Tolerance

CNC Process Tolerance Suggestion:                                                                                                                                       
Lathe ± 0.005" | 0.13mm 
Router ± 0.005" | 0.13mm 
Router (Cutting Gaskets) ± 0.030" | 0.762mm 
3-Axis Milling ± 0.005" | 0.13mm 
5-Axis Milling ± 0.005" | 0.13mm 
Engraving ± 0.005" | 0.13mm 
Surface Roughness (Finish) 125RA 
Flatness ± 0.010" | 0.25mm

 Tolerance Tips:                                                                                                                                                                                                                                                  

High Costs for Tight Requirements
For several reasons, aiming for tighter tolerances considerably affects machining costs as well as the turnaround time. A tighter limit requires more time and labour.

It also increases the likelihood of a part falling outside the range and being scrapped. The machine will need special jigs and fixtures to achieve these limits.

Finally, very tight tolerances will need special measurement tools for quality control.

Choice of Manufacturing Methods
The tolerances set by the designer dictate which manufacturing processes are more suitable to achieve them. As tolerances become finer, fewer CNC machines will be able to complete the job satisfactorily as they differ in their capabilities when it comes to precision.

The component may require further operations such as grinding and lapping to achieve the tight tolerances.

Tolerances Depend on the Material
The choice of material decides the ability of a manufacturing process to accomplish a certain tolerance range. The difference in material properties can significantly affect the final values.

Soft workpieces are hard to fix as they keep bending when they come in contact with the cutting tool.

On the other hand, an abrasive material can wear out the cutting tool and make it harder to achieve the preferred value.

The exposure to friction heat during the cutting operation can cause some materials (e.g. plastic parts) to distort. T hus, a material type may be incompatible with a manufacturing process when trying to achieve tight tolerances.

Inspection:                                                                                                                                                                                                                                                          

The finer the tolerances, the harder and more time consuming it is to inspect them. They demand better measurement tools and inspection methods.

This increases the manufacturing costs of the component.

For example, chatter marks can form due to vibration during the machining process. We can check these marks visually but to obtain important information such as the length and depth of these marks, we need advanced inspection equipment. These marks (especially when it comes to finer tolerances) can be disruptive,creating noise and vibration in the assembly.