Hi,
I'm trying to make this sweep along the path but I cant seem to have any success, even if I try to trim off the bad bits after the sweep something always goes wrong.
I know the curves is a strange shape, but I need the sweep to subtract from some other surfaces to try to do a blend.
I have only a few weeks experience so I must be doing something stupid. I have try in 2.0 and 3.0 beta.
Can anyone give me any advice?
Thanks,
Pete

Hi Pete - the corner mitering that usually happens with 1-rail sweeps is mostly for 2D curves.

When you have 3D curves bending around all over the place, they don't easily intersect with one another in the same clean way as a 2D curve path does - meaning that the pieces don't just intersect with a plane.

Also this particular kind of crossing tube intersection happens to be an area that the surface/surface intersector in the geometry library that MoI uses has some difficulty with.

So those are some of the reasons why you're having problems there, it happens to be a problematic area, not that you're actually doing something wrong.

- Michael

One tip is that if you can very slightly adjust the shapes of your curves right in the local area where they come together to be straight right in that local zone it could make it easier to intersect, also when the curves are straight right in that juncture spot then it is possible to slice them both with an angled plane instead of having to intersect them with each other.

- Michael

Another method that can work is to draw a polyline with some points snapped on to your bendy curves, then sweep using that polyline, which will succeed since the juncture between every pair of lines is able to use a planar intersection to cut it, so it won't have any section/section intersection problems.

That will make a segmented result like this:



But then to make a smooth result from that you can select all the edge curves at the ends of each of those segment pieces, and use Ctrl+C / Ctrl +V to extract them as standalone curves and then loft some smooth surfaces through each section like this:



The attached 3DM file was done that way.

In the future I want to add a mode to Sweep that will do this kind of corner construction as well - it is not the exact same "rigid tube" type shape as the true linear extended and intersected type of thing that the corner mitering only tries to do currently though.

- Michael

Hey Michael,
That method works great for what I want :)
I wish I could have though of it though :( Maybe when I have gained some more experience...
Thanks very much for the help - such a quick response too, I am very impressed.
Keep up the good work.
Cheers,
Pete

Hi Michael


I tend to work in mm , and some times I get these sort of errors with sweeps , say if I'm working on curves 30mm long, if I increase the scale , say by 3, so I working with 90mm , the sweeps that failed, started to work.... Is this just my imagination ?

Hi Steve, do you mean in particular on mitered corners for 3d swoopy path curves?

It is pretty difficult for the miter intersection to work in those cases, and yes it is possible for things that are sensitive to have different results at different scales when refinement tolerances are involved.

Also with 3D swoopy curves, there is are some fundamental geometric problems with trying to make an extension + intersection type mitering mechanism to actually work at all, particularly when the profile curve is not a circle due to the twisting action as the profile travels along the rail. See here for some previous discussion on that:
http://moi3d.com/forum/index.php?webtag=MOI&msg=3575.4

In the future I think that I'm going to switch to a different technique when you try to sweep along a path that is made up of curvy 3D paths, where it will automatically place some scaled and angled profiles for you at the corner point rather than trying to do an actual extension and miter cut.

- Michael