absolute accuracies for merging parts

[2ms1]

I'm having trouble with parts not merging into other parts because of
accuracy incompatibilities. Anyone really good at dealing with this? I have a
"mother" part with several smaller parts merged in. Sometimes when I
change something in one of the parts, a merge will fail because the
accuracies are too different.

What's the best way of setting things so this doesn't happen anymore? I'm
not sure whether to change just the smaller parts's accuracies, or just the
"mother's" accuracy, or all of them or what. And also my regen times are
already getting pretty annoyingly slow. How do I know what values to pick
for the absolute accuracies?
Edited by: 2ms1

 

[jimshaw]

If thereare descrepencies between the absolute accuracies of parts, it typically has to do with a particular feature or geometry. Try performing a "short edge" analysis and see what comes up. Perhaps this will help you isolate the part in question.


The best way to avoid this is to set everything to relative accuracy and let ProE calculate it all. I can't remember the equation, but it is a function of the length of the diagonal of the bounding box of the part and the shortest edge in the model. Do a search on google for "enable_absolute_accuracy" there are a couple of faq's out there which talk about how to troubleshoot challenges that may arise.


Let us know how this works out.


Jim

 

[jimshaw]

I addition, the absolute accuracy actually has units, so if you select .001, then the geometry of the model will be calculated to an accuracy of .001" If you are low on horsepower, this may be okay for a ball bearing, not so much for a full model of a skyscraper, you get the idea.


The short edge analysis could give you a starting point for selecting a feasible accuracy. If it doesn't like it, cut it in half and try again. The other trial/error method is to try something ridiculously small, then double it. You risk much wasted time with the latter of these two methods... good luck!

 

[Zestje]

To me it seems logical to have all parts with the same absolute accuracy, simply because I expect ProE to have the least mathematical problems with the algorithms when e.g. merging parts or simply adding a new feature to an existing parts.

The plastic parts we design are all in the same dimension range and require an accuracy in 0.01 mm for the parts, which means we must use an accuracy in ProE of 0.001 (or better) to prevent rounding during ProE calculations having significant (order of 0.01 mm) influence on the part's geometry. We always use identical absolute accuracy for all our parts.

I can only imagine relative accuracy making sense when thesize of the parts are in different orders of magnitude, e.g. a 1 cm long screw to fit a 1 meter long part, although I have no experience with relative accuracy.

One more note: The accuray influences how surfaces interact during all operations like merging, splitting and so on. I've found that on one hand a higher accuracy results in more accurate geometry, but on the other hand it can sometimes be a bit harder to get your feature going without an error because the different geometric shapes involved require a better 'fit' or 'alignment' for ProE to get the calculation done correctly.