In modern manufacturing engineering, tolerance synthesis is important becau
se it directly effects product quality and manufacturing cost. This paper i
ntroduces a new method for tolerance synthesis of machining parts. The new
method consists of three steps. First, machining parts are evaluated using
the second-order fuzzy comprehensive evaluation (FCE). Then, a mathematical
model for tolerance allocation is formed based on the machinability of the
parts. Finally, the model is solved using the genetic algorithm (GA). The
feasibility of the method is validated using a practical gearbox design exa
mple.