Creating a sweep or blend with laws

[on4now4]

I will start by saying I am a somewhat experienced CATIA user and have a number of years experience under my belt at this point. However this one has been stumping me for some time now and would really help me with my job if I can figure it out.

So basically what I am trying to due is:

Say we have two tubes one is square and one is round. Both tubes have a length of line of 200mm.

Lets say there is a 100mm gap between the tubes, Now I want to connect the two tubes with a transition area however I want the transition to stay at a length of line of 200 mm throughout. I could add a tolerance to it say +-2mm on the length of line.

Yes I know I can create a blend between the two but a blend will not hold a length of line through it. There has got to be a way to accomplish this any ideas would be appreciated. The best I have come up with so far is to create a multi-section surface and break the transition into many sections that I then manually shape until I have exactly what is needed... This is a very time consuming process.

 

[jackk]

could you explain "length of line" please

 

[on4now4]

Sorry, Length of line is just the circumference. If you were to take a string and wrap it around the part at any possible point. In a perfect part the string should be 200mm in length.

 

[jackk]

Thanks for the explanation. Unfortunately, I don't have a solution for you, but I do have a similar need.

I recently had to model a volute shape, but I was interested in controlling the cross-section area (linear decrease of area (air-flow) as the volute rotated around. Like you, I had to manually draw several cross-sections (sketches, in order to make a multi-section surface.

I hope I'm proven wrong, but I don't think there is a Law to control the Circumference (perimeter) or the Area.

 

[ferdo]

Hi,

Something like below ? Notice the offset distance for the plane is changed from 100 to 200...there are 4 surfaces which can be joined, I believe you can see the logic in the specification tree (I have r21 now).

Regards
Fernando

https://picasaweb.google.com/102257836106335725208

https://picasaweb.google.com/103462806772634246699/

 

[on4now4]

I can not see the picture for some reason... It is showing as a broken picture.

 

[ferdo]

Please see then the attachment.



Regards
Fernando

https://picasaweb.google.com/102257836106335725208

https://picasaweb.google.com/103462806772634246699/

 

[on4now4]

Thank you, That does not appear to be what I am looking for.

See the picture I attached for better explanation than my original post. All of the various sections through the transition I want to read 200mm.

jackk, Yes I believe we are on the same page with this. If you ever figure it out please let me know haha. With everything that can be done in CATIA there has just got to be a way to do it...

 

[jackk]

Fernando:

Looks like you broke the circle up into 4 arcs, added some lines between the sections and then made 4 Fill surfaces. How does that control the circumference as the tube transistions? Am I missing something? I also think it would be much easier to just make a Multi-Section Surface or Multi-Section Solid, with almost the same result.

On4now4:

In your fist post, you said you made a Multi-Section Surface and then adjusted the section cuts. I'm curious how close the Multi-Section Surface sections were to the target "length of line"?

 

[on4now4]

Attached is a picture of a real example of one that I did. As you can see in the picture I was able to keep it within about 0.6mm which in this case was okay because I was looking for a bit of expansion anyway. I have done it a little tighter it is just that much more time consuming the more precise I need it.

You can see in this example how most of it was modeled with splines that are used as guides in a multi-section surface rather than tweaking sections with sketches like you described. By just changing the tension on the splines I was able to shape to what I needed. Sometimes you can not get around sketches though. Sometimes a combination is required...

 

[ferdo]

You are right, I didn't understood the problem.

Regards
Fernando

https://picasaweb.google.com/102257836106335725208

https://picasaweb.google.com/103462806772634246699/

 

[ferdo]

Same approach like in first post (as Jackk described), with a last intersection to control along the 100 mm gap, all within 0.2 mm tolerance for length of the intersection curve (and with a little patient to play with scaling values can be better). Part is done in r21.

Regards
Fernando

https://picasaweb.google.com/102257836106335725208

https://picasaweb.google.com/103462806772634246699/