Material removal rate: Material removal rate is the volume of material a machining operation cuts away per minute, usually given in cm³ per minute, and it sets roughing time.
For milling, material removal rate (MRR) is the depth of cut times the width of cut times the feed rate. What a shop can achieve depends on the material (aluminium allows a far higher rate than stainless steel or titanium), the tool, the machine’s power and stiffness, and the roughing strategy in the toolpath.
What it means for the price
Roughing time is roughly the volume to remove divided by the MRR. A part carved from a large block therefore costs more in time as well as in material. Hard materials raise the cost twice: a lower removal rate and faster tool wear. An instant CNC estimate often starts from the volume between the stock and the finished part and a removal rate for each material, then adds finishing time from the surface area.
Example: removing 300 cm³ at 60 cm³ per minute in aluminium takes 5 minutes of roughing; at 10 cm³ per minute in a stainless steel it takes 30 minutes. The figures are an example.
Common confusions
MRR describes roughing. Finishing time is driven by surface area, step-over and tolerance, not by the volume removed, so a part with little to remove can still have a long cycle time. Read what drives CNC machining cost.
Go deeper: What drives CNC machining cost, and how estimators work it out