At Approved Machining, precision is not just a standard; it is a commitment we uphold in every project we undertake.
Our expert machinists are highly experienced in holding tight tolerances when a part’s function truly depends on them. At the same time, it is important to understand the trade-offs associated with overly stringent tolerance requirements. Specifying tolerances that are tighter than necessary can increase cost, extend lead times, and in some cases result in parts that are not practical to machine.
In this guide, we explain how to optimize your design for manufacturability, balancing precision and value so you achieve the best possible outcome for your CNC machining projects.
Table of Contents
- 1 Understanding Tolerances in Precision Machining
- 2 Why Opening Tolerances Boosts Your Project’s Efficiency
- 3 Collaborate With Us Upfront for Optimal Results
- 4 CNC Machined Part Tolerances FAQ
- 4.0.1 What are typical CNC machining tolerances you can achieve at Approved Machining?
- 4.0.2 How do tight tolerances affect the cost and lead time of machined parts?
- 4.0.3 Why is it important to evaluate if a tight tolerance is truly necessary?
- 4.0.4 Can Approved Machining help revise designs to improve manufacturability?
- 4.0.5 When is the best time to talk to your team about tolerances?
Understanding Tolerances in Precision Machining
Tolerances in CNC machining vary significantly based on the feature being controlled and how that feature relates to other geometry on the part. In many cases, our CNC machine shop can achieve extremely tight tolerances, such as holding holes for press-fit hardware to ±0.0005 inches. More complex requirements, such as true position relative to three datums, typically allow for tolerances closer to ±0.002 inches.
These values should be treated as general guidelines rather than absolute limits. While tighter tolerances may be achievable in certain situations, they directly affect machining complexity and overall pricing. As tolerances tighten, costs tend to rise due to increased cycle time, more frequent inspection, additional setup requirements, and a higher risk of scrapped parts.
Designs that apply tight tolerances where they are not functionally required often lead to unexpected pricing and longer lead times. In extreme cases, they can make a part impractical to produce. By limiting tight tolerances in your design to only those that are essential for fit or function, you can reduce RFQ surprises and improve overall project efficiency.
Why Opening Tolerances Boosts Your Project’s Efficiency
In some applications, particularly in industries such as medical, military, electronics, and semiconductors, tight tolerances are required for proper function or assembly. However, we frequently see designs where tolerances are specified far tighter than necessary for the part’s actual use.
When we receive designs with tolerance requirements that are likely to drive unnecessary cost, we proactively work with our customers to evaluate whether those tolerances can be relaxed. In many cases, modest adjustments still meet all functional requirements while significantly reducing machining time, inspection effort, and overall cost.
One recent project illustrates this clearly. The original design specified a flatness tolerance of 0.005 inches over a 24-inch span, while also removing approximately 0.25 inches of material from the entire surface. After reviewing the design, we explained to the customer’s engineering team that holding this flatness was not realistic due to the material’s tendency to bow and flex as internal stresses were relieved during machining.
We recommended splitting the part into two components rather than machining it from a single piece. Although this approach initially raised concerns, a collaborative review showed that the revised design reduced cost and lead time without compromising functionality. Once the change was approved, we successfully machined the part, reinforcing the value of early design collaboration.
Collaborate With Us Upfront for Optimal Results
At Approved Machining, we focus on building long-term partnerships with our customers. If you have questions about tolerances in your design, we encourage you to involve us early in the process. With experience reviewing a wide range of machined part designs, we can quickly identify opportunities to reduce cost and lead time while preserving functional intent.
Sharing your project timeline, budget targets, and application requirements from the start allows us to provide the guidance needed to make informed decisions. Ready to take the next step? Request a quote today and partner with us on your next CNC machining project.
