Problem with Extend a Surface

[esavini]

Hi

I have a problem with the extend surface command. I have an old model where a surface obtained by cutting a two cylindrical orthognol surfaces is extended; the result is a circular surface wrapped with a single green arrow for the direction of extension (see figure 1). when I try to recreate this situation in a new model the curve comes with the edges and the extension arrows are 4 (see figure 2). I can't understand why and can't recreate the model. attached you will find the ipt files.

thanks in advance to those who want to help me

[Xun.Zhang]

Observed the same result in the old file as well if extend the surface large enough.

The only differences between new and old is the diameter of that surface extrusion. 

Video - https://autode.sk/3kCNFkm 

[esavini]

it's not as you wrote. please see the attached figure. with the same diameters, the second model creates cusps.

it is as if in the first case it recognizes a single curve while in the second it recognizes four curves that it extends independently and strangely

 

[esavini]

to confirm what I say please try to modify the surface extension already present in the old model (do not create a new one)

[johnsonshiue]

Hi! I don't think there is a behavioral change. What is different here is that these two cases are topologically the same but geometrically different. At a distance, the models the same, but if you measure, you will see the difference.

The old one has the tube diameter is 60.3mm. And, the cutting surface "radius" is 1212mm.

The new one has the tube in 66mm in diameter, while the cutting surface diameter is 1212+20 = 1232mm

These are two completely different cases. If you match either one, the result will be the same.

Many thanks!

[esavini]

thank you for the answer but unfortunately what you wrote is absolutely not true.

As you can see from the attached image: identical measurements, different results.

in the first post I attached the files to try.

thanks

[johnsonshiue]

Hi! I guess the definition of truth is being redefined. Please open the two files you attached to the thread. Here is the measurement I got from the files. The New part has diameter of 1200mm, while the Old part has radius of 1212mm. These are two different cases. Please make sure they share the same dimension. And, you will see they behave the same when the dimensions are the same.

Many thanks!

[esavini]

Hi

the truth hasn't been redefined any more than you want to.

if you proceed as described in the previous posts, i.e. apply the same measurements to the two models (MAKE SURE NOT TO CREATE A NEW EXTENSION IN THE OLD MODEL BUT USING THE ALREADY PRESENT) you will see that you will get different results.

To help you understand, I have attached the models with the identical measures that definitively refute your theory.

I point out that the goal of the post is to be able to replicate an "extension" without cusps of the old model in a new one, not try to prove that in reality the two models are identical (also because they are not).

thank you so much 

[johnsonshiue]

Hi! Many thanks for the clarification! I think I was confused by the difference between two models dimensionally. Actually, the new one isn't needed to show the issue. The old one is enough. Simply suppress the old Extend feature and create a new one in the same distance. The extended shape will change. Something is indeed changed but I cannot explain it. I will work with the project team to understand it better.

Thanks again!