Specifying unilateral tolerances on CNC machined part

Engineer asked Mar 18,2025
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When entering part specifications for a CNC machined part, I wanted to specify tolerances, however the options are only for bilateral (+/-) tolerances. I want to specify a positive, unilateral tolerance as indicated on my drawing. Is there a way to do this, or will I need to change the dimensions on my drawing to be a bilateral.


Example: I have 10 mm +0.01/-0

Do i need to change my drawing to 10.005 mm +0.005/-0.005 ? I would prefer not to as the target tolerance fits better with a unilateral specification.

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    If the CNC machining system you're working with only accepts bilateral (+/-) tolerances, but your drawing uses a unilateral tolerance (e.g., 10 mm +0.01/-0), you may need to modify your approach. While you don't necessarily need to change the target dimension itself, you could adjust the tolerance to fit within the bilateral system.

    For example, to convert 10 mm +0.01/-0 to a bilateral tolerance, you could specify 10.005 mm +0.005/-0.005. This keeps the same overall tolerance zone (0.01 mm), but splits it equally as a bilateral tolerance.

    If you prefer to keep the unilateral specification on your drawing, you can also clarify your intent in the notes section of the drawing, stating that the tolerance is unilateral, and specify how it should be interpreted by the manufacturer. This way, they can still follow your intent while working within the bilateral system. However, using a unilateral tolerance directly in the system might not be possible unless the system specifically allows for it.

    Mar 21,20250 Comments
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    We can accept positive tolerance, you only need to mark it clearly in the drawing. Please note that the tolerance standard is not the full size requirement. The location that needs tolerance control must be indicated in the 2D technical drawing.

    Mar 19,20250 Comments
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