Machines are able to create extremely accurate parts, down to the thousandths of a millimeter. But making parts with such high precision can be very inefficient due to its higher costs and production time. This is especially true when this level of precision is not necessary for the part to function properly. This is where tolerances come into play.
Tolerances are measurements that denote the level of precision required for a specific part that is being manufactured, indicating the amount of flexibility or variation is acceptable when creating those parts. Tolerances are measured in plus or minus numerical values, usually indicated with a ±. For example, a tolerance of ±0.005” for a part measuring 1.25” means that the measured length of that manufactured part could vary anywhere from 1.245” to 1.255” and still function as needed. Tolerances are thus used to let manufacturers know how precise they need to be when manufacturing parts.
Smaller tolerances, also known as tighter tolerances, indicate the need for more accuracy. Manufacturing parts with tighter tolerances is generally more expensive and time-consuming, while larger tolerances, also known as looser tolerances, give manufacturers more leeway.
Tolerance levels vary based on a variety of factors, including the material being used, the machining process, and the design and complexity of the part being manufactured. Certain materials have unique physical properties that may make them more difficult to work with, such as its hardness, its shrink rate, and its resistance to heat. The part’s design and complexity, including its overall shape and size, can also have a major effect on tolerances. The table below shows various Machining Processes and typical Tolerance Achievable (* depending on material used and design of part) by Nyalt Precision.
|Machining Process||Tolerance Achievable *|
|CNC Milling (3 Axis & 4 Axis)||0.003mm (0.00012”)|
|CNC Turning (Live Tooling)||0.003mm (0.00012”)|
|Surface Grinding||0.002mm (0.00008”)|
|Cylindrical Grinding||0.002mm (0.00008”)|
|Customized Grinding||0.002mm (0.00008”)|
Tighter tolerances are generally required when designing fitted assemblies, where parts are being used to connect components together, such as with shafts that need to fit snugly into small holes. Critical components of certain machines require high precision parts that are made with very tight tolerances. Tolerances can vary within the individual components of a larger part being manufactured.
As tolerances become tighter, manufacturing costs grow exponentially. This is due to tighter (or close) tolerances requiring more expensive machinery and tools, as well as the machining process taking a longer time for tighter tolerances. Parts with tighter tolerances also require a more thorough inspection and require high-performance inspection equipment like CMM. Requiring high levels of precision means having less margin for error, so parts with very tight tolerances will also require in-process probe system measurement, like Renishaw Primo Twin Probe System, capabilities.
This is why it’s crucial to know what kind of tolerances are necessary when manufacturing a part. Choosing a tolerance that is too loose may lead to parts that aren’t precise enough but choosing a tolerance that is very tight will lead to wasting time and money creating parts with unnecessarily high precision.
Tolerance levels can depend on what materials you are using. Different materials have different physical properties and characteristics that can affect how they are manufactured, and thus affect their tolerance levels. For example, harder materials are better for machining to tight tolerances, as softer materials are more likely to break or lose their shape. Materials that are smoother and less abrasive are also easier to tool than those that are coarser. Lastly, some non-metal materials do not do well under heat, and are likely to lose their shape (warp) as temperatures rise during the machining process. Understanding what materials you are using is an important piece of deciding on tolerance levels.
As previously mentioned, choosing the right tolerance can have a direct impact on the quality of your product, production time, and overall cost. There are a few things you should consider when deciding on what tolerances to go with, but the main consideration is knowing what your parts will be used for. If you are manufacturing a high-precision part that needs to fit perfectly into another, then you should go with tighter tolerances. Otherwise, it’s not worth the additional time and cost to do so.
Choosing the right CNC machine shop will also play a large role in finding the right tolerance. A good machine shop will discuss your product’s requirements and specifications in detail to help you make the best decision possible. Nyalt Precision is a CNC machining company that has specialized in precision machining for nearly two decades. We are capable of working with virtually all metals, plastics, and composites, and excel in machining parts that require the tightest tolerances possible. Get in touch with us to learn more about how we can help you choose the right tolerance for your application.