About DatumCalc

The idea

Most machining math is public: the speed and feed formulas are textbook, and tap drill and thread data come straight from published standards. The good calculators that exist tend to be paid apps or dated desktop software, and the free ones are usually thin, vendor-locked, or assume you already know the surface speed and chip load. The aim here is the missing middle: free, fast, mobile-friendly tools with the working shown and the source cited.

How the cutting data is put together

The 21 materials behind the feeds and speeds calculator carry a starting surface speed for HSS and carbide and a chip load by tool diameter. These conservative starting values come from a mix of free published sources: tool-maker charts (Harvey Tool, Lakeshore Carbide) for most metals, manufacturer grade datasheets for the tool steels, Machining Doctor and Sandvik for the cutting-power constants, and a general speeds-and-feeds overview where no chart value existed. Every material lists its own sources on the cutting-data page, and any value that was generalized or estimated rather than read straight from a chart is flagged in the data so you can weigh it accordingly.

The numbers in tap drill and thread tools are derived from the thread geometry itself, not copied from a single chart, which is why the calculator agrees with the standard published charts on the common sizes while still handling any size you enter.

How the math is checked

Formulas compiled from the web can be plausible and still subtly wrong, and a spun-up calculator looks authoritative either way. So every formula here is held to a layered set of automated checks, strongest ground truth first: definitional results asserted to their exact value, published worked examples from standards and tool-maker datasheets pinned exactly, canonical formulas re-derived from the definition and cross-checked across a sweep of inputs, and hundreds of random-input property tests that enforce the structural rules a machinist would catch instantly, such as more depth of cut always needing more spindle power, or a smaller stepover always leaving a smaller scallop. A frozen baseline of reviewed input-output pairs then fails the build if any later change quietly moves a number. The methodology page lays this out in full.

Where established references disagree on a convention, we pick one, apply it consistently, and show it rather than hiding the choice: tap drills target seventy-five percent thread engagement, single-point thread depth uses the standard factor, hardness follows ASTM E140 for steel, and so on. Each calculator shows its formula and links its sources, so you can check the working yourself instead of trusting a black box. If you find something wrong, the page invites a correction, and a confirmed fix becomes a permanent test so it cannot come back.

Working with the calculators

Every numeric input is itself a small calculator: fields accept math the way CAD dimension boxes do. Type 3/8 + 1/16, a mixed number like 1 1/8, or parenthesized arithmetic, and length fields also take unit suffixes such as 25.4mm/2 or 1in + 2mm, converted into whatever unit the field is currently in. The expression stays editable in the field and the evaluated value appears just below it. Two more workflow tools live under each calculator: Transfer copies named values (a pitch diameter, a feed, an RPM) between calculators that share them, and Saved setups stores a calculator's inputs in your browser for reuse, with export and import. Units switch site-wide with the Imperial/Metric toggle on any calculator, and your choice sticks.

Who it is for

Hobby and professional machinists, CNC router and mill users, students, and anyone who wants a quick, honest starting point without a login or a paywall. The tools work on a phone at the machine and on a desktop when planning a job. There is no account to create, nothing to install, and no upsell; the calculators are the product, and the cutting data behind them is open.

What these tools cannot do

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.