Milling calculations (user guide)

mfgparams calculates parameters for two milling sub-operations — end milling and face milling — alongside drilling. This page covers using them from the interactive text GUI; see Milling API reference (developers) for the library API.

Selecting an operation in the text GUI

Launch the text GUI with:

mfgparams

A persistent menu bar stays visible at the top of the screen: Exit, Machining, Configuration, About, Help. Selecting Machining expands a tree in place, showing Milling and Drilling as flat leaves; selecting Milling opens its operation screen directly. It appears as a centered, bordered floating window over the menu bar and tree (which stay visible underneath, untouched): the left pane lists every milling input at once — the sub-operation choice (end milling or face milling), unit system, calculation mode, material type, material, and the appropriate tool (end-mill or face-mill), plus the geometry fields below — all simultaneously visible and editable, with no separate screen per field; the right pane shows the live result, updating automatically as you fill in or change an input. Changing the sub-operation choice switches which set of remembered answers the rest of the screen shows, without closing and reopening it. Selecting Drilling from the tree instead leads to the flow described in Drilling calculations (user guide).

Up/Down (or j/k) always moves to the next/previous field, regardless of its type. A radio field (sub-operation, unit system, mode, material type, material, tool) is always a single Label: value line — Left/Right/h/l/Space cycle its value with wraparound and commit it immediately, with no separate confirm step. Once metal is chosen as the material type, the Material field also opens a dedicated selection window on Enter, on top of that ordinary cycling — see Selecting a metal material below. Numeric fields become editable the instant you select them — start typing a digit (or ./-) and it edits the field’s buffer immediately, no separate “start editing” step; Left/Right nudges the buffer up or down by a small step: 1 display unit (mm or in) for number of teeth, available power, and target RPM. Cutter diameter, axial depth of cut, radial engagement/width of cut, and length of cut nudge by 1 mm under the metric unit system (unchanged), or 0.1 in under the imperial unit system — a whole-inch step is too coarse for these dimensions. Feed per tooth nudges by a finer step still: 0.1 mm/tooth under the metric unit system, or 0.001 in/tooth under imperial — a standard chip-load shop-practice increment, not a literal conversion of the metric value — for either sub-operation. Backspace removes the last character. That text is only written to the field once you navigate away from it (Up/Down) — text that still doesn’t parse as a number at that point is discarded (the field keeps its last valid value) and a message appears in the status bar beneath both panes until you correct it.

Pressing Escape moves focus back to the menu bar without closing the open screen; pressing Escape again, from the menu bar, closes it and returns to the menu bar/tree, letting you start another calculation without leaving the text GUI. Each operation (and each milling sub-operation) remembers its own previous answers as defaults for the rest of the session, so switching from end milling to drilling and back does not lose your milling inputs.

Selecting a metal material

Once metal is chosen as the material type, the Material field still cycles one material at a time with Left/Right/h/l/Space, exactly like any other radio field — but pressing Enter on it instead opens a centered selection window for finding a material by more than just cycling through the list. It lists every metal material in three columns — common name, EN material number (e.g. 1.0038), and shortened/DIN-style designation (e.g. S235JR) — with an independent search field for each column; a material missing a recorded number/designation shows that cell blank. Tab/Right and Shift+Tab/Left switch which column’s search field receives typed characters, without losing text already typed into the others; typing narrows the list to materials matching every non-empty search across all three columns at once. Up/Down move the highlighted row; Enter selects the highlighted material and closes the window; Escape closes it without changing the current selection. Reopening the window always starts with the material you already had selected (if any) highlighted, and every search field cleared. This behaves identically to Drilling calculations (user guide)’s own Material field (same columns, search, navigation, and confirm/cancel keys), for either sub-operation — see that page’s own “Selecting a metal material” section, or specs/023-material-selector-dialog/contracts/materials-config-schema-delta.md, for the materials-config schema that populates the extra two columns. Non-metal material types are unaffected and only ever offer the ordinary Left/Right/Space radio-cycling behavior, with no selection window.

End milling inputs

After the unit system, material type, material and tool, end milling asks for six geometry values:

Prompt	Meaning
Cutter diameter	Diameter of the end mill (mm / in).
Axial depth of cut	Depth the cutter is stepped down into the workpiece (ap), in mm / in.
Radial depth of cut	Sideways engagement into the material (ae), in mm / in. Must not exceed the cutter diameter.
Feed per tooth	Chip load per cutting edge (fz), in mm/tooth or in/tooth.
Number of teeth	Number of cutting edges on the cutter (a whole number).
Length of cut	Total distance the cutter travels through the cut, in mm / in. This drives the machining time.

Face milling inputs

Face milling asks the same six values, except that radial depth of cut is replaced by width of cut — the width of the surface being faced, measured across the cutter. As with end milling it must not exceed the cutter diameter.

Calculation modes

Right after choosing the unit system, the text GUI asks for a calculation mode: standard, power-constrained, or fixed-rpm.

standard

The unconstrained calculation used throughout the rest of this guide. Available power stays optional and only advisory: if the calculated power exceeds it, the result is shown anyway with a warning.

power-constrained

Available power becomes a required field instead of an optional one. If your machine can already deliver the calculated power the result is unchanged. Otherwise the spindle speed is reduced until the power required matches what you supplied exactly, and the result label reads “adjusted to fit available power” instead of “recommended”. A budget too small for any feasible spindle speed produces an error in the right pane — correct the available-power field in place to retry.

fixed-rpm

Adds a required “Target spindle speed (RPM)” field. The spindle speed in the result is exactly what you entered — labeled “user-specified” — and every other value is recomputed for that speed. Available power stays optional/advisory here too, so an insufficient machine still produces a result, with a warning.

Switching mode on an open Milling screen clears any previous mode’s power/RPM answer rather than carrying it over as a stale default.

Reading the results

A milling result looks like this:

Spindle speed:     1989.4 RPM   (recommended)
Feed rate:         397.9 mm/min
Machining time:    0.25 min
Torque:            0.6 N·m
Power required:    0.13 kW
Material removal:  3.98 cm³/min

The first five lines mean the same as they do for drilling. The extra line is specific to milling:

Material removal (Q) is the volumetric material removal rate — how much material the cut removes per minute. It is reported in cm³/min under metric and in³/min under imperial. It is a useful sanity check on how aggressive a cut is, and scales directly with depth of cut, engagement width and feed rate. Drilling does not report a material removal rate, so that line never appears in a drilling result.

If you supply an available machine power and the calculated power exceeds it, the result is still shown, with a warning line telling you the cut is beyond what the machine can deliver.

Limits and validation

Milling inputs are validated as part of the calculation itself: an out-of-range value produces a clear, actionable error in the right pane rather than a result, and the field stays editable in place to correct it — nothing is discarded and the session never aborts. Text that cannot be parsed as a number at all is caught even earlier, before it ever reaches the calculation, with its own distinct message. The bounds are configurable (see the configuration documentation); the defaults are:

Setting	Default	Applies to
max_mill_diameter_mm	200.0 mm	Cutter diameter.
max_depth_of_cut_mm	50.0 mm	Both axial depth and radial depth / width of cut.
max_length_of_cut_mm	1000.0 mm	Length of cut.

In addition, every value must be a positive, finite number; the number of teeth must be a whole number; and the radial depth / width of cut must not exceed the cutter diameter.

Assumptions

The milling model assumes full, symmetric engagement and applies no radial chip-thinning compensation. For light radial engagements the real chip load is thinner than the nominal feed per tooth, so the calculated feed is conservative. See specs/009-milling-calculations/research.md for the formulas and their sources.