Tool failure

The peak von-Mises stress experienced by the tool over one revolution is higher than the configured limit. Often, the peak stress will occur either at the upper end of the cutting flutes where the bending moments are already large but the endmill is weak, or, for long tool stick-out, directly at the interface to the toolholder/collet.

Even if the tool does not break immediately for conditions where this warning is shown, it will probably not last long because the high stresses are likely to initiate small cracks. As the stresses cycle with each revolution, these cracks will grow and soon lead to fatigue failure.

Alleviation: Increase tool diameter or reduce AP, AE or HEX.

Computation of tool stress is based on a representative tool geometry for each flute count. Stresses that are actually encountered by the tool can therefore be both larger and smaller than computed. Tools with large chip space will tend to encounter larger stress, while those with a larger core diameter and less chip space will be stressed less.

High tool stress

Peak stresses are approaching the failure limit or exceed the user-defined limit in the machine limit settings; there is a pronounced risk for tool fatigue when these conditions are maintained for long.

Reduce AP, AE or HEX or increase tool diameter.

Large rake angle

The tool geometry is probably not suitable for the material (steel/titanium/nickel alloy). Prefer a tool with smaller rake angle [GAMF] for high-strength workpiece materials to reduce the risk for edge chipping and extend tool life.

Small edge radius

The tool geometry is probably not suitable for the material (steel/titanium/nickel alloy).

Choose a tool with larger (lapped or honed) cutting edge radius [EDRD] for high-strength materials to avoid edge chipping and extend useful tool life.

BUE risk, low VC

The cutting speed is too low, there is a risk for built-up edges.

Alleviation: Increase spindle speed [N] or tool diameter [DC].


The cutting edge is at risk of ploughing or sliding over the material instead of cutting.

Alleviation: Increase chip-load [HEX], choose a tool with smaller cutting edge radius [EDRD], or switch from conventional to climb milling.

Chip space

The amount of material removed per revolution is too large for the tool geometry; there is not enough space in the flutes for this chip-load.

Ignore this warning if the tool manufacturer recommends the chosen feed/chip-load. Some specialized endmills (one or two flutes, marketed as large chip removal) are ground to allow for very large chip thickness values.

Alleviation: Reduce chip-load [HEX].

Torque limit

The required torque exceeds the capabilities of the spindle as configured in the machine limits (see Edit - Machine limits).

Alleviation: Reduce AP, AE, HEX or decrease tool diameter.

Peak forces

At least once per revolution, the user-defined peak force limit is exceeded.

Alleviation: Reduce AP, AE or feed.

Mean forces

Forces averaged over one revolution exceed user-defined limits. These forces are also responsible for the averaged tool displacement.

Alleviation: Reduce AP, AE or feed.

Unsuitable material

The selected tool is not nominally suitable to mill the current material. Depending on the material, this may or may not be a problem.

Using an endmill designed for aluminum (code N) for milling steel (code P or H), for instance, will produce simulation results that look good, but are utterly unrealistic: The cutting edges of tools for softer aluminum are usually ground very sharp and equipped with large gullets to allow for large chip volume. These features compromise the strength of the edges which will therefore be damaged very quickly when used in harder materials. Furthermore, the cutting force simulation for steel assumes that the tool is coated (TiAlN or equivalent), which endmills for aluminum are not.

Similarly, using a TiAlN-coated endmill that is ground for steel for cutting aluminum is possible, but not advisable. As the aluminum will tend to adhere to this coating much more than to a polished uncoated surface, it may accumulate, clog the gullets or result in built-up edges (BUE). None of these effects are simulated.

Alleviation: Choose suitable tool.*