4 Must Know Tips on Mechanical Design Tolerances

If you are in the process of designing a product or component, it is important to consider the tolerances that will be required for manufacturing. Tolerances are the allowable limits for deviations from the nominal or ideal dimensions of a part. Properly specifying tolerances can help ensure that your product meets its performance requirements and can be manufactured accurately and efficiently.

Understand the types of mechanical design tolerances

There are several types of mechanical design tolerances: form, fit, function, and assembly. Each type of tolerance has a different impact on the overall performance of the product.

Form tolerances are the most important type of tolerance for mechanical designers. Form tolerances control the shape of the part and how it interacts with other parts. Fit tolerances control the size of the part and how it fits into its intended space. Function tolerances control the performance of the part and how well it works in its intended application. Assembly tolerances control the fit of the parts during assembly and ensure that the product can be assembled correctly.

Tolerances are often expressed as plus or minus values. For example, a form tolerance might be expressed as +/- 0.005 inches. This means that the part can be up to 0.005 inches larger or smaller than the nominal (intended) size and still be within tolerance.

Tolerances are often specified by engineering drawings or other design specifications. It is important for mechanical designers to understand how tolerances work and how they impact the overall performance of the product.

Consider the impact of manufacturing process to tolerances

The type of manufacturing process that will be used to produce your part or product will have a big impact on the tolerances that are possible. Some processes are more precise than others, so they can produce parts with tighter tolerances. In general, machining processes have the highest degrees of accuracy, followed by stamping, casting, and injection molding.

There are many different types of manufacturing processes, and each one has its own inherent advantages and disadvantages. One important factor to consider when choosing a manufacturing process is the impact that it will have on tolerances. Some processes are much more forgiving of tight tolerances than others, so it is important to choose a process that is well-suited to the tolerances required for your project. The type of process you use will have a big impact on the tolerances that can be achieved.

For example, machining processes like milling and turning is a very precise manufacturing process that can achieve very tight tolerances. However, it is also a relatively slow and expensive process. And they can only produce parts with fairly simple shapes. On the other hand, processes like casting and injection molding are much faster and less expensive, and can produce parts with much more complex shapes. but it typically cannot achieve the same level of precision as machining. And the tolerances tend to be looser.

Ultimately, the best manufacturing process for your project will depend on a variety of factors, including the tolerances required, the quantity of parts needed, the timeframe for delivery, and the budget. Choosing the right process will ensure that your parts are manufactured to the highest quality standards and delivered on time and on budget.

The best way to achieve tight tolerances is to use a combination of different manufacturing processes. For instance, you could start with a casting or injection molded part, and then finish it off with some precision machining. This way you would get the best of both worlds: the complex shape from the casting/molding process, and the tight tolerances from the machining process.

Know the standards of engineering tolerances

There are a number of national and international standards that specify tolerances for various types of products and parts. When specifying tolerances for your product, it is important to check these standards to see if there are any applicable requirements that you need to meet.

There are many standards that apply to engineering tolerances, but the most common one is the ISO 2768 standard. This standard provides general guidelines for tolerances in linear and angular dimensions, as well as for form, orientation, and location tolerances. It is important to note that these standards are not mandatory, but they provide a good starting point for designers and engineers when creating or evaluating tolerance specifications.

Another common standard is the ANSI/ASME B89.1.5-2009 standard, which provides specific guidelines for geometric dimensioning and tolerancing (GD&T). This standard is often used in conjunction with the ISO 2768 standard, and together they provide a comprehensive set of guidelines for engineers and designers.

When creating tolerances, it is important to consider the manufacturing process that will be used to create the part or product. Different manufacturing processes have different capabilities and limitations, so it is important to choose tolerances that are achievable with the chosen manufacturing process. In some cases, it may be necessary to use multiple manufacturing processes in order to achieve the desired tolerances.

It is also important to consider the assembly process when creating tolerances. If a part or product will be assembled with other parts or products, the tolerances of those parts must be compatible in order for the assembly to function correctly. For example, if two parts are being joined together with a bolt, the holes in each part must be of a size that allows the bolt to be inserted and tightened without issue. If the tolerances of the holes are not compatible, the bolt may not be able to be inserted or the joint may be too loose and not function correctly.

In general, it is best to err on the side of caution when creating tolerances. It is often easier and less expensive to loosen tolerances during the design stage than it is to try to tighten them after the fact. Additionally, it is important to keep in mind that assembly processes can often introduce additional tolerance stack-ups that must be considered.

If you are working with a partner who will be manufacturing your parts or products, they may have their own standards that they prefer to use. In these cases, it is important to discuss the tolerances with your partner and come to an agreement on what will be used.

In summary, there are many standards that apply to engineering tolerances, but the most common ones are the ISO 2768 standard and the ANSI/ASME B89.1.5-2009 standard. It is important to consider the manufacturing process and assembly process when creating tolerances, and to err on the side of caution if possible. If you are working with a partner who has their own standards, it is important to discuss and agree on the tolerances that will be used.

Use GD&T wisely

In the world of engineering and manufacturing, there is a lot of talk about GD&T. GD&T is short for Geometric Dimensioning and Tolerancing, and it is a system used to define the precise specifications of engineering parts and products.

When used correctly, GD&T can be an extremely powerful tool that can help ensure that parts are manufactured to tight tolerances and meet the requirements of the design. However, when used incorrectly, GD&T can actually make things worse, leading to increased manufacturing costs and delays.

Here are a few tips on how to use GD&T wisely:

1. Make sure you understand the basics of GD&T before using it. There is a lot of specialized terminology associated with GD&T, and it can be easy to get lost in the details if you don’t have a solid foundation in the basics.
2. Be conservative in your use of GD&T. It’s always better to err on the side of caution when using GD&T, as using too many tolerances can actually make it more difficult to manufacture parts accurately.
3. Work with experienced professionals when using GD&T. If you’re not sure how to correctly apply GD&T to your designs, partner with an engineering or manufacturing firm that has extensive experience with the system.
4. Use software to check your GD&T specifications. There are now software programs available that can automatically check GD&T specifications for errors and inconsistencies. This can save you a lot of time and effort in the design process.
5. Get certified in GD&T. If you’re serious about using GD&T correctly, consider getting certified through the American Society for Quality (ASQ). This certification will show employers that you have a solid understanding of the system and how to correctly apply it.

By following these tips, you can help ensure that you use GD&T correctly and avoid any potential pitfalls. When used correctly, GD&T can be a powerful tool for ensuring the accuracy of manufactured parts.

Conclusion

When it comes to choosing a manufacturing process for a new product, designers and engineers must take many factors into account. One of the most important considerations is tolerances. Tolerances are the allowable variation in dimension or form for a component or assembly. They are critical to ensuring that parts fit together correctly and function as intended.

Designers must carefully consider tolerances when selecting a manufacturing process. If the tolerances required for a part are too tight for the chosen process, it may be necessary to use a different process or to make design changes that loosen the tolerances. Either way, it is important to understand the impact of tolerances on manufacturing processes before making any decisions.