Custom 20CrMnTi Carburized Helical Gear with Internal Spline

The component shown here is a custom 20CrMnTi helical gear combining external helical teeth with an internal spline. Both are functional transmission features: the outer teeth engage with the mating gear, while the spline connects to the shaft and transfers torque.

The gear is manufactured to the customer's 2D engineering drawing, including tooth geometry, spline specification and critical tolerances. It also requires quenching and tempering followed by carburizing and hardening, making the final heat-treated condition an important part of the production plan.

For this type of component, YS Precision provides custom gear manufacturing services covering gear blank machining, helical gear hobbing, internal spline machining, heat-treatment coordination and final inspection.

Gear Specification

One Gear, Two Critical Tooth Features

What makes this component different from a conventional helical gear is the splined center.

The external helical teeth control engagement with the mating gear. The internal spline controls the connection with the shaft. Although they perform different functions, both operate around the same rotational axis.

That relationship can be critical.

A gear may have acceptable external teeth and an acceptable spline when measured separately, but still create assembly or running problems if the relationship between the two does not meet the drawing requirements.

Where specified, characteristics such as runout, concentricity and positional accuracy therefore become part of the manufacturing and inspection plan.

Made to Your Gear and Spline Specifications

This is a drawing-based component rather than a modified standard gear.

The customer defines the external gear parameters, which may include:

Module · Tooth Count · Pressure Angle · Helix Angle · Helix Direction · Gear Width · Gear Accuracy

The internal spline is also produced to its specified profile, fit and tolerance.

We do not infer these parameters from the outside diameter or appearance of an existing gear. The customer's 2D drawing provides the manufacturing reference, while a 3D CAD model can be used as supporting geometry where available.

This allows custom helical gears to be produced around an existing transmission design rather than forcing the assembly to accommodate a catalog component.

Why 20CrMnTi Is Used for Carburized Transmission Gears

20CrMnTi is a low-carbon alloy steel commonly used for gears that require a hardened working surface together with suitable core properties.

For this project, the specified heat-treatment route includes quenching and tempering, followed by carburizing and hardening.

Carburizing enriches the surface layer with carbon before hardening develops the required case properties. The result is a gear designed around a hard, wear-resistant surface while retaining the specified characteristics beneath the hardened layer.

The important point for manufacturing is that “20CrMnTi” alone does not define the finished condition.

Requirements such as surface hardness, effective case depth and core properties should follow the customer's technical specification and actual transmission application.

From Gear Blank to Helical Teeth and Internal Spline

Producing the complete component requires more than a standalone hobbing operation.

A representative process route may be:

20CrMnTi Blank → CNC Turning → Reference Feature Machining → Internal Spline Machining → Helical Gear Hobbing → Deburring → Q&T → Carburizing & Hardening → Final Inspection

The exact sequence is determined by the gear accuracy, spline tolerance and final dimensional requirements.

For the external teeth, helical gear hobbing generates the tooth form according to the specified module, tooth count, pressure angle and helix geometry.

The internal spline requires a process suited to its profile, size and accuracy. The appropriate method is selected from the drawing rather than assuming one spline-cutting process for every design.

For purchasing teams, combining these operations into one manufacturing route can also reduce coordination between separate blank, gear-cutting, spline and heat-treatment suppliers.

The Real Target Is Accuracy After Heat Treatment

For a carburized gear, dimensional control before heat treatment tells only part of the story.

Carburizing and hardening can introduce dimensional change. What ultimately matters is whether the finished gear meets the requirements specified for its final condition.

Before production, several questions need to be clear:

• What gear accuracy is required after heat treatment?
• What is the final fit requirement of the internal spline?
• Is runout between the spline and external teeth controlled?
• Are any areas required to remain free from carburizing?
• Is finishing required after hardening?

These requirements influence machining allowances and the production sequence.

Where tighter final accuracy is required, post-heat-treatment finishing can be planned from the beginning rather than introduced later to correct an unexpected result.

Inspection Focused on Transmission Function

Inspection for this component is based on the features that determine how it fits and operates.

According to the customer's specification, checks may include:

• external tooth characteristics;
• internal spline dimensions;
• gear width and reference dimensions;
• runout and concentricity;
• surface hardness;
• effective case depth;
• edge and surface condition.

The relationship between the internal spline and external helical teeth deserves particular attention because both features ultimately work around the same transmission axis.

This functional approach is more useful than applying the same general inspection checklist to every gear.

Custom Gear Manufacturing Beyond Tooth Cutting

YS Precision provides custom gear machining and manufacturing services for non-standard transmission components.

Our production scope can include:

CNC Turning · Gear Blank Machining · Helical Gear Hobbing · Internal Spline Machining · Carburizing & Hardening · Dimensional Inspection

We support custom helical gears, splined gears, carburized gears and alloy steel transmission components made to customer specifications.

For a 20CrMnTi component like this, the goal is not simply to supply correctly cut teeth. The external gear geometry, internal shaft interface, heat-treated condition and final dimensional requirements are considered as one finished part.

What to Include in Your Gear RFQ

For quotation, please send the complete 2D engineering drawing and 3D CAD model where available.

Useful technical information includes:

Material · Module · Tooth Count · Pressure Angle · Helix Angle · Helix Direction · Gear Width · Internal Spline Specification · Gear Accuracy · Critical Tolerances · Heat Treatment · Surface Hardness · Effective Case Depth · Quantity

With these details, we can review the machining sequence, tooth and spline requirements, heat treatment and final inspection before quotation.