xiehe model

How CNC machining achieves tight tolerances on precision parts

In manufacturing, some degree of variation is inevitable. This is both between units and between jobs. With this in mind, our product teams are still able to come up with ways to ensure parts perform as expected.

This has nothing to do with the small differences that exist between the individual parts. We call these acceptable ranges of variation tolerances. Most manufactured parts have a margin of error. We often define them as a measurement range. Tolerances may also include other factors such as texture, color, shape or contour. Paying attention to machining tolerances can sometimes seem like a small step in the manufacturing process. However, this is a critical step in producing repeatable parts. Below are further insights into the tips we follow to achieve tighter CNC machining tolerances.

Proper tolerances are critical in CNC machining, as tighter tolerances increase production costs. For example, producing parts with specific tolerances and shapes requires multiple cutting operations. We also use different tools, which results in more time spent on the machine and higher costs. Some design features and shapes require CNC machining. Examples include sharp interior corners or parts we make with longer cutting tools. This increases the cost of achieving tighter tolerances if we cannot optimize them. While tighter tolerances will be more expensive, we can account for or offset them during production.

Here's how we cost-effectively achieve tight CNC tolerances

Optimizing part CNC machining tolerances for each application

The standard machining tolerance for plastic parts is +/- 0.10” and the standard machining tolerance for metal parts is +/- 0.005”. Certain parts may require less deflection to ensure proper fit. Tight tolerances end up being a necessary cost for a specific part application. Therefore, it is best to limit tight tolerances to necessary surfaces or areas of the part. This helps meet design standards while reducing additional costs. However, if the tolerances of the part do not need to be very tight, selection criteria are an easy way to reduce cost and machining time.

Effective matching of manufacturing methods

One thing to consider when using tight tolerances is to properly accommodate the manufacturing process. For example, using a vertical mill to machine a hole with a set of tolerances has special considerations. We first had to use a CNC lathe to drill with tighter tolerances. This increases setup costs and increases production time. Parts with tight fit or tight tolerance requirements may require additional steps. This helps ensure that every part has the desired finish and fit. Examples of these additional steps include grinding and grinding.

Don't ignore parallel and perpendicular

These refer to two important tolerances that we must prioritize. This is especially true when using multiple components. They are especially important for assemblies, where even slight changes can lead to larger misalignments. This can affect the overall quality and viability of the part.

Match tolerance expectations with material machinability

We often design parts using specific materials to provide specific physical, chemical or performance characteristics. However, we must also consider how these features affect the machinability of the workpiece. For example, milling plastic is easier than work hardening steel. Generally, the softer the material, the harder it is for the material to hold tight tolerances. Resins and soft silicones tend to bend during cutting operations. At the same time, plastics such as nylon may require additional tooling to achieve specific tolerances.

Designed with the final inspection process in mind

The more difficult the tolerance of the part to measure, the more complex the feature. In some cases, you may need special tools to measure certain features correctly. Smaller parts or parts with tiny features also require more creation and inspection tasks. Typically, features smaller than 0.05mm are difficult to see with the naked eye. If tight tolerances are required in this situation, you must have the right tools to accurately measure, check and verify those tolerances. Ideally, tight tolerances can only be ensured if the correct tool is used to measure them.

Advantages of Correct Geometry and Tolerance Yield

Ensuring your parts hold the required tolerances requires correct material selection, part design and production processes. Achieving tight tolerances efficiently can be a daunting task due to many variables. We must also consider a range of environmental and mechanical factors in the production process.

Fortunately, pairing it with an on-demand manufacturing partner like Concord simplifies the whole process. Our team of experts is proficient in various machining methods and optimized processes. We work hard to ensure in-house machined parts meet tight, accurate tolerances every time. You can visit our Resource Center to dive into the ins and outs of CNC machining. You can also further explore our capabilities and see how we can best meet your needs. If you have any questions or need a quote, please contact us.