Mechanical Design Guide
The calculations that hold machines together: torque and power transmission, fastener preload, bearings, springs, hydraulics and machining basics — each concept linked to its calculator.
Speed, torque and power: the triangle
Mechanical power is torque × rotational speed, always. Gears, belts and chains trade speed for torque at roughly constant power (minus a few percent per mesh). A 3:1 reduction triples torque and cuts speed to a third — that's all a gearbox does, and everything from cordless drills to truck transmissions applies it.
The gear ratio calculator works tooth counts; the pulley RPM calculator works diameters for belt drives; the torque-power calculator converts any combination into kW and hp. Speed ratios compose: two stages multiply.
Fasteners: torque is a proxy for stretch
A bolted joint works because the bolt stretches and clamps. Torque is just the proxy we control: roughly 90% of tightening torque is consumed by friction, only 10% becomes preload. That's why lubrication changes everything — the same preload needs 25% less torque with oil on the threads.
The bolt torque calculator computes the standard 75%-of-proof target for each ISO grade and size. When an extension or crowfoot sits in line with the handle, the effective lever changes and the wrench setting must be corrected — the torque wrench extension calculator prevents the classic over-torque failure.
Drivetrain elements: belts, chains, bearings
Belt and chain length geometry sets what you buy; sprocket and pulley diameters set speeds. The belt length and chain length calculators handle the classical wrap equations and recommend even link counts for chains (offset links are weak points).
Bearings fail by fatigue, statistically: L10 life scales with (C/P)³ for ball bearings — halve the load, eight-fold the life. The bearing life calculator turns catalog ratings into hours at your duty point.
Fluid power and structures
Hydraulics multiply force through pressure × area: a 63 mm bore at 160 bar produces 50 kN — five tons from a hand-sized cylinder. The hydraulic cylinder calculator shows extend vs retract (the rod steals area), and the pump power calculator sizes the motor behind the pressure.
Mass matters for structure and shipping: the metal weight calculator handles bar, plate and tube in ten common alloys. Springs follow k = G·d⁴/(8·D³·n) — the fourth-power wire sensitivity is why wire size dominates spring design (spring rate calculator).
Questions about mechanical engineering calculations
Why do most bolted joints fail?
Under- or over-torque relative to the friction conditions, fatigue from insufficient preload, and vibration loosening. Proper lubrication discipline and calibrated tools address all three.
Gear, belt or chain drive?
Gears for precision and compactness; belts for quiet, cheap, overload-tolerant transmission; chains for high torque at moderate speed without slip. Each calculator notes its domain's limits.
What is L10 bearing life?
The life that 90% of identical bearings exceed under identical load. It's a statistical rating — design targets are typically 30,000+ hours industrial, more for continuous duty.
All Mechanical Engineering calculators
- Gear Ratio CalculatorEnter driver and driven teeth to get the ratio, output speed and output torque — with the mesh efficiency and multi-stage notes spelled out.
- Torque to Power CalculatorEnter torque and rotational speed to get mechanical power in kW and hp, with the torque converted to lb·ft for imperial work.
- Bolt Torque CalculatorGet the tightening torque for a metric bolt from its size, grade and lubrication state — with the preload, stress area and K-factor assumptions documented.
- Belt Length CalculatorEnter both pulley pitch diameters and the center distance to get the belt pitch length in mm and inches, plus the speed ratio.
- Tap Drill CalculatorEnter the thread major diameter and pitch to get the tap drill at 75% thread, adjustable for other engagement percentages, plus the nearest real drill bit.
- Pulley RPM CalculatorEnter both pulley diameters and the driver speed to get the driven RPM and belt surface speed — with the V-belt speed limits flagged.
- Hydraulic Cylinder CalculatorEnter bore, rod diameter and system pressure to get extend and retract forces — the rod side is weaker, and this shows exactly by how much.
- Gear Geometry CalculatorEnter module and teeth to get the full set of spur gear dimensions — pitch, outside and root diameters, circular pitch and tooth depth.
- Metal Weight CalculatorPick a shape and material, enter dimensions, get the weight in kg and lb — with nominal densities and mill-tolerance guidance.
- Engine Displacement CalculatorEnter bore, stroke and cylinders to get total displacement in cc, liters and CID — plus each cylinder's swept volume.
- Compression Ratio CalculatorEnter swept volume and all clearance volumes (chamber, gasket, piston) to get the true static compression ratio — the number that decides fuel tolerance.
- Spring Rate CalculatorEnter wire diameter, coil outer diameter and active coils to get the spring rate — the classic k = G·d⁴/(8·D³·n) formula with manufacturability notes.
- Torque Wrench Extension CalculatorUsing a crowfoot or extension changes the effective lever length. Enter the target, wrench length and extension to get the corrected wrench setting.
- Pump Power CalculatorEnter flow, head and efficiency to get hydraulic power (water hp) and shaft power — the numbers for motor selection on any centrifugal pump.
- Chain Length CalculatorEnter both sprocket tooth counts, center distance and chain pitch to get the exact chain length — rounded to an even link count to avoid offset links.
- Bearing Life CalculatorEnter the bearing's C rating, the actual applied load and RPM to get L10 life — the standard (C/P)³ fatigue calculation for ball bearings.