The difference between coordinate tolerancing and geometric tolerancing are summarized below. When comparing these tolerancing methods, it is easy to understand why geometric tolerancing is replacing coordinate tolerancing.
Co-ordinate Tolerance
• Square or Rectangular Tolerance Zone
• Higher Manufacturing Cost
• Fixed Tolerance Zone
• Multiple Inspection Results
• Defect parts accepted
Geometrical Tolerance
• Diameter Tolerance Zone
• Lesser Manufacturing Cost
• Flexible Tolerance Zone
• Clear Inspection instructions
• Eliminates Disputes
GD&T BENEFITS
1. Improves Communication: GD&T can provide uniformity in drawing specifications and interpretation, thereby reducing controversy, guesswork and assumptions.
2. Provides Better Product Design: The use of GD&T can improve your product designs by providing designers with the tools to “say what they mean”.
3. Increases Production Tolerances: There are two ways tolerances are increased by use of GD&T. First, under certain conditions GD&T provides” bonus” – or extra - tolerance for manufacturing. Second, by the use functional dimensioning, the tolerances are assigned to the part based upon its functional requirements. This often results in a larger tolerance for manufacturing.
4. Lowers Cost: The result common to each of the three benefits listed above is lower costs for manufacturing and inspection of the part.
GD&T Standards
GD&T standards are based on ASME Y14.5-2009. This standard is considered as the national standard for dimensioning and tolerancing in the United States. ISO (International Organization of Standards) also has published geometric dimensioning and tolerancing standards called GPS 1101 which is 90% similar to ASME Y14.-2009 standard. This text is based on ASME Y14.5-2009 and ASME Y14.5-2018 and hence forth will be referred to as Y14.5.
ASME – American Society of Mechanical Engineer
Y14.5 – Standard number for Dimensioning and Tolerancing
2009 – Year in which the standard was published
2018 – Year in which the standard was published
GPS – Geometric Product Specification
1101 – ISO Standard number for GPS
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