Tolerance is the acceptable range of the dimension determined by the designer according to the shape, fit and function of the part. Understanding how CNC machining tolerances affect cost, manufacturing process selection, inspection options and materials can help you better determine product design.
1. Stricter tolerance means increased cost
It is important to remember that the tighter the tolerance, the higher the cost due to increased scrap, additional fixtures, special measuring tools and / or longer cycle times, as the machine may need to slow down to maintain tighter tolerances. Depending on the tolerance dimension and the geometry associated with it, the cost may be more than twice that of maintaining the standard tolerance.
The overall geometric tolerance can also be applied to the drawing of the part. Depending on the geometric tolerance and the type of tolerance applied, additional costs may arise 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. Stricter tolerances may mean changes in manufacturing process
Specifying a tolerance that is stricter than the standard tolerance can actually change the optimal manufacturing process of the part. For example, holes that can be machined on an end mill within a tolerance range may need to be drilled on a lathe within a tighter tolerance range, or even need to be ground, thereby increasing installation costs and lead times.
3. Stricter tolerance can change inspection requirements
Remember that when you add tolerances to a part, you should consider how to check the features. If the feature is difficult to machine, it is likely to be difficult to measure. Some functions require special inspection equipment, which may increase the cost of parts.
4. The tolerance depends on the material
The difficulty of manufacturing parts according to specific tolerances may be very material dependent. Generally, the softer the material, the more difficult it is to maintain the specified tolerance because the material will bend when cutting. Without special tool considerations, plastics such as nylon, HDPE and peek may not have the same strict tolerances as steel or aluminum.
