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Online calculators for CNC lathe work
Everyday lathe math right in your browser, in inch and metric. Turn the numbers into a ready program with the online generator or the Turn G-code app.
RPM ↔ cutting speed
Spindle RPM from cutting speed (SFM or m/min) and diameter — and back, plus feed per minute. For G96/G97.
Thread depth and passes
Metric and UNC/UNF, external and internal: thread depth, minor diameter, pass split.
TPI ↔ thread pitch
Threads per inch to pitch in mm and back, with the nearest standard pitches.
Three-wire thread measurement
Measurement over wires for metric and UNC/UNF, best wire size, pitch diameter from a reading and how much to recut.
Surface finish Ra from feed
Ra and Rz from feed and insert nose radius — and the feed for a target finish.
Machining time
Time per pass, part and batch from length, feed and RPM; passes from stock, handling time.
Taper
Angle ↔ taper ratio 1:N, diameters and length, Morse tapers.
Chamfer and radius
Chamfer legs and hypotenuse from length and angle, X/Z points and G1/G2/G3 lines for chamfers and edge radii.
Sphere and segment
Radius from base diameter and height and back: convex end, dish, ball on a neck — points and a G3 arc.
Drill point depth
How much to add for a 118°, 135° or 140° drill point: blind and through holes, Z for the program.
Hex and square
Across flats ↔ across corners, the round bar you need and the hex a bar will make.
Spot and center drill
Depth Z for a target spot diameter and back: 90° pointed spot drills, 60° center drills with a pilot.
Bar weight
Weight of round, tube, hex, square and flat bar by size and material — per piece, per foot or meter, per batch.
Right triangle
Any two values — legs along Z and X, hypotenuse, angle — give the rest.