Getting the Right Information Prior to Tolerancing

Before selecting tolerances, it’s essential to gather the necessary information about the part and its function. Here are a few steps to help you get started:

Determine the function of each geometric feature

The first step is to identify the function of each geometric feature. For example, if you’re machining a part for a car engine, you need to determine the function of each feature, such as the cylinder bore, valve seat, and oil passages. Understanding the function of each feature is crucial to ensure that the part performs optimally.

Determine the most important function of the part

Once you have identified the function of each feature, you need to determine the most important function of the part. For example, if you’re machining a part for a car engine, the most important function is likely to be the cylinder bore. Understanding the most important function of the part is critical to ensure that the tolerances are appropriate for the application.

Choose a datum reference framework and type of geometric control for each feature

Once you have determined the function of each feature and the most important function of the part, you need to choose a datum reference framework and type of geometric control for each feature. The datum reference framework is the set of references used to define the orientation and location of the part. The type of geometric control is the method used to specify the allowable variation in the size, form, and orientation of each feature.

Calculate the tolerance values

Once you have chosen the datum reference framework and type of geometric control for each feature, you can calculate the tolerance values. The tolerance values are the allowable variation in the size, form, and orientation of each feature. The tolerance values should be based on the function of each feature, the most important function of the part, and the manufacturing process used to produce the part.

Handling Competing Requirements

When selecting tolerances, it’s common to encounter competing requirements. For example, tighter tolerances may be required to ensure that the part performs optimally, but looser tolerances may be necessary to reduce manufacturing costs. Here are a few tips to help you handle competing requirements:

The Cost of Tighter Tolerances

Tighter tolerances generally require more precise manufacturing processes, which can increase the cost of production. Therefore, it’s essential to balance the benefits of tighter tolerances against the cost of producing the part. In some cases, it may be more cost-effective to accept looser tolerances and invest in post-processing or assembly operations to ensure that the part performs optimally.

Design for Manufacturing

Design for manufacturing is the process of designing parts and products that are easy and cost-effective to manufacture. By designing parts with manufacturing in mind, you can reduce the complexity of the manufacturing process and minimize the need for tight tolerances. For example, you can reduce the number of features that require tight tolerances or simplify the geometry of the part to reduce the need for complex manufacturing processes.

Conclusion

Selecting CNC machining tolerances can be a challenging task, especially when you have complex requirements. However, by following these steps, you can ensure that your parts meet the necessary requirements without overspending on manufacturing costs. Remember to gather the necessary information, choose the right datum reference framework and type of geometric control, calculate the tolerance values, and balance competing requirements. By doing so, you can produce high-quality parts that perform optimally at a reasonable cost.

If you have any questions or need help selecting tolerances for your CNC machining project, contact us today. Our team of experts is always ready to help you achieve your manufacturing goals.