Internal gear is 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 most common hobbing machine found in spur gear production can’t 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.

Because of the thinness of the ring, it really is sometimes difficult to produce high precision. On the other hand, gear grinding to improve precision grade is limited by the amount of manufacturers and their offered grinding facilities leading to very high cost.

Also, although it is generally too expensive to make helical teeth internal gears, Ever-Power has made it possible to create them by adopting equipment that can cut them by simply making pinion cutters and not needing helical guides.

Normally, internal gears can be used with the same module spur gears, based on the number of teeth combinations, nonetheless it is necessary to note the possibilities to getting involute, trochoid or trimming interferences. For using Ever-Power standard stock gears, please consult the PDF formatted “Technical Info of Internal Gears” section for usable number 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 star types. According to the type and the pattern of which shafts become input and result, many variations of quickness tranny ratios and rotational directions are produced.