Comparative Research on Process Thinking Between Conventional Lathes and CNC Lathes for Light Industrial Machinery

Amid the broader trend of transformation and upgrading in the machinery manufacturing industry, conventional lathes and CNC lathes have coexisted for a long time, each playing an irreplaceable role in different production scenarios.

Conventional lathes still account for a significant proportion of the total machine tool fleet, and a large number of enterprises continue to rely on this type of equipment for their daily production;

The rapid adoption of CNC lathes is evident to all, and their precision, efficiency, and level of automation represent the direction of development for the manufacturing industry.

The differences in the process logic between these two machining methods directly affect machining quality, efficiency, and cost;

However, the academic community’s systematic understanding of these differences remains insufficient.

Wan Haibo (2025) studies programming and process design technologies for CNC turning.

He conducts research from four dimensions: workpiece positioning, tool selection, toolpath planning, and program compilation and debugging.

He stresses the synergistic relationship between programming and process planning.

Mo Jianbin (2024) investigates the application of first-article machining in CNC turning.

He emphasizes that the first-article stage verifies machining programs and processes.

Zhu Min (2015) compares conventional turning and CNC turning.

He evaluates differences in operation modes, machining accuracy and production efficiency.

He states that each process has its own suitable application scenarios.Recent five-year research covers many topics.

These include parameter selection for thin-walled workpieces, machining of typical thin-walled parts, CNC lathe process optimization, and the numerical control retrofitting of ordinary lathes.

Most existing research focuses on cutting parameters, separate procedures or retrofitting effects.

Scholars rarely discuss two key issues. One is converting empirical knowledge into NC programs.

The other is realizing smooth transition between the two different process thinking modes.

Against this background, this paper carries out research from the perspective of “process mindset”.

It adopts the “experience–program continuum” theory. This theory describes the progressive relationship among conventional lathes, retrofitted CNC lathes and standard CNC lathes.

The paper also explores their applicable boundaries when machining light industrial machinery components.

Core Characteristics of the Machining Process for Conventional Lathes

• Reliance on Manual Operation and Experiential Judgment

Machining on conventional lathes relies heavily on operator skills and practical experience.

Engineers define process ranges for spindle speed, feed rate and tool position.

Nevertheless, operators evaluate multiple factors during real machining.

These factors include material characteristics, tool wear, chip morphology, cutting sound and vibration. Operators make timely parameter adjustments accordingly.

This control process exhibits a closed-loop characteristic of “perception—judgment—adjustment.”

Experience compensates for variations in material properties, differences in clamping, and changes in equipment condition, which also makes it difficult to standardize and formalize process knowledge fully.

Light industrial machinery manufacturing is precisely the field where experience with conventional lathes truly shines.

Turning triangular threads on slender rods is a common task in the repair and maintenance of light industrial machinery.

Due to the poor rigidity of these parts, even the slightest carelessness during machining on a conventional lathe can lead to tool vibration and part deformation.

Experienced lathe operators will adjust the position of the tool rest, change the feed direction, and regrind the tool angle;

None of these techniques have fixed parameters to refer to, relying entirely on on-site judgment.

This ability to “adapt on the fly” is precisely the essence of conventional lathe experience.

• The Trade-off Between Process Flexibility and Precision Control

The primary advantage of conventional lathes lies in their flexibility when switching between processes.

Shafts, discs, and sleeve-type parts typically do not require complex program preparation;

When dimensional deviations or changes in material conditions occur during machining, corrections can be made promptly by manually adjusting the tool holder, feed rate, and other parameters.

Conventional lathes feature a relatively simple structure, easy maintenance and low procurement cost.

They suit high-variety, low-volume production and repair tasks well, which is the key reason small and medium-sized light industrial enterprises continue to rely on them.

However, the flexibility of conventional lathes comes with limitations in terms of precision and consistency.

Manual operation errors, together with transmission system backlash, typically limit dimensional tolerances to IT10–IT13 grades and yield surface roughness (Ra) values of roughly 1.6 μm to 6.3 μm.

When parts require precision of IT7 or higher, or a surface roughness of Ra ≤ 0.8 μm, and involve complex contours and strict geometric and positional tolerances, controlling conventional lathes becomes significantly more challenging.

Therefore, they are better suited for tasks such as rough machining of blanks, general structural components, and repair parts.

Core Characteristics of CNC Turning Process Thinking

• Automated Machining Based on Program Control

CNC lathes replace continuous manual intervention with program control.

The operator first converts process requirements into a machining program, and the CNC system drives the spindle and tool holder movements according to these instructions;

Once the program, cutting tools, and clamping conditions are stable, the machine can operate continuously and automatically, shifting the operator’s role from real-time manipulation to program preparation and process monitoring.

Program control is still grounded in turning process expertise.

Process engineers analyze the material, cutting tools, and workpiece features.

They define cutting parameters, toolpaths, and operation sequences.

They convert this professional knowledge into repeatable instructions. Program quality directly determines machining outcomes.

• Advantages of High-Precision Control and Mass Production

The advantages of CNC lathes lie in their stable precision and repeatable control.

The CNC system controls feed based on pulse equivalents, while the servo closed-loop system corrects deviations in real time;

It can also compensate for pitch errors and backlash through software.

When CNC lathes are used to machine similar shaft components, they typically achieve a stable precision grade of IT7 to IT9, with a surface roughness (Ra) of approximately 0.4 μm to 1.6 μm.

Operators can control consistency errors within ±0.005 mm, so these machines suit mass production requiring high dimensional consistency.

The advantages of CNC lathes are also evident in the machining of complex contours.

Program-planned toolpaths machine steps, deep grooves, curved surfaces, and threads and reduce cumulative errors that repeated clamping and tool setting cause.

Take the outer ring of a light industrial machinery bearing as an example. CNC integration consolidates the original six-step process into two steps, cuts the number of clamping operations, and thus reduces deformation risk.

Engineers can also integrate CNC lathes with CAD/CAM and MES systems to incorporate the turning process into a digital production workflow.

Comparative Analysis of Machining Processes for Conventional and CNC Lathes

• Comparison of Operating Methods and Accuracy

Differences in accuracy control stem from the distinction between on-site compensation and program-based pre-control.

Conventional lathes typically follow a “machining—measuring—adjusting” cycle, with results easily influenced by the operator’s condition;

On the other hand, CNC lathe operators constrain errors in advance using programs, compensation parameters, and feedback systems.

The machines deliver superior repeatability after users stabilize the program.

The core differences are shown in Table 1.

Table 1. Key Differences Between Conventional Lathe and CNC Lathe Machining Processes

• Machining Efficiency and Applicable Scenarios

The efficiency advantage of conventional lathes lies primarily in their short setup times for job changes, making them suitable for repairs, prototyping, and small-batch, high-variety production.

Manufacturers produce workpieces in stable batches on conventional lathes.

Repeated measurement, adjustment and manual feeding extend the processing time for each part.

Operators carry out programming, tool setting and trial cutting for CNC lathes at the preparation stage.

Once the program stabilizes, the machine runs continuously and repeatedly.

Larger production batches better spread the one-time setup cost over all parts.

Therefore, light industrial enterprises should prioritize conventional lathes for repair work and prototype parts, while they assign stable-batch tasks such as bearings, gears, and standardized parts to CNC lathes.

• Critical Discussion: “The Experience–Program Continuum”

Characterizing conventional lathes as “experience-driven” and CNC lathes as “program-driven” helps identify differences, but it is still insufficient to explain the mixed machining conditions found in enterprises.

The experience associated with conventional lathes is not without rules.

Skilled operators’ judgments regarding feed rates, vibrations, and chip conditions essentially stem from a long-established understanding of cutting patterns, although this knowledge often exists as tacit experience.

CNC lathes are equally reliant on experience; cutting speeds, toolpaths, and process sequences all require judgment from process engineers during the programming phase.

Thus, CNC machining has not eliminated experience but rather shifted some on-site experience to an earlier stage and transformed it into repeatable programs.

When a conventional lathe is retrofitted with a CNC system, it can retain both manual operation and program control, forming a transitional form between purely manual machining and fully CNC machining.

Based on this, this paper proposes the “Experience–Program Continuum.”

At the left end of the continuum are experience-driven conventional lathes; at the right end are CAD/CAM-integrated CNC machines;

Manufacturers use retrofitted CNC lathes and manually programmed CNC lathes for applications falling between these two extremes.

The distinctions between different types of equipment are no longer viewed as a simple either/or choice, but rather as a continuous process in which the degree of explicit and programmatic expression of experience gradually increases.

Enterprises can determine their appropriate position within this continuum based on production volume, precision, cost, and personnel capabilities.

• Analysis of Typical Machining Cases in Light Industry Machinery

The following three machining cases in the light industry machinery sector validate the above analysis.

Case 1: Bearing Outer Ring. A certain company manufactures outer rings for a series of ultra-lightweight bearings.

Previously, they used specialized lathes, which required six machining operations and repeated setups—each of which could potentially cause deformation.

After switching to a CNC lathe, we consolidated the six operations into two and completed nearly all work within a single setup.

This resulted in improved precision, increased efficiency, and reduced costs.

Case 2:

Threads on Slender Rods. Operators widely regard thread cutting on slender rods as a challenging task on conventional lathes.

If operators neglect even minor details, tool vibration, workpiece deformation and thread misalignment can easily produce scrap parts.

On a CNC lathe, programmers predefine the toolpath and cutting parameters in the program, and the machine executes the optimal plan.

This delivers far greater stability than relying on human intuition.

Case Study 3: Thin-walled Parts. Deformation is the greatest concern with thin-walled parts.

On conventional lathes, clamping too tightly causes deformation, while clamping too loosely can cause the workpiece to fly off—it all depends on the operator’s judgment.

Operators using CNC lathes fitted with simulation software can identify potential deformation areas during programming and adjust the plan in advance, instead of waiting until a part fails to investigate the root cause.

These three case studies demonstrate that process selection must consider part structure, batch size, and precision requirements simultaneously;

Engineers cannot determine this solely based on equipment type.

Prospects for Technological Convergence and Light Industry Manufacturing

• CNC Retrofit of Conventional Lathes

As mentioned earlier regarding the “continuous spectrum,” the most typical example is the CNC retrofit of conventional lathes.

The high cost of purchasing new CNC lathes places pressure on some small and medium-sized light industry enterprises to upgrade their equipment;

Installing a CNC system on existing conventional lathes can improve repeatability and machining efficiency while keeping investment costs under control.

Operators can perform relevant accuracy inspections for the CA6140 conventional lathe, a typical horizontal lathe, in accordance with the current GB/T 4020—1997 Horizontal Lathes—Accuracy Inspection.

This type of retrofit has a particularly strong market in the light industry sector.

For example, variable-pitch screws are used in rubber extruders and plastic molding machines;

Machining them on a conventional lathe is labor-intensive, while purchasing a dedicated CNC lathe is not cost-effective.

The retrofitted machine meets the task requirements adequately. Operators can run programs on it and also operate it manually, effectively upgrading the equipment from “pure experience” to “experience plus programming.”

This is a prime example of the middle ground in the “experience–program spectrum.”

• Hybrid Machining and Skill Redesign

The development of hybrid machining has gradually expanded operational skills to include process planning, programming, and system debugging.

After light industry enterprises implement MES, process data, production schedules, and inspection information can flow online, and lathes become an integral part of the digital production chain.

Colleges keep practical training of conventional lathe operation in vocational education.

This builds students’ basic cutting skills. Meanwhile, educators enhance training in CNC programming, debugging and experimental verification.

Learners gradually turn handson experience into programming capabilities.

Summary

This paper delivers three contributions. First, it distinguishes conventional lathes from CNC lathes from the perspective of process thinking instead of individual parameters.

It clarifies the differences in control logic. These control modes include human perception, on-site adjustment, program planning and feedback compensation.

Second, it proposes an “experience–program continuum,” incorporating conventional lathes, retrofitted CNC lathes, manually programmed CNC lathes, and CAD/CAM-integrated CNC lathes into a single framework;

Third, using cases such as bearing outer rings, slender rod threads, and thin-walled parts in light industrial machinery, this paper verifies the applicability boundaries of different process paths.

Implementation decisions can be made based on a two-dimensional “batch size–precision” assessment:

In single-piece or small-batch production requiring precision of IT10 to IT13, conventional lathes are preferred for their rapid setup change and low-cost merits;

For small-to-medium batches with IT9–IT10 precision, enterprises with existing conventional lathes may opt for CNC retrofitting.

This approach enhances repeatability while preserving the flexibility of manual operation;

When producing larger batches at IT7–IT9 precision or components with complex contours, CNC lathes become the first choice.

Enterprises should also review their plans in light of personnel programming capabilities, equipment depreciation, and changeover frequency to ensure that process selection falls within a reasonable range on a continuous spectrum.