CNC Machinist Calculator

Free machining calculators for speeds, feeds, tolerances, and more

Cutting Speed Calculator — Convert between SFM, m/min and RPM for any tool diameter
Feed Rate Calculator — Calculate feed rate (IPM/mm/min) from RPM, chip load, and flute count
Machining Time Calculator — Estimate milling, turning, and drilling cycle times
Tap Drill Size Calculator — Look up recommended tap drill for Unified (UNC/UNF) and Metric threads
Tap Drill Size Chart — Complete UNC, UNF, and Metric tap drill size reference table with search
Thread Calculator — Calculate pitch diameter, minor diameter, and thread depth
Hardness Converter — Convert between Rockwell, Brinell, Vickers and Shore hardness scales
Metal Weight Calculator — Calculate stock weight for round, square, flat, hex, tube, angle, and channel shapes
Bolt Circle / Hole Pattern — Calculate X,Y coordinates for equally-spaced holes on a bolt circle
True Position Calculator — Calculate GD&T true position and check against tolerance zone
Lathe Speeds & Feeds — Turning, facing, and parting RPM and feed recommendations by material
ISO Fit & Tolerance Calculator — Calculate hole and shaft tolerances per ISO 286 standard
Gear Ratio Calculator — Calculate gear ratio, output speed and torque for single or multi-stage gear trains
Drilling Speeds & Feeds — Calculate RPM, feed rate, and surface speed for drilling by material and tooling type
Tapping Calculator — Calculate tapping RPM and rigid tapping feed rate for CNC G84 cycle
Bolt Torque Calculator — Tightening torque for SAE Grade 2/5/8 and Metric 8.8/10.9/12.9 bolts
Clamping Force Calculator — Calculate required clamping force from projected area and cavity pressure
Cooling Time Calculator — Estimate cooling time from wall thickness and material thermal properties
Shrinkage Calculator — Calculate mold dimensions accounting for plastic shrinkage rates
Shot Size Calculator — Calculate shot weight, volume, and hourly output
Hold Time Calculator — Estimate packing/hold time based on cooling time and gate freeze-off
Runner Design Calculator — Calculate runner diameter from part weight and runner length
Cycle Time Calculator — Calculate total cycle time from injection, pack, cooling, and open/close times
Belt Length Calculator — Calculate open and cross belt length from pulley diameters and center distance
Chain Length Calculator — Calculate chain length in pitches from sprocket teeth and center distance
Pulley RPM Calculator — Calculate driven pulley speed and belt velocity from pulley diameters and driver RPM
Lead Screw Calculator — Calculate linear speed, travel per revolution, and travel time for lead screws
Bearing Life (L10) Calculator — Calculate L10 bearing life in hours from dynamic load rating and equivalent load
Thread Stripping Strength Calculator — Calculate thread stripping shear area and strip load for UNC and Metric threads
Tensile Stress Area Calculator — Calculate thread tensile stress area and proof load for UNC and Metric fasteners
Gear Geometry Calculator — Calculate pitch, base, outside, and root diameters, center distance, and undercut check for involute spur gears
Spring Calculator — Helical compression/extension and torsion springs: index, Wahl factor, spring rate, shear stress, buckling check
Tribology Calculator — Viscosity index, grease relubrication interval, and bearing friction torque in one tool
Welding Calculator — Arc heat input (kJ/mm) and fillet weld shear stress / throat / required leg length in one tool

Introduction

MachiningCalc is a free machinist calculator hub that keeps shop-floor math for CNC milling, turning, drilling and mold work in one place, so you are not paging through a handbook or a spreadsheet between setups. The calculators cover the four jobs that actually eat setup time: cutting parameters (cutting speed, feed rate, lathe speeds, drilling speeds, machining time), hole and thread work (tap drill size, tapping feed, thread dimensions, bolt circle coordinates, true position), material and fastener data (metal weight, hardness conversion, bolt torque, tensile stress area, thread stripping, ISO 286 fits), and injection-mold process settings (clamping force, cooling time, shrinkage, shot size, hold time, runner design, cycle time). Everything runs in the browser, takes imperial or metric input, and shows the formula behind the answer so you can sanity-check it against your own experience before it goes into a program. The sections below explain what each core calculator computes, the equation it uses, and when a machinist's calculator beats a rule of thumb.

How it Works

Most machinist calculations on this site reduce to a handful of equations, and knowing them tells you which calculator to open. Surface speed and spindle speed are linked by RPM = (SFM × 12) / (π × D), where D is the cutter or workpiece diameter in inches: a 0.5 in carbide end mill at 800 SFM in aluminum lands near 6,100 RPM, while mild steel at 200 SFM drops the same cutter to about 1,530 RPM. The cutting speed calculator carries the material ranges the shop actually runs — 600–1000 SFM for aluminum, 150–250 for mild steel, 100–180 for stainless, 40–80 for titanium — and converts with m/min = SFM × 0.3048. Once RPM is fixed, feed follows from IPM = RPM × chip load × flutes, so a 3-flute cutter at 6,100 RPM and 0.004 in per tooth wants roughly 73 IPM, and machining time is cut length ÷ feed rate × passes + setup. Hole work uses different math: a tap drill is the thread major diameter minus the pitch (M8 × 1.25 → 6.75 mm, rounded to the stocked 6.8 mm drill), bolt-circle holes sit at 360 ÷ N degree steps around the pattern radius, and GD&T true position is the diametral value 2 × √(ΔX² + ΔY²) checked against the tolerance zone. Material and fastener figures come from densities and standards: 7.85 g/cm³ for steel, 2.70 for aluminum, 7.93 for 304 stainless and 4.51 for titanium; bolt torque from T = K × D × F with K near 0.20 dry and 0.15 lubricated; bearing life from L10 = (C/P)^p × 10⁶ / (60n) with p = 3 for ball and 10/3 for roller bearings; and ISO 286 clearance or interference from IT grades 5–11 for pairs such as H7/h6.

Usage Scenarios

Programming a new part: turn the tooling catalogue's SFM and chip-load recommendation into the RPM and feed your control actually wants, then estimate cycle time before you post the program.
Switching material mid-job: the same 1/2 in end mill that ran 6,100 RPM in 6061 has to come down to roughly 1,530 RPM in 1018 steel, and lower again in stainless or titanium.
Setting up a tapped hole: look up the tap drill for UNC, UNF or metric threads, then check the rigid tapping feed so the G84 cycle matches the pitch instead of pulling the tap.
Quoting a job: metal weight by shape and alloy gives stock cost and shipping weight, while machining time gives the labour side of the same quote.
First-article inspection: convert CMM X/Y deviations into a GD&T true position value and see at once whether the hole pattern falls inside its tolerance zone.
Assembly and fixturing: pick a torque for SAE Grade 5/8 or metric 8.8/10.9/12.9 fasteners, check thread engagement against stripping in a tapped aluminum boss, and size an ISO 286 press or clearance fit.
Dialling in an injection tool: clamping force from projected area × injection pressure, cooling time from wall thickness, plus shot size, hold time and runner sizing to close out the cycle.

FAQ

What is a machinist calculator?

A machinist calculator is a set of shop-math tools that convert catalogue and print data into machine settings: surface speed into spindle RPM, chip load into feed rate, thread size into tap drill diameter, measured X/Y deviation into a true position value. MachiningCalc bundles them on one site so milling, turning, drilling, fastener and mold work share the same page instead of needing a separate app or chart for each.

How do I convert SFM to RPM for a given tool diameter?

Use RPM = (SFM × 12) / (π × D) with D in inches; the 12 converts feet to inches. In metric the same relationship is n = (Vc × 1000) / (π × D), with Vc in m/min and D in millimetres. Because diameter is in the denominator, halving the cutter diameter doubles the RPM needed to hold the same surface speed — which is why small cutters run so fast and large face mills run so slowly.

How is the tap drill size worked out?

For metric threads the tap drill is the major diameter minus the pitch, which is the classic 75% thread-engagement rule: M8 × 1.25 gives 8 − 1.25 = 6.75 mm, and the chart rounds that to the 6.8 mm drill you can actually buy. Unified threads follow the same idea using threads per inch, so 1/4-20 lands on a #7 (0.201 in) drill. Going oversize eases tapping torque at the cost of thread strength.

Why does true position double the measured deviation?

GD&T states position tolerance as a diametral zone, not a radius, so the calculator reports 2 × √(ΔX² + ΔY²). A hole 0.003 in off in X and 0.004 in off in Y is 0.005 in from nominal by Pythagoras, which is a true position of 0.010 in — a pass against a ⌀ 0.014 zone and a fail against ⌀ 0.008. Comparing the radial error directly to the callout is the most common way to misread the print.

Do the calculators handle both imperial and metric?

Yes. Speed and feed pages accept inch or millimetre tool diameters and report SFM with m/min and IPM with mm/min side by side, the tap drill chart carries UNC, UNF, metric coarse and metric fine, bolt torque covers SAE Grade 2/5/8 and metric 8.8/10.9/12.9, and metal weight returns both kilograms and pounds.

How accurate are the results?

The formulas are the standard ones and the material tables use published ranges, but every number is a starting point rather than a guarantee. Machine rigidity, holder runout, tool condition, coolant, depth of cut and available spindle power all move the workable window, and the published SFM bands are wide for that reason. Take the calculated value as a first pass, confirm with a test cut, and trust what the machine and the chip tell you.