Hi all,

more curious then anything else, I'd like to undestand why the object named "spiral" and "center" don't union?

I've used sweep on P1 and P2 with the spiral as the rail.
Then extracted the edge of the "spiral" near the center and modified it (trim) to create "center" using revolve.

The only reason I can think of is that "spiral" as a self intersecting part.

Thanks,
Felix

Felix,
In this case it may be best to break the whole down into manageable parts. Maybe take a line through the center and Boolean Diff.

I was able to Union the center piece to an abstract section of the spiral, which would be a good start.

Make sure that the lower inside part of the spirals moving profile is a little higher than the back end, so that the two sides are not coplanar.

Also, there is a strange "kink" in the tightest part of the spiraled sweep that may cause problems.

Hi Felix,

> The only reason I can think of is that "spiral" as a self intersecting part.

Yes that is the reason - in general self intersecting surfaces will cause problems with the booleans, they don't have a clear positive and negative side to them and that creates ambiguity.

In your case here the particularly messy part is right near the center point of the spiral - that seems to be an area where the surface is not just intersecting other loops of itself but also kind of folded right back on top of itself and just generally messy:



Zoom in there to see the sudden tight bend where it is folded over itself:




That kind of sudden tight fold over top of itself will prevent surface/surface intersections from being able to get calculated cleanly.

- Michael

Michael,

As usual for you, excellent explanation.

Now, it's just a matter of creating a better "spiral" I suppose. I try it out.

Thanks,
Felix

That's one of the things that makes that scroll pretty difficult to model - it's kind of hard to avoid things bunching together awkwardly at the central hub.

But anyway that particular area of the shape is something to watch out for.

- Michael