CNC Accuracy: How to Achieve Precision in Machining

When we talk about CNC machining, it most of the times taken as CNC machining “Precision”. In some respects, it is precision but there are also other things involved in CNC machining of parts. For example, how do you verify a part's precision or how to achieve CNC precision in any machined parts or how to find a contract machining service or so on. In this article, we will discuss these things in detail.

What is CNC Accuracy?

CNC accuracy defines the manufacturing of machined parts to the exact dimension specified in design. It is essentially measuring how close the part is to the targeted dimension with minimal deviation from the design.

Defining CNC Accuracy in Manufacturing

It refers to the capability of CNC machine to create parts that are aligned with the targeted dimension and have no or minimum deviation from the actual value in manufacturing. CNC machining allows CNC precision and machining accuracy and consistent production of part,

How Accurate is CNC?

CNC machines are very accurate, with an accuracy tolerance of ±0.001 in or less. This implies that any dimension of length, width or height cannot deviate more than this value.

The Precision of CNC Machines

CNC Machines are designed in a way to have a very high level of precision standard. The standard machining accuracy tolerance is within +/- 0.005 inches (0.127mm). for ultra-high CNC precision, it can go as low as +/- 0.0002 inches (0.00508mm). This implies a CNC machined part can be produced with zero deviation from actual dimension.

CNC Accuracy Formula

There is no specified formula to measure CNC accuracy. It is measured by certain factors such as machining accuracy of positions, precision or repeatability, accuracy tolerance level, movement accuracy in dynamic mode, reverse error in linear motion or dead zone in parts.

What is the Difference Between Accuracy and Precision in CNC Machining?

Accuracy and precision are two important aspects of CNC machining. Details about them are discussed below

Understanding Accuracy in CNC

Accuracy in CNC refers to how accurate parts are created with respect to the desired dimension. It measures how closely a machine follows its program and gets the intended dimension without repeating the same error.

Precision vs. Accuracy: Key Distinctions

Precision is related to how consistent measurements are with each other. Accuracy refers to how close the measurements are to the designed specification. CNC Precision is the consistency of dimensions and machining accuracy is correctness of the values.

Why Both Are Important in CNC Machining

These are important in CNC machining because they directly impact the quality of machined parts. This tells that machined part is precisely adhered to the intended dimensions which is essential for performance and functionality. Parts have minimum defects, less material waste, better efficiency and client satisfaction.

Charts of Accuracy vs Precision in CNC Machining

CNC Precision and machining accuracy are used interchangeably and can be confusing sometimes. Both are indeed related but have definite meaning. The graphical representation below will help to understand the difference between them.

The Role of Tolerances in CNC Machining

Tolerance has a very important role in CNC machining

What Are Tolerances in CNC Manufacturing?

Tolerance refers to a permissible range of deviation in the dimensions of machined parts. It is determined in precise units such as inches or mm and have symbol of plus/minus (±) on drawing. A smaller accuracy tolerance value in CNC manufacturing denotes higher value of precision standardis required for the part.

Standard CNC Tolerances

The standard CNC tolerance is ±0.005 in (0.13 mm) for machining processes router, lathe, CNC milling (3-axis, 5-axis), engraving and screw machining.

Tight vs. Loose Tolerances: What's the Impact?

Tight tolerance refers to small deviation in the part's dimensions is allowed. This provides high precision standard but with higher manufacturing costs. Loose tolerance refers to larger acceptable variation. This creates cheaper product but potentially compromises the part's fit and function.

CNC Machine Tolerance: How to Achieve Desired Tolerances

Desired accuracy tolerance is achieved by using high-quality tools and materials. Machines require proper maintenance and CNC calibration, regular inspection of machines and tools. The right selection of machines according to designing parts with appropriate tolerances level can help in achieving desired tolerance.

CNC Machine Accuracy: Factors That Affect Performance

There are several factors that depend on the performance of CNC machine and machining accuracy

CNC Plasma Cutter Accuracy

CNC plasma cutter accuracy is affected by material type and thickness, plasma gas setting, torch height, amperage, kerf width, machine quality, cutting speed, CNC control precision, operating skill and the cut bevel angle.

CNC Lathe Accuracy

CNC lathe accuracy depends on factors like clamping technique, tool quality, cutting speed, feed rate and depth of cut, workpiece material, machine alignment, CNC program accuracy, temperature fluctuations, tool wear and part geometry.

CNC Milling Accuracy

CNC milling accuracy depends on factors like cutting tool selection, machine condition and CNC calibration, cutting speed, feed rate and depth of cut, workpiece material, clamping and fixtures, programming accuracy and machine vibration

Machine Construction and Design

Factors that affect the CNC machine construction and design include the work envelope which defines the maximum and minimum part size that can be processed, tool reach of a machine to the workpiece and material properties that can affect the machinability of parts.

Calibration and Maintenance

Factors that affect the calibration and maintenance of CNC Machines are environmental conditions (temperature, pressure, vibration, humidity, noise), CNC calibration records and calibration accreditation and calibration frequency

Temperature and Environmental Conditions

Factors affecting the temperature and environmental conditions are ambient temperature of shop, cutting speed, depth of cut and feed rate, coolant flow, tool geometry, tool wear, machine vibration, and overall design of CNC machines

What is Repeatability in CNC Machines?

Repeatability in CNC machines refers to the ability of the machine to consistently perform the same process and movement multiple times under same conditions. It determines that parts essentially be formed with exact same action with same dimensions throughout the machining process. It is measured in micrometers (μm).

Repeatability vs. Accuracy: A Clear Comparison

Machining accuracy defines how close a machine can create part to the required dimensions. While repeatability is the ability to create parts with consistency reaching the same position multiple times. Repeatability is hitting the same spot multiple time even if it is not perfectly centred.

Taniguchi chart for machining accuracy prediction

How Repeatability Impacts Manufacturing Consistency

Repeatability significantly impacts the manufacturing consistency. It ensures that CNC machine can consistently produce parts with same dimension and tolerance throughout the process. It maintains a high level of quality which is required in large-scale manufacturing,

Types of CNC Accuracy

CNC accuracy has many types. These are explained below

Geometric Accuracy

Geometric accuracy refers to measurements of how closely a graphical model matches the dimension of parts. It is important in architecture, surveying, and computer graphics

Positioning Accuracy

It is the degree to which the position of system matches the desired standard. It defines the accuracy of a mechanical system, geospatial layers, or positioning systems

Interpolation Accuracy

It is related to the sampling methods, number of sample points, and other factors. Interpolation accuracy is determined by cross validation is a common method.

Volumetric Accuracy

It is the degree to which a measured value matches the actual value of a given volume. It is normally utilized in measuring the accuracy of machine tools and 3D scans

Production Accuracy

It defines how exactly the dimension of a product is made with the design specifications. It is essential in production because it impacts the company's profits and reputation.

Common Sources of Errors in CNC Accuracy and Repeatability

There are a few common sources of errors in CNC accuracy which are discussed below:

Spindle Rotation and Guide Rail Errors

Spindle rotation is the deviation in the perfect rotational axis of a machine's spindle. It affects the accuracy of the machined part. And guide rail error describes the inaccuracy in the linear movement of the machine's guide rails. Machine precision is effect in both errors as these are crucial factors in CNC machining accuracy. They can affect the bearing wear, manufacturing tolerances, and thermal expansion.

Transmission Chain and Tool Geometric Errors

These refer to cumulative inaccurate positions and movement of cutting tool. It occurs due to defects in the geometry of each part within the transmission chain, including gears, bearings, lead screws, and the tool. It leads to deviations from the intended machining path and accuracy.

Positioning and Calibration Errors

These refer to inaccuracies in determining the precise location of a point. It occurs from issues with the measuring device, improper CNC calibration or design limitations. It can result in deviation from actual position and reported position

How to Measure CNC Machine Accuracy and Repeatability

CNC machine accuracy and repeatability is measured by laser interferometer. It precisely measures the machine's positioning accuracy by comparing the recorded position to the actual position through laser beam.

How to Check CNC Machine Accuracy

A "ballbar test" can be performed to check machine accuracy. It is a specialized tool to determine the machine's movement along each axis. It identifies deviations from a perfect circle and pinpoint areas of inaccuracies. Dial indicators can also be used to know the straightness and squareness of the axes.

CNC Accuracy Chart

The CNC accuracy chart shows the accuracy of CNC machines at different levels, like 0.020in, 0.010in, and 0.005in.

Using Precision Measurement Tools

Precision measurement tools like calipers, micrometers, and depth gauges determine extremely accurate measurements. It measures very small fractions of an inch or millimeter in manufacturing and engineering. It is used where high precision is essential for quality control and part fitting.

Calibration Methods

it includes working curve method, standard addition techniques, internal standard techniques, temperature calibration, pressure calibration and flow calibration for Precision measurement

CNC Accuracy Percentage

CNC machines are highly accurate so that they can measure the fabricating part as small as a 1/4^th of human hair. It can achieve accuracy of ±0.001 inches (±0.025 mm) or more

Improving CNC Accuracy: Best Practices for Your Machines

There are few best practices that improve CNC accuracy.

Regular Calibration and Maintenance

Regular calibration and maintenance of CNC machines is crucial for accuracy, safety, and quality, cost and equipment longevity. Calibration helps to meet quality standards and operational safety and no CNC errors. It ensures reliable and consistent measurements.

Upgrading Machine Components

Upgrading machine components can enhance efficiency, safety, and sustainability of CNC machines. Upgraded parts can provide better compatibility, less CNC errors and cost-effectiveness with the latest innovations.

Reducing External Factors (e.g., Vibration and Temperature)

External factors or environmental factors like temperature, humidity of machine shop, vibration, machine foundation must be monitored consistently to ensure part accuracy during machining. Using vibration dampening methods or air current minimization methods can increase precision and accuracy.

Why do high-accuracy CNC machines lead to better manufacturing outcomes?

CNC machining has higher accuracy by automating production processes. It minimizes human CNC errors and has a faster production rate with consistent quality. Parts have exact dimensions and with lesser risk of defects and failure.

CNC Parts Precision VS Manufacturing Cost

CNC parts generally have higher accuracy which results in higher manufacturing costs. Tight tolerance requires a complex machining process with specialized tooling and a longer production time. It increases the price per part which significantly impacts the overall cost

Choosing the Right CNC Machining Partner for Your Needs

There are a few points to consider when selecting a CNC machining partner. Prioritize the experience in the specific industry, capability to handle the materials and tolerances, quality control measures, production capacity, lead times, and finally the customer service. Tuofa CNC machining offers one of the best services in China keeping in mind all the factors.