Accuracy when Selecting Faces versus Bodies with Intersection Curve
Posted: Sun Feb 13, 2022 2:50 pm
I came across a situation where the intersection curve feature behaves a bit unexpectedly.
I'm in a 2D sketch. If I select a "surface body" for the intersection curve, I get a result with a looser tolerance than if I select the individual faces. Based on some experimentation, the chord arc tolerance when selecting a body is about 0.005mm. That isn't always good enough for a finish pass on anything with contours, so how can the software use such a loose value for modeling?
The accuracy is much better if I select individual faces.
I'd prefer to select surface bodies for this sort of feature, as a body intersection is more tolerance of changes higher in the feature tree. But I'd also like to be confident in the software accuracy if I'm modeling a small part, snapfit, or something that will be polished or have high reflectivity. If the machinist is running something like a few um chord error to achieve a nice surface finish in the world of atoms, I don't like the possibility that my modeling world of bits has approximations anywhere near that level.
Here's an example where the intersection of a body opts to use a line segment, while the intersection of the relevant face opts for an arc. The midpoints of these two entities are different by 0.005329mm.
The knowledge base reports a few SPRs on this. Has anyone else bumped into it? Am I right that the tolerance is about 0.005mm, or can it it be worse in some situations?
SPR 1191486: Intersect body with sketch plane yields different result if Intersected body is selected as surface or faces
SPR 480658 : Accurency [sic] in the intersection curve feature is not enough selecting a body instead of the faces.
S-035124: This is a known issue already submitted to our development team with the SPR 480658: Accuracy in the intersection curve feature is not enough when selecting a body instead of the faces. Note that this issue only occurs when selecting a body as a reference of the intersection curve feature. So the workaround is to select faces instead of bodies. Please refer to the SolidWorks Knowledge Base to find the latest status of this SPR.
SPR 573299: Intersection curves create extra lines when selecting face compared to selecting body.
I'm in a 2D sketch. If I select a "surface body" for the intersection curve, I get a result with a looser tolerance than if I select the individual faces. Based on some experimentation, the chord arc tolerance when selecting a body is about 0.005mm. That isn't always good enough for a finish pass on anything with contours, so how can the software use such a loose value for modeling?
The accuracy is much better if I select individual faces.
I'd prefer to select surface bodies for this sort of feature, as a body intersection is more tolerance of changes higher in the feature tree. But I'd also like to be confident in the software accuracy if I'm modeling a small part, snapfit, or something that will be polished or have high reflectivity. If the machinist is running something like a few um chord error to achieve a nice surface finish in the world of atoms, I don't like the possibility that my modeling world of bits has approximations anywhere near that level.
Here's an example where the intersection of a body opts to use a line segment, while the intersection of the relevant face opts for an arc. The midpoints of these two entities are different by 0.005329mm.
SPR 1191486: Intersect body with sketch plane yields different result if Intersected body is selected as surface or faces
SPR 480658 : Accurency [sic] in the intersection curve feature is not enough selecting a body instead of the faces.
S-035124: This is a known issue already submitted to our development team with the SPR 480658: Accuracy in the intersection curve feature is not enough when selecting a body instead of the faces. Note that this issue only occurs when selecting a body as a reference of the intersection curve feature. So the workaround is to select faces instead of bodies. Please refer to the SolidWorks Knowledge Base to find the latest status of this SPR.
SPR 573299: Intersection curves create extra lines when selecting face compared to selecting body.