Internal gear is certainly a gear with its teeth cut in 
the internal surface area of a cylinder and meshes with spur gears.
In its manufacturing, due to its shape, the most common hobbing machine found in spur gear production cannot be used. Generally it is made with gear shaper (or equipment shaping machine) built with a pinion cutter. More recently, the efficiency of internal gear cutting provides been improved by a different process called skiving.
Because of the thinness of the ring, it really is sometimes difficult to produce high precision. On the other hand, gear grinding to boost precision grade is limited by the number of producers and their obtainable grinding facilities leading to very high cost.
Also, although it is generally too expensive to make helical teeth internal gears, Ever-Power has managed to get possible to produce them simply by adopting equipment that may cut them by simply making pinion cutters rather than needing helical guides.
Normally, internal gears can be used with the same module spur gears, depending on the number of teeth combinations, nonetheless it is necessary to note the possibilities of getting involute, trochoid or trimming interferences. For using Ever-Power standard share gears, please consult 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 major types of planetary equipment mechanisms: planetary, solar and superstar types. Based on the type and the pattern of which shafts act as input and output, many variations of acceleration tranny ratios and rotational directions are produced.