Choosing CNC Tolerances: When Tighter Is Actually Worse

Many procurement teams request extremely tight tolerances without realizing the risks.

Why over-tight tolerances cause problems:

• Higher internal stress after machining
  
  

• Increased scrap rate
  
  

• Difficult assembly due to zero-fit conditions
  
  

• Unnecessary cost increase
  
  

A better tolerance strategy:

Instead of using the tightest tolerance everywhere, professional CNC engineers:

• Apply tight tolerances only to functional surfaces
  
  

• Relax non-critical dimensions
  
  

• Use GD&T (flatness, concentricity, parallelism) instead of linear tolerance
  
  

This approach:

• Improves assembly success rate
  
  

• Reduces machining time
  
  

• Maintains real functional accuracy
  
  

Precision should serve function, not the drawing aesthetics.