To be sure that the tolerances on your plastic parts are accurate, you can follow these steps:

1. DFM (design for manufacture). Designing your components with the production process in mind entails doing this. Avoiding intricate designs, precise tolerances, and challenging-to-mold materials are all part of this.

2. Pick the appropriate material. Shrinkage rates and thermal expansion coefficients vary among various plastic materials. It is crucial to take into account the working environment and necessary tolerances when choosing a material for your parts.

3. Work with a skilled molder. A skilled molder will have the knowledge and skills necessary to make your parts within the necessary tolerances. They will also be able to give you advice on the ideal layout and components for your project.

4. Offer precise and short requirements. Be sure to give precise and detailed instructions for the necessary tolerances when placing your order with the molder. This contains the kind of tolerance (for example, linear, angular, or positional), its value, and where it is located on the part.

5. Thoroughly inspect the components. It's crucial to properly verify your parts once you've got them to make sure they adhere to the necessary tolerances. Numerous inspection techniques, including calipers, micrometers, and coordinate measuring machines (CMMs), can be used to do this.

6. Use a chart of tolerances. You may find the typical tolerances that can be attained for various production methods and materials using a tolerance chart. You can use this to guide your expectations for your contributions.

7. Make use of SPC (statistical process control). SPC is a technique for keeping an eye on and managing production processes to make sure they are delivering consistent outcomes. This can assist in locating and fixing any issues that may result in parts that are beyond tolerance.

8. Implement a QMS (quality management system). A QMS is a set of rules and guidelines that guarantees that goods and services satisfy consumer needs. By doing this, you may assist in guaranteeing that your plastic components are constantly made to the right tolerances.

9. Request a process capability study (PCS) from your molder. A statistical analysis called a PCS demonstrates how successfully a manufacturing process can produce parts within a specified tolerance range. This might assist you in determining the likelihood of parts being manufactured outside of tolerance.

10. Make use of FAI (first article inspection). FAI is a procedure for checking the initial batches of components made using a new mold or production technique. This can assist in finding any issues that might result in the production of out-of-tolerance parts.

11. Employ the PPAP (production part approval process). To make sure that the production process can produce parts that fully satisfy the needs of the client, PPAP is a more thorough inspection procedure. For parts with a high volume or important application, this is frequently necessary.

These pointers might help you make sure that your plastic parts' tolerances are correct and suitable for your purposes.