Workshop calculators for the home machine shop
Speeds and feeds, thread sizes, tap drills, bolt circles and change gears, built with UK model engineers in mind. Metric first, imperial at a tap. Every calculator shows its working, so you can check it.
Open speeds & feeds →Calculators
How-to guides
Step-by-step: cutting a thread on the lathe and marking out a PCD.
Flanges & valves
RF, FF and RTJ facings, finishes, weld and socket ends, modifications, plus a bevel & counterbore calculator.
Glossary
Plain-English meanings of every term on the site.
Speeds & feeds
Turning, drilling, milling, parting, threading and more for 60+ materials, from EN1A through to duplex, Inconel® and titanium. Includes a derate for hobby machines.
Thread calculator
Metric, BA, BSW, BSF, ME, UNC/UNF, BSP, Acme and Trapezoidal. Gives major, minor and pitch diameters, depth and tool tip.
Tap drill finder
Pick a thread and a % of thread. It gives the nearest metric, number, letter and fractional drill.
Lathe RPM
Spindle speed from cutting speed and diameter (m/min or SFM), and the reverse.
PCD / bolt circle
Hole coordinates for a DRO, the chord for dividers, and a drawing.
Change gears
Simple and compound trains from your own gear set, including 127T metric conversion.
Why another calculator site?
Most speeds and feeds charts assume a rigid industrial machine and a US audience. Here you’ll find British material names (EN1A, EN8, EN24T, CZ121), British threads (BA, BSW, BSF, ME, BSP) and a derate for Myford-, Boxford- and mini-lathe-sized machines. Figures that couldn’t be checked against a published source are marked est..
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Just for fun
How many double-decker buses long is your workshop? How many Mars bars does your lathe weigh? Try the silly converter: length, weight, volume, area, speed and time, compared with buses, blue whales, Big Ben, Wales and more.