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What is involute gear?
All the gear teeth have top flat portion and two side curves. The side curves for the involute gears are in the form of involute curve of a circle.
Involute curve of a circle can be generated by the locus of an end point of an imaginary taut string unwounding from the circle.

What is cycloidal gear?
Cycloid is a curve generated by locus of any point on a circle which is rolling around another circle. If the second circle rolls outside the first circle then the generated curve is called epicycloid and if it rolls inside the first circle then the generated curve will be hypocycloid. The gear whose teeth profile is made up of cycloidal curves is called cycloidal gear. Each tooth profile will be combination of epicycloid and hypocycloid curves.

Advantage of Involute gear
• Contacts between two mating teeth in involute gear occur in a fixed plane of action irrespective of the centre to centre distances between the gears. Hence, Involute gears can handle centre sifts of the gears better. This provides assembly flexibility.
• Involute gear produces lesser noise than cycloidal gears.
• Manufacturing of accurate involute gear teeth is easy.

Advantage of cycloidal gear
• Cycloid teeth does not undercut or interfere with its mating teeth.
• Lesser number of teeth can be possible for cycloidal gears which facilities large reduction ratios.
• Cycloidal teeth are stronger than involute teeth.

Identification of involute and cycloidal gears
Curve portion of involute teeth is made up of a single curve where as the profile of a cycloidal tooth is made up of two different curves (epicycloid and hypocycloid). If the teeth attached sharply with the base circle then it should be an involute gear or else it may be a cycloidal gear.

Examples
Involute gear can be seen almost every where, car gear box, ships, robotics application, home appliances, machine tools.

Cycloidal teeth are found mainly in clock and watches.

Further readings

• How to Design a Helical Spring
• Force Analysis of Truss
• How to Draw Free body Diagram (FBD)

Shibashis Ghosh

Hi, I am Shibashis, a blogger by passion and an engineer by profession. I have written most of the articles for mechGuru.com. For more than a decades i am closely associated with the engineering design/manufacturing simulation technologies. I am a self taught code hobbyist, presently in love with Python (Open CV / ML / Data Science /AWS -3000+ lines, 400+ hrs. )