Internal gear is a gear using its teeth cut in the inner surface of a cylinder and meshes with spur gears.
In its manufacturing, because of its shape, the most common hobbing machine used in spur gear production cannot be used. Generally it is made 
out of gear shaper (or equipment shaping machine) built with a pinion cutter. Recently, the efficiency of inner gear cutting offers been improved by a different procedure called skiving.
Because of the thinness of the ring, it really is sometimes difficult to produce high precision. However, gear grinding to boost precision grade is bound by the amount of producers and their available grinding facilities leading to very high cost.
Also, although it is normally too expensive to make helical teeth internal gears, Ever-Power has made it possible to create them simply by adopting equipment that can cut them simply by 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, but it is necessary to note the possibilities to getting involute, trochoid or trimming interferences. For using Ever-Power standard stock gears, please seek advice from the PDF formatted “Specialized Details of Internal Gears” section for usable number of teeth combinations.
Internal gears tend to be used in applications involving planetary gear drives and gear couplings. There are three main types of planetary gear mechanisms: planetary, solar and celebrity types. Depending on the type and the design of which shafts act as input and output, many variations of rate transmitting ratios and rotational directions are produced.
