Jari Ojala's presentation on mechanical tolerance chaining provides essential insights into precision manufacturing and technical documentation.
As an experienced engineer who has worked across Finland, Sweden, and Denmark, Ojala brings practical expertise to the often-overlooked topic of tolerance management.
The core message is straightforward yet profound: clear questions lead to clear answers, and technical drawings must provide unambiguous specifications about part function.
The presentation systematically builds understanding through multiple layers.
First, it establishes that drawings serve as the foundation for tolerance chain calculations, with every specification carrying legal weight. Ojala then explores the relationship between different tolerance types—size, orientation, and position—demonstrating that these must be treated independently.
Through detailed examples, including a basic rectangular part with cutouts and a U-shaped component, he shows how to calculate total tolerance variation using the min-max method, where individual tolerances are summed to determine overall allowable deviation.
A particularly valuable section addresses material condition modifiers and their practical benefits.
These modifiers—maximum material requirement, least material requirement, reciprocity requirement, and envelope requirement—provide increased flexibility and reduced scrappage when properly applied, yet remain underutilized in many technical drawings.
The presentation also compares ISO and ASME evaluation methods, showing how different standards can produce different results from identical data. Ojala's real-world CMM examples powerfully illustrate measurement uncertainty and calculation methodology differences, demonstrating how half-millimeter discrepancies can result from different datum evaluation approaches.
The session emphasizes that GPS (Geometric Product Specification) and mechanical tolerance chaining work hand in hand, requiring both correct documentation and proper calculation methods to ensure parts function correctly during assembly and use.
From the meeting "Certain when Uncertain".
