Hi guys,

I used a simple sweep of 2 circles (at 90 degrees to each other) to produce a short pipe like object. I then produced a copy of that object, rotated through 90 degrees.
When I try to fuse the 2 objects together with a union operation it either hangs on "calculating..." or one of the objects disappears.

Can anyone suggest a technique to get this to work please?

Thanks,

Dave

This happens when your parts aren't perfectly aligned...

Zoom in on the front view and make sure the bottoms match in height (snap on to the other), then zoom in top view and make sure your "circles" align. (again, snap one to the other)
Then the Boolean union works.

Example attached (curves hidden, unhide if you want to see the sweep curves)

Hi Dave, if you're still stuck can you please post the .3dm model file with your objects instead of only a screenshot?

One comment though - on your screenshots notice these areas where it's all patchy looking with pieces of both objects showing through each other? :

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Those are areas where the objects are just barely skimming over top of each other with a nearly but not quite 100% exact overlapping surface areas. Things like that can be difficult to get a clean surface/surface intersection on.

In order to do a boolean, the intersection between the pieces needs to make well formed closed intersection curves that can divide the pieces up into different chunks. If you calculate intersection curves between your objects using Construct > Curve > Isect you'll probably see that the curves don't make a clean result like that. That's what is likely preventing your boolean from working well.

It's hard to tell for sure just from a screenshot though, please post the model file when you have a question like this so the actual geometry can be investigated and things like intersection curves generated.

If the pieces were more exactly constructed possibly with 3 pieces with exact cylinder/torus/cylinder surfaces instead of one longer sweep surface that could help.

- Michael

Thanks guys, I understand how complex it must be to run the math on these kind of operations. Hats off to Michael in that regard!
I thought I was keeping things relatively simple in this case as I used the same shape twice and produced the copy via a precise rotation using the center of the circle as the pivot point. In theory the 2 shapes should still be in precise alignment. They certainly look to be aligned when I zoom in like advised. I can only think the sweep operation has produced an object with small surface irregularities that become apparent when you rotate the shapes around the axis.

I attach the model file Michael.

Thanks for the help!

Dave

Hi Dave, yes 2 rail sweep is a kind of general freeform surface construction mechanism. It doesn't make 100% precise geometry it makes freeform surfaces as its output.

If you use Edit > Separate on your shape and then turn on surface control points for the surface you can see that it's kind of stretching out between the 2 rails, so yes it's not symmetrical and uniform like something made up from a cylinder and torus would be:



As the profile moves between your 2 rails it gets stretched out in one direction and so a rotated copy of it will not exactly align to other pieces of itself as an exact pipe that has a circular cross section would.

- Michael

Hi Dave, so for combining these pieces that can be done by cutting each of them with a 45 degree angled line using boolean difference, then delete the common face between them and use Edit > Join to glue the pieces together.

That's what I did to make the closed solid in the attached file.

It will be difficult to try to directly boolean them with each other because of the "barely skimming over nearly coincident surface areas" type of surface intersections that would be required for that.

If you select 2 of the pieces (be careful there's also a duplicate copy of one of them) and create intersection curves using Construct > Curve > Isect, you can see that the intersection curves are quite complex and chaotic:



- Michael

Thank you Michael! That technique worked a treat. In future I'll try to keep my joining surfaces as unambiguous as possible.

Cheers,

Dave

I dl'ed your file and it works if you do what I said earlier. Also: You had 3 objects, I deleted one, positioned the other 2 and presto: a union.

Attached is your file without the 3rd object and the 2 others aligned properly. Select them both and do a union, it works, took only like 3 seconds...