At low radial engagement, an edge does not reach the point where chip thickness equals programmed fz. Without correction, the cutter may work with an unexpectedly thin chip.
Why the chip becomes thinner
For a 90-degree shoulder end mill, maximum chip thickness depends on the engagement angle. Near ae = 50% of diameter, maximum chip thickness approaches fz. As ae decreases, the maximum thickness falls below programmed fz.
Simplified side-milling correction
Engagement angle
φ = arccos(1 − 2 × ae / D)Programmed chip load
fz = hmax / sin(φ)This assumption is for a 90-degree cutter and simple side engagement. Use tool-maker or CAM models for other entering angles, ball-nose tools and complex engagement.
Example: 10 mm cutter and ae = 1 mm
At ae/D = 10%, φ is about 36.9 degrees. To obtain hmax = 0.05 mm, programmed fz is about 0.083 mm/tooth. This does not mean feed can always be raised by 67%: power, deflection, corner engagement and axis-feed limits still apply.
Do not apply the correction blindly
- avoid automatic correction in a full slot or rapidly changing ae,
- check whether CAM already modifies corner feed,
- use the correct model for the cutter's entering angle,
- respect power, vibration, workholding and machine-feed limits.
Controlled engagement first. The correction is most predictable on toolpaths that keep ae nearly constant.