GlossaryKind of term: Manufacturing termRoughing and finishing
What are roughing and finishing?
Roughing removes most of the material and leaves an allowance; finishing takes that allowance off and brings size, form and roughness within the requirement.
Roughing is about removal rate: a lot of material off in little time, leaving an allowance on the faces that later have to be on size. Finishing takes that allowance off in one or more light cuts so that size, form and roughness meet the requirement. A semi-finishing pass sometimes sits in between to even out the allowance, so the finishing cut carries the same load everywhere. The distinction is about purpose and cutting data, not about a particular tool or machine.
What limits roughing and finishing?
Roughing is limited by spindle power and torque, the stiffness of machine and setup, the tool and chip evacuation. Finishing is limited by the requirement (tolerance, form and roughness) and by deflection of tool and part under cutting force. How much allowance you leave depends on material, tool, the distortion you expect and the requirement. Roughing releases residual stress locked into rolled, drawn or forged stock, and machining adds stress of its own, so a part can move after roughing. On thin walls you leave material in place as long as possible to retain stiffness. Stock supplied in a stress-relieved condition, such as stretched aluminium plate, usually moves less, but can still move.
How do roughing and finishing work in practice?
Roughing and finishing time each follow their own logic. Roughing time depends mainly on the volume to remove and the removal rate machine and tool can sustain; finishing time on surface area, contour length, roughness and tolerance. If a part may distort, stress relieving can sit between the two, often subcontracted, with transport, waiting time and a new setup. Whether stress relieving is possible depends on the material's condition: quenched and tempered steel is relieved below its tempering temperature, and precipitation-hardened aluminium can lose strength. Some plastics are left to rest or annealed after roughing before they are taken to size. That waiting time belongs in lead time, not cycle time.
What are roughing and finishing often confused with?
In English, finishing has two meanings: the finishing cut that brings a part to size, and surface finishing such as anodising, plating or coating. On a quote they are different things: one is machining time, the other usually a subcontract operation. Finishing is not rework either: rework is machining a part again because it fell outside the requirement.
How do you see roughing and finishing in Blake?
Machining is its own line in Blake, with the time labelled as an estimate. If that time differs from what your machines achieve, you correct the line with a reason; the previous value is kept. A subcontracted stress-relieving step is its own line from your subcontract library; if the price is missing, the line stays open. More on estimating.
Frequently asked questions
How much allowance do you leave for finishing?
Enough to remove the marks and distortion from roughing, and little enough to keep the finishing cut light and even. It depends on material, tool and roughness requirement, and on what happens in between: before stress relieving or hardening you leave more.
Why stress relieve between roughing and finishing?
To reduce residual stress released or introduced by roughing. The part then moves mainly before finishing, so the final size is more stable. Whether it is needed depends on material, shape, wall thickness and tolerances.
Can roughing run on a different machine?
Yes. Some shops rough on a heavier or cheaper machine and finish on the accurate one. That saves time on the expensive machine but adds a setup and a new work origin, which can weigh heavily when tight tolerances link features.