Definition
Operation sequence is the order in which a part's required operations are performed. The same set of operations can sometimes be sequenced differently, and the chosen order can affect achievable tolerances (which datum is established first), tool wear, and total cycle time.
Why sequence, not just the operation list, affects cost and quality
A well-chosen sequence can reduce the number of setups needed or avoid machining a feature that could distort a later, more delicate one; a poorly chosen sequence can force extra setups or risk damaging already-finished features.
Where operation sequence is decided
Not on the drawing; it's a process-planning decision informed by the part's datums, tolerances and features, not something the drawing specifies directly.
Common mistakes
Assuming any valid operation order works equally well; sequencing a delicate or tightly toleranced feature before a rough, high-force operation nearby can risk distorting or damaging it.
A well-chosen sequence can reduce the number of setups needed or avoid machining a feature that could distort a later, more delicate one; a poorly chosen sequence can force extra setups or risk damaging already-finished features.
See how Blake reviews a partFrequently asked questions
Can operation sequence change a part's achievable tolerance?
Yes, since it determines which datum is established first and how later features are measured and made relative to it.
Who decides operation sequence?
Typically a process planner or work preparer, as part of building the overall routing.
Does operation sequence always have one correct answer?
Not always; several valid sequences can exist, and the best choice can depend on the specific machine, tooling and factory capability available.