Custom POM Gear Manufacturing with CNC Machining and Gear Hobbing

A custom plastic gear cannot be defined by outside diameter and tooth count alone. Module, pressure angle, bore size, gear width and hub geometry all need to match the customer's transmission design.

For this project, we manufactured 500 custom POM gears for a U.S. customer from their 3D CAD model and technical drawing. The part is approximately 35 × 25 mm and combines a large external gear, a raised smaller gear section, a center bore and radial reinforcing ribs.

Production required both CNC machining and gear hobbing. CNC machining established the gear blank, bore, hub and structural geometry, while the teeth were generated according to the module, pressure angle and other gear parameters specified on the drawing.

POM Gear Project Specifications

The Gear Drawing Comes First

A request for a “35 mm POM gear” is not enough information to manufacture the component correctly.

Custom gear production starts with the tooth specification and the geometry that connects the gear to the rest of the mechanism.

Depending on the design, the drawing may define:

• module;
• pressure angle;
• tooth count;
• outside and pitch diameters;
• gear width;
• bore size and tolerance;
• hub dimensions;
• critical geometric requirements.

For custom POM gear manufacturing, module and pressure angle are particularly important because they define the tooth geometry required to work with the mating gear.

We manufacture according to customer-supplied gear drawings and CAD data rather than selecting a tooth form from general dimensions.

A Compound Gear Requires More Than Tooth Cutting

The geometry shown here is different from a conventional flat spur gear.

A large gear forms the lower body, while a smaller raised gear section is integrated around the center. Radial ribs connect the central hub with the outer body, and the bore provides a rotational reference for the component.

These features need to be considered together.

The blank geometry must be established before tooth generation, while the bore, hub and gear sections need to maintain the relationships defined in the customer's design.

For this type of component, POM gear machining is not a single cutting operation. It combines structural machining with dedicated gear cutting.

CNC Machining the POM Gear Blank

CNC machining creates the basic geometry before the gear-cutting operation.

Depending on the drawing, this can include the gear blank, center bore, hub, shoulders and other custom structural features.

For this part, the ribbed body and raised central section make the blank more complex than a simple round disc.

The machining sequence needs to establish the required reference features while keeping the component suitable for subsequent tooth generation.

Combining POM CNC machining with gear hobbing allows each process to do the work it is best suited for: CNC machining produces the custom body geometry, while hobbing generates the repeated gear teeth.

Gear Hobbing to the Specified Module and Pressure Angle

Once the relevant blank geometry is ready, the external teeth can be generated according to the customer's gear specification.

During gear hobbing, the hob and workpiece rotate in a controlled relationship while the cutting tool progressively generates the tooth profile around the circumference.

For a 500-piece production batch, this provides a practical way to manufacture repeated gear geometry without immediately investing in injection molding tooling.

The hobbing setup follows the specified gear data.

Module, pressure angle and tooth count are manufacturing inputs—not values that should be estimated from the outside diameter of the part.

This becomes particularly important when the new POM gear needs to mesh with an existing transmission component.

The Bore and Gear Teeth Work from the Same Rotational Reference

The center bore may appear much simpler than the teeth, but its relationship with the gear geometry matters.

If the bore locates the component on a shaft, it establishes the rotational reference of the part. The teeth operate around that axis.

The bore, hub, gear blank and generated teeth therefore cannot be treated as unrelated features.

During custom plastic gear machining, inspection should focus on the dimensions and geometric relationships identified as critical on the customer's drawing rather than applying unnecessarily tight tolerances everywhere.

POM for Machined Gear Components

POM (Polyoxymethylene), also known as acetal, is widely used for gears and other mechanical plastic parts.

Its combination of dimensional stability, low friction, wear resistance and machinability makes it useful for components that rotate or interact with other moving parts.

POM still needs appropriate machining conditions. Tool condition, cutting parameters and heat generation can influence edge quality, especially around smaller tooth features.

After machining and hobbing, the tooth area should also be checked for unwanted burrs or material that could interfere with the functional gear profile.

The specific POM grade should follow the customer's material specification.

Why CNC Machining and Hobbing Make Sense for 500 Pieces

Production quantity influences the manufacturing route.

For very high-volume plastic gears, injection molding may eventually provide a lower unit cost. For several hundred custom parts, however, the tooling investment may not always be justified.

This project required 500 pieces.

CNC machining combined with gear hobbing allowed the gears to be manufactured directly from the customer's current design without first producing an injection mold.

This approach can be considered for custom gears, engineering batches, replacement components, low- to medium-volume requirements and designs that may still require revision.

If the design changes later, the machining data can be updated without modifying production tooling.

From Gear Drawing to Finished Parts

A typical manufacturing route for a custom POM gear may include:

Drawing Review → Material Preparation → CNC Machining → Gear Blank Check → Gear Hobbing → Deburring → Final Inspection

The exact sequence depends on the component geometry and drawing requirements.

For repeat production, initial parts can be checked against the specified gear and dimensional requirements before the remaining batch is completed.

This helps keep production focused on the parameters that actually determine whether the gear matches the customer's design.

What to Include in a Custom POM Gear RFQ

For engineers and buyers sourcing custom POM gears or plastic gear hobbing services, complete gear data makes manufacturing review and quotation much more efficient.

A useful RFQ package includes:

3D CAD + 2D Gear Drawing + POM Grade + Quantity + Module + Pressure Angle + Tooth Count + Bore Requirements + Critical Tolerances

If the gear needs to mesh with an existing component, mating gear data can also be provided.

With these details, the manufacturing route can be reviewed around the actual component—combining CNC machining and gear hobbing according to the gear geometry, required quantity and drawing specifications.