evening, he reread Theoretical Mechanics.

He opened the chapter on rigid bodies, constraints, and virtual displacements.

In the past, when he read the content of these chapters, the images that emerged in his mind were very clean.

What he thought of were smooth sliders sliding on frictionless tracks, ideal light rods of constant length, mass points without volume, and generalized coordinates that could be defined at will.

They were the clearly-lined carts, inclined planes, and pulleys in the textbook illustrations, the force analysis diagrams that could be cleanly drawn on draft paper with a ruler and pencil, and the elegant equations of the principle of virtual work under ideal conditions.

But tonight, when his gaze swept across those familiar definitions and formulas again, they suddenly felt three-dimensional.

He no longer thought of those ideal sliders that did not exist in reality, but rather his own shoulders, elbows, wrists, waist, knees, and the lumbar spine and knees that provided support during pushing and pulling movements.

He thought of the imperfect trajectory when the manual hacksaw frame was held in his hand.

He thought of the low-carbon steel material clamped tightly by the vise.

Why was it that even though he had turned the crank to clamp it dead tight, even leaving indentation marks, when the sawing entered the final stage and the cutting surface of the saw blade became extremely narrow, that piece of steel would still experience slight lateral deviation?

The theory had not changed.

The laws written by Newton and Joseph-Louis Lagrange still ruled every atom on this Wasteland.

What had changed was himself.

It was these cold theories that finally found a foothold inside his body, amid his sore muscles and calloused hands.

Theory was beginning to find hands.

[Sawing is not a simple single action at all. It is a complex constrained system jointly composed of a person, a hacksaw frame, a saw blade, a workpiece, a vise, and even the ground.]

[In this system, the ideal trajectory of the saw blade is an absolute straight line. But in actual physical space, this trajectory is subject to the interference of too many non-ideal factors: the unconscious swing of the wrist, the phase difference when the shoulder and elbow cooperate, micro-vibrations caused by insufficient vise stiffness, or even the biasing force generated by uneven material when the teeth bite into the metal. The tiny errors of every link will be magnified in this system and ultimately reflected on that crooked kerf.]

After writing this paragraph, he stared at the four words constrained system, feeling it was a bit like classroom notes.

Like the countless Physics formulas he had memorized in the past and the pile of seemingly perfect theories he had derived, yet things that were never truly put into practice.

So he picked up his pen and added a sentence.

[Currently, theory cannot be used to solve even a millimeter of deviation, but it can only be used to remind myself where I should look and which link of constraint has failed when my movement goes wrong.]

On the third day, Jiang Lin did something he knew he had to do back in the garage, but had always avoided with various excuses and never truly done.

He began to seriously study his arms.

It was not research in the literal sense of medicine or anatomy.

He picked up the medium-toothed flat file from the workbench.

Clamped in the vise was still the twin brother of the flat steel 001 that had been filed intermittently for two days.

He took a good stance, held the wooden handle with his right hand, and pressed down on the front end of the file with his left hand.

Then, at a speed so slow that time felt like it was standing still, he began to push forward.

Under normal circumstances, pushing the file out only took a fraction of a second.

But now, he lengthened this process to a full five seconds.

When pushing to the halfway point of the stroke.

"Stop."

He shouted in his heart.

His body froze instantly, his muscles tensed to maintain this suspended posture.

Then, like an outsider, he slowly lowered his head, his vision leaving the contact surface of the file, moving along his left hand to the web of his right hand, then along his forearm, looking at his wrist, his elbow, and finally turning his head to look at his right shoulder.

For the first time, he looked.

Aside from feeling sore muscles, he didn't see anything.

Every joint seemed to be in the position it should be in.

Jiang Lin removed the file, straightened his waist, and took a deep breath.

He reset his posture and tried again.

This time, even slower.

So slow that even the sound of the file teeth rubbing against the steel material became intermittent.

Push, one-fifth.

Push, halfway.

Push, roughly at two-thirds of the stroke.

Jiang Lin's gaze was fixed intently on his right wrist.

At that very instant, he finally saw it.

He saw his right wrist undergo an unconscious inward-rolling movement at the node where his forearm continued to push forward.

The amplitude was extremely small.

So small that if he didn't slow down the speed tenfold to stare at it, it would be completely imperceptible.

If it were pushing the file at normal speed, with a swish, this inward-rolling movement would be completely swallowed by strong muscle inertia and the sharp sound of filing, like a speck of dust falling into a violent wind, disappearing without a trace in the blink of an eye.

No wonder he had always filed surfaces that were low at both ends and high in the middle, or skewed.

He had no idea he had this little habit before.

It wasn't because he didn't check his posture, but because the speed was too fast when checking.

Human visual persistence and brain processing speed simply couldn't catch the maladaptive movement happening in such a transient instant.

Jiang Lin put down the file, picked up his pen, and recorded this major discovery in the logbook.

[Discovery: When the filing action proceeds to about two-thirds of the stroke, the right wrist has a clear tendency to roll inward, with a visual estimated angle of about 5 degrees.]

[Hypothesized cause: This is the body's instinctive compensation. When pushed to this position, the range of motion of the shoulder joint may be close to the limit of a comfort zone, or the contraction of the pectoralis major is insufficient to continue providing smooth forward power. In order to push the file through the final third of the stroke, the body gave up using large joints and instead turned to the most flexible but also most unstable wrist to compensate for this distance.]

[Consequence: This compensatory action will cause the file to lose parallelism in the final stage, the front end to deflect toward the lower left, and the file teeth on the right side will produce an unplanned amount of cutting on the right side of the steel surface. Over time, this forms a systematic error of being low on the right and high on the left.]

When writing 5 degrees, Jiang Lin thought this number was too unrigorous.

Because this was not measured with a protractor, but purely visually estimated based on his sense of space.

So he rigorously added a set of parentheses afterward.

[(Note: The angle is only a rough visual estimate and has no data reference value. Subsequent verification of the destructive power of this angle must be done inversely based on the actual light-transmission inspection results of the filed surface.)]

Putting down his pen and looking at the scratch-covered flat steel, Jiang Lin turned the whole matter over and over in his mind for a while.

The inward rolling of the wrist was definitely not an accidental phenomenon that only appeared today.

It had always existed in every single one of hundreds, thousands of filing pushes.

His body was using a concealed erroneous action to make up for another physical limitation.

And in all his past training, in his self-righteous efforts, he had turned a blind eye to this error that happened thousands of times every day.

"Fine." Jiang Lin muttered to himself, "Since it has been found, let's uproot it."

He picked up the file again and started a new round of torture.

If just now was slow motion, now it was stop-motion animation.

He forced himself to reduce the speed of each filing push to one-third of usual.

Push a little, stop, see if the wrist rolled.

Push a little more, stop, see if the shoulders shrugged up.

Continue pushing, stop, feel if the angle of the elbow was correct.

A full twenty minutes.

The surface of the flat steel had almost no substantial cutting progress, and not even a layer of black scale had been completely filed off.

But Jiang Lin himself had already sweated through his clothes in the cold weather.

This deliberate slow-motion disassembly was a hundred times more agonizing than high-intensity normal filing.

Because it completely broke the coherent memory of the muscles.

Every pause would cut off the conduction of power, and every observation of a certain joint would cause other muscles to become stiff and unnatural in order to maintain that awkward suspended posture.

He found that in order to see clearly an action of his wrist, his neck and back would instead make another more distorted wrong posture.

A sense of irritability surged up in his heart like overgrown grass.

Jiang Lin slapped the file onto the table somewhat annoyed, turned around and strode to the door of the stone house, shoving open that broken door pieced together from waste wood boards.

The cold, dry wind on the Wasteland instantly poured into his collar, causing him to shiver, but it also cooled down his somewhat burning brain.

He picked up the thermos cup, tilted his head back to gulp down a few mouthfuls of hot water, and stood in the cold wind slowly rolling his sore right shoulder forward three times and backward three times.

A slight clicking sound came from the bone joints.

The feeling of obstruction left after long-term repetition of the same mechanical action was very obvious.

He felt it.

When the shoulder pushed the arm to the final stage, the joint capsule and ligaments were like a tightened rubber band, beginning to reject further forward extension.

The shoulder was unwilling to go on, while the command issued by the brain was that the file must be pushed to the end.

Thus, the wrist volunteered to jump out and finish the last bit of the journey for the shoulder.

This was very reasonable in biomechanics.

It protected the joints from being strained and saved physical energy.

But in the geometry of fitting, this was terrible.

Jiang Lin closed the door, locking the cold wind outside, walked back to the workbench, and instead of immediately picking up the file, he pulled over the draft paper with geometric figures drawn on it.

In the blank space of the paper, he drew a simple diagram of a stickman arm linkage mechanism.

Three small circles representing the shoulder, elbow, and wrist were connected by several thick black line segments.

Next to them were arrows pointing in different directions with varying lengths, indicating the approximate direction of movement and range of amplitude for each joint during the filing process.

He drew a heavy red circle around the small circle representing the wrist, and another red circle around the one representing the shoulder.

Finally, between the two red circles, he drew a connecting line with an arrow.

Beside the line were written two characters: compensation.

Looking at that word, Professor Lu Zhixing's words suddenly echoed in his mind without warning.

"A good experimental feel often comes from the hands, not from the brain."

When he heard this sentence back then, he felt it had a very philosophical meaning.

Only now did he realize that he hadn't truly understood it at that time.

Understanding doesn't mean you grasp the literal meaning of the sentence.

Rather, it means that one day, you force yourself to slow down a simple movement enough to clearly see the wrist pronating by a mere five degrees.

Then, you truly understand what these five degrees mean on the metal end face and in the subsequent assembly.

He picked up his pen and continued recording in his logbook, the words between the lines appearing much calmer.

[The human arm is essentially an extremely complex multi-degree-of-freedom linkage mechanism. Even if you just want to stably press the light-transmitting gap of a simple filed surface down to the order of one-hundredth of a millimeter, you can never rely on the brain to forcibly lock a certain joint with willpower. Muscles will fatigue, willpower will relax, and locking is ineffective.]

[The correct path is: By adjusting the standing posture and the method of exerting force, adjust this complex linkage mechanism into a motion configuration that is less prone to producing compensation. Then, in this configuration, repeat it tens of thousands of times until it bypasses the brain and becomes the default basic action of the cerebellum and muscles.]

[My current problem is not that the wrist is making a mistake, but that the wrist is making a mistake on behalf of the shoulder. The inward rotation of the wrist is compensating for the restricted movement at the end of the shoulder joint. Therefore, if I want to resolve this five-degree deviation of the wrist, my eyes cannot just stare at the wrist. I must first solve the stroke problem of the shoulder.]

After finishing this analysis, which was akin to a biomechanics paper, Jiang Lin put down his pen.

He started over.

"Adjust the configuration," he muttered under his breath.

He began trying to change his standing posture.

For the first time, he tried to rely on the inclination of his body to increase the shoulder's stroke.

He leaned his entire body forward a little bit, placing his center of gravity on the balls of his front feet.

Push.

As soon as the file moved forward a short distance, he immediately felt something was wrong.

Because the center of gravity was too far forward, the weight of his entire upper body pressed down along his arms onto the file.

The downward pressure in the first half was astonishingly huge, and his hands immediately felt the biting sensation of the file teeth sinking deeply into the steel material.

It couldn't be pushed.

This was no longer cutting metal; it was simply like trying to forcibly press the file into a steel plate.

He stopped immediately, retreated to his original position, and restored his standing posture to normal.

For the second time, he did not lean his body, but instead moved only his left foot forward by half a sole's distance, trying to widen the span of his lower stance.

Push.

The stroke was indeed a bit longer, but by the final stage, the wrist still unconsciously pronated slightly.

The pulling sensation in the shoulder did not lighten by much.

For the third time, he deflected the angle of his right foot outward by about twenty degrees.

Push.

This time his shoulders felt a bit more comfortable, and when pushed to the final stage, there was not such a strong sense of blockage.

However, because the lower body was twisted while the upper body had to remain straight facing the vise, it caused his waist to produce an awkward twisting sensation.

Standing like that for a long time would definitely be too much for his lumbar spine.

For the fourth time, he simply doubled the distance between his feet, standing in a posture similar to a horse stance.

Push.

When pushed to the middle stage, tragedy struck.

Because the chassis was too wide, his legs could not provide flexible fine-tuning, causing the core of force exertion to shift to the waist.

Once the waist got involved, the trajectory of his entire upper body became completely chaotic, and the file drew an ugly arc on the workbench surface.

Jiang Lin straightened up, rubbed his sore lower back, and picked up his pen to quickly record these failed attempts.

[Error Adjustment Record:]

[1. Excessive overall forward lean: Will catastrophically increase the downward pressure in the first half, which is not only laborious but will definitely introduce new surface shape errors (highly likely to cause over-cutting in the front half).]

[2. Excessive distance between feet: Causes the waist to passively participate in too much force exertion, resulting in an unstable core and the complete destruction of the linear trajectory.]

Then he continued trying.

His mindset had now completely settled down.

He was very clear that he wasn't looking for the single correct answer printed in textbooks.

Everyone's arm span, bone proportions, and muscle strength are different, so there is no universal perfect standing posture.

Among a pile of incorrect postures that would trigger various compensatory movements, he had to use elimination to get closer and closer to the sub-optimal solution suitable for his body, bit by bit.

The position of the front foot, the angle of the back foot, the distance between the two feet, the degree of slight bend in the knees, and the landing point of the center of gravity.

Every time he made a fine adjustment, he would pick up the file and push once.

He concentrated all his attention on that critical point at two-thirds of the stroke, feeling whether his shoulders were once again forced to their limits and whether his wrists were itching to come out and substitute for them.

This trial-and-error process was extremely tedious and energy-consuming.

Moving his feet back and forth in front of the vise like this, pushing and pulling the empty file.

He tried for nearly forty minutes. Sweat soaked the clothes on his back.

Finally.

Amidst who knows how many dozens of fine-tuning sessions, he found a relatively fitting standing posture.

The front foot was moved forward by about half a sole compared to the initial standard posture, with the toes pointing straight at the workbench.

The back foot was deflected outward by about thirty degrees to provide lateral support.

The distance between the feet was kept slightly wider than shoulder width.

The overall center of gravity was slightly forward, distributed sixty percent on the ball of the front foot and forty percent on the back foot.

But his upper body remained relatively upright, absolutely not pressing his body weight onto the file.

Under this specific standing posture configuration, he took a deep breath and pushed the file out steadily.

When the stroke reached two-thirds.

His shoulders slid forward smoothly without that blocked feeling of being pulled to the limit.

Meanwhile, his wrists still maintained a stable posture, no longer showing that obvious inward pronation.

Jiang Lin withdrew the file, pushed again, and did this continuously five times.

He observed carefully.

The inward pronation did not completely and miraculously disappear; that was an instinct of human muscle groups during fine operations.

However, the amplitude of the inward pronation had significantly reduced from the initially estimated five degrees down to only about two degrees.

It shrank to the point where it was almost controlled at the edge of acceptable error tolerance.

Jiang Lin let out a long breath, feeling as if he had won a localized battle.

He solemnly wrote down in his notebook.

[Phased achievement: After reconstructing and adjusting the standing posture, by releasing the effective stroke of the shoulder, the inward pronation compensation amplitude of the right wrist at the final stage is reduced to about 2 degrees.]

[Evaluation: Although it failed to achieve complete elimination under the ideal state, the systematic directional error should have a significant physical improvement. Specific conditions require continuous observation of the inspection results of the subsequently processed filed surface.]

After writing, he put down his pen and took down that tortured flat steel.

He brushed away the iron powder on the surface with a brush, then picked up the square and feeler gauge to begin inspecting this sample piece that bore all his early errors.

The inspection results were naturally very ugly.

The right side was indeed slightly lower than the left side.

When he leaned the square against it longitudinally and faced the light source behind, the leaking light gaps were distributed extremely unevenly.

The gap on the left was relatively large; he tried to probe it with a feeler gauge, and a 0.08 mm blade could barely be inserted.

On the right side, due to the long-term inward pronation and excessive cutting of the wrist, the gap was much smaller, and a 0.04 to 0.05 mm blade would get stuck as soon as it went in.

Jiang Lin calculated quickly in his mind.

Roughly estimated, the entire right side was lower than the left side by about 0.03 to 0.04 millimeters.

This data perfectly corroborated the direction of his previous deduction.

The inward pronation of the wrist led to excessive material removal on the right side.

Looking at this data, Jiang Lin instead let out a sigh of relief in his heart.

This showed that the linkage compensation mechanism he had spent so much time deducing before was not an illusion fantasized in his head, but a physical fact that truly happened on the metal.

As long as the cause could be found, it could be solved.

But at the same time, this also made him feel a deeper annoyance.

Because next, on the premise of retaining the height of the left side, he had to specifically deal with this protruding 0.03 millimeters.

This was a hundred times more delicate than rough filing.

He clamped the flat steel back in place, took a deep breath, and assumed the adjusted standing posture he had just confirmed.

This time, he did not file the whole surface, but specifically carried out local trimming targeting the higher part on the left side.

For this step, he switched to a fine-toothed file.

He dared not file with great force, for fear that a sudden excessive exertion would remove too much from the left side all at once, which would force the entire surface to drop lower again.

Every time the file was pushed forward five or six times, he would force himself to stop.

He picked up the small brush, brushed away the tiny iron filings on the surface completely, and then picked up the square, leaned it against the light to check once, and observed the changes in the light gap.

File five times, stop, brush clean, lean the square, look at the light.

File five times again, stop, brush clean, lean the square, look at the light.

This extremely patient and tedious cycle lasted for a full hour in the stone house.

An hour later, Jiang Lin felt that his eyes were almost going cross-eyed from looking.

When he leaned the square against it again, the light gap finally appeared somewhat more even.

The difference in the amount of light transmitted between the left and right sides was no longer so glaring.

But it was far from reaching the absolute flatness of zero light penetration in his ideal imagination.

He straightened his aching waist and looked at the workpiece in the vise.

The first practice piece was estimated to still need five to eight days to be completely trimmed flat.

However, there was no need to rush, because the problems exposed in this piece of material might be the underlying problems that would appear in the filed surfaces of all the parts he would make in the future.

Taking the time now to see it clearly and master it thoroughly was ten thousand times more important than finishing filing this scrap iron quickly.

...

Time ticked away; twelve days had passed since Jiang Lin began taking flat steel 001 seriously.

The first practice piece was basically declared complete.

The completion mentioned here did not mean that it had reached the perfect qualified standard of a grade-one fitter.

Rather, it was a judgment Jiang Lin made in his heart based on his training during this period.

Under his current technique control, physical state, and the standing posture he had found so far, this piece of material had been filed to the absolute limit of his personal ability.

Continuing to file would no longer produce any substantive improvement.

Instead, there was a high probability that a tiny slip of the hand or an unnecessary movement brought on by muscle fatigue would completely destroy the areas he had already carefully trimmed to be relatively flat.

Making this judgment to stop made Jiang Lin feel so uncomfortable that he was even somewhat aggrieved.

This was just like rock climbing halfway up, clearly seeing the summit, but knowing that his physical strength was exhausted and having to actively give up and let go.

Giving up always brings a strong sense of frustration.

In machining, especially in the training of manual fitters, the vast majority of bad results and complete scrapping often begin with this obsession of refusing to stop.

Seeing that the light gap was just the final few hundredths of a millimeter away, his heart always felt unsatisfied, always thinking: "If I make my hand just a little lighter and trim it just a little bit more, just a little bit will do."

As a result, when that stroke was pushed down, the force deviated slightly.

A small pit was gouged out of a place that was almost flat.

In order to smooth out this small pit, he would have to lower the surrounding height again.

The surface was trimmed lower and lower, the error grew larger and larger, and finally, the entire plane that originally had hope was trimmed into a complete disaster.

Jiang Lin knew this weakness of human nature deeply.

Therefore, he forcibly cut off the thought in his mind of trying just once more.

He turned the crank, took down the flat steel that had accompanied him for nearly half a month from the vise, and placed it flatly on the wooden board of the workbench.

He began executing the final complete set of inspection procedures.

First, using a clean coarse cloth and brush, he thoroughly cleaned away even the tiny iron filings on the surface that were invisible to the naked eye.

Even if a single particle of iron powder measuring dozens of millimeters remained on it, it would seriously affect the fit of the square.

Then he picked up the square and began to inspect this surface from every possible direction.

Longitudinal, transverse, left diagonal, right diagonal.

Every time he changed direction, he lifted the workpiece, faced the light, carefully observed the light gap between the edge and the metal surface, and then probed it with a feeler gauge.

The best direction was the left diagonal direction: the light gap was very thin, and when he pulled out a 0.06 mm feeler gauge, it could barely squeeze into the very edge, but when he switched to a 0.08 mm one, it couldn't enter at all.

The worst direction spanned horizontally across the left and right ends: the light gap was obvious, and a 0.12 mm feeler gauge could probe in for a short distance until it was completely jammed at 0.15 mm.

Between the best and the worst, the error differed by a full factor of two.

Placed in the standards of precision machinery processing, this result was definitely a failing scrap piece.

For Jiang Lin, this result was naturally not good enough, but it was complete enough.

It faithfully recorded the upper limit of his skill level and inherent flaws during this period of time.

He opened his logbook and solemnly wrote down the closing statement.

[Practice piece 001 completed.]

[Inspection data: Rough light-transmission inspection using the blade edge of a square showed that a feeler gauge of approximately 0.12 mm could be probed in at maximum, and about 0.06 mm in the better direction. This data can only be used as a phased comparison and does not represent strict flatness.]

[Feature analysis: The directional error remains obvious, with the overall right side still lower than the left side by about 0.04 mm. This is completely consistent with the mechanical model inferred previously where wrist inward-turning compensation led to over-cutting on the right side. The adjustment of the standing posture played a partial restraining role, but failed to completely eradicate the old muscle memory.]

After writing down the data, he picked up the red marker.

On the rough side of the flat steel, he wrote three large numbers stroke by stroke: 001.

Then, he took it to the corner on the left side of the workbench, leaned it against the stone wall, and placed it vertically.

Jiang Lin decided to keep all future practice pieces.

Because on them, in the ways of Physics and geometry, were deeply engraved every single foolish mistake he made in the Wasteland, his once-distorted standing posture, his trembling wrists, and the entire process from ignorance to understanding regarding these errors.

This was a personal museum of errors belonging to him.

[Phase 1 Memorandum:]

[The main problem of practice piece 001 is confirmed to be directional error (right side low, left side high), and the core reason is the right wrist inward-turning compensation. The mechanism has been successfully identified, and partial improvement has been achieved through posture adjustment. Subsequent long-term muscle memory training is required to completely eliminate it.]

[The sole core objective of practice piece 002: targeted improvement of directional error. Strive to forcibly control the difference in light transmission between the best and worst directions within 0.03 mm.]

After writing down this extremely specific goal, Jiang Lin closed the notebook and pulled out the second piece of low-carbon flat steel covered in black scale on the surface.

He clamped it into the vise and tightened it firmly.

He picked up the hand saw with a new saw blade and aimed it at the marked line.

Swish—

He started the first saw cut of practice piece 002.

The advancement speed of 002 was much faster than 001.

Having been tempered by the torture of the previous dozen days or so, he was no longer making a fuss over those low-level mistakes.

But on the afternoon of the fourteenth day, while he was filing 002, a new problem that gave him a headache surfaced unawares.

Before that, he had strictly maintained the adjusted standing posture.

With his feet apart, his center of gravity slightly forward, his brain constantly paying attention to the posture of his wrist at the end of the push-filing, he forcibly suppressed the final two degrees of inward turning.

He filed continuously for nearly two hours, only stopping twice to drink water in between.

The black scale on the surface of 002 had been completely stripped away, revealing a large area of silver-white metal matrix, and it was basically filed flat.

Feeling that it was almost ready, Jiang Lin picked up the square for a phased inspection.

The good news was that the directional error had indeed been greatly improved.

When he inspected it horizontally with the square, he found that the difference of the right side being lower than the left side had visually decreased from 0.04 mm of piece 001 to about 0.025 mm.

The amount of light transmission was much more uniform, very close to his set target of controlling the difference within 0.03 mm.

This showed that his deliberate control against inward turning was effective.

The bad news was that a new trouble had appeared which had never been encountered in piece 001.

When he placed the square on the metal surface, he found that the middle area of the filed surface was slightly bulging out compared to the two ends.

On a microscopic scale, the entire plane formed an extremely weak curved surface.

The curvature was very small and absolutely invisible to the naked eye.

But light could deceive.

When the sharp square was pressed down from both ends of the workpiece for inspection, the middle part would contact the blade edge first, causing both ends to tilt up.

Looking through the gap, the middle did not transmit light or transmitted very little light, while both ends emitted obvious bright light.

This was an extremely typical convex surface characteristic.

"Middle convex."

Jiang Lin frowned.

He gently lowered the blade edge of the square onto the surface of the workpiece again and looked at it against the light once more.

The middle section adhered first.

Both ends transmitted light.

This was not because the middle was filed lower, but because an extra layer had been eaten away by him at both ends.

He was not unfamiliar with this kind of problem.

On the first practice piece in the garage before, he had encountered a severe middle-convex issue.

At that time, he thought he was pressing too heavily on the middle section, and only later after repeatedly looking at the file marks did he understand that the real problem lay in those two moments when the file entered and exited the workpiece.

When the file first contacted the metal, his left hand would subconsciously press down a bit more to stabilize the file head.

When the file was about to leave the metal, his right hand would instinctively hook downward for fear that the tail end would float.

Consequently, the front and rear ends were repeatedly cut by an extra layer, while the middle was preserved instead.

Under the light gap of the square's blade edge, it manifested as a weak convex surface.

On piece 001, this problem actually existed as well, except that at that time the directional error of the right side being low and the left side being high was too large, completely covering it up.

Why did it blatantly pop out when it came to piece 002?

This was by no means a coincidence.

It was very likely that in the process of trying his best to improve the directional error, in order to control his wrist movement, he inadvertently introduced another error in force application.

These two problems affected each other at their physical root causes.

Jiang Lin sat on the stone bench, looked at this imperfect piece of iron, and thought for a full twenty minutes.

[Theoretical deduction—Possible causes of the middle convex:]

[Possible cause one: Over-cutting during the entry and exit stages. To suppress the inward turning of the wrist, my muscles were overly tense when the file just contacted the workpiece and was about to leave it, resulting in extra downward pressure from both the left and right hands respectively. This increased the amount of metal cut away at both ends, while the middle section was relatively preserved, forming a convex surface.]

[Possible cause two: The change in standing posture altered the pressure curve. After the standing posture was adjusted, the shoulder stroke was released, but the pressure distribution of both hands was disrupted again. During the push-filing in the middle section, the file might just slide across relatively smoothly; during entry and exit, because the blade angle, wrist control, and downward pressure changed simultaneously, it instead caused excessive local removal at both ends.]

[Conclusion: It is temporarily uncertain which specific one it is. It is necessary to first confirm the dynamic phenomenon, and then inversely adjust the movement.]

[Core understanding: This is a typical coupling between errors. After improving a single directional error, hidden at the bottom layer, a new surface shape error was stripped out and exposed.]

"Coupling."

Jiang Lin silently chewed on this Physics vocabulary in his mouth.

Coupling means that there are interactions and mutual influences between two or more systems.

You cannot isolate them for independent adjustment; they must be considered simultaneously as a whole.

He was too familiar with this word when he studied Physics.

Just like two small balls connected together by a spring.

When you move the ball on the left, the deformation of the spring will immediately transmit the force to the ball on the right, and the equation of motion for the ball on the right will change immediately.

Just like in Maxwells Equations, an electric field that changes with time will inevitably excite a vortex-like magnetic field, and the changing magnetic field will in turn excite an electric field.

Electricity and magnetism are entangled in life and death.

If describing a multi-degree-of-freedom vibration system in theoretical mechanics, such as this human linkage system, the equation would probably be in the form of a matrix like this.

[M]{x¨} + [C]{x˙} + [K]{x} = {F(t)}

In this matrix, there are a large number of off-diagonal elements in the mass matrix [M], the damping matrix [C], and the stiffness matrix [K].

These off-diagonal elements are the coupling terms.

Their existence means that changing the movement on any coordinate x1 will inevitably cause the displacement of another coordinate x2 through the transmission of stiffness or mass.

Now, this abstract concept that only existed in advanced Physics textbooks vividly appeared on this ordinary piece of flat steel in front of him that had been filed for over a dozen days.

In real metal cutting, he touched the tactile sensation of coupling.

The directional error and the middle convex, these two surface shape defects, were by no means two buttons on the workbench that could be turned on and off independently.

You couldn't pull down slider A first and then pull down slider B like on a mixing console.

They came from the same set of poor bodily movement patterns.

The rotation of the wrist, the thrust of the shoulder, the center of gravity of the waist, the dynamic pressure distribution on the file, the effective stroke of cutting...

All these variables were tightly twisted together like a mess of hemp, forming a huge nonlinear system.

In order to solve problem A, you slightly changed your shoulder posture.

Very good, problem A was improved.

But in this multi-degree-of-freedom system, the transmission of force changed instantly, and the pressure distribution of the wrist when entering the workpiece changed, so problem B popped up like bamboo shoots after a spring rain.

Looking at his hands that were trembling slightly from overexertion, Jiang Lin wrote lightly.

[The control system of the human arm is highly coupled. The directional error and the middle convex are two output results of the same defective motion configuration on different cross-sections.]

[They must never be adjusted separately, which would only lead to a vicious cycle of pressing down the gourd only for the ladle to pop up.]

[The only way out: Through continuous trial and error, in a multi-dimensional space, a delicate balance point must be found—a motion configuration that can compress both errors to a minimum simultaneously.]

After writing this long string of theoretical analysis, he raised his head to glance at the crude workbench and added the last sentence.

[It is expected that finding this configuration will be a very, very long process.]

[But no rush; there is not much else in the Wasteland, but there is plenty of time for trial and error.]

He calmly closed the logbook.

He loosened the vise, took out piece 002, picked up the red marker, and wrote 002 on its flat side.

Then he placed it side by side with piece 001, setting them up vertically.

Viewed with the naked eye, 002 was much cleaner than 001, with a more uniform metallic luster and more regular surface scratches.

But if one carefully inspected it with a square, they would cruelly discover that 002 had not become much more perfect.

It merely exposed the problem in a more concealed and complex way.

Late at night on the eighteenth day.

The wind howled outside the stone house, and Jiang Lin sat under the dim low-voltage lamp, making a comprehensive phased summary.

Over the past dozen days or so, he had been fighting those cold tools every day, and his nerves were stretched too tight.

If he didn't review periodically, it would be easy to lose his way in this boring quagmire.

He flipped the logbook backward page by page.

The crooked handwriting caused by hand shaking, the messy force analysis diagrams drawn, and the errors circled in red pen pieced together a complete panoramic view in his mind little by little.

He took out a new piece of blank paper and began to make a list.

Five problems were eloquently listed over more than half a page.

It seemed there were a lot of them, and each one required tremendous energy to correct.

But Jiang Lin was exceptionally clear-headed in his heart; these five problems were definitely not all of them.

This was merely all that he could see at his current extremely rudimentary stage with his existing naked eye and crude measuring tools.

This was just like his experience when studying Quantum Mechanics before.

When you only understand classical Physics, you think the world is a pool table perfectly governed by Newton's laws.

Only when you begin to contact the microscopic world and encounter wave-particle duality will you discover that your previous cognition was full of loopholes.

The most dangerous state is always not knowing what you don't know.

Because when you are in this state, you will have a false confidence, thinking that you have mastered the truth.

In fact, you just haven't gone deep enough, nor have you encountered those anomalous phenomena that can crush you.

The craft of a fitter is exactly the same principle.

The problems in Part 001 were not something he could see right from the beginning.

It was only after he foolishly filed away at the vise for over ten days, smoothing out the rough surface marks, that the underlying inclinations naturally exposed themselves.

The middle bulge in Part 002 only emerged like reefs after a receding tide after he exhausted all methods to flatten the left and right inclinations of Part 001.

Then what about the next piece of material?

Perhaps, when he finally spent ten days or half a month solving the problem of the middle bulge, he might despairingly discover that hidden beneath that smooth surface were distortions, deformations, or even more microscopic surface roughness problems.

Problems were never neatly lined up in a row right from the start, standing there waiting for him to eliminate them one by one.

Problems were an onion wrapped layer by layer.

The outermost layer was rotten; when you peeled it away, what you saw was the next layer that was slightly better.

But if you wanted to reach the very core, you had to keep peeling, getting brought to tears by the pungency as you peeled.

If you could not see the problem of the upper layer, the lower layer would seem as if it did not exist to you.

This was the phased, true result of all his current efforts.

It was not pretty, with no sudden enlightenment, no system blessings, and no rapid, genius-like advancement.

But it was real enough to make him feel at ease.

"As long as I am still moving forward, every time I solve an upper-level problem, I will inevitably see the next, more microscopic problem hidden beneath it."

"Problems will never decrease with training; they will only become more refined and clearer."

"Discovering a problem is not a bad thing; it shows that the cloth of ignorance covering the eyes has been torn open a crack."

After writing these words, Jiang Lin felt a sense of relief, stood up, stretched his back grandly, and his joints made a cracking sound.

He walked over to the workbench and took the practice piece numbered 003 off the vise.

For the third filing practice piece, Jiang Lin changed his practice method.

He no longer, like the first two pieces, impatiently pursued a breakthrough in a single indicator like a gambler.

Instead, he began to dismantle the movements like slicing sausage.

Every cut he made was divided into three distinct stages.

The initial stage upon first contacting the metal: strictly control the pressure of the left hand, and never apply heavy pressure out of greed for speed.

The middle stage during flat pushing: both hands exert force simultaneously to maintain absolute parallelism between the file and the ground, like sliding on ice.

The final stage during withdrawal: high concentration of attention on the right wrist, using the contraction of shoulder muscles to guide and control the wrist from turning inward, while maintaining joint flexibility and never letting it lock up like a stiff wooden stick.

Not only that, but to solve the problem of standing posture drift, he used a primitive yet effective clumsy method.

On the dirt ground in front of the workbench, matching his most comfortable and perfect standing posture, he drew two short lines neatly.

One line set the front toe, and the other set the rear heel.

Every twenty minutes of filing, he forced himself to stop and move his sore shoulders.

Every forty minutes of filing, he lowered his head, readjusted against the two white lines on the ground, aligned his unconsciously drifted foot position bit by bit, and regained his initial center of gravity.

This method was foolish to the extreme and even seemed somewhat ridiculous, but its effect was surprisingly good.

A stable chassis ensured that the direction of force output no longer swayed randomly.

Jiang Lin held a clean coarse cloth and carefully wiped away every trace of iron filings from the surface of 003.

Then he picked up the square and feeler gauge to inspect it.

The appearance of the light gap proved that his efforts had not been in vain.

The arc of the middle bulge that troubled him was visibly reduced compared to Part 002.

The depth penetrated by the feeler gauge became shallower. Rough measurements showed that the arc difference dropped from about 0.03 millimeters to within about 0.02 millimeters.

At the same time, that habitual directional error was steadily suppressed; it did not rebound significantly because he went to solve the middle bulge, and still maintained an extremely small level of around 0.02 millimeters.

The data for various errors were all converging.

Of course, according to industrial standards, it was still an unqualified piece of scrap iron.

But this did not matter.

What mattered was the trend; the downward error trend was correct.

Jiang Lin placed this 003 next to 001 and 002, the three brothers lined up side by side, neat and tidy.

From left to right, their dimensions and heights were almost identical, their surfaces were covered by the metal base color after the black scale peeled off, and their colors were similar.

If viewed by someone who did not understand the trade, they were merely three ordinary low-carbon steel flat bars with surfaces covered in deep or shallow file marks, repeatedly tossed about, and unattractive.

But Jiang Lin knew that as long as the 90-degree knife-edge square was leaned against them,

one could clearly see that the distribution of the light gap leaking between the knife edge and the metal was undergoing a long evolution.

From the disarray of 001, to the regular inclination of 002, and then to the gradual trend toward a faint uniformity in 003.

This was an error convergence curve jointly drawn by time, sweat, and the laws of Physics, slowly sloping downward.

And he was struggling to crawl along this curve.

Although the trend of 003 was very good, Jiang Lin did not strike while the iron was hot or impatiently go to the material box to open the fourth piece of material.

Haste makes waste. Before starting a new cycle, the traces of the previous round had to be completely cleaned up.

He took a large stiff bristle brush and began to clean the workbench.

He swept all the large and small sawdust and iron powder on the table without leaving a single bit into the scrap box on the lower right.

After sweeping, he found a slightly damp rag and wiped down the entire wooden tabletop, the vise base, and even the surrounding walls, until everything returned to that refreshing state from the very beginning.

After cleaning, he brought 001, 002, and 003 from the corner back onto the workbench.

According to the numerical order, they were lined up in a row from left to right.

Jiang Lin took a deep breath and began the last and most comprehensive re-inspection of these three practice pieces.

Measuring the path he had walked before all over again.

After inspecting each piece, he drew a table in his logbook and filled in the latest data.

After filling in the data, he began to write the final summary statement.

"Overall trend assessment: techniques are gradually improving, and systematic errors are gradually converging. However, the speed of convergence is extremely slow. According to data calculations, the improvement magnitude of each new sample on the comprehensive error is only maintained between 20% and 30%, and shows an obvious law of diminishing marginal effects."

"Pessimistic expectation: at the current rate of progress, it is estimated that it will still require the continuous consumption of more than ten samples and tens of thousands of repeated pushing and filing actions to steadily press this extremely simple end-face error to within 0.03 millimeters."

"The further order of magnitude of 0.01 millimeters is no longer something that can be guaranteed purely by brute force practice. That requires a more stable reference plane, more reliable inspection tools, and a repeatable detection method much more than the current crude 'looking at the light gap'."

"As for the true micrometer level, that is not a target that the workbench, a square, and a few feeler gauges right now should dare to dream of."

When writing this sentence about future expectations, following his previous habit of making project plans, he instinctively wanted to add a piece of bureaucratic jargon at the end: 'Current progress is basically in line with initial expectations.'

But in the end, he did not write this sentence.

Because he said to himself in his heart: "Does not fit."

This did not fit his initial naive and arrogant expectations at all.

When first preparing all this, he originally thought he was a transmigrator with a God's-eye view.

He had brought over enough modern high-strength tools and read enough theoretical materials on precision machinery.

More importantly, he had a brain forcibly stuffed with a massive amount of theoretical knowledge by time.

He took it for granted that with the blessing of these dimensionality-reduction-strike-like advantages, even if he could not become an eighth-grade senior technician overnight, at least in this most primary introductory stage, his comprehension and progress speed would definitely be much faster than those young people starting from scratch as apprentices in the Real World.

The reality was like a loud slap, hitting him mercilessly in the face.

None.

It did not get faster at all.

Those differential equations and mechanical matrices could allow him to see through the mechanical mechanisms behind errors faster than others, letting him know why they went wrong.

But they could absolutely not replace him in completing any extremely tiny Physics action.

His body had its own stubborn clumsiness and biological instincts that were difficult to break.

His wrist would not magically stop turning inward at the end of the push just because his brain suddenly understood the calculation formula for degrees of freedom.

His shoulders would not automatically find the most effortless and perfect straight-line trajectory in three-dimensional space just because he could silently write out the extremely complex Euler—Joseph-Louis Lagrange equations of motion on a blank sheet of paper.

The cold low-carbon steel he held in his hand would even less cut him some slack and automatically shed away into an absolutely flat surface just because he had struggled to survive for decades in this cruel Wasteland World, possessing a will that ordinary people could hardly reach.

The material world was fair and cold, listening to no theories and recognizing no suffering; it only generated feedback based on the absolute force acting upon it.

Jiang Lin looked at the three flat steels lined up in a column and wrote a paragraph at the very end of the quality inspection report.

"First-stage final conclusion reflection: I always thought I was learning how to process a piece of metal. I was wrong; I am not actually learning benchwork, but merely trying to train a huge, complex machine full of random errors that always wants to slack off. The name of this machine is Jiang Lin's flesh."

He felt that this final vulgar, plainspoken remark was more accurate than any professional craftsmanship description or error analysis introduction.

It hit straight at the bottom-most logic of manual manufacturing.

He was not relying on intent or illusory willpower to file those hard steel materials flat.

In the long process of trial and error, he needed to investigate and correct its error sources one by one on this flesh machine named Jiang Lin.

What was hand feel?

What was craftsmanship?

Truly effective craftsmanship training was by no means simple and boring repetition.

That was machine repetition.

Truly effective craftsmanship training was to repeat an action that was slightly more correct than the previous one in every fine adjustment.

Then, through hundreds and thousands of times of forcible writing, this slightly correct action was deeply engraved into the fibers of the muscles and into the synapses of the neurons.

Until that day, this awkward movement that originally required the brain to desperately control completely became the absolute default value of this body when touching metal.

To prevent himself from forgetting this bloody lesson due to temporary impatience.

He tore a blank page from his notebook.

He raised his pen.

"I am not filing iron."

"I am calibrating an unstable flesh machine named Jiang Lin."

Then, he found some clay and pasted this note on the upper right corner of the workbench.

That position was extremely conspicuous; as long as he raised his head or his sight left the file, he would definitely see it.