Most CNC quotes get built off the tightest number on the drawing, not the part as a whole. That is the wrong way to price a part, and it is the wrong way to design one too.
Here is what actually happens on the shop floor. A drawing comes in with a general tolerance block of +/-0.05mm and one callout at +/-0.005mm on a bore that mates with a bearing. The engineer who drew it was thinking about that one feature. The machinist quoting it has to think about every operation that touches the part before that bore gets cut, because each one adds to what the bore actually ends up seeing.
If a part gets machined in three setups and each setup holds +/-0.01mm to the fixture datum, the feature cut in the third setup is not sitting at +/-0.01mm relative to the first datum. It is carrying the error from all three operations. On a simple part that might still land inside spec. On a part with five or six features referencing different datums, it often does not, and the shop finds out during first article inspection, not before.
This is why a single tight tolerance on a drawing changes the price of the whole part, not just that one feature. Holding one bore to +/-0.005mm might mean machining it in a single setup off a shared datum instead of the sequence that would otherwise make sense for the rest of the part. That changes fixturing, changes operation order, and sometimes changes which machine runs the job.
Three patterns show up constantly on drawings that did not need to be priced as tight as they were quoted.
Blanket tolerances instead of feature-specific ones. A drawing with +/-0.02mm applied uniformly across forty dimensions forces every one of those forty to be measured and held to that number, even the ones where +/-0.1mm would never matter to the assembly. Feature-specific tolerancing, tight where it counts and open everywhere else, is usually cheaper to machine and just as functional.
Datums that do not match how the part actually gets used. A tolerance referenced to a machining datum instead of the functional datum (the surface or bore the part actually locates against in the assembly) can pass inspection and still not fit, because the stack-up that matters in the real assembly was never the one being measured.
Surface finish called out tighter than the tolerance requires. A Ra 0.8 finish on a surface with a +/-0.05mm tolerance is often unnecessary. Finish and tolerance are related but not the same thing, and a tight finish callout adds a grinding or polishing step that a tolerance alone would not.
Every drawing that comes to our engineering team gets a manufacturability pass before it gets priced. That means checking which tolerances are driving fixture and operation choices, whether the datum scheme matches the functional requirement, and whether any callout is tighter than the application needs. If something looks tighter than it needs to be, we flag it and ask, rather than quote it as drawn and let the price speak for itself. Sometimes the answer is that the tolerance is correct and load-bearing. Often it turns out one number was carried over from a previous revision and never revisited.
For reference, our CNC milling and turning holds +/-0.003mm as a standard capability, and our 5-axis grinding holds +/-0.001mm where a part genuinely needs it. Neither number should be the default tolerance on a drawing. They should be reserved for the features that actually require them.
Check that every tight tolerance is tied to a functional requirement you can name, not a default from the CAD template. Confirm your datum scheme matches how the part locates in the final assembly, not just how it is easiest to measure on a CMM. Separate tolerance from finish, they are two different specs and pricing them as one usually costs more than pricing them correctly.
If you are not sure which of your tolerances are actually driving cost, send the drawing over. We will tell you which ones matter before you get a number, not after.
Send us your drawing and our engineers will review it for manufacturability before quoting.
Request a QuoteUpload your CAD file, materials, and target quantity — we'll come back with a manufacturability review and a quote. Our engineers review every request personally.