External Helical Pinion Gear

Create a precision parametric 3D CAD model of a single external helical pinion gear for a two-stage industrial gearbox. Engineering specifications (all dimensions in millimeters): - Number of teeth: 20 - Normal module: 2.5 mm (not transverse module) - Normal pressure angle: 20 degrees - Helix angle at pitch cylinder: 11.1127 degrees - Gear face width: 60 mm - Reference pitch diameter: 50.955 mm - Outside diameter: 55.955 mm - Root diameter: 44.705 mm - Tooth profile: true involute helicoidal tooth geometry - Full-depth metric tooth system - One single solid gear body, with precisely 20 evenly spaced helical teeth - No keyway, no hub extension, and no separate shaft - Add a 10 mm diameter central pilot bore solely for later Boolean union into a solid shaft of diameter 30 mm in Siemens NX; this is not a final functional mounting bore - Make helix handedness a user-editable parameter, because its final direction has not yet been specified - Put the gear axis along the local Z axis, centered axially at Z=0 Requirements: - Generate a watertight precision B-rep CAD solid, not a polygon mesh - Expose tooth count, normal module, normal pressure angle, helix angle, face width, and helix hand as editable parameters - Calculate dimensions from the normal module and helix angle; do not reinterpret the normal module as a transverse module - Preserve exact dimensions without arbitrary scaling - Export a real editable engineering STEP file suitable for Siemens NX - If exact helical involute geometry cannot be generated, explicitly report the limitation rather than silently replacing it with straight, approximate or decorative teeth.

Parameters

Every value above is a live dimension. Open a model like this in the editor and each one becomes a slider you can drag before exporting.