Boolean Fail...simple structure...why?

The thing that scares me the most is having a boolean failure and I just dont why.
Attached is to me what appears a simple task, I wish to round off the back of this item with my U shaped solid doing the chopping.
Just why is this failing ?

What are the basic criteria for boolean to work ?

I even extended the item backwards into the ‘chopper’, still no joy.

BooleanFail_Why.3dm (80.0 KB)


Yes, this should work… please run DivideAlongCreases > SplitAttangents=Yes, then try again. The problem, and it is Rhino’s not yours or anything you did, is that you have single surfaces that are only tangent continuous and the intersector sometimes doe not like that… I’ll add this example to the bug pile.


Have you read this?

Run Intersect on your two objects and see why…


Pascal beat me to it for the “split at tangents” thing. The thing is you should avoid this situation altogether by not creating these internally tangent surfaces at the outset.

In order to to this, when you extrude objects, make sure first that UseExtrusions is set to “Polysurfaces” and not “Extrusions” so that Rhino will not make extrusion objects; and then within the Extrude command, make sure that SplitAtTangents is ALWAYS set to Yes.


Rhino’s surface intersector has a limitation when surfaces overlap. It only finds curves that are surface edges. If you call DivideAlongCreases as Pascal suggests, then the missing intersections will now be surface edges and the boolean will work.


As suggests the Wiki article referenced above, you can almost always get these things to work correctly manually. Attached is a manual Explode/Split/Trim/Join operation on your original objects (without doing a split at tangents) that took about 30 seconds.


ManualBoolean.3dm (152.8 KB)