Deviation between 2 splines...

[Shadowspawn]

Question of the day...

From the Pull down... <<Analysis>Deviation checking>Curve to Curve...>>

Given two splines, say the convex and concave sections of an airfoil, when checking the pitch (max deviation or distance between the splines), there is a difference in the results depending on whether you select first the concave or convex. In otherwords, a deviation check concave to convex is different than a check convex to concave.

Can anyone explain to me why this is? I had assumed that the max deviation would be the same regardless of which spline was picked first. This doesn't seem to be the case, regardles of the number of points along the line selected... If you do a max deviation, the resulting (*) on the splines clearly indicate where the deviation is measured on the spline, but they're obviously different...

As always, any help would be appreciated...
Any ideas??? Attached is a sample part for your viewing pleasure...

Regards,
SS

CAD should pay for itself, shouldn't it?

 

[FrankSwinks]

The deviaton check between two curves checks from the first curve selected at each point on the first curve to a point projected normal to the second curve. The point on the second curve is generally not on an equivalent point when the curves are interchanged for deviation checking. Hence the difference in results. You can see this if you have deviation setting to "all deviations". I have also added some points and lines in the attached part to demonstrate what is happening.

Frank Swinkels