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Comparison of whirling and milling
The comparison of whirling with milling, whilst showing similarities, shows that the chips are of different shape, and the resulting smoothness of the workpiece surface is also different. The more favourable cutting action and cutting force mean that, for a given angle of advance, a correspondingly greater rate of metal removal and rate of advance is possible with whirling compared to milling (see figure on the right).
For a given external diameter and root diameter, and a set angular speed, the chips from whirling and from milling are of similar size. The chips from whirling are however longer, and have a correspondingly smaller thickness. This means that significantly less cutting force is required, and the elastic deformations resulting are also less. Associated with this the surface quality is better than by milling.
Using the same maximum chip thickness, whirling achieves far shorter cutting times, because compared to milling, much higher rates of advance are possible, and material is removed at a much greater rate. Whirling does not form a circular cut, but a polyhedron that approximates closely to a circle. The polyhedral peaks are however very small, about a tenth of a micrometre (1/10.000 mm) so are practically imperceptible, and much smaller than the peaks resulting from milling. Using whirling, there is less deviation measurable at constant angular rate of advance from the pure required form of the workpiece than occurs with milling; or, put another way, within a given tolerance of conformity to the pure required form, whirling can deliver a much higher angular rate of advance than can milling.
Therefore it is possible to achieve workpiece rates of advance with whirling that are three or four times that achievable with milling, and at the same time deliver a very good cut surface, comparable to grinding.