GlossaryKind of term: Manufacturing termDepth and width of cut (ap, ae)
What are depth and width of cut?
Depth of cut ap and width of cut ae state how deep and how wide a cutter is engaged; with the feed rate they set the material removal rate.
In milling, depth of cut ap is the engagement along the tool axis and width of cut ae the engagement at right angles to it, often given as a share of the cutter diameter. In turning, ap is the depth of cut perpendicular to the feed direction: radial in longitudinal turning, so going from ⌀50 to ⌀46 mm in one pass is 2 mm per side, and axial in facing. Together with the feed rate vf, ap and ae set the material removal rate in milling: Q = ap × ae × vf / 1000, in cm³/min.
What do depth and width of cut depend on?
How large ap and ae can be depends on spindle power and torque, the stiffness of machine, workholding, tool and part, tool overhang and chip evacuation. The power required grows roughly in proportion to the removal rate and to the specific cutting force of the material. A 15 mm deep pocket with a ⌀12 mm cutter can, for example, be taken in three layers of 5 mm at a large ae, or at full depth in one go at a small ae. Strategies with a small ae and constant engagement, such as trochoidal milling, can use much of the flute length and keep the load steady.
How do depth and width of cut work in practice?
Together with the feed, ap and ae decide how many passes a pocket or face takes, and so the time. A bigger cut removes more per pass, but a thin wall or a long overhang forces smaller cuts. Whether full-depth milling at a small ae beats layer-by-layer milling depends on the material, the cutter's flute length, the machine's dynamics and the CAM strategy. The choice also affects tool life and wall finish.
What are depth and width of cut often confused with?
Depth of cut is not the depth of the feature: a 15 mm deep pocket can take one cut or several. Width of cut is not the cutter diameter: ae is the part of the diameter actually engaged. And ap is measured radially in longitudinal turning but axially in milling, which causes confusion when comparing catalogue data.
Frequently asked questions
What is the difference between ap and ae?
ap is the depth of cut along the tool axis, ae the width of cut at right angles to it. In milling you choose them together: deep and narrow, or shallow and wide. In longitudinal turning ap is the radial depth per side.
Why mill at full depth with a small width of cut?
Because the whole flute length works and the load per tooth stays even. That spreads wear, limits heat and often allows a higher feed. It needs a CAM strategy that holds engagement constant and a stable machine.
Why does a thin wall take more passes?
Because the wall deflects or chatters under a heavy cut. You spread the material over more, smaller cuts and keep the wall supported as long as possible by working both sides in turn. More passes means more machining time.