Posted January 28, 2021

Utilizing Precision Machining for Tight Tolerances and Efficiency

An automotive part in a finishing process by milling spindle.

Tolerances are what determine the room for error in manufactured parts. Those measurements are critical in high-stress applications like those seen in the automotive industry. Parts such as mounting plates require fabrication with dead-on tolerances, or the entire assembly will not fit correctly. Let’s take a look at precision machining for tight tolerances on parts like these and how a CNC machine shop can efficiently fabricate these parts to your specifications. 

Tight Tolerances That Matter 

Modern manufacturing requires parts meet specified tolerances to ensure functionality and aesthetic precision. Some industries, however, require tighter tolerances than others and rely on the precision that CNC machining affords:


Automotive parts endure a lot of stress due to the forces acting upon them. These strains require all the assemblies’ parts to have a tight and precise fit to function as designed. On top of that, the automotive industry continually changes with new requirements in its products’ performance and appearance. In addition to the tighter tolerances, precision machining gives automotive manufacturers the rapid development of new parts that they need and attractive surface finishes.


Three main areas of manufacturing medical equipment require particular attention to precision CNC machining:

  • Tools: Creating custom prostheses to fit each unique patient necessitates using tools precisely manufactured with tight tolerances.
  • Implants: Metal components engineered to replace bones and ligaments require precision machining out of hardened materials such as titanium to guard against long-term wear, friction, and chips.
  • Equipment: Robotic equipment for laser surgery and other demanding therapies rely on precision-machined parts for smooth and precise operation.


Parts for the aerospace industry, often with complex geometries, must withstand an incredible amount of stress in their operation. The manufacturing tolerances on these parts can vary according to requirements associated with the aircraft in which they are used, with high-performance fighters needing some of the tightest. These tolerances allow the parts of the aircraft to fit together as tightly as possible to withstand high temperatures and speeds to maximize the performance of the aircraft.

Effective Use of Precision Machining for Tight Tolerances 

To provide the tighter tolerance requirements of critical industries, CNC machine shops have innovated many new processes and procedures. One of the first innovations that a customer will notice is the online part request and evaluation system. Not only does this dramatically cut down the amount of time it takes to request a new part, but the customer also gets immediate feedback on the part’s manufacturability. Additionally, the software begins preparing for the job by making the appropriate tool selections and plotting the most optimum cutting paths.

An operator using an Optical Comparator.

During manufacturing, quality control processes help machinists meet tolerances. Each operator has the skills and training to ensure the quality of their work, and members of the quality control teams assist operators along the way. Precision devices verify and maintain the specified tolerances, starting with the use of standard calipers. From there, the quality control team uses optical comparators and coordinate control measuring machines to verify the tightest tolerances in the machined part.

Methods to Make Machining Tolerances More Efficient 

CNC machine shops have made strides in increasing their efficiency to manufacture parts with tighter tolerances faster. Take note, though, that the tighter the tolerances specified on a part, the more time and expense it takes to manufacture it. The tighter the tolerances, the smaller the tools used on the CNC machines need to be to hold those tolerances. Smaller tools will remove less material with each pass requiring more machining, and increasing the time required for production. Tighter tolerances also increase the setup times for manufacturing a part and the effort needed for the quality control teams to verify it.

The designer can help streamline the manufacturing of their part by remembering these simple guidelines about tolerances during the product’s development: 

  • Relax the tolerances when applicable: Tighter tolerances are necessary when the fit or function of the part requires it, but not all situations require this precision level. During the initial design, it may be acceptable to relax the tolerances to shorten the development time and cut expenses. Also, many design tools automatically instantiate a default tolerance when a new project begins that may be unnecessarily restrictive if it’s unknown to the designer.
  • Default tolerances: Most drawings will give the designer an option for stating a default tolerance unless otherwise specified. Default tolerances allow the designer to call out tighter tolerances when necessary but set a correct default value for the overall part. Sometimes these values also carry from project to project as a company standard that may not always fit each new design.
  • Beware of over-tolerancing: Some designers specify a tighter tolerance than is necessary out of an abundance of caution. Tighter tolerances require more complex machining and quality control measurements. The best practice for the designer is to specify the optimum tolerance for the part.
  • Materials can affect the tolerances: Tighter tolerances on softer materials are more difficult to hold, and therefore add cost and time to the project. Harder metals take more time to mill, and though they may offer more stability within their fixturing in the mill, they also take longer to mill. The designer should research the manufacturing limitations of the materials for the manufacturing of their parts.

By working together, the designer and the machine shop can ensure that manufacturing the part will go as efficiently as possible and at the tightest tolerances needed for the part’s success.

At Plethora, we understand the tolerance requirements that your parts need, and we are ready to help with any questions or concerns you might have. We specialize in manufacturing precision parts using the industry's most advanced CNC machining equipment and software. We are an ISO 9001 certified shop, and our quality control team continually monitors each part to ensure that it holds the tolerances you specify. Our online DFM and quoting systems are ready to receive your data so we can begin working with you on your next project. To get started, upload your design files to Quote My Part or call us at 415-726-2256.

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The Plethora Team

The Plethora team is your go-to CNC manufacturer for hardware done right the first time. We have the tools and experience needed to create high quality custom parts quickly and with precision, whether you need a prototype or production run.

Topics: materials, Design, Manufacturing, finishing, Defense, Aerospace, CNC machining, Quality, Prototyping, Medical