Sweep Problem

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 From:  Sharif (SR13765)
3812.1 
Hi;

I am trying to sweep a rectangle profile with these two rail curves. Is there a way to get the surfaces aligned at the intersection( see red circle mark)?


Thanks

Sharif
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 From:  Michael Gibson
3812.2 In reply to 3812.1 
Hi Sharif, it's not clear to me what kind of alignment you want - do you want everything to meet squarely there?

That would seem to be a geometric impossibility to have a slanted shape intersect a none-slanted one with each having the same thickness and profile.

That's like saying you want to have 2 boxes that have the same cross-section size that meet like this:





To somehow meet squarely, but they can't unless you rotate one - it requires rotation to make features align like that.

A circular tube is a special case since it has total rotational symmetry so it doesn't matter at what angle 2 circular tubes touch each other. For example if you rotate a circle around its own center point, it still has the same pattern to it no matter what the rotation angle is, that's not the case with any other type of shape.

- Michael

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 From:  BurrMan
3812.3 In reply to 3812.2 
If the intersection is the focus of alignment, you could sweep away from that as a start point...?

This is the result.

EDITED: 19 Jun 2012 by BURRMAN

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 From:  Sharif (SR13765)
3812.4 In reply to 3812.3 
Hi Michael and Burrman;

Thank you for your responses. This is a part of an exercise I am doing to build the Beijing National Stadium (Bird's Nest) model in MOI. I have built the mass and the base structure so far. I still have a long way to go to get the rest of structure modeled. As you can see in attached images all the structural tubes surfaces aligned at the intersection.

Thanks
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 From:  Michael Gibson
3812.5 In reply to 3812.4 
Hi Sharif, so sweep does not itself have any knowledge of how just one single starting profile should be rotated as it moves along the sweep in order to have it match up to all kinds of other sweeps like you want to do there.

You'll need to do something like place in a number of additional profiles along the sweep that are each positioned in a spot that you want the sweep to pass through - that's basically how you can add control to sweep, by putting in some more profile curves rather than just sweeping from just 1 profile and letting sweep do its automatic rotation.


Also another potential approach might be to make one unbroken surface, and then trim pieces of that large surface away to make the pattern, then thicken that with Shell, rather than trying to make individual sweep pieces that align with each other. If you work off of one large common surface that keeps everything meeting up in one outer shell more properly.

It's difficult to make sweeps on paths that are curving around all over the place to be aligned precisely with each other because to get a precise alignment and clean intersection there has to be a kind of area of co-planarity in the zone where the sweeps cross over each other.

- Michael
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 From:  Michael Gibson
3812.6 In reply to 3812.4 
Hi Sharif, or probably a good way to proceed would be a kind of combination approach.

That would be to have a big outer surface to start with but then build some sweeps that follow along it and intersect those sweeps with the surface to get the curves to trim the surface with.

That way sweeps can be used to help make the general outline, but you'll have a fully flush surface because instead of trying to make sweeps align with each other you'll have one big larger surface that starts out all continuous before it is cut up.

- Michael
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 From:  Michael Gibson
3812.7 In reply to 3812.4 
Hi Sharif, so here's an example with some steps.

Initially just focus on the full form that underlies the entire shape, don't worry yet about all the criss-crossing parts or holes, just get a big surface to start with, something like this:






Then you'll want to get some criss-crossing patterns that hug that surface, here I've drawn in a few lines and used Construct > Curve > Project to project them on to the surface:





You'll probably need to fuss with this part quite a bit to control the pattern that you want.

Then you want to make that pattern have some thickness to it, and the easiest way to do that is to do some sweeps with just a circular profile to make some tubes like this:



Then those tubes intersect the main surface leaving a kind of thickened trail.

You can at this point actually do a Boolean Intersection between the main surface shape and the tubes to get the areas of the surface which are contained within the tubes like this:



But that may have some difficulty finishing well if you get quite a huge number of things all kind of crossing over each other. So you may need to do a more low level surface trimming approach.

That would involve using Construct > Curve > Isect to intersect the tubes with the main surface to produce intersection curves like this:



Then trim those curves with each other to remove pieces you don't want, like this:



Then you can trim the surface with those curves.

Hope this helps!

- Michael

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 From:  Sharif (SR13765)
3812.8 In reply to 3812.7 
Hi Michael;

Thank you for the solution.I give it a try. Also in this case "OffsetCurveOnsurface" command will be handy, this way we can avoid two extra steps (Sweep and Boolean)

-Sharif
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 From:  Frenchy Pilou (PILOU)
3812.9 
And just Boolean Merge?
(of course you must kill pieces don't wanted :)

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