Custom CNC Turn-Mill Machining for 316 Stainless Steel Automation Shafts

This 316 stainless steel shaft was custom machined for an automation equipment customer in the United States. The part is approximately 75 × 20 mm, with stepped diameters, external threads and a milled flat in the center section.

Most of the geometry can be produced by CNC turning. The flat is the feature that changes the machining route: it requires milling and has to remain correctly positioned in relation to the turned shaft geometry.

Several critical dimensions are specified at approximately ±0.01 mm according to the customer drawing. The production quantity was around 1,500 pieces.

For this part, CNC turn-mill machining gives us a practical way to complete the turned and milled features within one coordinated production plan.

Project Overview

Mostly a Turned Shaft—Except for the Flat

The main body is a natural CNC turning job.

Different shaft diameters, shoulders and threaded sections all share the same centerline and can be produced efficiently on the lathe.

Then there is the flat.

It occupies only a small section of the component, but it introduces non-rotational geometry that conventional turning cannot produce. Milling is therefore added to complete the feature according to the customer's drawing.

The important point is not simply that the part requires two machining processes. The milled feature has to be positioned correctly in relation to the shaft geometry already established during turning.

That makes this component well suited to turn-mill machining rather than treating the milling work as an unrelated secondary operation.

The Drawing Decides Where ±0.01 mm Matters

Several critical dimensions are specified at approximately ±0.01 mm.

That does not mean every surface on the component needs to be held to ±0.01 mm.

During drawing review, we identify the tighter requirements and consider how they relate to the machining sequence. Depending on the design, these may involve a shaft diameter, shoulder position, thread-related feature or the relationship between the turned and milled geometry.

This is an important part of custom CNC machining from customer drawings.

The objective is not to apply the tightest possible tolerance everywhere. It is to control the dimensions that the customer's design actually requires.

Keeping Turning and Milling in the Same Plan

The production route for this shaft is relatively direct:

Material Preparation → CNC Turning → Threading → Milling → Deburring → Inspection → Packing

Turning establishes the main shaft profile. Milling completes the flat that cannot be generated around the turning axis.

Where the geometry allows, coordinating these operations reduces unnecessary handling and helps maintain the relationship between the turned and milled features.

For a batch of around 1,500 pieces, this also gives us a repeatable production route rather than solving the positioning again for every component.

The process follows the drawing. We do not add milling where turning is enough, and we do not try to force a turning-only process onto a part that clearly needs both.

Machining 316 Stainless Steel in Production

The customer specified 316 stainless steel.

Compared with free-machining stainless grades such as 303, 316 requires more attention to cutting conditions, chip control and tool wear. On this component, that applies across several operations: outside turning, threading and milling.

Tool condition becomes particularly relevant during batch production.

A worn cutting edge may gradually influence a diameter, thread profile or milled feature before the change becomes obvious visually. Relevant dimensions are therefore checked during production rather than relying entirely on inspection after all 1,500 pieces have been machined.

The goal is simple: the parts produced later in the run should follow the same drawing requirements as the approved parts at the beginning.

A Small Milled Feature Still Needs a Clean Finish

After milling, the edges around the flat need controlled deburring.

This sounds like a minor detail, and usually it is. But removing too much material around a precision feature can alter the geometry, while leaving a burr can create problems during assembly.

The same applies around threaded sections and shoulders.

We are not trying to turn ordinary deburring into a complicated process. The finished component simply needs to be clean without changing the features that have already been machined to size.

Made-to-Drawing Shaft Production

This shaft is not a standard catalogue component.

The customer defines the material, diameters, threads, milled feature and tolerance requirements through the engineering drawings. We use those specifications to determine the machining and inspection plan.

This is how we approach custom CNC turned parts in general.

Some shafts can be completed entirely through CNC turning. Others include flats, cross holes, slots or other non-round features that make CNC turning and milling a better production route.

The manufacturing method depends on what is actually on the drawing.

For this project, the combination is straightforward: turn the shaft geometry, machine the threads, mill the flat, remove burrs and inspect the dimensions that have been identified as critical.

Custom CNC Turning and Turn-Mill Machining Services

YS Precision provides custom CNC turning services for shafts, pins, sleeves, bushings, threaded components and other drawing-based metal parts.

When a component combines rotational geometry with flats, cross holes, slots or additional milled features, we can also provide CNC turn-mill machining services rather than requiring the customer to source the operations separately.

Materials include 316 and 303 stainless steel, aluminum, brass and other specified metals. Our work supports automation equipment, medical devices, electronics and other industrial applications, from prototype quantities through repeat and batch production.

Each quotation starts with the customer's drawing. Geometry, material, tolerance requirements and quantity determine the machining route.

When a Turning Part Needs More Than Turning

Most of this 75 × 20 mm 316 stainless steel shaft belongs on a CNC lathe.

The central flat is a small feature, but it changes the production plan. It requires milling, and its relationship to the turned shaft geometry has to remain consistent across approximately 1,500 pieces.

The selected ±0.01 mm tolerances add another layer: the dimensions that matter most need to stay under control not just on the first part, but through the production run.

For customers sourcing similar custom CNC turned shafts or turn-mill parts, the engineering drawing is the best place to start. Send us the 2D/3D files, material specification, quantity and critical tolerances, and we can review whether the part is best suited to CNC turning alone or a combined turning-and-milling process.