I am drawing a paddlewheel, and this beast just won't boolean union without leaving some funky surfaces. Rhino v4 booleans nicely, but with some tolerance being automatically increased.

Is there something for me to learn to avoid or improve? Or is there (gasp!) a problem in MoI?

Thanks,
Ditto

Hi Ditto - this model will be difficult to boolean well because you've got a lot of pieces that are just kind of barely skimming and nearly overlapping with each other but not quite exactly overlapping.

Here's an example of one area:



Zooming in closely there:



So note there that the pieces that the outer edges of the pieces that you're trying to boolean come really quite close to each other but are not quite exactly aligned - that kind of situation is difficult for the booleans to handle. In some areas they may try to form a small slivery fragment there and maybe in other spots they may try to treat those edges as coincident.

To get better results you want to have such things either have more clearance between them or be more exactly aligned on top of each other rather than coming about this far away but not quite exact.


... After a bit more of a look - the boolean union will actually succeed in MoI if you do it just 2 pieces at a time instead of all at once. But the result has little tiny slivery pieces in it because of that inexact matchup between the parts.

- Michael

And in this area here instead of a tiny overlap there is instead a pretty small (about 0.02 units) gap between the pieces:





- Michael

Hi Ditto - so what I'd recommend is a process more like the following - if you kind of try to keep the pieces that you want to union in the end start out as a simple big piece that then gets cut it will make it easier to have the parts all be connecting together with each other accurately in the end.

To start with get the wheel and the scoop as a full solid piece like this:




Now select the wheel and run Construct > Boolean > Difference, and set the "Keep objects" checkbox, and pick the spout as the cutting object.

The spout part will remain and the wheel will have a hole cut in it like so (spout hidden here to show you):




Now select the spout and run Construct > Boolean > Difference again, and choose the inner curve of the wheel as the cutting object:



That will slice the spout making it flush with that inside cylindrical surface:



Go to the spout piece and select the top and side faces like this:



Then run Construct > Offset > Shell - that will hollow out the spout part like so:



Now you can select the spout and the wheel:



And then use Construct > Boolean > Union to union them together - because they shared a full surface in common on the inside cylindrical area, that will actually get fused together into a single surface there and you'll get this result:




So note there that this process builds pieces that are initially just sticking through each other and then slices them to a common cut - that's generally the best way to make sure that pieces will be matching up properly rather than trying to build 2 pieces totally separately and then trying to position them into place, when they need to be flush where they meet.

Hope this helps!

- Michael