Internal Gear Generator
Generate an internal ring gear with teeth on the inside as an STL. Set module, tooth count, pressure angle and outer diameter. A mating external pinion needs compatible geometry and an interference check; a shared module alone does not guarantee an assembly.
What the internal gear generator builds
An internal gear has tooth tips toward its center and roots farther outward. A smaller external pinion can run inside it. With both axes fixed, ring and pinion rotate in the same direction. The separate outer-diameter setting controls material around the tooth roots and must enclose the modeled section.
The KHK internal-gear reference distinguishes involute, trochoid and trimming interference. Tooth counts, pressure angle and profile shift matter. An eight-tooth difference is not a universal guarantee, and a suggested wall thickness is not a structural load rating.
Check a standard internal pair
For an unshifted standard internal pair, reference center distance is a = m × (zᵣ - zₚ) / 2. A 60-tooth ring and 20-tooth pinion at module 2 mm place the axes 40 mm apart. This difference formula is distinct from the sum formula for two external spur gears. Actual interference and assembly remain separate checks.
Choose an outer diameter leaving material beyond the tooth roots, then inspect the exported section. Rigidity depends on material, mounting, wall section and load. Read the module guide for reference dimensions and the gear printing guide for process checks.
Use a ring in a planetary layout
For the simple unshifted layout used here, ring teeth equal sun teeth plus twice the planet teeth. Equal planet spacing adds a tooth-phasing condition and neighboring planets need clearance. Neither relation proves an interference-free tooth mesh or physical assembly.
The planetary guide explains the parts and the planetary ratio calculator separates kinematics from basic geometry checks. Use the planetary generator for a matched sun, planet and ring set. Design carrier, shafts, retention and supports separately.
Frequently asked questions
Which direction does an internal gear pair turn?
With both axes fixed, ring and pinion rotate in the same direction. In a planetary system the planet axes move with the carrier, so define the fixed member and reference frame before comparing speeds.
What outer diameter should the ring have?
The outer diameter must enclose the tooth roots with material appropriate to the application. Inspect actual root dimensions, modeled wall and mounting. No universal outer diameter or wall thickness establishes stiffness for all loads.
Can I use the internal gear for a print-in-place gearbox?
This tool generates a ring gear, not a complete print-in-place gearbox. A complete design needs carrier, retention, supports and tested clearances. No single gap or profile-shift setting guarantees release after printing.
Is an eight-tooth difference always enough?
No. Internal gearing has several interference mechanisms. Tooth counts, pressure angle, profile shift and the assembly path affect them. Check the conditions for the selected pair instead of relying on one universal difference.
What is the difference between internal and external gear mesh?
External mesh is what you get from two ordinary gears: teeth point outward on both, the gears counter-rotate, and the center distance is module times the sum of the tooth counts divided by two. Internal mesh puts one gear's teeth pointing inward so a smaller external pinion runs inside it; both parts then turn the same direction, and the center distance is module times the difference of the tooth counts divided by two, which is what lets internal gears pack a large ratio into a small housing.