Internal gear can be a gear with its teeth cut in the inner surface of a cylinder and meshes with spur gears.
In its manufacturing, because of its shape, the usual hobbing machine found in spur gear creation can’t be used. Generally it really is made out of gear shaper (or equipment shaping machine) built with a pinion cutter. More recently, the efficiency of internal gear cutting offers been improved by a different procedure called skiving.
Due to the thinness of the band, it really is sometimes difficult to produce high precision. On the other hand, gear grinding to boost precision grade is limited by the amount of manufacturers and their available grinding facilities leading to very high cost.
Also, although it is normally too expensive to create helical teeth internal gears, Ever-Power has made it possible to produce them by adopting equipment that may cut them simply by making pinion cutters rather than needing helical guides.
Normally, internal gears can be used with the same module spur gears, based on the number of teeth combinations, but it is necessary to notice the possibilities of getting involute, trochoid or trimming interferences. For using Ever-Power standard stock gears, please seek advice from the PDF formatted “Specialized Info of Internal Gears” section for usable quantity of teeth combinations.
Internal gears are often used in applications involving planetary gear drives and gear couplings. There are three main types of planetary gear mechanisms: planetary, solar and celebrity types. Based on the type and the pattern of which shafts become input and result, many variations of acceleration tranny ratios and rotational directions are 
created.
