Cutting Tool Calculators

Operation

Workpiece Material

Tool / Workpiece Diameter — D (mm)

Cutting Speed — Vc (m/min)

Number of Flutes / Teeth — Z

Feed per Tooth — fz (mm)

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Spindle Speed (RPM)

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Table Feed Rate (mm/min)

N = (Vc × 1000) / (π × D). Feed rate = fz × Z × N for milling/drilling, or fn × N for turning. This gives a starting point — fine-tune for machine rigidity, coolant and tool overhang.

Thread System

Thread Size

Nominal Diameter (mm)

Pitch (mm)

Thread Engagement (%)

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Recommended Tap Drill Diameter

Drill Ø = Nominal Ø − (Pitch × 1.299 × engagement%). Round down to the nearest available drill size. Reference charts below use the standard 75% engagement.

Quick Reference — Metric Coarse (75% Engagement)

Thread	Pitch (mm)	Tap Drill Ø (mm)

Quick Reference — UNC (75% Engagement)

Thread	TPI	Tap Drill Ø (in)	Tap Drill Ø (mm)

Quick Reference — UNF (75% Engagement)

Thread	TPI	Tap Drill Ø (in)	Tap Drill Ø (mm)

Quick Reference — Roll Tap / Form Tap, Metric (65% Full Thread)

Thread-forming (roll) taps displace metal rather than cutting it, so they need a larger starting hole than a cut tap of the same size — using a cut-tap drill size will leave too much material for the tap to displace. Formula: Drill Ø = Nominal Ø − (Pitch × 0.0068 × % of full thread). 65% is the typical recommended engagement (Machinery's Handbook); avoid exceeding 75%.

Thread	Pitch (mm)	Tap Drill Ø (mm)

Quick Reference — Roll Tap / Form Tap, UNC (65% Full Thread)

Thread	TPI	Tap Drill Ø (in)	Tap Drill Ø (mm)

Quick Reference — Roll Tap / Form Tap, UNF (65% Full Thread)

Thread	TPI	Tap Drill Ø (in)	Tap Drill Ø (mm)

Quick Reference — BSP Parallel / BSPP (Pipe Thread)

55° Whitworth pipe form — fixed standard drill sizes for direct tapping, not derived from the 60°-thread engagement formula above.

Pipe Size	TPI	Tap Drill Ø (in)	Tap Drill Ø (mm)

Quick Reference — BSP Tapered / BSPT (Pipe Thread)

Pipe Size	TPI	Tap Drill Ø (in)	Tap Drill Ø (mm)

Quick Reference — NPT (American Pipe Taper)

60° tapered pipe thread to ASME B1.20.1 — the North American counterpart to BSPT, used on NPT/NPTF fittings, nipples and couplings. Fixed standard drill sizes for direct tapping, not derived from the 60°-thread engagement formula above.

Pipe Size	TPI	Tap Drill Ø (in)	Tap Drill Ø (mm)

Quick Reference — BSW (British Standard Whitworth)

55° Whitworth thread form for legacy machinery, fasteners and restoration work.

Thread	TPI	Tap Drill Ø (mm)	Tap Drill Ø (in)

Quick Reference — Heli-Coil / STI Wire Thread Insert (Imperial)

STI (Screw Thread Insert) taps cut an oversized installation thread to house the coil — always use the matching STI tap, never a standard tap, for these sizes.

Nominal Thread	STI Tap	Tap Drill	Tap Drill Ø (in)

Quick Reference — Heli-Coil / STI Wire Thread Insert (Metric)

Nominal Thread	STI Tap	Tap Drill Ø (mm)

Pipe-thread (BSP/BSPT/NPT/BSW) and Heli-Coil/STI values above are standard published reference figures. Insert-system drill sizes can vary slightly between manufacturers — always confirm against the specific tap or insert maker's datasheet before running production.

Millimetres (mm)

Inches (in)

Cutting Speed — Metres/Min (m/min)

Cutting Speed — Surface Ft/Min (SFM)

1 inch = 25.4 mm exactly. 1 m/min = 3.28084 SFM. Type into any field — the rest update automatically.

Quick Reference — Fractional Inches

Fraction	Decimal (in)	mm

Material Section — Diameter or Wall Thickness

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Recommended TPI (Constant Pitch)

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Recommended Variable Pitch

The rule of thumb: keep 3–24 teeth in contact with the material at all times — too few teeth per cut chips or strips the blade, too many clog the gullets and slow the cut. Variable-pitch blades (e.g. 4/6, 6/10) smooth this out across a size range and reduce harmonic vibration/noise.

Quick Reference — Bandsaw Blade TPI by Section Size

General starting points for cutting mild/alloy steel bar and structural sections — for stringy/gummy materials (aluminium, non-ferrous, thin-wall tube) go one step finer; for free-machining or brittle materials you can go one step coarser. Always confirm against Lenox's blade selection chart for the specific alloy and blade type.

Section Size	Constant Pitch	Variable Pitch

Typical cutting-speed ranges by workpiece material — general industry reference values, not brand-specific specs. Click a material to send it straight into the Speed & Feed calculator.