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How do you verify Perpendicularity? (GD&T)

Written by:

Pete Jones

GD&T is not just a set of symbols on an engineering drawing; it’s the language that speaks volumes about the quality and accuracy of machined components. 

Through GD&T, engineers communicate design intent with clarity, specifying tolerances that go beyond traditional methods. This precision-enhancing tool is more than just a set of rules; it’s a systematic approach that ensures every element of a part is defined and controlled, ultimately leading to improved quality and reduced production costs.

Now, let’s pivot our focus to a key player in the GD&T lineup: perpendicularity and how to verify it.

Perpendicularity is a cornerstone in the stability and functionality of machined parts. 

Why does perpendicularity matter in manufacturing?

Consider it as the assurance that surfaces or features are precisely at right angles to each other, contributing to the overall integrity of the component.

Controlling manufacturing costs while maintaining the desired level of quality and precision is a crucial aspect for manufacturers.

By maintaining strict control over this dimension, manufacturers can significantly reduce the occurrence of faulty parts, saving on potential rejections and rework expenses.

This article aims to equip readers, especially quality and production managers, with the knowledge needed to navigate the intricacies of verifying perpendicularity in manufacturing

What is the definition of Perpendicularity in GD&T?

Perpendicularity is mentioned in both the ASME Y14-5 2018 (and previous standards) and ISO standards (specifically ISO 1101:2017 and previous standards) 

The primary role of perpendicularity in geometric dimensioning and tolerancing (GD&T) is to control the orientation of features within a part. It ensures that surfaces, axis, or lines are aligned at precise right angles to specified references, contributing to the part’s functional requirements and assembly integrity. 

Perpendicularity is crucial in applications where the angular relationship between features significantly influences the part’s performance

What is the difference between perpendicularity and angularity?

Perpendicularity in engineering denotes the strict requirement that a specified surface, axis, or line be precisely oriented at a right angle (90 degrees) to a designated reference plane. This geometric tolerance is symbolised by a line with a vertical line at 90 degrees. 

On the other hand, angularity defines the allowable angular deviation of a line, axis, or plane from a specified reference, represented by an “X” symbol with an associated angle value. 

Unlike perpendicularity, angularity permits a range of angular variations, providing flexibility within specified limits. In essence, perpendicularity mandates strict right-angle orientation, while angularity allows for controlled angular deviations in engineering and manufacturing applications.

Application scenario in the medical industry.

In the critical landscape of medical device manufacturing, where precision is not just a preference but a necessity, the production of components like the medical syringe demands meticulous attention. 

Among the myriad of crucial dimensions, verifying perpendicularity stands out as an indispensable step to ensure the reliability and safety of these lifesaving instruments.

Let’s take the example above, the drawing above shows a right angled shape component with 3 dimensions 

  • The datum symbol identified by [A]
  • A length measurement 50 +/-0.5

The perpendicularity calloutIn this case the length measurement is confirming the position of that feature however the perpendicularity is checking the orientation back to the datum feature. 

 What is happening in the background is two parallel planes are being established a total 0.2mm apart (indicated by the blue lines) the red line is the actual line. The actual feature is allowed to rotate within the 0.2 tolerance zone. Referenced back to datum A.

Key factors influencing perpendicularity specifications

When measuring perpendicularity the results will also vary depending on the manufacturing method used.

Some practitioners adhere to traditional methods using angle blocks, while others have embraced advanced Coordinate Measuring Machine (CMM) technologies. Let’s explore the comparative advantages and drawbacks of these approaches.

Traditional Methods with Angle Blocks:

  1. Risk of Inaccuracy: Traditional methods relying on angle blocks and manual tools introduce the risk of inaccuracies due to human error. The alignment process requires careful attention, and deviations can compromise the reliability of perpendicularity measurements.
  2. Limited Data Points: The use of angle blocks provides a limited number of data points for measurement. This can result in an incomplete understanding of the overall perpendicularity of a feature, especially in complex geometries.
  3. Time-Consuming Process: The manual nature of traditional methods makes the verification process time-consuming. This not only affects the overall efficiency of production but also increases labour costs associated with extended verification periods.

Using Advanced CMM Machines

1. High Precision Measurement: Advanced CMM machines, such as the Touch Probe System – Opticline T3D and RPS Arm, offer high-precision measurements. Automation reduces the risk of human error, ensuring accuracy in the verification process.

2. Comprehensive Data Collection: CMM machines provide a wealth of data points across the entire surface of a component. This comprehensive data collection enables manufacturers to scrutinise perpendicularity at a detailed level, capturing nuances that may be missed with traditional methods.

3 .Time and Cost Efficiency: CMM machines streamline the verification process, contributing to efficiency gains in production. Automated measurements reduce the time required for verification, leading to cost-effectiveness in the long run.

Best practice when measuring perpendicularity

Preparing the Part for Measurement:

1. Cleaning and Inspection:

  • Precision Starts with Cleanliness: Cleaning the part thoroughly is the first step in precision. Any contaminants such as dirt, grease, or debris can compromise measurement accuracy. Temperature-controlled cleaning environments ensure consistent conditions for reliable results.
  • Machine and Tool Temperature Control: Maintaining consistent temperatures for both the measuring machine and tools is essential. Fluctuations in temperature can introduce dimensional variations. Controlling the temperature ensures stable and repeatable measurements.

2. Datum Establishment:

  • Setting the Foundation: Datum establishment is a pivotal step in ensuring a reference point for subsequent measurements. Identifying and marking the datum features with precision is crucial. This establishes the foundation for accurate perpendicularity verification

Selection of Appropriate Measurement Tools and Equipment For Verifying Perpendicularity:

1. Versatility of Modern Systems:

From Manual to Automated: Modern measurement systems have evolved to handle tasks that were once manual. They offer versatility in tackling complex measurements with ease, ensuring efficiency and accuracy in the verification process.

2.Integration of GD&T:

Not all measurement systems handle Geometric Dimensioning and Tolerancing (GD&T) equally. Understanding the system’s capabilities in handling GD&T is essential. Some advanced systems seamlessly interpret and implement GD&T specifications, providing more robust measurement solutions.

Calibration and Alignment Procedures:

1. Sempre Calibration Services:

  • Ensuring Accuracy from the Start: Calibration is the backbone of accurate measurements. Choosing a reliable calibration service, such as those offered by Sempre, instils confidence in the accuracy of measurement tools and equipment.
  • Alignment for Precision: Calibration goes hand in hand with alignment procedures. Ensuring that the measuring machine is properly aligned enhances the accuracy and repeatability of measurements. Sempre’s calibration services encompass comprehensive alignment procedures, contributing to the overall precision of the verification process.

Perpendicularity Challenges and Common Errors

One common error is the misuse of perpendicularity when parallelism or angularity would be more fitting. Perpendicularity is specifically applicable when a feature must be precisely oriented at a 90-degree angle to the datum, not when it allows for different angles or constant offsets. 

Another misconception involves opting for perpendicularity when position or concentricity would be more suitable. Perpendicularity solely governs the feature’s orientation, overlooking its location or symmetry. In contrast, position and surface profile are more effective as they regulate both orientation and location.

Lastly, a frequent mistake is relying on perpendicularity when flatness or straightness would be adequate. While perpendicularity suggests a flat or straight feature, it introduces an additional constraint of being perpendicular to the datum. Flatness and straightness can effectively control the form of the feature without necessitating a datum reference.

Recommendations for Maintaining Precision in Manufacturing Processes:

1. GD&T Training:

  • Empowering Teams with Knowledge: Specialised Geometric Dimensioning and Tolerancing (GD&T) training is a cornerstone for precision. It empowers both design and production teams with a common language for communicating complex geometric specifications. Understanding GD&T enhances interpretation and implementation, reducing the likelihood of errors and ensuring consistent precision across processes.

2. Consultation with Sempre:

  • Confidence in Old and New Systems: Seeking consultation from The Sempre Group bridges the gap between old and new systems. Traditional manufacturing systems can be complemented with GD&T on prints, instilling confidence in manufacturers. This consultation not only aids in transitioning to more advanced methods but also ensures that existing systems maintain precision in line with industry standards.

Book GD&T Training with The Sempre Group

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