Geometric description: The model is designed as a high-performance, low-noise helical tooth synchronous pulley, with an overall appearance featuring streamlined twisted spokes supporting a precision transmission rotary body. The outer diameter of the main rim is set to 120mm, with an effective face width of 40mm. The circumferential surface is equipped with 47 arc teeth based on the HTD 8M standard, with a pitch of 8mm and a tooth depth of 3.4mm. Unlike conventional straight teeth, the grooves of this model are helically distributed along the axial direction, with a helix angle �� of 15 degrees. The tooth centerline follows a helical equation, where the angular offset ���� = Z * tan(15��) / R_pitch in the polar coordinate system, with Z being the coordinate along the face width and R_pitch being the pitch circle radius. This structure endows the model with complex helical swept surfaces.

The rim is not solid but is connected to the central hub via five evenly distributed, variable-section twisted spokes. The outer diameter of the central hub is 45mm, with a cylindrical bore of 25mm in diameter and a 6mm wide keyway. The cross-section of the spokes is an ellipse with a major axis of 12mm and a minor axis of 6mm. This cross-section undergoes a linear twist as it extends from the outer wall of the hub to the inner wall of the rim, with the major axis direction rotating 90 degrees from axial (parallel to the rotation axis) at the hub to circumferential (perpendicular to the rotation axis) at the rim, forming a ruled twisted surface with topological continuity.

At the root connections between the spokes and the hub and rim, there are fillets with a radius of R4mm to ensure smooth transitions. The edges of the rim have a 1.5mm �� 45-degree chamfer. The entire structure integrates helical meshing tooth surfaces with aerodynamic, twisted support structures, forming a complex synchronous pulley model.

Modeling procedure: First, initialize the modeling environment and draw an annular ring with an outer diameter of 120 mm and a width of 40 mm centered at the origin on the XY reference plane as the rim base. Simultaneously, construct a central hub entity with an outer diameter of 45 mm. For the synchronous belt tooth profile, sketch an arc tooth contour that meets the HTD 8M standard on the rim end face. Then, define a helical sweep path with a helix angle of 15 degrees and a height of 40 mm. Use the sweep and circular array commands to generate 47 helically distributed oblique teeth.

Next, enter the spoke construction phase. Establish reference planes on the outer wall of the hub and the inner wall of the rim. Draw an elliptical section with a major axis of 12 mm and a minor axis of 6 mm. Use the loft command to connect the two sections, constraining the major axis at the start to be axial and rotating the major axis at the end by 90 degrees to be circumferential, achieving a linear twist of the spokes. Then, uniformly array them 5 times around the Z-axis.

Perform an extruded cut at the central hub to create a shaft hole with a diameter of 25 mm and a keyway with a width of 6 mm. Finally, apply a fillet with a radius of 4 mm at the root of all spoke connections for smooth transition, and execute a 1.5 mm by 45-degree chamfer on both edges of the rim to complete the modeling of the entire complex transmission component.