[Ra...] Posted October 29 Share Posted October 29 Hi! I have a CAD and a mesh for a 3D printed part. When I do a surface comparison on actual, I get different min/mix dev values then if I do surface comparison on CAD. I also get 30M more points on actual. Am I not comparing the same thing here just with different display options? Why are these two inspections different when I have the Parameters for them exactly the same? It may also help to note that they are also giving 2% erroneously high deviations, like 20mm dev when it is clearly more like <0.5mm. Do these two things correlate? Thanks! Link to comment Share on other sites More sharing options...
[No...] Posted October 29 Share Posted October 29 Normally deviations should be the same, but it also depends on the exact geometry of your parts. A comparison on actual uses the actual mesh as a reference and calculates the distance from the selected point to the nearest CAD face. Comparison on nominal does the opposite. It uses the CAD as a reference and calculates the distance to the mesh. Now if the geometry of both differs, this will result in slightly different directions of the distance vector, so results may differ as well. Near sharp edges and other areas where the direction of surface normals changes quickly within a short distance, you may experience high deviations because the software compares the deviating geometry to the wrong CAD surfaces. You can leave out such areas by modifying the maximum allowed surface normal deviation in the expert parameters 1 Link to comment Share on other sites More sharing options...
[Ra...] Posted October 30 Author Share Posted October 30 THANK YOU! Link to comment Share on other sites More sharing options...
[Ra...] Posted November 6 Author Share Posted November 6 Please sign in to view this quote. Is this why my min/max deviation surface comparison values are completely different? Link to comment Share on other sites More sharing options...
[No...] Posted November 7 Share Posted November 7 They shouldn't be completely different under normal circumstances. But it's hard to tell without seeing the actual part and settings. Link to comment Share on other sites More sharing options...
[Ra...] Posted November 7 Author Share Posted November 7 Please sign in to view this quote. In any one area, they are different. But I think based on what you're telling me and other information, the difference has to do with the difference in polygon size in the mesh vs the CAD. The mesh is filled with peaks and valleys that are not on the CAD. As a result, the normal directions and therefore the calculation of deviation for mesh to CAD is more variable than going CAD to mesh. Right? The difference in min for these two images are ~ 2mm. And they are in relatively the same spot on the mesh. on CAD, the polygons are larger and so the visual is different, that makes sense, but I'm not sure why the actual data is different in that spot other than because of what I reasoned above. Basically, it makes the most sense that HOW it calculates the deviation is different so the min/max of that area is going to be different. Link to comment Share on other sites More sharing options...
[No...] Posted Monday at 09:43 AM Share Posted Monday at 09:43 AM Please sign in to view this quote. Yes, more or less. Please sign in to view this quote. 2 mm is quite huge. Such deviations CAN happen under certain circumstances. But it's still questionable. Unfortunately it's hard to say anything about your part from the screenshot. Have you tried playing with the allowed normal angle deviation? If you lower that value more and more, areas that are affected by this setting should become grey in the comparison view. Link to comment Share on other sites More sharing options...
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