Step Field Reference

Every simulated step carries a row of output: the NC line it came from, the kinematics, the load, and what that load did to the cutter. The field-by-field definitions are generated — MachiningStep is the complete and current list, and it is not copied here. This page states what each group covers, how the numbers are to be read, and the two readings that are most often misread.

How a Step's Numbers Are Formed

A step's data covers the time interval between two consecutive steps — from the previous step to this one — not an instant. Most fields are therefore a simplification over that period, and the prefix says which: Avg (average), Min / Max (extremes), Delta (range) and MaxAbs (maximum absolute value).

A field that depends on a frame carries the frame in its name: [W] workpiece, [TR] tool running, [SR] spindle rotation. The frames themselves are defined in Milling Physics Coordinates.

Field Groups

Group	What it covers
Source	The file, line, line text and flags of the NC command that produced the step, its index in the run, and the active tool id
Time and motion	End-of-step timecode, step duration (one spindle revolution in the default per-revolution mode), spindle angle at the start, the cutter location with its IJK normal, the machine coordinates, the displacement in program coordinates, and the feed / spindle-speed / cutting-speed / per-tooth family
Engagement and removal	Whether the cutter was engaged at all, radial and axial engagement (ae, ap), material removal rate, and the program-side cusp height and its distribution
Chip	Chip thickness, volume and mass
Force and torque	Average and maximum force on the tool, torques about the tool tip and about the sensor point in each frame, and the mapping-comparison fields that put a measured signal beside the simulated one — error ratios and symbolic error correlation
Power and energy	Spindle input power (what enters the spindle) and output power (what reaches the cut after spindle losses; the ratio between them is the spindle's configured EnergyEfficiency(API)), the instantaneous and continuous power and torque ratios against the spindle capability curve, and accumulated energy consumption
Thermal	Cutter body, cutter surface, workpiece surface and chip temperatures, cutter subsurface temperature at a given depth, and thermal stress with its yield ratio
Wear and deflection	Instantaneous and accumulated crater wear, accumulated flank wear depth and width, tool tip and bottom-edge deflection, and re-cut depth

For what the thermal yield ratio implies about breakage risk see Evaluating Process Machinability; for the wear model behind the wear fields see Tool Life and Wear.

Note

EndTimecode was named AccumulatedTime before the rename, and step CSVs written with the legacy header are still read.

Two Readings That Are Usually Misread

A cusp spike is usually a rapid-move collision, not a finish result

The program-side cusp is computed from the ideal program feedrate while the cutter is engaged with the workpiece. A rapid traverse is not meant to touch material; when it does, the cusp formula is fed the (very high) rapid feedrate, so the value spikes far above any real cutting cusp. Treat an isolated cusp peak at a rapid / G00 line as a likely gouge or collision to investigate. The same engagement-during-rapid usually shows up beside it as spikes in the availability ratios — yielding stress, spindle torque, spindle power.

A power or torque ratio over 100% is load damage, and it is read by duration

A ratio above 100% means the spindle cannot supply the demanded load at the commanded rpm, so it droops: with feed held, rpm drops, feed-per-tooth rises, and forces climb further — a runaway loop that, left unchecked, grows the chip until the cutter breaks and the spindle and drive are overstressed. That is load damage, not a tool-versus-workpiece collision (see NC optimization).

Read it by duration, not just by height. A one-revolution overshoot usually still completes the pass, leaving a slightly insufficient cut there; a ratio that stays above 100% across many consecutive spindle revolutions is a genuine overload to fix. A high-load step typically also shows large cutter–workpiece engagement, large tip deflection, and more vibration and noise. Because the ratio is normalized by the spindle-capability curve, a placeholder or guessed spindle skews it — confirm against the real spindle's speed–power and speed–torque curves before calling a cut overloaded.

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