Table of Contents

Cutter Adjustment Levers for Force Reduction

When force peaks push close to or beyond tool limits, three cutter-side levers reduce peaks without changing the NC or the toolpath.

Shorten the Flute, Not Only the Overhang

The bending moment at a section of the tool grows with its distance from the cut, and the section that decides the stress ratio is usually the top of the flute core — the thinnest section, and the one farthest from the cut along the flute. A cutter whose length of cut is no longer than the job needs keeps that distance short and lowers the ratio for the same NC.

The overhang — the stick-out below the holder nose — moves the ratio only where a section above the flute is weaker than that core: a long, thin neck, or a stick-out several times the length of cut. On a plain shank, shortening it leaves the stress ratio where it was, although it still makes the tool stiffer and its deflection smaller.

Process documents may fix the overhang for procedural reasons. A cutter with a shorter flute is often the cheapest mitigation before tuning anything else; shortening the overhang is the lever for deflection, and for the ratio only on a necked tool.

Adjust Core Radius

The core here is the flute's bending-equivalent core: at each height, the solid circle whose area moment of inertia equals that of the whole fluted section, web and teeth together — not the web, the circle inscribed at the flute bottoms. The cutter deflection reads its moment of inertia and area, the stress ratio reads the same moment of inertia with the outer fibre at the flute's own radius, and the shank-mass estimate and the shank thermal model read its volume; it does not change the cut shape. The physical core of a cutter cannot be measured from outside, and it would not be this core anyway: the literature puts the bending-equivalent diameter of end mills at 0.7–0.85 of the flute diameter.

The core radius is a fraction of the flute radius, one constant per cutter — the same at every height, in every direction and on a ball nose as on a flat end — and its default follows the flute count: 0.75 for two flutes, 0.76 for three and 0.78 for four, from the literature's static values; 0.74 for one flute and 0.79, 0.80, 0.81 and 0.82 for five, six, seven and eight or more, assumed on the trend that a section with more flutes is nearer to solid, with no measurement behind them; 1 with no fluting. A cutter on this default saves no ratio and reads the table when it loads; a ratio of your own is saved with the cutter. Heavy-cut cutters narrow the chip-evacuation flute to thicken the core, raising bending strength. If the cutter routinely tolerates stress ratios around 200 % without breakage, its fluted section is stiffer than the default — raise the ratio in steps of about 0.02–0.05 until the simulated ratio aligns with the observed safety margin: the literature's range is narrow, and the stress of a flute section goes with the inverse fourth power of the ratio.

The Tool House edits the ratio on the cutter's Inner Beam node, which is in the tool's Control Tree while Show Physics Options is on: Profile Type Flute Dependent Ratio Profile is the flute-count default above, and Const Ratio Profile takes a Radius Ratio of your own, between 0 and 1. Over HTTP the same edit is PUT /api/Cutter/{id}/inner-beam with {"Type": "ConstRatioProfile", "RadiusRatio": 0.7}. In the cutter's XML it is <InnerBeamProfile><ConstRatioProfile><RadiusRatio>0.7</RadiusRatio></ConstRatioProfile></InnerBeamProfile>, and through the .NET API it is InnerBeamProfile(API) set to a ConstRatioProfile(API) carrying the ratio.

Upgrade Cutter Material

WC-Co6-800nm is the usual baseline choice. It is not applied by default: a cutter carries no flute material until one is loaded, and without one the stress ratio is not computed and thermal physics is skipped (Tool-FluteMaterial--Missing). A carbide has no yield point, so the stress ratio divides by its tensile strength (TensileStrength_MPa), as it does for every shipped cutter material; its fracture strength (FractureStrength_MPa), like that of the other shipped carbides the median catalogue transverse rupture strength of current rod grades of its class, is divided by no ratio. A finer grain or more cobalt raises both strengths a little, and a finer grain also tolerates heat better; a coating does not raise them:

  • WC-Co6-TiC-400nm — finer grain with TiC. A reasonable upgrade when the cutter quality is unknown but suspected better than the baseline.

For a known cutter, configure the matching material file under Resource/CutterMaterial/ rather than guessing the grade: its tensile strength, the highest stress of a tensile test, in TensileStrength_MPa, the line the stress ratio divides a carbide's stress by; NotDuctile in YieldStrength_MPa, as the shipped carbides write it (<YieldStrength_MPa>NotDuctile</YieldStrength_MPa>), since a carbide has no yield point — the compressive yield or proof stress some vendors publish is another loading, and a yield strength given as a number would take the line; and, if you have it, the transverse rupture strength of its rod grade, from the rod maker's catalogue, in FractureStrength_MPa, which no ratio divides by. A file that leaves YieldStrength_MPa out reads it as not known, and its line is the tensile strength as well. A material file of your own is read as written — HeatConductivity_WdmK in W/(m·K), Density_gdcm3 in g/cm³, HeatCapacity_JdgK in J/(g·K) — and a constant that is not a finite positive number or lies outside the range of a solid is named when the material is loaded and when the tool is changed (Material-ThermalConstants--NotFinitePositive, Material-ThermalConstants--OutOfRange). An element the file lacks is not given, and no default stands in: the tool is left without a thermal step — its temperatures stay at ambient and its wear at zero — and the material is named at the same places (Material-ThermalConstants--NotGiven). A cutter material file without its hardness or wear-coefficient curve (TemperatureVsHardnessCurve, TemperatureVsWearCoefficientCurve) is named the same way (Material-WearCurves--NotGiven): the native thermal model does not run for the tool.

Before Reaching for the Cutter

The cutter-side levers above are for when the cutting parameters have already been tried, because the parameters are cheaper to change. In order:

  1. Reduce feed per tooth. The most direct route to lower force, and the one the optimizer itself takes.
  2. Reduce depth of cut, or width of cut. Where feed per tooth alone is not enough. Both cut the engagement rather than the chip load per tooth, so both cost more cycle time per unit of force removed.

Only when those are exhausted, or when they would cost more cycle time than the job can afford, do the cutter-side levers become the better trade.

See Also