Pro Smooth Blending of objects Advise

 From:  Michael Gibson
4781.2 In reply to 4781.1 
Hi Steve - so really the problem in this case is that it's having some difficulty figuring out how to slice the objects together because the objects are sort of barely skimming right along one another.

It can be easier for the booleans to handle stuff if your objects actually push through each other a little ways instead of the barely skimming over each other kind of situation.

So for example if you move your side piece inward a little bit so that there it actually pushes through the other one by a small amount, you should then find it will boolean union ok.

Another thing you can try is if you have a problem with booleans figuring out how to do stuff you can try to use Trim instead, which in some ways is a bit more simple of an operation, particularly when using curves.

In your case here if you use Trim to cut a hole in the object using the edge curve of the other one as the cutting object you can get a result like this (I moved one piece a little so you can see how I made the hole):

Then after doing that I used Edit > Join to join those 2 surface objects together into a full solid, see the attached 3DM file.

But basically the boolean operations are focused on trying to intersect objects to find cutting areas, and then they decide which pieces of things to discard according to what volume they are in.

But 2 surfaces that just barely hug right along each others surfaces can be a lot more difficult to intersect - it's hard to see it but in your case there, it will actually have a really slight amount of undulations where some areas of the surfaces are slightly apart from each other and some areas are pushed through one another. If you make it more all pushed through then that simplifies things for the intersection calculations with the booleans.

Also it won't always be an issue - there are a lot of cases where skimming surfaces for booleans can also work ok, and I suppose that can add to the confusion if you've seen other things like you've built here work ok before - but it's just generally a more difficult kind of calculation for the booleans to handle so it's better to try and make things push through a bit more as a best practice to give things the best chance of working more smoothly.

Hope this helps,

- Michael