Extrapolate command

[AFROUZ.E]

Steps:
1. I was able to create the extapolated surface by choosing the displayed boundary and tangency continuity of the propagation mode of the extrapolate command as it was expected.

2. With the same parameters except the prompagation mode (point continuity now), got a twisted surface!

3. With the same parameters as No.1 except the boundary, got an extrapolation suraface as it was expected.

It's strange for me. What abou you?

 

[MrCATIA]

All three situations worked fine for me, with no twisted surface.

But I used totally different geometry, so I'm not surprised. I suspect the twist is due to the fillet (is it variable radius?), or the boundary edges not being planar (hard to tell in the image).

To avoid the twist; you might want to add the fillet at the end (Extrapolate first, and then fillet the sharp corner)

 

[AFROUZ.E]

Sorry, I forgot mention that the example is taken from the CATIA documentation. And I must tell you, the No.2 expression is correct in 3rd step, not No.1.

It is possible to create a complete extrapolation by choosing the boundary displayed in 3rd step but not choosing another boundary displayed in 2nd step.

Thanks for your effort.