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precision vs accuracy

Precision vs Accuracy: How Are They Important in Machining?

Precision and accuracy are commonly used concepts in machining measurements. However, their meanings differ mainly in manufacturing and engineering, even though they are often relatively interchangeable in everyday conversations.

A measurement is not necessarily accurate just because it is precise and vice versa because they do not use the same measurement process. Understanding the differences between precision and accuracy for industries that depend on exact measurements is crucial.

This guide provides an in-depth explanation of both accuracy and precision, their benefits in machining, and their differences. Continue reading to the end to learn more about improving precision and accuracy in machining!

What is Precision?

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Precision CNC Machining

Precision refers to the proximity or nearness of two or more measurements. Measurements of machined parts are precise if the measured values are near or close to each other. Precision is one of the most essential concepts used in machining. It measures the variance range in a data set or the spread between data points. High precision is when your measured values or results are similar to low precision, with results that are all over the map.

Using the bullseye example, multiple measurements are a precise data set if gathered below the bullseye’s center. However, they aren’t wholly accurate since they are not near the center. However, we can conclude that these measured values are precise if they are focused around the bullseye.

Precision in machining represents the repeatability or reproducibility of several components with close dimensions when manufacturing. Precision CNC machines are at the core of modern industries as they directly impact machining reproducibility, efficiency, and accuracy. Demand for machining micro products or components with micro intricate features has increased significantly.

Meanwhile, machining CNC parts on large scales requires more precise design techniques and machining dynamics to meet the client’s requirements. Hence, precision is primary in machining operations because it represents the capability of a manufacturing process or machine to recreate the almost exact measures of the machined parts consistently over longer time periods.

What Is Accuracy in Machining?

Accuracy refers to the closeness of the measurements to a particular value or true value. A measurement is considered accurate if it is close to the true value. It can indicate the impact of systematic error. Accuracy is high if the systematic error is small and vice versa.

Generally, scientists and product engineers use accuracy to indicate how well a single measurement corresponds with its target or true values. A bulls-eye target is a good example used for illustrating accuracy and precision. A good accuracy shows how close any measured value is to the bulls-eye’s center, the target value. High accuracy indicates when you hit the target value directly, while poor accuracy or low accuracy indicates when you’re way off the mark.

More so, any values close to the true or accepted value are considered accurate if they land on the sides of, below, or above the center point. Closeness to the actual value is the most essential quality for accuracy.

Benefits of Accuracy and Precision in Part Fabrication

typical precision vs accuracy examples
Benefits of Accuracy and Precision in Part Fabrication

The ability of any manufacturing industry to consistently fabricate precise and accurate parts determines its success. CNC machines are widely used across manufacturing industries because of their relatively high precision and accurate capabilities.

The medical, aerospace, marine, automotive, military, oil and gas industries are typical manufacturing industries that use CNC machinery. Below are some of the expected benefits of precision and accuracy in part production:

Easier Calibration of Equipment

CNC machinery comprises computerized devices that enable product designers and machinists to calibrate different tools easily. Moreover, CNC machines save the manufacturing instructions until the machinists input new codes or make certain changes to fabricate various highly precise and accurate parts.

Hitch-Free Testing and Prototyping

High accuracy and precision in machining allow easier prototyping of several designs and parts, including complex titanium machining tasks. Furthermore, precision CNC machining helps reduce the cost of intensive labor and ensures machined parts are of high quality. Beyond this, high machining precision and accuracy facilitate seamless performance testing of fabricated products.

Safety Consideration     

Safety is one of the primary considerations of product manufacturing, especially in aerospace and medical industries where precise and accurate components are required. End users are exposed to risks if manufactured components are defective or below industry standards. Hence, fabricating precise and accurate parts helps to ensure customer satisfaction and safety.

How to Track and Measure Precision and Accuracy

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How to Track and Measure Precision and Accuracy

You’ll have to track and measure your results to determine if your measurements are accurate or precise. However, precision and accuracy are often calculated differently:

Precision Measurement: Precise measurements show how close measurements are to each other. You’ll need to establish a tracking system that indicates how multiple data points or measurements compare to each other over time to inspect precision.

Accuracy Measurement: It indicates how your result compares to the target value. The closer you are to the target value, the more accurate you are. Thus, you need to have clearly defined goals you are trying to attain to determine accuracy.

You will need an accurate and easy-to-manage measurement system for accurate measurements. A project management software with universal reporting can help track and react to results in real time.

For instance, if you discover consistent results (precise) departing from your known value or target goal (inaccurate), a systemic error may occur.

Typical Precision Vs. Accuracy Examples

what is accuracy in machining
Typical Precision VS Accuracy Examples

Precision and accuracy are independent parameters that are core to the success of any manufacturing operation. Most CNC machinery utilizes computer software to maintain programmed dimensions when designing and machining a part. However, a machining process can have different outcomes, such as:

  • Precise and accurate
  • Accurate but not precise
  • Precise but not accurate
  • Not precise and not accurate

Hence, it is essential to differentiate these parameters and document the measurements separately for an overall quality machining service. We’ll explore practicable analogies for a better understanding of the concept of precision and accuracy in part fabrication:

Precise and Accurate

It is the utmost desire of all manufacturing industries to create accurate and precise components for their clients. For instance, assume a manufacturer inputs instructions to drill a hole in a rod 60mm from an edge with a +/- 1mm tolerance. The manufacturing process is only considered precise and accurate if the CNC machine makes the hole within variable lengths measuring between 59mm and 61mm for all the rod batches.

Accurate but not Precise

Although some components may be machined accurately, not all manufactured parts are precise to the required values. For instance, let’s say an engineer plans to machine a piston compression measuring 1.4 inches in height with a standard deviation of +/- 0.005 inches.

Assuming some pistons are manufactured between the height range 1.395 and 1.405 inches, while others from this production batch are of heights below or above the tolerance limits. You can, therefore, conclude that this manufacturing process is accurate but not precise with quality inspections.

Precise but not Accurate

The machined parts have similar dimensions but are not near the required measurement. From the previous example above, if the manufactured pistons have heights of 1.41, 1.42, 1.41, and 1.415 inches. Then, we can deduce through quality inspection that this manufacturing process is precise but not accurate since the standard deviation limit is +/- 0.005″.

Not Accurate and not Precise

In some cases, manufacturing operations can yield unexpected outcomes, with the final parts deemed unprecise and inaccurate. For example, if a machinist intends to manufacture a plastic piece of 30mm in length with a tolerance of +/- 0.6mm, Possibly the machined plastic parts have individual measurements of 28, 32, 29, 27, and 31mm.

This calculation result indicates that the sizes of the manufactured parts in this batch are not closely agreeable as they entirely deviate from the required dimension. Hence, you can deduce that the components manufactured in this batch are imprecise and inaccurate.

How Does Precision Differ from Accuracy in Machining?

accurate engineering drawings are a prerequisite for precision machining
Accurate Engineering Drawings Are a Prerequisite for Precision Machining

To understand the difference between precision and accuracy in fabrication and manufacturing applications, hitting the bull’s eye in a target practice chart might not be the perfect illustration. More so, how closely a batch of parts corresponds with the design blueprint or CAD model represents the difference between accuracy and precision in machining.

Highly accurate CNC machines can create a part that closely matches the design model. For instance, imagine a part design requires a pair of 0.60-inch wide by 6.00-inch long slots machined on its surface, with each machined slot 3.0 inches apart.

A quality specialist can assess a single finished part by measuring it to confirm that the half-inch slots were cut to a length of 6.05 inches and spaced by 2.96 inches. The quality specialist determines if the machined parts match the design model accurately. The allowable tolerances specified in the machining drawing will decide whether the part will be rejected.

We can examine the precision of the CNC machines if a batch of 100 or 1000 of these machined parts is fabricated. High-precision CNC machines will exhibit higher reproducibility, with repeated measurements indicating values consistently close to the true model.

Now, let’s examine the differences between precision and accuracy:

Types of Error Indicated

Accuracy shows a manufacturing system or tool’s error, while precision measurements randomly reflect the error among fabricated parts.

Number of Measurement

Examining machining precision requires several measurements under the same condition. This is to verify the result’s conformity. On the other hand, machining accuracy requires a single measurement because you only have to compare the dimensions of machined parts to the standard value in accuracy measurements.

Different Description

Precision indicates the close agreement of variation present in the dimensions of machined parts with one another. Conversely, machining accuracy refers to the proximity of manufactured parts’ measurements to the standard specifications.

Good machining precision allows you to repeatedly machine almost exact dimensions of fabricated parts without introducing random errors. Conversely, good machining accuracy helps ensure your machined parts conform to the theoretical benchmark.

How to Improve Machining Precision and Accuracy

basic parameters in milling machining
Basic Parameters in CNC Milling Machining

Manufacturers employ various strategies to improve accuracy and precision in machining. These include a combination of techniques and the use of proper equipment. Here are the standard ways of improving machining precision and accuracy:

Optimize Cutting Parameters

Adjusting cutting parameters such as speed, depth of cut, and feed rate helps to achieve optimal machining outcomes. Similarly, it reduces tool wear and ensures better machining accuracy.

Use High-Quality Equipment

Investing in high-quality computer numerically controlled machinery helps to achieve precise control over cutting parameters. Hence, machined parts are produced exactly to the target values indicating the technical drawing.

Tool Selection

Cutting your raw material with high-quality CNC tools made from high-speed steel or carbide is advisable to achieve high accuracy. Choosing the appropriate tool geometry and coatings for a particular machining task helps to ensure machined components are precise and accurate to the accepted value.

Workpiece Fixturing

Machinists often use work-holding tools or CNC fixtures to firmly secure the workpiece during machining to mitigate vibrations and movement. These precision fixtures and clamping techniques allow the creation of precise machined parts.

Calibration and Maintenance

Regular CNC machine calibration and maintenance are essential to ensuring machining accuracy. Conduct routine regular machine inspections, ensure the components are well aligned and lubricated, and inspect the components for wear.

Measurement and Inspection

Conduct strict inspection procedures with a standard precision measuring instrument including calipers, micrometers, and coordinate measuring machines (CMMs) to confirm dimensions and tolerances when fabricating parts.

AT-Machining: Your One-Stop CNC Shop for Precise and Accurate Machined Parts

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AT-Machining Your Top China One-Stop CNC Machine Shop

From a manufacturing perspective, accuracy refers to how approximately a machined part matches the design model, while precision reflects repeatability when fabricating that part with the same results. Product designers and manufacturers aim to fabricate parts according to the client’s machining tolerances specifications. To produce high-quality parts that match the design model, you must achieve high precision and high accuracy in a production batch. AT-Machining is your best bet if you need professional assistance manufacturing precise and accurate components.

AT-Machining is a renowned CNC service provider known for quality and reliability. Our expert teams of engineers and quality specialists are committed to delivering parts that match the design model. With our cutting-edge CNC machining facilities, we can help you achieve the desired in your next fabrication process. Submit your CAD files now for instant quotes!

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