Feedwright CNC Calculator

What it does

Feedwright is a shop calculator for machinists, CNC programmers and operators, toolmakers and students. It works like a hardware calculator: a steel-blue chassis, real keys and a clear LCD, with each answer labelled so you know what you are reading. Results are shown in decimals, the way machinists read them.

Worked examples

• Spindle rpm. 800 SFM on a 1/2 in tool -> 6112 RPM.
• Feed rate. 6112 RPM, 0.002 in chip load, 4 flutes -> feed 48.9 in/min (then IPR).
• Tap drill. 1/4-20 at 75 percent thread -> tap drill 0.2013.
• Bolt circle. 6 holes on a 4.000 bolt circle -> hole 2 Y 1.7321.
• Taper. 1.000 to 0.750 over 3 in -> included angle 4.77 degrees.
• Metric rpm. Metric: 150 m/min on a 10 mm tool -> 4775 RPM.

How it's calculated

Every trade key and the formula behind it, as shown in the app's key guide. A second legend is the shifted function.

SFM m/minSurface feet per minute / Cutting speed, metres per minute

Stores the typed surface speed in feet per minute, or solves SFM = π × D × RPM ÷ 12; shifted works in metres per minute, Vc = π × D(mm) × RPM ÷ 1000.

RPM DiaSpindle speed / Diameter

Stores the typed spindle speed, or solves RPM = SFM × 12 ÷ (π × D) from the stored speed and diameter; shifted stores the tool or work diameter.

Feed IPRFeed rate / Feed per revolution

Stores the typed feed rate, or solves Feed = RPM × chip load × teeth; press again for feed per revolution. Shifted turns a typed feed per revolution into Feed = IPR × RPM.

Chip TeethChip load per tooth / Number of teeth

Stores the typed chip load per tooth, or solves chip load = Feed ÷ (RPM × teeth); shifted stores the flute count.

Thread TPI/PThread / Threads per inch or pitch

Stores the typed major diameter, or steps through it, pitch diameter D − 0.6495 × P, minor diameters and thread height; shifted stores threads per inch, or the pitch in mm for a metric thread.

TapDr %ThdTap drill / Percent thread

Tap drill = D − 1.299 × P × percent ÷ 100 for the stored thread; a typed drill size gives its percent thread instead. Shifted stores the percent thread, 75 by default.

Bolt HolesBolt circle / Bolt holes

Stores the typed bolt circle diameter, or steps through it, each hole's X and Y from the centre and the chord between holes; shifted stores the hole count, or a typed angle as the first hole's start angle.

Taper LengthTaper / Taper length

Type the large then the small diameter, pressing Taper after each; then gives the included angle 2 × atan((D − d) ÷ 2L), the compound setting, taper per foot and ratio. A typed angle gives the other diameter. Shifted stores the length.

Sine BarSine bar / Sine bar length

Gauge block stack = L × sin(angle) for the typed angle; a typed length gives the angle instead. Shifted stores the bar length, 5 inches or 100 mm by default.

Mat DataMaterial / Material speeds and hardness

Steps through workpiece materials; shifted shows starting surface speed ranges for high-speed steel and carbide (starting values only: adjust for machine and tool). A typed Brinell indentation in mm gives HB = 2F ÷ (πD(D − √(D² − d²))).

Results are computed from the formulas shown for each function and are provided for reference only. Material speeds are starting values: adjust for your machine, tooling, setup and coolant, and follow the tool maker's data. Verify every dimension before machining. The developer accepts no liability for loss or damage arising from use.