Internal gear is certainly a gear using its teeth cut in the inner surface area of a cylinder and meshes with spur gears.
In 
its manufacturing, due to its shape, the most common hobbing machine used in spur gear creation cannot be used. Generally it is made out of gear shaper (or equipment shaping machine) equipped with a pinion cutter. Recently, the efficiency of inner gear cutting offers been improved by a different procedure called skiving.
Due to the thinness of the ring, it really is sometimes difficult to create high precision. However, gear grinding to improve precision grade is bound by the number of producers and their available grinding facilities resulting in very high cost.
Also, although it is normally too expensive to create helical teeth internal gears, Ever-Power has made it possible to create them by adopting equipment that may cut them simply by making pinion cutters and not needing helical guides.
Normally, internal gears can be utilized with the same module spur gears, based on the number of teeth combinations, but it is necessary to notice the possibilities to getting involute, trochoid or trimming interferences. For using Ever-Power standard stock gears, please seek advice from the PDF formatted “Technical Details of Internal Gears” section for usable amount of teeth combinations.
Internal gears are often used in applications involving planetary gear drives and gear couplings. There are three main types of planetary equipment mechanisms: planetary, solar and superstar types. According to the type and the pattern of which shafts become input and output, many variations of velocity transmission ratios and rotational directions are produced.