The general procedure is to design to zero margin of safety on nominal dimensions and to show in formal report. However, in cases where adverse tollerance could produce a significant strength reduction, their effect should be consedered. The strength level below which tolerances cannot be neglected is that level at which there is appreciable possibility thet service difficulties will be encountered. The probabilities of the tollerances going bad, the material having minimum properties, the structure reacting to the loading condition as severily as predicted by stress analysis and the loading condition being achieved, should all enter into this decosion.
Rule: Use mean dimenion and total negative tolerance not exceeding the following values:
- 10% for single load path
- 20% for multiple load path