What do you need to know about CNC machining tolerances?

Tolerance is the acceptable range of dimensions determined by the designer based on the shape, fit and function of the part. Understanding how the tolerances of CNC machining affect cost, manufacturing process selection, inspection options, and materials can help you better determine product design.

1、Tighter tolerances mean increased costs

It is important to remember that the tighter the tolerance, the higher the cost due to increased scrap, extra clamps, special measuring tools and/or longer cycle times, as the machine may need to slow down to maintain tighter tolerances. Depending on the tolerance notation and the geometry associated with it, the cost can be more than double that of maintaining standard tolerances.

Overall geometric tolerances can also be applied to drawings of parts. Depending on the geometric tolerances and the type of tolerances applied, additional costs may be incurred due to increased inspection time.

The best way to apply tolerances is to apply tight or geometric tolerances only to critical areas when design criteria need to be met to minimize costs.

2、 tolerance depends on the material

The difficulty of manufacturing parts to specific tolerances can be very dependent on the material. In general, the softer the material, the more difficult it is to maintain the specified tolerances as the material bends when cut. Without special tool considerations, plastics such as nylon, HDPE, and PEEK may not have as tight tolerances as steel or aluminum.