Bisector surface in CATIA 2

[mtweeman]

Hello!

I have a model with two surfaces, which are intersecting. Looks like below:

As you can see the angle between these surfaces changes as we go along the intersection curve.
What I need to do is a surface in CATIA which will be bisector of the angle made by two given surfaces. Of course it should go all along, so the bisector suface should adjust when the angle changes.

Is that possible? If you don't have any plain answer, please, give me some hints, etc. Any help will be appreciated.

 

[weavedreamer]

Use the intersection curve between the two surfaces to construct a swept surface using circle w/ center and radius. Intersect the two surfaces with this and construct a ruled surface using the two new intersections. The median line of the ruled surface in conjunction with the original intersection curve will construct the bisector of the angle made by the two original surfaces.

 

[itsmyjob]

Can you describe a bit more the measures on your picture?

I did find a definition of bisector surface, and I have to say that creating such a surface in CATIA could bring some challenge.

The bisector of two surface is the set of points equidistant to both surface.

So if you offset x mm from surface A and surface B the intersection curve of those 2 offset is in your bisector surface.

Change the value of x to get more curve to build a surface from them.

I built the surface (in green) explained by weavedreamer and use distance analysis with several intersection curves from offset surfaces.

Sometime we take shortcut for geometric understanding and the result might be within our tolerance and it's fine, as long as we understand the shortcut and we can validate the result.

Eric N.
indocti discant et ament meminisse periti ​

 

[itsmyjob]

looking for an easy way to build this surface I used adaptive sweep.

in the sketch I made offset from surfaces and create points at intersection, then I have 1 spline joining all points.

As the sketch is swept along the spine, the offset curve will adapt to geometry and the spline will too.

Always check your results:

.007 away from intersection curve from offset...

I barely used this function but I am glad each time I find a good use for it.

Eric N.
indocti discant et ament meminisse periti ​

 

[mtweeman]

Thanks for all responses.

weavedreamer, I like your way the most. I tried it (a little bit modified) and it gives proper result. I'm presenting my way below.

itsmyjob, the measures on my drawing were angles between surfaces - at the beginning they were 90 deg. angled. Later, as a result of bent, the angle changes to ~80 deg. I'm explaining what I really wanted to achieve at the end of this post. It was just the beginning I tried your way with adaptive swept. However, it didn't work for me. I believe that the reason was small "bending radius" of mu surfaces. Adaptive swept just could not handle that. Perhaps I did something wrong. If you could present step by step how you guide and sketch looks that would be helpful.

Final way:
1. Intersection between two surfaces.
2. Two parallel curves, each 20mm away from intersection. I used two given surfaces as support for them.
3. Area between two parallel curves was blended.
4. Intersection projected on surface from point 3.
5. Intersection blended with projection.
6. Curve parallel to intersection from point 1, away 10mm.

Actually, my problem is a little bit more advanced.
I need to make a fillet between two parts and it should have constant height, even when the angle between surfaces (like in my first post in this thread) changes as it goes along the intersection. How to create surface going through last curve I created in point 6 above AND keep the angle between this surface and two given surfaces equal on both sides?

Above you can see the surface used for bisector generation. Hovewer, it was generated by parallel curves 20mm away along two given surfaces. What I need is to be able to control height of this "traingle", so somehow I need to offset surface on the top to intersect parallel curve 10mm away from intersection.1.

 

[itsmyjob]

in the GSD fillet function you can define a spine and a 'hold curve'... check the online doc, maybe this is what you're looking for.
[ul]
[li]create offset surface at 10mm from bottom surface[/li]
[li]get intersection A of offset with top surface[/li]
[li]get intersection B between top and bottom surface (like in 1)[/li]
[li]use fillet with spine option using B and holding curve A.[/li]
[/ul]

I define my adaptive sweep sketch as this:
[ul]

[li]I create the intersect curve named I (just like you in 1)[/li]
[li]I create a point P1 on I at ratio .5 from extremity[/li]
[li]I create plane normal Pn to I on P1[/li]
[li]I create a sketch S on Pn[/li]
[li]in sketch S I turn the standard option for construction[/li]
[li]I create intersection from both surface (gives me result in dashed lines)[/li]
[li]I make offset from each curves (with instances 5)[/li]
[li]I create points at desired intersection[/li]
[li]I switch option back to standard mode[/li]
[li]I create spline on points[/li]

[/ul]

Eric N.
indocti discant et ament meminisse periti ​

 

[weavedreamer]

mtweeman,

In retrospect, if you wanted to get fancier, i.e., gain more precision, use the intersection curve to generate 2 tangent surfaces of an equal extension to the respective surfaces (looking at the first illustration I took them as essentially ruled surfaces to begin with.)

Chord off the two extensions and derive the median curve to control the angle with.

You can also add a spine for unique directional control, but it appears you have the gist.

 

[lardman363]

How about intersecting the 2 surfaces to generate a curve, then offset both surfaces the same distance, in the direction you want the bisecting surface. Intersect the 2 offset surfaces to get a second curve. Sweep using 2 curves.

 

[weavedreamer]

Offsetting the surfaces to intersect will approximate the angular bisect. The greater the compound curvature of the two surfaces, the greater the angular error that would be produced by such an approach.

Developing two tangental surfaces commands the greatest control over the angular precision.