Free Internal Gear Generator - Planetary Ring Gear Calculator, Simulator & DXF Export
GearDXF is the web's premier free online internal gear generator and planetary ring gear designer. Create mathematically accurate internal involute gear profiles for planetary gearboxes, epicyclic speed reducers, robotic hub motors, and compact automatic transmissions. Customize tooth count, module, pressure angle, and structural rim thickness, then export clean DXF, SVG, and 1:1 scale printable PDF files for laser cutters, CNC mills, and 3D printers with zero cost and no sign-up required.
Internal Gear Mechanics & Conjugate Action
Internal gears feature teeth cut into the inside cylindrical bore of a ring. Because the tooth profile is concave, internal gear teeth have a larger surface radius of curvature compared to convex external spur teeth. This geometry yields higher surface contact area, reduced Hertzian contact stress, increased load-carrying capacity, and a noticeably higher contact ratio (ε > 1.5).
Planetary & Epicyclic Gearbox Formulas
In a standard epicyclic planetary gearset (Sun, Planets, and Ring), the ring gear tooth count (z_ring) must satisfy the geometric relation: z_ring = z_sun + 2 × z_planet (for co-planar planet gears). The center-to-center operating distance between the inner planet gear and ring gear is a = m × (z_ring - z_planet) / 2. GearDXF automatically calculates pitch diameters and positions meshed gears accurately in space.
Configurable Outer Rim Wall Thickness & Mounting
High internal gear forces generate substantial outward hoop stress. GearDXF allows engineers to configure custom outer wall diameters and rim thickness, ensuring 3D printed nylon/PETG housings and CNC aluminum gear casings maintain structural stiffness without ring flexing or tooth skip under high load.
Direction of Rotation & Dynamic Inside Simulation
Unlike external spur gear pairs which reverse rotational direction, an inner pinion meshing with an internal ring gear rotates in the identical rotational direction. GearDXF's interactive 2D simulation animates this relative rotation at true speed ratios, verifying smooth tooth engagement and continuous conjugate action before manufacturing.
Backlash Compensation for CNC & 3D Printing
Internal gears require precise tooth gap clearances to account for thermal expansion, 3D printing extrusion swelling, or laser beam kerf. The built-in backlash slider widens the internal tooth cavities symmetrically, ensuring smooth, low-friction operation straight off the manufacturing bed.
Production-Ready DXF, SVG & 1:1 Scale PDF Export
Export clean, closed-boundary vector paths with zero overlapping segments. Fully compatible with AutoCAD, SolidWorks, Autodesk Fusion 360, Vectric VCarve, LightBurn, and CAM nesting tools. You can also print true 1:1 scale templates to PDF for checking fitment and clearances on physical prototypes.
Frequently Asked Questions (Internal Gears)
What is an internal gear generator? A web CAD tool that models internal involute ring gear geometry and outputs clean vector files (DXF, SVG, PDF) for CNC machining, laser cutting, and 3D printing.
Do internal gears turn in the same direction as the pinion? Yes, a pinion meshing with an internal gear drives both gears in the identical rotational direction.
How is center distance calculated? Center Distance = Module × (Ring Teeth - Pinion Teeth) / 2.
How do I avoid tooth interference? Ensure the internal ring gear has at least 8 to 10 more teeth than the inner pinion gear.
- Planetary Reducers: Design compact, high-ratio planetary gear stages for robotics and electric vehicles.
- Robotic Actuators: Build high-torque cycloidal and epicyclic drives for robot joints and wheels.
- Laser Cut Transmissions: Cut acrylic or Delrin ring gears with dialed-in kerf compensation.
- 3D Printed Mechanisms: Print functional gearboxes with custom wall thickness and backlash tuning.
100% free client-side tool. Your designs remain private and secure on your device. No registration or credit card required.