Boolean union failure

 From:  eric (ERICCLOUGH)
Hi Michael (or anyone)

Please see the attachment ...

The orange objects are 3 solid objects whose touching corners and faces actually appear to be touching but this group will not boolean union for me.

The white object of the same shape is a solid created by using the exact footprint of the other group ... drawing it with a closed curve, extruding it to the proper height and cutting it with a 3 segmented closed curve (using boolean difference) ... perfect.

The question is, why wouldn't my initial attempt work? I drew the boxes first then the joining solid that joins them and tried to get them to union ... no dice.

Then I remembered Michael saying over and over again ... the best way is to subtract what you don't want.