Radial depth of cut
What is Radial depth of cut?
In milling, the width of cut refers to the lateral contact width of the cutting tool with the material being machined. The width of cut is typically denoted by the symbol aₑ. It's also called the radial depth of cut, as it describes how deep the tool penetrates the workpiece in the radial direction. In machining, the width of cut determines how much of the cutter’s diameter is engaged in removing material.
The width of cut is a key machining parameter in milling and directly affects cutting forces, tool load, vibration, and tool wear during machining.
Radial depth of cut in Milling
In milling, the width of cut determines the contact angle between the tool and the workpiece. When aₑ is small relative to the tool diameter, the contact angle is small and the chip is thinner. Conversely, a large width of cut increases the contact angle and the volume of material removed in one pass.
The width of cut is selected based on the chosen milling strategy, such as face milling, slot milling, or trochoidal milling. For example, in full slot milling, the width of cut is essentially equal to the tool diameter, while in dynamic milling, a small radial width of cut and a larger axial depth of cut are typically used.
Width of Cut and Average Chip Thickness
The width of cut affects the average chip thickness hₘ. The average chip thickness is not the same as the feed per tooth; it also depends on the tool engagement angle, which is determined by aₑ.
When the width of cut decreases, the chip becomes thinner, and the average chip thickness hₘ drops, even if the feed per tooth remains the same. For this reason, machinists often need to increase the feed per tooth to achieve sufficient chip thickness and avoid rubbing instead of cutting. Too small a chip thickness can increase heat load and reduce tool life.
Similarly, a large width of cut increases average chip thickness and puts greater strain on the tool. This is especially important to consider when using carbide tools and when machining hard materials like tempered steels or stainless steels.
The Effect of Width of Cut on Machining
In the manufacturing industry, optimizing the width of cut affects productivity, surface roughness, and process stability. A smaller radial width of cut allows for higher feeds and more even load, which is typical in HSM (high-speed machining) and dynamic milling. A larger width of cut, on the other hand, is suitable when removing material from a wide area in a single pass.
When choosing the width of cut, you should consider the workpiece material, tool diameter, tool overhang, holding solution, and the CNC milling machine being used. Stable fixturing and the right cutting parameters reduce vibration and help prevent premature edge wear.
Width of Cut and Optimization of Cutting Parameters
The width of cut is one of the main machining parameters, along with depth of cut and cutting speed. The balance between these parameters determines the overall efficiency of the machining process. In practice, the machinist adjusts the aₑ value based on the targeted material removal rate and tool durability.
In modern CNC machining, CAM programming enables precise control of the radial width of cut in different machining stages. Correctly chosen width of cut supports controlled chip formation, reduces heat generation, and improves process predictability.
Summary of Radial depth of cut
Width of cut, or aₑ, describes the radial contact width of the tool with the workpiece in milling. It affects average chip thickness hₘ, feed per tooth, cutting forces, and tool life. Properly dimensioned width of cut is a key factor for efficient and controlled machining.
