I have been in this trade for more than a decade.
The machines have been replaced a few times. So have the customers. But every year I run into the same kind of rework, and it never comes from a bad machine or a careless operator. It comes from one sentence that neither side said out loud at the time.
So here are the three things I most want to say to a customer.
1. Show me what you haven’t decided yet
Most drawings that arrive look complete. Lines are solid, dimensions are called out, tolerances are written down. But anyone who has stood at a machine can spot the two or three places that are really just placeholders.
It might be a locating face that only gets settled once the assembly is built. It might be a hole pattern that will move. It might be a wall thickness the customer is still arguing about internally.
People often leave those spots drawn as if they were final, because saying “I’m not sure yet” feels unprofessional. But that is exactly the thing that costs the most.
One line — “I haven’t fixed this yet, machine it as A, but B is possible” — buys more than you would expect. I can run both cases, leave a little extra stock, choose tooling and workholding that tolerate a change, or suggest you make one part to validate before we cut a batch. Draw it as a solid line, though, and I can only follow the drawing. By the time you want it changed, the material is gone.
Nobody is wrong here. The sentence just never got said.
One piece of background that isn’t as obscure as it sounds: what the drawing does not say still has to be governed.
In China, unmarked linear and angular tolerances are handled under GB/T 1804-2000, which is equivalent to ISO 2768-1:1989 — in the 6–30 mm band, medium class m means ±0.2 mm. Unmarked geometric tolerances follow GB/T 1184-1996.
Internationally, the picture changed recently. ISO 2768-2:1989 has been withdrawn and replaced by ISO 22081:2021, which gives rules for defining general geometrical specifications rather than a ready-made table of default values. In other words, “what happens where nothing is written” is handed back to the person drawing the part.
So ten minutes spent making that clear can save you a week of waiting.
2. The “simpler” the part, the more questions I ask
“It’s a simple part, just give me a rough price.”
Any machinist hears that and feels a small pause.
Parts that are genuinely hard to make keep everyone careful: the drawing is detailed, and we walk through the setup together. It is the ones that look simple that go wrong:
- A housing with 1–2 mm walls that springs out of shape the moment you clamp it, and springs back when you release the fixture;
- A deep pocket where the tool cannot reach the bottom, or chatter ruins the floor;
- A slender shaft that bends under its own weight while being cut;
- A large cosmetic face where one visible tool mark is enough to fail it.
What they share is this: the problem is not in the tolerance numbers. It is in the process and the condition of the part — neither of which is visible on the drawing.
So I ask a couple more questions. Where does this part sit in the assembly? Is that face cosmetic, or does it get covered by adhesive anyway? Is there a second operation after this one?
I ask because I don’t want you to discover, after the third rework, that it started with “just make it however.”
The hardest job is rarely the hardest drawing. It is the drawing nobody looked at carefully.
3. When something goes wrong, come to me first
This is the one I care about most.
What does a shop owner actually fear? Not rework. Rework has a price — you can calculate it, and you can absorb it. What we fear is silence.
A customer receives the parts, feels something is off, decides “let’s just use them”, and it surfaces on the assembly line months later. Or a customer has a complaint but passes it to a middleman, and a distorted version of it reaches me. Or one of our own machinists knew a batch looked wrong, saw the schedule was tight, and said nothing.
Once information takes a detour, it is no longer the original sentence. By the time it reaches me, it is usually past the point where one phone call fixes it.
So here is what I want to agree with every customer: when something goes wrong, don’t be polite about it — come to me first, and come early.
Even if you think the mistake is in your own drawing, say it. Even if it is only a feeling that something is not right, say it. We would rather eat the cost of a batch than hear the truth from someone else six months later.
Rework can be quoted again. Trust does not get a second run.
One line for you
I am not asking you to be satisfied into silence. I am asking you to speak up. Said early, we both save. Said late, nobody does.
Key references
- GB/T 1804-2000, General tolerances — Tolerances for linear and angular dimensions without individual tolerance indications (in force; equivalent to ISO 2768-1:1989) — National Standards Information Public Service Platform of China
- GB/T 1184-1996, Geometrical tolerances — Unindicated tolerance values
- ISO 22081:2021, Geometrical product specifications (GPS) — Geometrical tolerancing — General geometrical specifications and general size specifications — the ISO page lists it as replacing ISO 2768-2:1989
About Eternal CNC
We have made precision structural parts for twenty-three years. Among thirty machines we run a five-axis, and we often take parts like robotic joint-module housings, reducer components, and load-bearing structures — the kind where “a little off and it fails.”
The three sentences above are not written to sound good. They show up in what we do every day: at quoting we look for the places your drawing left open and ask about them, before machining we walk through the structure and the workholding, and when something goes wrong we say it first instead of hiding it.
If a failure on your part is not an option, send us the drawing — including the parts you have not decided yet.