How we verify
Methodology and verification
Machining math should be auditable, not just authoritative-looking. Every one of these 27 calculators shows its formula and cites its sources, and the math is held to a layered set of automated checks. Here is exactly what we do, and what we deliberately do not claim.
What we claim, and what we do not
We aim to match the established tools and references, and to win on delivery: free, fast, with the formula on the page and the sources linked. We do not claim our numbers are more accurate than the standards or the tool-maker data. Where a value is a starting point rather than a fixed truth, we say so.
How the math is checked
The calculators are verified in layers, strongest ground truth first:
- Definitional checks. Anything that is arithmetic against an agreed definition (RPM from surface speed, board geometry, thread depth) is asserted to its exact value.
- Published worked examples. Answers that an expert already computed and published, pinned exactly: standard tap-drill chart values, a tool maker's thread-milling feed example, ASTM E140 hardness points. These carry no circular-reference risk.
- Independent re-derivation. Canonical formulas are re-implemented from the definition and cross-checked against the calculator across a sweep of inputs, to catch a silent algebra slip no eyeball would.
- Property tests. Hundreds of random inputs check structural rules that any machinist would catch instantly if broken: more depth means more power, a smaller stepover means a smaller scallop, converting units then computing equals computing then converting.
- A frozen baseline. A battery of representative inputs and their reviewed outputs is locked in; any future change that moves a number fails the build until a human confirms it was intended.
Declared conventions
Where sources disagree, we pick one convention, apply it consistently, and show it rather than hiding the choice. For example: tap drills target 75 percent thread engagement; single-point thread depth uses the standard 0.6134 times pitch; form-tap holes use the published 0.0068 factor; hardness conversions follow ASTM E140 for steel. Each calculator's formula and sources are on its page.
What stays a starting point
Recommended surface speeds and chip loads are conservative published starting values, not the exact right number for your specific tool, coating, machine rigidity and coolant. Power and deflection figures are static estimates. Treat the output as a place to begin, verify against your tool maker's data, and start conservative. These calculators are for planning and as a starting point. Recommended speeds and feeds are published starting values that vary with your specific tool, coating, machine rigidity, workholding and coolant. Always start conservative, listen to the cut, and follow your tool maker data sheet.
Found an error?
Because the formulas and sources are visible, you can check the math yourself. A confirmed correction becomes a permanent test, so a fixed value can never quietly come back. The cutting-data table and the about page cover the data sources in more detail.