Tolerances Explained in CNC Machining (Defining for production)

Protolabs

14 Apr 202104:08

Summary

TLDRThis episode of 'Mastering Manufacturing' delves deeper into tolerance issues in CNC machining. It addresses common challenges like design for assembly, where parts may not fit due to nominal diameters being the same. It also discusses the impracticality of overly tight tolerances like ±0.02mm, which can be a nightmare for machinists and costly for customers. The video highlights the importance of focusing on critical dimensions rather than over-tolerancing, and the potential conflict between tight tolerances and surface finish requirements, suggesting masking as a solution.

Takeaways

🔧 The first issue discussed is design for assembly, emphasizing the importance of fitting parts together correctly.
📏 A common problem arises when male and female parts have the same nominal diameter, leading to potential fitting issues.
🔍 Engineers often face challenges when customers request very tight tolerances, such as plus-minus 0.02 millimeters, which can be difficult and costly to achieve.
💡 It's suggested to only tolerance critical dimensions that affect assembly or function, rather than applying tight tolerances to the entire part.
🛠️ The script highlights the potential conflict between surface finish requirements and tight tolerances, especially after processes like anodizing.
🎨 The example of anodizing type 3 finish shows how tolerances might be affected and advises considering masking off areas with tight tolerances to protect them.
🔄 The video script emphasizes the need to balance cosmetic requirements with assembly and tolerance needs.
📦 An example of an electronics casing needing to fit a PCB inside an aluminum case illustrates assembly requirements.
👥 The script addresses the challenges faced by both machinists and customers when very tight tolerances are specified.
📈 The video encourages viewers to subscribe for more content and invites feedback on topics of interest.

Q & A

What is the main topic discussed in the video?
-The main topic discussed in the video is the issues that engineers or designers may encounter when dealing with tolerances in manufacturing.
What was covered in the first episode of the series?
-In the first episode, they went over what tolerances are and what makes a tolerance in CNC machining.
What is one of the first issues mentioned in the industry regarding tolerances?
-One of the first issues mentioned is design for assembly, where parts may not fit together as intended due to tolerances.
Why might two parts with the same nominal diameter not fit together?
-Two parts with the same nominal diameter might not fit together if there is no margin for error in the tolerances, leading to both parts being at the maximum size and thus too large to assemble.
What is the significance of the tolerance example given with a diameter of 25 millimeters?
-The example with a 25-millimeter diameter illustrates that without a margin of error, parts are likely not to fit, emphasizing the importance of considering tolerances in design.
What assembly requirement issue is mentioned in the context of electronics casing?
-The issue mentioned is ensuring that an electronics casing can fit a PCB inside, which requires precise tolerances to be maintained.
Why is it challenging for manufacturers to meet an overall tolerance of plus or minus 0.02 millimeter?
-An overall tolerance of plus or minus 0.02 millimeter is very tight, making it difficult and potentially costly to maintain such precision across all features of a part.
What is the recommendation for tolerancing parts that are critical for assembly?
-The recommendation is to only tolerance the critical dimensions that are necessary for assembly or function, rather than over tolerancing the entire part.
What conflict might arise between surface finish requirements and tight tolerances?
-A conflict might arise because processes like anodizing can affect the tolerances of a part, even if it's assumed that tolerances remain the same before and after the process.
Why might masking off certain areas of a part be a good idea?
-Masking off areas where tight tolerances are required can prevent these tolerances from being impacted by surface finish operations, ensuring that they remain precise.
What does the video suggest doing if you want more information on the topic?
-The video suggests subscribing to the channel for notifications on new videos and providing feedback if you want to hear more on this or other topics discussed in previous videos.

Outlines

00:00

🔍 Understanding Tolerances in Manufacturing

This paragraph introduces the topic of the video, which is about tolerances in manufacturing. It mentions that the first episode covered the basics of tolerances in CNC machining, and this episode will delve deeper into issues that engineers and designers face with tolerances. The main issue discussed is 'design for assembly,' where parts may not fit together as intended despite being within standard tolerances. An example is given where a male and female feature have the same nominal diameter, leading to a fitting problem. The importance of considering assembly requirements and avoiding overly tight tolerances that could complicate manufacturing and increase costs is highlighted.

Mindmap

Keywords

💡Tolerances

Tolerances refer to the permissible amount of variation in dimensions of a manufactured part. In the video, tolerances are central to the discussion on CNC machining and assembly. The script mentions how tight tolerances can lead to difficulties in assembly unless properly managed. For instance, if two parts have the same nominal diameter with no margin for error, they won't fit together, highlighting the importance of considering tolerances in the design phase.

💡Design for Assembly

Design for Assembly (DFA) is a concept where products are designed with ease of assembly in mind. The script discusses issues that arise when parts are designed without considering how they will fit together, such as male and female features having the same diameter, leading to assembly problems. DFA is crucial for ensuring that parts can be assembled efficiently and effectively.

💡Nominal Diameter

Nominal diameter is a specified dimension of a part, such as the diameter of a hole or shaft. The video script uses the nominal diameter as an example to explain how, if two parts have the same nominal diameter without any tolerance, they will not fit together. This illustrates the need for a slight variation in dimensions to allow for assembly.

💡Standard Tolerance

Standard tolerance is a widely accepted level of variation for dimensions in manufacturing. The script mentions 'standard tolerance 2768 fine' as an example of a tolerance level that might be used for a part. Understanding standard tolerances is important for engineers to ensure parts meet industry standards and fit together as intended.

💡Assembly Requirements

Assembly requirements specify how parts must fit together in a final product. The video script discusses scenarios where customers want parts to fit within very tight tolerances, such as plus or minus 0.02 millimeter, which can be challenging to achieve and may not be necessary for the function of the part. Assembly requirements must be balanced with practical manufacturing considerations.

💡Surface Finish

Surface finish refers to the smoothness or texture of a manufactured part's surface. The script contrasts surface finish requirements with tight tolerance requirements, noting that processes like anodizing can affect tolerances. For example, a part may need to have a specific surface finish for cosmetic reasons, but this could conflict with the need for tight tolerances for assembly.

💡Anodizing

Anodizing is an electrolytic passivation process that increases the thickness of the oxide layer on the surface of metal parts, often used for cosmetic and corrosion resistance purposes. The video script mentions type 3 anodizing and how it can impact tolerances, especially when very tight tolerances are required post-process. This highlights the need to consider the effects of finishing processes on dimensional accuracy.

💡Cosmetic Requirements

Cosmetic requirements pertain to the visual aspects of a part, such as its appearance or texture. The script discusses a conflict between cosmetic requirements, like anodizing for a certain finish, and assembly requirements that necessitate tight tolerances. Balancing these two can be challenging and may require creative solutions, such as masking areas during finishing processes.

💡Masking

Masking in manufacturing is a process where certain areas of a part are protected or covered to prevent them from being affected by a particular process, such as painting or anodizing. The video suggests masking as a solution to protect areas that require tight tolerances from being affected by surface finish operations, ensuring that both cosmetic and assembly requirements are met.

💡Machinists

Machinists are skilled workers who set up and operate machine tools to produce precision parts. The script mentions the challenges machinists face when working with very tight tolerances, such as plus or minus 0.02 millimeter. These tolerances can make the machining process more difficult and time-consuming, affecting both production time and cost.

💡Over-Tolerancing

Over-Tolerancing is the practice of specifying tighter tolerances than necessary for a part's function. The video script warns against over-tolerancing, as it can lead to unnecessary complications and costs. Instead, it suggests focusing on tolerancing only the critical dimensions that affect the part's assembly or function, which can streamline the manufacturing process.

Highlights

Introduction to the second episode of a mini series about tolerances in manufacturing.

Discussion on design for assembly issues and how they relate to tolerances.

Example of a customer wanting two parts to fit together with the same nominal diameter causing assembly problems.

Explanation of how standard tolerances can affect the fit of parts.

The importance of having a margin of error when designing parts to fit together.

Challenges faced by engineers and manufacturers when dealing with very tight tolerances.

The impact of tight tolerances on the cost and manufacturability of parts.

The need to prioritize tolerances based on assembly or functional requirements rather than over-tolerancing.

Example of a nano satellite panel and the importance of tolerancing critical distances.

The conflict between surface finish requirements and tight tolerance requirements.

The potential impact of anodizing on tolerances, especially for type 3 anodizing.

Suggestion to mask off areas with tight tolerances to prevent interference from surface finishing operations.

The importance of balancing cosmetic requirements with assembly and tolerance needs.

Advice on how to handle parts that have both surface finish and tight tolerance requirements.

Encouragement for viewers to subscribe to the channel for notifications on new videos.

Invitation for viewers to request more content on tolerances or other topics covered in previous videos.