GlossaryKind of term: Manufacturing termMilling
What is milling?
In milling, a rotating cutter with one or more cutting edges moves along the clamped workpiece to produce faces, pockets, slots and contours.
Milling is machining in which a rotating cutter provides the cutting motion and the feed comes from the table, the spindle or both. The workpiece is held in workholding. Each cutting edge is engaged for only part of every revolution, so the cut is interrupted. It produces faces, pockets, slots, contours and chamfers. Drilling, reaming and tapping often run in the same spindle, but they are separate operations. The machine's axis count partly decides which directions the cutter reaches without reclamping.
What does the result of a milling operation depend on?
What a milling operation produces and how long it takes depends on the cutting data (cutting speed, feed per tooth, axial depth ap and radial width ae), the tool and its overhang, the stiffness of machine, workholding and part, and the material. In climb milling the chip starts thick and ends thin; in conventional milling it is the other way round. Climb milling is the usual choice on CNC machines; conventional milling can be preferred on a hard casting skin or mill scale, or on a machine with backlash in the drive. Face milling with the end of the cutter and peripheral milling with its side each give their own surface and their own load.
How does milling work in practice?
Cutting time is only part of what a milled part costs. The blank, the setups, programming, tool changes, deburring and inspection all count. How many setups a part needs depends on the features per side, the workholding, the machine and the tolerances between features. A part with features on four sides can take four setups on a 3-axis machine, and fewer with a fourth axis, a 5-axis machine or a fixture. For a rotationally symmetric part turning is often the shorter route, for a prismatic part milling; a part with both kinds of feature may go to mill-turn.
What is milling often confused with?
Milling is not turning: in milling the tool rotates, in turning the workpiece does. CNC machining is the umbrella term for computer-controlled machining. Milling is a process, not a type of control: it runs CNC-controlled or on a manual machine, as do turning and drilling.
How do you see milling in Blake?
In Blake a milled part, from 3-axis to 5-axis, is a set of separate lines: material, setup, programming, machining and finishing, per piece and per batch. You enter the setups per route yourself and accept or undo them. Envelope, axes and your own hourly rate come from the machine in your machine park. All results are labelled as estimates. More on milling.
Frequently asked questions
How do you calculate the cost of a milled part?
A common build-up: material for the blank, setup time for each setup, programming, machining time multiplied by the machine hourly rate, and subcontracted finishing as its own line. In that convention setup and programming are spread over the quantity. The result remains an estimate.
What does an extra setup cost in milling?
That is not fixed. A setup means clamping, aligning, setting the work origin and often a first measurement. On a one-off that can take longer than the cutting; over a batch it weighs less per piece, depending on how you spread setup time.
When is milling more expensive than turning?
Often on rotationally symmetric parts: a lathe makes diameters and shoulders from bar, while a mill cuts the same shape from a block. On prismatic parts it is usually the reverse. Parts with both kinds of feature often go to mill-turn.