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Meaning of accuracy in Pro/ENGINEER
Pro/ENGINEER allows you the individual setting of the shortest distance of two points which should be recogniced as two different points, or in other words the shortest edge that can be represented. This is done by the accuracy. Are two parts in contact (i.e. in an assembly) which have a different length of this shortest representable edge, the modeller may have a problem to combine the geometry of both parts at their contact points. This will not cause an error in every case but you will get warnings that the two parts have different accuracy.
This will cause extreme problems if you have a reference model with very low accuracy (i.e. shortest edge 0.001) in a mold assembly with a workpiece of accuracy 0.02 and want to part and extract the mold volumes. The modeller is not able to bring the very detailled geometry of the reference model in the "rough" workpiece and to represent the necessary short edges in the workpiece. Parting will fail. How can you avoid or reduce the effects of this problem?
1) Take care for equal accuracy
Take care that all components of your moldbase assembly have the same accuracy. You can achieve this by using start models with predefined absolute accuracy. With absolute accuracy you set the shortest representable edge length (independent from the over all size of the part!). To do this you have to set the config-option ACCURACY_LOWER_BOUND to a very small value (i.e. 10e<SUP>-9</SUP>) and enable absoulte accuracy by the option ENABLE_ABS_ACCURACY YES. The problem of relative accuracy is that it calculates the shortest representable edge length relative to the length of the body diagonal of the part, which means that big parts are rougher than small parts. On the other hand the absolute accuracy should not be too low because this will cause long regeneration times. For normal moldbase design up to part sizes of 1000mm take an absolute accuracy of 0.002 as a standard in your start parts.
All our startmodels and customer start models are changed to 0.01 absolute accuracy. We work alot with skeletons to create the enveloppe of a cab interior. If for example its a complex one and you have a small storage lid 'far' away from the default coord system, and when the part where you copy it to is in relative acc. it happens alot that in that part you cant create the thickness, but you can in the skeleton ...
Basically the less technical explanation of what Pro-Grizzly answered
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