Cannot Boolean Union three parts

gauthier_östervall

I have three parts which I can't seem to be able to union. Two of these (Finger 5a and Finger 5b) do not intersect, and I have created a third (an extrude of a face of Finger 5a) in order to fill in the gap.



Any pair from these three can be joined.

But the three of them? "Failed to return a valid part"



I don't get why the red edges would be a problem.

Here is the document. The boolean is the last "Rolled until".

Any clue?

john_mcclary

Instead of making the intersecting piece, use replace face
Select the blue part as the first face, then the upper face of the purple. Then you can boolean them.

gauthier_östervall

That works nicely! Is that a way of thinking that comes to you naturally, something like... you don't need the old face so you'd rather move it, than create new ones?

I'm still not sure why replacing the face works better than the extrude, or why there were issues on merging the 3 parts. A limitation of onshape? I do get that it can be very hard to make it work.

One problem with this solution is that the five top faces change shape, and I wanted to use their implicit middle Mate Connectors to place parts in their center. Ideally I'd connect the two parts resulting in a surface in the middle, that is not an extension of either of the other part. I've experimented with Fill, but got into resolution troubles again.

john_mcclary

Usually the simplest solution is the best.

I really didn't play around with the boolean much when I was looking it over. So I don't know what really caused it. Most likely zero length geometry where the parts meet.

As for adding a mate connector to the center, you can use the outside two faces and set the mate connector in-between, assuming they are parallel 

Was your intention to have that step in the part? Or did you want that all to be seamless?

gauthier_östervall

That's the thing, the edges of the faces are parallel, until the Replace Face operation. It's easy before that, but after, the face shape changes.

The steps in the part are kind of the main point for that project I'm doing something similar to this. The part in my document is a holder for keyboard switches, for the ring finger and pinky of the right hand.