In actual manufacturing, many cylindrical parts require multiple sections along their length to meet different mechanical and assembly requirements or reduce weight. In such cases, traditional CNC turning processes are difficult to meet the needs and a more targeted method is needed, namely step turning. Step cutting allows you to control the transition between different sections (diameters) of the shaft with a single setup. Although it builds on the foundation of traditional turning, it introduces some special considerations in tooling and setup that are worth understanding. This article explores the step turning process, its tools, and more. You will gain practical insights into how this method can meet complex machining requirements.
What is step turning?
Among other types of turning operations, step turning is a special lathe operation that uses controlled axial cutting to machine two or more parts of different diameters on a single workpiece.
Its notable feature is the sharp, right-angled transition of 90° between diameter sections, forming a unique “step” that gives the process its name. A typical step profile shaft looks like this:
Unlike a tapered transition, this square shoulder geometry prioritizes a precise functional interface rather than gradual material removal. The stepped portion can be used as a seat for a mating component, such as a sleeve, or to provide a shoulder for a bearing.
Advantages of Step Turning
The ability to create a stepped surface in a single operation opens up new design possibilities for machinists. Here are some of the key advantages for machinists:
- Multiple diameter machining in a single setup: Rather than requiring repositioning for each diameter, it allows multiple diameters and their transitions to be machined in a single setup, eliminating cumulative fixture alignment errors.
- Reduced thermal stress in transition zones: Fast cutting minimizes prolonged tool contact during transitions, which reduces the risk of heat build-up and distortion compared to tapering methods.
- Reduced cycle time: For parts that inherently require stepped diameters, step turning eliminates the need for multiple separate operations, reducing overall cycle time. This is a key efficiency gain unique to the process.
- Reduced cost: It costs less than straight turning, which requires frequent setups to machine steps of different diameters on a single workpiece. Step turning, on the other hand, can complete multiple steps in a single setup, significantly reducing production costs.
Challenges of Step Turning
While step turning offers significant advantages, it also presents unique challenges and limitations to the machinist.
- Setup Sensitivity: To step turn any cylindrical workpiece, the workpiece setup needs to be tightly controlled. Any misalignment will affect the accuracy of the step size. This may not be a problem in a CNC machine, but manual setup is still prone to error, and even experienced machinists have difficulty maintaining step tolerances when machining long workpieces, which often results in scrapped parts.
- Material Waste: Parts with large diameter differences (e.g., >20mm) require a large amount of material to be removed to form the step. This generates more waste than a process optimized for near-net-shape workpieces. To reduce waste, designers must prioritize stock material that is close to the maximum required diameter.
Step Turning Workflow
In a typical turning process, a single-edge cutting tool removes material from a rotating workpiece to produce a cylindrical part. Step cutting follows the same basic approach, but introduces some variations to allow different diameters to be machined on the same axis. Here’s how you can make the most of this process:
Step 1: Tool Fixturing
Mount a straight-edge cutting tool (such as a cut-off tool) on the toolholder. The cutting edge of the tool must be perfectly aligned with the centerline of the workpiece to ensure a clean, vertical step.For manual lathes, use shims to adjust the tool height until the tool tip coincides with the spindle axis. Tighten the tool securely to prevent movement during cutting.
Step 2: Facing the Ends
End machining is the initial step in a turning operation. End machining is done first because uneven ends affect subsequent step measurements. You need to face both ends to create a flat reference surface. Use light cuts (0.5-1 mm deep) with the tool feed perpendicular to the axis. This eliminates unevenness and ensures that the workpiece is perpendicular to the spindle.
Step 3: Measure and Mark
Use a vernier caliper or micrometer to mark the location of each step on the workpiece to be turned. When setting up manually, use a surface gauge to mark the transition point and lightly punch a hole in the center for easy viewing. On a CNC machine, enter these coordinates directly into the control system.
Step 4: Cut Depth
Calculate the total amount of material that needs to be removed for each step. For example, reducing an OD of 50 mm to 30 mm requires 10 mm step cuts (50 mm – 30 mm = 20 mm total reduction, divided by 2 sides).
Split this into a roughing process (2-3 mm depth per cut) to remove the bulk of the material, followed by a finishing process (0.2-0.5 mm depth per cut) to achieve the final dimension.
Step 5: Step Process
Start with the step farthest from the chuck. Position the tool to the marked Z position, then engage the cross slide to the calculated X depth. Feed the tool parallel to the workpiece axis to machine the vertical face of the step.
Repeat the roughing process until 90% of the material is removed, followed by a final finishing process to ensure accuracy. Verify the dimensions with a measuring instrument after each step.
Tools and equipment used in step turning
For step cutting, similar tools are needed as for standard turning, including lathes, cutting tools, and measuring tools.
- Lathe: A lathe is the basic equipment for turning operations. The spindle box contains a spindle that holds and rotates the workpiece, while the tool holder moves along the workpiece to perform various operations.
- Manual lathes require the operator to control tool positioning and feed rate, while CNC lathes use programming instructions to perform these actions automatically. Some CNC lathes also have multi-axis capabilities to perform other machining operations.
- Measuring tools (optional): When using a manual lathe, you will need a precision measuring device such as a vernier caliper or micrometer screw. Typically, machinists prefer to use digital calipers. Their minimum accuracy is about 0.01 mm.
- Parting tool: A parting tool is a narrow, rectangular tool with a sharp blade that is used to cut grooves or separate the finished part from the blank. This tool can be used for both end machining and turning. However, in step turning, it is used to machine the initial groove at the step transition point; the rest of the cutting is done by the turning tool.
- Turning tool: It is a single-point cutting tool with a replaceable carbide or high-speed steel (HSS) insert. The straight edge geometry enables it to cut axially, while the rigid shank maintains the integrity of the tool during operation.Turning tools are used for bulk material removal and, as with most turning operations, are introduced after the cut by the splitter. Turning tools come in a variety of shapes and sizes, each suitable for different operations such as roughing, finishing, threading or grooving.
Step turning vs. other turning operations
The step turning process should not be confused with other lathe operations such as facing, taper turning or flat turning. Each technique requires a unique approach and meets different geometric needs.
Straight turning vs. step turning
Straight turning produces a single, uniform diameter across the entire length of the workpiece. The tool moves parallel to the axis, maintaining constant contact to ensure dimensional consistency. If you step cut a workpiece, multiple diameters are created in sequence. Here, the tool cuts radially to a specific depth at a predetermined location and then moves axially to create a steep 90° transition.
Step Turning vs. Taper Turning
Both step turning and taper turning change diameters, but with opposite geometries. Step turning creates an abrupt 90° transition between sections, with the diameter change occurring immediately at a right angle. Taper turning creates a gradual, angled transition.
Both processes use similar tools, but the tool moves differently. Step turning requires the tool to plunge perpendicular to the workpiece after each axial pass, while taper turning requires the tool to make continuous diagonal movements along the axis.
Facing vs. Step Turning
Facing shortens the length of a workpiece by cutting material perpendicular to the workpiece axis, creating a flat face. The cross-sectional area remains the same. Step turning reduces the diameter along the length of the workpiece, changing the circumference of the workpiece while maintaining the original overall length. For face turning, the tool feeds radially inward. In step turning, the tool moves axially to define the step and radially to set the depth during step turning.
Xtproto’s CNC Turning Services
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Whether you need low-volume prototype production or large-scale production, Xtproto can provide cost-effective, customized solutions based on your design specifications. With cutting-edge technology, live tooling capabilities and expert technicians, we guarantee parts that are durable and feature features such as axial and radial holes, grooves, slots and flats.What are you waiting for? Start your next project with Xtproto today.