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参考基准须标全(Datum Features Must Be Referenced to Be Used.)

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发表于 2007-6-24 15:01:21 | 显示全部楼层 |阅读模式
参考基准须标全。
         
         
         
          Datum Features Must Be Referenced to Be Used.
          如图所示,孔的位置公差给出了基准A和B的要求, 而无相对于基准C的要求。

         
          孔只须满足垂直于基准A,距离基准轴线B为20mm的两个要求。则孔的位置不能唯一确定,孔的两种可能位置如右图所示。为了给定孔的位置,还须给出相对于基准C的要求。
         
         
         
          There continues to be the misconception that if a feature is labeled as a datum feature, its use is somehow implied. Take the drawing shown. The position tolerance on the hole references datum features A and B but not C. Therefore the hole must be perpendicular to the plane established by datum feature A and 20 mm from the axis established by datum feature B. Datum feature C has nothing to do with the position of the hole. Yes, the hole is shown on a centerline that is perpendicular to datum feature C. So, we know what the goal is. But, since datum feature C was not referenced in the position tolerance, there is no limit to how far the hole can be off the 90° angle. A couple of possible, acceptable parts are shown.
         
   


                        
                                             In order to avoid this, all                          you have to do is add datum feature C to the position                          tolerance.                                                                     

 楼主| 发表于 2007-6-24 15:06:20 | 显示全部楼层

回复: 参考基准须标全(Datum Features Must Be Referenced to Be Used.)

发表于 2009-6-27 19:06:22 | 显示全部楼层

回复: 参考基准须标全(Datum Features Must Be Referenced to Be Used.)

非常地感谢,看完这个,我懂了不少!
发表于 2009-10-15 23:11:56 | 显示全部楼层

回复: 参考基准须标全(Datum Features Must Be Referenced to Be Used.)

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