Numbers
CCEA A-Level Technology and Design 8900
Material Selection and Wood
Metals
Plastics
Composite and Emerging Materials
Processing Materials
Product Analysis and Design Communication
Design for Manufacture, Quality and Safety
Electronic Control SystemsOption A
Topic overviewControl systems, feedback and electronics safetyResistors, Ohm's law and power ratingsCapacitors and RC timingPotential dividers, sensors and comparatorsSwitches, pull-up and pull-down resistorsOutput devices and LEDsTransistors, Darlington pairs and thyristorsLogic gates, truth tables and flip-flops555 monostable and astable timers
Microelectronic Control SystemsOption A
Topic overviewMicrocontroller systems, ADCs and DACsStrain gauges and bridge circuitsOptical switches, encoded discs and Schmitt triggersOp-amp amplifiers and gainZener diodes and voltage regulatorsKarnaugh maps and binary countersSeven-segment, LCD and dot matrix displaysPIC flowcharts and programmingDC motors, stepper motors and driver circuits
Mechanical and Pneumatic ComponentsOption B
Topic overviewOpen and closed loop mechanical and pneumatic controlSafe working with compressed air and mechanismsLevers, linkages and momentsGear types and gear trainsPulleys, belts, chains and shaft fixingsCams, cranks and converting motionCompressed air supply and pneumatic valvesCylinders, shuttle valves, restrictors and reservoirsPneumatic circuits for logic, timing and speed control
Mechanical and Pneumatic SystemsOption B
Topic overviewHydraulics, system limitations and plant safetyTorque, work, power and air consumptionVacuum handling, proximity sensors and 5/3 valvesSequential and cascade pneumatic circuitsCam profiles and follower displacement diagramsGear geometry, pulley blocks and ratchetsToggles, treadles, shafts and couplingsFriction, brakes and clutchesBearings, lubrication and seals
Designing and Manufacturing ProductsOption C
Topic overviewResearch, questionnaires and specificationsIdea generation, critiques and computer simulationManufacturing planning and product evaluationCFRP, GRP, Kevlar and tungsten carbideSmart materials, nanotechnology and biophotovoltaicsIsometric, perspective and assembly drawingLaminating, steam bending, cutting and printing processesRisk assessment and product safety lawScales of production, JIT and cell productionQuality assurance, ISO 9001 and continuous improvementDesign influences and intellectual property rights
Product Design in Industry and SocietyOption C
Topic overviewLife-cycle environmental impact and climate changeThe 6Rs, waste and environmental legislationSustainable metals, plastics and degradable polymersProduct life cycles, consumer types and relaunchesCAD, CAM, 3D scanning and quick-change mouldingMarket pull, technology push and market strategyPrice, place and promotionJigs, fixtures and ICT in quality controlDesign for maintenance, inclusion and scale productionRendering, typography and presentationDyson, Baylis, Memphis and Apple
Product Development
Product and System Design and Manufacture
Mechanical and Pneumatic Systems
Gear geometry, pulley blocks and ratchets
- 3 things to know
- A2 1
Overview
Pitch circle diameter, module and centre distance with worked values, reverted gear trains, multiple pulley blocks with worked efficiency, and ratchets and pawls.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
What is the pitch circle diameter of a gear?
Key term
What is the pitch point of two meshing gears?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is the pitch circle diameter of a gear?
Model answer
The pitch circle diameter is the diameter of the imaginary circle on which two meshing gears effectively roll together. Gear ratios and centre distances are based on the pitch circles.
- 2
What is the pitch point of two meshing gears?
Model answer
The pitch point is where the pitch circles of two meshing gears touch. The pitch point lies on the line joining the two gear centres.
- 3
What is the metric module of a gear?
Model answer
The module is the pitch circle diameter divided by the number of teeth, in millimetres. Two gears must have the same module to mesh.
- 4
A gear has 40 teeth and a module of 2. Calculate its pitch circle diameter.
Model answer
The pitch circle diameter is 80 mm. PCD = module × teeth = 2 × 40 = 80 mm.
- 5
A 20-tooth gear meshes with a 40-tooth gear, both of module 2. Calculate the distance between their centres.
Model answer
The centre distance is 60 mm. The pitch circle diameters are 2 × 20 = 40 mm and 2 × 40 = 80 mm, and (40 + 80) ÷ 2 = 60 mm.
- 6
A 40-tooth gear has a module of 2. Calculate its outside diameter.
Model answer
The outside diameter is 84 mm. Outside diameter = module × (teeth + 2) = 2 × 42 = 84 mm.
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